Any tips for shifting by time instead of rpm?
 

Shifting by time,where to start.
Hey,new to the site and getting ready to start the race season.I have a small block altered that runs 8.40s and was going to shift by time instead of rpm. Does anyone shift by time? Do you think it's an advantage over rpm,I thought if you had a real good 60 foot it might short shift it and slow it down as to not break out. Also what would be a good starting point,any help would be great.

Re: Any tips for shifting by time instead of rpm?
 

Don't know what class you're running, but every Super Comp (and most Super class) racers I know shift on time. But they do it for a very specific reason. With the high-hp engines these days, you need to shift early to insure that the engine will not climb RPM when on the throttle stop. If you let the engine get high into it's power band while on the stop, it will be very inconsistent.

So we, like most people in SC, shift on time. We shift at 1sec, but I know people who are shifting at 0.1sec, heck I know people who start out in 2nd... all just to stay rock solid consistent when on the throttle stop. We used to shift at 1.2sec, but looked at the RPM data and after we added HP to the engine, it was climbing at bit on the stop, so we started shifting earlier.

Again, don't know if this is relevant to you, but there it is.
Chris

Re: Any tips for shifting by time instead of rpm?
 

Thanks for the reply Chris! Not running a stop,just bracket racing in a 7.00 to 8.50 class.Was just going to try somthing different,always looking for a edge.

Re: Any tips for shifting by time instead of rpm?
 

Well in your case , if you have a playback you can do this,........lets say you really like for the motor to shift at 6800 rpm (as in my case) . Make a run shifting at 6800 rpm and then run the playback to see what 6800 rpm equated to in time. Mine is 2.25 if I remember correctly. (been a while since I've ran without the stop, w/stop it's 2.02)

Hope this helps.

Rick

Re: Any tips for shifting by time instead of rpm?
 

Having shifted on time for years I can tell you your car will most likley need to shift somewhere between 2.1-2.7 sec depending on rear end gear, trans ratio, hp etc. If you have a computer or a playback tach it would make much easier to pick your exact number, otherwise start on the low end and work your way up to your desired RPM. Good Luck

Re: Any tips for shifting by time instead of rpm?
 

That's what I was looking for,a starting point.thanks for the help!

Re: Any tips for shifting by time instead of rpm?
 

Alaska Racer

We shift on time @1.0 sec. the stop comes on at .05 and off around 3.00 so we are in high gear when we come off the stop which seems to help consistency.:cool:

Re: Any tips for shifting by time instead of rpm?
 

Bill but that is with how much motor.......I'd guess u'd need some motor to be shifting on the stop, or at least that what I've always been told. I'd like to try it but I'm only a 477 (bg blk chev)

Thanks

Rick

Re: Any tips for shifting by time instead of rpm?
 

Almost exactly the same here. Except we go on the stop at .00, and off around 2.25 or so. We shift at 1.0 secs, and the RPM trace on the stop is like a laser line. When we shifted any later, it was much less smooth. FWIW, we have a 565BB at about 900hp.

Re: Any tips for shifting by time instead of rpm?
 

i shift on rpm and the stop comes on with time...i am gonna test a few other options,but i seem to have to formula worked out for what configuration i am running now...my stop comes on at 1.20 in the run and stays on till 2.50-2.90...and then as soon as it comes off the stop i am shifting at 6500...and i have a 434bbc...this weekend i am going to run super pro and i installed the air shifter and going to try to shift on time..but i did realize that the way i am doing it you have to be extra carefull with your throttle stop settings cause the computer predicts 1 thing and its not usually right on,i have learned that from time to time it picks up 1 hundredth in the 1/8 mile and sometimes it picks up almost 2 hundredths in the back end for a total of 3 hundredths on a run...you just gotta find out what works and try to copy the same data and infromation on everyrun...do things the same way each and everythime and more than likely you will find the consistancy you are looking for...flat out runs in the 1/8 mile my car is usually pretty consistant ...you can also adjust where you shift point to help with consistancy...its just all trial and error!!!
good luck