Biggest bore you should go with... with F/I

[ZGOBYBY]

Well, I am back from the Shootout, and needless to say, I have new plans with the LT1 short block I have sitting in my garage. What is the biggest bore you would recommend going on an LT1 block with a turbo (GT60 rear mount)? I was thinking .30 with a 3.8 stroke would be safe to give me a 388. Any ideas or suggestions? I am going to get cracking on this in the close of fall. Right now my motor is completely stock, and I want to go the biggest I can with my turbo. Thanks.

[QC97Z]

More than .030" is going to be pretty thin, especially for F/I, but it depends on how much boost you plan to run, what your compression ratio will be, what your RWHP goals are.
I've never heard of a 3.8" stroke. The only strokes I've heard of for LT1's is 3.75" and 3.875".

4.030" bore X 3.75" stroke = 383 CI
4.030" bore X 3.875" stroke = 396 CI

The extra clearancing for the 396's stroke can be a PITA, and a further weak point in the block if not done right.
If I were you, going boosted, a well-built 383 with a good set of heads will get you far.

My setup:
Forged eagle bottom end, SRP pistons. 9:1 CR ---- 383 CI
AFR 210 "Eliminator" style heads, comp. CNC ported
219/230 .565/.565 cam, 114 LSA
LT4 "Air-Gap" intake manifold
58mm TB
McLeod street twin, Moser 12 bolt w/3.90 gear
Procharger F1A, 15 PSI boost

Made 648 RWHP at 6500 rpm, 585 torque.

If your power goals aren't as big or you don't want to boost as much, you could start at a higher compression ratio, like 9.3-9.5:1.
A forged Eagle bottom end isn't all that pricey, and if it's good enough for mine, it will be good enough for yours (provided your goals aren't much higher than mine).

[ZGOBYBY]

GMPP, Eagle, and a few others make 3.800 strokes, but they are not as common as the 3.75s. Wanted to go .030 with this stroke for a 388, anyone attempt this?

[Fastbird]

I would say stick with a 3.75" crank as they're more prevalent and you ahve to do less block clearancing, IF you insist on going with the stroker.

For bore.....go with the smallest overbore necessary. Leaves thicker walls and more room should something happen that requires a block touch up. LT1's aren't good for more than about a .060 overbore, so figure with a .030 you've cut half of the life out of the block in terms of rebuilding. Sure, you can get another block, but why if you already have a good one. with a .010 hone to a .030 overbore, you're only talking a couple of cubic inches displacement difference, not enough to make a major difference.

I'd focus on maximizing the efficiency of the motor. Do a stock crank, forged rods/pistons, a good set of heads, and a well matched cam to work with your setup.

[ZGOBYBY]

I would say stick with a 3.75" crank as they're more prevalent and you ahve to do less block clearancing, IF you insist on going with the stroker.

For bore.....go with the smallest overbore necessary. Leaves thicker walls and more room should something happen that requires a block touch up. LT1's aren't good for more than about a .060 overbore, so figure with a .030 you've cut half of the life out of the block in terms of rebuilding. Sure, you can get another block, but why if you already have a good one. with a .010 hone to a .030 overbore, you're only talking a couple of cubic inches displacement difference, not enough to make a major difference.

I'd focus on maximizing the efficiency of the motor. Do a stock crank, forged rods/pistons, a good set of heads, and a well matched cam to work with your setup.

Thanks for your input, Fastbird. Stock cranks really won't hold up above, let's say 500 HP, right?

[AChotrod]

I dont know of any stock crank failures. They can take a beating.

[LT1_Fireman]

^ Hey Jen the stock crank will hold a lot of power, I made 707 rwhp with a 355, good quality top end, and a d1 procharger @15 lbs.

[Fastbird]

Stock cranks are stout. They'll take a bunch of power. Stock rods on the other hand........

[CALL911]

I'm with Fastbird. Better way to make power would be the smaller bore, giving you more life. Build it well, then do lots of boost. That will WELL make up the difference the larger bore will produce.

Sounds like you are pretty set on what you want, but IMO, from what I have seen, if you want to go the turbo route, you have a lot more potential at making big reliable power by going with a front mount, instead of the rear mount (like the STS junk). Just food for thought.

[Fastbird]

Now, I will contradict myself with one thing here. I personally think that the most efficient motor for forced induction would be the largest bore you can SAFELY get away with and stay away from the longer stroke. I learned a lot from my Vette build and found that it really makes it more efficient because you have a larger cylinder filling up with air faster and more efficiently than if you used stroke and a smaller bore to get the same displacement.

[ZGOBYBY]

Now, I will contradict myself with one thing here. I personally think that the most efficient motor for forced induction would be the largest bore you can SAFELY get away with and stay away from the longer stroke. I learned a lot from my Vette build and found that it really makes it more efficient because you have a larger cylinder filling up with air faster and more efficiently than if you used stroke and a smaller bore to get the same displacement.


Hmmmm.... interesting. I will take that into account. I have STS junk, yes, I know many people aren't fond of it, I know. But it's what I have, and I'm not saying I am very fond of it either. But I am going to try to improve upon what I have now. Turbo is blowing oil now through the exhaust and through the intake, so I am gonna have to get it rebuilt or put another one on for next year. There are a couple cars out there, like Hawks584 (although I don't think he has the car anymore), that had quick, reliable STS/rear mount turbo set-ups. To me, it's all in the combination.