Turbocharging

[Threshold]

Ok so I was reading this article from Howstuffworks.com on turbocharging, and while it did provide a lot of information, I still have some questions that I hope you guys can answer.


1. When Turbocharging an engine, the compression ratio does increase right?

2. What happens when the turbo pumps in too much air to the engine?

3. Will Turbo/Supercharged engines have a shorter life-span?

4. This is not really turbo related, but it came up in article anyways. To avoid knocking you need to use higher octane fuel. Because higher octane fuel can resist higher pressures without combusting. So higher octane fuel serves no purpose to engines with normal compression rations? The reason I ask this is because I've heard some people say that higher octane fuel increases the performance of their, non-turbocharged or compression ratio modified, engine.

-Thanks

 

[Jay]

Ok so I was reading this article from Howstuffworks.com on turbocharging, and while it did provide a lot of information, I still have some questions that I hope you guys can answer.


1. When Turbocharging an engine, the compression ratio does increase right?

2. What happens when the turbo pumps in too much air to the engine?

3. Will Turbo/Supercharged engines have a shorter life-span?

4. This is not really turbo related, but it came up in article anyways. To avoid knocking you need to use higher octane fuel. Because higher octane fuel can resist higher pressures without combusting. So higher octane fuel serves no purpose to engines with normal compression rations? The reason I ask this is of their, non-tbecause I've heard some people say that higher octane fuel increases the performance urbocharged or compression ratio modified, engine.

-Thanks

1. The engines compression ratio remains the same but the quantity of air in the cylinder is increased so the cylinder pressure is increased (compression increased) (over the same engine without forced induction).

2. If the turbo pumps too much air in the cylinders many things can happen. The engine management may not keep up (air flow meter, injectors, fuel pump maybe maxed), the cylinder pressure may be too high and the engine could fail in different ways, the compression temperatures maybe too high and cause detonation.

3. Engines like most factory turbocharged engines that are maintained and driven correctly could/should last just just as long as most other engines.

4. High octane fuels require higher temperatures to burn which in-turn allows higher temperatures before pre-ignition (detonation) which in turbo engines usually allow higher boost pressure to gain extra power, but the fuel itself isn't anymore powerful than regular fuel. I have never noticed any performance gains on standard untouched N/A tuned engines I've driven, but with higher octane fuel allows you to advance timing for a small gain. On the turbocharged engines I have driven its a must for safety reasons not power.

The fuel itself without tuning will not give you anymore power.

 

[daan]

The fuel itself without tuning will not give you anymore power.

On a recent test by Evo Magazine a Golf GTI went from 205bhp on normal unleaded to 209 on Shell Optimax and got 212bhp when using BP Ultimate (218 using Sunoco race fuel!) An M5 went from 501 to 534bhp on the Ultimate.

 

[Jay]

On a recent test by Evo Magazine a Golf GTI went from 205bhp on normal unleaded to 209 on Shell Optimax and got 212bhp when using BP Ultimate (218 using Sunoco race fuel!) An M5 went from 501 to 534bhp on the Ultimate.

Ok I went alittle overboard there, you may see some horsepower increase, in this case seemed quite effective, do those cars have smart ECU's that constantly adjust ignition timing for optimum power, economy and engine reliability? If they do (my car does, so assume they will too) that may have helped some.

 

[daan]

I would read the article to find out, but I'm at work and supposed to be working. I can play on a PC most of the day 'cos it looks like I'm working, but reading a magazine is a bit much!

I think they do have smart ECUs. It also seems to help if you have a bit of power to start with. It doesn't seem to work as well on your average car.

I did read that the drivers preferred the feel and responsiveness of the Golf when it was on the Optimax even though it wasn't the most powerful.

 

[TheCracker]

Ok I went alittle overboard there, you may see some horsepower increase, in this case seemed quite effective, do those cars have smart ECU's that constantly adjust ignition timing for optimum power, economy and engine reliability? If they do (my car does, so assume they will too) that may have helped some.

Our Cortina has no ECU or a fuel injection system to run it on, just two large Webers to dump petrol into the engine. You can really tell the difference between different types of fuel you run it on. We got hold of some foul smelling stuff from a guy who at the time worked for TWR - it made a real difference!

 

[Milliethemutt]

I would agree with the Optimax thing from Evo. I certainly makes my car (Leon Cupra 1.8T) pick up loads lower in the rev range.

 

[retsmah]

Ok so I was reading
1. When Turbocharging an engine, the compression ratio does increase right?

The compression ratio wont change, but as you would expect you will get higher pressures inside the cylinders. Compression ratio is talking about how much the piston is compressing air inside the cylinder, not how much the turbocharger does.

 

[Duke]

Your car will make no more power if you go above the octane for which it is optimized. In fact it will make less.

