Since a '92-'93 speed density computer can't 'measure' air like a MAF equipped car, is it true that it will appear to run lean on a chassis dyno as opposed to logging A/F ratios while actually driving the car, under 'load'?
DRIVING my '92 shows an A/F of 12.8-13:1 at WOT. On the DYNOJET (1 hour later) it showed as high as 14.8-15:1 near the top end of each run. Just increasing fuel pressure, on the dyno, a couple lbs showed 3-4hp and 6ft lbs increases.
Would these points make tuning a speed density car on the dyno somewhat counter-productive (overly rich), other than for hp/tq numbers?

 

Are you measuring this with a wide band in your car and is it the same one for both dyno runs and driving? Also, does the AF read about the same say at WOT in first gear as compared to third? Just trying to imagine what would cause this. If it was air pressure from driving, I would think 3rd gear, full throttle at say 5000 rpm would be leaner then 1st gear , full throttle at 5000 rpm.

 

Two different wide bands. Innovative A/F meter for driving the car, Dynojet's own meter during dyno runs. Both poked into the tailpipe. Only observed the dyno numbers in 4th gear. Actually driving the car WOT in 3rd and 4th, then from a slow roll...1st...2nd...3rd.
The techs at TPIS said this was typical for a speed density car, which is why they prefer to tune these cars based on actually driving under load. They said the car would respond to more fuel on the dyno, which it did, but once returned to the 'street' it would be unnecessarily rich. I forgot to ask them how these factors affect testing on an ENGINE dyno.

 

interesting discussion

why are SD system "normal" on the road, and lean out at WOT?

what i noticed, when i revv my 396 in neutral, the AFR goes up to 20:1, manifold pressure gets down to about 40kpa..

maybe just to lean under these conditions...

 

The biggest difference you will see is the difference in widebands used. The innovative widebands I've seen run on our dyno have almost read comical values compared to the dynojet.


Which is right? My money is on the dynojet.. I say that because I tune cars weekly with that wideband and it consistantly puts in me in the area that is best for power.


As far as SD cars leaning out on the street. While some of that is a touch true its not as serous as you would think. If the cars did lean/ richen that much based on load you would have to have a different fuel table for 1st, 2nd, 3rd, etc gears. We know that isn't the case.

 

Other than the concern of potentially leaning out the engine under some of these conditions, I was realistically expecting another 25 hp and 30 ft lbs 'at the wheels'. Was I then leaving this much power 'on the table'? Would richening up the A/F TWO FULL POINTS have gotten back most of this assumed 'lost' power? Increasing fuel pressure alone wouldn't have been enough, would it?
We only had time for one 'retuned' dyno run: Bumped FP to 48psi, and saw 429 hp @ 6,625 RPM (14.4 A/F), 399 ft lbs @ 4,750 RPM (14.5 A/F). Previous run at 46psi was 426 hp and 393 ft lbs. I am using 30 lb SVO injectors. I am also still relying on the Optispark (w/MSD cap, rotor, and 6A box) for spark distribution, which is probably NOT helping power at 6,600-6,700 RPM. We believed we had confirmed that it 'liked' more fuel, and had to end it on that note.
I know I am pushing the limits of the current ignition (LTCC coming soon!), but am I also asking for trouble using the '92-'93 GM speed density based system? From what I have learned recently, I now appreciate the switch to SFI in '94. I never thought the speed density/batch fire FI would have handicapped my efforts, though.
My experience is still very limited, but I think I have a good idea of how much power I SHOULD be making .

 

Maybe the owners Innovate WBo2 is in need of service or recalibration. I use a couple of the Innovates that I double check against a lab grade Horiba and they are normally spot on. I haven't had any issues with any of the Innovates that I have sold either. However its also funny that the Dyno-Jet Wide Band Commander (if that is the one you're using) uses the same Bosch LSU4 sensor as the Innovate systems. In fact many of the aftermarket WBO2 systems now use the LSU4 or a direct variant of it. Cadillac also uses a LSU4 based sensor in its Catera.

