N2OBaby

I see alot of press about 5.3L to 383 strokers & LQ4/LQ9 bored to 370 CID.

What about a LQ4/9 block bored to 4.03 with forged rods & low compression(8.7-9.2:1CR) pistons & a 4.8L(3.26 inch stroke crank) with ported LS3 heads.

A 2.8L or 3.6L KB twin screw blower to boost TQ & HP at a sane RPM range.

What do you folks think?

parks450

iTrader: (17)

the 4.8 cant have ls3 beads they require a minimum 4" bore. Their only 3.780, personally if vo with the 6.0l (408) package if im going to spend the money.

BSmiff

Im pretty sure his post says LQ4/LQ9 block. Reading is fundamental bro. You would be able to spin that thing to the moon destroked. With forged rods, good rod bolts, and some high flowing ported LS3s, I dont see why 9000 rpm would be a problem. The TQ hit would be lower. I would rather turbo an application like that if it was going to see some rpm. A billet wheel 76mm turbo would FLY.

redtan

iTrader: (5)

He's only using the 4.8 crank, the block that he is using is a 6.0 bored out to 4.03...which while not optimal, will accept L92 heads just fine.

If you're using the block only and building it with aftermarket rotating assembly, then it doesn't really matter which of the LQ4 or LQ9 blocks you use. They are basically the same, except the 4 came with dished pistons vs. flat-tops in the 9. There are a few other differences between the gen3 vs. gen4 blocks, but it is very minimal and it's not like gen3 blocks are outdated and useless.

There's more to rpm than just what you described, valvetrain will play a HUGE role in achieving 9,000rpm. That's a very high rpm to spin an LS engine to and will require some extremely expensive and well thought out valvetrain for that to happen. And considering that he's going with a TS blower, there's absolutely no need to spin it that high.

NemeSS

iTrader: (127)

Why give up all those CI capacity? What's the reason. The shorter stroke will allow for slightly higher piston speed, but not anything to re invent the wheel, it takes a lot more than just a shorter stroke to build and maintain very high RPM. At least for it to hold together.

Nelson

i agree, take advantage of displacement.

N2OBaby

In a 2800-3100 pound car the TQ hit would be less and 9000 rpm should not be necessary with a 2.8 LC or 3.6L LC KB twin screw supercharger.

RezinTexas

do you mean to say that the shorter stroke will allow for higher RPM's while keeping the same piston speed? thanks.

noice

Yes, that should be what he means. Any of the computer engine simulators out there will show exactly what the peak pistons speeds are. One program I saw would specifically tell you if the piston speeds were too extreme and if the valve train would survive. Even would estimate if valve float would occur. Now the only way to tell for sure on valve train is a spinitron.

The original poster should just use what he can get cheap, stock LQ4 cranks are just fine. A different piston/rod combination or head selection would be able to get the compression low enough to safely make a shitload of power. Doing something unusual is cool too though.

whitedevilWS6

iTrader: (10)

I've thought about this as well. Would like to see some input from the gurus. Maybe I'll actually do it.

EDIT: I was thinking about a rev-happy high compression N/A motor, not boost

mark21742

12.5:1 compression 408 here and I spin it to 8,000 rpms

JS01

iTrader: (10)

Destroking for RPM in this application is silly. You can turn a 4.00" crank 9000rpm. You are just giving up both avg and peak power by destroking. The piston speed of a 4.00" stroke is manageable and has been done for years. All the top all motor LSX shootout cars have 4.00" cranks (Although they are all probably CCW billet pieces). Like was already stated the most critical thing that demands attention is the valvetrain.

Big bore AND big stroke, have your cake and eat it too!