Not sure if this has all been posted before, but I found the following documents on GM Media Online

Highlights (or not):

LS3 intake used for G8

VVT only on the truck engines (vortec or L76):confused:

The Gen IV 6.0L (L76) is fitted with high-flow cylinder heads, based on those developed for the high-performance LS2 and LS6 car V8s. These heads have offset rockers, like those in the LS7. They also have larger valves than the Vortec 6.0L V8 heads used in truck applications, and increase airflow in and out of the engine for higher horsepower. Yet the 6.0L (L76) heads maintain a compression ratio and calibrations that allow these engines to operate on regular gas.

The third link, however shows that Premium fuel is recommended, It's not clear if the dyno chart was already based on running premium. If so, there may not be as much to be gained as we might have thought with an 87 octane requirement. :dunno:

Engine pic
http://media.gm.com/us/powertrain/en/product_services/2008/Photo%20Library/Gen%20IV/Gen%20IV%20Car/08%20L76%20G8.jpg

Dyno Chart
http://media.gm.com/us/powertrain/en/product_services/2008/HPT%20Library/Gen%20IV/Gen%20IV%20Car/2008_60L_L76_G8_GT.pdf

Engine Specs
http://media.gm.com/us/powertrain/en/product_services/2008/Spec%20Sheet/Gen%20IV/2008%20Gen%20IV%20Car/08_L76.xls


L76 Features
http://media.gm.com/us/powertrain/en/product_services/2008/Whats%20New/Gen%20IV/Gen%20IV%20Car/08_L76.doc

cheers

The Third Link is for an LS3 not an L76 Car ;)

"Yet the 6.0L (L76) heads maintain a compression ratio and calibrations that allow these engines to operate on regular gas. "

Link fixed.

So I'm confused over just what cylinder heads are actually on this. I had heard that the L76 came with the L92 heads, but the document from GM just states that the heads were based on the LS2/LS6 heads. Anyone have something more definitive regarding the heads?

"Yet the 6.0L (L76) heads maintain a compression ratio and calibrations that allow these engines to operate on regular gas. "

10.4:1 I believe.

The LS4 has a 10:1 compression ratio but premium is "recommened" at that lower compression ratio. Yeah, it will drive on 87, but knock sensors are pulling timing - especially when DOD is active - which drops you into the low timing table and robs some power.

The High Timing table is actually tuned for 87 in that car, I've got the calibration right here ;) Besides DoD has a seperate spark table anyhow.

Look at the torque curve on the dyno chart. Nearly flat!

Also something to make it easier to grasp as far as power vs octane goes, the L76 truck motor albeit with VVT makes 366 horsepower on 87 octane and thats with the crappy truck intake :D

UMMM, where the hell did they come up with that dyno graph??? Everyone who has every dyno'd anything knows that torque and horsepower ALWAYS intersect at 5250rpm not 3000 something like that graph. I call BS on the graph

Different vertical scales for HP and Torque, hmmm marketing got their hands on that:D

The High Timing table is actually tuned for 87 in that car, I've got the calibration right here ;) Besides DoD has a seperate spark table anyhow.

Well, that's interesting. My LS4 has Hi and Lo octane tables, but HP Tuners doesn't show me a separate timing table for DOD, must be new - it just reverts to the low octane table if you dump in 87 constantly, the knock learn factor drives it to the low octane table eventually.

No clue on HPT never really used it but there are seperate tables for DoD mode ;)

UMMM, where the hell did they come up with that dyno graph??? Everyone who has every dyno'd anything knows that torque and horsepower ALWAYS intersect at 5250rpm not 3000 something like that graph. I call BS on the graph

The horsepower is on a different scale than the torque.

The horsepower is on a different scale than the torque.

But they are on the same RPM scale

Link fixed.

So I'm confused over just what cylinder heads are actually on this. I had heard that the L76 came with the L92 heads, but the document from GM just states that the heads were based on the LS2/LS6 heads. Anyone have something more definitive regarding the heads?

08 vette LS3 intake manifold part number is 12602477
08 G8 L76 intake manifold part number is 12602477
The same!

