MurrayZA

Hi all,

I was wondering if anyone had MPG figures for a vehicle before and after a 2.2 stroker kit. In theory, should a 2.2kit use more fuel, or less fuel? Does ECU re-mapping on a 2.2 kit need to be done - or does the std ECU conpensate and if so - how does it know that it now needs to feed 2.2 litres instead of 2 - surely it will need more fuel per pulse?

Adam M

the engine will be pulling in (hopefully) 10% more air, and thee maf sensor would detect this and supply the appropriate fuel.

The lmabda sensor would also help make sure the fuelling is corrcet in the cruise zones.

Personally if changing the engien so drastically, I would not be happy running it everyday on the standard ecu without some kind of replacement ecu or at least a remap.

the choice is yours of course.

the fuel consumption should be worse than before since the engine is bigger, but it wont be anything like 10% worse. It depends on the efficiency of the engine and things like pumping losses.

theoretically it should require the same force to drive the car in the same way it was driven before, but the different nature of the engine (engine specific) will determine how much fuel is used to create that force.

Pavlo

Adam, why would it take in 10% more air?

You appear to assume that you would drive everywhere with the same throttle application, when really you would have 10% less (in crude terms)

paul

RON

10% more capacity = 10% more air.

Simple!!!

Pavlo

not so simple, as 10% more air = 10% more power, but you don't use that extra power if you're driving everywhere at the same speed/acceleration.

As a result, you would be driving with less throttle application on the larger engine, reducing the airflow back to a similar level of that of the smaller engine.

Paul

Pavlo

<mindless factory ECU speak>
how will it go lean? assuming the airflow will be the same or just a little more but reduced TPS, will put it into the leaner areas of the map I suppose, but not excessively so I would have thought, possibly 1 or 2 columns.

I did wonder if you could change the load measurement by swinging the TPS.
</mindless factory ECU speak>

Yes I suppose it will change the way the ECU deals with things, but overall the fuel consumption will be quite similar. In fact with higher gas speeds (but lower pressure due to throttle) one might expect better turbulence and mixing of air/fuel, which could infact reduce fuel consumption.

Paul

john banks

That is exactly what I mean Paul. The slight leftward bias on the map lookup from TPS is probably less significant that the rightward bias from higher MAF at same MAP.

Adam M

paul,

I did say this bit

"theoretically it should require the same force to drive the car in the same way it was driven before, but the different nature of the engine (engine specific) will determine how much fuel is used to create that force. "

I agree with you, you would not need the same throttle to generate the torque needed to move the car.

What I was getting at was that at a given throttle rpm point, in a simplified world, the 2.2 would draw in 100cc more per revolution.

MurrayZA

Thanks for the valuable input guys. I guess it boils down to the following - we have very poor fuel in ZA - so I see a 2.2 kit as a safe way to hit 300bhp. I think I can modify my question a bit to say:

What do people think I need to do to a STi V7 to run a 2.2 kit successfully at resonable, reliable boost (say 1.0 bar) - this would be on 95 octane. Will just the 2.2 kit and a restrictor
change / EBC work ? Or is it far more complicated ?

Pavlo

I think you could do as john says. You have the injectors on the Sti to cope, you might do well to just get an adjustable fuel pressure regulator and adjust to provide better AFR in the range of interest.

But in theory, you should be able to just put it all back together, turn the key, and the engine will run about right.

Paul

MurrayZA

S-AFC, Knocklink and off we go ?

MurrayZA

The plan (unfortunately in South African Rands):

New STI V8 - R385 000

2nd hand STi V7 with 30K kms (20 000 miles) - R 320 000
Stroker kit budget - R 40 000
Total - R360 000

So, for R25 000 less, I can have a car with a few more miles on
it, but brand new 2.2 engine and all thats really different is the headlights + rear fin and a dash of Geom...

MorayMackenzie

Unless you go for the a twinscroll turbo version of the sti8, in which case there is a bit more of a difference.

MurrayZA

Then you are talking even more money for the same performance. JDM's here are not readily available and come with a huge premium.

john banks

The fuelling may run slightly leaner because the load is a calculation based on MAF AND TPS. However, the ignition will be retarded because the airflow will be higher for a given boost level. Lean and retarded could give cooking EGTs.

A boost controller, fuel cut defender, S-AFC, wideband and a knocklink would go a long way to giving a reasonable setup. Fuel pressure/injector changes can help shift the offset between fuelling and timing to allow you to get what you want within reason.

You can also try combinations of various induction kits and injectors to sort things.

APS induction and 550cc injectors on a standard fuel map work quite well, but the ignition would be too advanced.

[Edited by john banks - 5/7/2003 12:32:32 PM]