On track A/F




mark_watkins

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I am racing a small rear engine dragster with a NA 2002 Hayabusa engine. I run premium pump gas, pretty much stock, except for a slider clutch and a MSD SB6. The car is running 9.80's at 130mph.

I just installed a Racepak Sportsman unit with A/F sensor mounted 12 inches down from the flange. I am seeing A/F ratios, running a stock ECU in the 14's. The curious thing is the ratios descend through each gear. For example, 4th gear around 8000 rpm is around 14.1 and when the thing gets up to 10,000 it has fallen to around 13.8.

Is this common? I am about the reflash the ecu to try to move the A/F into the low 13's.

Mark

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GoldenChild

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Yes the air fuel should drop lower as engine load increases. The fueling AF goes,if it goes up it is leaning out, down it's getting richer. You want to use up the fuel but still have some for cooling purposes as speed increases. I always on top end slowly keep adding fuel till it seems to slow down in et and back off just a touch. Once you go 100% throttle that is main range you need to concentrate on, just clean rest so it runs best... Fun Project there we have done a few rails, and other powersports with motorcycle engines.. We hope to get back to it now we have moved...
 

Boosted Cycle Perf

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Yes the air fuel should drop lower as engine load increases. The fueling AF goes,if it goes up it is leaning out, down it's getting richer. You want to use up the fuel but still have some for cooling purposes as speed increases. I always on top end slowly keep adding fuel till it seems to slow down in et and back off just a touch. Once you go 100% throttle that is main range you need to concentrate on, just clean rest so it runs best... Fun Project there we have done a few rails, and other powersports with motorcycle engines.. We hope to get back to it now we have moved...
 

Boosted Cycle Perf

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Peak torque is where you want it the richest as that is where the engine is most efficient. That’s typically around 8-8500 rpm.

In the dead heat of Texas summer I never see any gains over 13.2 afr.Depending on the time of year and application I tune between 12.8-13.2 afr.

That being said you’re leaving mph on the table being that lean.
 

mark_watkins

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Here is the Racepak from the run. Engine RPM, Axle RPM and A/F on traced. The pass was a 9.86 at 129mph. I was running VP C12 and the MSD SB6 shifted at around 9500.

Questions -I believe the engine RPM trace is showing the clutch is slipping in 1st and 2nd. I use a slider clutch set to engage at around 4000.
At the top of 6th, the engine RPM graph is showing the motor cutting out. Any ideas as to why?
The A/F is showing the engine getting leaner toward the end of each gear. I don't think I want this.
BTW-The temp was 80 degrees and Humidity was around 12%. Roughly 2000 ft. at AutoClub Dragway in Fontana, CA.
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Boosted Cycle Perf

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Do I dare ask if you’ve bypassed the factory clutch switch? I know you said you have a slider. 5th and 6th gear should read a little richer unless you have ram air compensation turned off.

Overall the afrs fallow the same trend every gear. They’ll go slightly leaner in the upper gears as engine load increases. However the afr shouldn’t be swinging almost one whole point throughout the rpm range. Ideally it should stay pretty flat overall and maybe a little fatter around peak torque.

Outside the spike in afr from shift kill I’m seeing 13.2-13.3ish afr. Not too bad honesty, but you did say this log you were running C12. Yet in your first post you said you run premium fuel. Premium as in pump gas 91? If you normally run pump gas, but on this pass on c12 the afr was at 13.2, I would fully expect it to run .5-.8 afr leaner on 91. That wouldn’t be good.

With that being said, you have a gen 1 gen. Suzuki states that they be run on 87 octane. You will always make the most hp on the least amount of octane you can run and avoid detonation. So running 112 octane is just a waste of money, and hurting your HP. Plus, it’s a leaded fuel so it kills spark plugs which could possibly be the reason the engine was breaking up in 6th. But if that was the case, I’d expect to see that happen in the lower gears as in 6th, combustion temps are at their highest. But still possible.

A more likely cause of your break up is ignition dwell. Stock coils overheat fast with longer dwell times. I’d put it back at 100, and leave it be.

I see you have dual side winder mufflers split between the cylinders. Is the o2 sensor in the collector where the two runners meet?
 

busakiller

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Is the speed limiter shut off? That could be your problem in 6th gear. Your gearing is pretty low if your in 6th gear and doing 129mph in the traps. I bet your hitting the speed limiter in 6th.
 

mark_watkins

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Thank you to all who weighed in with ideas. I will be back on the track at New Years for a bracket race. I leaked down both my motors and the are showing all the cylinders within 1.5% of each other.
I created a couple of maps that return the dwell to 100%.
FYI, the car is running 14-45 with 76 inch tires. I am going to put in all new friction disks in the clutch and button it up for a couple of weeks til race season starts here in SoCal around New Years.
 

Boosted Cycle Perf

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Thank you to all who weighed in with ideas. I will be back on the track at New Years for a bracket race. I leaked down both my motors and the are showing all the cylinders within 1.5% of each other.
I created a couple of maps that return the dwell to 100%.
FYI, the car is running 14-45 with 76 inch tires. I am going to put in all new friction disks in the clutch and button it up for a couple of weeks til race season starts here in SoCal around New Years.
I wrote a small book with some questions and answers to your problems. Aside from dwell, none of it was acknowledged.

From here on out I will not respond or try to help anymore.
 



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