Looking for Piston Dome Volume on L82 Piston

[Dennis H.]

Hi all

I have been dumpster diving the internet for the last 3 hours looking for specs on the GM 336754 piston. I'm crunching numbers using the Engine Compression Ratio (CR) Calculator and need the "Piston Dome Volume In CCs" number for a 1973 L82.

If my research is correct the as delivered OEM piston PN is GM 336754 that is a TRW 464664 or L2417??????

Also, I have GM service replacement head gaskets that measure .026 thick, what compressed head gasket thickness should I use in the CR calculator?

Thanks
Dennis

[Scott P.]

Re: Looking for Piston Dome Volume on L82 Piston

Dennis, the TRW L2417s info from the Federal Mogul book. Scott

4" Bore series SB
Dome volume -3.4
Weight 579
Comp Dist 1.56
Flat top w/single trough
Std thickness rings
Pin P or F
clearance .0040

[Duke W.]

Re: Looking for Piston Dome Volume on L82 Piston

I can confirm all that L2417F data from my 1995 F-M catalog, and it is the OE replacement L-82 piston, but I have to ask why would you rebuild a L-82 with that piston? L-82 is a low compression version of the '69 L-46 designed to operate on 91 RON fuel, which is equivalent to today's 87 PON.

With today's 93 PON you can comfortably run up to 10.25 true with the OE cam, but reduce 0.1 for every octane number below 93 if you don't have 93 in your area.

Check out Keith Black hypereutectic pistons. Likely they are much less expensive.

The OE head gasket was probably .018" shim type. The .026 replacement gasket assumed a head cut was taken and was thicker than the plant installed gasket to kept the engine out of detonation. The Felro 1094 is .015". Shim type gasket compressed thickness is simply the material thickness. Measure in a portion of the gasket that is not formed with a caliper or mic.

You have to be very careful with the algebraic sign of the piston volume. F-M lists net domes as a positive number, but I recall Keith Black uses the opposite convention. I don't know what CR calculator you are using, but web search the following:

"compression ratio explained" duke williams

This should allow you to download a pdf of this article from the Corvette Forum that I co-wrote and was published The Corvette Restorer.

Duke

[Dennis H.]

Re: Looking for Piston Dome Volume on L82 Piston

Duke

I was playing around with CR Calculator you recommended in your article and using the current L82 pistons for no real reason than that's what is currently in the car and I was researching those. It says use "-" number for Dome so I assume I'm using 3.4 for the TRW L2417F even though it says "-3.4".

This whole piston research thing is a by product of well while I'm here. I'm pulling the engine to remove a Torker II intake, Holley Carb, Comp 274H cam and set of World S/R I-052 heads. I have all the OEM as delivered parts to put back on the engine so while it's out I might as well rebuild the engine.

Engine has 43,450 original miles so until I get it apart and measured out I really don't know what I have or what direction I'm headed in. My guess is at the end of the day a bore and new pistons. That's assuming I can find a machine shop that can turn it around before Christmas (little sarcasm).

Thanks for the info on the

.026 replacement gasket that assumes a head cut was taken, I did not know that.

This rebuild is really not about saving money (

loose statement), I just want to make sure I'm using the right quality parts.

Dennis

[Duke W.]

Re: Looking for Piston Dome Volume on L82 Piston

Those pistons actually have a net dish, not a net dome. Note that the description says flat with a single valve relief trough. That's why it's negative and you should enter it in the cgnet calculator as a negative number. The 11:1 350 pistons have a net dome of 2.4 cc.

KB uses the opposite convention. A net "dome" is listed as negative. When you think about it a net dome actually subtracts from total chamber volume, so making the dome volume negative makes sense, but most piston manufacturers use same convention as Federal Mogul and list the dome as positive. So that's what you put into the cgnet calculator and it takes care of the sign.

You are wise to do this work now and develop a complete plan before you pull the engine. The Web is full of horror stories about engine rebuilds gone south, usually because the owner didn't do any planning often accompanied by turning the engine over to some "engine builder" who proceeded to machine the decks and fill it up with aftermarket hot rod parts.

The only non-OE parts I recommend are the KB pistons. You've got the "pink" rods and other than checking them for dimension conformity they need nothing...not even new bolts. If you want "more power" consider massaging the heads.

Duke

[Tom R.]

Re: Looking for Piston Dome Volume on L82 Piston

What's the link to the article (Duke's)? I searched but came up with everything but...including the forum.

[Duke W.]

Re: Looking for Piston Dome Volume on L82 Piston

Corvette forum... advanced search... threads started by SWCDuke.

You might find other articles that interest you.

Duke