Throttle Stop RPM Check
 

I wanted to check that my throttle stop RPM was correct before qualifications last week. I put the car on jackstands, turned off power to the stop, increased the 2-step RPM above the TS RPM and hit the trans brake button and gas pedal. RPM was high, so I adjusted the manual RPM knob downward and tried again. That attempt gave me the correct RPM. However, when I ran the first qualifier, I found the RPM 200 too low when I reviewed the run on my Racepak graph. What did I do wrong? Is there a better, safe, way to ensure my RPM on the stop is correct short of taking multiple shots down the track? Thanks for any advice you guys can provide.

Re: Throttle Stop RPM Check
 

First off the race pack and tach may be off compared to each other. Also the car is loaded differently against the trans brake than it is going down track. I only use the playback on the tach to check my cruise rpm after a run. If its 100rpm low I will unplug the stop and run it against the brake like you and note the rpm . I then make an adjustment and recheck untill its 100rpm higher . In other words I just use the brake rpm as a reference in order to set the rpm to what I want based on the playback of the last run. Also you only use one instrument this way

Re: Throttle Stop RPM Check
 

On our car we usually see 100 RPM less on the playback than on the RacePak. We use a linkage stop and have determined that we'll see approximately 150 RPM difference for each full turn of the stop nut.

Re: Throttle Stop RPM Check
 

They're all correct. You will see a difference is statically checking the rpm in the pits versus what you see on the track. It's all irregardless though as you use the static setting simply as a barometer. Example: You know that setting the rpm at 4400 gets you 4200 on the track. The important number is that your on-track rpm is always at 4200. When that number changes, it will affect 60' times (depending on your timer settings) and you can't have that to expect any consistency. That's what makes the use of (in your case) the Racepak helpful.