How can you tell if you have 305 heads or 350 on a stock motor? Is there a casting number? I know that you can tell if a block is a 5.0 or 5.7 by looking at the cast number on the back of the block beneath the driver's side head.

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1988 GTA 5.7L TPI Auto
355 ci. block,TPIS ZZ-9 Camshaft, SLP Headers, B&M Holeshot 2400 Stall Converter, 3.73 Richmond Gears

"Why ride a stang when birds can fly?"

http://www.geocities.com/thegta

 

Pull off the valve covers and there should be a casting # on the head somewhere. If you post it on the board, I have a book with all the casting #'s and I can tell you what it is.

 

And you don't even have to run the #s to find out if it's 305 or 350 heads you're looking at. 350 heads have the casting # in parallel with the long plane of the heads. 305 heads have the casting # written vertically.
...ed

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Ed Maher - Moderator @ The Carb Board
92 Z28 Convertible - Quasar blue / Tan top
LB9 4L60 GU2 G80 - stock, soon to be sleeper
-=ICON Motorsports=-

- Definitely prototypes, high powered mutants of some kind. Too weird to live, too cool to die

 

THE COMBUSTION CHAMBERS ON A 305 HEAD ARE FURTHER APART BECAUSE THE BORE IS SMALLER.350 POCKETS ARE 1-5/32 APART AND 305 POCKETS ARE 2-1/32 .

 

OF COURSE,IF THE HEADS ARE STILL ON THE CAR ,MY LAST POST IS USELESS.(GOTTA READ QUESTIONS MORE CAREFULLY)

 

Joesph, take off your valve cover, and you should see your casting number. For L98 iron heads, they should be 14101083.

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1989 IROC-Z 5.7L
NOS 150HP kit
ProBuilt 700R4, PI Vigilante 2800 stall lockup
Baer Brakes 12" Sport System

 

I finally got the chance to pull the V/C's off the car and the cast number reads 10110810 on the head and it is written vertically, parallel to the short plane of the head. Does this mean that I have 305 heads on the car? Should I scrap these heads because they are hurting my performance? Do these help me at all in gaining a couple of points of compression because the combustion chambers are smaller? I did have a rebuilt engine installed a few years ago (a rod went through the block on the original one). Is it possible that the rebuilders used 305 heads during the rebuild?

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1988 GTA 5.7L TPI Auto
355 ci. block,TPIS ZZ-9 Camshaft, SLP Headers, Borla Cat Back, B&M Holeshot 2400 Stall Converter, 3.73 Richmond Gears

"Why ride a stang when birds can fly?"

http://www.geocities.com/thegta