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My dad has a 402 he's building for the street. Has K/B 160 pistons, and the machine shop guys told him he needs 118cc heads to get him to around 9.9 or so on the CR. Can you recommend a closed chamber head for this? (thats what the machine guys say he needs) We need something generic, no exotic heads, just a good street head. Thanks, Jimmy ;) Oh ya oval port I think.
I am not Pat or Dave but I can help.Quote:
Originally Posted by jimmyjeep
A 118 cc heads is an open chamber head.
A good open chamber head would be a 781.
today i am not :3dSMILE: yes the 781Quote:
Originally Posted by erik erikson
We are wondering why the machinist says we have to have a closed chamber head for that piston configuration? He himself says to look for the 118cc head and we'd take it down a smidge to get hin into a good CR of araound 9.9 or so.
I had 781s on my 454 in my Monte and it ran great.
Erik and Pat are expert where I am a back yard engine builder at best, but what I can tell you that I do know is heads that are in the upper cc range of 113+ are typically open chambered heads. I have a set of 781 heads that I was gonna use and in my research in trying to learn about them as much as possible I dont one thing and that is the cc's on them can vary quiite a bit #1 and #2 that they are definately an open chamber head. Im sure words just got confused or someone is mistaken is all.
I think where the confusion has arisen is from my dad understanding that the engine builder said the KB160 pistons were made specifically for a close chamber head. I don't believe thats a good fact. Thats alot of dome to get into a small chamber isn't it? Course I'm a sb man so I haven't had the chance to check out too many bbc heads yet.I guess the 781 heads will work just fine. While I have you here whats the scoop on the 049 heads? Thanks guys.
I dont know anything about the pistons your dad is using but for example my 2349 TRW forged pistons have a decent sized dome on them and they are a "Closed Chamber piston" that can work with open chambered heads like the 781s and 049s....You actually need that dome a little I beleive to get the compression up on the opne chambered heads; so I wouldnt be surprized that the KB pistons your Dad has are closed chamber. 049 heads to my best knowledge are very similar to 781 heads except thier chambers are 121-122 cc versus the 781s at 118-119cc. Besides that they are very similar from what I have read; either of those heads in oval port configuration should work for your Dads engine. Im sure the experts on here can give you more/better info than I can.Quote:
Originally Posted by jimmyjeep
The reason why they want you to go a closed chamber is that is the ONLY way to get good compression on a 402 or 396. The smaller the bore, the harder it is to get good compression. The open chamber at 118cc will give you less than 8.5 to 1. It would need to be shaved A LOT. You have the same pistons as I do in my 402. I have a 96.4cc chamber, large oval port head. I have about 10.5-1 compression.
By the way- having the closed chamber piston means you can run either type- open or closed chamber head. If you had open chamber type pistons, you would not be able to use closed chamber heads. This is due to the shape of the dome.
Part of the reason I am not a big fan of the closed chamber head is due to the fact that they "shroud" the valves to much.Quote:
Originally Posted by 69elko
If it all possible I would rather use an open chamber head that has been angle milled and the block decked to raise your comp. ratio.
If you can't get the comp. ratio you want then the closed chamber head with a flat top or mini-dome may be your only answer.
69Elko, you using the 206 heads? Alll this info is appreciated, gang. We'd like to get this running for his next birthday, his 71st.Quote:
Originally Posted by 69elko
No, I am running the 215's, ported, 2.065, 1.72 valves, cc'd at 96cc's. The closed chamber heads are a little tight if you use the big 2.19 valves. They would need to be deshrouded with bigger valves. With the smaller valves there really isn't a problem. But you're limited to about 500 horsepower unless ported. But then again 500 HP is pretty good out of a stock head. If you're going for more than that don't run a 396 block. Too much hassle, not enough availability of different pistons, parts, etc.
Erik might be right on the open chamber heads, if you zero decked the block, shaved the heads, ran a .025 head gasket you might be able to get some decent compression too.