Rob S

My dyno runs today show that I’m running way too lean, but the numbers are pretty impressive nonetheless: 447 hp and 423 tq at the wheels. The engine is 3.4 liter (nominal 7.5:1), twin plug (TEC-1 running ignition and MAP boost retard only), boost at 0.85 bar (Tial, no EBC), 964 cams, Garrett turbo, Holcombe headers, Borla muffler, ported intakes and plenum, Kokeln IC. I’m running on 92 octane on pump gas, at 24 deg BTDC under load. And I’m using the CIS. Therein lies the problem, no doubt. I may have found the practical limit of the CIS system. It has been modified by Steve Weiner at Rennsport for greater fuel flow, but he said the benefit would be marginal (raising the hp limit from maybe 420 to 450 or 475), and I may have blown past its capability. The A/F ran has high as 14.2:1 at high RPM, which is well above what’s acceptable. It was interesting that the torque peak was at about 4950 RPM, probably 800 RPM lower than I'd expect, perhaps because I was literally running out of gas. The CO was initially set at 3.4%. In an effort to improve the A/F it got tweaked to a level significantly richer than that – to the point where the engine was stumbling at idle, but it made almost no difference in the A/F under high load. That leads me to believe I’m just plain out of fuel. First I’ll verify that the fuel pressure is a full 5 bar (or more?), which hasn't been checked but I suspect I’ll need to do something more radical. If a fuel pressure adjustment doesn’t bring it back into line, what is the current thinking about fuel enrichment devices? I have heard of the Andial and the Rice unit. I understand SDS makes a nice one. I may also be able to fire the cold start injector (or another one) from a TEC-1 injector output. I hate to tack on such a device, but I'm not sure I have much of a choice. Anyone dealt with this successfully or have any suggestions other than the ultimate, which would be to go to a full EFI system?

ZAMIRZ

please post the chart.

Rob S

I'm going to try to attach the first of two dyno charts. I think I have to submit them one at a time -- I haven't done this before. The lines on the chart are pretty faint, but I think you can see what's going on.

Steve Weiner-Rennsport Systems

Hi Rob:

Please, oh please, do NOT use the starting injector to add more fuel. These intake manifolds are designed to run "dry" and cannot distribute fuel equally to each cylinder. Its a recipe for disaster.

If you need more fuel, (and at 14.2:1, I think you do), add another set of injectors at the ports with a separate controller. Don't bother with the various band-aids that simply reduce control pressure under boost. BTDT, with unsatisfactory results,....

Rob S

It worked. Here's the second chart, showing the A/F ratio. Note that above about 5000 RPM (84 MPH in 3rd gear), I begin a steady climb from 12.2 to a peak of about 14.2. Note the "MAX AIR/FUEL =17.5" is bogus -- it has no meaning that I can determine.

Brent 930

I just recently dynoed at 424.4rwhp (14psi) with an A/F of 12.4:1 with CIS because I had my fuel head rebuilt and got 17% more fuel along with fuel enrichment and what Steve does. Nice numbers but there not reliable and at 14.2:1 you better not try it again until you get more fuel or turn the boost down. Turning up the CO won't help much as you found out. Set your system pressure to 6.7bar but this won't help you much. I hear the 7th injector is a very bad idea.

Goodluck

Brent 930

Looks like your safe up to approx. 390rwhp then look out. Your out of fuel my friend, take care.

Brent

Rob S

Steve,

Thanks for responding. I hoped you'd see this!

You and I have talked about the problems with adding fuel to the CIS plenum and the inherent risk of uneven fuel distribution. I agree it seems logical that doing so wouldn't be optimum. I've been hoping I wouldn't have a problem and that I'd "get away with it" with the CIS. There's nothing particularly exotic about this engine, but maybe it's a bit more built than the CIS (even the modified one) could handle. I have a few questions, many of which will be interesting to others as well as me. What is the optimum fuel pressure that I should be seeing (because I'll check that now). What would you recommend I do if the fuel pressure checks out okay (or if I increase it and it still isn't enough)? Do you consider the second set of injectors to be a reasonable mod to overlay on CIS? If not, is there anything more reasonable that I can do to the CIS to make it work?

Steve Weiner-Rennsport Systems

Hi Rob:

Very honestly, I'll tell you that you will not defeat physics here and the inherent limitations of the CIS system,... You cannot "get away with it" without buying many expensive parts. Many people besides myself have BTDT over the past 25 years,......

I shim the FD based on the A/F numbers on the dyno. The actual value is not as important as maintaining proper fueling.

Everyone has their own experiences but I've found that 450-460 crank HP seems to be the limit of the CIS to provide enough fuel to keep the pistons intact. 1 bar is the boost limit and beyond that terminal leanness occurrs.

If you cannot get your A/F ratio to 12.5:1 on boost at 1 bar, you need a different Engine Management System. There are no fixes or band-aids here.

When the CIS is going to be retained, I'll weld on some bosses for an additional set of electronic injectors and use one of the auxiliary fuel controllers. Your Tec-1 might be able to do this too; I am not sure since I never use them.

m42racer

RobS,

I was in exactly the same postion as you are in now. I went with Perfromance Development's Injector blocks. They are the lower injector blocks, but have ports for both the stock Injector and an additional electronic injector. They also have the additional fuel controller that will drive the other 6 Injectors. It controls these the same way an EFI system does, (fully mappable) and it has Boost control and Ignition control all built in. I think the cost for the controller is around $ 500.00.

Give them a call. I decided after I was in the build to eliminate the CIS altogether. I run the electronic Injectors and the CIS (930)manifold. It gave me 508ft/Lbs torque and 503 HP. Very simple upgrade using all the stock pieces. My next step is to upgrade the throttle Body and port the manifold. I'm all stock at the moment.

Brent 930

Steve,

Here is the proof that I did run the power with a safe A/F with CIS. I have yet to see any other chart from anyone running this power reliably with CIS. In fact it looks like I could have tried 15psi for another 10-15hp!

Brent

Brent 930

Without extra injectors)

Steve Weiner-Rennsport Systems

Hi Brent:

Good job, Sir. That's the first one I've seen with an A/F ratio like that and that kind of HP on a stock CIS system.

Geoffrey

Brent, except you are forgetting about the VERY, VERY rich section from 2k to 5.5k where you are giving up torque and HP and diluting your oil with fuel. If your car was running a 12.2:1 or so in those ranges, or 13.2:1 under low vacuum or low boost <.3bar), you'd spool the turbo quicker and get much better throttle response. I wouldn't say your A/F curve is anywhere ideal.

Brent 930

Yeah, I know. I have been thinking about that since the dyno day and trying to figure out how I can lean out yet keep the fuel at the top end. I know I could use an AIC controlling the control pressure by way of an injector to map out the fuel better. Or go back to the stock WUR and see if that will help any but I doubt it will be good enough. I think the only way is to use an injector to map out the fuel.