RPM shifting

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moparwedden

moparwedden

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OK I'm finally going racing, need to know what I should be shifting at. 72 Duster with full uniform, 4 speed, Center force dual friction clutch, 8 3/4 rear end with 410, large u-joint. 440 around 525HP. 255/60/15 drag radials. I was told too leave at 2500 but where should I be shifting after that, Crane fire ball with built in limiters, where should these be set at, do not want to break it right off the bat. this is just for fun.

Thanks.
 
The theoretical shift point could be different in different gears. What you NEED is a HP / torque curve for your engine, which you can then plot against the same curves with different transmission ratios. "Where they cross" is where you would like to shift

You can somewhat obtain this yourself in a street car, or in a car which you can get so track time into, by buying yourself something like a G-tech, which is a device which (depending on model) can trace acceleration, RPM and MPH, and store that

http://www.gtechpro.com/

Below is just a quick one I Googled on the www, and it doesn't properly show RPM, but this is the idea.

Look at the first circle. Imagine that you have created two different situations---coming up to the "cross" point and over revving in first, and secondly, (no pun) shifting WAY early from 1-2 and coming up to and passing the 1-2 "cross" in 2nd gear.

If you shift 1-2 LOWER than the crossing point, you can see the curve for 2nd is LESS than the output of 1st gear. But if you wind 1st PAST that, 1st then falls off to less output than 2nd gear for the 1-2 shift.

This might be a fair example, as you can see the 1-2 shift should occur at much less than the 2-3 or 3-4 shift, which could be rounded off to 6800. Since the hard acceleration at lower gears is very important for ET, this might be a critical adjustment.

12bolt-ShiftPoints.JPG
 
probably best with an unfamiliar car I would use something like 5500 to shake it down and try to key on that until you know how the car is going to react (leave, steer pull, top end, etc). You will have fun!
 
Rocky_JS said:
probably best with an unfamiliar car I would use something like 5500 to shake it down and try to key on that until you know how the car is going to react (leave, steer pull, top end, etc). You will have fun!
Click to expand...

This ^^^^^ is absolutely crucial with a first time car. Take your time and just get the feel of things.

There's so much to get the hang of at first, it would almost be impossible to tell you everything in one post. Make some safe passes, log some data about, leave rpm, shift points, tire pressure, etc. Main thing the first time out, take it slow and get the feel of things. Use your senses and you butt to tell you how far to take it for now. Once you get used to it, experiment, experiment, experiment, with different adjustments. Could take you all summer to get it totally right. Importantly, stay safe and have fun.

Just curious, i assume it's the first time out for the car, but will this be your first time on the track?
 
At what RPM did it make max power?

That should be some of your guide. Maybe try 100-200 over it to start. Anywhere from 5000-5500 could be a good target too. I never see the sense in killing the engine with RPM when shaking them down. Find a nice spot to shift and run it.

2500 isn't a bad spot to leave, BUT, you may have to walk it out a bit. Dump and stab will likely result in a smoke show!

Car looks good in your avatar.

Have fun.
 
OldmanRick said:
This ^^^^^ is absolutely crucial with a first time car. Take your time and just get the feel of things.

There's so much to get the hang of at first, it would almost be impossible to tell you everything in one post. Make some safe passes, log some data about, leave rpm, shift points, tire pressure, etc. Main thing the first time out, take it slow and get the feel of things. Use your senses and you butt to tell you how far to take it for now. Once you get used to it, experiment, experiment, experiment, with different adjustments. Could take you all summer to get it totally right. Importantly, stay safe and have fun.

Just curious, i assume it's the first time out for the car, but will this be your first time on the track?
Click to expand...

Sort of both Had never been racing before last year, thanks to Scott for getting me hooked, No I had it down last year but the fuel boiled, fixed that with a cool can, next time my ecu box was crap, put the Crane powerball unit on it, then lots of rain and could never get back out, ran out of time, so this will be hopefully a good run. I'll just play with it, lot's of old racers there, they love to help newbies out.
 
moparwedden said:
lot's of old racers there, they love to help newbies out.
Click to expand...

Exactly, that's where I was gonna go next. Most will be very supportive if you have questions. The car looks great and has a ton of potential. Wish I was in your shoes...lol, i haven't raced since the mid 80's. Good luck and keep us posted on how things go. :thumbrig:
 
moparwedden said:
Where should I set the rev limiters, there are two settings?
Click to expand...

If it was me, i'd just set a max rpm at just under what the engine can take and not put it in jeopardy. Maybe 6k, not sure how it's built. That should protect the bottom end and valvetrain on most engines if you miss a shift. I wouldn't worry about a low/launch setting at this point since you'll be varying you're launch rpm's to see what works best. I like to use my right foot for that with a new combo. :icon_smi:
 
moparwedden said:
Sort of both Had never been racing before last year, thanks to Scott for getting me hooked, No I had it down last year but the fuel boiled, fixed that with a cool can, next time my ecu box was crap, put the Crane powerball unit on it, then lots of rain and could never get back out, ran out of time, so this will be hopefully a good run. I'll just play with it, lot's of old racers there, they love to help newbies out.
Click to expand...
Sure John,try and blame me for your addictions.LOL:wack:When I raced my 4 speed car,it was a learning experience for sure.You,ll have to see what your car likes.Start off with say a 2000rpm launch and see how it likes leaving,then work your way up.My friend races a 383 alumi heads and has rev limiter set at 6500.Post some times once you get done.
Tip #1 bring your CAA card..JK.Have fun!
 
pettybludart said:
Sure John,try and blame me for your addictions.LOL:wack:When I raced my 4 speed car,it was a learning experience for sure.You,ll have to see what your car likes.Start off with say a 2000rpm launch and see how it likes leaving,then work your way up.My friend races a 383 alumi heads and has rev limiter set at 6500.Post some times once you get done.
Tip #1 bring your CAA card..JK.Have fun!
Click to expand...

