**Car Physics**

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Brilliant thread guys hats off to all that found all the data:thumbsup:
It will take a while to read through all this stuff but i sure will check it all out

;)
 
This excellent piece was posted by :star:12sec:honda::star: in the :gt:3 forum :thumbsup:

Ok, I will try and explain this like I am talking to a 6 year old.

There are 2 main points of interest on your tachometer (The dial that tells what RPMs the engine is revving at) One is the spot where the manufacturer has set the "Redline" this is where they recommend that you shift or else you will damage the engine, it is visible on the tachometer with a Red-Line. When you race with Automatic tranny it will always shift right at the red line.

The other point of interest is the "Feul Shutoff" This is programmed into the computer of the car to cut off the engines fuel supply at a certain RPM because revving any higher would severely damage the engine, There is no spot on the actual tachometer to show you where this is but the only way to tell is to hold R2 when accelerating and wait until the engine starts to surge. When racing, you want to always rev the engine as close to the "Fuel Shutoff" as possible.

Also, when you buy a "Racing Chip" or "Engine Balance" or most of the engine NA Stage upgrades, it will reset the cars computer and it will usually have a higher "Fuel Shutoff" point after you have done some upgrades.

If you race with auto trans, and you want to keep revving past the "Red-Line" and rev all the way to the "Fuel Sutoff" (The higher you rev the faster you go, no matter what, so you always want to rev as far past the "red-line" as possible and as close to the "Fuel shutoff") hold R2 until you reach the point right before the "fuel shutoff", which you will have to remember where this is in your head. let it go right before you are at the spot where the engine will surge.

Go out and experiment with finding the Fuel Shutoff points on certain cars you have upgraded and tell me how much faster your 0-400m's are when you rev to the red-line and when you rev to the fuel shutoff point.
 
Good piece but not completely factual.
Whether its the game or in real life, most cars have the torque and horsepower drop off at redline and fuel cutoff.
To go any higher in rpm is useless and will lose power and speed.
If you really want to get the most speed out of your car, be it in real life or the game, look at the peak hp and torque curves to determine the shift points of the car. Staying within these parameters will yield more speed and power.
Thought Id add that to keep anyone from losing speed. ;) Other than that, good article Alexy2K. :thumbsup:
Misnblu
 
Originally posted by Hooligan


That is one damned good explanation. Thanks for saving me half an hour of typing. :D
Click to expand...

Interesting stuff..so these part time 4x4 vehicles are actually pretty poor to drive because all the wheels spin :spin: at the same time when power is delivered front and back?
 
How many vehicles in GT3 can you buy the YAW controller for. So far I have only noticed it for the Mitsu Evo VII GSR.


Howstuffworks.com is such an awesome website. I bet I've read 70% of the articles there, no joke.
 
Im glad to have helped someone with it.
Its been a great help to me in many things and most importantly, helping me to understand certain things I didnt know.
Misnblu
 
Ok, here are some more articles that will fill this thread.
Ive posted this information on other site and deem it appropriate to post them here too.
Here goes.

Rotational Inertia
Rotational Inertia (or Momentum)
How about "Rotational inertia is a harder concept to deal with than..." Rotational inertia is a concept a bit more difficult to deal with than unsprung weight. Inertia can be thought of as why a car wants to keep rolling once moving, or remain in place once stopped (unless you forget to set the parking brake on that hill). I believe the terms momentum and inertia are interchangeable. The term "flywheel effect" also refers to these concepts. In a car, there are a number of rotating masses which require energy to accelerate. Up front, ignoring the internal engine components like the crankshaft, we have to worry about the flywheel, clutch assembly, gears, axles, brake rotors and wheel/tire. Out back its a little simpler (for FWD) with just the brakes and wheel/tire contributing most of the mass.
Before continuing with our informal analysis here, I want to point out something very important about rotational inertia. We've all seen the ice skating move where the skater starts spinning. She pulls her arms in and speeds up, then extends them again and slows down. Why is this? Well, the further a mass is from the center of rotation, the faster it must travel for a given angular speed (how many degrees of an arc it traverses per time unit). The faster anything moves, the more energy it has, so when the arms are pulled in, conservation of energy says that the rotation rate must increase. Applying this to wheels and tires, which have most of their mass spread as far as possible from the rotation center, I think you'll agree that it naturally takes more energy to accelerate them. Example: Take a two identical masses, but one is a solid disk of diameter D, the other is a ring of diameter 2D. The ring will require more force to accelerate it (in a rotational manner).
The point of this discussion is as follows: There is a great deal of rotational mass to deal with in a car and tires and wheels may only make up half of it.
Estimates for weight (O.K. for comparison since they're all in the same gravity field :-))
Front: Rear:
Wheel/tire: 30-35 lbs each 30-35 lbs
Flywheel: 15-20 lbs
Clutch: 15 lbs
Halfshafts: 7-10 lbs each
Gears: 5-7 lbs
Rotors: 3-5 lbs 3-5 lbs
Misc: 3-5 lbs 3-5 lbs
-------------------------------------------------------
Total: 115-148 lbs 76-90 lbs
So a couple pounds here and there on wheels and tires will make a difference, but that difference is magnified because that weight is placed further from the axis of rotation than any other mentioned (flywheel and clutch are closest) - remember the ice skater. All these masses must be accelerated, so any reduction is a good thing.
So, I've given you my view of things, but can I prove it? When we talk about handling, I'd be hard pressed to prove anything unless I went out and raced identical cars with differing wheel weights. Since larger wheels normally mean lower profile, stiffer tires, I'd also be hard pressed to tell you about ride quality. You'll have to decide for yourself on that account.
When it comes to acceleration, however, I think I can provide at least a datapoint in support of my argument. Motor Trend in June, 1995 did a test where they evaluated the benefits of +1 and +2 wheel tire combinations on a BMW 540i (automatic transmission, I believe). Here are the key stats for the test.
Motor Trend Stats on BMW 540i

