Straight Answers on a 964 Cam in a 2.7

[DohertyCM]

I posted this in the Engine Rebuilding forum....

I thougt I might have better luck here.....

Straight Answers on a 964 Cam in a 2.7
Noah (from this board) has prompted me to ask this question to get straight answers....He knows but he wants me to sleep good at night...

for reference...I have a 1974 911 with a 2.7l motor....plain jane....although my wife calls the car Shirley...because she is the "other woman" in my life....

Now...I have gotten 2 completely different answers to this question...

Will 964 cut cams work in a 2.7L CIS motor without changing anything else....use stock pistons and cylinders...????

Some say yes....

Some say no.....

Some say maybe if......

Someone who has done this mod please post......

Remember this is a 8:1 compression engine...not a 8.5:1 S motor..

[DohertyCM]

Of all the advice I have been given on Porsche's, I cant believe that no one has done this mod....And that all the Talk was just a bunch of Couch mechanics spouting crap....

No it wont... Yes it will...... It will but...

READ THE FORUMS!.....

I Did. And one guy even told me that I had to have a clearance of .045mm of clearance between the piston and valve.....

WHAT ARE YOU KIDDING ME! I am not piston mechanic, but I have worked on jet engines and let me tell you, I am not an IDIOT.


And out of all of you supposed PORSCHE EXPERTS....I cant believe that NOAH was the only one who has given a knowledgeable explanation of what will work.

SO, I will go forth and be the Ginny pig....and trust the answer I got from NOAH...


BUT YOU ALL SURE KNOW A STOCK ENGINE WONT REV TO 8500 RPM DON'T YOU!!!

pathetic...

[flmont]

All I can say is they work GREAT in a 81' 3.0 ....FM

[A Quiet Boom]

Seems to me the easiest way would be to compare lift and overall duration to the 2.7 cam. My best guess is that it will work as it's a common upgrade on SC engines and you did mention lower compression which suggests smaller piston domes.

I am not that knowledgeable about P-car engines but have lot's of experience with V-8 and 4cyl engines. If you can get a cam to test you can use what's called the clay method for measuring pistoin to valve clearance or you can install compress the valve until it touches the piston with the cam at full lift and use a dial indicator to measure the clearance, for V8 engines they make a special light spring for this. I prefer clay in the valve pockets and you get a true measurement at the closest point which may not be at full lift. Hope this makes sense.

Now i could be mistaken but I don't think a 964 cam will actually fit the cam towers of a 2.7 so you might have to go with a 964 grind on a 2.7 base cam.

I could go on an on about cam setups but I defer to the P-car specific experts as my knowledge is more broadly based.

Right now I'm in between deciding on 964 cams or different pistons so I can go more aggressive trouble is my engine is Alusil so I'd need either new cyls or have mine bored and Nikasiled.

Will you be changing anything else along with the cam? My exerience has always been that intake and exhaust need to be addressed even with a mild cam to get full benefit. Again that experience is with non-P-cars.

[47silver]

in waynes rebuilding book on page 113 he recommeds the 964 cams with a 2.7l engine. not sure about if the pistons are stock or not as he mentions je 90mm's with nikasil cylinders.

[randywebb]

Well if you are not satisfied with the free advice on this bss, you might try hiring an expert and paying them.

Yelling at people on the Internet is nearly as productive as shouting down a well.

[dweymer]

I thought it was the reverb that affected the throttle plate of the cis, not the clearance. So what did Noah tell you, since you have the straight answer?

[T77911S]

i bought my 2.7s and the cams were advanced 12-15* ( the intake was opening around 8* BTDC instead of 6* ATDC). i just set it back to spec and the car runs better than ever. no bent valves. it was driven at least 20k miles like this. it did ping at around 4000rpm or when you floored it though. am also interested in noah's answer.

[DohertyCM]

This is such a specialized subject, I needed to yell and knock the rust off of some of you guys.

Here is what Noah told me...

"Chris,
Did someone who knows anything tell you the 964 cams won't work in your engine, or was it some guy hanging out on the street corner? Lots of guys have put 964 cams in CIS motors. Yours even has 8:1 compression, not 8.5:1, so there's even more room in the combustion chamber. Time the cams to 1.26mm. And enjoy!
Noah"

Given that I will put them in. I will borescope the pistons to see how much room I have between the valve and piston during its cycle, because i dont want to pop the heads off...yet.

I have the lift and duration cycle somewhere in an email from the guy who cut the cam.

