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Discussion Starter · #1 ·
Hello Everyone, I have really enjoyed reading a lot of the posts on here and gathering new information. I could really use some help and direction on my budget rebuild project. I am not familiar with Pontiac engines so this is all new to me.

I recently purchased what I believe to be a Pontiac 400 engine.The casting in the back is 500557 with a stamp of YY in the front. The heads are 143 open chamber and look to have been ported. The pistons look forged but I am not certain. They are stamped 30 over and look like an eye brow. The cam has a 280 H stamp and the other numbers are hard to make out. It also came with an Edelbrock 4 bbl intake and carb.

I would like to find out if this is a good combination to go back together with or should I change out some things? I am only looking for 300 to 350 hp with a nice sounding cam that i can run pump gas on. I also have a pair of 4X heads with a 7H stamp on them and I'm wondering if perhaps they would be better to use? I am open to buying another cam etc. if needed. Please let me know your thoughts and recommendations. Thanks in advance,
 

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It's fine. May will say that's not the best block to use for high performance, and it's not. But you are not doing that. If you had further plans down the road it may pay to look elsewhere but for a good decent performer the block is fine. Plus, you already have it.
 

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Discussion Starter · #3 ·
It's fine. May will say that's not the best block to use for high performance, and it's not. But you are not doing that. If you had further plans down the road it may pay to look elsewhere but for a good decent performer the block is fine. Plus, you already have it.
Thanks, i read that somewhere else. Base on the components what would you go with?
 

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Discussion Starter · #4 ·
It's fine. May will say that's not the best block to use for high performance, and it's not. But you are not doing that. If you had further plans down the road it may pay to look elsewhere but for a good decent performer the block is fine. Plus, you already have it.
Aus, i am new to the forum. Did i post my question in the right place ? Or should i post in another place to get more responses? Thanks
 

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Just have the block magged and maybe Xray especially the main web areas.Seems like the luck of the draw on those blocks.I built one that made just under 600 HP and has lived fine in a 70 GTO for many years now.I hate reusing caams unless a roller.If me I would try to get a set of heads that will get you about 9-9.5 CR and maybe a Summit 2801 cam.Will make a nice driver.tom
 

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Discussion Starter · #6 ·
Just have the block magged and maybe Xray especially the main web areas.Seems like the luck of the draw on those blocks.I built one that made just under 600 HP and has lived fine in a 70 GTO for many years now.I hate reusing caams unless a roller.If me I would try to get a set of heads that will get you about 9-9.5 CR and maybe a Summit 2801 cam.Will make a nice driver.tom
Thanks Tom, i here a good bit about the 6x-4 heads is that what you would recommend as well?
 

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Discussion Starter · #8 ·
very popular.I have not actually used them.Tom
Thanks, this is my first Pontiac motor. I am mostly a Chevy guy. The more i read about Pontiac's the more confusing it gets. The combinations seem endless to achieve the same goal. I like your suggestion on the cam.
 

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Using a "557" block is a "luck of the draw" deal.

I'm one of the guys who wouldn't spend any money on one.

But, since you already have it, I'd run it, spending the least amount possible on it.

Was it running good in it's previous home ?

I'm not a fan of the Edelbrock carbs. Prefer a GOOD Q-jet. But, if you're not familiar with either, but do know how to work with a Holley, I'd go that route. It'll just be one less thing you'll need to learn.

Looks like the 143 heads are small chamber heads that were used on both 2 & 4-barrel 400 engines, in '67. Factory rated @ 10.5 CR.


Hard to guess at your exact CR, without knowing the exact chamber volume, piston specs, deck height, & head gasket thickness.

BUT, I'm guessing it's over 9.5. Would probably need to either run low timing or run some GOOD octane booster in the gas. IF you are planning another engine build fairly soon, you MAY wanna run it as is, while you plan the better engine. That is ASSUMING the engine is good & ready to run, as is. GOOD octane booster is a little over $20 a quart. But, unless the car is a daily driver, which you drive a lot, octane booster may be hundreds cheaper than a partial rebuild.

Another approach might be to go ahead & have a good set of larger chamber heads built correctly, run 'em on this motor, with plans to also use 'em on the next motor. Heads with aprox 100cc chambers are commonly used on 455 pump gas street engines. 6x-8 heads are said to have aprox 101cc chambers. I think they are probably the most common Pontiac head, which has 2.11 intake valves & screw-in rocker arm studs. They don't give a 400 much compression, but were run on lots of '75 thru '79 Pontiac 400's.

6x-4 heads are said to have 93-94cc chambers. They were used on 350's & some higher performance '77-'79 400's.

You mentioned having some 4x-7 heads. I've read that LOTS of these heads are cracked in the valve seat area. One machine shop guy even said that MOST of the 4X heads he checked were cracked. NOT all are cracked. But, I wouldn't spend all the $$$ it takes to have a set done right, on 4X heads. I'd try to use 6X heads. You can usually find some 6x-8 cores for about $100 each, sometimes less. The 6x-4's are usually a bit higher.

A Comp 280H cam has 230° duration @ .050 lift. That's too much cam for a lower compression 400.


As mentioned, the Summit 2801 might be decent for 9-9.5 CR. But, if you go with the 100cc heads, I'd drop back even a little more, to maybe the Summit 2800, although the idle may be a bit smoother than you'd like. It is strictly a low & mid range cam, the rpm range most street driven cars live in. There are other similar cams. But some are nearly double the price, last time I checked. Haven't looked lately. There also MIGHT be a supply shortage. May be limited to what's on the shelves, for a while.

Right now, Summit shows to have plenty of 2800 cams in stock. But the price is up about $20. I suppose we can blame the prez ?

 

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Discussion Starter · #10 ·
Thanks for sharing your knowledge Pony. The guy i bought it from shared a video of it running however, it was out of the car when i picked it up. It has some water in the engine not much but enough to milk it up a bit. That's the reason I tore it down. From what i can tell looks like a head gasket may be the culprit.I paid $800 for the complete engine so i am not to deep however, it sucks that i had to dig into it. Yes we can blame the Prez LOL.
 
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