911 SC Engine Power Help

[sjf911]

There is definately no such thing as cheap horsepower in these cars. How much is enough is a very individual question. I am just now at the point where I feel I have an acceptable amount.

[911st]

Brad,

Have you had it on a dyno?

I have heard of up to 265chp on a blueprinted SC long block w 1.5" racing exhaust and pro ITB EFI conversion.

[Hotwatermusic]

Originally Posted by brads911sc

3 things made a HUGE difference in my 83

1. Recurve the distributor for Mechanical Advance, no retard, 35 degrees inside.
2. Backdate Exhaust/SSI's
3. PMO ITB's with a good EFI setup.

Seriously what made the most difference was the Distibutor Recurve.

The EFI was pretty simple to set up with Studio Tuner. I have no issues with mine except Cold Start and I have a manual Throttle for that... and Im in TX...

You can also upgrade your suspension and it will feel faster...

Good luck...

How does one go about recurving the distributor? Can I do it here in my garage or does it take special equipment? I have an '83 too and would love to squeeze every last drop out of it as well. I'd love any further info or link to a "how to" if you know of one. Thanks!

[brads911sc]

I am sure you can do it yourself, but in my view its not a terribly expensive thing to have done by the Pros.
Steve Weiner on here does it. Jerry Woods does it as well... Think they charge about $300. Think Woods was abit more.
If you want it to include a rebuild, the best is Barry Hershon at IAE in Detroit. He is a little pricy ($550-600) but well worth it. Came back like brand new. Even replaced the screws so it all looked new.
I opted for this route because I was spending 5k on PMO ITB's and wanted it done right and I wanted nothing to be put back in worn or out of spec that could impact my PMO ITB tuning...
I did the distributor first (before the PMO ITB's) with the CIS still on the car. Was far more a dramatic impact than the PMO ITB's were. Together its great... But it was amazing the throttle response even with the CIS on the car doing the distributor install first...

Originally Posted by Hotwatermusic

How does one go about recurving the distributor? Can I do it here in my garage or does it take special equipment? I have an '83 too and would love to squeeze every last drop out of it as well. I'd love any further info or link to a "how to" if you know of one. Thanks!

[brads911sc]

If you want to do it yourself... Gunter on here is expert on these distributors...

[mca]

Are you saying you have 35 degrees of advance? Is that because of the carbs?

For a late SC I thought max advance was around 25-27.

[don gilbert]

I run 35 max advance with cis. My system is in perfect tune though, I run 93 Shell and i monitor my afr from a wide band 02 and gage. As some have said, getting your advance and afr working correctly together make a huge diff. The factory specs leave a lot to be desired. (emissions) I also run an electronic adj. control press. reg. to modify afr on the fly. These things are do-able without a dyno, but lot of wasted gas and testing. Spending a couple hundred bucks for an hour or two of dyno time will be good money spent to get the most out of your tuning. (after you put exhaust on it)

[Hotwatermusic]

Originally Posted by don gilbert

I run 35 max advance with cis. My system is in perfect tune though, I run 93 Shell and i monitor my afr from a wide band 02 and gage. As some have said, getting your advance and afr working correctly together make a huge diff. The factory specs leave a lot to be desired. (emissions) I also run an electronic adj. control press. reg. to modify afr on the fly. These things are do-able without a dyno, but lot of wasted gas and testing. Spending a couple hundred bucks for an hour or two of dyno time will be good money spent to get the most out of your tuning.

Man, when are you going to share how and what you did with your CIS with the rest of us? You seem to have the best running CIS system here, please tell us fellow CIS'ers how! I know that's probably a huge undertaking, to explain exactly what you've done from top to bottom, but could you at least tell one where to start? I am sure you would have a very widely-read write up if you did one. I always enjoy reading your comments when it comes to supporting CIS amidst all the bashers here.

