TireSmoke.org

I know the optimum shift points would best be determined by trial runs but I'm not going to make a lot of runs. So, I'd like to have some idea of where the 1-2 upshift should be. (Won't need 3rd gear for 1/8 mile track.)

Results below are from an online program that calculates best shift points baed on HP curve and transmission gear ratios. Don't think I'll be spinning it to 6K RPM, so I'll probably make the shift at about 5K and get it done between 5 and 5.5K. (Rev limiter is set at 6K.) Any thoughts??

I think the errors they listed are because I don't have HP numbers for higher RPMs. (I had to extrapolate to guess the HP at 6K.)

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Bowling's Optimum Shift Calculator
Input Parameters Are the Following:
Transmission Ratio One = 2.46 to 1
Transmission Ratio Two = 1.46 to 1
Transmission Ratio Three = 1.00 to 1
Horsepower = 100 at 2000 RPM
Horsepower = 150 at 3000 RPM
Horsepower = 192 at 3500 RPM
Horsepower = 235 at 4000 RPM
Horsepower = 260 at 4500 RPM
Horsepower = 270 at 5000 RPM
Horsepower = 250 at 6000 RPM
Computation Results:
Using the Criterion for Maintaining the Same Horsepower Before and After Shift:
Finding Best Shift Placement Points For Ratio 2.46 to 1.46: Error: Search outside range - need more RPM range in HP table! Finding Best Shift Placement Points For Ratio 1.46 to 1.00: Error: Search outside range - need more RPM range in HP table!

Maximumizing the Area Under the Horsepower Curve:
Finding Best Shift Placement Points For Ratio 2.46 to 1.46:

Found optimum shift RPM at 5998, which achieves maximum area under horsepower curve, and lowers the RPM to 3560 after shift
Finding Best Shift Placement Points For Ratio 1.46 to 1.00:

Found optimum shift RPM at 5993, which achieves maximum area under horsepower curve, and lowers the RPM to 4105 after shift


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Bruce Bowling
bowling@cebaf.gov
Bowling Superior

I remember reading a few times that shift points tend to be somewhere 300-700 RPM past the horsepower peak.

Bruce Bowling is one of the MegaSquirt designers.

-Dave

TireSmoker wrote:I remember reading a few times that shift points tend to be somewhere 300-700 RPM past the horsepower peak.

Bruce Bowling is one of the MegaSquirt designers.

-Dave

Hi Dave,

That's a useful guideline. Makes the 5K-5.5K shift point seem about right.

Dropping the RPMs to 3500 on the shift to 2nd brings it 80 HP down from the peakHP. I see why the program wants the shift point so high. And why 4-speeds are a good idea.

Jim

Jim,
I finally got your email and responded. Looking at your graph, assuming your car is still pulling strong at 5 grand I'd do the 1-2 shift around 5500. If its still strong at 5500 try to push closer to 5800. You are right, its the rpm drop that kills you.

I always felt that it was best to shift before the motor blows up!

GM

GMJohnny wrote:I always felt that it was best to shift before the motor blows up!

GM

Yeah, that too...

Thanks for comments. Think I have a plan now for the 2-3 runs at the strip. I'll do the 1-2 up shift between 5000 and 5500 RPM and adjust down if there's too much wheel spin (street tires) and up if wheel spin isn't a problem.

Online calculators estimate 1/4 mile ET for the Maverick weight and HP in the 12s. I'd be thrilled if its in the 13s on street tires. We'll see. WXO and I have a tentative plan for an 1/8th mile run on 1/15.

I guess if you expect to hit the 13's, I will have to move up my timeline to get the cold air ductwork on Smoke before the 15th.

wxo wrote:I guess if you expect to hit the 13's, I will have to move up my timeline to get the cold air ductwork on Smoke before the 15th.

More hope than expectation. I'd be thrilled if it happened.

Jim, I'm sure your combo can run 12's. But probably not with the tires and converter. But 13's, definitely. So mid 8's in eighth should be do able. Can't wait! In January we only bench race up here in the Arctic

oldvettedad wrote:Jim, I'm sure your combo can run 12's. But probably not with the tires and converter. But 13's, definitely. So mid 8's in eighth should be do able. Can't wait! In January we only bench race up here in the Arctic

Maybe you should come down for a mid-winter fix. Must be at least one of your cars you haven't run on the strip. We'll see how well the weather cooperates on 1/15.