08 vette LS3 cylinder head is 12600825
08 G8 L76 cylinder head is 12582714

12582714 is the same part number used on the L92 engines. I think the only difference between the two is the valves. Hollow and sodium filled for the LS3.

-Greg

Anyone taking bets on whether or not they will put the LS3 in it as the standard engine for MY2009?

Doesn't that mean the cylinder heads can't be the same castings as the LS7 head? I thought the angle of the intake valley was different between the LS3 and LS7 requiring a totally different intake?

I don't think the LS3 will be standard but it should be an option (GXP).
The LS3 and the LS7 heads are totally different. The LS7 head will not work on a 6.2L engine.
-Greg

Here's a quick Paint job with the scale corrected. It's not perfect, but the curves get close at the verticle line (guess for 5250).

http://i19.photobucket.com/albums/b184/jwikoff99/dyno.jpg

Not sure if this has all been posted before, but I found the following documents on GM Media Online

Highlights (or not):

LS3 intake used for G8

VVT only on the truck engines (vortec or L76):confused:

The Gen IV 6.0L (L76) is fitted with high-flow cylinder heads, based on those developed for the high-performance LS2 and LS6 car V8s. These heads have offset rockers, like those in the LS7. They also have larger valves than the Vortec 6.0L V8 heads used in truck applications, and increase airflow in and out of the engine for higher horsepower. Yet the 6.0L (L76) heads maintain a compression ratio and calibrations that allow these engines to operate on regular gas.

The third link, however shows that Premium fuel is recommended, It's not clear if the dyno chart was already based on running premium. If so, there may not be as much to be gained as we might have thought with an 87 octane requirement. :dunno:

Engine pic
http://media.gm.com/us/powertrain/en/product_services/2008/Photo%20Library/Gen%20IV/Gen%20IV%20Car/08%20L76%20G8.jpg

Dyno Chart
http://media.gm.com/us/powertrain/en/product_services/2008/HPT%20Library/Gen%20IV/Gen%20IV%20Car/2008_60L_L76_G8_GT.pdf

Engine Specs
http://media.gm.com/us/powertrain/en/product_services/2008/Spec%20Sheet/Gen%20IV/2008%20Gen%20IV%20Car/08_L76.xls


L76 Features
http://media.gm.com/us/powertrain/en/product_services/2008/Whats%20New/Gen%20IV/Gen%20IV%20Car/08_L76.doc

cheers
Good stuff!:yumyum:

Here's a quick Paint job with the scale corrected. It's not perfect, but the curves get close at the verticle line (guess for 5250).

http://i19.photobucket.com/albums/b184/jwikoff99/dyno.jpg

Ah much better!

Look at the torque curve on the dyno chart. Nearly flat!

I was thinking the samething. I hope with some bolt-ons the peak HP will climb up into the higher RPM's.

I don't think the LS3 will be standard but it should be an option (GXP).
The LS3 and the LS7 heads are totally different. The LS3 head will not work on a 6.2L engine.
-Greg

Typo! The LS3 is a 6.2L engine. I think you meant that LS7 heads wouldn't work on a 6.2L. I would believe that the LS3 heads would work on the truck L92 or G8 L76. But why bother? The L92 & LS3 heads will both flow exceptionally well with a little port work.

^^^^^^^^^ Thanks I will fix it. :P

well can someone tell me what i would have to do to get a few more horsepower by using premium.

Get the engine tuned for premium. They will advance the timing.

The question I have is what will a tune for premium fuel do HP-wise? One would expect OVER 400 hp since the LS2 makes that with the same displacement and supposedly inferior heads.....

I dunno, I think I'll have em tune it for premium, and change some of the ratios to keep 360HP for a bit better milage hehe.

Lots of opinions and confusion here...I just browes through but, to be clear.
The G8 GT Comes with L76 (LS3) Intake Manifold and matching L92 (LS3) cylinder heads and a 90mm TB with a 6.0L (LS2) Bottom.

Let the upgrades begins!

TiredGXP -

Great info - thanks for the post.