Craig the Standard on head flow is .350 and .500 lift and thats what the flow rate is measured on period...

 

Craig,

If you are using GT3 street cams like Markski, then your attainable lift is .500. This would being utilizing a NA duration. If you are using turbo heads with turbo cams (and the required turbo cam housings) then your attainable lift is alot less than .500. Turbo cam housings can use GT3 exhaust cams but cannot use GT3 intake cams. This is what is bad about using the turbo heads instead of GT3 heads. We have spent in excess of 60K making about a half dozen cams (intake and exhaust) No one that I know of (except us) has fooled with the intake cam. Few have used GT3 exhaust cams which the majority match with the turbo intake. Markski is the only other one who used the GT3 intake on a 996tt. This is because Protomotive has solved the GT3 software issue on 996tt ecu. About a month ago on the cjv turbo thread I posted this ........... which was the second to last cam we have made. The current cam will not be done until January 10th. I just confirmed that today.

This whole cam issue, which heads (GT3 or turbo) fit with which cam housings, cams, and different valve stem lengths (yes these are different with the different motors) is really confusing to say the least. If I have done a bad job in explaining, I apologize.

"We have had many people ask us what what is involved in our cam project. Here is a brief description.

First we completed the GT3 R heads. Minor touch up of the ports and combustion chambers, ceramic coating and then micro polish of the coating in the combustion chambers. The heads were then flowed to determine optimum lift and duration for the intake and exhaust cams. Now on to the cams. Here is a short description.

Design radius bucket follower intake cam profile to replace factory turbo lift variable lift profile.

Design radius bucket follower exhaust cam profile to replace factory turbo flat profile.

Manufacture intake master plate.

Manufacture exhaust master plate.

Grind engine set of new factory blanks with above masters.

Measure radius of cam follower and CNC machine probe to measure street GT3 cams.

CNC machine drive fixtures to reference cam lobes to slot in rear of cam for factory cam timing tools.

Fit GT3 cam trays to GT3 R heads. Fit GT3 cams with GT3 buckets, measure valve lengths and bucket clearances.

Final fit of new design cams with trays and buckets. Check bucket clearances on base circle.

The time involved has been about eight months. The cost to flow, design, profile, and manufacture specific intake and exhaust cams was more than a regular engine rebuild. One thing we have learned is we will pick up approx. ten hp for every ten thousands of an inch we increase the lift up to a certain point. In addition, by custom sculpturing the duration for turbo application, the motor should be as smooth as silk with excellent response throughout the entire usable rpm range (2000 to 9200). "

 

Alex,

What I am trying to convey to Craig is you can measure your head flow at any lift and duration you want. That doesn't mean the cam you installed will perform to those lifts and durations.

Furthermore, you understand with turbo heads you are limited to turbo cam housings. Turbo cam housings will accomodate turbo intake and exhaust cams or turbo intake and GT3 exhaust cams. The GT3 intake cam will not fit in a turbo cam housing. Right there there is a severe lift restriction.

Up until recently, you could not put a GT3 cammed motor into a 996tt with a 996tt ecu due to the different cam pointers on the different motors (996tt, GT3 Street, Cup/R motors all have a different number of pointers). Todd's genius solved this as to using the GT3 Street cam with a 996tt ecu.

Also in the mix is no independent cam maker has been able to make special intake/exhaust cams because they cannot also make the buckets with the same compatible material. If you don't have the same metal, the cams will prematurely ware out. That is why you haven't seen people making new cams from billet or welding and regrinding. We have just recently solved this issue.

 

If you want any assemblance of comparison use the .500 lift numbers. You have 324 @ 28 psi. That translates to approx. 306 cfm @ 25 psi @ .500 lift. Our July tests were 324.5 @ 25 psi @ .500 lift. That is about as close as we are going to be able to get as our valve sizes are a little different and so our our head port sizes.

The only thing that I can say with any certainty is differences are comparitively small as would be the corresponding differences in ability for the respective heads to make power. This just proves that the last few horse power go up geometricly price wise.

