Throttle Stop RPM creeping downward?

Jonathan Anderson · 04-26-2014, 06:43 PM

During testing my SST car I noticed the rpm's creeping downward. Go on the stop at .25 shift at .55 total stop timer 2.30 for a 10.905@133

The rpm starts out at 4900 and comes off the stop at 4600. The 60' only moved about .006 in 5 runs.

What would cause the rpms to drop like that? All transitions are smooth with no spikes or dips.
Thanks in advance.

Superstreet29 · 04-27-2014, 09:54 AM

Raise the rpm?

RacingRicki · 04-27-2014, 09:58 AM

You might want to try richening up the intermediate air bleeds. Assuming you run a 3 circuit dominator

C and W Racing · 04-27-2014, 11:24 AM

Quote:

Originally Posted by RacingRicki

You might want to try richening up the intermediate air bleeds. Assuming you run a 3 circuit dominator

That, plus it may be in the converter. Most cars that do not flat line on the stop, pick up rpm, not lose it.
Chuck

Jonathan Anderson · 04-27-2014, 12:58 PM

I thought about air bleeds but its an APD HP 950? Would changing them have the same effect?

I did raise the rpm I've been as low as 4200 and up to 4600 ( these are the rpms as it comes of the stop)....

My initial thought was converter too.

I've moved shift points too, it affects the sixty foot of course but not the rpm decrease.

I will call Greg at FTI tomorrow to get his thoughts.

Thanks guys for the information!

Bob Mendenhall · 04-27-2014, 06:34 PM

If you are shifting the transmission while the engine is on the stop it's not unusual to see the engine drop about 300 rpm. The key is that it drops the same amount at the same point every time. This is where a data recorder would prove to be a valuable tool.

Bob

Jonathan Anderson · 04-27-2014, 08:43 PM

Here is a picture of the last run I made today, the highest rpm was 4825 and the lowest was 4500. Am I trying to split hairs? I just don't want to be chasing a problem that I may not have. Thanks again for all the help!

C and W Racing · 04-28-2014, 08:14 AM

Quote:

Originally Posted by Bob Mendenhall

If you are shifting the transmission while the engine is on the stop it's not unusual to see the engine drop about 300 rpm. The key is that it drops the same amount at the same point every time. This is where a data recorder would prove to be a valuable tool.

Bob

I'm not sure about that. I shift mine on the stop, and mine flat lines the whole time I'm on the stop, and I am on the stop for about 4 seconds. I do have a FTI converter in my car.
Chuck

Jonathan Anderson · 04-28-2014, 11:53 AM

Troy Williams at FTI says remove the power valve! Didn't think of that, excellent customer service by those guys!

04-26-2014, 06:43 PM	#1
Jonathan Anderson Junior Member Join Date: Apr 2011 Posts: 48 Likes: 3 Liked 1 Time in 1 Post	Throttle Stop RPM creeping downward? During testing my SST car I noticed the rpm's creeping downward. Go on the stop at .25 shift at .55 total stop timer 2.30 for a 10.905@133 The rpm starts out at 4900 and comes off the stop at 4600. The 60' only moved about .006 in 5 runs. What would cause the rpms to drop like that? All transitions are smooth with no spikes or dips. Thanks in advance.

04-27-2014, 09:54 AM	#2
Superstreet29 Junior Member Join Date: Nov 2013 Posts: 30 Likes: 0 Liked 4 Times in 4 Posts	Re: Throttle Stop RPM creeping downward? Raise the rpm?

04-27-2014, 09:58 AM	#3
RacingRicki Sponsor Join Date: Sep 2005 Location: Colorado Posts: 106 Likes: 0 Liked 0 Times in 0 Posts	Re: Throttle Stop RPM creeping downward? You might want to try richening up the intermediate air bleeds. Assuming you run a 3 circuit dominator __________________ RacingRicki

04-27-2014, 12:58 PM	#5
Jonathan Anderson Junior Member Join Date: Apr 2011 Posts: 48 Likes: 3 Liked 1 Time in 1 Post	Re: Throttle Stop RPM creeping downward? I thought about air bleeds but its an APD HP 950? Would changing them have the same effect? I did raise the rpm I've been as low as 4200 and up to 4600 ( these are the rpms as it comes of the stop).... My initial thought was converter too. I've moved shift points too, it affects the sixty foot of course but not the rpm decrease. I will call Greg at FTI tomorrow to get his thoughts. Thanks guys for the information!

04-27-2014, 06:34 PM	#6
Bob Mendenhall Junior Member Join Date: Apr 2006 Location: Lakeside, Ca. Posts: 8 Likes: 0 Liked 0 Times in 0 Posts	Re: Throttle Stop RPM creeping downward? If you are shifting the transmission while the engine is on the stop it's not unusual to see the engine drop about 300 rpm. The key is that it drops the same amount at the same point every time. This is where a data recorder would prove to be a valuable tool. Bob __________________ No \"Home\" page, just an e-mail address

04-27-2014, 08:43 PM	#7
Jonathan Anderson Junior Member Join Date: Apr 2011 Posts: 48 Likes: 3 Liked 1 Time in 1 Post	Re: Throttle Stop RPM creeping downward? Here is a picture of the last run I made today, the highest rpm was 4825 and the lowest was 4500. Am I trying to split hairs? I just don't want to be chasing a problem that I may not have. Thanks again for all the help! Attached Thumbnails

04-28-2014, 11:53 AM	#9
Jonathan Anderson Junior Member Join Date: Apr 2011 Posts: 48 Likes: 3 Liked 1 Time in 1 Post	Re: Throttle Stop RPM creeping downward? Troy Williams at FTI says remove the power valve! Didn't think of that, excellent customer service by those guys!