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Back to ignition timing

I'm wondering what would be the proper full advance (total) timing for Speedway GT, given it has flat top pistons, a tad of head angle milling, 290 degree cam, runs at 6500 rpm on 91 octane gas, almost always at wide open throttle (350 cfm).
I don't quite yet have access to a dyno, until then we can only guess at total timing, we ran 36 degrees thus far, I just wonder if it should be more, and if we should up the octane...
Surely some of you have some experience with this you would share?
Thank you.
 

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The thread where this came from already had about three topics, so I thought that this deserved its own.
 

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jeff denton said:
I don't quite yet have access to a dyno, until then we can only guess at total timing, we ran 36 degrees thus far, I just wonder if it should be more, and if we should up the octane...
Surely some of you have some experience with this you would share?
Jeff, I've found there is nothing to gain from advancing timing beyond 36 degrees. Lower compression engines (under 9:1) can sometimes gain a bit from 38 degrees, but with a higher compression engine I saw a 12 hp drop going from 36 to 39 degrees! Not to mention it refused to rev up past 7800. It has nothing to do with fuel octane requirements either, we ran 114 octane fuel.

Bob
 

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jeff denton said:
Thanks Bob. I might be getting a little confused though. Are you saying I should stay at 36 degrees, and you're calling my engine a "high compression engine", and could benefit from using higher octane fuel?
You probably don't need any more than 93 octane pump gas if you have flat-tops and a bit of a cam. 36 degrees total timing should work fine too, but you can experiment a bit if you'd like. We played with it on the dyno of course, but also on the track where it counts. Every engine is a bit different (especially if cam timing is altered), so it warrants investigation. But I'd probably keep it within the range of 34-38 for testing.

Bob
 

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You probably don't need any more than 93 octane pump gas if you have flat-tops and a bit of a cam. 36 degrees total timing should work fine too, but you can experiment a bit if you'd like. We played with it on the dyno of course, but also on the track where it counts. Every engine is a bit different (especially if cam timing is altered), so it warrants investigation. But I'd probably keep it within the range of 34-38 for testing.

Bob
Humm this thread is the closest for my question.
I'm looking to close the intake valve sooner. That should in theory increase the effective
compression where the ignition timing may need to be lowered even more.

Right now the intake is closing @ 49 ABDC if it's changed to 35 ABDC to lower the
reversion in the intake. The compression should rise by 15 or so psi.
Oh poo am I'm even on the right track with this?
 

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You might have to pull some timing back. I think I ran 34 degrees with pump gas on my old 11.2:1 street 2.0 litre. I bumped it to 38 degrees when I mixed in race gas for track days. On the bigger engines (2.4, etc) you barely need more than 30 degrees, sometimes less.

Jeff's EFI-Megasquirted high compression 2244 cc engine needed just 28 degrees total. We started at 36 degrees but it pinged like crazy on the dyno.
 

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I used to work at a garage, back in 1980, that had a distributor machine. It's amazing the gains to be had with a recurve.

Anyway, Bob is dead right, a 9 to 1 opel needs 36 degrees, the low compression one can stand 38. Anymore than that and the HP drops, any less, and your not getting it all.

Back in the day, we had boxes of springs, ground weights, adjusted stops, and all kinda stuff to make the curve work. These days, all you need is a laptop.

But anyway, for total advance, those are the numbers.
 

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I'll take software any day over a dizzy.


Injected fuel quantity cylinder 1 0.194 ml
Injection time/cylinder 1 5.12 ms
VVT target angle 1 0.0 %
VVT modification angle 1 0.0 °
VVT OCV duty cycle 1 0.0 %
Solen. valve, var. valve control
1
Solen. v., var. valve cntl. 1 active
Injected fuel quantity cylinder 1 0.204 ml
Injection time/cylinder 1 7.30 ms
VVT target angle 1 0.0 %
VVT modification angle 1 0.0 °
VVT OCV duty cycle 1 0.0 %
Solen. valve, var. valve control
1
Solen. v., var. valve cntl. 1 active
Injected fuel quantity cylinder 1 0.471 ml
Injection time/cylinder 1 13.95 ms
VVT target angle 1 0.0 %
VVT modification angle 1 0.0 °
VVT OCV duty cycle 1 0.0 %
Solen. valve, var. valve control
1
Solen. v., var. valve cntl. 1 inact.
Injected fuel quantity cylinder 1 0.441 ml
Injection time/cylinder 1 13.06 ms
Remarks:
Date Signature
2/2
VVT target angle 1 0.0 %
VVT modification angle 1 0.0 °
VVT OCV duty cycle 1 0.0 %
Solen. valve, var. valve control
1
Solen. v., var. valve cntl. 1 active
Injected fuel quantity cylinder 1 0.461 ml
Injection time/cylinder 1 13.57 ms
VVT target angle 1 0.0 %
VVT modification angle 1 0.0 °
VVT OCV duty cycle 1 0.0 %
Solen. valve, var. valve control
1
Solen. v., var. valve cntl. 1 active
Injected fuel quantity cylinder 1 0.462 ml
Injection time/cylinder 1 13.70 ms
VVT target angle 1 0.0 %
VVT modification angle 1 0.0 °
VVT OCV duty cycle 1 0.0 %
Solen. valve, var. valve control
1
Solen. v., var. valve cntl. 1 active
 

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Gary
I'll take a dizzy any day over software: Timing light and a 13mm wrench.
I'll bet that there were days when you were "tweeking" this site that the tool of choice that you wanted to use was a hammer!
 

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Oh come on guys.
I've used the leading edge of the crank sensor for all the engine management chores.
This is 2011 btw.
Come on Dan, you know we're all a little bit stuck in 1975 right? Why else would we be tinkering with these dinosaurs?:lmao:
 
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