NA, turbo/super charge

[streetsucka204]

why can you only NA, turbo/super charge only certain cars and not others? for example, why can you not NA tune a Supra RZ or turbo charge a Viper? also why cant you equip NA stage 3 with a stage 4 turbo or something like that? one more question, how come you can only do the bore and stroke on some cars???

i just had to ask, hopefully some one will give a good explaination 👍

 

[Ezz777]

no real good explanation - only that that is what PD gave us, so be happy with it. I am sure someone will give a different version of this in relation to what is feasible for a given engine, but in the end, Reality <> GT4

From memory the skylines and miatas tend to have the most options available to them in case you care.

 

[Wolfe]

Yeah, Ezz777 is right, the cars just seem to get some things and not others for absolutely no reason at all.

PD has also got it set up so that fully-tuned Japanese cars are more powerful than fully-tuned cars from any other nation...

 

[amp88]

There's a decent (I suppose) explanation for not being able to both turbocharge and NA tune a car. Turbocharging a non-turbocharged engine (or increasing turbo boost/power output of an already turbocharged engine) usually requires a drop in the compression ratio of the engine. NA tuning, however, usually would maintain a higher compression ratio in the engine. It's not really possible to do both.

In real life, of course, it's possible to both turbocharge an engine and to tune it (e.g. to fit a turbo (or a bigger turbo) and to change the camshaft).

 

[Alfaholic]

Some cars, like the *EDITED* RZ *EDITED* you mentioned specifically, are already turbocharged, so an N/A tuning would be impractical. New engine internals would be required, for one thing, not to mention an new induction system and different exhaust design, all to make an engine less powerful.

Can't combine the two simply because n/a stands for normally aspirated, i.e. no forced induction. This means making an engine more powerful without the aid of a turbo or supercharger, and therefore by definition cannot be combined with a forced induction engine or upgrade. The principal I believe you are thinking of, that an engine's internals can be tuned as well as force induction added, however, is valid, and with more expensive and complex turbo upgrades, you will find that the internals are changed to optimise performance of the engine with the turbo. Pistons, compression ratios, cam profiles and timeing, all will be considered and possibly changed to suit the turbocharged motor, as will the fuelling system and engine management system.

In GT4, as has been said, there seems to be a few basic rules followed on some cars, but noone I have seen has yet been able to apply a good logical system that answers every case of why some cars are not allowed some upgrades. I certainly can't figure it out. But, it's what we got and we live with it.

 

[Greycap]

I don't want to sound boring Alfaholic, but the Supra SZ is the NA version and the RZ has a turbo. You probably meant the RZ.

 

[Sycoarkantos]

yea what is siad above and also that with some cars were only really designed for NA tuning. e.g NSX, RX8.... but i won't blabber on . the only way to really put on a turbo for these cars takes about 1-1.5years for a tuning componye.g HKS to make a turbo that is compatible with that engine, and wont cause all the engine internals to become worn down. and PD probly couldn't really bo bothered (or ran out of time) to make all these things.


Hope that clears some things up

 

[Alfaholic]

I don't want to sound boring Alfaholic, but the Supra SZ is the NA version and the RZ has a turbo. You probably meant the RZ.

*slaps forehead* Yes you are correct. I was thinking of the RZ. Editing my post now. Cheers Greycap

 

[Greycap]

You're welcome Alfaholic.

 

[Wolfe]

Hmm...I didn't notice Streetsucka had asked why NA and Turbo can't be put together...indeed, the whole point of NA is that it's "Naturally aspirated." In other words, no forced induction.

Anyway, although some unavailable modifications are logical, in many cases, it's just GT4. Besides, given the relatively extreme extent to which one can modify his/her vehicle in GT4, changing the compression ratio, boring and stroking an engine, etc. wouldn't be that big of a deal. Also, any engine ever built can be turbocharged if you do it right. The only notable exception to this that I can think of at the moment is the RENESIS. As far as I know they still haven't figured out how to turbocharge it.

 

[Greycap]

Well, the previous generation rotary was turbocharged, so that is just a matter of time, I think.

 

[Scaff]

Also, any engine ever built can be turbocharged if you do it right.

Quite right, in a lot of cars the engine is not the problem, it's the size of the engine bay. Having sufficent room to add a turbo/supercharger, and then still having enough room to ensure that the lot doesn't overheat.

