For roll on performance on an L99, is keeping VVT or LS3 conversion better?

[LCPLPunk]

Hey guys,


So I am like 99.9% sold on using a VVT cam in my L99, BUT, I feel like the LS3 conversion makes more HP. Knowing this, if most of my runs are highway roll-ons, would it make more sense to do a LS3 conversion?

[Moto-Mojo]

It’s a TQ v HP thing. Based on what I know, similar cams in both versions might net you more bang for your buck with VVT. If it’s DD then you might like the lower RPM torque of the VVT. If you track it for ET then you might like the straight cam and it’s upper end pulling power. But there’s all the variables of the AFM parts if you’re not pulling heads, etc. And that’s what I’ve learned here.

[LCPLPunk]

Speaking to the choir here! As I said i'm like 99.9% sure i'm going with VVT.


I'm just curious how a non-VVT SS1 vs a VVT SS1 cam on an L99 would perform during a roll-on on the highway.

[havelegs]

Every engine builder around me says no to vvt. Not sure why.

[LCPLPunk]

Honestly I think they may just not know how to work with it. Everything I've seen (even the dyno sheets) says that unless you are going full race build or need the most HP possible, VVT is the way to go.

[LCPLPunk]

Good article on why to keep it! http://www.superchevy.com/how-to/eng...n-iv-v-engine/

[Rock-It Man]

Originally Posted by Moto-Mojo

It’s a TQ v HP thing. Based on what I know, similar cams in both versions might net you more bang for your buck with VVT. If it’s DD then you might like the lower RPM torque of the VVT. If you track it for ET then you might like the straight cam and it’s upper end pulling power. But there’s all the variables of the AFM parts if you’re not pulling heads, etc. And that’s what I’ve learned here.

Torque and horsepower are not opposites. Horsepower is torque times rate. If you plot torque vs RPM, and two torque curves intersect on that plot at a particular RPM, they are producing exactly the same HP at that particular RPM.

So...peak HP for an engine occurs at the peak of the curve that plots torque as a function of RPM. However, a flat torque curve delivers more HP at lower RPMs and delivers more acceleration.

Comparing the Gen 5 engines, the VVT L99 generates way more HP between 2000 and 4000 RPM than the peaky LS3 and has the advantage on the drag strip.

Here's another way of looking at it: your car's speed is a measure of its kinetic energy. To deliver energy, you need sustained torque. In a torque vs RPM curve, the energy delivered is the area under the curve. Therefore, a flat torque curve delivers more energy than a peaky torque curve, if the max torques are similar.

Gotta love the calculus.

[LCPLPunk]

Ok, so adding all that into the equation, if the LS3 conversion has more peak HP than the VVT one, how does that affect roll on performance?

[Rock-It Man]

Originally Posted by LCPLPunk

Ok, so adding all that into the equation, if the LS3 conversion has more peak HP than the VVT one, how does that affect roll on performance?

You have to plot the two torque curves together. You will see that the L99 curve is above the LS3 curve up to a point, and up until that point, the L99 car will be accelerating harder. After the crossover, it's all about the area under the curve. The L99 will be accumulating more energy and hence more velocity up until the point that there's more area under the LS3 curve. But...but, if the VVT curve stays flat beyond the point that the LS3 curve takes a nosedive and crosses the L99 curve again, the LS3 car will begin falling behind again.

Comparing stock L99 and LS3 quarter mile elapsed times, the L99 is consistent the winner. Peak HP alone is pointless in a drag race. Again, it's all about the area under the curve.

[Moto-Mojo]

Originally Posted by Rock-It Man

Torque and horsepower are not opposites. Horsepower is torque times rate. If you plot torque vs RPM, and two torque curves intersect on that plot at a particular RPM, they are producing exactly the same HP at that particular RPM.

So...peak HP for an engine occurs at the peak of the curve that plots torque as a function of RPM. However, a flat torque curve delivers more HP at lower RPMs and delivers more acceleration.

Comparing the Gen 5 engines, the VVT L99 generates way more HP between 2000 and 4000 RPM than the peaky LS3 and has the advantage on the drag strip.

Here's another way of looking at it: your car's speed is a measure of its kinetic energy. To deliver energy, you need sustained torque. In a torque vs RPM curve, the energy delivered is the area under the curve. Therefore, a flat torque curve delivers more energy than a peaky torque curve, if the max torques are similar.

Gotta love the calculus.

Yeah, I wasn’t saying they were opposites. Just pointing out in more layman’s terms the trade off of torque lower in the curve you adeptly explain between the two cams. I think horsepower and a brick wall are opposites!

[havelegs]

Would going from a full bolt on L99 with 3.91s to a LS3 conversion "stage 1" cam and the same mods have a noticeable decrease in low RPM power? Two builders local said that the power is not noticeable or no one has ever complained about a lack of low power.

[LCPLPunk]

I don't see you having a decrease in power going from bolt-on to a LS3 conversion, but I think the consensus is you are leaving power on the table if you don't do VVT. Not sure if you saw this, but this has me sold on VVT...among other things. http://www.superchevy.com/how-to/eng...n-iv-v-engine/

[havelegs]

Originally Posted by LCPLPunk

I don't see you having a decrease in power going from bolt-on to a LS3 conversion, but I think the consensus is you are leaving power on the table if you don't do VVT. Not sure if you saw this, but this has me sold on VVT...among other things. http://www.superchevy.com/how-to/eng...n-iv-v-engine/

Thanks. I saw that article and that is why I'm so confused why really good builders here are willing to do vvt, but their first choice is a conversion.

[LCPLPunk]

I think because it's easier to do. I've seen some posts from Jannetty were he says he prefers the more simpler setup with less moving parts.