[don gilbert]

Thanks Hot Water. I do have one sweet K-Jet set up, as far as I know the only one of its kind, but nothing that has'nt been done before. But understand to get where I've taken K-Jetronic has taken 2 years of extensive modifying, dyno testing, money spent. There is more to be had from cis that most know. I was lucky enough to work for BMW NA for 16 years, have full time access to the most awesome dyno on earth, and have many contacts from the days of bimmer dirt tracking techs that ran cis on the 320's. It would be a very time consuming thread to write, and alot of modifing to your CIS, some things that most arent gonna have the expertice or want to do. When I'm done I will post a thread. I would love to share what i have learned, 224 rwhp and counting, 28 mpg when I want it, and awsome driveability. Show me that with carbs.

[GaryR]

Originally Posted by don gilbert

Thanks Hot Water. I do have one sweet K-Jet set up, as far as I know the only one of its kind, but nothing that has'nt been done before. But understand to get where I've taken K-Jetronic has taken 2 years of extensive modifying, dyno testing, money spent. There is more to be had from cis that most know. I was lucky enough to work for BMW of NA for 16 years, have full time access to the most awesome dyno on earth, and have many contacts from the days of bimmer dirt tracking techs that ran cis on the 320's. It would be a very time consuming thread to write, and alot of modifing to your CIS, some things that most arent gonna have the expertice or want to do. When I'm done I will post a thread. I would love to share what i have learned, 224 rwhp and counting, 28 mpg when I want it, and awsome driveability. Show me that with carbs.

Don, when you use the term "lot of modifying to your CIS" have you made changes to the base CIS system or is it just in optimum condition and fully tweaked?

[don gilbert]

Gary,every component on my cis (fuel dist, airflow meter, wur, has been disassembled and modified to some extent. The main benefit to any cis car is the wur (control press reg as it should be called, it is can do so much more than allow the car to warm up correctly) I deleted my stock one, and use an elec.. adjustable one.

[GaryR]

Can't do anything to modify my race car at this point (though as CIS parts become unobtainable I can see that changing). Look forward to seeing the article when you post it Don, LOT of worn out/semi-functioning CIS systems out there!

[911st]

Don,

I would like to encourage you to start a CIS thread. I love CIS and have put a lot into understanding them for 930's.

Was your WUR valve based on a Stepper Motor controlled valve? If so, very impressive and ahead of your time.

Someone has come up with a very usable Digital-WUR that would work well on the SC.

I to came up with my own programmable WUR some 7 years ago based on a frequency valve and programmable controller. Gave near perfect AFR's at all load points and reduced restriction at the metering plate with temporary aggressive lowering of Control Pressure with acceleration.

Still, I believe a lot can be done with a factory style WUR. Not sure if all have it but a WUR that lowers control pressure with acceleration could be set up to work very well.

Getting closer to an ideal for AFR's and the ignition could make for a nice running SC.

Here is a picture of my old programmable WUR:

[brads911sc]

I dont have carbs. I have PMO ITB's /EFI.

I set the car at about 4 degrees BTDC at Idle. I have it set at 32 degrees at 3k RPM. Full advance at 3k RPM. So the distributor had 35-36 total degrees inside. The actual advance at 3k and up is 32 degrees.

This what was recommended by Richard at PMO and Barry at IAE after having sold/done many of these. I just did what they said for max performance. I have no knock or issues running 93 Octane Chevron.

I use the EFI and wideband O2 to adjust fuel accordingly...

I think you can do better than 25-27 degrees even with stock CIS. I think that was an emissions driven setting.

Originally Posted by mca

Are you saying you have 35 degrees of advance? Is that because of the carbs?

For a late SC I thought max advance was around 25-27.

[don gilbert]

911st, we think a like, you turbo guys have it so easy, all the air you need. I to have been experimenting with various homemade wur's . You can dump all the fuel that your compression and spark can handle with cis, cis can make 300+ hp with a turbo, but as all know, the limiting factor on non-turbo cis h/power is air, (damn that sensor plate). But, as I have learned, not all air at wot has to go through the sensor plate. You are right, that is a stepper motor that i control by a knob on the dash.

[Superman]

Wanna be fast? Attend all the AX, DE and DS days you can. It's at least 90% driver.

Beyond that.....SSI's, reduce weight, suspension upgrades.

