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William, what are the principal improvements over a Web 20/21 cam that’s so popular in these cars? I didn’t think CIS could handle much more lift on stock pistons or more overlap due to reverberations. Know cam grinding is a dark art with a lot of special sauce but be interesting to get the broad strokes and what gains you see over and above the 20/21
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I will give you a broad explanation but I will not give the secrets to a cam we spent 10 years on as I do not want the cam scammers stealing my work. The 20/21 was designed for 3.2 DME and doesn't work well on CIS in my opinion. It makes less power on the CIS motor and I am 100% certain. This cam and I hate to say it but I learned from Ferrari technology on how to get more Hp and loose less energy. Sounds like some BS I know.. But it works, it had other advantages like reducing lower rpm knock due to todays fuels and it also runs cooler than the stock cams. It does not meet emissions nearly as easily as stock grinds. I personally do not like the 993 SS grind and the 964 is an antique emission grind at best. It is the best you can put on a CIS motor in my opinion.
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Yes 1981 only 930/10 engine code 9.8:1 but it CC's at about 9.45:1 on that one.
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as a gauge was insatalled, do you remeber ... - with normal/non knob adjusted CP ... what was the AFR at normal driving and what was the control pressure here (14.7:1 ?) - with knob adjusted CP ... what was the AFR at acceleration nd what was the control pressure here (12.5:1 ?) As you're one of the CIS godfathers here you already know, that with a 930/16 engine you can force a lower AFR at acceleration for optimal performance by trying rising the initial CO above 0.8% Vol. in tiny steps till you get the best afr at acceleration. Of course this will make the cold start resulting richer and therfore in most sunny states with a probably more uneasy idle at the cold start phase. |
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Icarp |
Any up date here from original poster or engine builders…?
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i will be getting my 3.0 9.3:1 engine back in the next couple weeks(hopefully) and the only change i made was early heat exchangers and the M1 cam. I will update the group with more info after break in and running it around a bit.
Sounds like i should look into this WUR delete kit as well.... |
M1 Cam
Please let us know how the M1 cam performs.
I have collected parts to “backdate” my small port ‘82 SC to large port early SC mechanics (early CIS set up, distributor, etc.) and I am adding Max Moritz P&C’s and the M1 cam in an attempt to get my redline up at least another 1,000 rpm’s. My stock SC falls flat at around 5,500 rpm’s (even with SSI’s and an M&K 2/1), and it drives me nuts - if I need torque I’ll drive my 345 Scout that has max torque at 2400 rpm’s! |
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The mention earlier in the thread about having to rev the motor to make it come alive with cams...http://forums.pelicanparts.com/suppo...oilet_claw.gif Everything about these engines is made for above 3-3500rpm, if you're running around shifting under that, might as well sell it because it's not being used. I just ran mine 4k+ RPM for 900 miles from Indy to CT, it couldn't have been happier.... |
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Blackrado, what model year is your car? I suspect its 80-83 if you have 9.3:1, which means you probably have a small port motor. They're great for low down torque bc the smaller ports improve the velocity of fueling at lower RPMs. I think all CIS engines tend to run out of air a little higher up the RPMs, but would make sense to me that the bigger port motors have slightly longer legs (but not dramatically so).
I have an 80SC small port motor with 9.3:1, SSI, and 20/21 cams. Fairly similar to yours. It's great in windy roads. Not sure where you live and if you've got some twisties around you. In Chicago, I'd love some more straight line exhilaration but wouldn't want to chop into a good SC to deliver it. Enjoy the new whip. |
hey there, its a 1977 911s that had an interesting life. I sold off the 2.7 i received in boxes with a checkered past and opted for a 3.0 out of a 1980 (so youre spot on).
I am in New Hampshire and am really looking forward to getting behind the wheel. We have plenty of twisites and long stretches if you knwo where to look.... This is my first Porsche, first air cooled, and first Rear engine, so im eager to get some miles behind me before the winter sets in. Exotech in Plaistow, NH is doing the rebuild on the engine, went through the 915 transmission, and gave it a good once over on the brakes and fuel distribution... the rest is up to me. :) Figured itd be best to have the professionals set it straight rather than dare attempt it myself... it would be 15 years before i got behind the wheel! |
Sounds great. You'll love it and it will love the fall temps. Those break-in miles will test your will power. Enjoy.
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This is a great read.
Curious about feed back from the aforementioned cams and WUR delete as far as longevity. |
Circling back around to this thread I started...
I've now completed the mods here: http://forums.pelicanparts.com/porsche-911-technical-forum/1118237-rhd-itb-megasquirt-install.html All bolt-on, above/below the case stuff - new intake, EFI ignition, headers & muffler. I opted for this route guessing it's the most bang for buck for simplicity. Dyno results were 192hp at the wheels, appx. 225hp at the crank. Up from 180hp crank spec stock. And it pulls well up to redline. I can probably get a bit more hp switching to an MDS ignition over the CDI+. Cracking open the engine - going to 10.2 pistons, head work, hotter cam I'm guessing between 245 - 260 depending on the particulars. Of course, why wouldn't one increase the displacement if one was to do this, and then we're looking at high 200s. |
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