305 pistons?
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Joined: Oct 2000
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From: Gulf Coast
Car: 1988 Trans Am GTA
Engine: 5.0 TPI
Transmission: TH700-R4
Axle/Gears: 3.27
I know the '88 5.0 HO on my GTA came with stock 9.5:1 pistons. As far as a source for replacements I have not searched.
The 305 heads are 58cc.
The 305 heads are 58cc.
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From: Carlisle, Ohio
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From: Loveland, OH, US
Car: 4
Engine: 6
Transmission: 5
There was no 305 HO in 88; that was a carbed motor, RPO L69, and the last year was 86.
305 HO heads (casting # 416) are 58cc. Most of the rest of the 305s used in F bodies AFAIK are also 58cc.
Federal-Mogul markets hypereutectic flat-tops for 305 under their Sterling brand name. Summit carries them. Use their site, you'll find them easily.
305 HO heads (casting # 416) are 58cc. Most of the rest of the 305s used in F bodies AFAIK are also 58cc.
Federal-Mogul markets hypereutectic flat-tops for 305 under their Sterling brand name. Summit carries them. Use their site, you'll find them easily.
Joined: Mar 2000
Posts: 43,187
Likes: 43
From: Littleton, CO USA
Car: 82 Berlinetta/57 Bel Air
Engine: L92/LQ4 (both w/4" stroke)
Transmission: 4L80E/4L80E
Axle/Gears: 12B-3.73/9"-3.89
With standard flat-top, 4-valve-relief pistons, steel shim head gasket, stock 305 heads (all factory 305 heads were 58cc, by the way), you'll get 9.5:1 compression.
Use a standard replacement composite head gasket, you'll lose a tenth or so CR. I believe JC Whitney lists 10:1 305 pistons with a slight dome. Others probably make them as well.
All 3rd gen carb engines after '85 had flat tops. All 305 TPI engines had the same 9.5:1 CR using flat tops.
If I was faced with the expense of buying pistons for a 305, I'd go get a 350 instead. But, that's just me.
Use a standard replacement composite head gasket, you'll lose a tenth or so CR. I believe JC Whitney lists 10:1 305 pistons with a slight dome. Others probably make them as well.
All 3rd gen carb engines after '85 had flat tops. All 305 TPI engines had the same 9.5:1 CR using flat tops.
If I was faced with the expense of buying pistons for a 305, I'd go get a 350 instead. But, that's just me.
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Joined: Dec 2001
Posts: 194
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From: ohio
Car: 1982 camaro
Engine: built 355 chevy
Transmission: th 350 w/ 3.73 gears
i have the stock heads on my car, 82 305 with flattops, no valve reliefs, and the machine shop said they were 10-5.1, i may be wrong but i thought after 85 with 9-5.1 had a slight dish on them oh well, oh and i tried to go with a 350 9-5.1 comp, 202 heads and everything else was the same (center manifold, carb, distributor, and the cam) on my 305 and my 305 would run side by side with it, now the 350 has a oil pressure prob with it so i am putting the 305 back on.
Last edited by camaro03; Feb 13, 2002 at 05:27 PM.
Joined: Mar 2000
Posts: 43,187
Likes: 43
From: Littleton, CO USA
Car: 82 Berlinetta/57 Bel Air
Engine: L92/LQ4 (both w/4" stroke)
Transmission: 4L80E/4L80E
Axle/Gears: 12B-3.73/9"-3.89
The '84-earlier LG4's had dish-topped pistons, same cc chamber in the heads. The dish is as deep (at least) as the valve reliefs, so no extra reliefs are needed.
Yes, dish-topped pistons will lower compression.
Yes, dish-topped pistons will lower compression.
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