A couple of questions about balancing the air/fuel on a CIS 930

[Maxx1]

How often does it need to be checked? I bought my car 3 years ago and there are no problems at the moment.

Is it easy for a newbie to balance the fuel / air using a LM2, or is there black magic involved?

[pkracer21j]

no black magic. CIS is simple to adjust, there are just a lot of hoses. lol I adjust mine when the weather changes. a little bit leaner in the spring and summer and a little richer in the fall winter. as long as your AFR's are in line you should be good to go. and if it ain't broke...

[mark houghton]

Remember, just little tweeks on the metering plate adjustment screw are all that's needed to make adjustments...like in the neighborhood of a couple degrees rotation to fine-tune. That'll change your idle and to some extent the mid range AFR's, but don't look to that adjusment to do much for WOT and will have no affect on boost enrichment.

[Maxx1]

I guess what I need to know is how to balance the WOT as well, I mean that's what's going to destroy the engine if it leans out too much. Dumb question, but I suppose you can only do that on a dyno?

[RarlyL8]

Adjustable or digital WUR and an LM-1 (or like AFR gage) are all that is needed to adjust the full range.

[mark houghton]

Originally Posted by Maxx1

I guess what I need to know is how to balance the WOT as well, I mean that's what's going to destroy the engine if it leans out too much. Dumb question, but I suppose you can only do that on a dyno?

A Dyno is ideal, of course, but a good AFR monitoring setup will tell you what you need to know on whether you're in the safe zone. And as Brian just said, full range adjustment can only be accomplished with a digital or mechanically modified adjustable WUR.

[Maxx1]

I haven't touched my car since I bought it other than a installing a MSD, new plugs, oil and retorquing a few nuts and bolts. I'm at the point where I want to fine tune the mixture so I can confidently run it hard and know it's not going to melt down. (So far I've been pretty easy on her).
Thanks, I'll do a search to gather more info on the adjustable WURs and what's required to upgrade from stock. Other items are the list are to upgrade the intercooler and to change the 1 bar BOV spring to a .8 (safety net).

[911st]

Checking the condition of your injectors is always a good idea. There is also some info hear as to how to verify the fuel quantity deliver to each injector is balanced.

As you have the ability to monitor AFR's, I would shoot AFR's on boost at TQ peak and HP peak in the mid to low 11's. Many makers of Turbo car's often have there on boost AFR's set in the 10's for safety so it is ok if you dip into the 10's some at first boost and or at TQ peak. For a street car it is also ok to bump up to about 12.5/1 near red line.

CIS definitely seems to have a 'fuel curve' on modified 911's.

There is more HP if you can run in the low 12's but with CIS there is not any features to adjust for varying environmental conditions like being able to adjust fuel or ignition when there might be detonation should the motor run lean or heat soak.

You kind of have to play off on boost AFR's against idle and cruse AFR's. The hope is you can be in the 14's at light load. Many end up in the 13's in search of enough fuel to support 1 bar and to improve off idle acceleration. Pre-boost acceleration is best when AFR in near 13/1.

If you can not achieve this with the stock WUR then you might be able to use an adustable WUR to get things closer. There might still be some comprises like being a bit to fat on first boost (in the 9's) so you can access the extra fuel available up top.

The D-WUR can make a significant difference in tune-ability of your AFR's and get you up to about 1 more point of fuel in the upper RPM range where a stock WUR will often run out of fuel on a tuned motor. It can also be used to increase MPG by running in the upper 14's at idle and cruse, drop to 13/1 with acceleration from idle, and just under 12/1 on boost.

Just my opinion.

[mark houghton]

Originally Posted by 911st

If you can not achieve this with the stock WUR then you might be able to use an adustable WUR to get things closer. There might still be some comprises like being a bit too fat on first boost (in the 9's) so you can access the extra fuel available up top.

Keith, you're being too gentle! Personally I think I would assign the term "pig rich" to that (9 AFR) if running a stock setup. Unless of course a person is running higher than stock boost and near redline, then the super rich might be appropriate once you get to the upper echalons of things. Get in the high ten's to low eleven's and you'll be plenty safe most of the time and not sacrafice HP or wash your cylinder walls with excess gas. There are about a hundred zillion posts on this subject (many of which Keith has graciously authored and cataloged for posterity).

By the way Maxx, if you've been running with a 1.0 bar spring and the stock intercooler without knowing where your air-to-fuel ratio is, then definitely go back to the stock .8 bar spring until you can verify your state of tune. Your stock WUR is calibrated against the stock wastegate setup. Increasing boost beyond .8 bar requires either a larger IC to cool the air charge and guard against detonation, and/or modifying the AFR to provide a richer and cooler mixture.

Currently there are two main sources of adjustable WUR's: one custom modified by Brian Leaske, and the other entirely digital. The price difference is about double, so it all depends on how much flexibility a person wants in tuning.

[Maxx1]

Thanks a lot, that's good info! I'm going to look further into the digital WUR, it seems it would pay off with more power on top once I get my IC and BOV spring sorted out... until then, I'm going to take it easy.

I suppose while I'm at it, I may as well look into EFI. I think cost will be the limiting factor there. Do the 964 EFI systems bolt up to the 930?

[911st]

Mark,

Agreed, going into the 9's is to rich. Some times this is lived with if it is brief to access sufficient fuel up top when lowering on boost control pressure. Andial and others have done this for years without issue.

Dropping into the mid 10's as not a big, big deal as many MFG's program there EFI Turbo cars to do that regularly.

Still, not the best way to make the highest average HP but livable for most.

No question a D-WUR has the best potential. I made my own some 7 years ago and got perfect AFR's everywhere but next time I will stay with a mechanical WUR just because I think it is cool and I think I can achieve very close to the same performance using some ideas I have (working the metering cone & a vacuum sensing WUR) without any add ons.

