Trying To Identify a cam (in the engine)

[Mike D.]

I recently picked up a carbed 78 3.0 engine. Got a great deal on it. The owner didn't know much about Porsches. He said he'd just bought the car in Vegas, drove it back to Ca. and "couldn't register it" because of "Carbs and headers" HA So he just bought a used motor with FI and cats.

Thought I was getting a 150k stock '78 with webbers slapped on. When I got it home I found that the carbs were 46 IDA's! woohoo! I figure I got my money right there. I pull them off to sell and get 40s but then I see that the heads have been ported. 44mm intake. And 3 of the heads have been replaced. So the motor has been rebuilt! Gets better, I break out the borescope and take a look at the pistons - Flat tops with valve reliefs cutouts!

I try looking for the cam part number. The only thing I can see is on the 4,5,6 side is "030" and under it "3s" and on another part of the cam D1. The only number I could see on the 1.2.3. side was "4s".

The PO said the car ran great at 90mph but bogged when driving around town. And the PPO was no help either.

Anyway, I'm just going to clean it up and instal it and pay for some Dyno time. But it would really help if I know what cams where in this motor.

Anybody have any ideas?

TIA,

[randywebb]

clamp a dial indicator gauge on and measure the lift at various crank positions (rotations) - do intake and exhaust to get overlap

[DanielDudley]

Those are big carbs. Bigger isn't better

[Mike D.]

I was planning on checking the cam timing anyway, so I can check lift and overlap then. And I may advance a few degrees for a little more on the low end to make more streetable.

I know the carbs are big. I was originally planing on selling them and buying a new set of PMO 40's. But now that I know the heads have been ported, I don't think 40s will work. With the intakes at 44mm I should have choke venturis at 42 or 40mm. Can't do that with the smaller carbs. I also don't know if the displacement was changed.

I could also go with taller air horns for more low end torque. right?

The engine runs, so I really don't want to tear it down. I'd just like to be able to tune it better. The guy at the dyno shop said to weld a O2 sensor bung on the headers and he could tune anything...

arrrg, wish this was easier...

[randywebb]

I have an O2 sensor on mine - it allows precise and nearly instantaneous monitoring of air/fuel, aka lambda - so in that sense it allows xlnt tuning.

It cannot, of course, compensate for mismatched components. Somebody tried to turn your 3L into a high rpm race motor. It will be unsuitable for in town use. It will be fun on high speed sweepers, open hwy, etc. ASSUMING it does not blow up.

I might worry about what rpm the valve train will take. What was done inside the motor???

I hope you have good conn. rod bolts, Ti retainers, good valve springs, and so forth.

Post what you want out of the motor/car & everything you KNOW about the motor - ask yourself - How do I KNOW this? Or am I just assuming it or believing what somebody else said and how do they know. IF the answer isn't certain, then you are risking a lot of 1,000 dollar bills if you treat it like a race motor.

If the motor is 'over-built' (mine is) then you can easily treat it like a hot street motor (and maybe put a hotter cam in later, if you get bored). It will be completely safe at - say - 6k rpm if built to handle 8k.

If you don't know anything else about it, then post what rpm it seems to start running out of ooompah. Lack of ooompah can be related to lack of air, or to you 'running out of cam.'

Always remember that a motor is like a real simple animal. If your sports medicine doctor (say, Dr. Demento) gives you bigger lungs, you get nothing without also getting a stronger heart, better blood perfusion in the capillaries, better exchange biochemically, etc. The whole thing is just a way to deliver O2 to the muscles. IF the lungs are weak for some reason then you'd "fix" them, if they aren't then you gain nothing w/o also upgrading all the other 'links in the chain.'

If the builder cheaps out then you can hotrod a motor for little money - that's why it was easy to get more power out of the old Chevys and Fords. If the motor has already been optimized in all its parts, then you have to upgrade everything - and that is a Porsche.

Like the above, your motor is just like an air pump...

Good Luck

and don't forget the oil pump...

[Mike D.]

The Borescope is a great tool. I hope to poke around a little more and hopefully answer a few more questions about this engine. I'll post findings later, maybe dyno results if I don't blow it up