Think I found why my car's a gutless turd.

[V_TastyTacos_V]

"The pistons are .155" in the hole, which means, that's 7.5:1 so after I put the heads on with the composition gasket instead of the factory steel shim, 7.4, so what's a tenth of a point between friends right?

 

[RemCharger]

"The pistons are .155" in the hole, which means, that's 7.5:1 so after I put the heads on with the composition gasket instead of the factory steel shim, 7.4, so what's a tenth of a point between friends right?

The 155 hole motor was the same 440 bottom I used to go 12.0s

 

[V_TastyTacos_V]

The 155 hole motor was the same 440 bottom I used to go 12.0s

Mine's a 383, though.

 

[padam]

The 155 hole motor was the same 440 bottom I used to go 12.0s

Your compression was 7.5 to 1?

 

[33 IMP]

Your compression was 7.5 to 1?

Pretty sure he said he had shaved closed chamber heads and steel shim head gaskets earlier. (If I remember right, which I'm probably not).

 

[RemCharger]

"The pistons are .155" in the hole, which means, that's 7.5:1 so after I put the heads on with the composition gasket instead of the factory steel shim, 7.4, so what's a tenth of a point between friends right?

They were talking about a motorhome 440

The 155 hole motor was the same 440 bottom I used to go 12.0s

As they showed in the first part

Mine's a 383, though.

Then they dynoed a 383 vs a 383

Your compression was 7.5 to 1?

Probably 8:1

Pretty sure he said he had shaved closed chamber heads and steel shim head gaskets earlier. (If I remember right, which I'm probably not).

Me? It was a buck 54 in the hole, with about an 82 cc 906 and a steel shim. Iirc. Pretty good for our air up here. I always came back to about 460 horse or so. But again, that's a 440 .

The heads were well- ported and it had a .528 MP cam

 

[V_TastyTacos_V]

Your compression was 7.5 to 1?

More like 7.28:1. Got a better measurement of my deck clearance, .140". That's the thickness of the red gauge I used, and 88cc estimate for the 906 heads.

 

[polyjohn]

So we are in 2025, five star Gas is a distant memory and where are we with Compression?
We have two choices at the pump now 5% or 10% ethanol.

What compression should we be running to maximise Pump Gas?
Just built THREE 440's with Six-pack (Indian) 2355 pistons and Felpro gaskets.

All three having the open chamber heads, the infamous 906 variety, so we are calling it TEN to ONE!
Is this a god or bad idea...(for 5% Ethanol pump gas)...

 

[DanielSlocum]

Me thinks octane is octane regardless of whats in the fuel. Therefore, me thinks 10:1 is likely about the limit for pump premium with iron heads as has been the generally accepted reality for a few decades now. Iv built a couple myself at 9.7-9.8 which are doing fine on 92 octane for what its worth.

 

[BSB67]

Just built THREE 440's with Six-pack (Indian) 2355 pistons
Is this a god or bad idea

Maybe, maybe not.
Not enough information to draw any conclusion.

Need exact CR, cam timing, and elevation.

If you have a small cam, and relatively low elevation, I think you’ll experience detonation.

 

[33 IMP]

So we are in 2025, five star Gas is a distant memory and where are we with Compression?
We have two choices at the pump now 5% or 10% ethanol.

What compression should we be running to maximise Pump Gas?
Just built THREE 440's with Six-pack (Indian) 2355 pistons and Felpro gaskets.

All three having the open chamber heads, the infamous 906 variety, so we are calling it TEN to ONE!
Is this a god or bad idea...(for 5% Ethanol pump gas)...

View attachment 1876678

Agree with BSB. That might be pushing your luck. I'd be thinking THICK head gaskets, since quench is already non existent. If I was building a mild cam pump gas street motor today, I'd shoot for 9 to 1.
Since I don't know where you are (Kiwi-land?) I'm not sure how your fuel is rated. I can run an iron headed 10.5 to 1 440 on 91 octane 10%, California cat pee, but only cause I've got a bunch of gear, cam and converter. And I sweeten the fuel with avgas, cause I can.

 

[68-500]

Honestly I wouldn’t even bother to use open chamber heads to build anything street able with respectable power. I know power can be built with open chambers but it to much of a fine line to walk. Start with pistons as close to zero deck as possible then a MLS head gasket to get the appropriate quench distance with closed chamber heads. That recipe you can just about forget about detonating or pre-ignition. Especially if you opt for aluminum heads. Probably run 10:1 on 87 octane.

