On a bbc 402 should I only go .030 to a 408? Or should I go .060 to a 414? What kind of gains in power can I expect?

I went .60 on my 402, and have no problems. Temp stays at 180 and she runs like a raped ape.

By the way I was stationed at Pope for 4 years.

Steve

Oh cool another AF memeber. What was your job? What years were you there?

I wasn'tsure if boring the engine .060 would be worth it or not...looking for extra hp.

Lets say you make 400 horsepower out of a 400 cid engine. Figure about one hp/cid.

The difference between .030 over and .060 over is about 6 cubes. So about 6 horsepower.

The big question is: When you wear it out, can you bore it again and not have to buy custom (expensive) pistons?

If you've assured piston availability for the next rebuild...go for it.

Personally, I'd bore only far enough to clean the cylinders. 6HP isn't worth the trouble. There's plenty more than that to be found in other areas.

I had a 71 402 taken out .125 to a 427 :D heated up a little cruising around town with a Moroso water pump drive.

Thanx for the info. Looks like I'm gonna keep it to a .030 bore.

Mine is .030 over, we had sonic checked it for max overbore, shop I deal reccommended .060 as max.. for reliability. Question, do you have a crank ready to go? If not you may want to look into using the KB361 stroker piston with a stock rod and 454 crank, ends up as a 434.

I had considered that but to my knowledge KB is the only one that makes the specialty piston needed to convert a 396 into a 434. I've been informed that KB's are pieces of crap hypereutetic pistons. I really want a forged piston that I know isn't gonna fall apart after I've put the engine together. If you know of anyone else that makes a forged reliable piston for a bbc 434 please let me know.

Oh yeah...any idea as to how a 434 would perform? Speedomotive.com says it's "427 power with 396 economy"....whatever that's supposed to mean. :confused:

"KB's are pieces of crap"? Sounds like vendor bashing to me. I've been running(drag racing) the KB's in my 439 for several years now without a problem. Yes properly tune the engine, but that is a given. They're a good piston for their intended use.

I know a few guys that run the KB hypers. Only real issue is the top ring gap has to be measured and file fit to spec with the larger top ring end gap. Should not be a big deal, as most guys I know file fit all their rings anyway. The only production forged pistons are the 19.8CC TRW L2354's for a 402 motor with closed chamber heads and whatever the correct part is for the 11/1 piston that could be used with an open chamber head for a streetable compression ratio. I had read that advertising also and didn't quite get what they meant either.

For what it's worth, we did drop a 4" crank into a 396 block that we have and there was no crank interference. You would need to do some rod clearancing though. If you were to get a set of aftermarket cap bolt type rods, you could possibly get away with little clearancing.

I will tell you this, other than being forged alum, the TRW's are all over the place in weight. All of the hypers runs real tight cyclinder to wall clearances. The other issue is do you have a good balancer and flexplate for the 402 already.

So how well did that 434 perform?

I'm probably going to reuse the flex plate and starter from the old 350 that's in there now. No I don't have a balancer yet.

I've heard of the TRW pistons you're referring to....and that's the actual piston used in the engine when it was manufactured some 30 + years ago?

Speedopro makes a forged piston kit with rings, oil pump, rod and main bearings, gaskets, etc....all you gotta do is reuse your rods and crank which I do have. What's your take on this kit?

As mentioned I really want a forged piston...any ideas where I can get one made for the bbc 434?

The statement made about the KB pistons was not intentionally made to bash those guys but rather how several people had the pistons crack into pieces inside the engine after the install and cause problems....and really this board needs to be more liberal on the difference between an actual bashing versus "Hey man watch out I've been there and have problems before and so have others."

If someone wanted to screw you over and your friends were trying to warn you, I hope you wouldn't look at it as "man stop saying that about him, you're only trying to bash him." ;)

The L2354 is still listed as the Speed Pro L2354. Or you could just get 396 +.060 pistons. But make sure you get the pistons first. 396+.060 is 4.154 Bore, 402+.030 is 4.155 Bore. THe forged pistons will work with a loose fit so .001 isn't that big of a deal unless the bore and hone was done for the 4.155 with the max clearance, which I think for a NA street motor with a forged piston should be .004. Also today's pistons use a more stable alloy than what I have. My 402 was already bored at 4.155 with pistons that were installed in around 1978 - at least that was the date on the cam but the cylinders were glazed. most likely from the crap carb that was on the motor. No cylinder wear though, so all we did was cook the block, line hone, deck the block, new cam bearings and freeze plugs. Polished the .010/.010 crank, installed ARP rod bolts and resized the big end. Reassembled with new ring set and bearings.
If I would have had to bore it, I probably would have went to the 434 stroker, or in my case, we would have went to .040 over and went like 436CI. .060 over gets you to a 440CI motor with the 4" crank. When you lay it out and examine it that's only 14CI off a 454 motor. I would bet in most cases you would hardly be able to tell the difference. However, I am one of those guys that although I enjoy different things and experimenting, I am not one to just throw money into something just for the heck of it. If you already have a good crank and rods, then by all means use them. You may want to double check the flexplate though. Most smallblocks use the smaller flexplate, big blocks use a larger diameter 168 tooth unit-gets a lot more output from the starter with the larger diameter. As far as balancers, stock 325-350HP motors got a 7.25" balancer, HI-PO's got an 8". I wound up installing a new Pioneer 8" nodular unit when I did the cam change. Haven't really driven it yet to tell, but I would assume it should be little smoother with the larger balancer.

I'm pretty sure my 350 has the 168 tooth flexplate.

Yes I do already have the rods and crank and they will be reused. I do however plan to run ARP bolts on the rods and the mains.