Another way of looking at this and helping with the explanation is by examining Alexander's and Markski motors. Alexander has larger valves and I am assuming slightly larger ports than Markski. Yet Markski produces at almost any given rpm range (when at boost) approximately 80 additional hp. Why is this when Alexander's heads flow more? It is my opinion, the difference probably lies with Markski's has a higher intake cam lift. Our test showed us that for each that (if other things are equal) for every additional ten thousanths of lift added there was an additional 10 hp was to be had.

 

Chad,
stock cams are 30 degrees of lift... gt3 cams are 45 degrees... but u already know this LOL

 

Markski also runs 8200 RPM and is able to stay in each gear longer. In a head to head race against a stock TT, Markski will be in first while the TT hits redline at 6500 and has to go to second. It's easy to see how first gear will out-accelerate second, etc..

 

Chad, I use GT3 exhaust cams and stock intake cams.

Craig

 

Craig,

I tend to be a polarizing person even though I don't try to be. I try to read all your posts. You had said over time that you had your heads ported and used larger valves. I believe you also said you had a different lift.

From the information you provided, I assumed your had a stock 996tt intake and a GT3 exhaust. Which I might add was the state of the art when you did your motor build. With one exception, at the time there was two choices ......... stock intake and exhaust and stock intake with GT3 exhaust. The lone exception is a set of cams from FVD that are made for the GT2. They add a little power, but the redline is about 7200 max. The stock cams with proper breathing will made hp up to 7500 rpm's and there duration is profiled for a turbo motor. The above cams will fit in the turbo cam housings. The GT3 intake cams will not fit in the turbo cam housings. Furthermore, turbo cam housings don't work on GT3 heads and GT3 cam housings don't work on turbo heads. Therefore, unless you have GT3 heads and cam housings you can't use the GT3 intake cam. To my knowledge motors that fall into this catagory are VRAlexander's, Elliott750's and yours. People advertise for a special exhaust cam. I could be wrong, but I would bet these are stock GT3 exhaust cams. To make a special cam from billet would risk mixing a non compatble cam material with the Porsche lifter material. Most likely this would result in premature wear.

Now comes the next advancement .............. Markski's car. It uses GT3 heads, GT3 cam housings and GT3 intake and exhaust cams. The advantages are non varioable lift, higher lift and duration. The disadvantages are although the lift is better, it isn't optimum for the heads under turbo applications nor is the duration optimum for turbo applications. An improvement over the limitations of 996tt heads ....... yes. This option wasn't even available until Protomotive came up with an solution for running a GT3 intake cam on a 996tt ecu.

Now the latest advancement, we have come up with a cam that is material compatible with the tappets, has higher lift and a turbo motor profile duration. In addition, we have found that the GT3 intake/exhaust cams have a harmonic distortion, that when eliminated makes notable increases in power. To my knowledge doing this to a GT3 intake cam is a first.

I realize all the above is a little confusing. It took us alot of time and mistakes to get where we are today. I am also sure it will be improved upon once the cat is out of the bag so to speak. I am in no way degrading any of the above advancements.

 

I simply refer to it under different terms .............. upslope and downslope of duration. The profile of this angle on the stock cams is where the harmonic distortion was found. By adjusting it, it was eliminated.

 

Now Imagine (see Stephen gets involved now ) your same logic using a 3.18-1 ratio first gear!

 

Alex...I thought you said that you were going to be at Pinks today. I was at Firebird and didn't see you, I got a VIP pass and was in the pits. I spoke to Rich Christensen and asked him where you were, he said "how should I know?" You told me that you would call me, I tried calling you but no luck.

What's the deal?

 

You are 100% dead on!! I am so happy with the power my turbo is making with factory lift cams!! On the other hand....how much more hp do you think I could make with a set of custom cams????


I never made it to Scottsdale ...I am still in LA...hope you had fun at the event...I will call you when I get to Scottsdale...

 

[quote=VRAlexander]You are 100% dead on!! I am so happy with the power my turbo is making with factory lift cams!! On the other hand....how much more hp do you think I could make with a set of custom cams????

Back to the mad scientist to find out I guess. And you said you needed a change.

 

cjv are you referring to harmonic distortion in the valve train or intake manifold air flow?

 

Now that's a damn shame.