blu00rdstr

I'm searching for 'off the shelf' forged pistons for a 4.125" bore which would work with my existing 3.622" stock crank and 6.125" rods. Does such an animal exist, or are my options custom pistons or going to a 6L crank?

Also, would a 6.0L crank work for an LS1 motor, and would 6.125" rods work with that?

Jason99T/A

iTrader: (21)

6.0l crank has the same stroke as a 5.7l. They are nearly identical cranks, other than being balanced for a different bobweight from the factory and not being gun drilled , which makes them a bit heavier.

Diamond at one time made an off-the-shelf piston in that configuration. Not sure if they do anymore as that is not as popular of a setup as it once was.

Jason

blu00rdstr

Ah, got it. I didn't know the 5.7 and 6.0 cranks were both 3.622.

I'll check diamondracing.net again, maybe I can special order from them.

Thanks!

98RedZone

iTrader: (1)

Just curious, what kind of block are you using?

blu00rdstr

A Katech sleeved LS1.

blu00rdstr

So, considering bore/stroke, I wonder if there's a benefit to go further oversquare with a 4.8L crank? I'm kinda thinking outloud, but I have WCCHR/A&A Stg 3 LS1 heads (and a D1SC) which may not be big enough for 388ci. I'm considering going from D1SC to P1SC1 and replacing long tubes with shortys to make it smog legal in CA (don't want the car crushed by some overzealous state socialist-ecowarrior globalwarming-religion LEO).

This is a second shot at a long-ago motor replacement, so I'm not excited about spending too much. I scored big time since I got the new Katech block/studs/main caps for near the price of a new LS1/LS6 block. I wonder if I can dig up a used 4.8L crank and avoid having to go the L92 head L72 intake route to make it run 'right'.

DONAIMIAN

iTrader: (18)

If you were to throw a 4.8 crank in there along with LS7 heads and intake, that would be a bad *** little motor. No replacement for displacement, but I sure love RPM....even tho it kills ****, lol.

blu00rdstr

Those high-rev'g imports have about a 3.5" stroke. But our valvetrain is pretty heavy, wouldn't that limit revs more than the reciprocating mass?

I've heard Morel and Cadillac racing lifters would help reduce lifter weight, and Scorpion rockers and hollow valves would help also.

SLED28

iTrader: (7)

I can get you those 4.125 pistons for the stock stroke and 6.125 rods. They are off the shelf and in stock. PM me for cost.

98RedZone

iTrader: (1)

According to my calculations that would be 349 ci with the 83 mm stroke. Pretty interesting combo.

SLED28

iTrader: (7)

A 4.125 bore and 3.622 stroke is a 388.

blu00rdstr

Ah, looked at your site. How would you compare your 388ci motor to your 383ci? I would suppose the 383ci is a torquer, and the 388ci revs like a stock 347ci but with more power.

SLED28

iTrader: (7)

Yes you hit it on the head pretty much. I like the big bore stuff personaly.

98RedZone

iTrader: (1)

The 349 was with the 83mm 4.8 crank.

blu00rdstr

You're correct, 4.125 x 3.26 is about 349ci.

I'm wondering if there's any advantage to keeping the ci down (besides not having to upgrade the heads), and making it rev easier. I read there was an engine builder who built his motors to hit redline faster with a given load instead of peak power, and the cars that used his motors were faster than cars with higher peak HP. That might partially explain how cars with head/cam and lower HP often have quicker 1/4mi times than high HP FI motor cars (FI belt drag may slow how fast the motor can rev). Maybe a smaller crank would rev faster.

Edit: Oh dammit, just realized the LS1 cylinder head combustion chamber wasn't designed for a 4.125" bore. The deep side of the chamber will have a 1/8" ledge into the bore. I wonder if this will be a problem.

crazyfokker

iTrader: (2)

If you want a 4.8 crank I have a good one ill sell you. Let me know!

blu00rdstr

Thanks! I'll do some research first to see if it's a good idea, and what piston/rod I'd end up with. Don't know if the 6.125" would work with a custom piston, the total length would need to be .362" longer. But I would like a taller top ring down piston.

98RedZone

iTrader: (1)

I think the 388 with some L92 heads/L76 Intake would be cool.

blu00rdstr

I've browsed the web for destroking experiences, and it looks like the only valid reason to do so is to stay within racing rules for a certain class.

In addition, I would need 6.487" or 6.462" rods, and the closest off the shelf rods are 6.3" or 6.56" (about $625/set). I'd like to reuse the rods I have, so I think I'll stick with the 388ci.

L92 heads would be cool, except that it'd cost about $2,200 to convert (http://www.slponline.com/coming_soon_12292.asp).