10-22-2013 08:54 PM #1
402 big block build
So I got a 1971 Chevy 402 2 bolt short block that needs to be rebuilt. What I want out of the engine is 500 torque 500 horsepower or more something around that. What heads, cam, pistons, and intake should I run? Can the stock crank and rods hold up the power I'm looking for? Any help would be much appreciated.
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Problem with that engine and your desired results is that you didn't mention how you were going to use it-----You need good air flow to make big numbers and your bore size will limit the size of the valves----unless you are doing a numbers matching thingie, get rid of the 402 and find a 454 to start with, then add some Dart, Afr,Edelbrock heads ,manifold, etc---------
Your available fuel will severely limit the compression ratio so do respond with if its a daily driver, nud bogger, comp dragster, etc
I want to use it for mud/off road/street not a daily driver would like to use stock big block heads if possible. If I can't get the power I'm looking for what power numbers you guys think I can get.
Agree with Jerry, sell the 402 to someone you don't like and buy into a 454. But you may be one of those hard-headed guys who has to do it his way and see how it turns out. In that vein, here's how to build a 427/434/440 out of a 396/402.
396/402 block, bored to 4.125" to build a 427 or 4.155" (+0.030" KB pistons) to build a 434 or 4.185" (+0.060" KB pistons) to build a 440.
Keith Black KB361 hypereutectic pistons/rings
Here's the best price I've seen on these pistons....
11.1:1 SCR with 96.5cc chambers
10.2:1 SCR with 105cc chambers
9.0:1 SCR with 119cc chambers
If this rig has to run on pump gas, I'd be using heads with chamber volumes somewhere between 112-118. 112cc chambers would make ~9.60:1 and that's where I'd build it. We're talking iron heads here, so that's gonna be about the limit for pump gas and iron heads. You may be able to skate by with a little more SCR today, but none of us have any idea what the fuel quality will be tomorrow. I remember sitting in line for fuel during the Arab Oil Embargo and the only thing you could buy was cat piss regular unleaded. Don't ever think it couldn't happen again, so build on the safe side. A decent set of oval port heads would help some, I would think. Something like 049 heads milled to 112cc's.
Running this solid flat tappet cam installed straight up with the 9.60:1 Static Compression Ratio would produce a Dynamic Compression Ratio of 8.245:1 on the KB calculator, just right for a street motor on pump gas. Will it make 500/500? Probably not, but it should be a lot of fun on the street from 2000 to 6000 rpm's. Use lifters that have the 0.012" oiling hole EDM'd into the crown. Big block Chevies are tough on flat tappet cams.
Pat McCarthy and Jerry Clayton are the resident BBC experts and I doubt they would put their blessing on this build, but like I said above, if you're hard-headed like some of us, you'll have to try it.
Last edited by techinspector1; 10-23-2013 at 09:19 AM.
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