All the cars mentioned above are programmed or tuned to take advantage of higher octane fuels. In the case of the modern street cars above, the cars did not actually GAIN horsepower, they RESTORED horsepower that was lost when the engine control software retarded the spark as required to prevent pre-ignition when running on the cheap stuff. The owners manual will list the the octane rating for which the car is optimized, and putting higher-octane gas than that in a stock car is a total and complete waste of money.

If you take a stock M5 and put race gas in it it will make slightly less power than a stock M5 running the Premium recommended by BMW, due to the higher ignition temperature and reduced volatility of higher-octane fuels.

 

[boombexus]

Ok so I was reading this article from Howstuffworks.com on turbocharging, and while it did provide a lot of information, I still have some questions that I hope you guys can answer.

1. When Turbocharging an engine, the compression ratio does increase right?

No, the compression ratio does not change at all. In most cases, when you turbocharge an engine that was originally naturally aspirated, you need to lower the compression ratio. But by simply slapping on a turbo, the engines compression ratio does not change.
You may need to lower the compression ratio due to the fact that the turbo is pushing in more air than the original engine was designed to take.
If the original engine was designed to have a compression ratio of 10.5 to 1 and you decide to put on a turbo, you have to lower the compression ratio a bit, (or run very conservative boost levels 5 to 6 psi) the usual seems to be at about 8.5 to 1 to allow for the excess air and temperatures that will be in the combustion chamber.

2. What happens when the turbo pumps in too much air to the engine?

If I remember correctly, this phenomenon is called "surge" and it can be very damaging to the compressor and engine. However, it's not a very common occurence with the computer controlled engines these days.

3. Will Turbo/Supercharged engines have a shorter life-span?

It dependes, if your car was originally designed with a turbo, then not really, but if you are modifying your engine with either new, or turning a N/A car into a turbo charged car, then yes, it can. But if you keep up with scheduled maintainence, and your engine management system is keepin all of your paramaters in the norm, your engine should last you as long as it was originally designed for.
However, another thing that you need to take into consideration is that if you are putting a new turbo on a car, then you will probably be driving like a bat outa hell more often, so this will add excess wear and tear on your engine.

4. This is not really turbo related, but it came up in article anyways. To avoid knocking you need to use higher octane fuel.

You don't necessaraly need to use higher octane fuel if you are running at conservative boost levels, but most people will increase octane levels after installing a new turbo on their car, as they will want more power gains. And because higher octane fuel can resist higher pressures and temperatures without combusting.
Lower octane fuels will not deliver this, and will make the fuel ignight before the cylinders reach top dead center.

When you are adding boost, you are greatly increasing engine temperatures and this will cause a low octane full to combust too early. This is a very BAD thing for an engine. If your fuel is ignighting before the cylinder is reaching top dead center, then you are putting a great strain on the engine parts.

So higher octane fuel serves no purpose to engines with normal compression rations?
-Thanks

Just like Duke said, it is a waste of money to add a higher octane fuel than the car was originally designed for.
Usually, higher octane fuels contain fuel cleaners, so any performance gain that one might be feeling, (other then a psychological one) is that the fuel system is being cleaned and returning the car towards its original performance levels.

 

[Jay]

Our Cortina has no ECU or a fuel injection system to run it on, just two large Webers to dump petrol into the engine. You can really tell the difference between different types of fuel you run it on. We got hold of some foul smelling stuff from a guy who at the time worked for TWR - it made a real difference!

Like Boom said, the more expensive higher octane fuels have cleaners and like Duke said your probably feeling some restored horsepower and response, if you were to advance the ignition timing some while using this high octane fuel you probably would feel even more of a difference. Many late model cars do this automatically.

If your fuel is ignighting before the cylinder is reaching top dead center, then you are putting a great strain on the engine parts.

Yes and unfortunately I know all about that .

 

[niky]

Like Boom said, the more expensive higher octane fuels have cleaners and like Duke said your probably feeling some restored horsepower and response, if you were to advance the ignition timing some while using this high octane fuel you probably would feel even more of a difference. Many late model cars do this automatically.

Actually, that's the only way to make extra power with high octane fuel on many "economy" engines... advance quite a bit past the stock factory advance. Nets you something like 3-5 hp, but if you go back to regular unleaded, it'll start knocking.

On an untouched car, some economy engines actually lose around 3 hp or so on premium versus regular unleaded.

 

[Jay]

but if you go back to regular unleaded, it'll start knocking.

Yes and thats why you only bother advancing timing if your willing to stick with the higher octane fuel, but its not worth it in my opinion. If the manufacturer recomends regular unleaded then stick to it (unless modifications require it obviously).

 

[Threshold]

So compression ration is the measurement of volume/space in the cylinder, when the piston is all the way at the top, right? Regardless of how much air/gas is in the cylinder. So for example, if you have a cylinder that has a space of 100 cc when the piston is all the way to the bottom, and 10 cc of space when the piston is all the way to the top, that engine will be rated at a 10:1 compression ratio, right?