Good points all but I think the general problem is "This is how to make VVT cams work and why they are better than non VVT cams" that guys like future user and the LEGIONS of them over at Camaro5 are having troubles digesting. It seems to me that as a result theres a lot of customers who would run VVT cams that dont because there is just NO good clear cut info out there for it. It looks like around 9/10 L99 cam swappers are still ditching VVT and going for static grinds and thats a shame. I suppose its a bit of a PR problem. Plus the new engines are coming soon so this window is getting smaller by the day.

 

Agreed. I think if more shops actually did a little R&D and tested the VVT stuff, they'd be hooked and start recommending people keep it rather than ditching it. This is as much an issue with shops not knowing what they're doing as it is a customer knowledge issue, in my opinion!

 

Funny you say that...because its the truth...I actually DO! (5) min. conversation with a sales tech. at an NHRA event and I was a (WD) wholesale dealer 30 days later. Lol This is also the reason I ONLY recommend parts from Texas Speed or Patrick G for customer cars. I can't risk not being in the "know" as you call it. And R&D? $hit thats a bonus you get for trusting the right vendor to buy parts/tuning from. I work to live...not for free...so thank you vendor relationship for doing it for us!

 

LOL, hope I didn't come off as a dick there. But you're proof that anybody CAN have an account with so many manufacturers/vendors, and why we and others don't divulge all our "secrets."

 

Also very valid. It goes both ways i suppose. Anyways here we are playing around with it and in time when there are no engines NOT running it we can all say we told ya so right?

 

So Texas Speed do you have a cam I can toss in my L76 Vortex Maxx Truck? lol She did about 285 whp stock NA. I'd like to see a lot more lol.

 

I have the TSP VVT-3 cam, my goals are more 1/4 mile based than rwhp and the VVT-3 cam has been proving it self at the track. Stock the car put down 319rwhp with the VVT-3 cam,ported heads,Lt's and Cai thru a Yank 3200 converter it put down 440 rwhp. That is a gain of 121rwhp,that is out standing gains in a H/C car with bolt ons in my book!!! I could not be happier with the cam. New 1/4 mile times coming soon.

2010 SS a6 with TSP VVT-3 cam,PRC ported heads,Yank 3200,Kooks and CAI inc.

http://youtu.be/ApuLKlsy_ho

http://youtu.be/QAI2__APs1g

http://youtu.be/OK8aBwiFhuM

 

Have you tuned the truck yet?

But, I am interested in hearing about a cam for an L76 truck, as I have one.

 

Shoot us a line with some details, bolt-ons, etc and we can make a recommendation. The last 6.2L VVT truck that came through here was COMPLETELY stock. We installed a cam kit and tuned the truck and it picked up about 60rwhp and drives like stock!

 

I'd like the most radical cam (With the best tq & hp) that will still idel lol. Truck has long tube headers, dynomax cat back, airaid intake tube, K&N filter, ported and polished TB, FLT Stage 5 4L80E, and a 3700 RPM stall. My wife DD's it! I'll have to give you a call, PM me who to ask for.

Yes I tuned it myself via HTP. Haven't dyno'd it but it feels great. My wife outruns 350z's in it all day long. LoL

 

VVT has issues at higher RPM and higher spring pressure rates. So, what you will typically find is VVT being used in lower RPM applications. Also, the VVT gives an auto a slight benefit in MPG. A manual typically already has those economy numbers because of less parasitic loss. So, that may be another reason why you don't find it in manuals (along with what happens iif you miss a shift in a manual).

I'm telling anyone who doubts the merits of VVT that you are overlooking the obvious. If you have ever dyno'd an engine and played with advancing/retarding the cam, you will understand what I mean. You will move the power around by moving the cam.

The same hold true for VVT, except that instead of having to pull off the time cover and swap bushings on the cam sprocket, you do it in software. I guess I need to break out some dyno graphs to illustrate, and fire up the modeling software again....

 

That is not true in fact Jason at TSP has run there VVT-3 cam with PRC dual springs to 7800 rpm with out issue. I run dual PRC springs on my car and it completes the shifts at 6800 rpms in fact I need to bring the shift points down 100 rpms because it bumps the limiter between shifts.

 

I think a lot of the miss information about VVT comes from people including big name shops thinking VVT and DOD/AFM are one in the same and they have nothing to do with each other. If you keep the DOD/AFM (junk) lifters then you would need to run single springs or the lifters will fail in short order.

 

Yes and a lot of miss information comes from people thinking that vvt on a (gm LS gen iv) is comparable to other vvt systems that vary intake valve timing seperate than exhaust and can also vary lift and duration in many cases. Gm (LS gen iv) vvt is different than the other types and inferior because the exhaust valve timing is slaved to the intake. The reason many shops don't use it is because they can't make it work as well. I don't think a vvt cam in my LY6 would have made more torque or horsepower. Someone prove me wrong.