Stock +1 +2
Tire 225-60/15 225-55/16 235-45/17
Wheel (in) 15x7 16x7.5 17x8
0-60mph (sec) 6.9 6.9 7.0
1/4 mile (sec/mph) 15.3/96.5 15.3/96.1 15.4/95.8
Rolling Diameter (mm) 651 654 643
Note the steadily increasing acceleration times as the wheel size increases. Even with what should be superior traction from stickier compounds (I admit that a taller tire might launch better), the +1 and +2 combos don't perform. Especially the 17" setup which, with it's smaller diameter, should have a theoretical acceleration edge. Now this is only one datapoint where many more are needed, but it's important. It matches the seat of the pants reports from several Integra owners. It also pays to remember that despite the fact the BMW weighs around two tons (U.S.), it still has a superior torque to weight ratio over the latest generation Integra (~14:1 vs ~21:1). This will help reduce the effects of added weight.
"O.K.!", you say, "I am convinced, but handling is also important. It could be a worthwhile tradeoff." This is undoubtedly true, but how much handling do you really get? I have never seen a tire test where +1 and +2 combos are compared with the exact same tire type and width. Here we are comparing a P600 vs. a PZero! The handling gains were fantastic, but I'll bet if they had run a 15" PZero (if they could find a 60 series version), the difference in handling would have been noticeably less.
Finally, what about appearance? Well, you'll get no argument from me on that. Without a doubt, big beefy wheels with O-rings for tires just plain look good. Hey, I went the same route and replaced 13" wheels on my old Civic with nice big 15" hunks. Now, however, I think there are better choices. Here are my recommendations.
Max Performance (accel and corner):
15x6.5 or 15x7 with 205/50 or 215/50 tires
Best Looks:
17x7.5 or 17x8 with 215/40 tires
Best Compromise:
16x7 or 16x7.5 with 205/45 tires

Motor Trend Responds!
As the author of the Motor Trend article you quote in your wheel/tire article over at the Integra board, I thought I'd let you in on a few of the considerations made while performing that test.
First, there's really no way to go from a 15-inch wheel up to a 17 without increasing tread width (if you're attempting to maintain overall tire diameter). This is particularly true on the heavy BMW 540i (automatic) we used in our test. Load carrying is directly related to the volume of air in a tire. Of course as you reduce the aspect ratio of a tire, you reduce the volume of air available for load carrying. The solution, obviously, is to make the tire wider and therefore maintain a consistent volume of air (this is also why the 18-inch wheels used on the Porsche 911 Turbo have hollow spokes). Go back and re-read the article and you'll see that our trip up in wheel diameter was accompanied by considerations to maintain air volume.
One reason ride quality deteriorates so dramatically in Integras wearing large-diameter rubber is because the combination wasn't determined with an eye toward maintaining air volume. That's a consideration you may want to pass on to your readers as well.
We chose to use Pirelli tires consistently in our test so that we at least wouldn't be comparing between manufacturers. However, the reason we picked the P600 for the stock size, P700 for the 16-inchers and the PZero for the 17 was simply because that's what Pirelli sells and what they provided us. You're right, there aren't 60-series PZeroes around. However, when stepping up to larger diameter wheels, most buyers will likely also step up in the aggressiveness of tire tread and compound.
Again you're correct, the handling gains were tremendous. However, we did give up some ride comfort and probably poor weather traction (something we couldn't test here in sunny California).
All in all, I've enjoyed the Integra site quite a bit and found your article informative. You may just want to pass my thoughts along.
Sincerely,
John Pearley Huffman
Editor at Large
Motor Trend Magazine

Thanks to www.vtec.com for the information and the guys on www.j-body.org for their post on this.
Misnblu
 
