Hottest 3.6 cams w/ stock pistons?

[petevb]

I’ve got a couple related questions regarding cams for a 3.6 993 with stock pistons. I’ve gotten some advice, but I can’t find anyone who is totally sure...

I’m doing a hot solid lifter cam in a 993, but I’m going to be limited by the stock pistons and the MAF sensor. Has anyone run something like a factory GT2 EVO, Dougherty Racing DC24, or Elgin 282/276, etc in a 993 with stock pistons before?

Related question: Does anyone know if the valve relief in the 993 pistons is more, less or the same as a 964 piston?

I’m basically trying to figure out if I’ll probably need to cut bigger valve pockets in the 993 cams or go with a smaller cam before I get all the way to claying the clearance.

Any guidance or experience would be appreciated.

-Pete

[Bill Verburg]

The only ones that I know work are the 993SS also called Cup cams. An otherwise stock 3.6 will pull just under 300hp w/ them.

[Steve@Rennsport]

LOL,....Just bear in mind that Cup cams (993 SS) do not idle well below 1000 RPM and will not pass any smog tests.

A 3.6 with or without V-ram, RS intake valves and a good exhaust makes well north of 300 HP with these cams. A V-ram version with Motec did 330+ HP here,........

[Bill Verburg]

Hey Steve, What do you think of GE60 or 80 w/ the thick base 102s RS valves, will Motonic still be viable or do I need DTA/Motec?

[petevb]

Would you be keeping your VRam intake and mass airflow meter with those cams, Bill? Those GE cams, as normally ground, have lots of overlap...

Steve- where did the 993 cup cams/ motec setup make peak power, and how much would it have fallen off by 7500 rpm? I'm looking at a very similar setup, but I'm not sure if I need a hotter cam to keep the power from crashing up to a 7500 rpm redline?

I'll add what I've been told regarding cams clearing stock pistons: The DC 24 or Elgin 282/276 has been used on a 964 motor with stock pistons. It's probably very close, though. This would suggest that anything milder, including the GT2 Evo, would fit (on a 964, anyway). The DC24s 282/276 are set at about 2.5mm, as are the GT2 evos. The Cup cams are 2mm, so they have significantly more clearance...

[Jeff Alton]

The checking height is used for timming the cams, not to determine if one has more "clearance" than the other.......

Jeff

[Steve@Rennsport]

Hi Bill:

GE60 cams should clear with the 52mm RS intakes but we do machine the intake pocket diameters a bit for clearance. With GE80's, I would check those VERY carefully. There are lots of variables here; cylinder group height, deck height, chamber volumes,...etc.

Now,......the question of whether or not to use Motronic or another Engine Management system with those cams is not the biggest problem, intake reversion with a common plenum, single throttle is. The drivability below 4000 RPM will be just plain horrible.

Using any of these longer duration, high overlap cams requires an intake with individual throttles per cylinder. There is no question that such intakes do need something like DTA or MoTeC to be able to program the thing,.....

Here is what we do: http://www.rennsportsystems.com/1-c.html shows our own tall butterfly intake system. There are several variants for different engines. The picture shows a 340 HP 3.4 with DTA. Please e-mail me directly for more information.


Pete:

993 Cup cams make power from 4000 to 7000. At 7500, its headed well downhill. Besides, at 7500 one needs many modifications to the oiling system to live.

[petevb]

Thanks Steve. Question:

With a somewhat "milder" cam like the Cup cam does the Motec make more power than custom chipped Motronic? If so, why? It's my impression that Motec gives you lots of tuning flexibility, but it really only makes sense with more extensive mods that take you further away from stock?

[Bill Verburg]

Thanks, it is understood(to me anyway) that the Vram manifolds would be replaced by individual stacks, either TWM or Steve's.

I am considering swapping the 3.8 engine into a track car where the vram benefits would be moot.

[Steve@Rennsport]

Pete:

LOL,...thats a more complex question than you might know,...

Motec offers almost unlimited flexibility and resolution in tuning fuel and timing to suit each individual motor's configuration. The main drawback is that it doesn't support closed-loop knock sensing by itself like Motronic does. There are add-on components than can be used with M600 or better but it adds significantly to the initial expense and dyno time to install and tune.

A GOOD custom chip does very well but I'd need to know a lot more about the details of your engine to answer your question accurately.

Bottom line; If you plan on using pump gasolines, then you really should stick with Motronic.


Bill:

You would be stunned at the difference in throttle response and HP when a six-throttle intake system is employed.

[petevb]

Hmm. Thanks Steve, that's about what I thought regarding Motec. DTA has the same knock sensing limitations, or is it even worse?

