The Stovebolt Site Forums The Shop Area Engine Shop Chevy 400

I just acquired a ('76 I think) 400 from a motor home that was run out of oil. I also have a customer interested in a "mildly built" 400 for his '66 Nova SS. I'm pretty sure the block & heads are OK.
I remember some discussion about overheating and drilling "steam holes", but I'm not clear on how, where, and why. Many opinions...
Also, I need more the topic of "externally balanced"...
My SBC experience is limited to 283's & 327's, with an intro to 350's, so any input appreciated.

A factory 400 would have steam holes drilled in the block and heads. If other heads are to be used, steam holes would have to be drilled to match up with the block or it will overheat. I'm not sure if 400 SB's are externally balanced but if you use the balancer and flex plate from the donor vehicle you should not have any problems.
Fred

Hy guys, the Chev 400 small block is the only externally balanced small block, it requires a special harmonic balancer, and a special flywheel. The 454 big block is also externally balanced, but the part numbers for the balancer and flywheel for a 454 are not the same as the part numbers for the 400 small block balancer and flywheel. Hope that helps.

A 400 block has a simeased bore, the cylinder walls don't have a water jacket between them. All other small blocks do have water jackets between them. I'd be very cautious of a block that was ran without oil. A good hot tank, crack check to start. Then check out having it align bored. I'm sure Hotrod Lincoln will be here with more information. Just be cautious of a big bees nest with that block.

Oil starvation can do a lot of damage, so inspect everything carefully before doing a buildup. How bad was the failure- - - -did the engine lock itself up, or just hammer the rod bearings and crankshaft? If you're going to hotrod it, definitely get a line-bore done before fitting a new crankshaft. Pull all the oil gallery plugs, and scrub all the passages with a shotgun brush and solvent, followed by a thorough pressure wash.

The "steam" holes are for coolant circulation between the siamesed cylinders. As long as you use the original 400 heads, no problem- - - -they're drilled to match the block holes. If you decide to use 350 heads for more compression, use the 400 head gasket as a template to drill the steam holes in the heads between the cylinders.

400's have a bigger bore (4 1/8") and a longer stroke (3 3/4") than a 350. Their main advantage is torque, due to the longer stroke. The long stroke makes it difficult, if not impossible to put enough counterweight inside the crankcase to balance the crankshaft, so an off-balance harmonic balancer and flywheel is used. 400's DO NOT like high RPM! Put a relatively short-duration, high lift cam in it, and try to keep the RPM under 6,000, and you'll have a torque monster! A set of 76CC cylinder heads with enlarged exhaust valves (1.6") and some pocket porting will give you good compression and good enough breathing to support good low end and midrange torque. Just don't expect to be able to run the RPM that you can with a well-built 350.
Jerry

Thanks, guys...all good advice and info.
Can we discuss further the balancing? Assuming this will be a 4-speed application, I won't be using the original flex plate. Will my machine shop know about this stuff? Can I do this, or is there special machinery required?

cm

Hy starfire4, if you buy a flywheel designed for a 400 small block no further work will be required on your part, other than to bolt it on, hope that helps.

3B, that sounds simple enough! Thanks.

cm

STARFIRE4
Look at using 350 connecting rods, this will stroke the engine to a 406 cu in .I have a 406 that's a street strip engine in My 1965 nova .Built the engine in 1993 never had any problems with it .Its a lot more than you plan to build I think. AFR heads ,comp cam 306 sold lift cam.It has around 17.000 miles on it drove it cross country on the Hot Rod POWER Tour in 1994.Just car shows and the track since.I really need A/C the car is capable the driver is spoiled.
Like others have said check the block first !

The 350 connecting rod is 5.7" and the 400 connecting rod is 5.565". A 400 block that is .030 calculates out to a 406 cubic inch. If I remember right a 350 crankshaft in a 400 block that is .030 is a 377. If you use a 400 crankshaft in a 350 block that is .030 you end up with a 383. Lots of combination's and each have their own things that have to be machined separate.

I think the length of the rods only changes where the pistons ride in the bore, not the stroke, which is determined by the crank offset. Longer rods might raise compression ratio, depending on wrist pin location and other piston factors.
It'll be a 406 or bigger, with mildly ported stock heads and a mild cam, and we're thinking about an EFI.
Thanks again for the input.

cm

Update...
Heading to machine shop for inspection of block. Had to sleeve one cylinder. Heads are ready for intake port matching (picking up gaskets today), and hopefully, we can bring the block home, too.
It's almost time to start ordering parts!

cm