Thread: Open or closed chambered ????? Help

Tweet

I have a question, I got my 70 402 engine apart and it has closed chambered pistons with about a 3/16 dome and I'm pretty sure the heads are open chambered.

I've heard some people talk of semi open chambered ????????

I'm just really trying to find out what I need to do next, on finding out what compression this engine will be if these heads are open chambered.

If this heads are open chambered does any one sell factory replacement open chambered pistons for the 402 I'm trying to get to 10.1 or 10.5 compression, so I can use a pretty decent cam.

Heads are casting # 3975950

Thanks

I believe the 3975950 heads are from 1968-70 366T, 396, 402, and 427 truck engines. It has 2.06/1.77 valves and closed chamber oval ports. I don't remember if I have never seen this particular casting number, but all credible sources say that it's an oval port, closed chamber head. Check this web site for more details:

http://www.chevcarclubvic.org.au/tec...ng_numbers.htm

Regards,
Glenn

This site says open chamber ?????

Originally Posted by glennsexton

I believe the 3975950 heads are from 1968-70 366T, 396, 402, and 427 truck engines. It has 2.06/1.77 valves and closed chamber oval ports. I don't remember if I have never seen this particular casting number, but all credible sources say that it's an oval port, closed chamber head. Check this web site for more details:

http://www.chevcarclubvic.org.au/tec...ng_numbers.htm

Regards,
Glenn

what do you want to know ? if you need the cc of the head put it face up and level it and check the cc.s of the head go to a animal supply and buy a cattle syringe and check the volume . i think that head is like the 929 casting if your useing a 325/350 hp piston you will have a hard time getting to 10.5 here is a set i did for a 402

Must be my eyes! You are correct. I checked a few other sites and these are OPEN Chamber heads.. However -

http://www.nastyz28.com/bbcmenu.php - says they're closed
http://www.novas.net/forums/showthread.php?t=4334 - says they're closed

Take a picture of the bottom of the head and post.

Take a picture of the bottom of the head and post.[/QUOTE] thats a good idea i can not remember all the casting numbers for all the gm bbc heads are they like the 929 cast like in my photo ? this head was used on alot of the 402 the 396 used a closed chamber we called them bath tub heads like 65to67. then i think in 68 to69 they trim more off above the spark plug then went to the 929 type chamber

Those are probably an open chamber head since they came on truck blocks and tall deck blocks. www.Mortec.com has been really accurate for me so far. The only way you're going to get decent compression with a 396 is with a closed chamber head. The small bore size is what kills it with an open chamber. You can run a closed chamber dome with an open chamber head but not vise versa. The biggest dome TRW makes for the 396 I think is a 35cc closed chamber dome. Not sure what that would give you for CR. The other option which I had already looked into is that JE will make you any piston you want but it will cost $900+ bucks or so.

look at wisco pistons they make a 369/402 piston shelf piston .i did look in to his not to long ago for a 402 build .at the time i do not think JE SRP did not have any thing .it could be cheaper to find small chamber heads less you have alot of $$ in them . the old trw /speed pro are limited if you use the close chamber O port head with the 396/402 piston with the trw/speed pro 375 hp pistons they will hit on the ex side of the chamber and will need some work on the pistons or chamber it is a good idle to check it any way you go open or closed piston

OK these heads are open chambered and 116 cc, and checked the bore and it is 4.155 which would be 402...30 over or a 396...60 over would these closed chambered pistons work ?????

http://store.summitracing.com/partde...0&autoview=sku

Any suggestions
Thanks

well you would get some were around 10.2 cr with what you have for heads s would check dome like i said

I want to thank everyone for there help !!!!!

I went ahead and purchased these pistons so it should be around 10.1 compression, my next question I need to pick a cam.

This Truck is a 65 Chevy C10 that I'm doing a frame off restoration, not a daily driver. I'm wanting a cam with a good bit of duration that beats the payment out from under the truck while still keeping some drivability.

It has 411 gears with a 700R trans with a 2500 stall.

Any suggestions on a cam ???????????????

hyd or solid roller cam ? or solid flat lifter or hyd .i have a super nice crane hyd roller cam that would work good for you

I am wanting a hyd. roller, once I'm finished with truck I want to call it a day

What cam do you have that might work for me ????

Originally Posted by pat mccarthy

hyd or solid roller cam ? or solid flat lifter or hyd .i have a super nice crane hyd roller cam that would work good for you

Originally Posted by 198plus

I am wanting a hyd. roller, once I'm finished with truck I want to call it a day

What cam do you have that might work for me ????

was a take out on two blown 502 in a boat i recam them both .the cam is like new and would work very good. i wanted to keep it but i need to sell it have the numbers at the shop for the cam pm me on more info

Pm sent. Do you have the lifters too.

Originally Posted by pat mccarthy

was a take out on two blown 502 in a boat i recam them both .the cam is like new and would work very good. i wanted to keep it but i need to sell it have the numbers at the shop for the cam pm me on more info