Elgin 330/Sport SC cam in '78SC

[schiarchianis]

Is anyone running the Elgin 330/Sport SC cam in a '78 or '79 SC? I just had my '78 SC motor rebuilt and I went with the Elgin 330/Sport grind. Engine is all stock. WUR and FD were both rebuilt and a new airbox installed. However, I'm having drivability issues that the engine rebuilder (and a second shop) can't figure out. It bucks and surges when cold, and runs a little better when warmed up. Once the cam comes on around 3500-3800 with the pedal to the floor, it smoothes out. Seems to only run poorly when at part throttle in any gear, ie cruising. I've only owned air-cooled 911's with stock cams, so I have nothing to compare it to. So my question is, is this how it's supposed to run with slightly hotter cams? Or do I have other issues? I took it to the second shop for a second opinion, and they did a leak down test, checked fuel pressures, fuel flows, cam timing, engine timing, checked ignition, adjusted the WUR, and did a valve adjustment. Everything was within spec., although the second shop said vacuum at idle was a little low (can't remember the number). Both shops think it's the cams, but before I invest in a set of stock cams, I wanted to check here on the forum. Thanks in advance for your reponses...Steve

[reclino]

https://forums.pelicanparts.com/porsche-911-technical-forum/150334-elgin-super-sc-cam-grind.html
I am not a cam expert but reading through this thread the 330sc grind you have should run well on CIS. So you may have another problem, have you verified fuel flow and, system pressure,. control pressure?

[GothingNC]

Prior owner of my 82 Targa installed the Elgin cams a little over 22 years ago.
90,000 miles later, it has plenty of torque at the lower RPMs.
9.8 Pistons and SSI’s help too.

[schiarchianis]

Originally Posted by reclino

https://forums.pelicanparts.com/porsche-911-technical-forum/150334-elgin-super-sc-cam-grind.html
I am not a cam expert but reading through this thread the 330sc grind you have should run well on CIS. So you may have another problem, have you verified fuel flow and, system pressure,. control pressure?

Yes, the second shop verified fuel flow, and system, cold, and warm control pressures. It's been a real head scratcher. Both shops recommend replacing the 330/SC cams with stock grind cams. Doing so will put a big dent in my wallet, and my concern is I'll have the same drivability issue with the stock cam grind. At this point, I'm not sure where else to look.

[Otter74]

I have an ‘80 SC with these cams. Small port heads, otherwise stock internals (stock compression), Megasquirt. They’ve been in my car for around 15 years and, I dunno, 40,000 miles? I do not have the driveability problems you have. Engine has been great. I do have some mild driveability issues with a surging cold idle and stutter on throttle tip-in under certain conditions, but this is a relatively recent thing and I suspect it’s due to a small vacuum leak that I haven’t found yet. It’s not the cams.

[walt]

If the vacuum was low at idle maybe a small vacuum leak. Just did a smoke test on mine and found a cracked intake boot and leaking pop-off valve. Agree with above - not the cams.

Interesting the WUR was adjusted unless you have one modified to do so.

[Fleetwood]

Same cams on my 1979 SC rebuilt to 3.2 by Chris Powell in 2009. 210 rear wheel HP after and now with over 80K on the rebuild and going strong

[schiarchianis]

Originally Posted by walt

If the vacuum was low at idle maybe a small vacuum leak. Just did a smoke test on mine and found a cracked intake boot and leaking pop-off valve. Agree with above - not the cams.

Interesting the WUR was adjusted unless you have one modified to do so.

Both shops did a smoke test. The first shop discovered there was a leak at the EGR valve, and also where the vacuum line goes into the WUR. Both were fixed. The second shop also did a smoke test, and found no leaks.

Tony rebuilt the the WUR and made it adjustable.

[Tyson Schmidt]

I’d start with a valve adjustment as new cams wearing in will change quite a bit.
From there I’d richer up the mixture a bit at a time to see if the bucking goes away.
Don’t waste your time and money swapping out the cams.
Before I did that I’d verify the cam timing and that there are the same timing left and right.

Maybe put a smoke tester on the intake too to check for vacuum leaks. Make sure the vacuum advance is getting ported vacuum.

[mikedsilva]

Just a thought - is it possible that your new cams aren't cut right? No idea, just a thought.. Not sure if you can verify opening and closing angles of each bank?

Grabbing a set of stock SC cams wont cost much, most people give them away and at least you could eliminate it to allow you to move on in your diagnosis.

[schiarchianis]

Originally Posted by Tyson Schmidt

I’d start with a valve adjustment as new cams wearing in will change quite a bit.
From there I’d richer up the mixture a bit at a time to see if the bucking goes away.
Don’t waste your time and money swapping out the cams.
Before I did that I’d verify the cam timing and that there are the same timing left and right.

Maybe put a smoke tester on the intake too to check for vacuum leaks. Make sure the vacuum advance is getting ported vacuum.

Both shops did a valve adjustment. And the second shop said they really dialed in the mixture, although like some shops, they did it by sound and feel, not with an exhaust gas analyzer. I agree about being hesitant to swap out the cams without knowing for sure if they’re the culprit. The second shop reached out to Elgin and spoke to the tech who actually did the grind, and he verified the cam timing left and right. It’s just a real head scratcher.

[schiarchianis]

Originally Posted by mikedsilva

Just a thought - is it possible that your new cams aren't cut right? No idea, just a thought.. Not sure if you can verify opening and closing angles of each bank?

Grabbing a set of stock SC cams wont cost much, most people give them away and at least you could eliminate it to allow you to move on in your diagnosis.

I actually thought the same thing Mike. I just bought a set of used cams from a guy who pulled them out of another SC. Since I have all new rockers, I think it’s best to have them inspected and, if needed, reground to stock specs if I’m gonna end up using them.

[mikedsilva]

this might sound strange, but did you change your exhaust system when you rebuilt and if so to what?

[Tyson Schmidt]

Your cam grinder will know the specs of your cams, but not how they were timed. That’s up to the engine builder to do it right and get them both the same left and right.

[eastbay]

AFR gauge?

[schiarchianis]

Originally Posted by mikedsilva

this might sound strange, but did you change your exhaust system when you rebuilt and if so to what?

The original muffler was rusted out, so I replaced it with the "Dansk Original", JP Group part no. 1620608700. Otherwise, the exhaust system is all stock.

[schiarchianis]

Originally Posted by Tyson Schmidt

Your cam grinder will know the specs of your cams, but not how they were timed. That’s up to the engine builder to do it right and get them both the same left and right.

Would the bucking/surging be symptomatic of cams that were not timed the same, left and right?

[PeteKz]

Not in my experience. I tend to think you have an ignition timing problem. I would start by making sure the hoses are connected correctly, and use a timing light to verify the timing advance curve follows the specs, with and without the vacuum hoses connected.

[99boxster559]

I have had the same problem with the mildly built motor in my 82SC. The 964 cams lead to some strange tip in surging in 2nd gear at low RPM. I was told that this is due to the more aggressive profile of the cams and that the air flow sensor plate under the intake boot is very sensitive to changes in cam profile. I would not suspect that your cams are bad or misaligned as I believe it would run extremely poorly if that were the case. As mentioned above I would make sure timing is advancing correctly through out the entire rev range. Smoke test on the intake system should show if you have a leak which will give you a rough condition under tip in throttle. I hope this is of some assistance.

[schiarchianis]

Thanks everyone for the input. I've got a second set of stock cams I'm having Web Cams inspect, and service if needed. I might bite the bullet and have them installed and see how it runs. It might be a few months, though, but I'll post as soon as I have more intel. Thanks...Steve