400 SBC Build

Looking to rebuild the original 400 SBC out of my '76 K15 and looking for some suggestions for what I should do.
I have a XE262H cam I plan on putting in it. I also plan on getting a set of 062 vortec heads, some flat-top pistons, and other goodies but not exactly sure what else I should do to it.
It's for a daily driver but wanting to build something mild, more smiles per gallon then miles.
(400sbc/Th350/NP203, to a NP205. D44, 12 bolt w/ 3.73 gears.)

Make sure the vortec heads can handle the lift of that cam. Aftermarket vortec heads are machined for higher lift than the GM ones.

Zayshley said:

Looking to rebuild the original 400 SBC out of my '76 K15 and looking for some suggestions for what I should do.
I have a XE262H cam I plan on putting in it. I also plan on getting a set of 062 vortec heads, some flat-top pistons, and other goodies but not exactly sure what else I should do to it.
It's for a daily driver but wanting to build something mild, more smiles per gallon then miles.
(400sbc/Th350/NP203, to a NP205. D44, 12 bolt w/ 3.73 gears.)

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Take a look at the most recent engine masters episode. After watching that, you would be better off getting a set of the assembled AFR aluminum heads. You aren't going to spend much more than buying a set of fresh vortec heads and you won't need a vortec specific intake manifold, which would likely make up the extra cost of the heads anyways. They were making almost 500hp with those heads on a 383.

Zayshley said:

'76 K15

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That's a great looking truck. I had one very similar about 30 years ago except the 400SBC. Vortec heads make good power for their price but the intake manifolds have gone up (along with everything else) lately. I wouldn't screw a big stick in it for daily driving and would definitely make certain the cooling system was in order as 400's can be very temperamental when under a load or if the timing isn't set perfect.

Strickland

Get the crank magged. Changed out quite a few with broken cranks.

I almost went with a 400 because a block was available from a friend. After researching I found the blocks cylinder walls were "Siamesed" and were susceptible to heat if bored over too much. I read about guys getting quality radiators that can keep that engine cool. You also need to be careful about the special water jackets (steam holes) 400s have. The heads need to be drilled to match....google that So lesson to learn with a 400....Keep it cooooool.

Best of luck.

Here we go again...

SquareRoot said:

Here we go again...

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Square you got something to say? No offence meant....if I am wrong let me know.

If the heads need drilling just set a 400 gasket on the head and do it, not a big deal.

I was around back when these motors were new. Although I agree the more an engine is bored the more suspectable they are to overheating, didn't see 400 overheating issues any more frequent than say a 350. If overheating is a concern Griffin radiator has a solution.

Really, the only issues I saw was the propensity to break cranks and overall longevity. Because of the siamese bore, rings didn't seem to last as long as a 350. Ring technology has advanced in the last 50 years and shouldn't apply in this case anyway. It will likely not get driven 80-100k.

fast 99 said:

If the heads need drilling just set a 400 gasket on the head and do it, not a big deal.

I was around back when these motors were new. Although I agree the more an engine is bored the more suspectable they are to overheating, didn't see 400 overheating issues any more frequent than say a 350. If overheating is a concern Griffin radiator has a solution.

Really, the only issues I saw was the propensity to break cranks and overall longevity. Because of the siamese bore, rings didn't seem to last as long as a 350. Ring technology has advanced in the last 50 years and shouldn't apply in this case anyway. It will likely not get driven 80-100k.

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I appreciate the input....new guys don't really know much about 400 engines and their quirks. I've studied them but am still not the expert other than what I've stated. I appreciate the hands on experience.

Kurnacopia said:

I appreciate the input....new guys don't really know much about 400 engines and their quirks. I've studied them but am still not the expert other than what I've stated. I appreciate the hands on experience.

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It's the old saying there's no substitute for CI. I saved a couple 400's for the future. Would have used one in my last truck except couldn't get heads, pistons or much else during covid. So went with an off the shelf 350 rebuild.

Don't be afraid of a 400. Back then GM built good engines.

They were also used in circle track racing twisted to around 7200rpm with a 350 crank and the thick adapter bearings.

I've got a 400 that I'm going thru myself.

Vortec heads removed the heat passage/plenum that used to go under the intake manifold. This isn't needed nor wanted when you have multi port fuel injection. However- if you don't have multiport injection you get a very cold intake manifold in winter. So cold that fuel can and will drop out of atomization and will puddle on the floor of the intake. To make things worse GM performance makes an intake manifold that had no waffle pattern on the "floor" under the carb. Typically intake manifolds have "speed bumps" or a "waffle pattern" there. The raised edges will help if fuel puddles. The puddle will get moved to the top of the raised edge where hopefully it will break free and re-enter the airstream.

Mine ran like crap in winter for 2 years before I figured this out. All the research I did where everyone said things are GREAT! were a lot of guys from warm climates.

I'd vote for aftermarket heads that had a heat plenum if you want to drive in winter.

I'll try to find the build sheet on my 400 build. 400HP was the plan. Flo-Tek heads. I called Flo-Tek and they have 400SB heads with the steam holes. Performer RPM, Holley Q-Jet EFI. Fired it up for the first last week first time. OMG! Wish I could post the video some how.

1st off... I am a big fan of the 400 SBC and have had several. As you are aware they do run a few degrees warmer than a comparable 350. Proper cooling takes care of that. Aluminum heads will help as well. Name brand aluminum water pump, good radiator and you'll never notice any increase in temp.

Since this is a street motor, I'd probably do studs on a 2 bolt block if you are going to build it up. Bolts are fine with 4 bolt blocks. The cap registers on 2 bolt and 4 bolts are the same size so no need to worry about upgrading to splayed caps unless you are going past 500hp in my opinion.

Things I would do on a street motor:
I would look into going to a 5.7 rod, and matching piston to decrease the rod angle and side load.

If you have to get your crank turned, id look at offset grinding it to make it around 417"

If you go aftermarket crank, not that much more to build a 434 nowadays. I'd look at complete reciprocating kits and if they are in your budget.

Summit/ Jegs, etc used to drill the steam ports for free when you buy the heads from them. Just have to ask when ordering.

There are blocks out there that allow you to go bigger displacement. I have a Rocket(GMPP) block that can go as large as 482", Mine is in the 450" range. I used a custom crank done at Castillo's and used some one-off billet ARAO/ Dominion 32v heads with TT set-up. We could never get the heads to work consistently and I put the motor in storage and its been sitting ever since. One day I plan to pull it out and finish it. I don't think the fuel mgmt technology was where it needed to be back then.