What's the hottest 3.2 cam you would use?
 

I'm just about to take the engine out to properly recam my 3.2 as I made the mistake in my top end rebuild of putting my stock cams back in after I went to Mahle "Euro" 10.3-1 p/c, Ollies full race heads (every option on the menu 'cept porting), ARP rod bolts & head studs.

The engine runs great except that with the stock cams it seems to start running out of breath around 5500 rpm. It's a 80% track car....

So here's the question.....964 cams are too mellow in my opinion, the webcam 20/21 grind seems to be a little better with similar duration and a little better power due to increased lift compared to the 964 grind.

But the "3.8 Super Cup" Grind from DRC is a little hotter- with a tad more lift and a tighter lobe center than the 20/21 grind and I'm thinking I would like to go with that.....

Anyone out there have experience with this cam? I've spoken with JD (camgrinder) via emails and he's done a great job of helping a driver (as in not a 911 mechanic...) like me out so I now understand the basic's of this cam stuff....

Any input is most welcome, I will have the shop order up my cams next week....

Many thanks in advance....:)

Just for the heck of it, have you tried retarding your cam timing for a little more top end?
-Chris

I believe your piston choice will severely limit your cam choice. Assuming you have Motronic and enough valve clearance the Super-Cup grind is about at the most aggressive and is a huge improvement over the stock profile. IMO.

My feelings exactly....that's why I posted this. My question still stands....anyone out there used this grind in your 3.2?

I was very concerned about piston to valve clearance on this cam as well.....several emails b'tween cam grinder & myself as well as pm's to fellow pelicanites Rdane and carrera 3.5L.

Concerning the piston to valve clearance on this particular cam, which was on my mind constantly, I decided to chk out Rennlist and found a thread....

http://forums.rennlist.com/rennforums/showthread.php?t=169098

Look for Camgrinders comments half way down regarding the factory 3.8 Super Cup Grind ....

Camgrinder quote fm rennlist:
"Most people think adding total valve lift will put the valve closer to the piston. But full valve lift occours 112 degrees past top dead center on this cam. Meaning the piston is more than halfway down the cylinder bore at full lift. The parameters that have the most effect on valve to piston clearance are,
Duration ( The time the valve spends open) and
Lobe centers ( the centerline of the lobe in degrees from top dead center )
The rule of thumb is:
More duration or tighter lobe centers = the valve/piston will have less clearance
Less duration or wider lobe centers = the valve/piston will have more clearance
98 degrees would be a tight lobe center and 112 is a wide lobe center.
__________________
John Dougherty
http://www.drcamshafts.com

(John I hope you don't mind me using this... )

The above explanation REALLY cleared things up for me - Thx JD.

Based on this info I am alot more comfortable with it..... My mechanic will check every thing very closely....(my wife is the office mgr and signs his pychk!!) If I have to go with a more mellow cam I will...but based on my engines parameters this is the one JD recommends.

Any one out there put it in a 3.2...??? or am I going to be the first?

:eek: :D

I'm doing an upgrade rebuild on my '85 3.2 -I will go to 3.4 P/C's and use the super-cup grind because IMO it has good lift and duration for a performance street engine plus the lobe centerline is still conservative enough to run with Motronic. In other words it is the most aggressive grind that you could run and still retain stock-like driveabilty.

I'll use JE's (pistons) because they allow me to custom order the dome shape, compressio ratio I want.

From what I've learned here and other credible P-car engine guys is that the Mahles do no have enough valve relief and you can't modify them any further.

I recently spoke with John; DrCamshafts about this build and he was very informative and helpfull. My main concern was maintaining good cylinder pressure with 9:8-1 with this cam profile. His experience was that it would work great and result in about 175-180psi for my combo. Exactly what I wanted.

I'll buy my cam and springs from him.

Mahles do no have enough valve relief for this cam? or for other more aggressive grinds?

Like John points out in the quote above:
".... full valve lift occours 112 degrees past top dead center on this cam. Meaning the piston is more than halfway down the cylinder bore at full lift."

based on that I am understanding that if this is the case, with the piston halfway back down the cylinder at full valve lift there should be no clearance issues.

