AM2

Well hello forum. I am buying an LS1 to eventually be dropped into an FD RX7 after it is built. But i had a few Q's about the engine.

Since this is going to be a turbo application i would like to be able to rev the engine upwards of 8K maybe even 9K. the reason being making the most out of pump gas that i can (93 oct) with 16-19 lbs of boost. more overall useable power ON THE TRACK. barely on the street.....if at all. plenty of gear.
i understand this engine does not have an overhead cam(s) so rotating weight will be a factor. but i am not very familiar with this engine so if somebody could tell me what would be the LOWEST possible displacement fromt he 5.7L i could get..just curious.

Thank you

Drew

HumpinSS

iTrader: (1)

Prolly 302 and someone on the net has done it before. Maybe someone with better knowledge of what crank needs to be used could chime in.

DONAIMIAN

iTrader: (18)

I think the crank comes out of a 4.8 or 5.3 truck motor.

Lostpatrolman

iTrader: (3)

You should be able to use the crank from a gen3 4.8 liter engine. The stroke of the 4.8 is 3.27", stock stroke is 3.622". With this crank and stock bore you would come out with somewhere around a 312. The 5.3L engine uses the same crank as ls1.

LSs1Power

iTrader: (5)

If u found a 3.200 stroke you can get a 306CiD LS1 with the stock Bore of 3.622. Going to 8K or even 9K in a V8 will require a stout top end too. U might want to get forged pistons and rods too. I never heard of anyone taking their LS1 to 8k yet. If you are going to turbocharge the LS1 then u dont need to take it that high since u will have full boost around 3K RPM with a T76. U can take the 346CID to 7200RPM or so with no problems, but again u will need to change pushrods, springs, ti retainers, and valves to do so safely. Also the choice of the Cam will be really important to hold the power you want to redline. Good luck.

Lostpatrolman

iTrader: (3)

ls1power. Stock stroke is 3.622, stock bore is almost 3.9. Where would you find a 3.2" stroke crank? Can you use cranks from the old SB chevys?

LSs1Power

iTrader: (5)

I know that the stroke is 3.622 and the bore is almost 3.900. That is why i said u will have to find a smaller stroke than thr 4.8 engine to get a 306. I'm sure u can find a custom made stroke. Because i remember than GM did make a 302CID LS1 and they must have used a smaller stroke than the 4.8 engines. They had to use a 3.165 stroke with the stock bore to get a perfect 302CID engine. Thats why i was assuming u can find such a small stroke out there. I'm not sure of the SBC cranks will fit the LS1.

AM2

man you guys respond QUICK! thanks

302ci would be doable.

turbo yeah i know it would be full boost at 3K but holding 16 lbs to 8K is what i am after. not holding 16lbs to 6K...you get me? i would have a much broader flat curve with more usable power up top. say 4-8K is 600+hp flat...thats what im after. i will most likely be running far less boost than that but that is MAX.

im sure a stock bore/stroke LS1 can be made to spin that high...but for how long?

most of the time the engine will be at the top of its powerband whatever that may be. i would just pfrefer to have a longer powerband than 4-6K i would rather have 4-8K and i know i will have no probs making any amount of power i want with either setup. hehe....i was actually hoping you guys would tell me 4.8 or maybe just maybe even a 4.5 but that is impossible with the ls1 right?

thanks everybody!

Drew

LSs1Power

iTrader: (5)

The 4.8 crank will work with the LS1 engine, but that would put u around 312-314CID. I think its the cheapest route to go to because u dont have to look for a 3.165 stroke. Good luck.

Lostpatrolman

iTrader: (3)

If you can use the old SB chevy cranks then you can go with some crazy small strokes, Im just not sure if you can. I know the bore spacing is the same. Just wait, Im sure someone will be on soon that can help you out more.

AM2

thanks man.....do you happen to have any email address's of people who have don it or web sites i can take a look at these parts and give the specs to my mech.

AM2

thanks lostpatrolman,

thats what im looking for i believe. crazy small strokes.

marc_w

I'd just like to bring to the table P/V issues with the smaller stroke, and larger cam durations needed to spin that high and still make power...

Would simple fly cutting, cut it?

Lostpatrolman

iTrader: (3)

I dont really see how p/v would be too much of an issue as long as it isnt high compression. Since the motor is going to be built for a turho, compression should be down low anyways.

marc_w

That's true - I was 'looking' at it wrong.

I'm thinking the pistons won't "get out of the way" quick enough, when they won't be up as high to begin with.

AM2

just fyi.... the engine is going to be a completly forged rotating assembly, i dont know what heads yet...and compression......maybe (just throwing out numbers) 8 or 8.5:1 of course this is just speculation.

all i know is will be Forged.

Rokko

iTrader: (2)

You cannot use the old school SB cranks in the LS1. If you want a crazy small stroke your best bet would be to use a 4.8 and have it welded up and re ground to whatever stroke you want.

The chevy 302 of old had a 4" bore and a 3" stroke. Which was made out of a small journal 350/327 block and 283 crank.

DONAIMIAN

iTrader: (18)

What about an off set ground crank.

XIII

Read this thread

https://ls1tech.com/forums/showthrea...t=piston+speed

This was posted recently. It has a lot of good information. There are a lot of very knowledgeable people in it who have done a lot of R&D.

Grant B

I don't get it

If you decrease the displacement, you will hurt spool and therefore your powerband will shift upwards. Also, forces on the rotating assembly rise with the square of RPM. These forces are almost always greater than the forces from combustion. So if you cut the stroke in half, no way can you double the RPMs, it would be more like you could rev 41% higher.

I just can't think of any good reason why anyone would want to do this?? Its not like the rod/stroke ratio on a stock LS1 is that bad, I think its 1.68:1.

Some people like to say that RPM stands for Ruins Peoples Motors. Without any detonation more boost and less RPM is usually better for the bottom end than less boost and more RPM. Of course the stock LS1 rings and head don't work too well with high cylinder pressures from high boost, but thats another story...

Then you've got more valvetrain wear to worry about at 8000 rpm.