Down pipe and fuel issues
29 April 2001, 10:36 AM
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I am thinking of changing the down pipe on my 94MY UK Turbo. At present I am running the car on normal unleaded, if I do this mod will I have to then run the car on SUL or will it be safe enough to continue as I have been doing. I realise that I will have to change the standard air filter, but will the air & fuel mixture need adjusting to to compensate for easier breathing. If so in general how will this effect fuel economy.
I seam to remember hearing that cars of this age that had the prodrive mod done had to be run on SUL, why? I am thinking it is to do with the increased power and possible engine temp's?
Jamie
I seam to remember hearing that cars of this age that had the prodrive mod done had to be run on SUL, why? I am thinking it is to do with the increased power and possible engine temp's?
Jamie
29 April 2001, 08:03 PM
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Jamie,
Not sure if 94MY's have knock control or MAF meters (perhaps someone could confirm/deny?).
If you have a MAF meter the additional air flow will be measured and the ECU should compensate accordingly. However, by getting more air into the cylinder the knock limit will be reduced (increases the tendency for the engine to knock). The knock control system should cope with this, but if it retards the ignition you may not get the performance benefit you were hoping to get. To ensure optimum performance (and to protect your engine) I'd run on SUL.
If you don't have a MAF meter the engine will run leaner. The ECU will not have been programed (calibrated) to account for this extra air. However, I believe that the Impreza is calibrated to run slighty richer than is absolutely necessary so you should be fine.
Assuming you have knock control - If you run on SUL theoretically you'll get better fuel economy as the knock control system will advance the ignition to SUL settings and the engien will run more efficiently.
As for the PPP, I guess the ECU updates includes running higher boost pressures (again can anyone confirm this?) With higher boost pressure the knock limit is reduced (as above). Therefore using SUL realises the full performance potential. In this case the extra boost will lead to increased fuel consumption as more fuel is required to maintain the same or lower Air:Fuel ratio.
Hope this helps,
Paul
Not sure if 94MY's have knock control or MAF meters (perhaps someone could confirm/deny?).
If you have a MAF meter the additional air flow will be measured and the ECU should compensate accordingly. However, by getting more air into the cylinder the knock limit will be reduced (increases the tendency for the engine to knock). The knock control system should cope with this, but if it retards the ignition you may not get the performance benefit you were hoping to get. To ensure optimum performance (and to protect your engine) I'd run on SUL.
If you don't have a MAF meter the engine will run leaner. The ECU will not have been programed (calibrated) to account for this extra air. However, I believe that the Impreza is calibrated to run slighty richer than is absolutely necessary so you should be fine.
Assuming you have knock control - If you run on SUL theoretically you'll get better fuel economy as the knock control system will advance the ignition to SUL settings and the engien will run more efficiently.
As for the PPP, I guess the ECU updates includes running higher boost pressures (again can anyone confirm this?) With higher boost pressure the knock limit is reduced (as above). Therefore using SUL realises the full performance potential. In this case the extra boost will lead to increased fuel consumption as more fuel is required to maintain the same or lower Air:Fuel ratio.
Hope this helps,
Paul
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