LT1CST

Hello.
Just wondering which motor was better. MY buddy up the street has a very very nice 400 sbc in his nova with a Demon Carb 750CFM and one of those windie gear drives. Took me around the corner and its hellafied fast. About 6 months ago I took my LT1 and stroke it out to a 385ci and sold it like an idiot because im sick and tired of EFI. So just wondering what you yall thought. Im leaning towards the 400sbc to go in my 4th gen fbod. Im just worried about how everything would line up as far as motor mounts etc.., People always say if im going carbed then ditch the LT1, well thats what im doing. If I did stay with the 350 and stroke it what 350 motor year and model should I pick? Thanks in advance.
Chris

angel71rs

400 block will slip right in place of a gen I 350, can reuse same mounts. Think it's the same for LT1s, but not sure.

Issues specific to the 400 block: on the 4 bolt main blocks, some bolt holes are said to weaken the main webbing area, can lead to cracks. So the 2 bolts are more sought after. Some get converted to 4 bolt aftermarket splayed caps for high hp applications. That said, I've known guys that ran factory 4 bolt blocks in street/strip cars without issue. 2 bolt casting #509 blocks are said to be the best production blocks.

400 blocks bored more than .030 have a rep for running hot, some guys use block fill for > .030 bores, ok for strip, not recommended for street. .030 is fine, mine doesn't run hot at 30 over, even with just a 3 row radiator for a 75.

Your LT1 has reverse cooling, so you'd need to work out cooling setup with a gen I SBC.

The 4 bolt 350s don't have issue of bolt holes going into webbing, better than the 2 bolts, unless the 2 bolts get converted to aftermarket splayed 4 bolt caps. Never heard of any particular 350 block being much better, other than the rumoured "higher nickel" content of 010 casting # blocks used from 69 thru mid 70s. Supposed to make block stronger. Be aware that early 350s have 2 piece rear main seals, mid 80s up have one piece seal, can't mix n match cranks.

That said, I'd go LSx for your 4th gen, maybe LQ4/9 out of a truck/suv. Bunch of those engines available in wrecking yards in good condition, ready to run. Good 400 blocks are getting hard to find. Took me months to locate a block in good condition that would clean up at 30 over. And that was back in 02, probably worse now.

317 heads that come on a lot of 6 liter truck motors flow as good or better in stock form than some aftermarket heads for SBCs. They are basically LS6 heads with larger chambers. And you can buy worked LS6 heads from a variety of vendors for very reasonable $ that have great flow numbers and a smaller chamber if you want to kick up compression. Or worked 317s if you want to stay around 9-1 (LQ4 pistons) or 10-1 (LQ9 pistons). For a SBC, you'd need $$$ aftermarket heads to match/beat worked LS6/317 flow numbers, like AFRs.

You could throw a stroker kit in a 6 liter block for 402/408 cubes, but plenty of guys are making good hp with just heads/cam on factory short blocks. Like this: http://www.ls1tech.com/forums/dynamo...o-numbers.html

Last, you can carb LSx engines if you really want to get away from efi.

LT1CST

Very good information Thank you.
Chris

AlwaysCode390

I heard carbed lt1's are actually strong. Roller blocks are definately a plus ---

LT1CST

Yeah I thought about doing that Carbing an LT1. I have had several posts on that subject. But Ive Always herd that if I were to go to a carb. To go with a Traditional 350 or 400 block.
Chris

Stupified85

the only problem with the 400 sb is that thye are hard to find and the walls are oh so thin...i know im a little late on this thread but i just joined as i just finished my 85 z28, dart now makes a 400sb that is able to be bored .080 safely. the carbed lt1 i dont know much about but i cannot stand the lt1 i think it was a horrible idea and i think the motor is junk. in my oppinion

as for your question on which 350 to pick up...any 350 from a truck with a 4 bolt main. as for stroking. i think that is completely unnecessary.

i have a 3.08 austrilain 9 bolt chevy rear and a 350 hooked up to a 5 speed borg and warner. i am pushing well over 430 and its plenty of power, i ran a 13.1 at 112 with a 3.08 rear and some old d.r. with a 3.73 id run well into the low 12's maybe 11's
good luck with your build man choose wisley

LT1CST

Stupified. I would have to agree with you somewhat on the LT1 commet. Yes the motor isn' all that great. Im upset that the opti is right under the waterpump. God knows that LT1 owners have had their share of of opti's that went out on them. However I think the motor is somewhat stout and I enjoyed it (WHEN IT WAS RUNNING) It pisses me off with EFI cars. WHEN ONE SENSOR GOES BAD. The whole world was gonna end. I built an 385 stroker (specs in th sig) Could not get that motor dialed in because of all of the EFI crap, OH well thats the past. Thanks for the information. Im leaning towards Big Block soon.
Chris