RPM dip doing onto stop, w/ racepak graphs

triplezero · 03-25-2024, 12:47 PM

Been having a problem with the RPMs dipping going onto the stop or right after going on. It seems random, doesn't seem weather related or any pattern really. Thinking of trying to tighten up front suspension not to bounce as much, and also thinking maybe making the first timer smaller and raise cruise rpm. Where would you guys start?

468bbc, 760 hp, glide, 4.10s, 30x9, 3370, T1 .400, cruise 4050, shift on rpm

Car is pretty good except this issue that'll change the 60ft .02-.04. Also notice at times, the transition from the falling rpm to the cruise at times will be a sharp "L" and sometimes slowly curls out, which will also change the 60. Don't know if its related or not.

Pauley · 03-26-2024, 09:30 AM

Whos carb and what size?
What size carb?
Electric or air stop?
Are shifting on stop or on rpm?

I dont know much but maybe i can help

ep

1320racer · 03-26-2024, 10:11 AM

Don’t let Pauley bullshyt you, he’s a bad man running a throttle stop.

Pauley · 03-26-2024, 01:17 PM

dont let 1290 bullchit you sir. i blind squirrel it most of the time.

by the looks of your graph i would say the you are shifting on rpm. the creep in it leads me to think rpm. most will say to try and get your graph to lay as flat as possible which you can do on time not on rpm so much. the creep has never bothered me that much as long as it repeats. but you definitely don't want the dip. that will make you pull your hair out. that is why i dont have hair. i would like to know also how fast your ride is wide open also.

ep

Pauley · 03-26-2024, 01:22 PM

gas or alcohol?

Pauley · 03-26-2024, 02:05 PM

Sorry for the dumb shift ? I see the shift.

ep- told you blind squirrel

Adger Smith · 03-26-2024, 04:21 PM

Timing issue?
Timing of low gear band release and Hi gear clutches apply..
Both applied at the same time could drag RPM down.
Different servo spring or adjust the spring pressure higher.
or
More clearance in the Hi clutch pack can increase time to apply and free up drag when in low gear.

Phil S/ST · 03-28-2024, 09:41 AM

Not knowing the O2 readings, my guess the carb is a tick fat causing to 60ft to change. Try switching to shifting on time and try a bigger intermediate air bleed on the carb. Other fixes include raising the stop RPM, slowing stop closing speed. A smaller carb may work also. Just some thoughts

Phil S/ST · 03-28-2024, 09:45 AM

Quote:

Originally Posted by Pauley

Sorry for the dumb shift ? I see the shift.

ep- told you blind squirrel

You looked good at SGMP until Webb kinda ran over everyone! Myers was too.

Lenny5160_v2 · 03-28-2024, 10:34 AM

This setup is pretty similar to mine, although you have more power and are 200 lbs lighter.

Shifting on time would cost a lot of MPH. I wouldn't do that. I'd probably go up a bit on the cruise RPM to 4300 or so.

I go on the stop at .500 to get things moving. You seem to have a similar thought. Moving that timer would be a good thing to try, but I don't know which way might be helpful in this case.

Do you have a crossover hose on your carb bowl vent tubes? Maybe some fuel slosh.

Intermittent issues are always the worst.

03-25-2024, 12:47 PM	#1
triplezero Junior Member Join Date: Jun 2013 Posts: 12 Likes: 0 Liked 0 Times in 0 Posts	RPM dip going onto stop, w/ racepak graphs Been having a problem with the RPMs dipping going onto the stop or right after going on. It seems random, doesn't seem weather related or any pattern really. Thinking of trying to tighten up front suspension not to bounce as much, and also thinking maybe making the first timer smaller and raise cruise rpm. Where would you guys start? 468bbc, 760 hp, glide, 4.10s, 30x9, 3370, T1 .400, cruise 4050, shift on rpm Car is pretty good except this issue that'll change the 60ft .02-.04. Also notice at times, the transition from the falling rpm to the cruise at times will be a sharp "L" and sometimes slowly curls out, which will also change the 60. Don't know if its related or not. Attached Thumbnails Last edited by triplezero; 03-25-2024 at 07:47 PM.

