Optimal RPM range for peak performance

3,500 to 5,500 rpm,s I forget what the dymo charts shows. With the Hahn intake it takes me to almost red line

Here is a dyno sheet of a bone stock Slingshot plotted out by RPM. You'll see power still climbing out to 6k but torque starts tapering off around 4400rpm and is on a steady decline by about 5k.

Hadden stock RPM.pdf

don't ya just mash it to the floor?

Quote from MACAWS

don't ya just mash it to the floor?

Mash it to the floor and let her spin to 9k. It's fine, it'll do it..........once or twice.

Quote from Edward Neal

I am curious to know if there is a way to determine the optimal RPM range for an NA motor by looking at the RPM at which peak torque and peak HP are produced?

Is there a formula or rule of thumb that I could use to find the optimal range to try to keep my RPM in as I go through the gears? and also to compare what that range would be if changes were made that changed things or also to compare with the new engine?

oh - and just to be clear, when I say "optimal" I am talking best performance, not best gas mileage

Thank you

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There is a simple way to do it using any spreadsheet if you have a dyno that shows the engine torque across the engine RPM range.

Basically you enter the torque value for different engine RPM's, the more data points the better. Then enter in the transmission geartins, final drive ratio and tire diameter, which all contribute to the ultimate gear ratio from engine to the rear wheel. Once all of that data is entered, a graph is generated for each gear, look for the spot where one gear crosses another gear and that is the shift point. If you go beyond that point, you are making less torque at the wheel then if you shift.

Here is what the spreadsheet looks like for a fictitious engine -

Here is the graph it creates showing the shift points. In this fictitious engine, you would run 1st and 2nd gear out to redline, then shift 3rd and 4th gear at the noted speed -

Here is what that curve looks like based on the dyno that Kyle D posted -

Quote from Edward Neal

Thanks Dave, that is very helpful in knowing when to shift to maximize performance, but i was thinking more about knowing the best rpm range for optimal performance if for some reason I suddenly needed all of the power I could get in the gear I am already in without having to down shift. Is this simply a matter of staying in the range with the best torque or is it some range between peak HP rpm and torque? Looking at the torque curve in the chart Kyle posted above it seems to fit with my feelings when driving my sling that I get the best response in the 3,500 to 4,500

For a given gear, the peak engine torque will be the best acceleration for that gear. On a naturally aspirated Ecotec that is pretty easy to see since the torque curve is pretty flat for the midrange area, 3600-5200RPM

Quote from Edward Neal

Thanks Dave, that is very helpful in knowing when to shift to maximize performance, but i was thinking more about knowing the best rpm range for optimal performance if for some reason I suddenly needed all of the power I could get in the gear I am already in without having to down shift. Is this simply a matter of staying in the range with the best torque or is it some range between peak HP rpm and torque? Looking at the torque curve in the chart Kyle posted above it seems to fit with my feelings when driving my sling that I get the best response in the 3,500 to 4,500

That is the way you do in the mountains, keep the rev's up

I am more surprised by the stock rear wheel dyno number being 163. Is this a common number for a stock slingshot? I thought GM only rated this motor at 173? Also love the fact that it hold the torque above 160 from 3600-5200. Would love to see how much improvement just getting rid of that cat would make.

Quote from Edward Neal

I agree that the drivetrain loses seem to be less than I would normally expect if it were a regular 4 wheel vehicle - perhaps the noisy angle drive that so many love to hate is actually more efficient than a regular differential - -

Also, different dyno's read differently. A dyno is strictly a measuring device that should be used to measure the power output before and after changes are made. All the ones I know of are calibrated, but in general some will read higher than others.

That being said, we do typically see higher power at the rear wheel on the Slingshot because of less drivetrain losses due to the single wheel in the back and the belt drive is pretty efficient at transferring power.

Quote from neverenoughtime

I am more surprised by the stock rear wheel dyno number being 163. Is this a common number for a stock slingshot? I thought GM only rated this motor at 173? Also love the fact that it hold the torque above 160 from 3600-5200. Would love to see how much improvement just getting rid of that cat would make.

The cat Polaris used isn't restrictive. I did testing on this and I think when I removed the cat we picked up something like .2whp. If you want to see the NA testing write up I did you can see it here The Truth About Natural Power - A Look At What Makes Power and How Much

Quote from Kyle D

The cat Polaris used isn't restrictive. I did testing on this and I think when I removed the cat we picked up something like .2whp. If you want to see the NA testing write up I did you can see it here The Truth About Natural Power - A Look At What Makes Power and How Much

It might not increase HP but the Cat Delete pipe and the Alpha CAI got me an extra 4 MPG on gas mileage. I do not know which one did it because both were done at the same time. 2,000 average on a Maggie Valley trip at the time 30 MPG and jumped to 34 MPG. I did Bob's tune and the Welter Dual's on the same day a year later and dropped back to 30 MPG. With Bob's tune the mileage should have at least stayed the same, we never did find out why unless it was the exhaust. With Sling II I will be going back to Bob's current tune from Sling I to the 1320 header with the cat delete pipe and also the cat bypass in the stock muffler. We will find out this coming summer what kind of mileage this will be. I will say this one more time all of my mileage post have been trip mileage of 1,500 to 2,000 mile average. This is on a NA build date Dec.2014 SL

I get 34-35 mpg since day one. Running 1320, header, cat delete and injen cai, no tune. It did drop to 26 mpg doing 1,100 miles back from Maggie valley in 2015. But that was all turnpike going 70-90 all the way. Normal driving is back roads 55mph or less.

I never look, I shift by the sound of the motor. EricRedSL 70-90 is normal driving

I never look at the tech either I shift like sound also. If your normal driving is 70 to 90, you must have a lot better roads that we have in Maine.

None of us here are race drivers that need perfect shifts, so shifting when the engine starts whining like a little b.... should be good enough .