Strange sensor (?) on head, 73 small block

Chevyforever

Veteran Member
Jan 4, 2011
1,555
Canada
I have wanted to try a mild 400 for years. Had a complete core that I had to give away years ago (long story) and have regretted it ever since. Good luck on your build, and please post some pics as you progress.
 

KFORCE

New Member
Nov 22, 2008
15
Sacramento, CA
Early Z28's had 2 bolt mains. Just sayin'. The only issue with the 400 blocks is the cylinders are siamesed' together. No flow between cylinders. With a mild build, it shouldn't make much difference.
 

sandlapper

Veteran Member
Oct 9, 2020
1,757
SE CSA
fwiw --- bowtie & Dart & world etc 4.125" sbc blocks are all siamese --- same goes for LS platform.

All above sbc and LS have 4.4" bore center spacing --- w/ 4.4" spacing and larger bores, siamese is unavoidable --- hence aftermarket $pricey$ versions with 4.5" etc spacing; $special$ heads to match as well.
 

tom3

Veteran Member
Aug 1, 1999
15,157
ohio
Going to get out the mics. and do some measuring. If it needs bored, decked, etc. and full crank machining it'll probably wind up back in the corner. Machine work, and the 400sb parts (if even available) and balancing costs might be more than it's worth for what I'm wanting to do. 400 cubic inches sure sounds like fun though.
 

sandlapper

Veteran Member
Oct 9, 2020
1,757
SE CSA
plenty replacement 400 pistons, rings & inserts available.
plenty affordable upgraded versions of those as well.
JMO, I wouldn't consider the very heavy replacement pistons along w/ those short rods.
but Tom, as ya know, any deviation from direct replacement will likely require balancing.
400 heads are pretty much pigs & not worth lipstick.
before I proceeded, I'd have any OE 400 block closely checked for cracks, magged, and have liners sonic checked for minimum thickness. A relative few bucks toward pro inspection could prevent a several thousand dollar mistake. Block first.
 

kenneth burns

New Member
Jul 24, 2021
4
i built a 400 small block bored 30 over stuck a nice cam in it and let me tell you that thing is a beast
20190316_152713-EFFECTS.jpg
 

John Wright

Veteran Member
Lifetime Gold Member
Aug 9, 2002
15,446
Rustburg, Va
Had this back in the corner for 20 years, finally got some time to play with it. Going to rebuild shortblock as stock, small cam, good heads, 4 bbl, exhaust. See what a mild 400 will do compared to a similar 350 thats in the 70 now.

View attachment 151785

Poor old small block was really neglected looks like. Got some work ahead, cylinders look real good so far.
View attachment 151786
Reminds me of one of those old Quaker State only engines....lots of ashy looking build up in the lifter valley. There was something like paraffin or something in the original Quaker State that would cake up like that.
 

John Wright

Veteran Member
Lifetime Gold Member
Aug 9, 2002
15,446
Rustburg, Va
plenty replacement 400 pistons, rings & inserts available.
plenty affordable upgraded versions of those as well.
JMO, I wouldn't consider the very heavy replacement pistons along w/ those short rods.
but Tom, as ya know, any deviation from direct replacement will likely require balancing.
400 heads are pretty much pigs & not worth lipstick.
before I proceeded, I'd have any OE 400 block closely checked for cracks, magged, and have liners sonic checked for minimum thickness. A relative few bucks toward pro inspection could prevent a several thousand dollar mistake. Block first.
yeah, core shift while casting.
 

tom3

Veteran Member
Aug 1, 1999
15,157
ohio
I did check pretty close around the lifter bosses and the lifter bores are dead centered. But I'm not going to bore this anyway, cylinders and stock pistons look really good and fit the bores snug. Want to keep the factory balance as possible. Even see a balance weight on the front Vbelt pulley. I guess a land yacht has to have a smooth running engine. Going to need some crank grinding though. And lots of cleanup, that sludge is just nasty stuff. Very well preserved. Might stick it back in the corner until spring, but I know what I have to work with now.
 




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