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[F1 9LFG]

hi people

i have a 2.6 v6, and am building a stainless steel system, do the v6's perform better with less back pressure, i've been told different things!

most n/a motors do run better with lower back pressure, just want to know about the v6's.

cheers

[2woody]

any engine will run better - i.e. more power - with less exhaust back-pressure.

BUT in order to do so, the fuel map has to reflect the "new" back pressure.

so yes more power, but only if you re-map the engine control.

[Kevin Wood]

It's not really as simple as just back pressure. You will get waves of both positive and negative pressure propagating up and down the length of the exhaust as it acts like an organ pipe.

If you happen to get a negative pressure at the port on the engine as the exhaust valve is open it will help evacuate the cylinder quickly and actually draw a little more air/fuel mixture in during the valve overlap period, giving more power.

If you have a high pressure at that point, the cylinder won't evacuate well and the next combustion cycle will have exhaust fumes in the charge, giving less power.

The behaviour of the exhaust will depend on how its resonant frequency interacts with the engine at different RPM. At some RPM you will win, at others you will lose and the engine will go flat. All you can hope to do is to ensure a reasonably flat torque curve by avoiding deep resonances - or a peaky one, will all the power in one small rev range, of course, depending on the application.

So, no simple answer. Unless you're going to look in detail at the engine's cam timing, and adjust the exact length of the exhaust components to achieve some result the best you can do is make it as free flowing as possible while keeping the lengths as close as possible to the original system, which was presumably designed competently.

Kevin

[2woody]

Omega has non-resonance manifolds fitted, so the tuning aspect of the downpipes and exhaust aren't going to be an issue.

[F1 9LFG]

thanks for your help there both of you, so would i need any updates appling to the ecu?

[Kevin Wood]

thanks for your help there both of you, so would i need any updates appling to the ecu?

I wouldn't say so. The difference in required fuel will be small enough that the ECU will compensate either by virtue of the fact that it's measuring intake airflow through the MAF or that it's correcting the fuelling based on feedback from the Lambda sensors.

Kevin

[F1 9LFG]

thanks for your help there both of you, so would i need any updates appling to the ecu?

I wouldn't say so. The difference in required fuel will be small enough that the ECU will compensate either by virtue of the fact that it's measuring intake airflow through the MAF or that it's correcting the fuelling based on feedback from the Lambda sensors.

Kevin

Just as i suspected...

Thanks chaps

[2woody]

you'll be hard-pressed to notice a difference I think.

but if the new exhaust does cause it to run badly, you could always put in a restrictor plate to give it a bit of back-pressure