I'm doing a H/C on my '06 GTO. The parts already on my shelves for support are: GMPP CNC ported LS3 heads, FAST 102 intake and NW 102 throttle body, JBA 1 3/4" long tubes with catless mids, Vigilante 3600 T/C, and a g-force engineering one piece aluminum drive shaft and better axles. Also, I have two different cams on the shelf right now. a BTR stage IV LS3 N/A cam: 618/598-233/248 on a 113 LSA. I also have a VRSP2: 614/624-227/235 on a 115 LSA. I'm leaning toward using the VRSP2 for the drivability/closer valve events, and the possibility of shaving .030 off my heads to bring compression back up and also using a .041 cometic head gasket for quench factor-all hopefully without having to fly cut. I may have to fly cut to get the better quench and the milling done anyway. I could also use the BTR Stage IV which would definitely require fly cutting to recover the compression and achieve better quench. I'm also considering the TSP stage 4 LS3 cam: 627/624-235/239 on a 112 LSA. Again, this cam would definitely require the fly cutting given my plans of a thinner head gasket and milling to recover the compression ratio. I'm not sure which cam offers the all around best bang for the buck. Specifically, the larger cams would probably still have some surging/bucking at lower rpms and easy throttle no matter what tuning is done. The VRSP2 cam would be easier to live with in its drivability but, might it not pull hard enough in the big end when I have the car at the track (which is about 3 times a year). Could anyone with experience in using their cars daily or semi daily with a bigger cam chime in; and also, anyone who decided to go with something a little more street friendly like the VRSP2. I'd like to get the perspective from someone who has lived in either or both camps. Sorry this is so long-
Thanks!!

 

Those are big *** cams to be even thinking about not flycutting, especially if you're going to be shaving the heads and running a thinner headgasket.

Although the 2nd and 3rd choices are not really rectangular port type of cams. The BTR cam would not be fun to drive on the street and you're really only giving up 10-15hp over a much better driving cam so I would say it's not worth it unless this is a 100% strictly track car. You're not going to miss that kinda power the 3 times a year you go to the track, but you will surely enjoy driving the car more the 99.9% of the rest of the time you're on the street.

 

Well, what would you consider as an appropriate cam given how I intend to use the car? I had also considered the TSP 229/236 112 LSA cam as well
Thanks!

 

If you want to mill the heads .030", you are going to want to fly-cut too. LS3s don't have a ton of valve clearance. Several of those cams that you referenced are maximum cams for an LS3 without fly-cutting. You could mill about .015" with this cam:
http://store.cammotion.com/titan-3-ls3-camshaft. If you don't mill, or if you fly-cut, you could run this one: http://store.cammotion.com/titan-kin...-port-camshaft

 

Thanks Guys: I've decided to go with the BTR Stage II LS3 Cam-225/238 .612"/.585" 113+3. I think this will be a much better choice that will have pretty good driving manners once tuned, and it will have enough "Go" for the few times a year I go to the track. Once again thanks for shedding some much needed light on this issue.

 

With that cam I bet you can mill your heads the .030" that you mentioned.

 

I would go with this cam and not worry about fly cutting or milling the heads. My H/C LS3 in my Impala has the Lingenfelter GT1-1 cam (229*/241* w/114* LSA) and it doesn't require fly cutting at all.

With .040" head gaskets and assuming 70cc combustion chambers on those GMPP heads, your engine should come it 10.8 to 10.9:1.

Just my $.02

KW

 

Im confused, why do you need to flycut?

I put the BTR Stage 4 LS3 NA cam in my 2012 SS this summer. Any drive-ability issues I have (cam buck) would EASILY get swallowed up by your converter in the auto. I wouldnt even think about going smaller, hell id go much bigger if I had to do it all over again.

470rwhp and 443rwtq w/ 2" headers, 3" TSP exhaust, stock heads w/ BTR .660 platinum spring kit, stock intake, stock throttle body.

Other's have milled the stock heads and run this cam too all on the stock bottom end without flycutting. The relatively low lift for a "big NA cam" should give better PTV than other "max effort" cams, IMO.

 

The lift doesn't really dictate the PTV clearance. It's the valve events when the piston is coming up (EVC) and down (IVO) the bore. When the valve is at max lift, the piston is nowhere near the valve.

 

The need to fly-cut arises when you are trying to keep a safe distance between the valves and the top of the piston when installing a larger performance camshaft. This distance diminishes as the intake valve is opened sooner or the exhaust valve is held open later in an effort to increase overlap and/or duration.

When it comes to piston-to-valve clearance, it is not the lift that is the primary consideration, it is the valve events as mentioned above.

The aftermarket performance LS3 cams you typically see tend to have a smaller intake duration because the large intake valve combined with the flat top piston limits how soon you can open the intake valve. And, since the LS3 will typically perform best with an earlier intake valve close, you end up with shorter durations.

I looked up the Tooley camshaft that you mentioned and the website list the specs as 233/248 113+5. This puts the intake centerline at 108 degrees after top dead center. With those specs, this camshaft has an IVO of 8.5 degrees before top dead center. This is about 2 degrees earlier than most of the shelf cams that I have seen offered for an LS3. To see what this actually means in terms of piston-to-valve clearnance, I used the incredibly accurate piston-to-valve clearance calculator from PCM or NC. http://www.pcmofnc.com/index.php/com...nce-calculator

Here is what I found:





As you an see, this cam will have about .026" intake piston-to-valve clearance. The cam that I suggested will have about .040" intake piston-to-valve clearance. For some perspective, for decades, most people would cite .080" as minimum safe intake piston to valve clearance on your typical American V8 and .120" minimum piston-to-valve clearance for the exhaust valve. The LS aftermarket has pushed this tighter. These days performance camshafts will typically get as tight at .040" intake and .060" exhaust. How close a person is willing to push it is up to them. Of all the places you could try to find an extra couple horsepower in a camshaft, pushing valve clearance comes with the most risk. In the end, it is the vehicle owners decision as the vehicle owner is the one who will be writing a check if it all goes wrong.

 

Agreed with pretty much everything in this post except ^^^THIS^^^

Common misperception among those who really don't know how an engine works.....but cam lift has absolutely nothing to do with PTV clearance.

KW

 

Man.....this is some good stuff!!!!!

Thanks for posting

KW

 

Wow, I had no idea there was such a great PTV calculator available online. I'm definitely sending the stage 4 cam back. Yes, the drivability issue would be really softened by the 3600 converter. However, after I purchased that cam I started really researching the causes of PTV conflict and speedtigger is definitely right. Everything I've found indicates the prime culprit is not lift as one might easily assume. It's the valve events (timing of intake and exhaust valve movements relative to the piston position in the bore) that really dictate your clearances. I have a dial indicator on a stand and I'm definitely going to check the PTV clearance for the BTR Stage II cam I'm installing. In my mind this cam will have sufficient clearance, but I'm going to check it anyway. In fact, I think I will use the site suggested by speedtigger to check the correlation between the math modeling and the actual PTV clearance measured by the dial indicator. I'll post my findings when I'm finished. Over the years I've learned this: you get what you inspect, not what you expect. Thanks to everybody for making this a really great discussion-Happy Holidays!