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Old 03-07-2004, 02:41 PM
mts mts is offline
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69 firebird 400 engine heads

HI again, I posted the thing about the exhaust. Now I have another question. I have stock heads. They are the 130cc (I think) anyway huge. My son says "dad we need new heads", to which I want to say "yeah go get a job that pays more than the one you have and knock yourself out", anyway, the edelbrock ones I think are in the 70-90 cc, depending on street/strip. I've heard that my heads can be cut down to reduce the size of the chambers. What do you suggest? I think this all has to do with the fact that pontiac engines notoriously have low compression, and by making the capacity smaller increases it. Thats how it was expained to me. I want it to go ROAR and peel out if the occasion allows, not put all this $ into it and have something my grandmas old plymouth volare (with corinthian leather seats) could take. You get the idea. Thanks for your help......

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Old 03-07-2004, 06:58 PM
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shaving the heads will increase your compression. just like you said. how much to shave is the question.
i have no idea what cc the heads would be, and even less an idea how much you can safely shave, but yes, it can be done.

how much shaving can be done before pushrod length is affected?

just thinkin' outloud........
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Old 03-07-2004, 08:57 PM
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I guess what started this was that the guy at the parts place said pontiac is typically a low compression engine and its hard to make it high performance??????????????????/ Maybe he's just a guy making 8$ an hour at the parts place who is clueless and maybe he is right. Thats what started all this. Thanks
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Old 03-07-2004, 08:59 PM
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if you were to change 130 cc heads to 70 cc heads you would be gaining unrealisticly high compression.
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Old 03-07-2004, 09:53 PM
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I doubt those chambers are that big. Here's a chart of common Pontiac heads & compression ratios:

http://www.dapa.org/jhpages/jhand4.htm

& here's some more aluminum Pontiac heads:

http://www.krepower.com/dport.htm

& here's more interesting reading:

www.pontiacstreetperformance.com
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Old 03-07-2004, 10:20 PM
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Try www.wallaceracing.com for more info on head shaving and numbers info.
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Old 03-08-2004, 01:36 AM
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Please post the casting number that is cast on the center exhaust ports. I would guess you will find a "13" if you still have the stock 1970 400 heads. There were no large chamber heads made in 1970, and the 13 heads were 72 cc's. As it is, your compression is going to be on the high side at about an actual 10.48:1 - so you don't want to go higher by shaving them. You will find that a true 9.5:1 ratio is about the highest you want to go with a Pontiac and pump gas. The age and wear on the engine will work in your favor, and you might get by okay with the stock setup. Just watch for detonation. If you freshen up the engine and get things back tight, you will want to consider dropping the compression ratio. I'd slap the parts guy silly for such an ignorant comment about Pontiac's being low compression.
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Old 03-08-2004, 10:20 PM
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patience please, the only casting #'s I can find, without taking the valve covers off are as follows: GM1==A236, and the #2 head is A276. If these mean nothing (I know what the gm1/2 is) but if the a#'s mean nothing, let me know what the correct # would look like and would it be under the valve cover. thanks
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Old 03-08-2004, 10:38 PM
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The identifying codes should be on the center exhaust ports within an inch of the exhaust manifold. The A236 sounds like a casting date. If so it would translate as January 23, and either 1966 or 1976. The other head would have been made January 27th. I would have expected the date code to be under the valve cover area. Just for kicks, while you are crawling around the engine compartment, take a look at the code numbers right next to the distributor at the back of the block. This will let us confirm whether the engine is original to the car or not.
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Old 03-09-2004, 11:14 AM
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mts - Here's a good web page with pictures to help you identify your heads. As lust4speed mentioned, look on top of the center exhaust port for a cast-in number.

http://www.yearone.com/updatedsingle...ontengid3.html
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Old 03-09-2004, 10:52 PM
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Lust4speed and 6567GTO like myself are very knowledgable on Pontiacs. As far as the Edelbrocks the chamber sizes are 72 and 86 cc's. Pontiac never made a head with 130cc's. The largest chambers were I believe 6X's on 76 455's, chambers were 114 cc's resulting in compression ratio's of around 7.5:1. The guy at the parts counter definitely knows nothing about Pontiacs if he made that remark. Let us know what the casting numbers are and we can give you all the info you need.
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