April 06, 2002 11:33 Unsprung Weight
The Benefits of Low Calorie Donuts
(or Cutting Weight from Your Wheels and Tires)
By: Shawn Church
Yokohoma A008RSII (205-50ZR15) - 20 lbs
'94 GS-R wheels - 15 lbs
So you finally decided to take the plunge and modify your Acura (or Honda or just about any other car for that matter). You've looked at engine parts, you've looked at exhaust systems, you've even looked at body kits but nothing seems to offer the appearance and performance benefits of a good set of aftermarket wheels and performance tires. Congratulations chum, you've joined a pretty large group of car enthusiasts who have added uniqueness and performance to their cars...but do you know the whole story? There is no doubt that new wheels look great and going to bigger and better tires adds grip. There is more to choosing your running gear than just wheel size and offset (I know you already knew about those). "What else is there?" you say. What else indeed, it's the bane of all cars - added weight.
Before I start spouting off with a bunch of half-cocked (well hopefully closer to three-quarters) theories and partial proofs, let me say this. This is not intended to be a physics course. I've been out of college long enough to have forgotten a couple years of physics (took about 3 hours and a case of beer) and I have no desire to find, let alone read, my old textbooks. I'm going to try to show you the effects of weight using as much common sense as possible. If I've made errors, or if you'd like to work up some proofs, I will gladly listen.
Alright, down to business. Why is wheel/tire weight so important? Two concepts: Unsprung weight and rotational inertia. We'll address each one individually.
Unsprung Weight
How do you describe the job of a car's suspension? Well, there are a few different ways, but lets take the easy one. Your suspension is supposed to suspend your car above the road. If that was the only reason for the existence of springs and shocks though, why don't we just solidly mount the car to the axles? "That's obvious!" you say. Of course, you'd have a lot of trouble with bumps and corners with a solid suspension. This is because a suspension is supposed to allow your wheels and tires to follow the road, irregularities and all, while the body of the vehicle travels smoothly. Turning things around, the suspension should also keep the wheels and tires in maximum contact with the road for the best performance (this is more important than ride for us driving enthusiasts). So, to continue, for a suspension to be effective, it must allow the wheels and tires to accelerate and decelerate rapidly up and down while not allowing them to make excess motions (example - axle hop). The springs prevent the wheel assembly from traveling too far, while the dampers prevent oscillation by the spring.
O.K., time to tell you how wheel/tire weight plays in all this (in case you haven't figured it out). You see, every time you hit a bump, the wheel assembly is accelerated upwards, decelerates to a stop, then accelerates downward till it reaches equilibrium. If the wheel can't accelerate fast enough, shock is transmitted to the body, which may upset the balance of the car. As an example think of small, sharp edged speed bumps versus those gigantic, but wide, monsters in some lots. The sharp edged ones are much more annoying to traverse, aren't they? That's because they require the suspension to accelerate more rapidly. Now imagine going over some stutter bumps in a corner. You'll have a very rapid series of accelerations and decelerations. If the wheel is lighter, it will accelerate upwards and downwards faster (a=F/m). This means it will follow the road better and, even more importantly, allow the suspension to work better. The shock and spring will have to control less unsprung mass (weight will also suffice here), which means they can stop and start the motion of the assembly more easily. Unsprung mass (or weight) is commonly defined as mass not suspended (or sprung) from the suspension. This will typically include the wheel/tire, hub, brake, and some of the suspension pieces. On your typical FWD Integra, you'll probably see the following numbers (estimates).
Wheel/Tire: 30-36 lbs/each
Rotors: 3-5 lbs/each
Calipers: 1-2 lbs/each
Susp Pieces: 10-15 lbs/corner
-------------------------------------
Total Weight: 44-57 lbs each corner
I think that I've probably over estimated some of the weights, especially the unsprung suspension pieces, but the wheels and tires are accurate according to reports. What happens if we increase the wheel weight by 10 lbs? Well, we just added between 15% and 20% to the unsprung weight. Guess we'd better add better springs and shocks as well. If we drop weight, we'd see the opposite of course and might benefit with better ride and handling.
In all reality, the effect of unsprung weight changes aren't very noticeable (unless the changes are large), but they are there. If you race, they are even more important, so be careful. If you're going to add 17" wheels to your Integra, you probably should think about upgrading your springs and shocks too.


