911 SC 3.0L Rebuild -> Feedback on JE9.8 with 964 Cams

[Ryvinios]

I have a question for the Pelican Forum related to putting in 964 cams and increasing the compression from 8.5:1 to 9.8:1 in a 1978 911 3.0L engine.

Car is a 1978 911 SC, completely original only 145,000kms, was a Canadian car from the beginning and has been in the same City since new and has its COA. Car has been lightened and I kept all of the parts. I drive it on nice sunny days, it never sees winter and minimal rain. I use it for in town trips, a couple dozen trips of ~150 kms and one long trip a year of approximately 1000 kms. I track it on a go-cart track 6 times a year as there are no actual race tracks anywhere near where I live and I enter it into to a half dozen car shows.

I very recently found that I need to do a complete rebuild on my engine due to past issues that were not noticed before I bought the car 5 years ago. The car ran very strong and aside from oil leaks no indication there were issues and performed significantly better than 3 others I was looking at the same time with much less mileage. It had the standard upgrades of the Carrera oil tensioners, 930 valve covers and CIS relief valve.

It originally went in for a transmission rebuild due to dog teeth from first gear found in the oil and that my first gear would kick out randomly under power at times. Then while the engine is out, I asked the mechanic to do a valve adjustment and hit some of the oil leaks. He found 3 broken heads studs which meant a top end rebuild, then once they got in there they found impacts from the valves on the pistons and scoring from the chain on the side chain case/cover so now the lower end rebuild. The cam needs to be reground on one nub.

As the rest of the engine is in good shape the complete rebuild is not that bad but now I have never considered doing any performance upgrades but this is now the time as I want another 40 years out of this car before the next rebuild. As a result I did not have a wish list of things to consider doing to increase the performance as this was unexpected, aside from doing the “while you’re in there”.

I am willing to do some enhancements as long as they don’t:

1. Impact longevity of the engine
2. Lose low and mid end power, as I don’t really care about the high end power and I never liked the power in 2nd gear
3. I can put it back to stock if I ever decided to sell the car to keep original

I have been reading the forums for over the last 2 weeks and ordered the book from Wayne on performance upgrades but I’d like to ask people who have done the upgrades, are you still happy or are you still unhappy with it?

The general trend seems to be that the 964 cams reduce power in the low and mid-range and give more at the upper range and allow for higher red line. There seems to be some argument that timing can be adjusted to gain that back. Is that the case otherwise the 964 cams violate #2. Is there any consensus on this as a lot of the posts are dated, what it like now; better or worse? I also assume I’ll do new springs with the cams.

As for the compression, I need to replace the heads anyhow so I can go with ones that allow JE9.8 to be used to increase the compression from the 8.5:1 to the 9.8:1. Is there anything that may cause me to regret that or violate #1? Since the later SC 3.0L have higher compression I done think that’s an issue, I don’t want to go duel plug or need fuel over 91 octane. I’m also assuming that I’ll get power closer to the late SC’s.

I’ll go with SSI regardless of the other options above, just because.

So please provide some feedback as I need to give instructions to the mechanic soon.

Thanks.
Ryan.

[Jeff Alton]

We have built a couple of 3.0 motors with 964 cams. One with 9.5 CR and one with stock compression. Both were noticeable improvements over stock when coupled with SSI exhaust. Though not on the dyno, these motors did not seem to loose any low end grunt.

['76 911S 3.0]

I ran 9.5:1 98mm JE's with 964 cams in a 1979 base engine platform with fantastic results. Still single plug and had no issues (other than having to have the WUR adjusted for the larger displacement). Low end grunt is excellent and top end is great too. Here is the dyno plot, on a Mustang Dyno, with CIS and distributor still in place:



The RPM calibration was a little off, actual redline was 6500 not 6000 as indicated.

[Ryvinios]

Thanks Jayson that is very helpful, was the dyno done as a 3.2SS with the mods listed or was this only with 9.5:1 CR and 964 cams before you did the mods?
Ryan.

