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Discussion Starter · #1 ·
Just out of curiosity all you single plate system guys, in the eighth mile, what kind of RPM increase are you seeing on your cars after the low to high shift? I noticed in a race with the fastest car in our class, I looked at the time slip and on the incrementals (and from inside the car) up until high gear it was almost a dead heat. The reason I ask is I was going over some acq files from the 7531 and noticed something strange.

The car will shift, and the drop is pretty substantial. Most of the time around 1100-1200 rpm, but after the car is solidly engaged in second the rpms will drop about another 100 or so then only come back about 300 rpm from about 300 ft to the 660. In fact, after the second rpm drop it takes over a second for it to just climb back the 100 or so to get back to where it was. Something about that just doesn't sound right. The car doesn't break up, spit, sputter, hesitate, surge, or anything. It just kind of lays there in high gear like there is some kind of limiter on it. And this is with a 400 shot plate system turned on as well.

There is no limiters, retards, or anything like that in high gear. It just flat out lays down like something is holding it back. I'm no converter or transmission expert by any means, but I did have Marty at Neal Chance look at my data file and he said the converter looked like it was working well...from what he could see. Is there something in the transmission that would cause this?

1.80 straight cut Deadenbear cased 1600 h.p. capable glide. Honestly I've been fighting this problem for a while, the car has never MPH'd at all. But I just never really looked at the lack of acceleration in high gear on the acq files, it's like something finally made it jump out at me. I've changed gears, nitrous kits, launch rpm's, shift points, converters, valve lash, suspension adjustments, had the springs checked, and the car always runs around the same...no matter what. But the high gear is the same on all combinations...nothing there.
 

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X275!
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Take the nitrous jet out for your next pass. Thatll make her pull better in high gear ;)

Seriously though, post your aquisition files somewhere so others can take a look at them. It sounds like one person has already looked them over and said that things looked normal.
 

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Discussion Starter · #3 ·
How

How can I post them? Will they show up from photobucket?
 

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Not unless you can turn them into a JPEG. Photobucket doesn't like any other file extension. I had a friend host mine but not sure how he did it.
Mine does the same thing. It kind of flat lines after the shift and then it shoots back up. Not sure why but I am not loosing sleep over it any more. Steve J. thought maybe it was going rich.
 

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Discussion Starter · #5 ·
I wonder

I wonder if anyone has tried the gear advance feature with nitrous? Maybe putting in a degree or two of timing at the shift point for just a second or so would help. I just wouldn't want to burn anything up.
 

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Not unless you can turn them into a JPEG. Photobucket doesn't like any other file extension. I had a friend host mine but not sure how he did it.
Mine does the same thing. It kind of flat lines after the shift and then it shoots back up. Not sure why but I am not loosing sleep over it any more. Steve J. thought maybe it was going rich.

Similar situation,not on all runs.I look at the data logger after a nice pass and see a flat line after the shift drop.RPM flatlines for approx. half a 1/10th then climbs nice,been driving me nuts.I've had issues with my Lokar throttle cable stretching,which still engages the n2o switch but was only about 75%-80% wot,I was thinking that was the culprit.
 

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Discussion Starter · #7 ·
Similar situation,not on all runs.I look at the data logger after a nice pass and see a flat line after the shift drop.RPM flatlines for approx. half a 1/10th then climbs nice,been driving me nuts.I've had issues with my Lokar throttle cable stretching,which still engages the n2o switch but was only about 75%-80% wot,I was thinking that was the culprit.

Man, I'd love it if it were half a tenth on mine. It flatlines for a full second on mine!
 

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Similar situation,not on all runs.I look at the data logger after a nice pass and see a flat line after the shift drop.RPM flatlines for approx. half a 1/10th then climbs nice,been driving me nuts.I've had issues with my Lokar throttle cable stretching,which still engages the n2o switch but was only about 75%-80% wot,I was thinking that was the culprit.
Hmmmm..........I have one of them too.
 

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Sounds like you need more rear gear to help the car accelerate in high gear. The only thing is that may bring on more problems elsewhere. What gear is in the car now?
 

