hey guys,

just bought a 400 sb out of a 71 4 door impala. i saw it in the car. the dude said the car had a 400 trans as well. he wanted $500 firm for the motor and trans so i went for it, later found out it was a 350 trans (don't know how i missed it). i called him and he was pretty cool about it and he's gonna let me swap the 350 trans for a powerglide. motor came with all the bolt ons and the compressor, ps pump, alt etc. the car as either a 2 barrel or a 1 barrel, didn't look at it too closely. think it's a four bolt main? my boy counted the freeze plugs and said it was but he is a big time trash talker. anyway, think i got a good deal or robbed?

It's definitley not a one bbl.,and is a powerglide more desirable than a turbo 350?

4 bolt blocks are junkyer then 2 bolt blocks. your gonna want a 509 or 817 block. the 511 are usaly 4bolt mains and arnt as strong as to bolt blocks. i however think all 400 blocks are junk! and im speaking from experiance

71 should be a 4 bolt block I think they went to two bolt in 74, dont know if its a good deal, I bought my last two. I paid 200 for each of the 74 caprices. they have the big two barrels on them. the turbo 350 was probably a long tail. Jim

Decent deal, especially if you specifically wanted a 400, I would keep that th350, but thats just me.

Is the main webbing weaker in the 4 bolt blocks, than in the 2 bolts?? Or is that just BS?

Is the main webbing weaker in the 4 bolt blocks, than in the 2 bolts?? Or is that just BS?


that what the word on the street is. i think alot of the roundy round guys usta use them, and they all say the two bolt is stronger due do more metrial in the main webs.

IF it really is a sb 400 from a 71 Impala it is a 4 bolt.

Sounds like a pretty good deal to me.

IF it really is a sb 400 from a 71 Impala it is a 4 bolt.

Sounds like a pretty good deal to me.


its a good deal until it cracks

You could do a search, OR, I guess I can go over all of this again.

FIRST, ALLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLL 70-72 Chevrolet Small Block 400 cubic inch V8 engines have 4bolt main caps-----ONLY! PERIOD.
SECOND, ALLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLL 73-80 Chevrolet Small Block 400 Cubic inch V8 engines have 2bolt main caps---------ONLY! PERIOD.
There WERE NOT any 2bolt 70-72 SB400s.
There WERE NOT any 4bolt 73-80 SB400s.
That part should now be cleared up.

THIRD, For an everyday, street performance engine, the 4bolt blocks are fine. The structural integrety of a SB400 block may, or may not, be quite as strong as a 350. The 400 was pushed waaaaaaaaaaaaaay beyond its design limits. But, a 400 that has not been severely abused, over heated or extremely neglected, is USUALLY a good foundation for a moderately healthy street/performance engine.
IF IT IS MANDATORY TO HAVE AN ABSOLUTELY KILLER, HARD CORE, SERIOUS 4OOci RACE ENGINE, THEN BUY AN AFTERMARKET BLOCK, SUCH AS WORLD.

FOURTH, It is generally considered that a 4bolt block is not as ideal, structurally, as a 2 bolt block for serious performance. I have personally never seen a 4bolt block failure, but there have been reports of cracked and/or failed 4bolt main webs. The reason is because of the fact that the 400 main bores are first of all, larger than 350 main bores (less metal in the web) and second, the outer bolt holes for the 4bolt caps additionally reduce the strength of the main web. Again, I have never seen a 4bolt block failure in the main web area. Three of the SB400s in my family are 4bolt blocks. They are doing just fine.
Generally, the major concensus of opinion for SB400 desireability in regards to strength is the following:
1. Two bolt block with aftermarket splayed 4bolt caps and studs.
2. Two bolt block with main studs instead of bolts.
3. Four bolt block with studs instead of bolts.
4. Two bolt block with bolts.
5. Four bolt block with bolts.
3, 4, 5 are just about tied, thus the ACTUAL order is 1-2 and then 3/4/5 in just about a 3-way tie.

As I mentioned earlier, if a SB400 has had good maintainence and not abused or severely overheated, it very probably will be an excellent core for building into a very nice street performance engine.
SB400 that are in good, solid rebuildable condition are becoming a little scarce, but if you can get a good core, GET IT. Building a 400-450hp SB400 is going to maybe cost $100 more than building a healthy 350 and just about equal to building a 383.
I absolutely DO NOT subscribe to the philosophy that SB400s are junk and are do not make good cores for building a healthy performance engine. I've been building engines for about 40yrs and in the past 30yrs, I've built about 25 SB400s. I ALWAYS have my machinist inspect and magnaflux blocks and heads (ESPECIALLY 400s) before I spend good money on lots of machine work. Usually, if you have the machinist do the inspection/magnaflluxing and all is good, and then he also does the machine work, he will frequently cut you a little break.

