L48 pistons
Thread Starter
Melting Slicks
Joined: Oct 2010
Posts: 2,276
Likes: 337
From: "ɹǝpunuʍop", Adelaide, South Australia
L48 pistons
how much dish (in cc) is there on original '72 350 L48 pistons?
heads are the 993 castings - 76cc - giving 8.5:1 comp
just thinking about freshining up without a pull out of motor.
heads are the 993 castings - 76cc - giving 8.5:1 comp
just thinking about freshining up without a pull out of motor.
Pro
Joined: Aug 2000
Posts: 610
Likes: 168
From: Vancouver B.C.
Most of the info I have says a 15.7 cc dish. But some other info says 9.92.
The other number you may need is Piston to Deck clearance. I think stock is around .025" in the hole. After market I have heard is zero. Not sure. Gasket thickness and gasket bore diameter can also affect your CR calculation.
You never know what you really have until you pull the heads.
I also have a '72 L48, but when I pulled the heads, I found out the motor was bored .030 over, and replaced with forged dish pistons. Go figure. Most of these motors with the 76 cc head are rebuilt with flat tops. So you never know.
If you have dished pistons, I think going with 64cc heads and a .018" thick head gasket will get you up to around 9.3 to 9.5:1 compression. With that compression, you have more options when considering a cam. Of course I am assuming you are thinking like many L48 guys, how to get some more HP.
The other number you may need is Piston to Deck clearance. I think stock is around .025" in the hole. After market I have heard is zero. Not sure. Gasket thickness and gasket bore diameter can also affect your CR calculation.
You never know what you really have until you pull the heads.
I also have a '72 L48, but when I pulled the heads, I found out the motor was bored .030 over, and replaced with forged dish pistons. Go figure. Most of these motors with the 76 cc head are rebuilt with flat tops. So you never know.
If you have dished pistons, I think going with 64cc heads and a .018" thick head gasket will get you up to around 9.3 to 9.5:1 compression. With that compression, you have more options when considering a cam. Of course I am assuming you are thinking like many L48 guys, how to get some more HP.
Race Director
Joined: May 2005
Posts: 10,674
Likes: 122
From: Millington Illinois
St. Jude Donor '08-'09
Le Mans Master
Joined: Mar 2008
Posts: 5,948
Likes: 72
From: Oxford MA-----You just lost the game!!!!
According to my compression ratio calculator, a stock bore and stroke chevy 350, with a stock head gasket (.028"), 4.1" gasket bore, .025" deck clearance, 76 cc combustion chamber, needs to be told to use a 12cc dish in order to come out at 8.2:1 compression ratio. I know, it's not very scientific, but it's my best guess: 12cc.
Keep the shiny side up!
Scott
Keep the shiny side up!
Scott
Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
Those piston part numbers are lost in old cataloges.
I don't know if this can help but looking at the piston mfr's for Sealed Power #423NP with a 0.067" by 3.160" dish i get 8.61cc but that's with out the 4 vlv reliefs. Clevite/Mahle #224-2644 has 0.080" by 3.160" dish and i get 10.28cc again without the 4 vlv reliefs.
Hope this can help and please post anything you find on these legacy pistons - this forum has a lot of them,
cardo0
Le Mans Master
Joined: Mar 2008
Posts: 5,948
Likes: 72
From: Oxford MA-----You just lost the game!!!!
I would lay odds that about 10% of the people on this forum have some old L48 pistons laying around somewhere. Wouldn't take a whole lot of effort to measure one, a solve this mystery. Unfortunately, I am part of the 90%, and cannot do it.
Keep the shiny side up!
Scott
Keep the shiny side up!
Scott
Burning Brakes
Joined: Feb 2011
Posts: 849
Likes: 0
From: Woodland California
It depends what he is going to do with it.
Is he going to just cruise with it or is he going to beat on it.
For years people refreshed their engines.
If just wants 40,000 miles or so out of it then $200.00 may be well spent.
New bearings and cast iron rings. Lap the valves, I've used a drill to do it.
Not everyone has a couple thousand to put into a new motor.
I will admit I've always like new.
Ralph
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