Does adding a header system affect d-jet fuel metering?

[Alfred1]

I think that I've finally settled on how I'm going to rebuild my 2.0. I'm going to rebuild it close to stock (with the stock cam and heads) but with 96mm KB pistons and cylinders and an MPS calibrated for a 2056cc motor. I'm hoping to pick up a few more hp by adding a header system - will doing so affect the d-jet fuel metering?

[Dave at Pelican Parts]

Yes, it will. How? Not sure--but it does to at least some extent. I know cars that have run with that for quite a few years, but the metering will still have changed.

--DD

[Bleyseng]

No matter what you will have to dyno tune the MPS when all is done to get the correct AirFuel mix/

Geoff

[Scrappy]

Ok - ya want an answer. Adding a header system improves the exhaust flow to a degree. It could possibly cause a leaner condition in the cylinder as it could feasibly "over scavange" the cylinder on fill (raw air/gas down the exhaust pipe). Since the fuel is port injected and is fixed by throttle opening and ECU timing, additional air could be drawn in and alter the fuel/air mixture. This is really reaching, as the other variables are cam timing, effeciency of the intake tract, etc, but theoritically feasible.