SS101

iTrader: (2)

goals:
1. 700-800rwhp
2. 80% street and 20% road race car
3. as light weight as possible (iron block is too heavy, must remain aluminum - i know that this will limit my displacement choices and i can live with that. also, resleeving is kind of hit or miss so i dont want to mess around with that)
4. high compression, ~10:1 (i do lots of long distance driving and i'll sacrifice a few psi for better driveability and to save on gas in the long run)

sanity check:
i WAS going to go with a forged 347, but for the money i can just as easily go with a forged 383 and keep my aluminum block. now there's not a whole ton of info but from what i can see, a 383 has about the same power potential as a 347 but will make more torque across the board. this is ideal for me because torque is the name of the game in road racing where i'll be spending all of my time in the mid-range RPM band...besides, i'm limited on the max power by my trans and clutch.

so...is this true about 383's? same-ish power as a 347 but more torque?

btw, this is in the FI section because i'll be slapping twins on the motor no matter what the displacement is...but thats for a different post

thanks for any input! i really appreciate any help you can lend!

ss.slp.ls1

iTrader: (36)

I'm no expert, but seems like you'll need a lot of psi of boost to make 700+ rwhp on a 383. That paired with the fact that you are unwilling to go below 10:1 CR means that you will have to spray meth or run e85 or race gas.

Couple of questions. Why do you thing that a lower compression motor will run like a dog off of boost? What do you think an iron block weighs? The LQ4/9 blocks only weigh 88lbs more than a LS1 block. And if it's a 80% street car, that 88lbs won't matter much...

You could always build a 402 LS2...that's aluminum.

If you keep your current block and go with a forged rotating assembly, definetly go with a 383 over a 347. About the same cost but the additional cubes will help you reach your goals more easily.

quicksilverado

iTrader: (8)

A 383 will reach your goal in the area of 12 psi. You can achieve the same power level with a 347 at about 15 psi. Small twins will give you instant boost. If you are on a road coarse the tq may hit so hard that it will be difficult to control and keep traction. 10-1 cr will be fine as long as you are using the correct cam.

3.8redbird

iTrader: (3)

and a dead on tune

98Z28CobraKiller

iTrader: (17)

Build a stock stroke LS2 6L or stock stroke LS3/L92 6.2L. Save the $1k on the forged crank. You wont need it. Throw a couple 67mm's on and you're there with room to make more easily. Probably only really need 60's. The smaller they are the faster they spool. I'm not a road racer but this should be more than enough torque. Maybe too much.

SS101

iTrader: (2)

88lbs is actually more than i thought it would be...i was thinking around 70lbs. with a full weight street car i'm trying to cut the fat anywhere i can, ~90lbs is just more than i'm willing to go. additionally, i like the better heat transfer aluminum offers - road racing makes it hot!!!

its not that it will necessarily be a dog out of boost...i know that these motors get pretty doggy below 9:1, but the trade off in throttle response on the track and lower efficiency on the street just leave a bad taste in my mouth. i may go as low as 9.5:1, but i'd like to avoid it.

as far as tuning i want to go speed density with a 2bar map and for a cam im just going to call VA speed

KILLER-LS1

iTrader: (18)

my new motor is 9.5:1 compression. with the added power from the larger displacement engine, my motor has more low end power than the sock 346, even while out of boost. i would at least try to get around 9.5:1

KILLER-LS1

iTrader: (18)

also, the tune (timing etc), & cam/manifold/head choice can effect your off-boost response as well

ttranssam

iTrader: (10)

if its the cooling factor your after, darton sleeves are friggen wicked...im having my motor built and he showed me a darton sleeved block...1900 for em...they directly move the coolant around the sleeve for like a 45% cooler running bore, there perfect for road racing. if you look at a stock block there is almost an inch of aluminum between the cylinder and sleeve, with dartons its like a 1/8 inch. now seeing it looks like we have some deep pockets add a forged rotating assembly and your twins and you will be good for around 1000 fwhp.

couple months back gmhp did a artical on some dude from purto rico, he built a forged 347 with twin mp70's and made 1032 rwhp on 106 and 800ish on pump...its doable but you gotta dump the 10.1 CR thats nuts his was 9.1. also with this kinda power torq will be kill you, ITS GOING TO BE NUTS for road racing...and the weight....dude that will not evin be a factor with that power. id say worry more about a 50/50 weight distrubutation...

ttranssam

iTrader: (10)

BTW....no you are insane....500hp is almost too much for road racing and is there evin a class for that kinda power?

elias_799

iTrader: (8)

what do you mean by allot of boost ?
10-13 psi ?

SS101

iTrader: (2)

as far as a class? i dont think so, its mostly for open track days and general road racing fun...i just really dont enjoy drag racing. its not thats its not fun or anything but if i'm gonna drop 20k on my car i want to race for more than a few seconds at at time lol.

fwiw, to me anyway, i'd rather have way too much power than too little.

for a 383 do you think well ported ls6 would be okay or do i need to step up to some AFRs or trickflows etc?

crf538

iTrader: (3)

this sounds like the best idea to me, remember bigger turbos will will help keep IAT's down a bit

davemaro98

go with the 383, tons of torque, my dad had a 1996 z28 bored to a 383 with lts and intake and that ****** was fast, but then again im not sure bout the torque figures on the 347, good luck man.