Regards

Scaff

 

[streetsucka204]

Hmm...I didn't notice Streetsucka had asked why NA and Turbo can't be put together...indeed, the whole point of NA is that it's "Naturally aspirated." In other words, no forced induction.

lol yeah... what was i thinking??? everything now makes sense. one more thing though, why are the front wheel drive cars not as powerful as rear/all wheel drive cars?

ugh... im sure theres a really simple answer that i just havent thought of. 👍

 

[amp88]

The reason most front-wheel drive cars are less powerful than rear- of four-wheel drive cars is simply a matter of how the engine power is transmitted to the road. In a front-wheel drive car, the front tyres have to do a lot of things. They not only have to steer the car, but they also have to transmit the engine power/torque to the road.

Say, for example, a car's tyre has 10 "grip units". If the current load through the tyre (i.e. what it has to do) is anything less than a total of 10, the tyre will grip. Anything more than 10 and the tyre will lose grip (i.e. start to spin or slide). In a powerful front wheel drive car, when accelerating you might need something like 6 or 7 units of grip just for the acceleration. Now, start turning round a corner. That would take another 6 or 7 probably. So, you end up going a lot over 10 and the tyre can't cope. Now take a powerful rear wheel drive car. Again, it's going to need about 6 or 7 units of grip for the acceleration. However, the acceleration is done by the rear tyres, leaving the front tyres with basically all 10 of their grip units free. Hence the car can be turning and accelerating at the same time whilst putting down a lot more power.

Another reason is weight transfer. Whenever you see a car accelerating you'll notice the front of the car rising and the rear squatting. This is caused by weight transfer, the acceleration forces "weight" backwards. Now, in a rear- or four-wheel drive car, this weight transfer is actually handy in launching the car. Because the weight is moving towards the driven wheels, there is more force available to the tyres, meaning the grip level of the tyre increases, allowing it to put more power down (this is basically what downforce gives you: more weight on the tyres). Of course, in a front wheel drive car, the weight transfer has the opposite effect. It takes weight away from the front wheels, decreasing the grip level of the tyres, meaning less power can be transferred to the road.

Most people would agree that a sensible limit for the engine power of a front-wheel drive road car is something between 220 and 270bhp.

Of course, it IS possible (in real life at least) to have a front-wheel drive car with a hugely powerful engine, however, the power transmission problem still exists, so having all those extra horses isn't helping your acceleration at all (and is almost certainly hindering it), at least at low speeds.

 

[niky]

Actually (just to add my 0.0017 cents), the state of the art for FF keeps pushing the "hp barrier" further and further back. Ten years ago, most people would've said 250 hp is too much for an FF Hot Hatch (never mind the big FFs), and Twenty years ago, they would've said 200 hp was too much. I agree with amp88 that 270 appears to be the current limit. Most of the "hottest" hot hatches have some traction issues at around 220-250 (notably the Alfa 147 GTA), and those without suffer terrible torque steer and camber change issues.

The most powerful FF I can think of with sporting intentions, the Nissan Altima V6 SE-R, does 0-60 in under six seconds at around 260 hp, but take note, it's a heavy car (which definitely HELPS power transmission), and it still suffers from a lot of torque steer.

Another problem in power transmission is... errh... transmissions. A lot of the older transmissions on FF cars (pre-2000) will crap out if you turbocharge the car to ridiculous power levels. Front Wheel drive SR20 Sentras, which can be tuned to around 500 streetable horsepower, are notorious for crapping out transmissions. The problem is that packaging and placement issues don't allow you to put a really big beefy tranny in there, unlike in FR cars. Newer FF trannys are more durable, but you won't be seeing much use out of trannies designed for 170-200 hp if you're pushing over 300. Oh, and drive-axles are also a problem, as they can't make these very thick on FF cars (interferes with steering). I should know, I've broken one. I met someone who goes drag racing with his car (we used to have the same cars... don't know if he still has his) who has had to replace three of them.

Some of the newer cars are pushing the envelope, though... the SRT4 has beefy equipment up front to deal with the power. Won't be surprised if they do release a sport compact in the next few years with 300hp even to the front wheels... but it seems that the best balance nowadays is around 200-220hp. Maybe in a few years, they'll "rediscover" four wheel steering (last seen in FF on the Prelude, I think), and will be able to put much more power in without horrible understeer and tire wear.

