10.2 Compression Iron Head Setup

[mario03srt]

All,

How safe is it really to run a 367 LA with 10.2 static compression? Engine has Indy X Iron Heads w/2.02 valves and CP116's slightly in the hole. A .042 HG for quench was used on the original build and 93 Sunoco was used always and 34/35 degrees of timing. In the 3 years of use the car did not audibly ping. The engine is in for rebuild, due to vibration and some mains/rod bearing that were making some copper in my oil filter. The engine is being rebuilt/rebalanced with new forged rods. The builder is trying to sway me to running a thicker Cometic gasket to bring down the comresssion. This is a street car primarily. Other details include going to a mechanical solid roller lifter setup, the cam selection has not been made yet. We deliberately built the engine that way in 2017.

I know people run 10.2 motors on pump gas but I want to be sure. My concern is that a thicker gasket (.060 + ?)will open up the quench dimention and it will ping or be less effective in detonation prevention.

What are your thoughts?

Thanks,
Marion

 

[33IMP]

It kinda depends on how big your solid roller is gonna be.
And, how "street" its gonna be.
My opinion only! With enough camshaft you will be fine. I ran a 11 1/2 to 1 iron head big block on pump 91, but it had a 265/271 at .050 roller in it.
You could always leave the quench side of the piston intact, and machine a little away on the chamber side. Lowers compression, retains quench.
Edit: i forgot to mention, now that i have access to 100LL, theres no way i would run just straight pump gas. I would sweeten the pump, plenty!

 

[toolmanmike]

I think we need @AJ/FormS to give a explanation. Ready?

 

[shittyslant6]

@AJ/FormS i cannot wait.
Always good to read your stuff.

 

[toolmanmike]

I think we need @AJ/FormS to give a explanation. Ready?

Hey @rigger3006

 

[RustyRatRod]

@AJ/FormS i cannot wait.
Always good to read your stuff.

"His" stuff? LMAO

 

[dano]

Your thinking is correct unless your pistons are above deck. Thicker gasket is the wrong way to go to lower static compression and could induce more detonation due to killing what little quench you might have.

Lack of audible ping doesn't mean it didn't exist and the bearings being beat up might be the clue it could have been there. I was told typically the rod side bearing will be worn more than the cap side bearing of the rods if detonation was prevalent. Never seen it myself but something to look for.

 

[RustyRatRod]

Lets look at the math you've thrown out so far. You say it had .042 quench, right? That's with CP116s "slightly" in the hole. Correct? Lets examine the real math. That piston has a compression height of 1.660. With the stock 6.123 rod length and stock "approximate" deck height, you get a deck clearance of .026". That's .026" in the hole at TDC. Then you add on the "normal" .039" head gasket. To get quench, you add the .026 plus the .039 and get .065" for quench, so the .042 figure was not right to begin with. But, it's real easy to get better by just milling the block to zero deck height. Once that's done, then "whatever" your head gasket measures WILL BE your quench distance.

 

[TT5.9mag]

What do the tops of the pistons look like? What do the plugs look like? Those two things, as well as rod bearings being hammered on are how to tell if it rattled.

 

[RustyRatRod]

What do the tops of the pistons look like? What do the plugs look like? Those two things, as well as rod bearings being hammered on are how to tell if it rattled.

IMO, it was experiencing detonation. With 10.2 and .065 quench, it was very likely.

 

[mario03srt]

What do the tops of the pistons look like? What do the plugs look like? Those two things, as well as rod bearings being hammered on are how to tell if it rattled.

The pistons looked great. Here are the bearing examples.

 

[toolmanmike]

The pistons looked great. Here are the bearing examples.

View attachment 1715722984 View attachment 1715722985 View attachment 1715722986

Yikes!

 

[512Stroker]

The pistons looked great. Here are the bearing examples.

View attachment 1715722984 View attachment 1715722985 View attachment 1715722986

Just my opinion but I think you have more issues than detonation happening.

 

[mario03srt]

The rods were replaced some I Beam Eagles, crank turned, and the rotating assy was balanced. Turns out there were 3 different sb mopar rods in it per the builder. The cranks had material removed and everything now is within .3 grams. I had been experiencing vibrations when I cut open the oil filter I found copper. So it's being redone. Pistons are .025 in the hole on a decked block with cc'd chambers around 62cc, 5 cc reliefs etc.

