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I'm sure this has been beat to death but I couldn't find what I wanted.

I have learned the combustion chamber volume of ci LT-1 head is 64cc where as the aluminum head is 54cc. Holding all other relevant dimensions constant (bore, stroke, deck height,etc) the compression ratio swings pretty dramatically. I thought I'd read where the LT-1 was typically at 10.6:1. With a 64cc chamber it's 10.51:1 but it jumps to 11.97:1 using 54cc heads. (4" bore, 3.48" stroke, 5cc piston dish, 0.015" deck height and gasket thickness).

Am I doing something wrong here? Is the piston dished more? 5cc was a number I got from the Mahle site.

It seems the motor may get cranky on pump gas with this ratio yet this would have been a factory design. I also read somewhere that the gasket on the ci engine is 0.029" and not 0.015" which would drop the ci ratio to 10.16:1.
 

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yeah something is wrong with your calculation, probably on the piston end of things. 5cc doesn't sound quite right. not that i've measured, but the valve reliefs alone probably hold more than 5cc

static compression ratio of an aluminum headed LT1 is definitely somewhere around 10.5:1 in every document i've ever seen

of course the LT1 can survive at pretty high compression on pump gas due to reverse flow cooling; keep that in mind...
 

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Dynamic compression is more important than static compression when trying to figure if it will run on pump gas. Dynamic compression takes the cam advertised duration, rod length and several other factors, in addition to what your already factoring in to get the compression number. Which will be lower than static compression.

There are dynamic compression apps available on the web. If you can't find one, pm me with your e-mail address and I'll send you one.
 

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Calculators and LT1 specs

8Cyl

4.0" Stock Lt1 Bore

3.48" Stock Stroke

5.7" Connecting rod length

Compression Ratio 10.4:1

Head CC's Stock aluminum LT1 56cc LT4 54.4cc's Iron LT1 64cc

Stock head gasket bore diameter LT1 4.125"

H Gasket compressed thickness .050" Aluminum LT1
Cast iron LT1 .028"
LT4 .043

Piston to Deck Clearance stock .025"

Piston valve relief or dish volume 4cc

LT1 vs LT4

LT1 piston volume - LS1TECH

LT1 Piston to deck clearance vs. deck height? - LS1TECH

Stock Lt1 deck height? - CamaroZ28.Com Message Board

what is the stock 350 LT1's head gasket compression thickness? - LS1TECH

LT1 Head Gasket thickness ? - Corvette Forum

LT1 Pistons and compression ratio question - Corvette Forum

LT1 piston volume - LS1TECH

Stock bore lt1 head gasket. - CamaroZ28.Com Message Board


Wallace Racing: Dynamic Compression Ratio Calculator

Engine Compression Ratio (CR) Calculator


With my numbers and my cam intake closes 61deg ABDC stock compression ratio

10.421:1 Static Compression Ratio Dynamic Compression ratio 8.553 With my cam 61ABDC stock dimensions

Good with cheap gas but 9.0:1 dynamic compression ratio makes a much nicer street engine.
.039 fel progaskets 1074 takes me to 10.729 compression ratio dynamic at 8.8:1

Polished combustion chambers while porting so milled the heads .010 to arrive at lt4 spec chambers 54cc

With my cam this gives me 11:1 static compression ratio and 9.017:1 Dynamic compression ratio still good with street gas and lots of torque throttle response and mpg.

United Engine & Machine Co. Incorporated


The 92-97 Corvette Firebird and Camaro use LT1 engines

The LT-1 engine was a 70 1/2 Corvette Z28 engine

http://ls1tech.com/forums/lt1-lt4-modifications/1287288-lt-1-vs-lt1-article.html
 

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Calculators and LT1 specs

8Cyl

4.0" Stock Lt1 Bore

3.48" Stock Stroke

5.7" Connecting rod length

Compression Ratio 10.4:1

Head CC's Stock aluminum LT1 56cc LT4 54.4cc's Iron LT1 64cc

Stock head gasket bore diameter LT1 4.125"

H Gasket compressed thickness .050" Aluminum LT1
Cast iron LT1 .028"
LT4 .043

Piston to Deck Clearance stock .025"

