Grape Ape

Too much trouble. Just use the transverse version of the LNF. One in the front and one in the back. That way you also get AWD & AFM (just turn off one engine).

HAZ-Matt

I don't completely agree with your thoughts on VVT, but I mostly want to comment on your observations about the L76 versus the LS2. AFM does not eat 38 HP. The L76 is rated on 87 octane gasoline whereas the LS2 is rated on premium. While the heads, essentially heads off the L92 revised for the smaller bore, seem superior than those on the LS2, they are not hand finished. Compression ratio is slightly less than the LS2. Additionally, although the displacements are the same the L76 has a smaller bore and longer stroke. Cam is smaller, weaker valve springs, and so it also has a lower rev limiter than the LS2. It isn't as if the L76 was just an LS2 with better heads + AFM/VVT.

FWIW with tuning for premium octane fuel you can get the L76 up to ~400HP.

teal98

The LS2 was never SAE rated either. In road tests, the G8 isn't that far behind the LS2 GTO, even though most examples tested are about 300 pounds heavier, and the GTOs were mostly 6Ms.

Grape Ape

I find it hard to believe that GM would design a new 6.0 block (and redesign a bunch associated parts) when they have the LS2 block design sitting around. So I checked and GM media says they are both 101.6 x 92mm. GM media also says that premium is recommended for both.

http://media.gm.com/us/powertrain/en...2007/07car.htm
http://media.gm.com/us/powertrain/en...2008/08car.htm

I have not been following the G8 too closely, but I thought the best tune result I’d seen was around 385 (est flywheel) hp. I know everyone seems to expect a tuned L76 to produce 400hp on premium, but I don’t think the stock cam is up to it.

It is my understanding that the size of the cam is limited by the amount of lift that the deact lifters can absorb when AFM is active and that the lobes for the AFM cylinders are smaller than the other lobes for the other four cylinders. So I reiterate that as implemented on the G8's L76, AFM eats a heard of horses.

BTW: I don’t believe that the G8’s L76 has VVT.

teal98

No it doesn't have VVT.

Interesting hypothesis. The Honda 3.5 V6 is rated the same with or without AFM. But the non-AFM versions are much faster in the 1/4 -- more than could be explained by 5A vs 6M.

Still, we don't really know the HP difference between LS2 and L76, do we? AFAIK, no LS2 has been SAE rated. Also, the L76 is based on the L98, which only has a couple more HP than the L76.

Btw, everyone is trying to figure out premium versus regular on the L76. The change from regular to premium was made late last year.

Grape Ape

I have no idea how Honda implemented AFM on it's 3.5. I would think that an AFM engine could have the same cam as its non-AFM version if it was designed for AFM (like the Gen V small block I hope).

The Honda could have valve train inertia issues that give it a lower red line or cause the power to fall of peak faster. Or the AFM gear could limit the effect of the VVT gear giving the AFM motor the same peak numbers on a narrower curve. Either one would lead me to expect lower 1/4 miles times. Or the M6 could just have better gear ratios.

The big question is what is a honda doing on a drag strip?

teal98

IIRC, about 14.1 for the non-AFM and 15.2 for the AFM.

Tests of Acura TLs with and without auto have nothing like that kind of difference.

HAZ-Matt

Interesting. I was wrong when I said they have different strokes, but the bores are different... LS2 is 101.6 and L76 is 101.3mm and both are 92mm strokes. I don't know why GM's page lists them as having the same bore. We are getting into a debate over semantics though if you believe that the small cam is the reason AFM causes a loss of power in the L76 though. I wouldn't necessarily disagree with that idea, but even so I wouldn't say it was AFM eating the power.

As for the fuel recommendation, I still have read nothing but that the motor is rated and tuned for 362HP on 87 octane but if it was changed recently then I am wrong. The guys in Australia were getting 400HP on the L76s with premium gas, but that might be in part due to the difference in the max octane available. But if they do make a conservative 385HP on premium that would be a loss due to every single change compared to the LS2 of -15HP which is a far cry from the 40HP from AFM that started off this whole discussion.

teal98

Looking at the 1/4 mile times of the G8 with A6 and comparing to the 1/4 times of the GTO with M6 and 250-300 pounds less weight, I think 15hp is probably much closer to the real difference.

Remember too that the LS2 was never SAE rated.

Grape Ape

0.3mm is the next best thing to zero.

Since we both agree that the small cam is holding the L76 back, the question is why is it there?

I guess GM could have decided that it needed more room between the G8 GT and the G8 GXP (and the corresponding Holdens). I’ve been wondering why GM didn’t change the rocker ratio to maintain LS2 level valve lift with the smaller AFM cam, and that would be a pretty good answer. That and the fact that they don’t need to spend the extra cash, since the G8 GT is still considerably faster than a Charger R/T.

TrickStang37

the small cam probably works better with the cylinder deactivation.

cjmatt

3.6 < 6.2 < 6.2 S/c

vonmoldy

why don't you nerdz wait till it comes out

vonmoldy

BTW the last post was sarcasm...anyways I want a 4.8 DI in a stripped down model. 295 HP 305 LB/FT would be pretty sweet if it weighs about the same as a 4TH gen.

97z28/m6

it won't.