Rotational Inertia
Rotational Inertia (or Momentum)
How about "Rotational inertia is a harder concept to deal with than..." Rotational inertia is a concept a bit more difficult to deal with than unsprung weight. Inertia can be thought of as why a car wants to keep rolling once moving, or remain in place once stopped (unless you forget to set the parking brake on that hill). I believe the terms momentum and inertia are interchangeable. The term "flywheel effect" also refers to these concepts. In a car, there are a number of rotating masses which require energy to accelerate. Up front, ignoring the internal engine components like the crankshaft, we have to worry about the flywheel, clutch assembly, gears, axles, brake rotors and wheel/tire. Out back its a little simpler (for FWD) with just the brakes and wheel/tire contributing most of the mass.
Before continuing with our informal analysis here, I want to point out something very important about rotational inertia. We've all seen the ice skating move where the skater starts spinning. She pulls her arms in and speeds up, then extends them again and slows down. Why is this? Well, the further a mass is from the center of rotation, the faster it must travel for a given angular speed (how many degrees of an arc it traverses per time unit). The faster anything moves, the more energy it has, so when the arms are pulled in, conservation of energy says that the rotation rate must increase. Applying this to wheels and tires, which have most of their mass spread as far as possible from the rotation center, I think you'll agree that it naturally takes more energy to accelerate them. Example: Take a two identical masses, but one is a solid disk of diameter D, the other is a ring of diameter 2D. The ring will require more force to accelerate it (in a rotational manner).
The point of this discussion is as follows: There is a great deal of rotational mass to deal with in a car and tires and wheels may only make up half of it.
Estimates for weight (O.K. for comparison since they're all in the same gravity field :-))
Front: Rear:
Wheel/tire: 30-35 lbs each 30-35 lbs
Flywheel: 15-20 lbs
Clutch: 15 lbs
Halfshafts: 7-10 lbs each
Gears: 5-7 lbs
Rotors: 3-5 lbs 3-5 lbs
Misc: 3-5 lbs 3-5 lbs
-------------------------------------------------------
Total: 115-148 lbs 76-90 lbs
So a couple pounds here and there on wheels and tires will make a difference, but that difference is magnified because that weight is placed further from the axis of rotation than any other mentioned (flywheel and clutch are closest) - remember the ice skater. All these masses must be accelerated, so any reduction is a good thing.
So, I've given you my view of things, but can I prove it? When we talk about handling, I'd be hard pressed to prove anything unless I went out and raced identical cars with differing wheel weights. Since larger wheels normally mean lower profile, stiffer tires, I'd also be hard pressed to tell you about ride quality. You'll have to decide for yourself on that account.
When it comes to acceleration, however, I think I can provide at least a datapoint in support of my argument. Motor Trend in June, 1995 did a test where they evaluated the benefits of +1 and +2 wheel tire combinations on a BMW 540i (automatic transmission, I believe). Here are the key stats for the test.
Motor Trend Stats on BMW 540i

Stock +1 +2
Tire 225-60/15 225-55/16 235-45/17
Wheel (in) 15x7 16x7.5 17x8
0-60mph (sec) 6.9 6.9 7.0
1/4 mile (sec/mph) 15.3/96.5 15.3/96.1 15.4/95.8
Rolling Diameter (mm) 651 654 643
Note the steadily increasing acceleration times as the wheel size increases. Even with what should be superior traction from stickier compounds (I admit that a taller tire might launch better), the +1 and +2 combos don't perform. Especially the 17" setup which, with it's smaller diameter, should have a theoretical acceleration edge. Now this is only one datapoint where many more are needed, but it's important. It matches the seat of the pants reports from several Integra owners. It also pays to remember that despite the fact the BMW weighs around two tons (U.S.), it still has a superior torque to weight ratio over the latest generation Integra (~14:1 vs ~21:1). This will help reduce the effects of added weight.
"O.K.!", you say, "I am convinced, but handling is also important. It could be a worthwhile tradeoff." This is undoubtedly true, but how much handling do you really get? I have never seen a tire test where +1 and +2 combos are compared with the exact same tire type and width. Here we are comparing a P600 vs. a PZero! The handling gains were fantastic, but I'll bet if they had run a 15" PZero (if they could find a 60 series version), the difference in handling would have been noticeably less.
Finally, what about appearance? Well, you'll get no argument from me on that. Without a doubt, big beefy wheels with O-rings for tires just plain look good. Hey, I went the same route and replaced 13" wheels on my old Civic with nice big 15" hunks. Now, however, I think there are better choices. Here are my recommendations.
Max Performance (accel and corner):
15x6.5 or 15x7 with 205/50 or 215/50 tires
Best Looks:
17x7.5 or 17x8 with 215/40 tires
Best Compromise:
16x7 or 16x7.5 with 205/45 tires

Motor Trend Responds!
As the author of the Motor Trend article you quote in your wheel/tire article over at the Integra board, I thought I'd let you in on a few of the considerations made while performing that test.
First, there's really no way to go from a 15-inch wheel up to a 17 without increasing tread width (if you're attempting to maintain overall tire diameter). This is particularly true on the heavy BMW 540i (automatic) we used in our test. Load carrying is directly related to the volume of air in a tire. Of course as you reduce the aspect ratio of a tire, you reduce the volume of air available for load carrying. The solution, obviously, is to make the tire wider and therefore maintain a consistent volume of air (this is also why the 18-inch wheels used on the Porsche 911 Turbo have hollow spokes). Go back and re-read the article and you'll see that our trip up in wheel diameter was accompanied by considerations to maintain air volume.
One reason ride quality deteriorates so dramatically in Integras wearing large-diameter rubber is because the combination wasn't determined with an eye toward maintaining air volume. That's a consideration you may want to pass on to your readers as well.
We chose to use Pirelli tires consistently in our test so that we at least wouldn't be comparing between manufacturers. However, the reason we picked the P600 for the stock size, P700 for the 16-inchers and the PZero for the 17 was simply because that's what Pirelli sells and what they provided us. You're right, there aren't 60-series PZeroes around. However, when stepping up to larger diameter wheels, most buyers will likely also step up in the aggressiveness of tire tread and compound.
Again you're correct, the handling gains were tremendous. However, we did give up some ride comfort and probably poor weather traction (something we couldn't test here in sunny California).
All in all, I've enjoyed the Integra site quite a bit and found your article informative. You may just want to pass my thoughts along.
Sincerely,
John Pearley Huffman
Editor at Large
Motor Trend Magazine