My favorite WUR add on is the AIC/Frequency Valve based system like I built but with the second channel tied to a boost solenoid programed to set boost levels at all rpm points like Thierri did leveraging off my original build. The Monster CIS build also had programable boost by rpm for a huge mid range to fit the wide ratio 4spd turbo transmission. Boost can also be pulled back in the later rpms to live within the motor's thermal limits and the limits of the CIS fuel system. However, this approach is not a turnkey set up like the D-WUR.

Aren't these cars fun.

[JFairman]

Keith, there's no way I would ever run 9:1 AFR's under boost by choice again... I've done it and not only does the car missfire making black smoke while accelerating that rich, I can't stand the smell of unburned gasoline hydrocarbons in the car and on my hair and clothes after driving it.
It seems some exhaust fumes are drawn forward into the cabin. Mostly when the windows are down.

I agree that these cars are tons of fun, but from peoples experiences I've read here the DWUR hardly sounds turn key.
Look at the origonal heavy duty cast aluminum mechanical WUR. You could beat someone to death with it and put it on the car and it will likely work for the next 20 years no problem.
Then the DWUR, a generic little plastic box.. someone said there's had an internal circuit board held in place with double sided tape and the tape came unglued and the board moved and shorted out. A teflon/plastic line like a cheap mechanical oil pressure gauge kit uses that better not rub against anything for long with engine vibration and a very questionable stepper motor to change the control pressures.

The AIC controller with bosch frequency/pulse valve bleeding off control pressure and returning it to the tank like you put together years ago sounds much more reliable, and the bosch inline injector valves have been proven to last a very long time.

I guess some of the dwur's have worked well for people. I'd like to hear how they work 4+ years from now on cars that get some miles on them.

Keep your origonal Bosch WUR as a backup if going with a DWUR.
Send it to Brian Leaske and have him rebuild it and make it fully adjustable. If you keep the car and the K jetronic you'll probably eventually put it back on.
...just my opinion.

[WinRice]

Originally Posted by JFairman

Keith, there's no way I would ever run 9:1 AFR's under boost by choice again... I've done it and not only does the car missfire making black smoke while accelerating that rich, I can't stand the smell of unburned gasoline hydrocarbons in the car and on my hair and clothes after driving it.
It seems some exhaust fumes are drawn forward into the cabin. Mostly when the windows are down.

I just had to laugh at that one, perfect description!

Stomp 2nd gear hard and it get's by the 9's quickly, roll into it easy and it stays in the 9's too long and bucks like a bronco, spewing black smoke.

[mark houghton]

I run 11.5 AFR at .8 bar boost, and high 10's at 1.0 boost. No issues, runs like a raped ape (or so I've been told that a sexually assulted ape will run like a strong Porsche 930).

[911st]

Sorry if I implied 9/1 is ok. Nor would I run 9/1. That is way to rich.

However, many well running modified 930's do often dip into the 9's (high 9's). It is not desirable but even an adjustable WUR or Andial Fueler can only do so much.

It takes a D-WUR or modified WUR with rpm delayed boost clamp (the first done by Brent930 some 7 years ago at my suggestion) to try to over come this issue on a 930 that is flowing much, much more air than originally designed to.

Going to rich to fast is a function of where the metering plate sits in the metering cone. The metering plate moves quicker relative to changes in air flow at earlier rpm's. Lowering control pressure in an effort to get more fuel up top only exaggerates this.

I do think someone can build a 500chp CIS motor with mechanical WUR and stay in the 11's to red line with out a boost clamp but it will take some work to the metering assembly.

[fredmeister]

Originally Posted by 911st

I do think someone can build a 500chp CIS motor with mechanical WUR and stay in the 11's to red line with out a boost clamp but it will take some work to the metering assembly.

Wasn't someone looking into reintroducing the additional profiled metal cone that mounts on top of the stock metering plate to better control the plate from stalling at high flow rates?
there was some posting a few months ago on this but I haven't heard any progress or where i can get one of these.
Should this be a new post or who knows whats happening in regards to this?

[911nut]

Originally Posted by 911st

I do think someone can build a 500chp CIS motor with mechanical WUR and stay in the 11's to red line with out a boost clamp but it will take some work to the metering assembly.

Keith, chp? (chipmunk horse power?)
Craig 930 is at 500 fwhp with a Leask wur and IA fuel head. He tracks his car so I'm assuming that his fueling is adequate.

[911st]

Yes Paul, we can get the fuel to make the HP from CIS. I figured that out some 8 years ago or so ago with I came up with the idea for the first high flow fuel head that Larry at CIS Flowtec built for Brent930 in Colorado and later sold exclusively through IA.

Try to do it with a mechanical WUR without a boost clamp to delay the enrichment circuit of the WUR. That was my point.

[911nut]

Originally Posted by 911st

Try to do it with a mechanical WUR without a boost clamp to delay the enrichment circuit of the WUR. That was my point.

Gotcha...

[TurboKraft]

Funny that there's interest again in that little venturi cone thingy for the top of the air flow plate.

About 14 years ago the notorious Chris Fisher (then of PowerHaus) had those made because there was a similar part on his Euro-spec 500SEL. Did it help? Did it matter? He could sell it, so he had them made locally in Phoenix and sold them. Dynos were scarce back then, sophisticated Lambda dataloggers more so, and it was never installed and tested back-to-back.

Has anyone tested one back-to-back since?

Cole kindly lent us his modified CIS air flapper assembly that included one of these venturi / cone devices. We installed it onto a built 3.4L 1981 930 (same car used for testing of digital WUR and comparison of Leask WUR when it was a 3.3L, posted in another thread here). I couldn't see a really measurable difference in fuel delivery in back-to-back chassis dyno testing.