400sbc build ideas

[82rock]

alright yall i got some questions. first off, i got a early 70's 400sbc standard bore for free. i have a 1982 k20 that i drive al the time around town and in the mudpits. what would be the best way to build this motor? 377, 400, 406, 0r bigger. or a 383 ( using a 350 block) I appreciate the help

[eventhorizon66]

If the block checks out, run the stock stroke and the smallest bore (0.020", or 0.030") that cleans the bore up.  There is NO reason to destroke it, unless you like revving high and breaking parts more than meaty torque.  Another suggestion would be to ditch the stock rods and go with a 5.7" or 6.0" rod.

[82rock]

Ok say i bore it 30over, with 5.7 rods, what pistons would i use to get around 10to1 compression ratio? or would i need the 6" rods?

[eventhorizon66]

Rods don't determine the static compression.  Piston dish/dome, combustion chamber size, head gasket bore/thickness, and piston-to-head clearance (aka: quench distance) do.

What heads are you planning on running?

[82rock]

right i realize that. what i was reading about that you can only use certain pistons for different rod's. can you use slight dome pistons with the 5.7 rods  use 64cc patriot heads and have around 10to1 c/r? (something good for pump gas)

[eventhorizon66]

A 72cc combustion chamber, a 12cc dish top 4.155" piston, zero-decked block, and a 0.040" thick head gasket would yield about a 10:1 CR.

64cc chambers plus dome pistons would give you ratios of over 12:1.

[VileZambonie]

Don't go with the longer rods. If you were trying to squeeze every last drop of power out of it and racing with it I'd say go that route. But for longevity with a balanced compression height and reduced cylinder wear just use the stock 5.565" rod. Don't go crazy with the compression ratio either. You can easily modify a decent set of heads and you'll be happy with it. The 400 is a stout motor and you'll love it but if you're gonna get crazy with it you might as well sink your $ into a big block.

[eventhorizon66]

The reason I suggested longer rods was specifically for reduced cylinder wear.  The power you gain from longer rods would be negligible for a street engine.

[82rock]

yall help is awesome, thanks. so stock rods 12cc dish piston's with 72cc heads would be a decent hp motor for a 4x4?

[eventhorizon66]

depends on the heads, cam, intake, exhuast, tune...

[VileZambonie]

Break out a piston catalog and take a look at the piston when you go with a 6" rod. The problem lies with the placement of the rings and the lack of surface area on the top of the piston. You don't want a flat top piston or you'll be driving around a pinging machine on pump gas. If the stock rods are good just keep em.

[VileZambonie]

Is this going to be a budget build? Is your goal maximum power? durability? reliability?

[eventhorizon66]

Break out a piston catalog and take a look at the piston when you go with a 6" rod. The problem lies with the placement of the rings and the lack of surface area on the top of the piston.

I'm not trying to be a wise guy.  Because I'm not.  I'd like to understand what you are arguing here.

What do you mean "the lack of surface area."  Are you saying the margin between the crown of the piston and top ring land gets too small?  Issues with the oil ring running across the pin bore?

My position was the reduced angularity of the rod would reduce side loading of the piston, decreasing wear and friction.  But you are saying this would be negated by the ring spacing(?) or positioning(?).

82rock: When in doubt, Vile is the one you should listen to. He's got a ton of very valuable experience to share (which is about a ton more than me).

[82rock]

really i never had wanted to mees with a 400sbc but sense i got it free it will due untill i get a 454. I dont want to spend more then around 2 grand. power is nice but durability is nice too. also if i used forged pistons would a 100 shot of nitros be good also?

[VileZambonie]

Event, forgive for me not being too detailed as I was off for the night. Surface area probably wasn't the best choice of words. As the rod moves further upward into the piston this will prevent him from running a decent dish wich he would probably want if he's going to run 64cc heads. I'm not arguing that a longer rod has it's benefits but the benefits aren't worth it if it's a budget build. And yes I think you get where I was going with the rest.

82rock, if you plan on running nitrous then my suggestion would be new splayed main caps, a forged crankshaft, a good set of rods again I'd keep a standard length or 5.7" rods as you will need a good dish on that piston, and a forged piston.

If you want to keep it as a budget build, just get a summit rebuild kit with hypereutectic pistons and leave the rest of the bottom end stock.