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Old 11-04-2002, 08:19 PM   #1
Ryan77
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Default What type of pistons does a '77 L48 have?

I just noticed that I have no idea what type of pistons are in my motor, are they forged, or :confused:
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Old 11-04-2002, 08:20 PM   #2
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Default Re: What type of pistons does a '77 L48 have? (Ryan77)

Cast aluminum.

-Steve
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Old 11-04-2002, 09:07 PM   #3
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Default Re: What type of pistons does a '77 L48 have? (Pacin'California)

CRUDDY ONE'S but who cares? I run 12's with the "cruddy one's" that came in my 78 l48.................smokem :smash: :smash: :smash:
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Old 11-04-2002, 11:49 PM   #4
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Default Re: What type of pistons does a '77 L48 have? (Ryan77)

Low compression ones!!!
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Old 11-04-2002, 11:58 PM   #5
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Default Re: What type of pistons does a '77 L48 have? (Ryan77)

The L48 used cast aluminum alloy pistons. The L82 used aluminum impact extruded pistons.

tom...
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Old 11-05-2002, 02:38 PM   #6
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Default Re: What type of pistons does a '77 L48 have? (Ryan77)

dumb question but, if our pistons are aluminmum then how can that be crappy. This car is still a corvette, i mean their reputation may be poor but people who drive other cars of similiar vintage would probably love to have aluminmum pistons.
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Old 11-05-2002, 05:12 PM   #7
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Default Re: What type of pistons does a '77 L48 have? (sharkthehunter77)

I thought almost all car pistons were made of aluminum..? :confused:
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Old 11-05-2002, 07:38 PM   #8
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Default Re: What type of pistons does a '77 L48 have? (zymurgist)

Quote:
I thought almost all car pistons were made of aluminum..? :confused:
Me too. Aluminum or aluminum alloys.

Mostly the "crappieness" comes from the shape of the piston's top. The L-48 pistons in a 75 are dished with valve reliefs. They, along with huge cc heads make for low compression.
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Old 11-05-2002, 07:52 PM   #9
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Default Re: What type of pistons does a '77 L48 have? (zymurgist)

:yesnod:

The L82 uses this: 464664
Click the image to open in full size.

The L48 looks somewhat like this w/ 4 valve reliefs wich makes that all the pistons in the engine are the same, as in they're not cylinder or even bank specific (like most single relief ones are) This isn't the L48 piston but it's a cast sealed power one
Click the image to open in full size.

Marck


[Modified by Twin_Turbo, 5:53 PM 11/5/2002]
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Old 11-06-2002, 08:07 PM   #10
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Default Re: What type of pistons does a '77 L48 have? (Schmucker)

Quote:
Low compression ones!!!
Click the image to open in full size., that's for sure.

Grosspolluter60--what setup do you have that you are running 12's with stock pistons?


[Modified by Ryan77, 7:10 PM 11/6/2002]
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Old 11-07-2002, 02:13 AM   #11
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Default Re: What type of pistons does a '77 L48 have? (Twin_Turbo)

Quote:
:yesnod:

The L82 uses this: 464664
Click the image to open in full size.

The L48 looks somewhat like this w/ 4 valve reliefs wich makes that all the pistons in the engine are the same, as in they're not cylinder or even bank specific (like most single relief ones are) This isn't the L48 piston but it's a cast sealed power one
Click the image to open in full size.

Marck


[Modified by Twin_Turbo, 5:53 PM 11/5/2002]

The stock L-48 piston does not have valve reliefs. It is a dished piston so no valve reliefs needed.
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Old 11-07-2002, 07:19 AM   #12
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Default Re: What type of pistons does a '77 L48 have? (glen242)

Oh yeah? Strange, I did an L48 of a buddy of mine and it had those kids of pistons in it, with 4 valve reliefs and a sort of ridge around the side. No big flat dome. That was on a 79. They were stock std. size pistons.

