Thread: 402 BBC buildup - combos???

Tweet

Hey everyone, I have a 396 BBC thats .030 over from the factory.so its a 402 big block chevy thats .030 over now at the moment. But I'm considering boring it .030 more over. I'm looking to get 400-425 HP with 500 FT/LB of torque out of it.
Its gonna be a street engine primarily, with some weekend fun. Its going into a 88 chev truck.
Anyone have any COMBOS you have used in this type of motor, or know of any?
Any help would be great!
thanks

I am also considering the AFR aluminum rectangle port heads. 305 cc

Don't go the rectangles unless you plan on getting some massive HP and RPM's out of it. If you want aftermarket heads I'd go for the Brodix aluminum oval ports. They are a 255cc intake runner, so they are perfect for a smallish big block chevy. I'd get them with the 2.19 intake valves NOT the 2.25's. The 2.25's will not clear the valve notches in the pistons. The Edelbrock performer RPM heads are another option, 290cc oval port, a little on the big side but have a smaller 110cc chamber so they will be better for compression. I'd shoot for around 9-9.5 to 1. What kind of heads do you have right now? What #'s on the heads?

Any chance you could sell it or trade for a 454 block?? It's way easier to meet your goals with more cubes. A 454, .060 bore, 1/4" stroker crank, and you'll be at 500 hp/tq without even blinking an eye. You can do it with a 402 also, but not as easily. Or cheaply. Just throwing it out there.

I did it. It's not that hard if you know what you're doing. 425 horse should be cake.

Originally Posted by 69elko

I did it. It's not that hard if you know what you're doing. 425 horse should be cake.

I agree.....Im just saying it's easier if you can start bigger. And how do you know the valves wont clear? We dont know for sure what pistons are in there, and it shouldn't be an issue if he doesnt get crazy with the cam.

Originally Posted by 69elko

Don't go the rectangles unless you plan on getting some massive HP and RPM's out of it. If you want aftermarket heads I'd go for the Brodix aluminum oval ports. They are a 270cc intake runner, so they are perfect for a smallish big block chevy. I'd get them with the 2.19 intake valves NOT the 2.25's. The Edelbrock performer RPM heads are another option, 290cc oval port, a little on the big side but have a smaller 110cc chamber so they will be better for compression. I'd shoot for around 9-9.5 to 1. What kind of heads do you have right now? What #'s on the heads?

I was breifly looking at the AFR's just to throw it out there. and they said they pick up good at 2500rpm and said they arent too big for a 396 to perform. i'll be spinning it at least 5500.
i have a set of 336781's at the moment, open chamber, 113 cc heads. Ii bowl blended them and gasket matched them. since they are originally for a 454. I'm thinking they are too big. After the port work I did, i had them flowed and they are too close to eachother, they are 95%. so if I keep those heads, i plan on cutting the intake to a 2.19 to make them 75%
Im considering aftermarket heads. but im willing to go with stock as well. I wanna peak my torque at roughly 3600 RPM and peak the horsepower at 5000 RPM.
im shootn for 425 hp and roughly 500 ft lb torque.
any help would be appreciated. Thanks!

Those 781 likely dropped your c/r quite a bit. I dont know who told you 113cc....I think that's mis-posted somewhere. I have worked on several sets of 781's and 049's, and not one was ever less than 118cc. Mortec lists them at 118 or 119cc. So unless you had them milled quite a bit, they are more than 113cc. Is that what you meant by too big?? Other than the large chamber, they are great heads. Runners are about 256cc or so, nice size. But a set of closed chamber heads would get your c/r up. It all depends on if you still have the stock pistons in there. And you wont see any added benefits of the bigger valves unless you are running over 5K or so...the stock valves flow surprisingly well.

my block is decked .060, and heads are decked .060. i didnt know the chamber size so i did a quick google search and they had claimed 113. but yeah i jus checked mortec and i would trust they're stats. and as being too big, i mean do you think they would flow too much and not be able to pick up at low end. I dont have my sheet by me of my flow. but i do need to cut the intake to 2.19 to bring the % to 75%

ill find it in a bit and post the flow..
im running a forged crank, rods, and KB pistons

Well, something doesnt make sense...I dont think your block can be decked .060, when the 'average stock' deck hgt is something like .025 or .030...at .060, your pistons would be out of the block by .030 at least. And .060 off the heads would leave the intake valve edges below the deck surface of the head. I had a set of 781's milled about .038, and the intakes were just at surface level. Is it possible you messed up your numbers? And as far as the heads being too big, No...not a problem. The intake runner size is what determines your air velocity. For a smaller cube big block like yours, you dont need much runner size. Those 305cc AFR's for example, are pretty big. The 781's should be about 256cc. That's all you need. The original heads (closed chamber Im sure) that came on your engine were about the same runner size, so that's where you want to stay. Dont go too big, or you will start to lose you low end torque. I dont know too much about the % of intake to exhaust flow, but for what you're doing, dont get too hung up on it. They will be fine whether you go with the bigger valves, or stay stock. What KB pistons do you have?? That will help to figure your c/r with different heads.

Brand: Keith Black/KB Pistons
Product Line: Keith Black Hypereutectic Pistons
Bore (in): 4.155 in.
Bore (mm): 105.537mm
Piston Material: Hypereutectic aluminum
Piston Style: Dome
Compression Distance (in): 1.765 in.
Dome Height (in): 0.180 in.
Piston Head Volume (cc): -17.00cc
Valve Reliefs: Two
Wrist Pin Style: Floating
Pin Diameter (in): 0.990 in.
Top Ring Thickness: 5/64 in.
Second Ring Thickness: 5/64 in.
Oil Ring Thickness: 3/16 in.
Quantity: Sold as a set of 8.
Notes: Hollow dome design.

Pistons, Hypereutectic, Dome Top, 4.155 in. Bore, 5/64 in., 5/64 in., 3/16 in. Ring Grooves,Chevy,402,Set of 8

here is the description of my pistons. I can post pictures if you want, im not 100% sure how to though.

yes ok something is not right .060off the heads and deck.060 no way and the with big valve they will hit the pistons with out much lift hanging down in the bores if heads are cut that much the 45 on the 2.19 valve will be on the deck of the head you will be sinking the valves big time .do the pistons like this?

my mistake my heads are .065 decked, and my block is .035 decked. And the pistons sit .005 below the deck of the block

with your pistons you will need 108cc head for 9.4 and 119cc is 8.5 may be a bit more with your deck cut down go to kb web page and you can get you cr work out the bad thing is you can not get a small headgasket for the 396 bore so the cc will go up

I have pictures here. If they work that is.