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I recently picked up an aluminum short block 6.0 for $800. Guy told me it came out of a G8, but the pistons are dished, and have 2 valve reliefs that oppose each other. Has gen4 rods and x58 crank and everything, but I'm pretty sure L76 engines had flat tops? Could this be a truck variant? Or is it more likely that someone put cheap pistons in it for some reason? Its still stock bore...
The L76 TRUCK engine had dished pistons, 6.7cc with valve reliefs, giving a 9.7:1 CR. Car engines had flat tops, yielding a 10.4:1 ratio
The weird part is, the car engine is rated at 355HP, 384 #-ft of torque, and the truck version does 367HP, 375 #-ft.
The truck has MORE HP in spite of lower CR, which does explain the lower torque figure.
Same heads and cam. Possibly more restrictive exhaust on the car? They did put good exhausts on the trucks.
The trucks had VVT, the cars did not. Another possible reason for more truck HP
Both had AFM/DOD.
I have the L76 out of my old Max edition Sierra and it is as you described, dished pistons with valve reliefs on opposing sides. still a good foundation!
My L76 6.0 that is currently at RED did not have bay to bay windows. Steve had to drill breathing holes in the block.
I found it odd and was surprised that it didn’t have bay to bay windows, but upon some online search I found description explaining differences between car and truck L76 blocks. Same casting #, truck doesn’t have bay to bay windows. I will try to find link and share.
Reminds me of gen II LT1 blocks that all had same casting #, but only Corvette blocks had 4 bolt mains, while the rest had 2 bolt mains.
My L76 6.0 that is currently at RED did not have bay to bay windows. Steve had to drill breathing holes in the block.
I found it odd and was surprised that it didn’t have bay to bay windows, but upon some online search I found description explaining differences between car and truck L76 blocks. Same casting #, truck doesn’t have bay to bay windows. I will try to find link and share.
Reminds me of gen II LT1 blocks that all had same casting #, but only Corvette blocks had 4 bolt mains, while the rest had 2 bolt mains.
can you show a pic of what you are talking about? I have the truck L76 and plan on building it soon, so I'd like to see this to have it done
My block is at RED right to be sleeved to 434 ci.
Steve knows exactly how to drill main webs for breathing.
I won’t have my block for awhile and don’t have pictures of main webs.
It is more related to rpm than power output.
There is always possibility of installing vacuum pump, but at 600 crank hp it is not something I would consider.
The L76 TRUCK engine had dished pistons, 6.7cc with valve reliefs, giving a 9.7:1 CR. Car engines had flat tops, yielding a 10.4:1 ratio
The weird part is, the car engine is rated at 355HP, 384 #-ft of torque, and the truck version does 367HP, 375 #-ft.
The truck has MORE HP in spite of lower CR, which does explain the lower torque figure.
Same heads and cam. Possibly more restrictive exhaust on the car? They did put good exhausts on the trucks.
The trucks had VVT, the cars did not. Another possible reason for more truck HP
Both had AFM/DOD.
The G8 had a terrible restriction in the exhaust. It got necked down to 1.75" roughly as it came into the 'TOP' of the cat converter and then out the back again. So both necked down and a bad turn. Headers on the G8 along w/ a good tune are worth a TON.
Some say this was done intentionally to not encroach on the halo car's power (vette).
Some say this was done intentionally to not encroach on the halo car's power (vette).
They did roughly the same to the LS1 in the Camaro vs the Vette version.
But the Vette DID get better exhaust manifolds because there was more room for them. Might have been the issue with the G8 vs Vette too. So it might just have been a tight chassis fit in both cases.
So, at what rpm does the lack of bay to bay breathing become an issue? I am wanting to build one of these blocks, so I want to make sure I get the right one.
So, at what rpm does the lack of bay to bay breathing become an issue? I am wanting to build one of these blocks, so I want to make sure I get the right one.
No personal experience.
From what I was reading, it’s 6000-up, the higher the rpm , the more hp loss.
I think Steve mentioned years ago it’s roughly 20hp loss on 700+hp engine.
Steve drill passages through main webs to regain most of potentially lost hp while keeping block considerably stronger than the one with window bays.
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L76 Confusion 
