Elgin "super" SC Cam Grind

[echrisconnor]

I'm looking at changing out cams on my '75 Carrera 3.0 along with a top-end rebuild. The car is mostly driven on the street with as many DE events as I can attend. It's not a daily driver and I like to let it rev.

In the past, I'd read about various profiles to gain some performance. I'd settled on either a 964 grind or Elgin's version of the Webcam 20/21 grind. However, I gave Eligin a call and talked to them. Their key question was my compression ratio. This will remain stock at 8.5:1 . Given this compression ratio, their suggestion is to not go with a more aggressive profile and instead go with their "super SC" grind. This is somewhere between the 964 grind and stock. With a more aggressive profile and a low compression ratio, they fear it will be a dog at low revs.

Has anyone ever used this grind? Does this logic make sense about compression ratio and cam matching? Would peformance at lower revs likely be the same as stock or worse? Is it worth it then to swap if there is a minimal performance gain without swapping P&Cs?

Yes, I realize they are the experts, but I thought I'd see what others may have done.

[jfpound]

Hmmm, very interesting. I have a 964 motor and just sent my stock cams to Elgin to have them ground to the SuperC2 profile. According to the data that John faxed me this is a step up in lift and duration, making it more agressive that the 964, not less. I can let you know how it does for me if you want but the compression ratio difference may make the comparison realatively useless. Sorry I can't offer any insight on results of a hot cam + low compression. But the word is that Elgin has been doing this for a long time.

[kstylianos]

The SC330 is what I think Chris is referring to as the 'super sc'. Its a little milder than the 964 grind and Elgin recommends them for CR's less than 10:1 . I have the SC330 grind in my rebuild and it really evens/smooths out the the torque curve throughout the RPM range. It also helps out the bottom end as well. Very smooth and linear power curve.

See the recent dyno results of my engine to get an idea of the torque/hp curve this cam offers:

Dyno Results - Thoughts?


"My engine performs totally different than in stock form and pretty much exactly as I expected. The mid range pull is strong and even mashing the pedal at 3K rpm will put you back in the seat.....all this starts tapering off at around 5.5K, as is shown in the dyno chart. When researching and talking about what I wanted out of the engine, I told Walt that I wanted a very streetable engine (as this is where it lives for the most part), with good midrange torque. I wasn’t going to be driving in the upper RPM range, and didn’t want to travel to high RPM's to get max performance out of the engine. I like its characteristics and probably won't change the cams for something hotter......at least that’s what I say now"



Jeff, you are Correct. The Elgin SuperSC is very similar to the Webcam 20/21.

[camgrinder]

I hope this will clarify the grind names...

(Sport SC) is the same as 330 SC and is a one step up camshaft I recommend for 8.5-1 compression ratio engines. It also works well in Turbo engines.

(964 ) is the our version of the factory 964 C2 profile. Its a 2 step up over the SC stock grind and I like to see 9.3-1 or better with it.

(Super C2) is one step up for a 964 C2 and a big step up for an SC. I like to see at least 9.8-1 compression with it.

If you need more cam than the Super-C2 , there are other profiles available and we dont mind doing custom stuff and changing lobe centers.

Hope this helps,
John Dougherty

[speeder]

I have the SC330s with 9.3:1 (stock) CR, small runners, (it's an '82), and SSIs. The cams are nice, motor breathes well and gets nice reviews from everyone who has driven it, maybe I would get a little more w/ 964 grind. When I was building the motor, both Walt @ C.E. and Elgin recommended the SC330s over the 964s.

I haven't dynoed it yet, but I am guessing around ~200 crank HP.

[echrisconnor]

So, does a more aggresive cam like the 964 grind have more overlap, and therefore at lower revs with lower compression ratio it will actually loose power? I may find a performace gain from the 964 cam, but only at high revs, and at the expense of much of the low-end driveability. This would make sense to me.

What I'm hearing is that the Sport SC/330 SC is a good compromise which will work well given my compression ratio. It will outperform stock and still make better power at the high end.


Thanks,

Chris

[speeder]

It is my understanding that none of the cams mentioned have any overlap to speak of, the 964 cams are simply "bigger", ie. more lift/duration, ie. they flow more air.

Overlap in a cam design does not depend on compression ratio, the 2.4 "S" motor was only 8.5 CR. I think that maybe there is some confusion here over the relationship between cam design and CR.

[Rondinone]

Even the stock SC cam has overlap. At crossover, both valves are open 1mm. I have the SC330 cams also, at crossover both valves are open ~1.4mm. You might have noticed when you timed the cams that at 1.8 mm (TDC intake valve lift setting) the exhaust valve was still open.