 

Those big name shops must be some big idiots like the two biggest names in Atlanta.

 

My digestion is fine thanks. I would love to retard or advance my cam a few degrees on the fly. But there is a reason that I'm not doing it.

 

kaler - I know the difference between AFM/DoD and VVT. My truck has both, and I tune for both features. I also understand the mechanics behind each. But, if you look at most cam phasers, if you put enough spring pressure against them, it doesn't matter what you command in software, the phaser can't accomdate it due to spring pressure. I fully agree that AFM lifters are much more lift limited than conventional lifters. But, all I am trying to say is that there are limits to VVT as well. That is why you see hollow stem valves, etc... instead of just using heavier springs. Its my opinion that uou need to do what you can to reduce mass in a VVT setup for optimal performance at high rpm rather than just adding lots of spring pressure. Also, did you mean 7800 or 6800 in your post.

futureuser - Yes, your cam is physically constrained by the way it is ground. So, LSA is set. That will change in the Gen V which is going to have 3V OHC with cam phasing.

But, as I pointed out. If you have played with any engine, I'll use the Gen I SBC as an example, you can demonstrate moving the power band by advancing/retarding the cam in it as well. The same holds true for an LS1.

If you look at valve events you will see that exhaust valve events are much less critical than Intake valve events. So, you can play with moving the IVO/IVC around and the exhaust (EVO/EVC) will follow, and take care of itself.

This is due to the importance of the intake closing point on performance. Earlier intake closing leads to increased cylinder pressure and better responsiveness. As a general rule of thumb, advancing the cam will help low-end torque, but, retarding the cam a few degrees helps extend high-rpm power.

To maximize flow on the induction stroke, you will have the cam start opening the intake valve well before the piston reaches TDC. Likewise, on the power stroke the piston has done somewhere around 80 percent of its work by the time the crank has turned just 90 degrees, so you will have the exhaust valve go ahead and begin opening while the piston is still moving down in the bore. The higher the rpm the sooner these events need to take place.

Valve overlap is subject to the same rules. Because the flow of air and fuel into and out of the engine is so dependent on mixture velocity and momentum, cam designers have found that engines respond better if the overlap period isn't centered around TDC, but actually begins a little sooner.

Because of this, and also because people tend to overcam their engines many cams are automatically ground with four degrees of advance built in. It helps wake up what would be a soggy engine if you left it at +0.

That doesn't mean, though, that four degrees is the magic number. Manually advancing or retarding the cam to change the valve timing events in relation to the crank's location can help you determine the engine's preferences. Just remember: If you are advancing a cam to have the intake valve open earlier, it's also closing earlier. The exhaust valves are also following suit. In our case you optimze the cam and take advantage of being able to retard that cam on the fly.

So, lets assume that moving the cam 4 degrees move the power 150 - 200 rpm when you move it with a adjustable cam set. Now move the cam 20 degrees and spread the power band 1000 rpm... Make sense?

 

Much of what was talked about above regarding IVC is talked about in the Hotrod Magazine article "15 degrees of separation": http://www.hotrod.com/techarticles/e...t/viewall.html

futureuser you had great results on the dyno from your nonVVT cam, but until you can compare it to a similar spec VVT cam in the same engine I wouldn't draw any conclusions. Comparing your curve to the magazine curves doesn't quiet work since (1) you have no absolute point of reference to compare their engine dynos to your chassis dyno and (2) none of the magazine articles cover the LY6. I am not saying you are right or wrong, I'm just saying the jury is still out. I really would like to see tiresmokinv8 dyno his Sonoma since he has basically the same engine as you and I with the TSP VVT-2 cam.

I do wonder if it's possible to grind a nonVVT lobe onto a VVT core and just run it as is (with some added advance to allow room for VVT) or if nonVVT lobes wont play well with the VVT phasor or valve clearance. If so, you may be able to take your exact cam and grind it into a VVT core, in which case I am sure you could improve on your results.

 

Hey now dont bring me into this, I have no problem with the vvt yet.

 

So et me see if a picture might help illustrate this a bit better. The graph below is an EA Pro model of a stock Ls1. The only thing I have done is run a stock dyno of the engine, then I have retarded the cam 10 degrees and re-run the test. You can see how it changes the HP and Tq output of the engine even with the very small stock cam.

Stock cam timing and 10 degrees retarded


10 degrees advanced and 10 degrees retarded


You can see how the a physically retarded cam looses power down low, and comes on up top. Same applies to a cam being used in a VVT application.