LS7 bore limits...
Thread Starter
Joined: Sep 2004
Posts: 3,212
Likes: 1,612
From: Michigan & Florida
LS7 bore limits... I know the OEM LS7 sleeves are brittle and thin. I realize a lot of guys don't want to bore them. All this said, is there such a thing as a safe overbore size? I'm wondering if a .005" oversize hone job, with new oversize pistons would be OK? I'm thinking it would be, but would like to hear from guys who've done it, good or bad. Thank you......
Yes, 5 over is considered within the safe margin for stock-mild builds.
However, its also known you probably wont get perfectly round cyl numbers. The ls7 blocks/sleeves just move around too much to hold tight numbers.
Which as you know, means (potentially) more blowby. ultimately it’s up to you to decide your tolerance for larger tolerances.
However, its also known you probably wont get perfectly round cyl numbers. The ls7 blocks/sleeves just move around too much to hold tight numbers.
Which as you know, means (potentially) more blowby. ultimately it’s up to you to decide your tolerance for larger tolerances.
.005 is .0025 off the wall. It’s not much, but the LS7 has very thin walls to start with. Mike, I don’t see .005 affecting anything unless the cylinder has a lot of taper or is badly out of round (OOR). I’ve not seen the LS7 sleeves move around anymore than any other sleeved block. It’s why Steve at RED uses red loctite behind his. Ernie Elliott here in town uses green loctite, but admits they are all gonna move in an aluminum block application. The aluminum block deck grows a bit more than the sleeve does, so there is room to move unfortunately. I’ve talked with Cometic about addressing this with gaskets built for aluminum sleeved blocks, that help hold the sleeve down. Cometic just released a new DST headgasket that hopefully addresses this issue. I’m not saying I helped with the design, but I talked with Stephen at length about helping us out with sleeve movement at big power levels. I haven’t seen any money yet, so I doubt it was my idea…LOLOLZZZZ.
I had a nightmare of a time trying to get round cylinders with a .005” over hone on my ls7. Everyone told me to just send it, and the engine did well enough on the dyno. I think partly why we see such outperformance with SBE LS7’s is due to the OEM machine work and ring seal.
A successful engine builder out west went to either 4.15 or 4.155 with a boring bar and a very light hone to set the surface finish for his drag race engine and has had great luck with it. He said the larger cut with the boring bar was easier to keep round than trying to over hone.
Sounds extreme for a stock ls7 sleeve, but can’t argue with the results. 780hp hydraulic roller and 5.60’s in a winning shoebox nova.
If I were to do another ls7 block I’d work with my machinist to tell me what the minimum cut is they can do with a boring machine, and build it to the next closest shelf piston size. Done with trying to hone these aluminum blocks.
I’ve also seen a shop on YouTube take ls3 blocks to 4.125” and run destroked 4.8 crank for a badass 350” build.
It’s scary to push the boundaries when it costs so much $$$ but sometimes there are better options than the status quo.
A successful engine builder out west went to either 4.15 or 4.155 with a boring bar and a very light hone to set the surface finish for his drag race engine and has had great luck with it. He said the larger cut with the boring bar was easier to keep round than trying to over hone.
Sounds extreme for a stock ls7 sleeve, but can’t argue with the results. 780hp hydraulic roller and 5.60’s in a winning shoebox nova.
If I were to do another ls7 block I’d work with my machinist to tell me what the minimum cut is they can do with a boring machine, and build it to the next closest shelf piston size. Done with trying to hone these aluminum blocks.
I’ve also seen a shop on YouTube take ls3 blocks to 4.125” and run destroked 4.8 crank for a badass 350” build.
It’s scary to push the boundaries when it costs so much $$$ but sometimes there are better options than the status quo.
The best thing you can do with the LS7 block is to have it re-sleeved with Darton sleeves. That’s what I did with Darths shortblock. It will go out to 4.190 without a complaint and have a dead nuts round cylinder. It doesn’t get talked about much around here, but you can EASILY find 40-50hp in cylinder prep for max effort builds.
The best thing you can do with the LS7 block is to have it re-sleeved with Darton sleeves. That’s what I did with Darths shortblock. It will go out to 4.190 without a complaint and have a dead nuts round cylinder. It doesn’t get talked about much around here, but you can EASILY find 40-50hp in cylinder prep for max effort builds.
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Steve has sleeved them for me, along with LS2’s, LS3’s, and plenty of LC9 5.3’s. He prefers the LC9 over them all, but he will do the LS7. Darths was an LS7R…pretty rare block with solid bulkheads like the LC9. Steve was pretty excited to see that block show up.
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Verdad Gallardo If I remember right, Steve won't sleeve any damaged block. In other words, if the sleeve is damaged and it damaged the alum behind it, that's a no go. He would sleeve a cracked sleeve block if the alum behind it survived, but it's a crap shoot.
4.140" is the max. bore on stock LS7 sleeves. This would be for a stock engine not one that is modified for more power.
__________________
Steve Demirjian
Race Engine Development
Oceanside, Ca.
760-630-0450
web: www.raceenginedevelopment.com/
e-mail: race-engine-development@***.net
Steve Demirjian
Race Engine Development
Oceanside, Ca.
760-630-0450
web: www.raceenginedevelopment.com/
e-mail: race-engine-development@***.net
Up until around five years ago I had good success welding up cracked bores to save the LS7 block. Some blocks had two cracks in a bore 2+ inches long. However as the blocks age they become more and more brittle. Weld it up and it will most likely crack elsewhere in the bore on cool down. Pre heat, post heat, vibratory stress relieve on cool down with the same result. Worse the block cracks after I install the sleeves. The sleeves aren't coming out at that point so I lose a day's work and half a set of sleeves. I gave up. On top of that shipping charges usually $500 to me is lost if the block can't be saved. Not worth the effort any longer. I've gone to replacing them with sleeved LC9 blocks which are a stronger casting to begin with. Non cracked LS7 blocks I get in and sleeve no problem.
__________________
Steve Demirjian
Race Engine Development
Oceanside, Ca.
760-630-0450
web: www.raceenginedevelopment.com/
e-mail: race-engine-development@***.net
Steve Demirjian
Race Engine Development
Oceanside, Ca.
760-630-0450
web: www.raceenginedevelopment.com/
e-mail: race-engine-development@***.net
Thread Starter
Joined: Sep 2004
Posts: 3,212
Likes: 1,612
From: Michigan & Florida
Thanks for the info, guys. My LS7 is a standard bore. 2 cams (one lobe because a stock LS7 lifter body cracked, and took out the lobe), and several lifters, have failed. Other cam had a bad lobe. As a result, the lower sleeves are scored. I am amazed it's not using oil. I know from Toolroom experience that many times an I.D. looks much worse than it is. Early in my career I was very surprised how much better, if not perfect, the I.D. looked after going .005" oversize, or .0025/side, as Scott said. It does run pretty darn good, and never smokes. I just don't know if I have enough left in my tank at 72 years old to pull the motor...Again!!
Last edited by grinder11; Jan 12, 2026 at 12:07 PM.
Thanks for the info, guys. My LS7 is a standard bore. 2 cams (one lobe because a stock LS7 lifter body cracked, and took out the lobe), and several lifters, have failed. Other cam had a bad lobe. As a result, the lower sleeves are scored. I am amazed it's not using oil. I know from Toolroom experience that many times an I.D. looks much worse than it is. Early in my career I was very surprised how much better, if not perfect, the I.D. looked after going .005" oversize, or .0025/side, as Scott said. It does run pretty darn good, and never smokes. I just don't know if I have enough left in my tank at 72 years old to pull the motor...Again!!
