Hello,
This is a simple question. I want to build a 391 in my garage next year. I dont want to bore. I just want to increase the stroke. The block has 93k miles mostly highway. I can still easily see and feel the cross hairs in the walls, so boring it .030 over would not be required. Technically all I need is a 396 crank. I can use the same size rods and pistons correct? Any pistons and rods made for a 350 should work with this. I know I have to clear the rod end bolts on the oil pan seal. That should be all the block work I need to do. If you think I am wrong with any points let me know.

Thanks
Derek

 

You might want to reconsider. Even if you can see the original machine marks, it doesn't mean the bores are still round. And you can't just use any old 350 pistons and rods... when you increase the stroke, you have to either change the rod length (you don't want them any shorter than they are now... you probably want them longer), or change the height of the wrist pin in the piston. Since you are likely going to end up with new rods and pistons, you can get any size overbore you want... it isn't going to affect the cost.

So consider going with a 0.010" overbore. By the way... 4.000 X 3.875 = 389.6ci, 4.010 X 3.875 = 391.5ci.

 

Thanks for the reply. So if I do have to bore it. I might as well go with the .030 over bore. I was just trying to save a trip to the machine shop. Look over these parts. They all should fit together.


SB Chevy Scat 3.875 4340 Crank 396 Crankshaft
http://cgi.ebay.com/ebaymotors/ws/eB...category=33616


SBC Chevy Scat 6.0 H Beam Connecting Rods
http://cgi.ebay.com/ebaymotors/ws/eB...category=33623

SRP Forged Flat Top Pistons
SRP-144995 4.030 3.875 6.000 420 -5cc 1.062 12.2 11.4 10.6 10.0 494.95
http://www.impalass.racenet.net/engine.php
Il be using a 67 cc to obtain a 11 to 1 compression ratio.
But I am not sure on using forged aluminum. Im sure I can find this size piston in forged steel. Reason being I do want a supercharger sometime in 2005.

 

I can't see the difference being huge, and am left wondering. Is it worth the cost (if any) of going with the .030 overbore instead of the .010 overbore?? I don't know if there would be any cost difference, but what you would have is a lot of wiggle room left on the motor for more rebuilds.

 

Check that crankshaft again. Scat doesn't make a 396 crank for a LT1 block. Not taking a trip to the machine shop is a big mistake.

 

Agreed its a huge mistake not going to a machine shop. Bores become tapered, the deck may not be flat, heads should be milled, align the mains, and clearance the block. Block must be clearanced for rods and crank, and if you go too deep.....water!

Forged steel pistons? Those things would be awful heavy if they made them. Everything is aluminum or its alloys.

Not a flame or anything, but it doesnt sound like you are ready to build a motor yet. You need to do a lot of research.