Thanks to the guys at vtec.net for the information.
Thanks to J-body for the post too.
Misnblu
 
Since this all involves Car Physics, this should apply too.


Posted this on JBO and Speed Street.. so I'll post it here too..

Hopefully this will clear up some stuff when it comes to cams.

What is a camshaft? It’s the heart of the engine. It regulates the amount of fuel/air mixture that the engine can pull in and push out. It’s that simple. The amount of fuel the engine can efectively and eficiently burn and get rid of, will dictate the power the engine will generate. Not only that, but the cam will dictate where the peak power happens and how flat the power curves will be. That’s why it’s so crucial to select the right cam for every engine built. The wrong cam will destroy the engine’s potential for power no matter how much money you invest in the rest of the build.

Before I go any further on cams, we need to look at the piston as it pumps up and down and what the valves are doing.

Power stroke. The piston is at top dead center, intake and exhaust valves are both closed and the spark plug has just fired. The expansion of the ignited fuel/air mixture forces the piston down. Before the piston reaches bottom dead center, the exhaust valve starts to open.
Exhaust stroke. The piston is at bottom dead center and starts to come back up. The exhaust valve opens fully and starts to go closed. Before the piston reaches TDC, the intake valve starts to open and the exhaust valve is still partially open.
Intake stroke. The piston is now at TDC, both the intake and exhaust valves are partially open. As the piston travels back down the cylinder, the exhaust valve goes fully shut and the intake valve goes fully open and starts to shut.
Compression stroke. The piston is at BDC and starts to travel up the cylinder. The exhaust valve is still shut and the intake valve goes fully shut.
You’ll notice that during the piston travel, there is a time when both valves are open. This seems counter productive, but it is necessary for optimum performance. This is a term called "valve overlap". I’ll try to explain why this is necessary.
After the fuel/air mixture is ignited, the expansion of the burning gases will be complete prior to the piston reaching BDC, but there will still be pressure contained in the cylinder. When the exhaust valve starts to open prior to the piston reaching BDC, some of the pressure in the cylinder will flow past the exhaust valve into the head’s exhaust port. As the piston starts its’ travel back up the cylinder, the piston forces the remaining gasses in the cylinder out through the exhaust port. The velocity of the exhaust gasses flowing past the valve into the port creates a negative pressure (vacuum) in the combustion chamber (it’s the same principle as blowing across the top of a straw in a cup of water. Water will flow up the straw). Prior to the piston reaching TDC, the intake valve starts to open. The previously created vacuum in the combustion chamber will draw fresh air/fuel mixture into the combustion chamber and some will even escape into the exhaust port. This will ensure that all of the spent gasses are removed from the combustion chamber. This process is called "scavenging". When the piston reaches TDC and starts its’ travel back down the cylinder, the exhaust valve will go fully closed.

The point in the cycle where the intake valve opens is very important. If the intake valve opens too late in the cycle, the initial amount of fuel/air mixture draw into the combustion chamber is reduced and spent gasses will not be effectively flushed from the chamber. If the intake valve opens too early in the cycle, vacuum will be reduced and exhaust gasses will be forced into the intake manifold. When exhaust gasses are forced into the intake manifold, vacuum is adversely affected and the intake runners will soot up. This effect is called "reversion".

The point where the exhaust valve goes fully shut is also important. If the exhaust valve closes too late in the cycle, the combustion chamber will be "over-scavenged". This will cause an excessive amount of fuel/air mixture to escape into the exhaust port because the intake valve is still partially open. If the exhaust valve closes too soon, the scavenging effect will be reduced, trapping exhaust gasses in the combustion chamber.

As you can see, valve overlap is a touchy time frame in the piston’s travel. Cam grinders have spent countless hours of research trying to get it just right.

Continuing the piston’s trip through the overlap phase and back down the cylinder for the intake stroke, the intake valve will go fully open and start to shut. After the piston reaches BDC and starts its’ way back up the cylinder for the compression stroke, the intake valve will go closed. The point that the intake valve goes closed has a large effect on cylinder pressure. When the piston is traveling back up the cylinder, it will force some of the fuel/air mixture past the still open intake valve into the intake port. When the intake valve closes early in the cycle, more fuel/air mixture will be trapped in the cylinder and more cylinder pressure will be created. If the intake valve closes later in the cycle, some of the fuel/air mixture will be forced past the intake valve into the intake port, which will reduce cylinder pressure.

