What RPM should I shift at?

-
4spd340Swinger

4spd340Swinger

Well-Known Member
Joined
Mar 29, 2019
Messages
460
Reaction score
1,061
Location
Cincinnati, OH
I have a stock 1969 340/4sp Dart with the 3:91 sure grip. I am newer to racing on the track. I have been shifting around 6K but I wonder if I should be a shifting a little sooner? Looking for advice. Thanks!!!
 
Are you redlined when you pass the finish line?
 
I don't know with info offered. If stock 340 cam maybe 4,800-5,200 rpm, if bigger cam and springs, more. Peak shift points and trap rpm often different for best ET.
 
Easiest way for me is run the car up thru the rpm range under load - when it stops pulling you back in the seat - what’s the rpm? Remember that 5800 is for stock lifters and springs.

My 1972 Demon 340 4 speed 3.91 gear is shifted at 5800 even though It still pulls higher. 25.5” tall street tires.
 
Find the rpm that produces the least amount of rpm drop after the shift.
 
The correct answer is...........

IF you have or can get a dyno curve, either for the engine or chassis, OR if you can muster up some sort of performance instrument like the old G-tech, or "I'm sure" there are now smart phone aps for that........in other words something that gives you an acceleration curve.

So you can use a curve for HP, for G force, or for torque. If you cannot generate curves for all gears, then pick a gear that is convenient and endeavor to do an accurate curve in that gear, from below the peak by far, to about as high as it will rev, in other words PAST the peak.

Plot the peak, and then plot the other gears using math to multiply the gear ratio

YOU WANT TO SHIFT where the curves for each gear CROSS

Here see this old thread

www.forabodiesonly.com

maximize shift points

I am looking to maximize my shift points the next time I hit the track. I hit my best torque at 3900 to 4900 rpm. I had been winding to 6000 before shifting, but I wonder if I should shift sooner and use the torque to pull me faster. Being a novice, I am open to opinions. What do you all think...
www.forabodiesonly.com www.forabodiesonly.com

What you are gonna find is that for some gears you will be shifting at HIGHER RPM than the HP peak because even though you are past the peak, you will still accelerate faster in that gear at that RPM range than in the next higher gear with whatever the RPM drop is, because the engine will be off the curve so much. "It varies." "It depends"

This is overly complicated
www.evodynamics.com

Calculating Shift Points

A question we get asked nearly every time we dyno a car is "where should i be shifting at?" This question is actually quite easy to determine and i will use a couple of our good customers cars as reference points. Before we start going through the math of calculating the shift point, we will...
www.evodynamics.com www.evodynamics.com
 
Last edited:
I'm no expert but you got to experiment, try for eg.. moving 1st to 2nd shift point around like a 100 rpms at a time until you get best et then same with 2nd to 3rd etc..
 
Tell you what, make a bunch of passes on a dead night at the strip. Shift at a different and consistent rpm each pass. Find your best et and use that as a baseline for your competition passes on race night.

Remember the more racing you do, the more you learn about your car and you and your competition.
 
I would do three passes, shifting at 5200, 5600, and 6000, and compare MPH, not e.t. E.T. varies too much, especially with a four speed.
I'd be willing to bet, you'll be fastest shifting around 56-5700.
 
I just simply play the shifting games at the track and let the car decide. IF you are at 5800, then make the next pass trying to shift at 5500. IF the car goes faster or slower, adjust accordingly. I always try to shift at the least rpm that runs the best ET/MPH. Example: I shifted a car at 6k, but it ran the same at 5700, so I shifted at 5700 and it still was the best ET/MPH.
 
Agree with 318WR. My 440 pulls to 6500 easily, but shifting at 6200 was quicker. When I shifted a 5900, it ran the same as 6200.
So, shifting at 58-5900 it is. (Good camshaft, restrictive 906 heads. With better heads, results WILL be different)
 
The car will tell you where to shift it, you can easily feel where it goes numb at. Back up just a hair from that rpm and have fun.
With stock setup like you have, should be somewhere between 5500-6000 rpm.
 
Every engine is different.
Download a G-meter app, based on the accelerometer chip not GPS, (screen rotates), tape the phone beside your tach, when the g's drop, that's your shift point, you're slowing down when it drops.
Shift points can be different in every gear .
Good luck
 
It depends on what you are trying to accomplish.
1) lowest et?
2) consistency for bracket racing?

The answer is different for those 2 goals.
 
I had a really good running 1971 340 demon it was a bone stock engine with a 4 speed and 3.91 gears. It ran its best et's 5800 on the 1-2 shift 6000 on the 2-3 shift and 6200 on the 3-4 shift it would get into valve float at 6600.
 
I use the tach as a tool to set idle speed and get an AFR reading at xxxx RPM as things get dialed in. I shift when the engine noses over. Shifting as high as possible keeps engine in it's power band.

For example, if I shift over 6k with an 2.65 gearset a833 something isnt right if it falls back to 4000rpm, even with a loose clutch.

The Wallace Racing page has a handy calculator:



Here is the data for a 2.65 Hemi box shifted at 6500 with a 3.23 rear gear and 25" tire.


After 1st Shift: 4,734 RPM. 27.17 % RPM Drop
After 2nd Shift: 4,681 RPM. 27.98 % RPM Drop
After 3rd Shift: 4,676 RPM. 28.06 % RPM Drop
1st Gear is 56.50 MPH at 6500 RPM
2nd Gear is 77.58 MPH at 6500 RPM
3rd Gear is 107.72 MPH at 6500 RPM
4th Gear is 149.73 MPH at 6500 RPM
 
Did several runs at the Mopar Nats last weekend. Tried a little of what I read here and found the the best MPH was shifting around 5700 RPM. ET times were also a little better. Ran fairly consistent times of a 14.68. Guess it's ok for a 100% stock car. I am now on the fence about just dropping the coin and ordering an engine from Blueprint. Thanks for everyones input!!!
 
inertia said:
Every engine is different.
Download a G-meter app, based on the accelerometer chip not GPS, (screen rotates), tape the phone beside your tach, when the g's drop, that's your shift point, you're slowing down when it drops.
Shift points can be different in every gear .
Good luck
Click to expand...
I tried to tell him that many posts ago
 
4spd340Swinger said:
I am now on the fence about just dropping the coin and ordering an engine from Blueprint.
Click to expand...
Why not do some mods to the 340 1st, There's good power waiting to be unleashed with just Headers Carb Intake and Cam can really wake up a 340 do them all together or one at a time. and if you want even more down the road a set of aftermarket heads etc...
 
You must log in or register to reply here.
-

Back
Top