LS3 vs L99?
 

According to GM High Tech some of the major difference between the two motors are
1. VVT
2. AFM
3. 10.4:1 Compression ratio
4. lower lift cam

But one thing that really caught my eye was the lower fuel cut off rpm for the L99. GM High Tech Mag states that the fuel cut off for the LS3 is 6600 rpms, while the fuel cut off for the L99 is 6200 rpms. Is this really the fuel cut off for the L99? That seems too low.
If this is true then red line must be somewhere around 6000 rpms for the L99 vs 6500 rpms or so for the LS3. I'm wonder how much this will affect the peformance of the L99 A6 vs the LS3 M6.

To compare- My LS2 GTO's redline is 6500 rpms and I'm not sure about the fuel cut off.

the cut-off is there to protect the valvetrain at higher rpms from getting torn up.


the thing to look at is the power curve. as ive said before, its nice to rev to the moon, its nicer to move.

I have read much of the same for the L99 motor (I have one on order).
In addition to not needing as high an RPM due to less cam, I read that the AFM does impose some restrictions to the valve train at higher RPMs.
This should not be an issue if you keep the motor stock. If you are looking at adding traditional performance mods, then this RPM limit needs to be taken into consideration.
I’m keeping my ears open for ways to beef up the valvetrain to handle more, but have yet to see any useful information short of removing the AFM

A shorter Valve Duration will reduce the peak RPMs at wich you reach Peak HP. Also if the Valve lift is less then less HP at the given RPM peak will be realized. Short Lobe Centers usually create quicker HP and TQ curvers. Where a longer Lobe Seperation usually increase the length og the HP and TQ Curves.

So the Auto with AFM and VVT uses the smaller cam to better manage the fuel consumption and there by reducing the power levels and making the peak RPM range lower. However the TQ curve will start at a lower RPM and reach is peak quicker. So the Auto car will basically show simular performance as the manual tranny car and the gearing in the Auto is usually lower per gear than a manual making the Torque multiplication effectivally higher per gear.

This made more sense inmy mind I am sure than it does in print. So take it with a large grain of salt if it confuses you more. :) I was havig a hard time trying to make something technical make sense in lehmans terms. I am not necessarily that good at.

You are right. Pointy cams, less duration, have greater torque at low RPMs but less HP.(they peak sooner) Longer duration cams have more HP but you need more RPMs to get it due to scavenging caused by overlap of intake and exhaust lobes. (more of a top end motor)

There are many other factors involved. Just some basic cam theory.

Also, the L99 may have the same heads found on the L76, since that too has AFM. Although the castings are the same as the L92 heads, to save costs the L76 (and possibly the L99) has heavier solid valves vs. the lighter sodium filled L92/LS3 valves.

True, but I would guess camshaft powerband has a lot to do with this along with the valvetrain.

I am looking for some advice. I ahve a 2SS A6 on order and keep thinking I should get the LS3 instead. Is there anyhting that says one is better than the other? Back in the day it was stick all the way. I have a stick in my 2000 SS, but have to admit, it gets old in traffic, maybe I'm just getting old, who knows. Technology today seems to point to the L99, any advise, I'm starting to get a headache and I have months yet to wait

L99- more moving parts, less efficiency

L99 has more moving parts?

Yes, The AFM

the auto's of old were not the greatest. the new 6 speed auto that GM has is a bad mofo.

this new auto isnt the slushbox of yesteryear.



depends on what kind of efficiency you are looking at. fuel efficiency? AFM rocks. lol

Efficiency period, of course Fuel efficiency is gonna kick ass

for the person that wont be modding their car to hell because 400hp seems to be MORE than enough for me, lol.. Im fine with the way things are.