I've got mixed responses about this. I thought if you put a 4" crank in a bone sock 396(in my case 402) that it would equal a 427. Is this true?

no it would be a 434 if im not mistaken I looked into doing this with my 402 but I came to the conclusion that it was not worth the time or money

427 cid BBC was a 396 bored 0.125 inch over stock 396 bore. Only the '65, and early '66 block could take an overbore like that and they are as rare as hen's teeth.


Larger Dave

I've got mixed responses about this. I thought if you put a 4" crank in a bone sock 396(in my case 402) that it would equal a 427. Is this true?
A 4.125" bore and the 4.000" "arm" will yield a 427 stroker. It would be real sleeper looking like a stock 396". If you catch the post up here about our "Old-school" 396 BB, you could be looking at the same HP numbers easily but substantially higher Torque numbers, and all available with pump-gas also. Thanks, Gary in N.Y.
P.S. It would have to be internally balanced to pull it off however.

Yes a 4 inch stroke in a 396 block does yields 427. 7 cid, but you still have the 4.125 inch bore to contend with.

4.125" bore in a SBC is awesome, in a BBC it is a hindrance. Chevy had to notch the top of the block on the 396 to clear the valves so it will never be a deep breather. People flocked to the BBC initially because of the flow characteristics of the heads (a lot of those same people flocked to the 426 Hemi for the same reason when it came out a few years latter). The cylinder walls shroud the valves in the smaller bore (yes I know they were canted for this reason). That is why Chevy introduced the open chamber head as an over the counter part in 1969; not to lower compression as mandated in '72, but to unshroud the valves.

A major consideration when selecting where your money goes is bang for the buck (cost analysis) and I think this combo would be lacking (check the price of pistons).

The external balance issue would be addressed by going with 454 stock harmonic damper and flywheel/flexplate with a mandatory rebalance to compensate for the difference in bob weight.


Larger Dave

Dave brings up a VERY good point here, but looking at it from a SB to BB angle, the BB heads breath better regardless.

402 BB vs 400 SB deal here is all.. (AND I know we aren't talking SB/BB too)...

The pistons will be pricey to say the least.. But if you want to do it, fine in my book. In fact, I would bore your 402, 060" over and would then stick a cheap, cast 4.25" crank in it and use 1/4" longer rods and make it a 468" motor!

A motor like this is more along the lines of the 455 Pontiac and Olds engines due to it being undersquare and it should be a TORQUE MONSTER like Gary talked about.. You wouldn't need to rpm it b/c of all the grunt, imho.... Plus, it will still have better heads on it than either onna them have stock-wise, imho...

I can see above 500T and 450hp easy out of a motor like this! OR fine tweek it like Gary's motor and make way more!

Personally, I would start with a 454 core motor with a bad crank and make a 496" motor and be done with it.. Then you are talking about BIG power easy.... Which I did.

pdq67

If I can find a 454 for CHEAP I would like to do that, but as of now I've already got a 402 and have the opportunity to purchase a 4" steel crank(already machined for 100$). I have to be very budget minded with this so that's the reason I'm trying to go the cheaper route. With this said, I will not go cheap with parts and cut corners on the engine build. I want it to be safe and dependable. Also on that note. What can I expect to spend on a build of this nature? Looking for 400hp and 450 tq.
Someone on chevytalk.com gave me the link below to a budget 434 stroker kit which looks like something I would be interested in except for the fact that it includes a crank. I can't find this kit minus the crank. Anybody find anything I can't? Are there other/better/cheaper(but quality) kits out there?
Thanks Jason Hopson
http://www.speedomotive.com/396%20TO%20434%20BBC%20BUDGET%20STROKER%20KIT.htm

All you need are the pistons.You can use your stock rods and the 4" crank.The bearings and rings are standard stuff.I think 400hp and 450TQ is doable with a 402.What do you want to do with the engine.Race or cruise?What trans and rear gear do you have?

I think S-O-M will sell a kit anyway you want it if I remember right..

You just have to spec. what you want is all.

See what Ohio Crankshaft Co. has to offer too??

pdq67

Sell your 402 block and find a good 454 bare block core. It'll be some of the cheapest hp per $ you ever get.

One further hazard I forgot to mention when stroking a 396-402-427 block for a longer stroke is you must grind the bottom of the block to clear the rods and the counter weights (already set up to clear a 4.00" stroke in a 454 block) and I don't mean just a little bit either. Look at the bottom of both blocks and you will see you have to drill for water to clear a 4.00 inch stroke, and you will be using both epoxy and hard block if you go for anything longer with the small bore 396 block.

Larger Dave