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Old 07-15-2014, 07:05 PM   #1
Straightliner
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Default Time vs RPM?

I have a few questions. 1) Do I need to figure out my T stop ratio doing the, a lot of timer then a little timer and doing the math or can I just let Crew Chief do it using the Calculate ratios tab once I have some good runs? 2) I currently go on stop at .500 and come back off the stop while still in first gear and then shift to high at 6500 rpm. What I want to know is can I shift on time at the time it hits 6500 knowing that depending on timer 2 number that time would in fact be changing but I wouldn't actually change it to compensate it would just be what it is. Can I do it and be consistent? My thinking is that the time it takes to get to 6500 is also a changing time due to the timer 2 number so I think it will be fine but wanted opinions.
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Old 07-16-2014, 12:50 AM   #2
Don Higgins
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Default Re: Time vs RPM?

I don't like to use the huge timer change to calculate ratios.

My strategy is:
2 runs, same day, same lane. 60 foot can't be more than .008 off. Must be normal cool down period, no hot lapping for this test. ( Hot lap is anything less than 55 minutes ).

Put what you think will be close in the timer for the first run, then at least 10 numbers but no more than 20 numbers different on the second ( higher if too quick, lower if too slow ).

After entering both runs Crew Chief Pro will calculate the ratio for you if it needs to change.

Predict the third run and it should be very close.

I don't like to use RPM shift on Throttle Stop classes. Some make it work but I prefer to shift on the stop, as early as possible to minimize RPM creep.
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Old 07-16-2014, 06:33 PM   #3
Straightliner
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Default Re: Time vs RPM?

When you say *numbers* in the timer is that thousandths? I'm still on Crew Chief default ratios/factors. Because my car is heavy and only a 10.40 car I have been advised by most t-stop guys to go on and come off in low gear. Don is my logic correct in regards to the time shift that matches when it gets to 6500? If I should call you instead what is a good time for you?

Thanks
Brad in Canada!
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Old 07-16-2014, 10:17 PM   #4
Don Higgins
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Default Re: Time vs RPM?

Quote:
Originally Posted by Straightliner View Post
When you say *numbers* in the timer is that thousandths? I'm still on Crew Chief default ratios/factors. Because my car is heavy and only a 10.40 car I have been advised by most t-stop guys to go on and come off in low gear. Don is my logic correct in regards to the time shift that matches when it gets to 6500? If I should call you instead what is a good time for you?

Thanks
Brad in Canada!

OK, well that changes things a bit. Lets go over the basics of a throttle stop movement. It takes close to .40 seconds to open and close a throttle stop on average. That means you basically have .40 seconds of your stop timer that is wasted ( .20 to close, .20 to open ). So anything under .80 of a second in stop isn't doing much to your ET, at least not consistently. Not thousandths, hundredths.

You may need to shift on RPM in order to get some timer. You may also need to be on the first timer far longer than someone who runs quicker.

I believe the best way to find out is to test. 5 - 8 runs trying to make sure you can get to the 10.90 index with at least ONE SECOND of timer. If you can't do that with your current setup then bring #1 timer longer by .20 at a time until you can.

No magic unfortunately, every car is different.

Call us after you make a few passes that get to your goal.
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Old 07-17-2014, 09:35 AM   #5
Straightliner
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Default Re: Time vs RPM?

Okay. I will try and get some data next weekend. Thank you Don.

Brad
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Old 07-19-2014, 03:12 PM   #6
Straightliner
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Default Re: Time vs RPM?

Hi Don, While waiting to get back to the track I realized I didn't give you my current numbers. Last event- bracket racing on the stop, so I wasn't changing timers just dialing the car accordingly (because I wanted to go rounds, not test during an event)

Timer one on at .500 and timer 2 set at 1.667 still in low gear, and shifting to high at 6500 rpm this had my car going 10.69 and repeating. If that helps you help me!!!

I'm still having a little trouble understanding the calculate ratios I just get a lot of negative numbers so I have yet to change from your program defaults. I have watched the video many times trying to grasp it, lol.

Brad
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Old 07-20-2014, 02:13 AM   #7
Don Higgins
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Default Re: Time vs RPM?

If you are trying to get a throttle stop ratio then you will need to change the throttle stop to get it to do anything.

If you are doing weather ratios then negative numbers usually mean the fuel type is alcohol and it runs better in worse air. Negative numbers on a gas car are a sign the mixture is too lean.
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Old 07-23-2014, 04:39 PM   #8
Straightliner
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Default Re: Time vs RPM?

Don or others can I get your opinion on 1 part of my post?

What I want to know is can I shift on time at the time it hits 6500 knowing that depending on timer 2 number that time would in fact be changing but I wouldn't actually change it to compensate it would just be what it is. Can I do it and be consistent? My thinking is that the time it takes to get to 6500 is also a changing time due to the timer 2 number.

Last edited by Straightliner; 07-23-2014 at 04:41 PM.
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Old 07-25-2014, 11:36 PM   #9
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Default Re: Time vs RPM?

Just curious, what is your cruise rpm set at? Raising the cruise will cause you to need more timer.
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Old 07-28-2014, 11:29 AM   #10
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Default Re: Time vs RPM?

Quote:
Originally Posted by hookdaddy View Post
Just curious, what is your cruise rpm set at? Raising the cruise will cause you to need more timer.
4400 rpm on the playback tach.
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