I know the Motown block is the biggest small block available, but what is the biggest Genuine GM Small block available?

 

The largest sbc to ever be put in a automobile? That would be a 400 (4.125" b and 3.75" s).

There are also GM performance racing blocks (although they where never installed in a car they are still made by GM) that can be bored more than the 400 block, a 400s max bore is .060" I believe.

It depends on what you consider a "real" GM block i guess.

 

On to the next question, in what type of vehicle would one find a 400 block? Also were they 4 bolt main?

 

From '70 - '76 you could find them in large pass. cars blazers and P/Us. In '77 - '80 or '81 (I forget wich was the last year for the '400) they were only installed in heavy duty work trucks and suburbans.
They did make 4 bolt main 400s from '70 - '72 (I beleive those are the correct years, maybe longer), but the 2 bolt 400s are said to have more meat in the bottom end and are there for stronger then the 4 bolt.

 

impalas, caprice, biscanes, trucks, i believe olds also put 400s iin some of their cars. 400s could be had in what most consider the weaker block with 4 bolt mains

 

in the mid 70's, they were mainly 2 barrel carb equiped stock

 

400 4-bolts are next to impossible to find. Plus, the 2-bolts are considerably stronger if you do a splayed main cap kit, which I would if you want serious power.

Don't be folled by the old freeze plug myth either. Some 400s have three, some have two. I've seen both types.

Look for a 70s land barge and you'll probably find one.

Max overbore for a 400 is .060" if you're lucky. Anything over .040" should be sonic checked for core shift. That would get you a 4.185" bore if you can go .060" over.

There are AM blocks now that can go out to 4.250" bore and enough stroke to get 454 or more cubes from a standard deck small block Chevy.

 

A stock 400 block + stroker crank is good for 434 cubic inches give or take a few for what ever overbore you have to use.

 

True, but then you are tied to the ultra short rods, and RPM will be pretty limited. Granted with 434 cubes on tap you probably don't need all that much RPM. Depends on what you're trying to accomplish.

 

You can run 6" rods in a 434 in a stock block.

Been there, done that, got the smile.

I usually get my 400s out of mid-70s land barges. Although, when my wife bought a 74 Monte Carlo back in about 77, it turned out that it came with a 400; so look in those too.

Too hard to find them in trucks, although they're definitely there. Too many 350s you have to look through.

 

I may be wrong but won't the piston skirts in a short (under 6") rod 434 stroker hit the counter weights on the crank? I have never seen a 4" stroke crank for anything less than a 6" rod.

 

Yes, in fact, you may be.

The ONLY WAY to make a motor with that much stroke is in fact to lengthen the rod. The penalty is of course that the wrist pin has to be moved up higher in the piston when you do that.

The deck height of a SBC stock block is 9.025" from crank center line to deck surface. Therefore, a 6" rod plus half of a 4" stroke gives 8", which is how far from the top of the piston the wrist pin center will be with this combination. It puts the pin well up into the rings. So it's not exactly a long-lived street package, usually; but it is definitely possible.

Here's an example. Since Eagle doesn't have a web site that I know of, I have to use some other source of a list of part #s.

http://cgi.ebay.com/ebaymotors/ws/eB...category=33616

Notice the descriptions; it doesn't say "must be used with 5.565" or shorter rods"; it says "Must be used with 6" rods or longer".

The one I dealt with had the 440040006000 crank.

 

eagles web site

 

The blueprint deck height on a small block Chevy is 9.025". This is a perfect stock block. If the block's been decked, or wasn't perfect to begin with, it isn't uncommon to knock that down to 9", or just a hair over because the typical small chevy piston is way down in the hole.

2+6=1" from the top of the piston to the center of the wrist pin. The small chevy wrist pin is .900 or so inches in diameter, which means that the top of the piston to the top of the wrist pin bore is only 0.55" or so. The 1st and 2nd rings are typically 3/16" thick, so that's another .188", which leaves only .362" for two spaces between lands and the distance from the top of the piston to the 1st ring land.

I guess it is possible to run a 6" rod with this package, but the piston design is severely compromised. I wouldn't expect this combination to hold up very long under continuous and strenuous use.

BTW, you can run shorter rods, it just requires the piston skirts to be very short.

 

that is what I ment. Guess I wasn't too clear.

 

I am proud of owning 3 400's . The best 400 2 bolt is cast#509.
Mine was out of 77 Chevy truck 4x4.

1973-80 cars and trucks cast# 330817 were 2 bolt main

1970-80 cars and trucks cast#3951509 were 2bolt main and I think some of 'em came 4 bolt main

1970-73 B & G body cast# 3951511 were 4 bolt main

 

434 should have no problem running to 6K. some of these dirt track racers use 434s that sping to 8000 rpm. I would've thought you'd be stuck with 6" rods because piston-crank clearance wouldn't happen with smaller ones. every stroker kit I've seen is 6" rods and requires a small base circle for clearance.

 

The real reason a lot of strokers are using 6" rods has nothing to do with clearance. It's because long rods offer a fair number of advantages over short rods.

Long rods dwell at TDC longer, so they are less prone to detonation, and tend to make a bit more power. I once saw an article where they built a small block using ultra-long 6.3" rods from a Ford 300 I-6. They ran a static compression ratio of 12.5:1, but because of the rods and other tricks were able to run 89 octane without detonation, even with an agressive timing curve.

Smokey Yunick always said to run the longest rod you can cram into the motor. Citing that it improved the rod/stroke relationship, and higher ratios means an engine that accelerates better. Typically 1.7-1.8 would be considered good, and anything over that is just gravy.

Also, depending on what rods you use, even a 383 can have cam to rod clearance issues.

 

also come in 2 bolt I have one.

 

I do too