A little about me since I'm new here - I help tune and sponsor my brother's dragster (240" Racecraft 4 link slipper).
We updated the EFI system to Holley in September and he took off on an East Coast tour in October-November. At a stop in Indiana, the car went backwards on the enhancer and found the band strut folded over when he took it apart at Darlington. He then took the parts over to FTI and they freshened everything up. The car seems to 60ft the same as before but the rpm while on the convertor is way different. If you look at the data overlay, you can see what I'm talking about - the rpm difference between before and after pretty stark. (Solid line is "before", dashed line is "after".)
My question is:: Have you seen this before and what might the difference be?
Second, when hot lapping, do you notice any ET pickup with a hotter trans?

The first thing i see is it looks like the drivers foot is coming off the throttle when the transbrake releases. That happening alone can be inconsistent enough to cause the difference you are seeing.

-DALTON

^^^^^what he said^^^^^

quote:

Originally posted by FTI:
The first thing i see is it looks like the drivers foot is coming off the throttle when the transbrake releases. That happening alone can be inconsistent enough to cause the difference you are seeing.

-DALTON

I have a question about this having seen it a couple times before when viewing friends graphs....I developed the theory that the weight of the t-stop and/or enhancer hanging on the throttle cable might be causing the throttle cable to move enough to let the carb close some during the instant g-force at launch...all drivers said there was no way their foot was lifting off the mechanical stop they were pushing down against with full force... so this is all I could come up with...

Thanks for the responses.

We noticed the dip in TPS when developing the tune in September. It's got 2 Accufab TB's, I think they are 2000cfm units so 60% throttle is fundamentally WOT. The dip in TPS goes down to 86% or so. (I think the foot pedal needs to be moved back a skinch to eliminate the dip.)

The other EFI system didn't have TPS data logging so we never saw it before.
The interesting thing is that the little flash at the hit (dotted red line) is consistent along with the flatness after that at the 4 races he went to out there (about 40some laps).

So, I take it the dotted line RPM is not really an issue but see if it changes after fixing the foot-feed?

Does it not log driveshaft speed?

quote:

Originally posted by Rick!:
Thanks for the responses.

We noticed the dip in TPS when developing the tune in September. It's got 2 Accufab TB's, I think they are 2000cfm units so 60% throttle is fundamentally WOT. The dip in TPS goes down to 86% or so. (I think the foot pedal needs to be moved back a skinch to eliminate the dip.)

The other EFI system didn't have TPS data logging so we never saw it before.
The interesting thing is that the little flash at the hit (dotted red line) is consistent along with the flatness after that at the 4 races he went to out there (about 40some laps).

So, I take it the dotted line RPM is not really an issue but see if it changes after fixing the foot-feed?

I wouldn't say the difference with the dotted line is negligible, something is causing the inconsistency and we don't want that. I would start with the throttle and see if it improves. I'm willing to bet it does since the inconsistency is right after the throttle blip and the rest of the graph is almost identical.

quote:

Originally posted by Rick!:
I have a question about this having seen it a couple times before when viewing friends graphs....I developed the theory that the weight of the t-stop and/or enhancer hanging on the throttle cable might be causing the throttle cable to move enough to let the carb close some during the instant g-force at launch...all drivers said there was no way their foot was lifting off the mechanical stop they were pushing down against with full force... so this is all I could come up with...

I'm not familiar with the mechanics of the starting line enhancers as i've never ran one, but anything is possible right?
I've been the driver swearing my foot was at WOT the whole time too. A camera in the footbox of my dragster quickly humbled me to that. We chalked it up to i was a little to stretched out to reach the pedal, and that coupled with the padding in the seats, was causing the issue. We moved the pedals back and car came right back around.

-Dalton

quote:

Originally posted by FTI:
I'm not familiar with the mechanics of the starting line enhancers as i've never ran one, but anything is possible right?
I've been the driver swearing my foot was at WOT the whole time too. A camera in the footbox of my dragster quickly humbled me to that. We chalked it up to i was a little to stretched out to reach the pedal, and that coupled with the padding in the seats, was causing the issue. We moved the pedals back and car came right back around.

-Dalton

I positioned my throttle pedal so I'm actually pushing myself back in the seat slightly with my right foot. I wanted to make sure I'm full throttle. I also positioned the pedal so that my foot is not more than about a 45* angle at WOT....for me it's easier to go WOT at that position....Just what I do anyway

Also the right AF ratio shows 3.2?? Could there have been a tune up issue there?

This is where a rear facing camera will tell the truth @ the 2.08 mark. He swore he was on it.
Not!!! A friends car....Look closely at the throttle side.And that was only a 63.

https://www.youtube.com/watch?v=W2saBFg3rUc

quote:

Originally posted by TD3550:
This is where a rear facing camera will tell the truth @ the 2.08 mark. He swore he was on it.
Not!!! A friends car....Look closely at the throttle side.And that was only a 63.

https://www.youtube.com/watch?v=W2saBFg3rUc

That's pretty enlightening. Wow.

I don't have a TPS, but I have pictures of mine about 30' out with the throttle blades (hat) only 2/3rds open. I adjusted the pedal stop so the blades are at WOT before the pedal hits the stop, problem solved.

quote:

Originally posted by Coloradoracer:

quote:

Originally posted by TD3550:
This is where a rear facing camera will tell the truth @ the 2.08 mark. He swore he was on it.
Not!!! A friends car....Look closely at the throttle side.And that was only a 63.

https://www.youtube.com/watch?v=W2saBFg3rUc

That's pretty enlightening. Wow.

I told him that thing on the right "IS NOT your Friend. Stab the B***. Well now the car has become violent at the hit. Has to lower the hit and work with the rear bar. The car is very capable of 30's and that's on a bad day. Car weigh's about 1680 loaded.

quote:

Originally posted by CURTIS REED:
Does it not log driveshaft speed?

Unfortunately, that is logged by the car data acq (Autometer 10 channel) and the download dongle was broken during the races. I have to go back and see if the new dongle will recover the runs still left in memory and compare DS speeds to earlier laps.

As for the O2, it went wonky not long after tuning and the new one has not been installed yet. At least that's what I think it is. Fuel pph is right where it needs to be for the AFR based off of the left O2 sensor though 4.8 is a bit fat for the combo.

WTH is a "dongle"

Sounds dirty....

quote:

Originally posted by "The Bender":
WTH is a "dongle"

Sounds dirty....

On the software I run it's a small usb with the software key on it.

quote:

Originally posted by CURTIS REED:

quote:

Originally posted by "The Bender":
WTH is a "dongle"

Sounds dirty....

On the software I run it's a small usb with the software key on it.

Ahhh, that's much different than what I was thinking

I never heard that word before. Sounded like it might be a politician name or something That RED in the video leaves so hard it looks like it would push the driver out of the seat.

quote:

Originally posted by Footloose:
I never heard that word before. Sounded like it might be a politician name or something That RED in the video leaves so hard it looks like it would push the driver out of the seat.

I was thinking more like some porn star...….Dirk Dongle