Effect of Injection timing on EGT, with Port Injected Gasoline.

Hi,

This is my first post, so please be gentle.

I’m looking at ways to try lowering my EGTs at WOT (other than fueling and ign timing), and am wondering if injecting into an open valve/chamber as opposed onto a closed valve might achieve this.

I’m thinking that injecting in to the chamber (and hence the fuel evaporation occurring within the chamber) should help cool things down a bit.

For the sake of a stable idle I’m using an injection end angle of 240deg (closed valve), it’s also around this across the revs/load range.

My ECU allows me use either start or end angle for injection, and calibrate the angle as a function of revs and load on a 3d table. I’m considering swapping to a start angle strategy and starting my injection in high load/rev areas (where EGTs are high) at an angle just after the cam overlap phase, so around 385deg when the exhaust cam closes fully.

Clearly I could just go and try it, but am asking in case I’m way off the mark, or there are other things I need to consider?

Thanks,

Jezz

I don't think you will find much difference in EGTs with injection timing, and I think you should try it and report what you find.

Why are you not willing to change fueling and timing to achieve your goal?

He may have reached the limits he's happy with that way?

Not sure how much difference it will make, if any - might even hurt it rather than improve it?

About the only thing I can think being useful is if the injection timing is such that there is no fuel being pulled through to the exhaust on overlap and possibly being combusted there, but that's a long shot if it is actually an issue?

Hi David,

Thanks for the reply, I'll give it a go if/when it stops raining...

I'm probably close to the limit with respect to both fuel and ign; going from 11.3:1 to around 10.7:1 makes little difference to the EGTs (if anything it made them worse, is that conceivable?) and I don't really fancy adding any more timing; so was looking to investigate if there were any other avenues to explore.

FWIW I've just ordered a new EGT sensor and gauge to validate the one I'm running to make sure I'm not chasing a dodgy sensor, though I've no reason to believe there's an issue with the existing one.

Cheers,

Jezz.

Gord said

>>>About the only thing I can think being useful is if the injection timing is such that there is no fuel being pulled through to the exhaust on overlap and possibly being combusted there, but that's a long shot if it is actually an issue?

TBH I had an issue roughly relating to this, I noticed a reasonable (embarrassing?) amount of black smoke as I was coming on boost which I fixed by moving the end angle back, I think what was happening was fuel was being injected and blown through during overlap whilst EMAP ratio was low enough to allow it. Moving the timing back to fixed that issue.

You're right it may make it worse if atomisation/evaporation is poor.