['76 911S 3.0]

Originally Posted by Ryvinios

Thanks Jayson that is very helpful, was the dyno done as a 3.2SS with the mods listed or was this only with 9.5:1 CR and 964 cams before you did the mods?
Ryan.

This was with the 3.2SS, I changed the cams and pistons/cylinders at the same time. I think the gist of this is that the 964 cams provide a very broad torque band.

[arbita1]

I recently did my rebuild using JE 9.5:1 Pistons and DC-15 cam profiles from John. This is one step down from the 964 specs. It's labeled as a Sport SC cam.

I too was concerned about losing too much low end torque with the 964 cam. I got some varying opinions so I decided to go with the D.C.-15 and play it safe.

I'm glad I did. This cam seems to come on around 3,300 rpm and pulls out past 5,000. It's definitely better than stock and very street usable. Check it out if you are concerned for low end.


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[Reiver]

Originally Posted by arbita1

I recently did my rebuild using JE 9.5:1 Pistons and DC-15 cam profiles from John. This is one step down from the 964 specs. It's labeled as a Sport SC cam.

I too was concerned about losing too much low end torque with the 964 cam. I got some varying opinions so I decided to go with the D.C.-15 and play it safe.

I'm glad I did. This cam seems to come on around 3,300 rpm and pulls out past 5,000. It's definitely better than stock and very street usable. Check it out if you are concerned for low end.


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I've a 930-10 Euro '83 SC w/ 9.8-1 comp...stock except running SSI's (altho I've lightened the car considerably, about 2300 now)...street prepped and need the low end grunt.

I note they rec that grind for the 8.5 comp but you seem very happy with the result.

My stock cam comes on strong at 3400 as it is so I suspect the 964 would be more in order....I too do not want to lose any mid range....I suspect I should give them a call.

Interesting that that grind works so well with the higher comp.

[tcsracing1]

Originally Posted by arbita1

I recently did my rebuild using JE 9.5:1 Pistons and DC-15 cam profiles from John. This is one step down from the 964 specs. It's labeled as a Sport SC cam.

I too was concerned about losing too much low end torque with the 964 cam. I got some varying opinions so I decided to go with the D.C.-15 and play it safe.

I'm glad I did. This cam seems to come on around 3,300 rpm and pulls out past 5,000. It's definitely better than stock and very street usable. Check it out if you are concerned for low end.


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is that cam much different then stock?

[Trackrash]

Dougherty Racing Cams Porsche 911, 930 and 964 camshaft profiles

[tcsracing1]

Originally Posted by Trackrash

Dougherty Racing Cams Porsche 911, 930 and 964 camshaft profiles

says for 8.5 compression ratio.

if you have a 9.5 or 9.8 compression ratio upgrade would their be a better cam without going 964?

[Trackrash]

Originally Posted by tcsracing1

says for 8.5 compression ratio.

if you have a 9.5 or 9.8 compression ratio upgrade would their be a better cam without going 964?

Assuming you are going CIS or Motronic system you are limited to a 964 or similar. Webcam makes a 20/21 that some use.

You can contact John Dougherty aka camgrinder for his recomendation.

If you give us the details of your build others with direct experience will hopefully chime in.

[arbita1]

I felt like the Dc-15 was a good middle ground between stock and 964. I did a lot of research and there were a lot of mixed reviews for and against for the 964 due to loss of power at lower range.

I was nervous and went more conservative. I know it lists 8.5 compression on his website. My engine is 9.5 and works fine. Don’t all SC’s have the same cam regardless of stock compression anyway? 8.3 vs 9.3.

It’s not a huge difference from stock but you can definitely tell the difference. It seems to “wake” the car up more in the 3,500 range and up.


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[mikedsilva]

I wonder what the original poster ended up doing.. only 2 posts, here, back in 2017.
Maybe he's still rebuilding it?