What he said.... Start out getting used to the box ,staging , lights and launch...start out launching at lower rpms..

Get a tach with total recall..you will be too excited at first to remember anything.
Write all shift points ,60fts , ets and mph in a logbook.

Get rid of drag radials.... You will toast them at any higher rpm launch!
Unless you have the best set up chassis around .....
 
If you dont have a dyno sheet pay attention to where you power starts falling off.
Then go to www.automath.com and calculate your shift points according to trany/rearend ratios...

You want your next gear to start just before your torque curve starts to rise.. Then shift about 500 rpms after hp starts to fall off....

Its more complex than this but its a start....

Tell me if im wrong...
 
67Dart273 said:
The theoretical shift point could be different in different gears. What you NEED is a HP / torque curve for your engine, which you can then plot against the same curves with different transmission ratios. "Where they cross" is where you would like to shift

You can somewhat obtain this yourself in a street car, or in a car which you can get so track time into, by buying yourself something like a G-tech, which is a device which (depending on model) can trace acceleration, RPM and MPH, and store that

http://www.gtechpro.com/

Below is just a quick one I Googled on the www, and it doesn't properly show RPM, but this is the idea.

Look at the first circle. Imagine that you have created two different situations---coming up to the "cross" point and over revving in first, and secondly, (no pun) shifting WAY early from 1-2 and coming up to and passing the 1-2 "cross" in 2nd gear.

If you shift 1-2 LOWER than the crossing point, you can see the curve for 2nd is LESS than the output of 1st gear. But if you wind 1st PAST that, 1st then falls off to less output than 2nd gear for the 1-2 shift.

This might be a fair example, as you can see the 1-2 shift should occur at much less than the 2-3 or 3-4 shift, which could be rounded off to 6800. Since the hard acceleration at lower gears is very important for ET, this might be a critical adjustment.

12bolt-ShiftPoints.JPG
Click to expand...



Yeah.... What he said....lol
 
pettybludart said:
Sure John,try and blame me for your addictions.LOL:wack:When I raced my 4 speed car,it was a learning experience for sure.You,ll have to see what your car likes.Start off with say a 2000rpm launch and see how it likes leaving,then work your way up.My friend races a 383 alumi heads and has rev limiter set at 6500.Post some times once you get done.
Tip #1 bring your CAA card..JK.Have fun!
Click to expand...

You are a hout,lol
 
Just remember if you are shifting off of a shift light and have it set at 5500 then by the time you shift it will be 5800 or so... Keep this in mind...
 
I thought about what I said about just using your right foot for now to adjust starting line rpm. I made the assumption that your tach was in a line of site. I shouldn't "ASSume"....lol.

If you use a starting line chip/limiter, do like Scott says and start about 2000. If no bog, then make a few passes there and move up 500 at a time making a few runs at each setting until you start blowing the tires off.

Also, a "slight amount" of spin at the hit will not necessarily slow your et's and would be a little easier on the drivetrain.
 
moparwedden said:
OK I'm finally going racing, need to know what I should be shifting at. 72 Duster with full uniform, 4 speed, Center force dual friction clutch, 8 3/4 rear end with 410, large u-joint. 440 around 525HP. 255/60/15 drag radials. I was told too leave at 2500 but where should I be shifting after that, Crane fire ball with built in limiters, where should these be set at, do not want to break it right off the bat. this is just for fun.

Thanks.
Click to expand...

There are two ways to do this, dyno the car or pick a shift RPM (say 5000) and increase is 250rpms per pass and see what the timeslip says.

You launch RPM is solely dependant on 2 things. Traction and RPM limit of what the engine can take. I like to launch stick cars on a limiter so i'd highly recomend getting a 2 step for your launches. There are about 8 million things all happeneing at once when you approach the line combined with about 8 grams of adrenaline. The less you have to think about as the light start dropping the better....
 
Just a hint, before you go to the track do you know how to speed shift,(throttle to the floor and not lifting) you might want to practice alot at lower rpm's so when you get to the track YOU CAN BEAT THE HELL OUT OF IT and hope nothing comes apart. Have fun.
 
I wanted to maximize my et's
I went ahead and put the car on a chassis dyno and did a all gear dyno pull.
This gave me the dyno numbers for each gear.
I also learned that this is very hard on your car.
By doing this I gained et and learned where my peak tq numbers are for each gear.
 
moparlvr166 said:
Just a hint, before you go to the track do you know how to speed shift,(throttle to the floor and not lifting) you might want to practice alot at lower rpm's so when you get to the track YOU CAN BEAT THE HELL OUT OF IT and hope nothing comes apart. Have fun.
Click to expand...

IF you are going to power shift it make sure you have a rev limiter. (i'd have one no matter what unless you truly don't care about blowing your engine) YOu don't need to powershift to run fast at the track though. It will help you pick up some time if you can do it.

womanator said:
I wanted to maximize my et's
I went ahead and put the car on a chassis dyno and did a all gear dyno pull.
I also learned that this is very hard on your car.
.
Click to expand...

how is this any harder than running your car in each gear on the street? I've never understood this thought process?
 
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