Marck
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Old 11-07-2002, 07:55 AM   #13
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Default Re: What type of pistons does a '77 L48 have? (Twin_Turbo)

mine has forged high compression ones :D:yesnod: BIG improvement along with the shaved heads.
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Old 11-07-2002, 01:13 PM   #14
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Default Re: What type of pistons does a '77 L48 have? (glen242)

Quote:
The stock L-48 piston does not have valve reliefs. It is a dished piston so no valve reliefs needed.

I have to disagree.
Click the image to open in full size.

May be different for different years but at least 75 is dished with valve reliefs.
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Old 11-07-2002, 02:22 PM   #15
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Default Re: What type of pistons does a '77 L48 have? (Ryan77)

Cast aluminum pistons aren't neccessarily bad. They are great for the production engines that require oil control, quiet start-up, and aren't going to be subjected to huge compression ratios brought on by turbo charging, supercharging, or Naaaaaaawwwwwwwwwwssssssss. :rolleyes:

Forged pistons are stronger and tolerate higher compressions better. But they expand more, and therefore must be run with higher piston to wall clearances. Thus, the cold start up clatter (that doesn't fly in showrooms these days).

Hypereutectic pistons are made of an alloy that can be a nice compromise between forged and cast pistons. Hypereutectic pistons don't have as much thermal expansion, so they can be run at tight piston to wall clearances. So most shouldn't make noise at start-up (don't talk to late model F-car owners about this--lots of noise problems here). Also, they are stronger than cast, but not as tolerant of high compression and juice as are the forged pistons.

So while the cast pistons in the Vette may not seem like James Bond tech, given the crappiness of the heads, and the ever present pressure of the bean counters, the cast pistons were a logical, if not exciting, choice.

:cheers:
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Old 11-07-2002, 02:51 PM   #16
Twin_Turbo
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Default Re: What type of pistons does a '77 L48 have? (Cookwithvette)

Quote:
The stock L-48 piston does not have valve reliefs. It is a dished piston so no valve reliefs needed.


I have to disagree.
Click the image to open in full size.

May be different for different years but at least 75 is dished with valve reliefs.
Yup!!! That's the ones I mean.
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Old 11-08-2002, 04:20 PM   #17
glen242
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Default Re: What type of pistons does a '77 L48 have? (Cookwithvette)

Well, my '76 L-48 has original dished pistons, no valve relief. As my official GM spec form calls them "sump head". The same spec sheet says L-82 has "flat head, notched". I have had the heads off enough to know what I have. '75 may be different, but I thought all 8.5 c.r. used the dished pistons as the heads are all 882 76 c.c.. So if the heads are the same, how can the c.r. be the same with the flat tops? BTW, the c.r. is listed @ 9.0 for the L-82 (flat head notched).
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Old 11-08-2002, 05:53 PM   #18
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Default Re: What type of pistons does a '77 L48 have? (glen242)

Quote:
Well, my '76 L-48 has original dished pistons, no valve relief. As my official GM spec form calls them "sump head". The same spec sheet says L-82 has "flat head, notched". I have had the heads off enough to know what I have. '75 may be different, but I thought all 8.5 c.r. used the dished pistons as the heads are all 882 76 c.c.. So if the heads are the same, how can the c.r. be the same with the flat tops? BTW, the c.r. is listed @ 9.0 for the L-82 (flat head notched).
Ryan:
As said, L48 had cast aluminum pistons with a recessed head (aka dish/sump) ... dunno if yours had valve reliefs or not. My 71 L48 had 4vr dished.

Glenn:
Varying CRs with same head, gasket, stroke deck height could be explained by 3 things: Primarily, the dished pistons came with different recess dimensions ... both diameter & depth; Also the dished pistons' CD (compression distance from pin to piston head) varied; Lastly the cam lobe profile affects dynamic CR. I reference Sealed Power OE-replacement parts manual for the first two causes. Also, similar variances for forged. Overall pre-1980 chevy 350s' CD's ranged about 1.540" - 1.563"
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Old 11-08-2002, 05:53 PM
 
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