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Discussion Starter · #11 ·
Sounds like you need more rear gear to help the car accelerate in high gear. The only thing is that may bring on more problems elsewhere. What gear is in the car now?
Well, it's got a 4.10 now, I have thought about putting the 4.57 back in now that the converter is tighter. I had a 4.57 in it with a looser converter, but it was blowing through it in high gear. And the car is relatively heavy. 3348lbs
 

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A shift extension of 1,000 - 1,200 rpm is ideal. That is the rpm drop at the gear change. Based on your comments here I agree with Marty, the converter is doing it's job..

Generally speaking the issue is a lack of wheel speed at a given MPH, that will "lug" the engine down. And then it gets behind the stator in the converter. Or in other terms, the converter is sucking the engine down after the gear change.

Usually I see this condition when the driver is short shifting. This can happen because of many conditions... Gboyd mentioned rear axle gear ratio, that's one, tire size, simply not enough power for the combination, short shifting, incorrect rotor phasing, too much timing pulled out for the hit and the list goes on.

The 1st thing you gotta ask yourself is what was changed prior to noticing this condition?

I help guys figure these problems out often, feel free to give me a shout here at the shop.

g
 

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needs more gear ,i run into the same thing when i run my big tires...needs more gear or more power in my case.
 

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Discussion Starter · #14 ·
A shift extension of 1,000 - 1,200 rpm is ideal. That is the rpm drop at the gear change. Based on your comments here I agree with Marty, the converter is doing it's job..

Generally speaking the issue is a lack of wheel speed at a given MPH, that will "lug" the engine down. And then it gets behind the stator in the converter. Or in other terms, the converter is sucking the engine down after the gear change.

Usually I see this condition when the driver is short shifting. This can happen because of many conditions... Gboyd mentioned rear axle gear ratio, that's one, tire size, simply not enough power for the combination, short shifting, incorrect rotor phasing, too much timing pulled out for the hit and the list goes on.

The 1st thing you gotta ask yourself is what was changed prior to noticing this condition?

I help guys figure these problems out often, feel free to give me a shout here at the shop.

g

Cool Ratcht, I'm terrible with names.....I remember call signs, but never names. What was your name again?
 

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Sounds to me like the converter is a bit too tight. When the gear change is made, the motor drops out of it's power band and the wind gets knocked out of it for a moment. That is usually the flat line you see. Once it recovers, the motor begins to accelerate again.

A few ways to rectify this is moving your shift point up. In some cases, this will help by keeping the motor closer to it's powerband after the gear change. Adding more power will also loosen up the recovery. Depending on the setup (multi system vs. single) the timers might need to be moved around to accomodate this in 1st gear.

The best way I've found is loosening the converter. The sixty foot usually will pick up by freeing the motor up and it should accelerate clean on the gear change. I've experienced the runs picking up a 1/10th and 2mph by just the stator change on some of the cars I work with.
 

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Discussion Starter · #16 ·
Sounds to me like the converter is a bit too tight. When the gear change is made, the motor drops out of it's power band and the wind gets knocked out of it for a moment. That is usually the flat line you see. Once it recovers, the motor begins to accelerate again.

A few ways to rectify this is moving your shift point up. In some cases, this will help by keeping the motor closer to it's powerband after the gear change. Adding more power will also loosen up the recovery. Depending on the setup (multi system vs. single) the timers might need to be moved around to accomodate this in 1st gear.

The best way I've found is loosening the converter. The sixty foot usually will pick up by freeing the motor up and it should accelerate clean on the gear change. I've experienced the runs picking up a 1/10th and 2mph by just the stator change on some of the cars I work with.
I've tried some different shift points, but I've never twisted it past 7600 on the shift. Maybe I need to be turning a few more rpm's before the shift. As far as the nitrous goes, the whole 400 shot is all in well before the end of first gear. I'm thinking what ever is causing this is why I have tried a bigger shot on the car and it doesn't make any more difference. In it's current state it will run the same on a 300 shot as it does on a 400 or 450 shot. I have tried two different kits on the car too. Thinking the nitrous kit was the culprit. But with a bigger kit it will get up in low a little faster, but the high gear flatline is longer. If I could make the car pull in high it should be with the rest of the pack. I only need about 3/10's to be in the hunt.
 

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Discussion Starter · #17 ·
Gilbert

Thanks, for all the ideas and help Gilbert....maybe I can get this thing competitive before the end of the season!
 

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Discussion Starter · #20 ·
Mail

Get me those files and I'll take a look at 'em!

No doubt in my mind that after talking to you there is allot in the can with that combination.

g
You have mail!
 
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