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Camaro V8 LS3 / L99 Engine, Exhaust, and Bolt-Ons Bolt-Ons | Intakes | Exhaust

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Old 02-07-2009, 04:57 PM   #1
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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.
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Old 02-07-2009, 05:07 PM   #2
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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.
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Old 02-11-2009, 01:54 PM   #3
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Originally Posted by SGOS252382 View Post
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.

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
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Old 02-11-2009, 04:32 PM   #4
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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.
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Old 02-11-2009, 04:47 PM   #5
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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.
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Old 02-11-2009, 11:59 PM   #6
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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
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.
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Old 02-14-2009, 10:58 PM   #7
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True, but I would guess camshaft powerband has a lot to do with this along with the valvetrain.
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Old 02-16-2009, 04:37 PM   #8
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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
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Old 02-16-2009, 04:38 PM   #9
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L99- more moving parts, less efficiency
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Old 02-16-2009, 04:41 PM   #10
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L99 has more moving parts?
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Old 02-16-2009, 04:43 PM   #11
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L99 has more moving parts?
Yes, The AFM
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Old 02-16-2009, 04:56 PM   #12
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Quote:
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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
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.



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L99- more moving parts, less efficiency
depends on what kind of efficiency you are looking at. fuel efficiency? AFM rocks. lol
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Old 02-16-2009, 05:00 PM   #13
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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
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Old 02-20-2009, 05:23 PM   #14
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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.
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Old 02-21-2009, 08:39 AM   #15
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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
Stock for stock its going to be a drivers race between the a6 and m6. If you are going to keep it stock, stick with what will make you happier on a daily basis. If you are going to mod it, I'm willing to bet the m6 is going to be a better place to start out at.
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Old 02-21-2009, 08:47 AM   #16
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i would say if your going to mod it go with the auto, a 3000 stall converter and delete the afm, cam and a tune and you will blow away a 6speed manual with the same cam/bolt on mods
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Old 02-21-2009, 09:36 AM   #17
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Part of the AFM package is VVT and that will help with power efficiency from low to high RPMs. Just like advancing and retarding the spark does.
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Old 02-21-2009, 10:34 AM   #18
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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.
The AFM gear is in the block, not the heads.
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Old 02-22-2009, 01:49 PM   #19
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Here are some pics of the lifters for AFM/DOD which will be used in the L99:




The LS3 will have normal hydraulic lifters, a different valley cover, and it will not have this in front of the camshaft which is for VVT:

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Old 02-22-2009, 02:46 PM   #20
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i would say if your going to mod it go with the auto, a 3000 stall converter and delete the afm, cam and a tune and you will blow away a 6speed manual with the same cam/bolt on mods
that will be debated. actually it already has been debated.

but to add to your argument, there are a nice group of AFM G8's out there running superchargers as well with no problems.

regardless of which one you go with. they will both be bad ass from the factory as well as with adding mods.
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Old 02-22-2009, 02:51 PM   #21
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that will be debated. actually it already has been debated.

but to add to your argument, there are a nice group of AFM G8's out there running superchargers as well with no problems.

regardless of which one you go with. they will both be bad ass from the factory as well as with adding mods.
at the cost of fuel economy, don't see the point of still having it active, the AFM
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Old 02-23-2009, 08:57 AM   #22
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at the cost of fuel economy, don't see the point of still having it active, the AFM
I dont know what their mpg's are after the sc install, ill have to look into it. but the other thing to keep in mind is that EPA estimates are just that.... estimates.

just like the 4th gens where people were getting 30+mpg in their cars, im sure that both the LS3 and L99 will get better than the EPA estimates
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Old 02-23-2009, 09:02 AM   #23
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that will be debated. actually it already has been debated.
I agree, I take back my statement about the m6 being better to mod from. Might be a little simpler to start with, but in the end, once you get to a cam swap, there isnt that much more to swap out with afm than you would with a normal ls3. Guess its all up to driver preference.
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Old 02-23-2009, 09:16 AM   #24
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I agree, I take back my statement about the m6 being better to mod from. Might be a little simpler to start with, but in the end, once you get to a cam swap, there isnt that much more to swap out with afm than you would with a normal ls3. Guess its all up to driver preference.
camming the L99 will be a little trickier as you have to allow some leeway with the AFM and the lifters. now if you tune it out and remove all that stuff and basically convert to an LS3, then cam swap to your hearts content
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Old 02-23-2009, 09:25 AM   #25
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Well, I'm not sure if anyone is making a cam right now thats compatable with AFM. I would think with the l99, if you are going to cam it, youre going to have to take out the AFM, which is a couple more parts than doing a cam swap on a ls3, but really not that much more labor.
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