You can make an FF car ridiculously powerful and streetable, but it won't be nearly as fast as an FR or AWD car at the same power, and you won't be getting much life out of your engine, transmission or front tires.

 

[amp88]

...

Interesting post. I hadn't thought about lack of space limiting the strength of components in FF car's gearboxes 👍

 

[niky]

It's something they've been working hard at. Drag racing can only improve the breed. I'm particularly disappointed, though, that "Pro-FWD" dragsters are now resorting to what appears to be a longitudinal mount engine with a beefy tranny, especially since manufacturers are now getting much more into it. I would prefer to see them develop transverse mounts and gearboxes to their fullest, and have a trickle down effect from this.

Fun fact: Volkswagen's DSG allows them to package the gears more efficiently. Third gear is usually a breaking point for transverse FF gearboxes, but it's more robust in a DSG. Problem is, the DSG can't be made manual, as you'd have to have an IQ of 200 remember the maze you'd have to go through while shifting.

 

[mafia_boy]

Hey Streetsucka, there are a couple of reasons why you can only do certain things to certain cars in the game but it doesn't apply to all cars.

1. On some versions there is an NA AND a turbocharged/supercharged variant. The best examples are the Supra RZ (turbo) and SZ-R (NA), the 3000GT SR (NA) and the MR/VR-4's (turbo), the R32 Skyline GTS-t and GT-R (both turbo) and the GTS25 (NA)....and last but not least, the S13/S14 K's (turbo) and Q's (NA), and the S15 Silvia Spec R (turbo) and Spec S or Varietta (NA). Therefore they concentrate on working those cars with those appropriate parts. While it's true that most factory NA cars on GT4 you CAN turbocharge or supercharge, PD isn't always on the ball when it comes to keeping up to date with what's out for the aftermarket, although they did a good effort with the Tuners Hall.

2.Some cars have the ability to have NA AND turbo work done and then select between what mods you need for the appropriate races, not just NA or turbo only, the best examples of this are the Civics, but also apply to a lot of cars. Most cars have have NOS ability but not all cars. I feel it's just the choices that PD makes but to me it adds to the challenge IMO. It also shows some semblance of realism to the game but then gets hypocritical on itself very hard (seeing you can't NOS a Jaguar LeMans car.....but then you can supercharge a Speed 12 now or get 7s with a 501hp WRX?? ).

I dunno, it's a driving game, the gameplay and graphics are unmatched for a console driver.....I love it so I tolerate it's flaws.

Mafs!!

 

[Alfaholic]

Interesting post. I hadn't thought about lack of space limiting the strength of components in FF car's gearboxes 👍

There's also a limitation on space available for the engine itself, because the gearbox has to more-or-less line up with the front axle,so the engine has to sit either in front or behind the axle. Therefore very few FF cars have room for a nice big V8 under the bonnet. Since more power generally means a bigger engine, this limits power. Truth is, the 250odd BHP that you can currently get in an FF car is as much power as you will find in most similarly priced mainstream RWD competition for that car, and although 300bhp doesn't sound that special nowadays, you will find that there are not actually all that many cars available that exceed it, and most of those that do have more than 6 cylinders and more than 3.5 litres, i.e. very big engines, and they tend to be small volume luxury or sportscars. FF cars aren't really lagging behind in the power race in any market in which they are competing at the moment.

There are exceptions. The Lancia Thema 8.32 had a modified (different crank at least) Ferrari V8 from the 308 QV, mounted in front, and driving only the front wheels. Cadillac, also, have put a Northstar V8 powered front wheel drive car on the market. I believe it was an STS, and I don't believe that Cadillac are unique in the North American market for offering a V8 FWD car. Both of these were large cars. It's not common, because it does not make packaging sense, but it has been done, and noone, to my knowledge, has found room for a V10 or V12 in an FF layout yet. On the other hand, I am quite sure that there are plenty of tuned 4 cylinder cars out there throwing more than 400bhp through their front wheels. Evo (or Car, can't remember) recently tested a new Mini with way beyond 300bhp.