 

[icetech]

Honestly I wouldn’t even bother to use open chamber heads to build anything street able with respectable power. I know power can be built with open chambers but it to much of a fine line to walk. Start with pistons as close to zero deck as possible then a MLS head gasket to get the appropriate quench distance with closed chamber heads. That recipe you can just about forget about detonating or pre-ignition. Especially if you opt for aluminum heads. Probably run 10:1 on 87 octane.

I was wondering how high of CR you could get away with 87 on... i know it depends on the cam and other stuff though

 

[V_TastyTacos_V]

Me thinks octane is octane regardless of whats in the fuel. Therefore, me thinks 10:1 is likely about the limit for pump premium with iron heads as has been the generally accepted reality for a few decades now. Iv built a couple myself at 9.7-9.8 which are doing fine on 92 octane for what its worth.

Combustion chamber shape plays a big part. Everyone should have heard of quench by now. Another very important factor is the intake closing event, which determines how much air gets trapped for the compression stroke. People are running compression ratios which would sound insane to street racers in the '80, on pump gas, but they have long durations and wide LSA which moves the intake closing much later, limiting low rpm trapped air, but increasing high rpm power. There are many dynamic compression ratio calculators to help figure things out.

 

[V_TastyTacos_V]

Honestly I wouldn’t even bother to use open chamber heads to build anything street able with respectable power. I know power can be built with open chambers but it to much of a fine line to walk. Start with pistons as close to zero deck as possible then a MLS head gasket to get the appropriate quench distance with closed chamber heads. That recipe you can just about forget about detonating or pre-ignition. Especially if you opt for aluminum heads. Probably run 10:1 on 87 octane.

I found the lifters that were in the motor, and I numbered them, so while I wasn't excited to try breaking in another flat tappet cam, or dumping money into a turd with a roller cam, I'm happy to put the original cam back in and get it running while I'm putting the other motor together.

 

[Krooser]

Well I have never seen a BBM with 7.4 cr except a motorhome or big truck.

Pull a head and do some real measuring.

I would bet a right sized cam, new timing chain and a good tune up would wake up that engine.

I lived thru the muscle car era. Worked at Mopar dealers as a front end/ ac techbfrom '68-'72. A stock 383 would best many a GTO, SS396,390,442 etc. Not one was a slouch.

Are you certain you have a passenger car engine? Did you run the block serial numbers?

When you change the cam pick the one you want then buy the next smaller one which is what you usually need.

And buy a cam designed for the .903 lifter like the one that Mopar installed from the factory. Most shelf cams are Chevy grinds and you leave HP on the table.

 

[DanielSlocum]

My post #49 was in response to #48 which was about open chamber iron 906 heads on pump fuel.
Of coarse there are many other factors at play and especially under other circumstances including quench,closed chambers,aluminum,altitude,cam timing etc. .
That said... the combo in #48 will work quite well as it did back in the day. Not earth shattering,but very respectable at around 10:1 with a typical street /strip type performance cam such as a .484 or .509 or something simular. Not every build is state of the art no stones left unturned trying to squeeze out every last possible horsepower. A basic 440 is still pretty good contrary to what some seem to think.

 

[V_TastyTacos_V]

Well I have never seen a BBM with 7.4 cr except a motorhome or big truck.

Pull a head and do some real measuring.

I would bet a right sized cam, new timing chain and a good tune up would wake up that engine.

I lived thru the muscle car era. Worked at Mopar dealers as a front end/ ac techbfrom '68-'72. A stock 383 would best many a GTO, SS396,390,442 etc. Not one was a slouch.

Are you certain you have a passenger car engine? Did you run the block serial numbers?

When you change the cam pick the one you want then buy the next smaller one which is what you usually need.

And buy a cam designed for the .903 lifter like the one that Mopar installed from the factory. Most shelf cams are Chevy grinds and you leave HP on the table.

What is real measuring? What is using gauge blocks, snap gauges, feeler gauges, or a machinist scale? I measured the red gauge, which fits perfectly between the piston and cylinder head surface. It's not measuring the open step. You can see the head gasket surface. TDC was verified with a piston stop and timing wheel. 906 heads cc at 88. Using 84, or 80 cc doesn't shoot the compression ratio up to 10:1. It doesn't even crack 8:1. You think I'm just guessing, but tell me, what do you think I have done that is unreasonable, how far off my accuracy is, and how much that would affect what the real accuracy is?

As for getting a real .904" lifter Mopar cam, many suspect these modern high rate cams are the reason we have so many cam failures, and why this cam went flat. What do you think?

 

[68-500]

I suspect your not far off on your compression ratio guess. What does a few points either way really making anyhow.

 

[Geoff 2]

The modern 'high rate' cams are not the problem; they have been around for decades. The problem is the crap lifters, poor metallurgy & inaccurate machining.