Which short block (stock dimensions) would be more efficent for a twin turbo setup?. 400 or 440. Everything else would be the same either way I go ie, heads, intake, cam, valve train (other than the B/Rb diff.) I'm thinking 400 =lighter rotating and reciprocating weight. The extra cubes are not really nessecary in a turbo app. am i on the right track?

 

the "B" blocks (361-400) are known to be inherently stiffer and less likely to have "cap walk" as is dreaded in most high-hp RB's.the 6.358 rods are also known to be stiffer than comparable RB rods such as the LY's.

plus the 383 forged crank is known to be very stout as is and can be put though a good deal of abuse.

scott dickinson of SDCE (superchargers) is putting out somewhere in the neighborhood of 900 HP his stock block and crank 383.

 

Yeah, and he's actually making a fair amount more, since his motor is also having to spin the blower, which is power that does not show up on a dyno. So, it's a pretty safe bet he's making over 1000 hp in real life as far as the crank and block are concerned.

I'd build a lowdeck motor. Like roadrunner said, they're stiffer and have a little less problem with cap walk. Plus, they're a little lighter AND narrower, which helps with running plumbing. As a final small note, if you happen to use Stage VI aluminum heads, you can run a regular RB manifold, since the intake ports on those are raised by just the right amount to fit an RB manifold on a B block. Conversely, if you run them on an RB block, you must use an RB manifold plus a set of spacer plates between each head and the manifold, since the gaps between the raised intake ports is now wider than any normal manifold. Those alone will set you back roughly $150, plus you have to deal with the extra height they impose.

Anyway, just run a 400 block. They're just about falling out of trees in many localities, so they're cheap. Same with forged 383 cranks-the only POSSIBLE year to get a cast crank in a 383 was 1971, and only on 2 barrel motors then.

 

I am splitting the difference and running a 451(400 block 440 crank). While the longer stroke isn't as crucial with a turbo, it never hurts either. The problem with this combo is cost. Machine work will normally be a little extra, as will a 440 steel crank.
Tom

 

Concentrate more on the airflow of the heads and the intake. A v6 grand national can pull 4 digit power because of the airflow of the heads and intake, keep that in mind
issuez

 

Yeah, I'm leaning toward the 400. The small strength advantage is not much of a concern. Although we've built a 451 short rod, roots blown with good success. already have everything to do either one and its time to make a choice, even have a 383 block, but I dont like the small bore.

 

In the turbo world, a 383 is a huge bore
issuez

 

So lets talk about this some more, Does the 383 have an advantage over the 400?

 

I don't think that there is a whole lot of difference between them. The 383 might end up with a bit thicker cylinder walls, but like any good rebuild with an overbore, you would want to sonic test each block anyway.
Tom

 

there are no forged lower compression pistons for th3 400 , you would need custom pistons.

the TRW L2315F forged 383 pistons can be set up from anywhere to 8:1-9:1 CR and have can take a good bit of boost even though they are a heavy forged pistons.

hmm...i didnt know the 383 standard bore of 4.250 was small , thats what a 454 has.

 

I wouldn't think that a stock replacement forged 383 piston would give much compression at all. Most big block chryslers have the pistons well below the deck surface at TDC, great for hurting power and helping detonation (no quench). In terms of static compression ratio, if I had a 383 I wanted to run boost on, I'd just put a set of heavy-ass stock replacement TRW's in it and ride.

 

Less rotating mass, and per the specs given above, easier to obtain lower compression pistons without going custom. Turbos truly are a replacement for displacement, you pick up more power from the top of the engine, the bottom end just has to stay in one piece.
issuez

 

Why would a 400 have less rotating mass than a 383? They use the same crank, unless you count the fact that most 400's had cast cranks and most 383's had forged cranks. Other than that, all the dimensions on the cranks are the same.

 

The 400 has a heavier piston than the 383. The displacement is only 4.5% greater so you're really not gaining much volume.

 

I guess that's true, but I don't see the piston weight difference being much either.

 

the pistons actual weight does not come into play until the revs start approaching 6k.

a 383 with a reasonable amount of boost would really not need to go past 5k even with heavy pistons.

 

i have heard that the cast cranks are SUPPOSED to be lighter.

i dont have any concrete evidence to support this though.

 

Very little lighter, on the order of 5 pounds or so if I remember right. A bad tradeoff if you have a forged one available. In any case, that's not the result of a 383 vs a 400. Furthermore, if you follow that logic, the 400 actually has less rotating weight. RECIPROCATING weight is what tears stuff up. That's what you really want to minimize if you want to turn high rpm, and the weight difference between 383 and 400 pistons just isn't that much.

 

I guess the one other factor might be valve restrictions. I am not sure if real big valves would cause shrouding issues in a 383(never tried). But we are probably talking B1 or Indy heads anyway.
Tom

 

I just don't see a real reason to use a 383 over a 400, unless you for some reason can't get a 400. There is virtually no reciprocating weight penalty, and there is a 17 cubic inch advantage to the 400. Additionally, the displacement difference is all bore, which helps unshroud the valves. The only POSSIBLE downside I can see to a 400 is that maybe the bigger bore would tend to cause detonation. I've read somewhere several times that bores bigger than some point are impractical for heavy turbocharging because as the bore grows, so does the tendency for preignition. Don't know how or why, but that's what I've heard. It may well be though that this does not happen until you're beyond the bore capabilities of a stock 400 block.