 

[Verbal]

(...)
Say, for example, a car's tyre has 10 "grip units". If the current load through the tyre (i.e. what it has to do) is anything less than a total of 10, the tyre will grip. Anything more than 10 and the tyre will lose grip (i.e. start to spin or slide). In a powerful front wheel drive car, when accelerating you might need something like 6 or 7 units of grip just for the acceleration. Now, start turning round a corner. That would take another 6 or 7 probably. So, you end up going a lot over 10 and the tyre can't cope. Now take a powerful rear wheel drive car. Again, it's going to need about 6 or 7 units of grip for the acceleration. However, the acceleration is done by the rear tyres, leaving the front tyres with basically all 10 of their grip units free. Hence the car can be turning and accelerating at the same time whilst putting down a lot more power.
(...)

That's not quite right, the rear tires will need to transmit just as much (depending on the weight distribution) lateral force as the front tires, i.e. if you need "6 units" for cornering at the front, you also need "6 units" at the back. So when accelerating in a corner with the RWD your front tires are allright, but you use up your "grip units" at the rear, i.e. now you have power oversteer instead of a fwd's understeer. The traction advantage of a rwd is only due to the dynamic weight transfer you describe.

 

[Alfaholic]

That's not quite right, the rear tires will need to transmit just as much (depending on the weight distribution) lateral force as the front tires, i.e. if you need "6 units" for cornering at the front, you also need "6 units" at the back. So when accelerating in a corner with the RWD your front tires are allright, but you use up your "grip units" at the rear, i.e. now you have power oversteer instead of a fwd's understeer. The traction advantage of a rwd is only due to the dynamic weight transfer you describe.

That's also not quite right, because the front wheels are not facing straight ahead (since you are going around a corner, you will have some lock applied on the wheel) and therefore are attacking the road surface with additional load than the rears, regardless of the car's layout.

 

[amp88]

That's not quite right, the rear tires will need to transmit just as much (depending on the weight distribution) lateral force as the front tires, i.e. if you need "6 units" for cornering at the front, you also need "6 units" at the back. So when accelerating in a corner with the RWD your front tires are allright, but you use up your "grip units" at the rear, i.e. now you have power oversteer instead of a fwd's understeer. The traction advantage of a rwd is only due to the dynamic weight transfer you describe.

It was of course a simplified example, meant to describe the basic concepts rather than the fine details. The cornering load on the rear tyres would not be as much as on the front tyres, as Alfaholic has already said

 

[Verbal]

That's also not quite right, because the front wheels are not facing straight ahead (since you are going around a corner, you will have some lock applied on the wheel) and therefore are attacking the road surface with additional load than the rears, regardless of the car's layout.

No. It would appear that way when you look at the wheels' angles relative to the car's body, but that's not what matters. The angle between the direction the wheels are facing and the direction they are actually moving will be the same front and rear (static cornering, same wheel loads).

 

[niky]

No matter what you do, actually, the front tires will always carry more load in cornering, regardless of the drivetrain layout, at the initial turn-in. The load only balances out during steady-state lateral acceleration, and then transfers to the rear upon acceleration. In general, unless the car is MR or RR, the front wheels will always generate more cornering load.

In static cornering, the lateral load is usually perpendicular to the front tire's rotation and at an angle to the rear tire's rotation. Understeer midturn is exacerbated by the angle of the lateral load to the rear tires, the greater the angle, the greater the tendency for understeer, as the rear tires will tend to want to go in the original direction of travel.

Most of the load is on the front tires because they're the ones that are actually trying to turn. There is maximum lateral force at work on the fronts, as they're more perpendicular to the turn. The rear tires are experiencing only partial lateral loads, partially because they're not perpendicular to the lateral load, and partially because most of the weight (usually) is up front, no matter what the car... except in MR cars, but then, that's why they turn so well, because the rear tires share more of the cornering work with the fronts.

Now, in an FR car, due to a better weight balance, there is slightly more load on the rear tires than in FF cars, but this does not remove understeer. Some FR cars understeer like dogs, most FR cars can turn better because their suspension geometry is not compromised by having to share the steering wheels with the drivetrain. And under power, the REAR wheels will push WIDE of the line and cause the car to rotate faster (increase in angle of turn... oversteer). In an FF car, under power, the FRONT wheels will push wide and cause the car to rotate slower. (Simply, decreased angle of turn, UNDERSTEER).

What IS true, is that In static cornering, FR and FF cars may react in the same way while freewheeling... especially if it's one of the newer and better balanced FF cars. It's what they do when you brake or accelerate in corners that sets them apart.