While valve overlap is ground into the cam and can not be changed, the point during the piston’s travel that the intake valve closes can be changed. This is called "valve timing" which is not to be confused with ignition timing. It is also referred as "cam phasing" or "degreeing". When you here the phrase "advance/retard the cam", it simply means to change the position of the intake valve closing point. To advance the cam, you are closing the intake valve earlier in the cycle and retarding the cam will shut the intake valve later in the cycle. Now, before you get all excited and fired up to advance your cam, you need to remember that the intake opening, exhaust opening and exhaust closing points will also be advanced. I’ll cover cam timing in more detail latter.

Lobe Separation Angle (LSA) is also called Lobe Center Angle (LCA). This term is often confused with Lobe Centerline, which I’ll address later. The best way that I can describe LSA is to imagine yourself holding a cam in front of you looking at either end of it. Now cut off the journal so you can look directly at the intake and exhaust lobes. You will notice that the bottom of the lobes closest to each other, actually overlap. Remember valve overlap that we’ve already discussed? Now find the center of each lobe at their highest points. Draw a straight line from these points to the center of the cam. The angle these two lines create is the LSA. The angle is expressed in degrees of angle. If you move the lobes closer to each other, the LSA gets smaller/tighter and the overlap is increased. When looking at different cam profiles for an engine, you will always (almost always) see the LSA listed. While this is a very important consideration, the valve overlap is often forgotten. A profile with a tight LSA will also have more overlap and this is what you should be thinking about when picking a cam, but that’s for a different article.

I mentioned that the cam’s Lobe Centerline is often confused with LSA/LCA. I’ll try to explain LC now. Remember when I was talking about cam timing and the intake valve’s closing point? This is the cam’s Lobe Centerline. It is the intake lobe’s center (at its’ highest point) position in relation to the position of the piston at TDC of the intake stroke. The LC is expressed in a measurement of degrees like LSA is. It is usually with 4 degrees of the LSA designation, so it is often confused. When the piston is at TDC intake stroke, the intake lobe will be pushing the lifter up, opening the intake valve. The center of the intake lobe will be around 106 degrees before the piston is at TDC, or the piston’s position of 0 degrees. I’ll try to clarify that last sentence a little. For every two revolutions that the crankshaft makes, the cam will rotate once. All measurements of degrees are actually "crank degrees". One full crank revolution is 360 degrees. When the piston is at TDC, piston position is 0 crank degree and when it is at BDC, piston position is 180 crank degrees. When the piston is at approximately 106 degrees past TDC intake stroke, the intake lobe will be straight up and the intake valve will be fully open. Cams will come with a recommended centerline position from the manufacture. The one in this example is installed on a 106 Lobe Centerline. When a cam is advanced or retarded, the Lobe Centerline is changed. If we were to advance this cam 4 degrees, we would install it at 102 degree Lobe Centerline and 110 degree Lobe Centerline if we retarded the cam 4 degrees. I mentioned earlier that advancing the cam will increase cylinder pressure. It will to a point. When the cam is advanced, the intake valve will open earlier during the exhaust stroke and the exhaust valve will shut earlier during the intake stroke. If the cam is advanced too far, reversion will occur and the exhaust gasses will not be adequately scavenged. Four degrees advance is usually the most that you can safely advance a cam beyond the manufacture’s recommended LC. When the cam is retarded, cylinder pressure will be reduced but the scavenging process is increased. If you are experiencing pre-detonation, retarding the cam will help. It also has a tendency to move peak hp to a higher rpm. Again, care should be taken when changing cam timing. Another consideration when playing with cam timing is piston to valve clearance. When you change the valve events (timing), the clearances will change and should be checked.

Since we talking degrees, I might as well cover duration. Duration is the amount of time that the valve is open in relation to crankshaft rotation. It is expressed in crankshaft degrees. If we have a cam with a duration of 300 degrees, the valve will be open for 300 degrees of crankshaft rotation. There are two methods used to describe duration. Seat-to-seat or Advertised duration and at .050" duration. The advertised duration is the measurement from the very beginning to the very end of the lobe ramps. It is difficult to get an accurate measurement using advertised duration. Theoretically, you should be able to find zero lift of the lobe ramps, but it is harder than it sounds. To simplify this method, cam grinders pick an arbitrary number unique to themselves. It could be anywhere from .002" lift to .008" lift. Because cam grinders wont get together and give us consistent advertised duration lift points, they came up with a standardized method of @.050" lift. When the lobe is at .050" lift, the duration starts and ends when the lobe is at .050" lift on the other side of the lobe. When comparing cam profiles, it’s best to use the .050" duration numbers.

