Ran into a car guy, has a clone Motion Camaro 427 and we started talking about my 454. He's telling me with my setup, my compression has got to be into the 10's. I'm not at all familiar with the LS-6 pistons(which are in my engine) and how much of a dome they have. Anyone know?

My quench is about 49, bore is 4.31 and a 4 inch stroke.

 

YOu need the part number of the piston and head size ( cc's )

 

Jughead,

I love your car! - have seen it time and again on these pages - and I looked at your posted photos as well.

Anyway: Get the specs on your heads - are they stock GM or something from the aftermarket? If they are made by GM check newer Chevy Big Block rebuild/hop up books and figure out their chamber volume. Otherwise consult the vendor. It's likely between 107 - 119 cc. Then look up your pistons (typically listed with specs such as dome height, etc) on their manufacturer's pages (GM in this case) and get their readout based on chamber volume.

From memory, I think the LS-6 pistons were flat tops or nearly so as the 1971 motor was a last stab at serious performance in the big block by GM. (They also made the SD455 for the Pontiac Firebird during the same era - ending that one in '73 or '74) I think they wanted about a 9:1 CR out of it... If you are running stock GM heads that would make your chamber volume likely 110cc or so... but check the specs and you will know for sure. My heads are 119cc (stock 1973 LS-4) and with the flat top pistons (stock) I get an overwhelming 8.25:1 stock CR. That will go up when I either replace or rebuild the engine...see related post I started!

With more specifics, we can help you figure it out here...

 

Here's a shot of the intake ports on the aluminum heads(12363390). They're listed as having 110cc chambers. 290cc Intake runners and 2.25 valves.





Here's the pistons. I should have stated that these are TRW LS-6 replacements.



Here's the specs on the pistons:


TRW-L2399F60 Piston Specifications:
* Bore: 4.310 in.
* Stroke: 4.00 in.
* Rod length: 6.135 in.
* Compression ratio: 9.63:1 (109.4cc heads)
* Head type: .095 in. Dome
* Oversize: .060 in.
* Ring size: 5/64 in. top/second ring, 3/16 in. oil control ring
* Weight: 693 grams
* For 454 (LS6) with open chamber heads


I think I figured the compression to be about 9.3-9.4 and I don't remember what dome volume I used or where I got it.

This "engine guy" was insistant that my compression was over 10!

 

I should have asked before, which LS-6 pistons - the 1970 Chevelle motor or the 1971 Corvette motor? I think those are the same heads that GM puts on its ZZ502 engines. The heads have smaller intake valves for the ZZ454. What casting numbers are on your heads? Did you get the block decked for zero piston height - in other words, does the side/edge of the piston come right up to top of the block? Any detonation? I think you have a good setup. What cam is in that beast? Have you got a picture of the chambers on those heads? I like the GM roller cams I am seeing in the 454HO and ZZ502 engines...

Here's the ZZ502 spec list:

Displacement: 502 cubic inches
Horsepower: 502 @ 5,200 RPM
Torque: 567 @ 4,200 rpm
Max. Rec. RPM: 5,800 RPM
Fuel: Premium Unleaded 92 Octane
Spark Plugs: #4 Rapid Fire Gap .035, R43XLS Gap .035 (not included)
Bore & Stroke: 4.47” x 4.00”
Compression Ratio: 9.6:1
Engine Block: Cast Iron, for bolt main caps (P/N 10237292)
Crankshaft: Forged Steel (P/N 10183723)
Connecting Rods: Forged Steel shot peened, 7/16” bolts (P/N 101988922)
Piston: Forged Aluminum (P/N 12533507)
Piston Rings: P/N 12524293
Camshaft: Steel Hydraulic Roller (lift: .527” I, .544” E) (Duration @ .050”: 224° I, 234° E) (P/N 12366543)
Timing Chain: (P/N 3891519) Single Roller
Cylinder Heads: High Velocity 356-T6 Cast Aluminum Alloy Oval Port, 110cc Semi-Open Combustion Chamber, with valves and springs. (P/N 12363390)
Intake Valve: 2.25” Stainless Steel (P/N 12366987)
Exhaust Valve: 1.88” Stainless Steel (P/N 12366988)
Valve Springs: (P/N 12462970)
Valve Lash: Zero
Rocker Arm Ratio: 1.7:1 Stamped Steel (P/N 12368082)
Valve Covers: Premium Die Cast Aluminum
Flexplate: 14” for Automatic Transmission
Spark Timing: 36° total at 5000 RPM, 8° BTDC @ 800 RPM
Technical Notes: Distributor P/N 1104067 or melonized distributor gear P/N 10456413 must be used on all crate engines with steel camshafts.

