Brutus

Guys I would really welcome your thoughts on this. I need to build myself a forged bottom end. This is for a Vortech blower up to 15psi of boost. I have been toying between a 383 or LS2 402 (I would rather a aluminum block). What I really want to know is what advantages there are in my paying the extra for the LS2 402 + LS1-LS2 conversion kit over an LS1 based 383.

Any thoughts greatly appreciated.

THE LAST Z

iTrader: (5)

Ive thought about this too...
I guess once you come into boost it really doesent matter. Ive noticed with boost, other things make little difference like cam, intake, C.I., heads,... I would do a 383 LS1 block.

james562

iTrader: (35)

A 383 LS1 and a 408 LQ4/9 would cost roughly the same and the 4.0XX Bore of the 402/408 will open up alot better head selections and make more power/torque over the 383 all throughout the rpm range.

MelScrilla

iTrader: (2)

That is a good point, but I would think that with a centri blower the heads available for the LS1 bore would be enough since it would be under pressure from the blower. Kinda like when people use stock 317 heads and make 800hp.

Point being that on a street driven FI car where budget is a concern, the difference in head choice between a 3.9" bore and a 4" bore wouldn't be much of a concern. If the OP is going to be entering a class and heads up racing his car then head choice is important but on a non max effort car I would think some AFR 205's, TFS 215's, or even cnc 317's would be more than enough to support what the OP is looking for.

I think the head choice is more important when you are building a N/A engine or building an all out race engine.

Any opinions on this.

TransAm2002

iTrader: (3)

383 is the way to go.

Boo"SS"t

iTrader: (2)

You're better off with 402/LS2 if budget allows, a 383/LS1 on 15lbs of boost would be pushing those thinner cylinder walls closer to it's limits. There's a reason why you don't see alot of guys here going 383 on LS1's for forced induction application.

TheFallen

how about a 383 iron block?

Brutus

That is exactly what I needed to hear. I think that plus the larger bore size should be enough to justify the additional money. I really wanted to make sure I was missing anything too fundamental.

Lastly, I assume with the correct conversion kit the LS2 into LS1 swap is relatively painless?

stevieturbo

The 383 can work just fine. I used it for long enough. BUt....if anything at all happens, the block is at the end of its life.

At least with a base LS2 block...there is room for repair or to grow a little. And the LS2 block is the better platform.
The extra cubes arent really needed, but will certainly do no harm to have them as well.

And I think I'd be right in saying that the LS2 platform now, would offer more plentiful parts as the LS1/6 gets older ?

That said...if you already had an LS1/6 block with a good standard bore and budget was tight. Maybe I would stick with my existing block, and bore size, and do a 382. That would still leave a little room for error.

98Z28CobraKiller

iTrader: (17)

I preffer less stroke and more bore. I would never build a 383. You can build a forged LS2 370ci with a stock crank for the same amount and it would hold up WAY better than your other 2 options. Plus open the door for all the premium head options.

THE LAST Z

iTrader: (5)

A 370 iron would be great if you dont care about the extra weight. Thats the Speed inc. "Boost" short block. Great price...

bandito

I heard that there is a piston problem with 383's Im not sure it helps any but isnt bigger cubes the way to go? I would more potential.

Aster

iTrader: (9)

Can you elaborate on this piston problem you’ve heard about for 383’s Bandito? I’m using a forged 383 right now and just recently got the blower back on it.

stevieturbo

No problems with my old 383 pistons....until I melted them

2001WS6Vert

I like the shorter head studs that the LS2's use. I feel it holds the heads down better.

stevieturbo

Length of stud is not an issue. Securing a stud at the top of the block deck however, is an issue. Thats why GM tried to get most of the studs down to the base of the cylinder, so less cylinder distortion would occur when they are tightened.

long studs secured at the base of the block is the best way.

IT_SS

iTrader: (5)

It's just honed cylinders, no sleeves are harmed in the process....

2001WS6Vert

As far as lifting heads I feel a shorter stud would be a better way to go because it would be less susceptible to a stud flexing and would do a better job at holding the head in place. For that reason and probably others it is probably why they made that change to the later blocks. As far as I have seen on the all out builds the LS2's are able to outperform the LS1's, ie Koehler, Fireball, Brown etc.

helicoil

iTrader: (104)

I like the LS2 blocks better than the LS1's, LS3/L92's 6.2's better than both. A good choice if starting from scratch. Although if you have an LS1, I'd use it, been plenty that hauled the mail.

A short stroke 370 'iron' isn't bad either if you don't mind the weight on the nose.

Bigger bores are better no question, but with boost it is somewhat of a moot point at a 'street' level. All out race, different story all together.

As mentioned a 346" with AFR 205s or TFS 215s and 12-15# would probably do 700-750RWHP no problem.

Spend the money on good thick deck heads and the supercharger set-up.

stevieturbo

Studs pulling at the top of the deck can cause the deck to distort and offer poor sealing. Thats why where possible, its always preferable to secure the stud at a lower location.