 

[Wolfe]

The only cornering-related load placed on the rear tires is the friction, or resistance, against the rear end's inertia. The front tires are pulling/pushing the front end into the corner, and the car's body and chassis rotate along with the front end (obviously, or hopefully ), causing the rear end to rotate as well. All the rear tires then have to do is continue rolling, resisting the inertia of the rear end, which wants to keep going straight. If they are overloaded by this inertia, they slide/spin, the rear end goes wide, and you have oversteer.

 

[Verbal]

Most of the load is on the front tires because they're the ones that are actually trying to turn. There is maximum lateral force at work on the fronts, as they're more perpendicular to the turn. The rear tires are experiencing only partial lateral loads, partially because they're not perpendicular to the lateral load, and partially because most of the weight (usually) is up front, no matter what the car... except in MR cars, but then, that's why they turn so well, because the rear tires share more of the cornering work with the fronts.

I suck at drawing, but anyway, this is about what it looks like (reduced to a bicycle model) when a car is going through a turn:

All parts of the car are on a circular path around the same midpoint, the momentary direction of movement of any point on the car is tangential to that path. Steady state movement on a constant radius means there's a constant acceleration towards the midpoint at all points of the car. If the mass is evenly distributed between front and rear, that means there has to be also the same force front and rear. For the same force the same tire under the same load will also need to have the same slip angle (so actually when you're going through a turn, you're always in a slight drift, as that's how a tire produces lateral force...).
This is assuming an equal weight distribution of course, but what I'm getting at is that the idea of the front wheels being more stressed "because they're the ones that are doing the turn" is a misconception. Of course FWD cars typically have a more forward biased weight distribution and therefore are more prone to understeer, no question about that.

 

[Wolfe]

Here are pictures of the forces being applied to each tire in a clutch disengaged (engine disconnected from transmission), constant-steering-angle situation, in an FF, FR, and RR (in that order):



In both of the front-engined vehicles, the front outside tire is being worked harder than the rear outside tire (And this is without trying to accelerate or brake).

In the front-wheel-drive car, the front inside tire is also working much harder than the rear inside tire. In fact, the front inside tire is losing grip, and what is actually happening with the rear inside tire is that the wheel is starting to slightly lift off of the ground.

With the rear-wheel-drive car, the front inside tire is working less than the rear inside tire, even though the front tire has lost grip and the rear is still working. This is because the FR is more balanced than the FF, and the rear tires are resisting the rear end's urge to follow its inertia and slide out.

The rear-engined, rear-wheel-drive car turns everything upside-down. Not only are both of the rear tires working harder than the front tires, the front inside tire has lost grip, and the rear inside tire is still holding on. The reason why everything has changed like this is because the front tires have much less weight to shift, and the rear tires have to do all the work by themselves to prevent the engine-and-drivetrain-burdened rear end from following its inertia and sliding.

Conclusion? The front tires generally work harder than the rears, since they are shifting the weight of the car. The rears generally do less work, since they are only preventing the shifting of weight. The opposite holds true with RR cars, since the weight is in the rear of the car, the burden of keeping it in place is higher than the burden of shifting the weight in the front.

 

[Verbal]

Here are pictures of the forces being applied to each tire in a clutch disengaged (engine disconnected from transmission),(...)

So all you're looking at is the different weight distributions of those three specific examples. Of course that has an effect (as I've also said above), and yes, FWD cars in general have more weight in the front.

Conclusion? The front tires generally work harder than the rears, since they are shifting the weight of the car. The rears generally do less work, since they are only preventing the shifting of weight.

Wrong conclusion. Take a car with 50/50 weight distribution, do a constant radius turn, and the forces at the rear and the front will be the same. Fronts and rears are doing the same thing, they transmit the forces necessary to accelerate the car in direction of the center of the circular path they're on.

 

[Wolfe]

So all you're looking at is the different weight distributions of those three specific examples. Of course that has an effect (as I've also said above), and yes, FWD cars in general have more weight in the front.

Wrong conclusion. Take a car with 50/50 weight distribution, do a constant radius turn, and the forces at the rear and the front will be the same. Fronts and rears are doing the same thing, they transmit the forces necessary to accelerate the car in direction of the center of the circular path they're on.

Okay, you're right; I thought the XR GT was 51/49, but its 54/46.