Injector timing
Discussion
Just a general wondering for those who roll their own tunes, have you explored injector timing? In particular, B3702? Most setups on here are pretty similar, and I'm wondering what gains were seen from typical monaro/vxr8 setups. Maybe not numbers, but more stable AFR on idle, better low-end feel. Cam specs would be helpful.
KMud said:
Just a general wondering for those who roll their own tunes, have you explored injector timing? In particular, B3702? Most setups on here are pretty similar, and I'm wondering what gains were seen from typical monaro/vxr8 setups. Maybe not numbers, but more stable AFR on idle, better low-end feel. Cam specs would be helpful.
Unless you're using a gas analyser when tuning, or testing on a dyno for the upper rpm's, just leave them as is.stevieturbo said:
Unless you're using a gas analyser when tuning, or testing on a dyno for the upper rpm's, just leave them as is.
My AFRs bounce around a lot when idling, and so I'm tempted to fiddle a little bit +/- as I have read of AFRs being more stable with a minor tweak. That said, I'm about to do intake/TB/injectors, so I'm not fiddling with the little things until my tune is somewhat back together!edit to add: I think you're probably right that it's hard work to analyse the gains up top.
Edited by KMud on Monday 26th January 23:04
stevieturbo said:
The chances of any tuning issues you are having being down to injection timing using GM values....are almost zero.
I have no major issues, just optimising - thanks for the input though. I've seen some tune files for fairly brutal cars with stock values, although they may just have not known better! I've bought more injector than I need to be honest, so I'm antsy to get it running well. With relatively lower duty cycles it might be more sensitive.KMud said:
Just a general wondering for those who roll their own tunes, have you explored injector timing? In particular, B3702? Most setups on here are pretty similar, and I'm wondering what gains were seen from typical monaro/vxr8 setups. Maybe not numbers, but more stable AFR on idle, better low-end feel. Cam specs would be helpful.
You could advance the injector timing by the difference of the stock cam inlet valve opens and your new cam IVO, that way you would maintain the stock duration between EOI and IVO injecting on the back of the closed valve.The PCM advance value in the E40 {B1205} table is 490 at 20° C reducing to 220 at normal operating temperatures, I set mine 6 degrees earlier at 226 in the normal temp range.
Edited by Gelf VXR on Tuesday 27th January 02:47
KMud said:
There's a good hptuners thread I have been reading advocating just that Gelf - did you find it made any difference?
I cant say I notice any difference, I didn't expect to from a small change, its mainly those with a lot of overlap that notice the changes to smell of raw fuel.It was a logical/intuitive decision to advance EOI so the time between then at the inlet valve remained the same as stock.
stevieturbo said:
The general consensus is end of injection should occur at or around the opening of the inlet valve.
I see little reason to vary this unless someone has really done a lot of testing and has reasons to do otherwise.
I've researched this, if I remember correctly, the E40 injection boundary is 520° ATDC (power stroke). That is 160° ATDC (induction stroke), its latest EOI for current cycle and or earliest SOI for next cycle, remembering there is an injector off time between cycles, if IDC is maxed out the infectors are on 720° minus the off time.I see little reason to vary this unless someone has really done a lot of testing and has reasons to do otherwise.
For example when up to normal temps, EOI is the boundary 520 - 220, which 300° ATDC (power stroke) or 60° BTDC before IVO, stock IVO is around 16°ATDC at 0.050". EOI injection is 76° before IVO.
As rpm and IPW rises, so SOI will meet the boundary and EOI will start happening later with the inlet valve open and when intake velocities will be very high.
Intuitively I advance EOI to the same amount as the earlier IVO to maintain 76° between the two events, enough time for vaporisation/valve cooling.
Edited by Gelf VXR on Tuesday 27th January 13:26
Gelf VXR said:
You can compare cam timing events below
And as you can see IVO is almost identical with them all..Edited by Gelf VXR on Tuesday 27th January 23:19
Really...you're thinking far too much into it all, and without hundreds of hours on a dyno and with a gas analyser to quantify results....you wont really get anywhere.
stevieturbo said:
And as you can see IVO is almost identical with them all..
Really...you're thinking far too much into it all, and without hundreds of hours on a dyno and with a gas analyser to quantify results....you wont really get anywhere.
Up top I don't question it's pretty academic (my profession...), but down low interests me. I'd be thinking less if the EFI live tables didn't appear to be slightly messed up (or at least the associated documentation)!Really...you're thinking far too much into it all, and without hundreds of hours on a dyno and with a gas analyser to quantify results....you wont really get anywhere.
edit: I think you think I want to stray from ending injection on intake valve opening - right now I'm running a cam with IVO ~16 degrees earlier, but stock injector timing (so at least partially spraying onto an open valve)...I am just looking to align the events again really.
Edited by KMud on Wednesday 28th January 00:10
stevieturbo said:
And as you can see IVO is almost identical with them all..
Correct and correspondingly engine coolant temp injector timing is the same for all gen 4~5 that I've seen, I expect GM did put a lot of time and analysis to come up with the duration angle between EOI and IVO. Advancing EOI to maintain GM's duration angle to IVO is a logical step.At 0.004" lift stock LS2 IVO is 9° BTDC, only 51° after EOI.
EOI is advanced 490° when cold compared to 220° (normal temp) to allow extra duration for the fuel to evaporate in the runner before the valve opens.
EOI advances with rpm also.
Advancing EOI ensures proper vaporisation and this all happens before the valve is opens, in any case I think advancing further than GM duration will not significantly affect the AFR, 5 gas analysis or dyno, it can not harm.
On the other hand retarding EOI later or advancing the IVO which has the same effect could lead to raw fuel to puddling on the back of the valve being drawn into the chamber and in the case of high overlap cams being drawn straight out of the exhaust valve, hence the strong smell often reported, accompanied by wild AFR swings, high fuel consumption because of the poor homogenous charge.
Some suggest to retard EOI so that SOI happens after the exhaust valve has closed to remove the smell of fuel, but that would surely lead to injectors spraying and washing the cylinder walls at low rpm load charge velocities.
Again, you're wayyyyy overthinking and worrying about this.
Unless you have the dyno time and gear to conduct proper test...you're basically wasting your time.
Batch fire doesnt care about injection timing and it works perfectly....so while it's nice to have timed injection events...any real world differences will be small as far as performance goes.
And making essentially random changes with no way to verify what response you get from them...is just pointless.
Spend some time making it go faster instead of worrying about the silly things
Unless you have the dyno time and gear to conduct proper test...you're basically wasting your time.
Batch fire doesnt care about injection timing and it works perfectly....so while it's nice to have timed injection events...any real world differences will be small as far as performance goes.
And making essentially random changes with no way to verify what response you get from them...is just pointless.
Spend some time making it go faster instead of worrying about the silly things
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