Shoptalkforums.com

The oil running through your draw through manifold is to heat it up and help the manifold to not ice up when the air and fuel run through it.

panel wrote: ↑Sat Oct 25, 2025 10:29 am The oil running through your draw through manifold is to heat it up and help the manifold to not ice up when the air and fuel run through it.

Yes Sir. I understand that. And I bet it would be important if I lived in Minnesota or Wisconsin, but living in Texas, am I artificially elevating my iat, when it's not desirable?

What has your IAT been while running? Run it without. Some of the 4 barrel guys don't have that.

Doghouse style coolers have pretty small air passages vs say a radiator or such, need a bit of air pressure to work.
Sticking it in airstream would probably work at front of car as a lot of intercoolers are about same design set up that way. Dont put a muffin (axial) fan on it, blower style fans are things and they can develop decent air pressure.

The oil heated intake can work ~well, esp if you have the thermostat/flaps working for the engine, but wads of densely packed aluminum foil jammed between the manifold and block worked on a weber progressive setup on a T4 in upstate NY.... at least stopped it icing up when temps outside wre 40-60ish, stops being an issue below freezing as there is a lot less water in the air. It probably doesn't cool your oil very much tho..

Quick warmups and good filtration (air and oil, gauze filters are trash as filters) make your engine last a LOT longer, at least the cylinders/ring seal.

I got to spend some time in the shop this morning. With the new pistons and cylinders on the shelf, I got them mocked up for the first time. Using a .030 and an .040 cylinder shim, the piston sits .020 down in the cylinder. Greg Tims tells me that his turbo heads come out at 67ccs in the combustion chambers. So using a. 050 copper shim i get a compression ratio of 8.2 : 1 and a deck height of "only" 0.070". Just about half of what it was the first time. Feeling good about this time. Fingers crossed

What pistons and cylinders are those?

Mahle/Cima 94b

The 'rule of thumb" for non-squish engines is generally that .060"-080" is the no-go zone, prone to knock. (~90mm bore range) .030-050 ideal for good squish (more ok as bore increases, talking 4" bores ok .060") and .090" to .120 in the next safe zone, where you rely on swirl and tumble for good mixing, 2 valve heads have reasonably good swirl by default.
This range is relative to bore size, bigger the bore, you can go looser as pistons rock etc.

You MIGHT be OK at .070" at 94mm bore.... I'd personally be happier with .050 and a little more CR/squish, esp if you are running any cam much north of stock..

The bulletproof Dodge turbo 4 cylinders ran .120" deck.

Hi piledriver,
I was just patting myself on the back for getting my deck height down from .135 or whatever it was, only to hear about the "no-go" zone. This is the first I've heard of it???

I am using the Engle W-125 cam. It's pretty far from stock, as far as I'm concerned.

More research to be done

The "no squish" setups are supposed to eliminate trapped areas that might cause knock.
May only matter over 30 PSI.

Personally I'd aim for 1mm deck or even slightly less on something street driven, esp with a non-stock cam.

A 10-11:1 CR with a 240 degree (actual @.050") cam and mild boost (<1 BAR) would be not out of line, esp if you have a flex fuel setup that can alter fuel and spark based on ethanol % automagically.

If still running a central carb and long plumbing, giving nonuniform fuel distribution/erratic AFR maybe 9:1 ish.

Thanks again for your input. I have another batch of barrel shims ordered up, and I spoke with Greg Tims about combustion chamber size.

I have an "old school" draw through arrangement and no plans to run e85 or any flex fuel setup. My goal is a static compression ratio of "about" 8.5:1.

Paul

Piledriver wrote: ↑Mon Nov 03, 2025 5:55 am The 'rule of thumb" for non-squish engines is generally that .060"-080" is the no-go zone, prone to knock. (~90mm bore range) .030-050 ideal for good squish (more ok as bore increases, talking 4" bores ok .060") and .090" to .120 in the next safe zone, where you rely on swirl and tumble for good mixing, 2 valve heads have reasonably good swirl by default.
This range is relative to bore size, bigger the bore, you can go looser as pistons rock etc.

You MIGHT be OK at .070" at 94mm bore.... I'd personally be happier with .050 and a little more CR/squish, esp if you are running any cam much north of stock..

The bulletproof Dodge turbo 4 cylinders ran .120" deck.

I can vouch for this information with a 30 over Chevy 327 and a 471 blower 40 years ago that would ping on premium.
My dad and I were in it at one of his cousins and he asked what pistons, head gaskets, etc. it had.
He said that we had to either get the pistons closer to the heads or further away.
He said to ditch the thick composite head gaskets and install thin stainless ones with copper spray on them.
I was not convinced since that would raise compression, but my dad said Max knew what he was talking about.
We did it and I learned to pay attention to him.
Smart man that last I knew was still building winning circle track engines in his 80's.
IIRC it was 8.7 to 1 with the composite gasket and 9.4 to 1 with the stainless gasket.

Interesting. At what point does static compression begin to be too much for a boosted application? I'd love to make 15 pounds of boost one day once my project doesn't die a premature death. Surely, I can't run 9.5-10:1 compression and a higher amount of boost, just because the NA motor wants that.

ETA on pump gas

That 471 was only making 10 PSI of boost so it could have decent compression and that was back with leaded fuel.
How much compression really depends on a lot of variables.
Intercooling or methanol injection helps a bunch.
The longer the duration of the camshaft the less effective compression you will have.
Fuel, A/F ratio, and timing also come into play.
I will have to let others answer with numbers since I am running E85, a twin screw supercharger, and a very efficient intercooler system.
With mine I was at 16# with 9-1 and 22-degrees timing and did not see any indicators of knock when I tore it down, but apples to oranges.

The longer the duration of the camshaft the less effective compression you will have.

And that holds true even under boost? According to the cam card with my W125 cam, it has 262 degrees of duration at 0.050" of lift?

ETA 46 degrees of crankshaft rotation overlap


Yes... and a 471 is a very small blower