Wondering what is possible for different cubic inch displacement with a LT1. I have a 2 bolt block that is going to built for FI and I'm wondering what the pros and cons of the three different cubic inch LT1's. My first pic is to build a

1:
355 LT1 stuffed full of forged components, Eagle crank & H-beam rods, splayed billet caps front to rear, forged pistons (of course) maybe in the 8.8 to 9.0 CR range ?

2:
389 LT1 (same basic stuff) just wondering if it's possible to come up with 389 cubic inches (bore & stroke)

3:
401 LT1 (same basic stuff) and wondering what the bore & stroke would be on this CI motor.

I know that when you put alot of boost on a LT1 it is better to stick with the smaller cube motor, but I'm just exploring the possible differences before I start on the block. The 355 LT1 would probably be running a S80 Airwerks Turbo, If I did the 389 probably a S80/S85, If I did the 401 probably a S85/S88.

I'm just not sure on the big cube motors if the LT1 block will handle the big power even if it's built right. Obviously there will have to be some block fill involved with this project

Maybe you guys can help me out a little bit and start pointing me in the right direction. Most everything I'm discussing in this thread are just random thoughts to get my project moving forward in a specific direction. Thanks for any help in advance

 

JMO, if you go with any of the "S" series turbos, I go with some cubes to help with the spool.

 

FYI my 388.3 cid LT1 is 4.060" x 3.75".

Smaller cubes have more power potential on most turbo combo's, but you have to run the boost way up past 20 psi to realize this potential.

I have never regretted adding cubes, but it could cause some durability problems in some cases.

Mike

 

Engineer Mike,
Thanks for the Bore X Stroke info. The only reason I was trying to see if I could come up with 389 CI because its a pontiac and I thought that would be kind of cool to have the same CI as their old school motor. I know if I use 355 CI I will definitely be in the 20 psi range to make the S80 pound out the big numbers. I was thinking the 389 will bring down my max psi and obtain my numbers under less stress. I'm assuming a S80 should put down 750 ish on any of the CI's that are being discussed, but different issues come up depending which one I decide on (355ci, 389ci, 401ci LTx)

 

You also need to consder the cost/convenience of off-the-shelf components. My favorite blower LT1 is a "379": 10 over (4.010") bore for maximum cylinder thickness, 3.75" stroke with 5.7" rods. This requires custom pistons though. So a 383 is probably the best way to go for most people.

Rod length is debated much more than it deserves, BTW. But on a blower SBC if do prefer the short rod because of the potential slight advantage in terms of detonation resistance as well as leaving plenty of room for the rink package. A deep top ring land in a necessity for a blower motor, IMHO.

Rich

 

Cost is a definite factor to consider in this build. I will spend good money to get what I want, but I don't want to have a CI that is so exotic that it will start making the project cost prohibitive. I really like the idea of a 355 or even the 383 as suggested by you. Especially, when doing the S80 I think the extra cubes would probably help the spool a little bit. I'm wondering how I approach the block fill situation. The car will mostly live on the street, so I don't wants to create a situation where the car constantly want to overheat from daily driving duty. I've done some research on how much block fill I should put in a LT block, but no-one seems to agree on the amount the block should be filled (IE: 1/4, 1/2, 3/4 block filled ?). I would appreciate some input on this subject pertaining to LT1 blocks.