Or am I missing something here?

One things for sure nobody will know until you bolt it in (with the proper set up) and see what the valve to piston relationship is. Several experienced builders tell that once you pass the 964 grind (Lift and duration) things get close.

If your short block is all good, get the heads set up and see just how much clearance you have.

Yes and No. If you use the Mahle's made for the CIS/Motronic dome then it could get close depending on the cam selection. I don't have enough experience to say what cams would be okay for CIS/Motronic pistons but at least the 964 grind and the 20/21 would be fine. These are the profiles generally used by people retaining CIS/Motronic but if camgrinder says his grind works then I would trust him. It will be interesting to see how the "supercup" grind works out for you guys.

If you use the Mahle's designed for carbs/mfi (which I did), you will have much more clearance and it won't even be an issue. I used Web 20/21's and Web states that the piston to valve clearance should be at least .050" intake and .080" exhaust. No problem at all for my pistons, as this piston set was designed for much more aggressive cam profiles.

I just have to retain Motronic to pass smog and thus need a "civilized" cam grind.:(

Good call on the JE's providing you the CR you want, don't even get me started with the Mahle's on that one. I think the JE's are made with the carb/mfi style dome as well, so you might consider twin-plugging in addition, especially if subjected to 91 octane like I am.:( Johnny, you are in SoCal but I think that you mentioned that yours is more a track car so I assume that you are using better gas?

Both of you guys keep us informed with the latest developments, it is always nice to watch the build process and see what other people are doing.

Ralph

wow...!! always nice to hear your .02 Ralph....very much appreciated:)

And yes you are right Ralph, I normally run higher octane than the std pump piss we have...specifically a blend of 50/50 91 & 100 octane for an average octane of 95.5.....and truth be known with the standard OEM 3.2 gasket set from SSF that was used in my top end rebuild I now feel I would be lucky to actually have the advertised cr of 10.3-1....especially after following Ralph's CR ordeal on his beautiful hot rod motor rebuild....If I had to throw down a few $$$ in a bet I'd probably say ...and a pure guess it is....would be I'm in the neighborhood of 9.8-1...??? I will have that chkd in the coming weeks tho....

My Mechanic has built alot of 3.0 & 3.2 motors over the years and I will go over the cam issues with him prior to the cam install......I will not run the motor until I am DARN sure there is safe clearance with the piston/valves.

to be continued.......

Johnny: 3 questions for you:

Are you stock (not twin-plugged) Motronic?
Did you ever run your motor on straight pump gas?
Other than running out of breath at high R's, how much different feel did you get from the high comp pistons?

I am puzzled at all the talk. If you do not MEASURE the valve to piston clearence, you shouldn't put it back togather, let alone run it.

Yeah, what he said!

I would suggest obtaining a program called Dyno 2003. Its an engine simulator program thats quite accurate, within a couple of percent, maybe better if you are careful and feed it very correct info. I don't know if our host sells it but if he dosen't he might want to check it out.

With this program you can plug in what you have and you should see a result thats pretty much what you have now. If not go back and measure some things in your engine until you get good results. Things to measure: cam timing, valve lift vs crankshaft degrees, compression ratio of every cylinder, actual stroke of Each throw, valve size, intake runner type and size, injector size,or carb size. These are all things you should already have done if you rebuilt the engine, if not you will need them for any track car. For the program you can use estimates for some or default values for a start. Play with cam timing and see where if dies, should be same as real engine. Then start modifying program (not engine) and see what you can do. Once you think you have it check with everyone who has already done one to see if they concur or if there might be a problem thats been over looked. Its real cheep compared to real engine parts and you can predict what you will end with.

I would go for a cam that peakes at about 6800 and red line it at 7200. Thats a qualified 6800 meaning you do whatever else is necessary to make it work right.

Jack,

Of course you should measure, I don't think any of this talk leads to the assumption of just bolting it together without checking.