[mca]

Thanks for the info.

I considered having my dizzy recurved following my engine rebuild. But I never pulled the trigger because I just didn't feel comfortable sending it out to someone who couldn't test it on my car. Always worried about pre-detonation (which can't always be heard anyhow).

Is there an advantage to getting max advance at 3k RPM as opposed to higher in the range?

Originally Posted by brads911sc

I dont have carbs. I have PMO ITB's /EFI.

I set the car at about 4 degrees BTDC at Idle. I have it set at 32 degrees at 3k RPM. Full advance at 3k RPM. So the distributor had 35-36 total degrees inside. The actual advance at 3k and up is 32 degrees.

This what was recommended by Richard at PMO and Barry at IAE after having sold/done many of these. I just did what they said for max performance. I have no knock or issues running 93 Octane Chevron.

I use the EFI and wideband O2 to adjust fuel accordingly...

I think you can do better than 25-27 degrees even with stock CIS. I think that was an emissions driven setting.

[Porsche Head]

Not as scientific as most, I curved my dist. as well and found that to really waken up the car to the point I held off on any major engine changes until a planned supercharger (Rotrex - pending install).

I went with a set of Moroso springs from Kragen, these fit fine on the 911 dist. I tried lighter weights at first then played with the timing up and down from 0 to about 12 deg BTDC and this proved to be not what I was looking for. I then tried heavier weights and about 15 deg BTDC and that seems to be the sweet spot. Instant response and a whole bunch more fun to drive. You have to also consider other changes you are making to complete the tuning like go back and readjust the mixture and idle. I also have a dual out Dansk and SSI setup w/7:31 gears and a fairly light car (remove AC/back seats/FG parts etc) so low end load is reduces and a need for a quick response to RPM is needed, this is not new stuff.

Note: I have a dual pod vac dist with 20 deg total advance which is not correct for my car so that added to the need for tuning.

I think the ball park should be max 35 deg total in by 3k RPM should prove to be a good start (as mentioned here). Just so happens that my 15+20=35 works out to be about the same just that I load up a bit quicker by adding some weight to the springs and adding more initial.

P.S. My car was setup prior by PO to 5 BTDC but only 20 adv = 25 because of swapped dist.

[911st]

CIS can easily make within 10hp of carb's.

It's weakness is more its lack of throttle response.

IMO, CIS has two issues that effects acceleration.

First is being CIS it dumps fuel 100% of the time. At idle and low duty the spray pattern is on the weak side which makes for poor atomization and it tends to coat the intake ports in wait for the intake valves to open. Then when they do and air accelerates in to the motor a low power points it just dose not mix very well.

This makes for a potential lean condition with acceleration the poor air fuel mixing that can be difficult to ignite and burn. (Note that the funny piston tops and smaller intake ports on late SC's are probably an effort to minimize this.)

The second issue is the metering plate's restriction as it works to sense air flow.

The metering assembly has both control pressure pushing against it and its own mass to over come with changes in air flow (acceleration). As such this also can lead to a lean condition with first acceleration as the metering function can not keep up with said air flow changes.

We can get the AFRs' close to ideals and can also reduce the metering plate restriction to a degree.

There are WUR's that senses loss of manifold vacuum that comes with acceleration and lowers control pressure. I believe the euro SC's may have had this. Not sure if any of the US SC's did or not.

With a acceleration sensing WUR , acceleration can quickly lower control pressure. This can help to motivate the metering plate movement and help us to achieve AFR's that are more conducive to acceleration. Peak power on an air cooled 911 is at about 13 to 13.2/1 AFR.

Thus, with the right WUR and getting it adjusted right more AFR's at idle/cruse, and with acceleration can be had-- a great running and fast CIS can be had.

Then there is the ignition side.

[911st]

Total advance it the total of vac-retard and or vac-advance, mechanical advance, and static timing setting.

Here is some timing and advance curve info for a low compression almost pre-smog earlier motor from another thread. They ran up to 38 deg of total advance.

Thread: Need Mechanical Advance Curve table for 2.4T

Originally Posted by Early_S_Man