Camshaft selection advice 3.4 twin plug

[Jmorski]

Need some advice on camshaft selection and was hoping for some suggestions. Have a 3.2 Carrera engine out at a shop for a build. Planing on 3.4, twin plug, 10.5 compression ratio, Rasant EFI on PMO 50MM throttle bodies. Car is a 76 911 hotrod that I am building. Duty will be mainly road use with occasional track days (1-2 per year). I realize there are a lot of options out there for cams, as well as custom grinds and find myself overwhelmed with choices on a topic I am not that familiar with. Would like the car to make good broad streetable power and rev to 6800/7k and not be too temperamental pulling away from a stop light or around town ect. Discussion with the builder has been around a custom GT2 style cam with 104 or 108 lobe separation. Im no expert on this topic (although I did read the camshaft selection info on the Supertec site which was helpful) and thought I seek some advice from some of the experts on this forum. Does that cam selection sound reasonable for this engine spec or are there other grinds that may be a better fit? Any help or suggestions would be appreciated. Thanks - Jason

[Trackrash]

It really depends on the "flavor" of motor you are after. Do you want a motor that will produce power at 7K rpm, but will not have anything below 4,5K rpm?

Or do you want a motor that will have nice response and have power NOW when you hit the throttle? The GT-2 cams will do that. I have GT-2 with 102 lob separation cams in my 3,O w/ webers and it is very responsive and pulls great up to above 6500 rpm.

I'm not sure how a 3,4 motor will behave with a GT-2 cam. Maybe others will chime in with their experiences.

Contact John Dougherty, AKA Camgrinder on this board, at Dougherty Racing Cams to get his opinion.
Dougherty Racing Cams Porsche 911, 930 and 964 camshaft profiles

[lvporschepilot]

DC60 all the way. In a 3.2-3.4 it will be about out of steam by 7000-7200 ish. In an earlier engine they will spin higher with big ports.

[Jmorski]

Trackrash & lvporschepilot - Thanks for the comments/suggestions. I definitely want the power to be usable in street driving rpms and pull strong to about 7k. Not too concerend with how much more power it makes above 7k. I'll take the advice into consideration as well as reach out to John.

[Jeff Alton]

Built a couple of twin plug 3.4 with DC44/108 cams. Made great power and long torque curve. Still pulling strong a 7200...

We have a third one on the go right now. Just waiting on cams and heads to come back... This one will again use jenvey ITBs but we are using AEM ECU and coil on plug...

The last one we did (with PMO ITBs) ...

[mikedsilva]

Originally Posted by Jeff Alton

Built a couple of twin plug 3.4 with DC44/108 cams. Made great power and long torque curve. Still pulling strong a 7200...

We have a third one on the go right now. Just waiting on cams and heads to come back... This one will again use jenvey ITBs but we are using AEM ECU and coil on plug...

The last one we did (with PMO ITBs) ...

@Trackrash
Cams really confuse me.
Looking at this article on the Supertec website, it seems that 'where' the torque and hp is made is determined by the intake and exhaust duration. https://supertecperformance.com/pages/how-to-select-a-porsche-camshaft

Using those numbers, I listed 3 cams I am considering.
Currently, my 3.0 with 10.3 compression, (single plugged) itbs, aem infinity kit from Rasant, is running the webcam 464/465.
To me, it feels like it really starts pulling around 3500 and keeps going till around 7000. It pulls hard.
Using the basic formula from supertec article, it shows the characteristics of the 3 cams as


Yes, the webcam has a LSA of 101.. this may or may not explain some resonance I am experiencing at lower rpm, but only really noticable with a closed throttle.
I'm leaning toward trying the GT2 with a 108 lobe centre from John. This should bring the performance a little earlier in the rpm range, but hoping it wont run out of steam up top..

Thoughts?

[mikedsilva]

Originally Posted by Trackrash

Or do you want a motor that will have nice response and have power NOW when you hit the throttle? The GT-2 cams will do that. I have GT-2 with 102 lob separation cams in my 3,O w/ webers and it is very responsive and pulls great up to above 6500 rpm.

thinking of trying this cam on my itb efi 3.0... but with a 108 lobe centre..

[Trackrash]

Originally Posted by mikedsilva

thinking of trying this cam on my itb efi 3.0... but with a 108 lobe centre..

Could be a good choice. I would recommend emailing and asking John himself. He is the cam guru.

[Iciclehead]

I am building a 3.4 motor as well (twin plug, PMO ITB, Motec etc) and the good Mr. Doherty recommended his DC35 cam as a nice cam for street use with good power, tractability and fuel economy.

Have not got the engine together yet, we shall see how reality goes...

Dennis

[mikedsilva]

Originally Posted by Iciclehead

I am building a 3.4 motor as well (twin plug, PMO ITB, Motec etc) and the good Mr. Doherty recommended his DC35 cam as a nice cam for street use with good power, tractability and fuel economy.

Have not got the engine together yet, we shall see how reality goes...

Dennis

Interesting

for my 3.0, he recced the GT2. I am currently running webcam 464/465. Here are the specs for all 3.

[Iciclehead]

Originally Posted by mikedsilva

Interesting

for my 3.0, he recced the GT2. I am currently running webcam 464/465. Here are the specs for all 3.

The two look awfully close...but I don't know camshaft stuff very well....maybe the GT2 is a refined DC35?

Dennis

[Trackrash]

Keep in mind that the LSA can be adjusted on a custom basis. That can tailor the characteristics of the cam to your preferences.

Some of us are running a GT-2 102 with great results. Others are talking about 108 LSA.