FIFTH, and last. If you are planning to build a REALLY serious SB400, and decide that the aftermarket block will be more desireable because of its increased strength, WHY? Always keep this in mind. It is VERY, VERY easy to get into a SB400 waaaaaaaaaaay deeper than what a healthy 454 would cost you. For example, just the cost of a bare World SB400 block will be 2-3 times more than a complete, rebuildable 454 core!!! That's for starters, then you have heads for the 400 (I presume that if you are going to buy a World 400 block you are also going to buy aftermarket heads, right?). So now, you've got $4500-5000 in just block/heads alone. No pistons, no rods, no crank, no rings, bearings, cam, lifters, timing set, oil pump, gaskets, bolts, hardware, etc, etc. AND, on top of all that, you still have machine work to be done. By the time you're finished spending all this money on a killer SB400, you could have built two very healthy 454s!!!!!!!!!!!!!!!!!!!!!
So, when building a SB400, be careful about what and how much you want to invest in it. For a really, really, good all around healthy, performance SB street engine, you just can't beat a SB400. Its about 150lbs lighter than a BB and 400-450 hp is realistically possible and it will live on the street.
Cooling a SB400????? If you have a good, efficient cooling system with a 3-4 core radiator, NO PROBLEM! Heating problems with a SB400 are no worse than any other engine.

What Tom said. I've been building 400s for nearly 30 years, have not experienced or even personally seen the blocks cracked around the outer main bolt holes, regardless of all the collective wisdom of the all magazine readers.

I don't believe you're going to hurt a 400 block with any reasonable facsimile of a street engine. I've trashed a couple running them hard in sprint cars, but that was 700+ HP running WOT for 20-30 minutes at a time. This usage is not similar to a street or strip car.

DZ,

You forget that some 2 bolt blocks were used as gm replacement motors between 70-73

sounds like a fair deal to me. I normally dont reuse anything but the block and sometimes the crank so I pay a bit less, but chalk one up for 4 bolt 400's running high 11's in a stick shift 3800lb chevelle.

I'm running a 2 bolt block converted to a splayed 4 bolt for the past 9 years in a 3800lb 69 chevelle. Absolutely no problems. Been to N. Carolina, Boston, Maryland, Jersey shore more times than you can shake a stick at, with absolutely no problems. Runs at 185-190 degrees all day long. Short block built by Pat Musi; 5.7 rods, forged crank, H-beam rods, flat tappet .510 lift, 10:1 comp., HEI, Performer RPM, 3310 750 Holley, sportsman II heads, alum. roller rockers, stock replacement waterpump, HD A/C radiator (stock), clutch fan, TCI 2800 10" stall, beefed TH350, 3:73 12bolt, Gear vendors OD, 275/60-15's.
Runs all day anywhere! Musi said it's making about 475HP. Plan on chassis dyno this spring. Ran 13.3 @ 94 mph in 90degrees, no slicks, spun thru 2nd gear, .35 light, 2.3 60 ft. Friend who races professionally says the car is good for low 12's even better with a good driver. 400's junk? Not in my opinion, I love 'em! Keep them cool, use good parts and they'll last. By the way I paid $200 for a complete engine in '97, for $500 you stole it!

What Tom said. I've been building 400s for nearly 30 years, have not experienced or even personally seen the blocks cracked around the outer main bolt holes, regardless of all the collective wisdom of the all magazine readers.

I don't believe you're going to hurt a 400 block with any reasonable facsimile of a street engine. I've trashed a couple running them hard in sprint cars, but that was 700+ HP running WOT for 20-30 minutes at a time. This usage is not similar to a street or strip car.


ive only hurd of them cracking around the main webs. i had two crack on me last summer. the first one was a small crack at the bottem of the number 4 cylinder. the 2nd was between the 3 and 5. from the head bolt to the steam hole. from the steam hole to the #5 cylinder and down. then a crack heading towards #3. the machine shop who provided the block and machined it tryed to sleave it. but it cracked even more. at that point i was told to go fornificate myself and i was out $1200

considering i cant even find a 350 shortblock in the area for under 800 bucks if that thing is capable of running as is its a hell of deal.

I spun a bearing and am at the point where it would be easier to just replace the shortblock and yet somehow when I need a shortblock I can't find one for the life of me haha

400 sb .060 over, 280d 480l cam, 2.02 1.60 heads, HEI, Vic Jr. intake, new 3 core and water pump. No problemas (knocking on wood). Runs pretty mean too. Built by a local guy (Lauritsen) and he builds alot of 400 sb I know, he likes them and has been in the buisness a long time. Roger, I think you got a good deal there. Also, when we mothballed the original 307 and powerglide, we did go with a th350.

http://i143.photobucket.com/albums/r130/headjimmiepig/motor1.jpg
http://i143.photobucket.com/albums/r130/headjimmiepig/park1.jpg

DZ,

You forget that some 2 bolt blocks were used as gm replacement motors between 70-73

Carl,
That is exactly, 100% correct. But, those replacement 2 bolt blocks were exactly that, replacements. The ORIGINAL, factory installed 4bolt blocks (70-72 model cars) is what I was referring to. It MAY be possible that some VERY, VERY early 73 model cars got a 4bolt 400, but those would have been left over 72 model engines. For the 73 production year, the 400s were 2 bolt, and THEORETICALLY, the 4bolt blocks no longer existed. So that's where the "official" seperation between 4-2bolt blocks occured, between 72-73 models. It just makes me sick to think of all the 2bolt blocks I passed on years ago!!!!! Back then, I was like everyone else, why have a 2bolt when you can have a 4bolt. DUH! I remember that one guy tried to give me a nearly complete 2bolt 400 (he kept the carb, pan, valve covers and dist). Oh well---------------------

I did take a 400 out of my fathers car, a 72 caprice wagon and if I remember correctly it was a two bolt. It was the original engine in the car.