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  #1 (permalink)  
Old 10-18-2008, 10:15 AM
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350 or 400 pontiac

Im trying to decide which engine to go with in my Ventura. Id like to stay with Pontiac. What do you think is the better block to start with for a max of 500hp. I dont have endless amounts of cash to spend, somewhere in the middle. I have an old 350 that came out of the car, but not sure if it is capable of producing the power i need. THANK_YOU!

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Old 10-18-2008, 10:22 AM
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I would strongly suggest the 400. The 350 and 400 share the same 3.75" stroke, but the 350 has tiny 3.876 bores while the 400 has 4.121" bores. In design, the pontiac 350 is like a stroked chevy 307, and the pontiac 400 has a lot in common with the chevy 400... from a bore/stroke ratio standpoint.

small bores means small valves and small breathing. You'll spend more money getting the 350 to breathe up to 500 hp than you would buying a 400 and working it up. That is to say, if you're a smart shopper, you can buy and build a 400 cheaper than you can build up the 350 you already have.

Plus, cubes are king

also, not that you asked, but a common question is often, "can I bore a 350 out to 400?" and the answer is no. That would require .245" overbore, and the most you can safely go is about .060"
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Old 10-18-2008, 11:27 AM
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they're both good motors but i would also go with the 400 and easy way to get one would be to find a late 2nd gen firebird theres tons of those at the junkyard
i frequent and a couple have 400s in 'em unless someone already got 'em
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Old 10-18-2008, 12:30 PM
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In the middle of the '75 model year, Pontiac started casting 400 blocks with thinner main webbing. I have seen a couple of these blocks, that were built for performance, crack in the main webbing. The blocks to avoid have casting #500557 or 568557. All prior blocks are good.

here is a picture showeng where to find casting codes:
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Old 10-19-2008, 02:59 PM
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yup its the 400

Im going with the 400, thanx all, but what about a stroker- after all cubes are king, right?
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Old 10-19-2008, 04:49 PM
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The 4.25" w/6.8" rods is pretty popular. I personally have one. Scat forged crank w/Eagle H beam rods and JE pistons in an Indian Adventures block. With a .030" over 400, you would end up with 460 cu. in. Going .060" over is risky, unless you have the block soniced and find out that you have enough cylinder wall. Ther are also 4.5" cranks that would give you 487 cu. in. with a 400 block bored .030".
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Old 10-20-2008, 06:05 AM
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Engine

Quote:
Originally Posted by WDCreech
In the middle of the '75 model year, Pontiac started casting 400 blocks with thinner main webbing. I have seen a couple of these blocks, that were built for performance, crack in the main webbing. The blocks to avoid have casting #500557 or 568557. All prior blocks are good.

here is a picture showeng where to find casting codes:
Good advise thanks for sharing that with us I didn't know this. Also here's a site to help you www.wallaceracing.com good luck on build.
RJ
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Old 11-29-2008, 10:48 AM
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350 v. 400

Pontiac Racer: What are you going to use for cylinder heads? A stroker motor is going to need sufficient cfm to be efficient. Another factor is the combustion chamber size - which controls the compression ratio - and dictates what fuel you will need. It's easy to spend a bunch on money putting a potent Pontiac motor together, but with careful planning you can reach the 500hp area w/o emptying out your retirement fund.
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Old 12-10-2008, 09:54 PM
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You need 1966-72 block(400) any code (most desired by engine builders because of strength & can be bored safely) for the Pontiac Hot Rod build.
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