Dempsey has JE Pistons in the example he used, but doesnt say if they were notched, domed or plain...Not much info on this, thats why on my first post i wanted him to chime in. But he didnt.
I have the backdated(well original exhaust) and a just added a burshe muffler on this motor and I will add a fidanza lightweight flywheel during this evolution. The intake I will not touch. I actually like the CIS system because of its reliability. I have the MSD ignition with the pointless system in the distributor...so the car runs really good but I want just a little bit more. It seems almost like a challenge to see how much power you can get out of a 2.7 with just basic bolt on mods.

The cams i bought were 2.7 cams reground to the 964 spec.

So if anyone else has any use info or experience with this I would appreciate the input.

HOWEVER....when I am done I will post my findings and lessons learned and if I can find a dyno around here I will also post a dyno run.

Anyone Else..

[davidppp]

One more heads up..the fidanza has a bad name round here.

Also do not rely on the borescope..it is practically impossible to estimate clearnces because of the type of optics.

The shade-tree method done with great care will acurately tell clearnaces.

The adjusting screw is 1mm pitch...turn it in slowly while slowly gently turning the engine over..I like to see 2mm clearance on exhaust but 1.5 will do..

Kind regards
David

[Jubbie]

I though the story from Camgrinder (John Dougherty) was that you can put a 964 grind in a 2.7, but it won't work as well in a low compression engine due to the relationship between valve opening, compression and performance. He recomends a modified SC grind I think was called a SC300. I used it on my C3 and it has worked fine.

[T77911S]

u can put a dial gage on the valve, set cam to its highest lift point, adjust the valve til it hits the piston.

[DohertyCM]

OUTSTANDING COMMENTS....
Alternate methods of adjustment.....Excellent.

the borescope, your right about the clearance, I was merely looking at a clearance issue for initial install and as a QA to final adjustment.

I had asked John D. about it and his suggestion was to go with a Sport SC cam because of a clearance issue. He had said nothing about the low compression motor. He called it a DC10. And I will go with that if this radical cam idea doesnt pan out for me..

Not to change the subject....But I have asked on the board about the Fidanza flywheels and no one has given any feedback what so every on them, So why the bad reputation....They are not in bed with Motor Meister are they?

Chris

[MotoSook]

Who's cutting your 2.7 cams for you? Or do you think you are going to put one of the commonly sold 964 grind cams on your 2.7? The 964-grind cams you see for sale these days are generally 4 bearing cams, which will not bolt on your 2.7 engine.

Good answers start with good questions and a good attitude. I suspect most folks with anything good to say are now fixing their couches. You all should see the Lazy Boy cushions I swapped into my IKEA lounger. It's the best upgrade I ever performed .

[DohertyCM]

Elgin cut the original 2.7 cams and reground them to 964 specs.

When I get home I will post the part number just to see if anyone has any comments.

IKEA...wish I had one around here.

[Porsche_monkey]

Originally posted by Souk
You all should see the Lazy Boy cushions I swapped into my IKEA lounger. It's the best upgrade I ever performed .

I did the same mods. I just work on calibrating them each night now.

[randywebb]

"I will post my findings and lessons learned and if I can find a dyno around here I will also post a dyno run."

- That would be Zehr Gut!

BTW, I haven't seen anyone say anything about the more advanced ramping that we'd expect to be on a 964 cam...

But, why not back up a bit... what is the percieved advantage to a 964 over getting a custom grind for your 2.7 - even using your original cams??

[SC-targa]

I'm guessing the 964 cams will work just fine in this application. The advantage over the stock base model 74 911 cams should be more duration and greater lift. This should boost the top end power over the stock cams. Because of the minimal overlap, it has been proven to work on CIS motors.

The only potential downside I can see is that he has such small ports (even smaller than the 80-83 SC's) that they may choke off some of the potential top end.

I think we've seen the same issue with 80-83 US model SC's with these cams. When you look at dyno sheet data folks have posted on this BBS, you can see that the 964 cams just don't wake up those small port engines like it does the big port 78-79 SC's and the Carrera 3.0 & 3.2 motors.

Just my guesses,

Jerry Kroeger

[CARRERIC]

I have a 1975 Carrera 2.7 with CIS.

When my engine was rebuilt two years ago my cams were sent out to webcam for a SC grind. Webcam hard-welds and then regrinds (there is a difference), and Case was sent to CE in Bodfish CA. Also a brand new set of RS pistons and cylinders installed. These cams really woke the car up!!!!! Car has major pull straight up to redline.

When I started I thought about the 964 grind but too many uknowns. After my rebuild I am very happy I went w/ the SC grind. Not sure the CIS would handle 964 grind.

[DohertyCM]

I like the car, very nice. And thanks for the input.

Chris