What is the most agggresive cams with stock 964 pistons?

Axel84 · Axel84's Garage

993SS?
DC21?

planning a 964 engine rebuild and a set of custom pistons is probably 400-500 bucks more compared to what I can buy a set of new stock 964 pistons for.

fairly stock build with ARP rods and bolts, on EFI but likely standard plenum.

My understanding is that with the 964 pistons you are running into problems if you go for more aggressive cams than 993SS?

where is the powerband peak with those cams? 6700?

Classic 911 · 10-25-2023, 11:02 PM

Following

Sent from my iPhone using Tapatalk

Jeff Alton · 10-26-2023, 07:02 PM

Have you inquired with any cam grinders?? DRC, WEB or Elgin, Or Neil Harvey who post her regularily?

Cheers

Axel84 · Axel84's Garage

Im inquiring here and now so that the information they share with me is also available to others.

Jeff Alton · 10-26-2023, 08:42 PM

Quote:

Originally Posted by Axel84

Im inquiring here and now so that the information they share with me is also available to others.

SO you have some answers? Or are you still looking?

Find a cam vendor you are comfortable with, and buy their product, report back on your results...

Axel84 · Axel84's Garage

If I had the Answers I wouldnt have made this thread 24 hours ago. Im in a different timezone to cam vendors as well. But the principal reason for making this thread is to hear other peoples experiences and results - after all that is the purpose of a forum - non?

targa72e · 10-27-2023, 11:21 AM

Here is Dyno of my engine with 993SS cams. It is internally stock except for the Cams and ARP rod bolts. I also have a Steve Wong chip but it is for standard cams and performance exhaust. I think I am leaving some power on the table without a chip specific to the cams. This is a comparison of stock heat exchangers, cat bypass, and secondary muffler bypass and FVD headers and muffler. Peak Power with headers was at 5760 RPM.

john

Axel84 · Axel84's Garage

interesting! yes you would probably benefit from a custom chip, peak power at 5760 with 993SS cams sound a bit low to me!

targa72e · 10-27-2023, 09:43 PM

A little low for sure. I also have the Cam as advanced as possible as my testing has shown nice gains everywheere below peak power with very little top end HP loss. Here is the same dyno graph with A/F as well. You can see I am too lean below and thru peak torque and going lean again at top end.

I have two other header/exhaust systems I want to install and dyno before making a final decision. One is shorter and the other is longer (same tube diameter). Once I get this done I will look at a custom chip. Over time I have found dynoing my cars to be the cheapest way to find what works.

john

JoeMag · 10-30-2023, 08:56 AM

John - Would you mind posting the differences you saw in dyno by changing cam advance/retard?

targa72e · 10-30-2023, 11:11 AM

Most of my cam testing was originally done on 3.0 and 3.2 motors. These engines used the same cams with a variety of settings. I posted a comparison in the thread below of a big port 3.0L with stock cams and CIS. The dyno is with cam settings at both extremes of what was used advanced and retarded.

1979 911 SC - valve overlap adjustment

I have since tested with earlier engines and E-Cams and found the same results. This is why I set up my 964 cams in the most advanced end of the specifications given. Pretty much all my testing has resulted in being advance providing more area under the curve with very little change in peak power.
Some cam and piston combinations do not allow much variation in settings while maintaining minimum piston to valve clearances. From reading others testing the William Knight's Melissa M1 cam uses all the duration it can and just meets minimum piston to valve clearances on intake and exhaust when installed as recommended with stock pistons.

john

Classic 911 · 02:14 PM

Quote:

Originally Posted by targa72e

A little low for sure. I also have the Cam as advanced as possible as my testing has shown nice gains everywheere below peak power with very little top end HP loss. Here is the same dyno graph with A/F as well. You can see I am too lean below and thru peak torque and going lean again at top end.

I have two other header/exhaust systems I want to install and dyno before making a final decision. One is shorter and the other is longer (same tube diameter). Once I get this done I will look at a custom chip. Over time I have found dynoing my cars to be the cheapest way to find what works.

john

Wrong reply.

JoeMag · 10-31-2023, 09:02 AM

John -- ...interesting results. The difference between the blue (most retarded) and red (most advanced) lines is really quite large (~10% difference in HP). You noted that peak Hp did not change and there was some exh and ign'n timing changing on red line. Are you saying that if you lowered red line down to peak hp of ~178, that the difference in the lines was due to cam adv/retard change?

Also, does anyone know how many degrees the cam timing changed going from full advance to full retard?

targa72e · 10-31-2023, 02:03 PM

Yes, I think the important think is the general shape of the curve. The advanced cam peaks earlyer and the retarded cam later as expected. If you look at the trajectory of the blue line (retarded), had I run to a little higher RPM the blue and red line would intersect at about 6400 RPM, above that the retarded cam makes more power. In my mind it is not worth a couple more (single digit) HP above 6400RPM for all that you give up below that RPM. As I said I have seen similar trends with other cars and other cam grinds. Most of the engines that I tested back in the day were either big port SC or 3.2 Carrera, they showed similar results to advancing the cam timing. I am not sure if you would see the same result with the later small port SC motors as the small ports tend to limit HP up top.

john

Tippy · 11-02-2023, 12:34 PM

Quote:

Originally Posted by targa72e

Yes, I think the important think is the general shape of the curve. The advanced cam peaks earlyer and the retarded cam later as expected. If you look at the trajectory of the blue line (retarded), had I run to a little higher RPM the blue and red line would intersect at about 6400 RPM, above that the retarded cam makes more power. In my mind it is not worth a couple more (single digit) HP above 6400RPM for all that you give up below that RPM. As I said I have seen similar trends with other cars and other cam grinds. Most of the engines that I tested back in the day were either big port SC or 3.2 Carrera, they showed similar results to advancing the cam timing. I am not sure if you would see the same result with the later small port SC motors as the small ports tend to limit HP up top.

john

John, thank you so much for sharing this data. I had accidentally installed 993SS cams to SC/3.2 specs dead middle at 1.55mm (while rebuilding to the 3.2 Bentley). John Doherty states to use 1.6 to 1.8mm for the ground cams to 993SS specs. Albeit larger cams, the car lost lots of midrange wallop. This is a boosted 3.4. It didn't make sense at first, but later I figured I had the cams really retarded and went "ah-ha". I too do not care the engine makes a really sharp peak of HP up top, I rather have under the curve power be stronger as torque can be fun.

I am going to go for 1.8mm and see if I can get it all back then some. I should have plenty of clearance as I have flat top pistons and lots of deck height.