messix

the reason is that i have a very light car and a trans axle that is limited in torque capacity.

why 312? well i have a line on a ls1 5.7 and a 4.8 short block. the 5.7 has a questionable lower end. so for cheap i think i could put together a rev happy 312 ci that will put out really good power.

so has any one done this yet?

usnfenix

iTrader: (11)

5.7 questionable low end? have you ever worked with the 5.7 or and of the LSX motors? the low end is very good in stock form and will only get better with mods. and no ive never heard of a 312 cid ls based motor.

messix

questionable as in needs new crank and rods from spun bearings and the 4.8 has a good crank and rod set.

usnfenix

iTrader: (11)

again thats not that common. yea it happens but no more so than any other motor. all my time with ls1's and friends with ls'1s ive seen it once. the stock crank in the ls1 is plenty fine most of us here keep it even past 700hp.

i think your getting bad info on lsx motors from someone lol

messix

i think you've missed the key point.....

i will be building a 312 ci motor from a 4.8 crank and rod set using a ls1 block and pistons to get a engine with the characteristics of power higher in the rev range and lower torque than a ls1 configuration.

i am NOT questioning the soundness of the ls1 lower end but stating that in this ls1 that i have an option to pick up, it has a known fault as in a spun rod bearing and the mains show undesirable wear and will need machining of the crank and rods to make servicable again.

bww3588

iTrader: (49)

Should be a stout combo. Just pay close attention to the sleeves in the ls1 block. If they are scored beyond a .003-.007 clean up hone (depending on year) the block is basically junk unless you can get it sleeved for cheap.

jimmyblue

iTrader: (11)

I think I'd be pulling the crank before believing the
spun bearings story. Rods don't care about bearings,
the wear face is at the crank. And I'd be surprised if
more than one "spun", unless the thing ran completely
dry.

I've never had a spun bearing in any of my 20+ cars
including the 4 or so motors I have personally rebuilt.
I don't know how people manage it.

The 5.7 will be plenty rev-happy with a cam swap,
and ought to be marginally lighter than the 4.8 iron
block I expect.

messix

the motor is apart and spun rod bearing is confirmed, a rod does "care" when the bearing is spun in the rod big end [kinda ruins the machined surface] so the crank needs a grind and a new rod if i went with the 5.7 crank and rods.

again i would only be using the "crank and rods" from the 4.8!

i know i'm new here but i'm kinda dismayed here with the lack of responses from knowledgeable people.

granted most of you guys are pushing around 3,300 - 4,000 pound boats and need all the torque you can get...... but i'm dropping this in to just 2,200 car with the engine in it. monster torque is not what i need!

87gnx

iTrader: (3)

That combo isn't a popular choice. Some older members have posted, sorry that nobody has the plethora of knowledge you demand.You were VERY vague on what kind of vehicle the motor was going in. G/L NOOB

murphinator

iTrader: (2)

interesting idea... like a modern day ls version of a dz 302.

sounds like you have all the parts to make it happen , do it and let us know how it works out for you