My suspicion is that I’d be better off with Motronic. Maybe you can confirm this based on the motor specs, which as currently planned are:
V-Ram 993 motor, stock pistons and mass flow
52mm intake valves, port work.
Solid lifter conversion and cam (Super Cup?) valve springs and retainers
7500 rpm rev limit (normally revved to 7000)
1 7/8” headers with Coast mufflers
91 octane pump gas

I happen to have a DTA system on the shelf, which is why I’m particularly interested. I do a lot of autocross, which is the reason for the VarioRam and higher rev limit (I’m looking for a very wide power band to avoid shifting). Any suggestions on the motor spec would be appreciated as well...

[Steve@Rennsport]

Hi Pete:

Both DTA & Motec require other aftermarket solutions for knock sensing but if you will use 91 octane, IMHO your only practical choice is Motronic.

I think a custom chip made with your car on the dyno is the best solution given the listed parameters. I'll also tell you that 91 octane fuel is a BIG limitation and several compromises are required to prevent premature, unintended knock-sensor intervention.

Last, I would strongly advise you to rethink your choice of cams and solid lifters as these engines are NOT safe to 7000 and beyond with the stock rods, oil pump, valve springs & retainers. Further, other lower end mods are required for it to live at 7K.

1 7/8 headers are also too large and will kill the bottom & mid-range without any benefit at the top.

BTDT, on ALL of these things many many times,....

[petevb]

We’re straying from the initial thread, but then RPM and cams are directly related.

So I am building the motor from the bottom up Steve, and had already planned to change a fair bit of what you've listed for duty to 7.5k. Rods, rod bolts, retainers, and valve springs (along with rockers) are going to be changed. Looks like you're suggesting the stock oil pump needs to go to for a 930 or GT3R pump? Then what else needs to happen in the bottom end?

I guess I'm a little surprised at the extra things I hadn't planned on for duty for brief periods from 7k-7.5k in 2nd gear. I've seen a number of 3.6l motors revved between 7 and 8k. Jerry Woods did a 964 motor with a stock bottom end but Webbers, exhaust and a cam the he revved to 7.4k? I guess there is more to it than it appears.

If you don't like the cup cam for this application then what would you suggest?

Yes, the 91 octane requirement sucks, especially since I’ll have access to higher 90% of the time. Not sure what I can do about that, though...

[Steve@Rennsport]

Hi Pete:

I'd agree,...the subject matter has strayed.

Everyone has an opinion and you can collect a lot of them. One simply chooses the one(s) that have the experience to support the statements,....

IMHO,..one chooses a camshaft that is both compatible with the mission and with the other components to be used. Its not like choosing things al la carte on a menu,.... Everything has to work together, otherwise the end result will disappoint you in many ways. After that, the rest of the motor must be able to support the intended RPM range and in some cases; sustained high RPM operation.

Everyone's expectations of engine life are different and some race engines need inspection every 50-100 hours. The 993 crank is not as robust as the 964 one is (that why Porsche never used it in any race motors) and one must accept certain built-in limitations of the parts in use. I would not run the 993 crank over 7K, sustained.

You should use the GT-3R oil pump (cheaper than 930).

LOL,...There is a LOT more to this than it appears.

You may use the Cup cams (with 1.75" headers) and a proper race muffler as long as you accept the RPM limitations of 7K. IMHO, anything over that constitutes abuse,... Its not necessary.

Lastly, ...91 is too low for any track work. You should plan on mixing 50/50 unleaded race gas.

[petevb]

Thanks for the education Steve. Most of the time I'll be able to mix in 100 octane race gas into the tank, and I will certainly do this any time I can. Thanks for the heads up on the rev limitatains, etc. I'll lower my expectations and do some more research to avoid an expensive mistake...

[KobaltBlau]

not to derail the thread again but here is an "open source" type (like megasquirt) engine management with knock sensing built in, called VEMS:

http://www.vems-group.org/products.html

I hope to install one next winter but as of yet I have no personal experience with it.

[STROSEK]

Not to further de-rail.... The electromotive tec3r also has knock sensor capabilities. I adapted the stock knock sensor location and use a single wire GM sensor. Works great! The system also does away with the distributor and uses individual coils.

Cheers!


Even though this thread has gotten off topic it's been a great one...

[camgrinder]

You might talk with Steve Timmons at http://www.instant-g.com/
He has a programming package to go along with my DC22 cams that works very well.
I have also been making the super cup cams on a wider LSA (lobe center angle) of 114 instead of 112. This cleans up the idle and widens the power band.

[Steve@Rennsport]

John:

AFAIK,...The only difference between SuperCup and RS cams is the lobe centers; 114 vs 112 so those would simply be RS cams,...

Thats my understanding after careful review of the factory manuals and a short discuession with someone at Porsche Motorsports several years ago.

[camgrinder]

Steve,
That might be true. Do you know the code on the front of the RS cams? 993 246 XX etc.