Piston valve relief or dish volume 4cc

LT1 vs LT4

LT1 piston volume - LS1TECH

LT1 Piston to deck clearance vs. deck height? - LS1TECH

Stock Lt1 deck height? - CamaroZ28.Com Message Board

what is the stock 350 LT1's head gasket compression thickness? - LS1TECH

LT1 Head Gasket thickness ? - Corvette Forum

LT1 Pistons and compression ratio question - Corvette Forum

LT1 piston volume - LS1TECH

Stock bore lt1 head gasket. - CamaroZ28.Com Message Board


Wallace Racing: Dynamic Compression Ratio Calculator

Engine Compression Ratio (CR) Calculator


With my numbers and my cam intake closes 61deg ABDC stock compression ratio

10.421:1 Static Compression Ratio Dynamic Compression ratio 8.553 With my cam 61ABDC stock dimensions

Good with cheap gas but 9.0:1 dynamic compression ratio makes a much nicer street engine.
.039 fel progaskets 1074 takes me to 10.729 compression ratio dynamic at 8.8:1

Polished combustion chambers while porting so milled the heads .010 to arrive at lt4 spec chambers 54cc

With my cam this gives me 11:1 static compression ratio and 9.017:1 Dynamic compression ratio still good with street gas and lots of torque throttle response and mpg.

United Engine & Machine Co. Incorporated


The 92-97 Corvette Firebird and Camaro use LT1 engines

The LT-1 engine was a 70 1/2 Corvette Z28 engine

LT-1 vs LT1 article - LS1TECH - Camaro and Firebird Forum Discussion
Something is wrong with this data
All of the LT1 heads between 92 and 97 were 68cc

I'm working on a 95 Fleetwood which came with iron heads. I'm putting aluminum heads on it and have been struggling to determine the proper gasket thickness to use. Hence how I stumbled upon this post.
However, while most of the data looks accurate, I see no evidence of the aluminum heads being any different than the iron heads other than material.

What I want to know really is, stock bottom end, aluminum heads using 643 or 374 casing and a Comp Cams 502 grind what will I end up with for compression say using .029 or .050 gaskets. I don't mind being around 11:1 but I don't want to go much over that on a stock bottom end.
 

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There are sites online to determine the dynamic compression ratio. The 11 to 1 ratio you give in your post is the static compression ratio. The sites that calculate dynamic compression ratio, let you plug in all the data & specs of your parts. As long as your static compression ratio doesn't go over 9.5 to 1, you will be ok on pump gas.

Since your pistons and heads are stock your static compression ratio is 10.5 to 1. However the longer the cam duration is, and the higher the lift, actually lowers the dynamic compression ratio.

When I had my 95 trans am, the lt1 I rebuilt had 11.8 to 1 pistons, the GM hotcam, standard deck height & head gasket thickness. My dynamic compression ratio was 9.5 to 1. Engine ran fine on 92 octane non-ethanol fuel.
 

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I forgot to add that lt1 cast iron heads actually flow a little better than aluminum heads.
Kind of. I think this was true at one time but tests have shows that is not true. Especially if both are polished. They used to say if you polished the iron they flowed better but that's been debunked.
 

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There are sites online to determine the dynamic compression ratio. The 11 to 1 ratio you give in your post is the static compression ratio. The sites that calculate dynamic compression ratio, let you plug in all the data & specs of your parts. As long as your static compression ratio doesn't go over 9.5 to 1, you will be ok on pump gas.

Since your pistons and heads are stock your static compression ratio is 10.5 to 1. However the longer the cam duration is, and the higher the lift, actually lowers the dynamic compression ratio.

When I had my 95 trans am, the lt1 I rebuilt had 11.8 to 1 pistons, the GM hotcam, standard deck height & head gasket thickness. My dynamic compression ratio was 9.5 to 1. Engine ran fine on 92 octane non-ethanol fuel.
OK, so part of what I'm trying to figure out is this. The 502 cam is
218/224 Duration at .050". 112 Degree Lobe Separation Angle
The heads will be milled about .020
block is stock

I'm told the stock head gasket thickness on the iron head engines was .029. I need to know if that's absolutely true.
I also see numbers all over the place but from what I know, the bowl in the heads is the same on all castings, and that is 58cc but I also need to know if that is positively true. I think they're the same but are they 58cc

I do not want to do all of this work and lose compression so I'm trying to target either keeping the 10.5:1 or bumping it to 11:1.

Someone somewhere has to have good information.
 

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For the specifics you want, I would say you need to find a LT1 engine specialist. They are few & far between, but still out there.

My best guess would be that by jumping up to 11. to 1 compression, you would make up for the longer duration higher lift cam.

As for specific data like head combustion chamber cc, & head gasket thickness, you have to keep in mind that these are mass produced components and will vary in their specs.
 
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