03-26-2024, 09:30 AM	#2
Pauley Junior Member Join Date: Jan 2024 Posts: 13 Likes: 1 Liked 49 Times in 7 Posts	Re: RPM dip doing onto stop, w/ racepak graphs Whos carb and what size? What size carb? Electric or air stop? Are shifting on stop or on rpm? I dont know much but maybe i can help ep

03-26-2024, 10:11 AM	#3
1320racer VIP Member Join Date: Nov 2007 Location: New Jersey Posts: 1,778 Likes: 70 Liked 400 Times in 191 Posts	Re: RPM dip doing onto stop, w/ racepak graphs Don’t let Pauley bullshyt you, he’s a bad man running a throttle stop.

03-26-2024, 01:17 PM	#4
Pauley Junior Member Join Date: Jan 2024 Posts: 13 Likes: 1 Liked 49 Times in 7 Posts	Re: RPM dip doing onto stop, w/ racepak graphs dont let 1290 bullchit you sir. i blind squirrel it most of the time. by the looks of your graph i would say the you are shifting on rpm. the creep in it leads me to think rpm. most will say to try and get your graph to lay as flat as possible which you can do on time not on rpm so much. the creep has never bothered me that much as long as it repeats. but you definitely don't want the dip. that will make you pull your hair out. that is why i dont have hair. i would like to know also how fast your ride is wide open also. ep

03-26-2024, 01:22 PM	#5
Pauley Junior Member Join Date: Jan 2024 Posts: 13 Likes: 1 Liked 49 Times in 7 Posts	Re: RPM dip doing onto stop, w/ racepak graphs gas or alcohol?

03-26-2024, 02:05 PM	#6
Pauley Junior Member Join Date: Jan 2024 Posts: 13 Likes: 1 Liked 49 Times in 7 Posts	Re: RPM dip doing onto stop, w/ racepak graphs Sorry for the dumb shift ? I see the shift. ep- told you blind squirrel

03-26-2024, 04:21 PM	#7
Adger Smith VIP Member Join Date: Dec 2001 Location: Texarkana Ark/TX Posts: 2,348 Likes: 435 Liked 677 Times in 261 Posts	Re: RPM dip doing onto stop, w/ racepak graphs Timing issue? Timing of low gear band release and Hi gear clutches apply.. Both applied at the same time could drag RPM down. Different servo spring or adjust the spring pressure higher. or More clearance in the Hi clutch pack can increase time to apply and free up drag when in low gear. __________________ Adger Smith (Former SS) Last edited by Adger Smith; 03-26-2024 at 04:24 PM.

03-28-2024, 09:41 AM	#8
Phil S/ST Junior Member Join Date: Apr 2022 Posts: 19 Likes: 13 Liked 21 Times in 6 Posts	Re: RPM dip doing onto stop, w/ racepak graphs Not knowing the O2 readings, my guess the carb is a tick fat causing to 60ft to change. Try switching to shifting on time and try a bigger intermediate air bleed on the carb. Other fixes include raising the stop RPM, slowing stop closing speed. A smaller carb may work also. Just some thoughts

03-28-2024, 10:34 AM	#10
Lenny5160_v2 Member Join Date: Feb 2023 Location: Inver Grove Heights, MN Posts: 108 Likes: 248 Liked 156 Times in 62 Posts	Re: RPM dip doing onto stop, w/ racepak graphs This setup is pretty similar to mine, although you have more power and are 200 lbs lighter. Shifting on time would cost a lot of MPH. I wouldn't do that. I'd probably go up a bit on the cruise RPM to 4300 or so. I go on the stop at .500 to get things moving. You seem to have a similar thought. Moving that timer would be a good thing to try, but I don't know which way might be helpful in this case. Do you have a crossover hose on your carb bowl vent tubes? Maybe some fuel slosh. Intermittent issues are always the worst. __________________ Tony Leonard S/C & S/ST 5160