 

[toolmanmike]

The rods were replaced some I Beam Eagles, crank turned, and the rotating assy was balanced. Turns out there were 3 different sb mopar rods in it per the builder. The cranks had material removed and everything now is within .3 grams. I had been experiencing vibrations when I cut open the oil filter I found copper. So it's being redone. Pistons are .025 in the hole on a decked block with cc'd chambers around 62cc, 5 cc reliefs etc.

The crank is shot and the bearings are toast. All that material has traveled throughout the engine. You're walking on thin ice there!

 

[TT5.9mag]

Looks like an oiling problem to me. And good on you for catching it before it got catastrophic.

 

[TT5.9mag]

IMO, it was experiencing detonation. With 10.2 and .065 quench, it was very likely.

I agree it was high probability but without more info we shouldn’t guess. The rod bearings don’t look like typical detonation to me. And he says the tops of the pistons looked great.

 

[TT5.9mag]

He’s .025 in the hole and had a .042 head gasket so .067 quench. Worse than RRR predicted.

 

[TT5.9mag]

@mario03srt What cam is in this thing?

 

[rumblefish360]

All,

How safe is it really to run a 367 LA with 10.2 static compression?

VERY SAFE BTDT

Engine has Indy X Iron Heads w/2.02 valves and CP116's slightly in the hole. A .042 HG for quench was used on the original build and 93 Sunoco was used always and 34/35 degrees of timing. In the 3 years of use the car did not audibly ping.

I would not expect it to ether. What is slightly in the hole. That’s a huge issue. Slightly?

will open up the quench dimention and it will ping or be less effective in detonation prevention.

What are your thoughts?

Bad idea since you’ll increase the chance of detonation.

 

[rumblefish360]

Lets look at the math you've thrown out so far. You say it had .042 quench, right? That's with CP116s "slightly" in the hole. Correct? Lets examine the real math. That piston has a compression height of 1.660. With the stock 6.123 rod length and stock "approximate" deck height, you get a deck clearance of .026". That's .026" in the hole at TDC. Then you add on the "normal" .039" head gasket. To get quench, you add the .026 plus the .039 and get .065" for quench, so the .042 figure was not right to begin with. But, it's real easy to get better by just milling the block to zero deck height. Once that's done, then "whatever" your head gasket measures WILL BE your quench distance.

This above is a long winded AJ reply whittled down in a nut shell, just the thing I tease AJ about all the time. There really is no need for a huge reply. If you like AJ replies, yes can understand that since I would say anybody can come to the same conclusion if they LEARNED about engines via READING A BOOK instead of waiting on those who know something for the easy answer.

He’s .025 in the hole and had a .042 head gasket so .067 quench. Worse than RRR predicted.

And what now for a cylinder head cc amount on what size bore using a gasket with what dimensions?

These are the pertinent facts that are needed to help, you the reader, figure out what is going on.

Ladies and gents, please take note of this since many here like to help but cannot when there is not enough known about the problem. Those helping hate to but will often assume in hopes everyone is on the same page.

Take note that the octane rating of fuel is detonation resistance and using more than what is needed will most always likely NOT result in more power. But just lighten your wallet needlessly.

 

[6PakBee]

I was doing some rough calculations and I don't think he's anywhere near 10.2 with that combination. I'm coming up with something in the 9.5 range assuming about 9 cc pistons, a 62 cc head, and a 0.045 gasket.

 

[72Dart6pack]

10.2? Swap those numbers around to 12.0.

 

[RustyRatRod]

He’s .025 in the hole and had a .042 head gasket so .067 quench. Worse than RRR predicted.

I missed the .042" on the head gaskets. My bad. I just used .039" as a guess.

 

[RustyRatRod]

I was doing some rough calculations and I don't think he's anywhere near 10.2 with that combination. I'm coming up with something in the 9.5 range assuming about 9 cc pistons, a 62 cc head, and a 0.045 gasket.

Yeah, probably another of many that just needs to actually measure.