Thread: chevy sb 400

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I was just at an auto parts store buying some parts, and the guy running the place told me that the 400 was built for one reason....smog, i didnt really stick around to chat with him, but i dont really know what this means, i just recently put a 400 in my truck, with the help of a friend and i was expecting a little more power then my prior 350. i understand the basics of an engine, and i can say that i have some mechanical skill, im justa young guy and i would like some info from some of you more exp. older guys on this eng, maybe some mods that would improve its performance. some tuning tips, its in a 83 k10 4wd, i dont want a strip truck, but some thing with a little more pep. its got a accel dist, 450cfm edel and a torker2 intake, as for the other specs, i have no clue, i would guess it is all stock. the engine was out of a 80-81 plowtruck. any info on this engine would be very much appr. thanks

-Jesse

[B]what the guy said is partially true, yes originally due to the increased weight and restrictive emmissions controls it was easier to build a bigger engine so the increased torque would get the land barges rolling with those numerically low rear gear ratios, That being said a 400 will probably be a great engine for your truck and with the help of some of these guys on this forum I am sure you will be pleased with the outcome.
I have learned so much by just asking and paying attention to our resident experts.
good luck with the truck

WWWhhhhaaattttt?????....I had to come back and edit this post.....I'm realing from the fact that boneheads are handing out garbage from behind the counter still. Gets my dander up when they speak without knowing of which they are talking about. Do as denny suggests in the following post and learn that you will have a base to start from. Then get here and share info and get some good help from these guys.

ok will do, just got to figure out how to do that? a special tool i would guess? thread into the spark plug hole?

If it's a 1980-81 engine it should be right around 8-1 compression. The first couple years they made the engine they had about 9-1 in 1971-1972? But smog got really bad after that hence the big drop in compression. It will be a great engine as long as you don't go wild on the cam, if you put one in.

when testing compression, the motor will turn easier if you remove all the spark plugs. To let it breathe, wire the primary throttle blades open. To prevent a fire, disconnect the hot wire to the distributor.

can i get a compression tester at an autoparts store?

i got the tester, i read the instructions, and heres what follows.....

__________
160-8 | | 7-170
144-6 | | 5 -170
165-4 | | 3-160
165-2 | | 1-160

psi. that is, whats next guys.
(i did not do a wet test........if so should i do that in all cyl?)

can i do it with all the plugs back in it?? or would it give me invalid results?

ok same reading, i disconnectted the dist. and tryed with the plugs in and got the same number... 145, then i took some 1/4 in. tube about 12in. in lenth and filled it half way with 10w30 and droped it into the cyl. and it went up to about 150, 5 pound diff. ....

Originally Posted by glassjawjm

ok same reading, i disconnectted the dist. and tryed with the plugs in and got the same number... 145, then i took some 1/4 in. tube about 12in. in lenth and filled it half way with 10w30 and droped it into the cyl. and it went up to about 150, 5 pound diff. ....

All you really need to do was a couple of quick squirts.
It sounds to me like it is time for some new rings.

ok, so if i have to pull the engine out, i might as well get a new cam, and set of lifters, maybe even rebuild the whole valvetrain, but if they are smog heads(low comp.) then i can only get so far with a new valvetrain, or at least not its full potential....does that make sense? new heads? pricey, would cheap heads be a waste?

400's are a little bit tricky to build. If you want to build one with the stock bottom end that is fine, as long as you don't plan on reving the thing past 5500 rpm's. The short connecting rod length is the problem. They are made for making torque, not high rpm's. You can change this, but it requires new connecting rods(5.7 or 6.0 length), and custom pistons. You're getting past the budget build at this point. I would do this if you plan to rebuild the entire engine and have a couple grand to throw in it.

If you want to get new heads, and keep the stock rods and pistons, get some small heads... something like a 165-170cc intake runner. And put a small cam in it, no bigger than 220 duration @ .050. You'll want a rev limiter as well. Don't rev it past 5200 rpm's and it should be fairly reliable.

ok, so if i do get new heads, and new cam, are they going to be compatable with each other, i dont realy know alot about this, but wouldnt you have to get a cam that would work for your heads. and if so how do i figure that out, plus i have to get steam holes drilled, there just alot i dont know about here, im not asking you to research my parts but how do i figure this out?

I have a 406 (bored 400) If it was up to me, I would just do a good rebuild, using the stock parts. (He said he was not building a race motor). use the cam for your needs, (I run a 221/230 @ .050 for 9.5-1 to 10.5-1) , almost any head will help, almost! (I hear most 400 sb heads are cracked!) I run 305 heads (custom milled 58cc & 2.02 valves), but, I wanted to raise my comp. and a drilled Q-jet. Runs strong, and it's quick off the line. 400's are good low rpm torque motors stock. So build it around low end torque, not high rpm's (beat them out of the hole, and let them try to catch up to you!)

Use the head gasket to mark where to drill the steam holes.

Three years pushing my '68 El Camino around stacked at times higher then the roof, 365 day's a year, 100+ to -40 it takes me 20 miles to work, and no problems!

Pat