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I'm a bracket racer where all-out engine build efforts aren't necessary . My current 421 Gen One piece has a Dart Little M block that was chosen for durability and it has delivered . I was getting ready to build a replacement for it due to over 4 years of racing , etc and untold thousands of 1/8th mile WOT runs ... I had never really investigated the LS platform but decided to check it out before proceeding with parts collection . When I saw the flow numbers of the LS7 heads , I was sold ... my Brodix 227's are about 40cfm behind the factory LS7 and about 60cfm behind everyone's porting or aftermarket heads . I also learned that the LS7 block was not a durable piece . While the weight saving of an aluminum block is enticing , my C4 is already having some front end anti-gravity issues off the line and my machinist cautioned against the aluminum architecture from a long term reliability angle . (Too much flex and expansion) . I have decided on and purchased a Dart LS Next Pro block for my next powerplant . Meanwhile , the Gen One is still running strong and will likely stay in place until it loses it consistency or its guts .... 3360# 1.34 60's 6.50-6.60 in regular 2000'+ Florida air ... 6.40's in under 1000' DA's @103mph
I'll say this. If you already have a Dart Little M, go buy some better SBC heads/topend and run it. The SBC stuff has come a long way. If you were starting from scratch, def go LS, but since you are already invested, I would stay SBC.
The 5.3 12571048 and 12601900 are the strongest of the GM aluminum production blocks that can be dry sleeved with Darton ductile iron sleeves. These castings are the only two castings with siameesed bores. Can't dry sleeve a non siameesed block. These also have solid main bearing bulkheads, no breather holes which weaken the blocks. Breather hole blocks can crack between the breather holes and cam bearing bores when highly stressed. Weight is around 110 pounds with main caps. I don't think you would want the weight of an after market iron block in the front of a Vette. An aluminum Dart block costs more than double what it costs to sleeve a 5.3 if you can get one. Great if you are looking to make 2000 plus horsepower. I'm a Dart dealer as well. I can sleeve any make block that can be sleeved.using Darton off the shelf or custom sleeves I design for the application.
Hi Steve. I thought the LS7 was siamesed and you dry sleeved them? I realize the breathing windows do weaken it compared to the 5.3...
Yes the LS7, LS2, LS3 and variants are siameesed and can be dry sleeved. The only two 5.3 castings that are siameesed are the 12571048 and 12601900. Other castings including front wheel drive can't be dry sleeved.
Bracket race, I'd want the aluminum LS block any day over a heavy iron Dart if only making 800HP. The Dart, or any of the iron LS blocks are just plain heavy! Sleeved 5.3's are very strong and more than up to the task for a NA bracket race build. Save the weight, adjust your chassis if you have a wheelie problem.
5.3L iron truck blocks tend to be used because they are readily available and inexpensive. And the truck engines don't have any bay-to-bay breathing holes in the main webbing so there is added strength for high power applications. Downside is you don't have bay-to-bay breathing which helps with oil control & return.
That's not entirely accurate. The Gen-3 iron truck engines don't have bay-to-bay breathing. The Gen-4 iron truck engines do. I know the gen-4 aluminum car engines have bay-to-bay breathing, but I'm not sure about the truck engines. Maybe it's just the 6.2L engines that have bay-to-bay breathing, and not the 5.3L. I'm not sure on that, but I know the gen-4 iron truck engines have bay-to-bay breathing.
Just a small joke I'm no genius on LS's. And as for that ls7 sleeve still running wow that's insane I don't need Spock to speed so googling used ls7's lol
Last edited by Guy with a Chevy; Feb 7, 2023 at 12:36 PM.
I'm sure the ls7 block isn't as forgiving. BUT-This was a failed piston that damaged the block, NOT a block failure that damaged the piston.
Absolutely ... it was definitely a piston failure ... Both were ... the LS7 block will make a nice coffee table ... the Little M is making passes at the drag strip . Durability to withstand something as commonly occurring as detonation .
Out of curiosity, got a guess how large the holes are? Comparable to LS3?
The LS3 doesn't have a "hole" drilled like the iron blocks. The LS3 has half-moon shape cutouts in the saddles. I'm not certain on the size of the iron block holes. If I had to guess, I'd say between 1/2" and 7/8". If I remember, I'll measure the one I'm about to tear-down.
So, I measured the "bay-to-bay" breathing holes in the Gen-4 6.0L block that I have. I got about 1.115". It's kinda difficult getting the caliper in there, so the measurement might be a little off. Here's a few pics that I took:
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