 

Alvin or TJ, do you have a concensus of speed density tuning indicating any patterns of lean-out on the dyno? How much does 'load' factor into MAP and fuel enrichment on a max effort NA 383 like mine?
Does this much variance in wide band O2 readings really mean that one is wrong, or does it give these A/F thoeries some credibility?
Should I crank up my fuel pressure past 50 PSI until my exhaust turns black, to see if I feel a difference on the street under load?
Is there a specific hand held WB set-up I should consider buying that would be particularly helpful in this situation? Or do I need to put it back on ANOTHER dyno and play out the lower, richer A/F ratios?

I appreciate ANYONE'S opinions or experience--Thank you!

 

We are comparing it against the a dynojet double pump wideband. I don't think its called a commander. I actually did some work for a innovative dealer and he was displeased that the dynojet wideband was reading consistantly .5 different. While tuning his personal car.

Which one is right? Who knows.. I just know that every time I tune a car to 13.0 on the dynojets wideband i know I don't have much to go before I find the AFR it really likes. (always between 12.8-13.25 depending on the car)

These AFR's are almost always reported to be low 12's on the innovative LM1's.

 

It will change the AFR some on the road. But it should be a very small change. There is nothing wrong with speeddensity EFI as all aftermarket fuel injection uses it without trouble on real race cars.

 

Hey Joel, I'd pull a couple of plugs front and back if you can to see if they look lean. Even though it's more work, I would think you can get a bit better tune on a SD car.

 

I see FAST makes a couple different WBo2 meters. Of course there's the Innovate we've been referring to. Autometer now offers WB set-ups with several of their different guage offerings.
Are any of these going to be better than 'nothing', or is there a 'tried and true' model out there that is going to serve me best in MY situation (based on these previous posts)??
Where is the best place to try and install the additional sensors on a C4 exhaust (TPIS LTs, no cats '92)?

 

500hp,

Did you run the Innovate and the Dynojet WB at the same time? I'm assuming you are running C/L for Part throttle. If so, did you notice what the BLM was when you went into PE? If it was above 128, it will affect the WOT AFR because the ECM is expecting 128 and sees a motor running leaner. It then richens the WOT AFR. Anything <128 and no mod to the PW for WOT.

 

Dom, we did NOT have both WBs in concert. Dynojet session was at another facility attended by only myself and the dyno owner. I had my AutoXray with me, but did not think to hook it up since I was 'driving' the car on the dyno, watching RPMs and hand signals from the operator during the runs. Closed loop operation seems to be 'normal', otherwise.
Will the BLMs reflect accurately on a short WOT blast down the highway with just the heated Bosch O2s? The integrators will only react during CL, correct?

As a side note, my front 4 cylinders appear to be lean/hot as evidenced by the spark plugs' appearance. However, this is after driving the car 'nice' on the street or highway (little or no WOT/PE). Logical theory says that some of this is due to the physical location of the throttle body on the LT1/4 intake and the inability of the batch-fire injection to individualize cylinders/injectors.

 

500hp,

You should hook up your scantool on the dyno. From the times I have used a dyno, the dyno operator will take the motor to about 2000rpm and stabilize the rpms, then punch it. With my motor, my BLMs are in the 140s when its being held at about 2000rpm and the MAP is about 35-40kPa. If the BLM doesn't drop to 128 or lower before the ECM sees PE, it will calc the WOT PW based on the higher BLM. Meaning that the ECM sees a motor running leaner and so it increases the PW for WOT thinking that will get the AFR to the commanded. Unless ALL your BLMs at any point of the VE table are 128 or lower, the WOT will be richer than what you are expecting. You can either address the area of the VE table that is just prior to PE, or set a calibration that locks the BLMs and INT to 128. Then tune WOT. Basically that will run the motor strictly off the VE table(with no mod by the O2) for Part and WOT. You may have heard that some people disconnect their battery just before they run the 1/4. That's because it resets all the BLMs to 128 so you get a more consistent AFR for WOT. Since we're discussing tuning on a dyno, you're aren't necessarily tuning the WOT AFR you'll see going through the gears at the track.
Final point. If you want to read the plugs on the dyno, then install a new set before you do the run.