Duration is probably the most important aspect of a cam’s profile to pin down when selecting a cam. Cubic inch displacement, cylinder head characteristics, EFI, NOS, aspiration, compression, drive train, vehicle application and weight, desired peak power, desired engine operating rpm…….etc are all factors to consider when picking a cam. I’ve found that it’s usually a task best left to the cam grinder to make. I’m not going to get into cam selection in this article, but I should talk a bit about the effects that duration has on an engine.

LSA for a performance ground cam is typically between 106-114 degrees. Sometimes even less than 106 is ground for stroker engines. When duration is increased and LSA is constant, the valve overlap is increased. When overlap is increased, vacuum is lower, cylinder pressure is reduced and reversion is increased. These are all undesirable traits for low end and midrange torque. You need cylinder pressure and vacuum for low end torque. Unfortunately, we cant have our cake and eat it too. For high rpm power, duration must be increased but we cant widen the LSA or the valve events will be occurring during wrong points in the piston’s travel. As piston speed is increased, the time that the cylinder can adequately fill and evacuate is drastically reduced. To compensate for this, we must increase the time that the intake valve is open to admit more fuel/air mixture, and the exhaust valve must be open longer for exhaust gas evacuation. The only way to do this, is to increase duration and lift. We are limited to the amount of lift because the lobe flanks/ramps have to spread out or the lifter will not ride up and down the lobe properly. Roller lifters help because they will transverse up a much sharper lobe flank than a flat tappet lifter, but there’s still a limit for them as well. A very aggressive profile is also hard on the entire valve train and camshaft.

Lift is the total height of the lobe. It is a measurement that is described in inches. A lobe lift of .500" is ½". To get the total valve lift, we simply multiply the lobe lift by the rocker arm ratio. A lobe lift of .500" and a rocker arm ratio of 1.5 would give us a total valve lift of .750". If we used rocker arms with a 1.6 ratio, our total valve lift would be .800". When looking at cam profiles, the lift listed is typically total valve lift using 1.5 rockers. If you want to know what it would be with 1.6 rockers, simply divide the lift by 1.5 then multiply the sum by 1.6. .750 / 1.5=.500 X 1.6=.800

Cams lobes are ground either with either a symmetrical or asymmetrical profile. A symmetrical profile is a lobe that has mirrored opening and closing ramps/flanks. If you were to cut the lobe in half, both halves would be identical to each other. An asymmetrical profile will have different opening and closing ramps/flanks. Depending on the grind, one ramp will be more aggressive than the other. Cam grinders have found that the speed in which the valve opens and closes can greatly affect performance. Typically, the closing ramp will not be as aggressive as the opening ramp on asymmetrical grinds. This will prevent the valve from bouncing off the valve seat when closing.

As the cam rotates and the lifter makes the transition from the cam’s base circle to the opening flank, a ramp is ground into the base of the lobe on better cam profiles. The ramp provides a gentle transition from base circle to the flank. Ramps were first used for mechanical lifters that ran with a lot of lash. Picture a lifter riding on the cam’s base circle with .012" of free play (lash). As the cam rotates and the lifter hits the flank, the lash it taken up immediately causing a shock to the lobe and a noticeable tap when the rocker arm hits the valve stem tip. The ramp will allow the lifter to ride up on the lobe flank gently. As the lifter is traveling down the closing side of the lobe, another ramp is used to have the same effect on the lifter prior to making the transition from flank to the base circle. What many people don’t realize, is hydraulic lifters need this same gentle transition. When a hydraulic lifter makes the transition from the base circle to the flank, the initial shock will compress the spring in the lifter affecting total valve lift and duration. The opening and closing ramps reduce these initial and exiting shocks. Not all cams are ground with transition ramps and even fewer have closing ramps at all.

To aid the engine to effectively evacuate the exhaust gasses, dual pattern cams are used. A dual pattern cam will have a different lift and duration between the intake and exhaust lobes. Small Block Chevy’s for example, have poor exhaust ports that needs a little help evacuating exhaust gasses. A little more duration and lift on the exhaust lobe will give the engine more time to expel the exhaust gasses.

If you’ve made it this far, I hope your not more confused than before you started. I have a tendency to ramble when I get talking about hottrodding.

Thanks to Robogeek for this tidbit of information and hopefully this thread will enlighten everyone just a bit better on Car physics and engine dynamics.
Good luck with your cars ppl.
Misnblu
 
power to weight ratio is the torque and it is usually expressed as lb/ft or something like that.
 
Originally posted by BMW X5 SPORTS
power to weight ratio is the torque and it is usually expressed as lb/ft or something like that.
Click to expand...

Um, no it's not. Read a couple of posts back. Might learn something...or many things.
 
Insurance companies used to use Weight to power ratios to determine if a car was "high performance" . Anything less than 13 to 1 Weight to power ratio increased your premium amount accordingly!
 
