1987 Monte Carlo SS Build - Aka Project Grown

Tony1968

Royal Smart Person
Supporting Member
Jul 1, 2018
1,313
113
NW Indiana
My neighbour has been running his 427 @ 12.5 with no issues on pump gas (94 octane) . I want to avoid new heads as those AFR heads were big money and they have less than 1000kms on them. I would rather sell the pistons and get new pistons at that point.

What would cause the detonation? just the heads further from the deck?
Too much quench will cause detonation. Your neighbor has to have a very high duration cam that bleeds off a lot of cylinder pressure at lower to mid rpms. Wouldn't be streetable to me anyway
I'd get different pistons if you need to keep the heads.
 
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Pro86tourn

Apprentice
Thread starter
Apr 26, 2020
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Too much quench will cause detonation. Your neighbor has to have a very high duration cam that bleeds off a lot of cylinder pressure at lower to mid rpms. Wouldn't be streetable to me anyway
I'd get different pistons if you need to keep the heads.

Cam Motion building me a cam that will help my car run better with higher compression - 246/252 111.5+2.5 with a .90 gasket should put me 12.15.1 with dynamic compression of 8.5

My concern is with the gasket.. I know cometic can make me any thickness but... again my gut tells me its not right
 
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Pro86tourn

Apprentice
Thread starter
Apr 26, 2020
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I have Cometic .042 I believe
Some of the best MLS gaskets imo
that's good to hear!

I might try calling wiseco tomorrow and see if I can safely shave some of the dome off the piston... but again wouldn't that create the same quench issue?
 

64nailhead

Goat Herder
Supporting Member
Dec 1, 2014
2,481
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Upstate NY
Cometics won't leak.

Items that cause detonation : heat - both stored in the head, block, piston and spark plug, and high intake temps; poor squish most commonly caused by too much quench or lack of quench pad; too much timing for chamber efficiency; too much timing for fuel and compression; too lean; excessive coolant temp, and much more including combinations of any of these.


You are unlikely to detonate it if running at the track due to lack of heat soak and large amount of air flow due to WOT driving if you have the AFR in the 11.0-11.8:1 range. Detonation happens at slower speeds, short blasts with heavy heat soak (street driving red light racing).

A couple of things to keep in mind - you could run 15:1 with 94 octane in a race only build without issue if you can tune. The difference between 12:1 and 11:1 won't be 10-20hp with everything else the same, but will be much more tolerant of the items I mentioned above. Regarding quench, an LS is not affected by too much quench near as much as most old school stuff due to the chamber design, but there is a limit. I would recommend against much more than .065" if street driving in the hot days of summer will take place.
 

64nailhead

Goat Herder
Supporting Member
Dec 1, 2014
2,481
113
Upstate NY
that's good to hear!

I might try calling wiseco tomorrow and see if I can safely shave some of the dome off the piston... but again wouldn't that create the same quench issue?
Are they solid or hollow domes? What do they weigh?
 
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