[speeder]

Yes, all cams have *some* overlap, the point is that CIS cams are very limited in the amount of overlap that they will tolerate and still idle properly. The amount of overlap that we are talking about w/ the 330s is very small.

[Craig 930 RS]

BTW -

Just got off the phone with John at Elgin - he said a 274/284 grind - a step ABOVE the Super C2 - will work in a Motronic engine

Craig
@RS

[echrisconnor]

I guess I still don't understand then. If there is no significant overlap, and a more aggressive cam has more inlet/outlet time, what causes a power loss? Is it just too much of a good thing?

[jluetjen]

Letsee, a couple of ideas....

1) at some point you will start to close the intake too late or open the exhaust too early and you'll start to reduce the combustion efficiency of a motor.

2) Depending on your port sizes (and the head's resulting flow rates), you may have more lift then the engine can take advantage of.

3) Increasing the duration of the intake valve being open (past a certain point) may reduce the intake velocity and thus reduce turbulance in the cylinder. The result will be a less efficient combustion process

4) I believe that CIS engines tend to run a slight vacuum at high rev's as a result of the airflow meter's resistance in the airflow. In certain situations when there is significant overlap, this drop of pressure in the intake could result in mixture being pushed back into the intakes by the pressure of the exhaust. Even in the absence of overlap, I wonder if too much intake duration could result in some of the mixture backing out of the cylinder. This is just a guess.

That's a few guesses on my part.

[Thunderbone]

I put WebCam's 20/21 in my engine (now a 3.4) just bolts from 3500rpm to redline. CR is 9:53-1. SSI's,flowed intake, MAF, chip. Big fun.

[camgrinder]

To compare apples to apples in regard to overlap.
The point where the intake valve opens until the point where the exhaust valves closes can be measured in degrees.
The stock SC cam has 37 degrees of overlap.
The Sport SC cam has 43 degrees.
and the Super C2 cam has 50 degrees.
And an extreme example would be an MFI 911 S which
comes in at 89 degrees!
Increasing overlap will dilute the intake mixture with exhaust gases until the engine is in the intended RPM range. Once in the RPM range of the engine it can and will increase the VE.

Another thing to think about is where the intake valve closes. This is the most important valve timing event. The compression stroke is 180 degrees from BDC (bottom dead center) to TDC(top dead center). Lets say you have 8.5-1 compression measuring the swept volume of the cylinder from BDC to TDC. The stock SC cam closes the valve 67 degrees after BDC. Now you have lost a percentage of your swept volume. Your dynamic compression ratio is much less than your static compression ratio. The exact loss can be calculated by measuring the rod length, the crank stroke and volumes and doing a bunch of math. I have the formula but I use a program we made.
The later you close the intake valve the more static compression the engine will need and tolerate. Once the formulas are done and valve timing set most engines operate in the 7-1 to 7.5-1 range dynamic.
The Sport SC cam closes the valve at 70 degrees.
The Super C2 closes it at 74 degrees.

John Dougherty

[Craig 930 RS]

T-Bone!

Tell me (us) more about your engine.
What P&Cs?
HP/TQ #s from Dyno yet?

I will be building an almost identical engine....

THX,
Craig
@RS

[mtelliott]

If you go with new cams, do you have to purchase new rockers as well?

[350HP930]

You will at least need to get your old ones reconditioned if you don't get new ones.

I am planning on having my 930 cams reground to a SC330 spec. I am looking for good low RPM to mid range power so I am hoping they are a good match.

[Bill Verburg]

John thanks for contributing. I'm sure that you will be a valuable resource here.

Most of the modern factory cams have very little overlap for primarily for smog and secondarily for engine management reasons. The more aggressive ones use more lift but little additional overlap.

The more overlap the more important the exhaust tuning becomes. This is where the SSIs and other tuned exhausts will begin to really shine.

[5axis]

350 if your going for low, then I would stick with the regular SC grind. I have the 330's and really like them for the wide open farm country around me. If I had some tight twisty canyons, I would probably swap in the SC's.

[350HP930]

Well, I am also concerned about maximising power and the SC330 cams are supposed to make more power than a regular SC grind.

When I say low I am also being relative. I can reach full boost by about 3K RPMs but I know a lot of other turbo cars have to rev even higher before they can reach full boost.

For this reason I know I want a cam that favors the 3-6K RPM range which my research seems to indicate the SC330 cams should compliment nicely.

I am also keeping the turbo CIS too so I can't go too radical.