I measured piston to valve clearance on my motor and had plenty of clearance, helped in part by using the carb/mfi piston that has the deep valve relief cut-outs. These were designed for much more radical profiles then the docile 20/21's I'm using.

You should always measure, whether using the CIS/Motronic dome or carb/mfi piston dome. Never assume anything!:)

Hopefully his former mechanic who performed the top-end rebuild for Johnny has a "build sheet" with all the pertinent information but if not he should make sure his new mechanic can provide him the info.

Ralph

Who said I wasn't going to have the clearances measured? I kind of figured that is a no-brainer..... Don't mis interpet my intentiuons because of the quote I used above from camgrinder.
As an initial "point of reference' his comments are encouraging, and are leading me to pursue this path. However as all here are quite aware the proper checks and measurements must be taken.

As a point of interest, during my rebuild, I had the opportunity to hold and very closely compare visually both one of my original 9.3 USA DME pistons and one of my new Euro 10.3 DME pistons.

I honestly held both in each of my hands for at least 30 minutes...staring and comparing from every angle and honestly - for the first 20 minutes I could not tell the difference. I actually began to get concerned (read: panic) that I was not sold what I had ordered.
Then I realized that the difference was in the height of the tapered shoulders that wrap around the top. The difference was in that the taper of the dome shoulders as I call them, that wrap around the circumference of the top have a more gradual angle or slope down towards the center of the piston top where it is flat. The max dome height was virtually the same from my measurements.

Again, it was very, very hard to distinguish any difference between the two by my eye. and I was not in a rush or hurried and had the rest of the day to stare at these 2 pistons and believe me, I took my time to be sure. There is a difference...but not a very big one at all...marginal at best in my opinion.

But rest assured, I will have the p to v clearance measured on each cyl.

Ralph, I am still using my same mechanic who built my motor originally. I do have a build sheet in my file on the top end rebuild, I will go to the shop and check it out.

Ed - I have not run normal premium (91 octane) pump gas since my rebuild. It is not a daily driver, used 80% for track events. As I mentioned in an ealier post I run a minimum 50/50 blend of 100 & 91 octane for a total octane of 95.5 yes I am single plugged DME W. a chip. the new p/c give a bit better mid range torque and push up to that mid 5k range where the push begins to taper off ...just like every other stock cammed 3.2 I suppose.

Johnny,

If its a street engine, the builder may not have measured valve to piston clearence because its so large to begin with. On a track enging the clearence is usually half a hare from total destruction all the time.

I too doubt the valve to piston clearance was measured. specifically because of the stock cams that were being re-installed. But my wife, who is the office mgr (and has worked with 911's for 22 yrs now...) sez she has all the notes the mechanic made during the rebuild.....I guess I'll find out.

But with the new cams, that will be a different story. I am going to have all cyl clayed to measure the p to v clearance.

I've learned alot so far... the education continues.....:)

Couple of things:

- See my diagram of piston / valve clearance in the Engine Rebuild Book for a clear understanding of when the conflict typically arrises. It is not what most people think (at TDC).

- The Motronic system here is your biggest limiting factor. To run really aggressive cams, you need individual throttle boddies (like on carbs or MFI). See Chapter 4 of the book for more on this and fuel reversion effects...

-Wayne

This threas is exactly what I have been looking for. I am in the middle of modifying my euro spec 3.2 to a 3.5 using Mahle pistons and barrels. It will have a Mtec M48 pro and throttle bodies. The primary use will be as a fast road car with occasional track day use.

Can anyone advise me of the most aggressive grind I can use while still providing street reliability and smooth idle? Is it the 964 super cup or an early 'S' grind.

BTW, does anyone have the profile data for these CAM's?

Many thanks
Pete

The most aggressive cam that you can run would be the 993SS cams.

They do make the idle just ever so "cammy", if you know what I mean. That's because they were designed to work with a mass-flow sensor, and not a flapper box airflow meter.

But they sure do make great power, if you don't mind slightly diminshed idle quality, and possibly the occasional fall off idle.