For comparison, here's the ZZ454 cam and related specs:

Camshaft 24502611 Steel Roller (Valve lift: .510” I, .540” E; Duration @ .050” 211° I, 230° E), Lobe Center Line 112°

Cylinder Heads 12363399 Signature Series 356-T6 Aluminum Alloy Bare Head With Seats And Guides. Oval port, 110cc simi-open combustion chamber, 7/16” Rocker Stud Holes. Accepts all stock accessory brackets except Gen VI where the bracket holes have been enlarged to 7/16” The roller studs and exhaust bolt holes are heli-coiled for strength. High velocity 290cc intake runners enhance mid range throttle response and torque. 110cc exhaust runner volume. Casting number 14097088.
Intake Valves 12366986 2.19” Stainless Steel, 11/32” Stem Size
Exhaust Valves 12366988 1.88” Stainless Steel, 11/32” Stem Size

Pistons 10215228 Forged Aluminum, Wrist Pin, Std., 8.75 To 1 Compression

Like I said - you have a great engine! To be sure of your CR without doing any volume tests on the heads, just look up the GM pistons used in the engines listed above and compare them to yours - you want to see what kind of dome the GM pistons have, then compare the volume taken in by the domes on the various pistons... Since we are dealing with the same heads but different pistons, if your piston domes are bigger than those used on the ZZ454 (and 454HO) then it would follow that you have a higher CR than 9.6:1..

 

Compression ratio: 9.63:1 (109.4cc heads)

That's your compression ratio with standard deck and stock cylinder head gaskets, it may be sightly less if you chamber size is a little bigger

 

Rock on with your bad self Jughead! Love them heads!

 

Hmmm..8.75 to CR on that engine. I woulda thought it'd be higher.

Yeah, those are the same heads. Casting 12363390. Here's the pics of the combustion chambers.

 

Thanks.

I think the pistons were 0.004 out of the hole. The head postion of the block wasn't "decked" but they did say they shaved it just to clean it up.

Just remembered that, quench should be 0.043 because the gasket (Ls-7's) is 0.039.

 

I also caught that on the ZZ454 cam spec. I think they copied it over from the 454HO spec sheet in error (the 454HO is a 8.75:1 engine with the larger 118cc iron heads) - it is the same cam on both engines and slightly less aggressive than the cam on the ZZ502. The ZZ454 really is a 9.6:1 engine when they put the 110cc aluminum heads on it. Your heads are works of art - I would've had a tough time bolting them on and no longer seeing all that machined aluminum on my bench!

 

That's why I took a few pictures before bolting them on.

And I paid like they were a masterpiece too.

 

The original LS6 was 11.1 compression with domed pistons. I ran a set of TRW replacement and with my 109 cc heads I had 11.4 compression.

 

That's what the Motion guy I was talking with said. That's why he thought I should be at least 10! Maybe because they're replacements? The dome isn't as tall?

Norval, did your pistons look like the one I have pictured above?

 

It's hard to tell but the original 375 horse 396, the 425 horse 427 and the 465 horse 454 were all solid lifter and 11.1 compression.
The TRW book will tell you the compression ratio knowing the cc's of the combustion chambers and your piston part number. Not sure about the part number? Measure the dome height and compare it to what is in the book.

 

dome vol is 13.8 cc. with aluminum heads you can run .5 CR over CI heads because of the heat lost thru the alumium heads and you need to do that to get equal power to the CI heads

 

Thanks Clem, I'm about 9.8 - 9.9 then.

 

I think maybe the original LS-6 pistons must have been these:

L2349F
http://www.21cgt.com/FMWebCatalog/frmPartDetails.aspx

 

Your piston dome shape looks like the ones in my '70 LS5. My motor is completely stock with 101cc heads and it has 10.25/1 compression.

Hope this helps.

BigBlockk

Later.....

 

The repacement originals are TRW-L2349F and with open chamber of 119CC give 9.99 and with 107 cc closed chamber heads gave 11.18.
Dome height was .265

 

2349 were 1970 454 LS-6 pistons for closed chamber heads,with 106.9 heads =11.18 cr