Misnblu does an excellent job of explaining camshafts. However, I wouldn't suggest running out to your garage and changing your cam timing. If you do successfully get your timing belt off, without damaging it, and reinstalled. You may set into motion a possible catastrophic effect. In some modern engines there is not enough clearence inside the combustion chamber for the piston to be at TDC and the vaves to be open. They may collide. Also, if your engine has a camshaft position sensor on it , it's reading will be inaccurate, therefore casusing your vehicle control module to enter an error code. It will turn on your malfunction indicator lamp.And set an error code which will not go away until the system is repaired.
 
Power to weight ratio is always wanted to be in the high #'s, however it can only benefit you to a point. To little weight and too much power adds to traction loss.
telling the torque on one car to the torque on another car would require 2 of the same identical cars in a simulated environment where wheelspin was not a factor. Curb weight is how much the car weights with no driver and not in motion. and what you said about "IS there an idea power/weight ratio...Maybe there is, not that I'm sure of, however there IS an ideal R/S Ratio or Rod To Stroke Ratio. It is the ratio of the length of the connecting rod to the length of the piston stroke, or the distance the piston travels from the top to the bottom of its stroke. As the ratio gets lower, the amount of stress on engine internals increases exponentially, killing long-term reliability. The higher the number is, the slower the piston is traveling, killing power output.in which the B16A is .01 off of ideal, that's why it's such a good engine. Ideal R/S Ratio is 1.75:1 the B16A is 1.74:1
 
I really hate american measurement system!!!
You mix everything like the liters of the engine wich is SI with cubic feet!!!
This makes you have to be always adding constants so that the calculationos don't fail, it just dfoesn't make sense!!!
At least it seems that there is a tendence in changing to the much more simple and easy to use metric system.
 
Americans are the only country in the world using this antiquated system and should be up to date.
I dont know whats up with the American way, but we need to get with the world economy and change to the metric system. :banghead:
Oh well, leave it up to ppl that dont want to change anything.
Misnblu
 
The funny thing is....The american measurment of distance is the most humanly relevant...90% of it's measurments are derived from the human body itself....Second I've never heard of anyone measuring an engine with cubic feet....I don't know who in the hell you're talking to..But I've only heard of CC's and CI'S (inches) if you didn't know that already
 
The funny thing is..It was the foreigners that cost us billions of dollars in $ due to their inability to realize american science doesn't use the metric system...I forgot what vessel it was for, but Russian scientists used SAE measurments to build their derivitive of a space shuttle for us, and sent it to america to finish, and american scientist, being the SI standradists they are..used the metric system on the other half..And to make a long story short..IT failed, because of Foreign countries using America's measurment
 
Originally posted by alex_gt
This excellent piece was posted by :star:12sec:honda::star: in the :gt:3 forum :thumbsup:

Ok, I will try and explain this like I am talking to a 6 year old.

There are 2 main points of interest on your tachometer (The dial that tells what RPMs the engine is revving at) One is the spot where the manufacturer has set the "Redline" this is where they recommend that you shift or else you will damage the engine, it is visible on the tachometer with a Red-Line. When you race with Automatic tranny it will always shift right at the red line.

The other point of interest is the "Feul Shutoff" This is programmed into the computer of the car to cut off the engines fuel supply at a certain RPM because revving any higher would severely damage the engine, There is no spot on the actual tachometer to show you where this is but the only way to tell is to hold R2 when accelerating and wait until the engine starts to surge. When racing, you want to always rev the engine as close to the "Fuel Shutoff" as possible.

Also, when you buy a "Racing Chip" or "Engine Balance" or most of the engine NA Stage upgrades, it will reset the cars computer and it will usually have a higher "Fuel Shutoff" point after you have done some upgrades.

If you race with auto trans, and you want to keep revving past the "Red-Line" and rev all the way to the "Fuel Sutoff" (The higher you rev the faster you go, no matter what, so you always want to rev as far past the "red-line" as possible and as close to the "Fuel shutoff") hold R2 until you reach the point right before the "fuel shutoff", which you will have to remember where this is in your head. let it go right before you are at the spot where the engine will surge.

Go out and experiment with finding the Fuel Shutoff points on certain cars you have upgraded and tell me how much faster your 0-400m's are when you rev to the red-line and when you rev to the fuel shutoff point.
Click to expand...

I think your a lil wrong on this one. From what I know, "Fuel Shutoff" happens because the engine is ingesting more air then the injectors can provide fuel for so the computer shuts it down to make it quit. Upgrading the Fuel Pump, Bigger Injectors, etc. will help stop this. Also, another thing, the "Rev Limiter" that you didnt mention, was added b/c the stock tires with are usually pretty poor, have a low speed rating, so they add the "Rev Limiter" to make sure you dont excess that set speed. Upgrading tires and getting a new chip or ECM is the only way to get past that. Also, on post #12 by talentless, I noticed how he had some Bar measurements, as most may or may not know, that is the popular medium in japan for measuring boost. But one Bar equals atmospheric pressure or around 14.7 lbs/in.
 
Thanks Early for the input man.
Oh and welcome to the site for sure. ;)
Misnblu
 

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