11:1 CR+pump gas+iron heads = detonation.

Hotter ignition? You're stock with dual points?

I think you need to read a little>> http://alcoholinjectionsystems.com/...r-Methanol-Injection-System/product_info.html

Just a question but do you guys think if he WAS running aluminum heads with 11:1 and premium gas he would still ping

All other parameters being the same, I think running aluminum heads would give the same problem. I don't think aluminum dissipates heat fast enough compared to the speed of the combustion process, to make any difference.

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By the way, 62 Dart, do you know how far below deck your pistons are at TDC? This added to your gasket thickness of .040" will give the quench distance.

Drum roll please......

Cold engine, cranking pressure is 175psi.

To answer some questions - dual point removed, orange box electronic went in ages ago, plugs are Accel copper core 137.

Piston to deck clearance was measured at 0.4mm = 0.016" (so add 0.040" gasket, quench distance = 0.056"?!).

Cam degrees checked?

Please excuse if you've already answered this. I'm lazy this morning..

look for oil contamination in the combustion chamber. just a small amount of oil will cause a lot of problems.

9.5:1. Happy at WOT. No rattle. No bragging rights. **** pump California gas 91.

Sounds like this is one of the "that sux" threads. Being here in Cal, we know about heat and low octane, built my 493 with that main thing in mind and used -24 cc dished pistons to get the CR down to 9.6:1. Hope you get it fixed.

175 should be doable for 93.....but....your domed pistons might be the achilles heel in this combination. I have experience with high comp engines (the highest was 11.5-1 with 180 psi) using flat tops but not domed. Domed pistons interfere with the flame front somewhat vs flat tops. One of the things you want to do with a tight quench is to force the fuel/air charge towards the spark plug (combustion chamber side of the head). In a nut shell, this helps create better swirl within the combustion chamber and a dome on top of a piston has a tendency to get in the way of that process. There's a ton of info on what takes place in a high performance engine combustion process if you want to spend the time doing research. It can make your head spin......well, it did mine anyways lol

Is the ping happening at partial throttle or only full throttle?

Do you have vacuum advance? If so, try disconnecting it and plugging everything up and taking it for a spin. Mine would act really touchy at the track with my vacuum advance hooked up. I'm not convinced the vacuum canister can react fast enough to avoid detonation when suddenly going full throttle. When I'd disconnect the vacuum advance and make a pass everything would be fine. Probably a band-aid but it works for me so far.

This is on a car with 9.5:1, open chamber iron 452s, California pump gas and racing at temperatures between 70 and 100 degrees.

Good point 67 ^^^^ In the past I have experienced the same as you and either disconnected the vac advance or got the allen wrench and dialed it back to limit the amount of advance.

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Cranky said:

175 should be doable for 93.....but....your domed pistons might be the achilles heel in this combination. I have experience with high comp engines (the highest was 11.5-1 with 180 psi) using flat tops but not domed. Domed pistons interfere with the flame front somewhat vs flat tops. One of the things you want to do with a tight quench is to force the fuel/air charge towards the spark plug (combustion chamber side of the head). In a nut shell, this helps create better swirl within the combustion chamber and a dome on top of a piston has a tendency to get in the way of that process. There's a ton of info on what takes place in a high performance engine combustion process if you want to spend the time doing research. It can make your head spin......well, it did mine anyways lol

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Agreed!! But if the domes are really short like the MW pistons he might still be OK. However, nothing beats a flat top piston in these old wedges for good flame travel. Typically, a sign of an inefficient chamber is it requires more lead to get the job done. A large bore doesn't help either but something in the way adds to the problem.

something doesn't add up to me, if i understand this correctly. 175psi, 11:1 pistons with chambers that may be smaller than max wedge, small cam closing the intake valve around 65 degrees ABDC? unless i'm missing something, this doesn't make sense to me. cylinder pressure should be well over 200psi. i don't know how aussie octane ratings are derived but if they're like u.s. then 98 octane would be at least equal to our older 100 octane, maybe higher. i'm not getting 2+2=4 here,....?

lewtot184 said:

something doesn't add up to me, if i understand this correctly. 175psi, 11:1 pistons with chambers that may be smaller than max wedge, small cam closing the intake valve around 65 degrees ABDC? unless i'm missing something, this doesn't make sense to me. cylinder pressure should be well over 200psi. i don't know how aussie octane ratings are derived but if they're like u.s. then 98 octane would be at least equal to our older 100 octane, maybe higher. i'm not getting 2+2=4 here,....?

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Same here Lew.

To answer more questions -

I have discounted vac advance. Disconnected = same problem.

Detonation is at heavy to full throttle, with no where near the advance it should have in it...

have you checked the TDC mark on the dampner to make sure the outer ring hasn't slipped?

Quench, Bigger cam, E-85 conversion, Race gas and Water injection ....blah blah blah. :laughing4:
All of this stuff sounds very familiar! I dealt with detonation for years and tried plenty of things to stop it. I had critics here telling me that thicker head gaskets wouldn't help my situation, a BIGGER cam would. Okay....The bigger cam did NOT help in my case, it only shifted the power band UP in the rpm scale. I read from guys that said I needed to recurve my distributor and delay the advance. I did that and again, it did not help. I read that a LEAN mixture can lead to detonation so I installed a wideband 02 guage. I was running in the 12.0 to 12.8 range at WOT, so it was not running lean. My engine knocked at operating temperature on 91 octane even with total timing set to 28 degrees.
There may have been a successful combination other than the route I took, but I went with thicker head gaskets because I didn't want to pull the engine again at that time. I had .051 quench when I was knocking. This was with a .039 head gasket. I went with a Cometic .075 gasket pushing my quench to .087. My compression ratio WAS over 11.0 with aluminum heads before, it now is 10.07. I have NO detonation now unless I use vacuum advance. With the vacuum advance, it pings a bit at part throttle but the knocking goes away at WOT. I have not tried cranking back the vacuum advance by adjusting the screw through the can nipple.
Currently, I am able to run the timing out to 19 initial and 34 total with no knocking, all with 91 octane. Even with the ONE point drop in CR, the car is faster than ever and does NOT knock. Several people were strongly against the idea of thicker head gaskets but it has clearly worked for me.
If I were to start over, I would use dished pistons with flat sections on the quench side. This would lower compression while maintaining quench. This would almost guarantee the ability to make great power even on 87 octane, allowing me to drive anywhere without worrying if the gas stations along my journey had Premium fuel


*****Regarding the 98 octane: *******
Our gasoline octane is rated based on the two testing standards that are added together, then divided by two.
RON is Research Octane Number. MON Is Motor Octane Number. This is the backstory behind the
R+M /2 that you see on the stickers affixed to the gas pumps. Some other countries only use one testing standard, the higher number of the two. This means that the Australian 98 octane may be equal to our 90 or 91 octane.

lewtot184 said:

have you checked the TDC mark on the dampner to make sure the outer ring hasn't slipped?

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Yep.

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Kern Dog said:

*****Regarding the 98 octane: *******
Our gasoline octane is rated based on the two testing standards that are added together, then divided by two.
RON is Research Octane Number. MON Is Motor Octane Number. This is the backstory behind the
R+M /2 that you see on the stickers affixed to the gas pumps. Some other countries only use one testing standard, the higher number of the two. This means that the Australian 98 octane may be equal to our 90 or 91 octane.

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Not sure which standard is used here for octane rating. I do know I've run the best 98 premium pump fuel we have here with an extra bottle of octane improver and it still pinged like a prick.

My plan to drop CR by head gasket was based on your success Greg.:icon_pirat: