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Cam variables that can affect detonation in a high compression engine

I am curious what 2 cams you tried at 10.9:1. I assume you have aluminum heads and what elevation your at.
I had the Mopar Performance 292/509 at first. I tried adding 1.6 ratio rocker arms but that only resulted in evening out the cranking compression numbers. The stock 1.5 ratio arms must have had some variance in lift because the 1.6 rockers raised some cylinder numbers and lowered a couple. My averages were still around 180.
Second cam was the Lunati solid 316/326:
DSCN1890.JPG

A pretty racy cam but it didn't help stop the knock.
The same FABO member that suggested it also suggested that I look at the distributor and find a way to S L O W the rate of advance. I have noticed that many guys report that they have, say...36 degrees of total advance all in at 2000 rpms. I wonder why ALL the advance has to be in place at such a low rpm? The FABO guy was onto something with that advice.
If full advance can be delayed until 3000 rpms or so, maybe whatever tendency there is to knock may be diminished ?
 
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@Moparfeind, I just checked my trw book. Says your compression distance is 1.839, piston dome is 10.7 cc.piston weight is 675 gr, plus or minus 4gr, pin weight is154gr, also p or m 4gr.
So, at a blueprint deck of 9.6, and a blueprint rod of 6.123 plus 1.839, those trw's should be .017 out of the hole.
Assuming a 64 cc head, a .039x4.1 head gasket, 10.7 net dome, and a .017positive deck, you are at 12.13 to 1, according to Wallace calculators.
 
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Also theoretically , a 70cc head with a .060x4.1 head gasket gets you down to 11.23 to 1. 64cc head, with .090 gasket, also around 11.25 to 1.
75cc head, with a .090 gasket: 9.8 to 1
You could always pull it apart, and mill the solid domes to what you want. I would sure do that before I bought hypers (ugh). Take off half the dome and you might not even have to rebalance. TRWs don't appear to be real close tolerance out of the box.
As always, the right answer is: use the right piston.
 
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................it is a good tool when combined with real world experience. Without experience it's just a number that can be misleading................I don't think it's going to be helpful unless you are trying to run a specific octane and have a dcr number in mind that someone has experience with.

This.

People cannot even agree on what is the right valve closing point to use in these DCR calculators.

All that said, if your at 210 psi now with an iron head, there is no reasonable street cam you will be able to install to run on pump gas.
 
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I am reading all your inputs guys. Looks like the best thing to do is cut the pistons down or put new ones in. This in my mind is the same as a rebuild since its coming out. Should freshen the block up align bore and hone the cylinders etc.
 
@Moparfeind, I just checked my trw book. Says your compression distance is 1.839, piston dome is 10.7 cc.piston weight is 675 gr, plus or minus 4gr, pin weight is154gr, also p or m 4gr.
So, at a blueprint deck of 9.6, and a blueprint rod of 6.123 plus 1.839, those trw's should be .017 out of the hole.
Assuming a 64 cc head, a .039x4.1 head gasket, 10.7 net dome, and a .017positive deck, you are at 12.13 to 1, according to Wallace calculators.
This was exactly what I was looking for 33! I understand to take it as an estimate. Also that it could be off but as you are using it is exactly how I wanted to run numbers to look trends and movement direction playing with some of the variables that I can actually change without pulling the motor. Is the calculator free if so can you tell me where its at? Thanks!!
 
I am reading all your inputs guys. Looks like the best thing to do is cut the pistons down or put new ones in. This in my mind is the same as a rebuild since its coming out. Should freshen the block up align bore and hone the cylinders etc.
Ever heard of anyone using a wood router for milling the pistons in the block? Yeah....not kidding lol
 
This was exactly what I was looking for 33! I understand to take it as an estimate. Also that it could be off but as you are using it is exactly how I wanted to run numbers to look trends and movement direction playing with some of the variables that I can actually change without pulling the motor. Is the calculator free if so can you tell me where its at? Thanks!!
Google Wallace Racing calculators. A freebie, and he has probably 200 math formulas for everything automotive you can think of. A fabulous resource!
(He's a Pontiac lover, but don't hold that against him, LOL!)
 
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Looks like cosmetic makes a mls (multi layer steel) head gasket up to .120 thick. May be an easy way to get where you want, but those gaskets are not cheap.
@Moparfeind, per your post 12, if the cam you have now is too aggressive, a milder cam certainly won't be able to give you what you are looking for.
Edit: damn auto correct! COMETIC!
 
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Ever heard of anyone using a wood router for milling the pistons in the block? Yeah....not kidding lol


Honestly, I would give it a good look. And I think it would work with the right tools, prep and set-up. Dowel pins would need to come out, and firewall clearance might be an issue.
 
Honestly, I would give it a good look. And I think it would work with the right tools, prep and set-up. Dowel pins would need to come out, and firewall clearance might be an issue.
So far of all the 'quickie' ways to do stuff like this, the router was one of the better ones. What prompted me to bring that up was the mention of Steve Dulcich doing it lol. Imo, doing that with the short block out of the car would be the best thing as I'd rather not have all the shavings all over the engine bay....
 
So far of all the 'quickie' ways to do stuff like this, the router was one of the better ones. What prompted me to bring that up was the mention of Steve Dulcich doing it lol. Imo, doing that with the short block out of the car would be the best thing as I'd rather not have all the shavings all over the engine bay....

Hmmmm. Good point. But my engine bays don't look that great to begin with.
 
I used to be a machinist and I don’t think I could bring myself to the point of using a router lol. Even if Steve Dulitch did it. My trepidation is being physically able to pull the motor (again) by my self and put it back in. Not afraid of rebuilding it as you guys are a great resource.
 
.017 out of the hole just like op said in page 1
still do not know his head X,J U 360 but no biggie
he most likely has more than 64 cc but not enough to fix the problem
cam won't fix it
FIx 1 recurve the dist so max adv is not till after max torque rpm
Fix 2 double up the gaskets or get those compression lowering rebuilder shims
(this is a weekend fix- anything else takes longer)
you could also retard the cam and report back- might help but most likely will not fix)

Fix 3 get some KB pistons with the quench dome if you are going to keep those heads (like they are fresh guides, springs etc)
that gives you some quench
or mill the domes flat if you are thinking of new heads with wedge chambers
either way you have to rebalance- KB's are lighter

detonation can cause disasterous rod bearing problems in addition to the usual piston problems
or like I said above E-85 or propane
E-85 conversion is also relatively quick
 
Hey guys how ya doin? Now that you gave your honey her valentines gift and dinner its time to get back to reality lol.

I have two questions:

1. What variables can I use in cam shaft selection that can help soften the effects of detonation in high compression motor?

2. If I am running a 12:1 piston and a 64cc head (unknown gasket about 017 out of the hole) how can I estimate compression? Is there a good formula that I can use?

Thanks for reading.......

Intake valve closing point. Sooner closing point after BDC = more dynamic compression, Later closing point = less dynamic compression.
Exhaust/Intake Overlap. Depending on Engine speed and exhaust system, larger overlap can increase the exhaust content of the intake air at lower rpms (think EGR) which will reduce combustion temps.

What you really want is cold air/fuel entering the chamber then the heating effect of the high compression won't matter as much compared to compressing already hot air/fuel.
 
Dynamic compression basically is a tool for low rpm
once he get's it reved up then intake fill rules
what Kern dog said- bigger cam made it worse
most likely all the way to max torque max VE
you might want to pm yellow rose -yr over at fabbo - he has done well with high compression tuning but I think you will end up with similar advice
cheers
 
Is there any machining that can be done to the heads to increase volume to lower compression?
 
that was supposed to go in the hellcat thread
oops- I deleted it
will delete this one too
thanks for noticing
 
Hey guys how ya doin? Now that you gave your honey her valentines gift and dinner its time to get back to reality lol.

I have two questions:

1. What variables can I use in cam shaft selection that can help soften the effects of detonation in high compression motor?

2. If I am running a 12:1 piston and a 64cc head (unknown gasket about 017 out of the hole) how can I estimate compression? Is there a good formula that I can use?

Thanks for reading.......
 
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