Why doesn't anyone ever run a dyno at half throttle?
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From: Southeast
Why doesn't anyone ever run a dyno at half throttle?
Okay, I may not be the sharpest tool in the shed, but I've been thinking about something.
We read about how we should pick a cam and other components as a unit designed to work with our style of riding. THEN, we use graphs of engines at WOT to make our determination. Why not watch the throttle and use the dyno to measure hp & torque at 50-70%? I know some dynos factor in how quickly the drum accelerates, but aren't there also dynos out there that can measure how much hp or torque an engine is making on a constant pull? They measure how much force is needed to prevent any acceleration and can figure out how much power is being made by how much force is necessary. I watched a video where a guy was adjusting timing and A/F and you could watch the engine's power increase or decrease, depending on what it wanted. Thinking about it, he set the RPM and let the dyno keep the engine wherever he set it.
So, if we're shopping for a nice touring cam, wouldn't it be better to know how that cam would act at an RPM range where it'll be operating at? Take for instance, the Andrews 21 or SE 203 cams. They pull right off idle, but you typically don't see dyno charts starting below 2,000-3,000 RPM. You're already heading out of the cam's happy zone by then, aren't you?
OKay, maybe you can chalk this one up to a winter topic. Maybe I know enough to be dangerous. But, it's something I had thought about and figured I'd toss it out here for the local brain trust. Thoughts?
We read about how we should pick a cam and other components as a unit designed to work with our style of riding. THEN, we use graphs of engines at WOT to make our determination. Why not watch the throttle and use the dyno to measure hp & torque at 50-70%? I know some dynos factor in how quickly the drum accelerates, but aren't there also dynos out there that can measure how much hp or torque an engine is making on a constant pull? They measure how much force is needed to prevent any acceleration and can figure out how much power is being made by how much force is necessary. I watched a video where a guy was adjusting timing and A/F and you could watch the engine's power increase or decrease, depending on what it wanted. Thinking about it, he set the RPM and let the dyno keep the engine wherever he set it.
So, if we're shopping for a nice touring cam, wouldn't it be better to know how that cam would act at an RPM range where it'll be operating at? Take for instance, the Andrews 21 or SE 203 cams. They pull right off idle, but you typically don't see dyno charts starting below 2,000-3,000 RPM. You're already heading out of the cam's happy zone by then, aren't you?
OKay, maybe you can chalk this one up to a winter topic. Maybe I know enough to be dangerous. But, it's something I had thought about and figured I'd toss it out here for the local brain trust. Thoughts?
Great question.
We do runs on dynos all the time at partial throttle. You can see one of those charts at this LINK, along with an explanation of why we do them, and what we were looking for.
To be fair, a good dyno tuner will run the throttle at all partial throttle locations to get a good tune.
I think the charts that are generally published/given to folks are more a bragging rights piece of paper than any representation of what they are going to experience in their everyday riding.
We do runs on dynos all the time at partial throttle. You can see one of those charts at this LINK, along with an explanation of why we do them, and what we were looking for.
To be fair, a good dyno tuner will run the throttle at all partial throttle locations to get a good tune.
I think the charts that are generally published/given to folks are more a bragging rights piece of paper than any representation of what they are going to experience in their everyday riding.
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From: poway
Great question.
We do runs on dynos all the time at partial throttle. You can see one of those charts at this LINK, along with an explanation of why we do them, and what we were looking for.
To be fair, a good dyno tuner will run the throttle at all partial throttle locations to get a good tune.
I think the charts that are generally published/given to folks are more a bragging rights piece of paper than any representation of what they are going to experience in their everyday riding.
We do runs on dynos all the time at partial throttle. You can see one of those charts at this LINK, along with an explanation of why we do them, and what we were looking for.
To be fair, a good dyno tuner will run the throttle at all partial throttle locations to get a good tune.
I think the charts that are generally published/given to folks are more a bragging rights piece of paper than any representation of what they are going to experience in their everyday riding.
So where is in in the link? I searched for partial and throttle and found nothing. Do you have a key word or location?
It is the 2nd chart in the link. I have posted the image below, with the accompanying explanation to the chart.
This next chart shows the improvement in the stock AFR on the M8's. You can see, except for the shift points (which are the peaks) that the blue line is staying between 14.5:1 and 15:1 AFR while cruising thru the gears.
On stock Twin Cams it was normal to see it up in the 16.5:1 to 17:1 range.
The red line in the chart is showing a base "Stock Improved" tune from the Power Vision. It is a tad richer, but not much, since it was already pretty good from the factory as far as AFR.
This pull was done at cruising (partial) throttle, Not WOT, keeping it in closed loop to see the AFR while cruising, vs WOT.
Last edited by DK Custom; Nov 25, 2022 at 05:56 PM.
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From: poway
It is the 2nd chart in the link. I have posted the image below, with the accompanying explanation to the chart.
This next chart shows the improvement in the stock AFR on the M8's. You can see, except for the shift points (which are the peaks) that the blue line is staying between 14.5:1 and 15:1 AFR while cruising thru the gears.
On stock Twin Cams it was normal to see it up in the 16.5:1 to 17:1 range.
The red line in the chart is showing a base "Stock Improved" tune from the Power Vision. It is a tad richer, but not much, since it was already pretty good from the factory as far as AFR.
This pull was done at cruising (partial) throttle, Not WOT, keeping it in closed loop to see the AFR while cruising, vs WOT.
This next chart shows the improvement in the stock AFR on the M8's. You can see, except for the shift points (which are the peaks) that the blue line is staying between 14.5:1 and 15:1 AFR while cruising thru the gears.
On stock Twin Cams it was normal to see it up in the 16.5:1 to 17:1 range.
The red line in the chart is showing a base "Stock Improved" tune from the Power Vision. It is a tad richer, but not much, since it was already pretty good from the factory as far as AFR.
This pull was done at cruising (partial) throttle, Not WOT, keeping it in closed loop to see the AFR while cruising, vs WOT.
I suspect what he wants is a partial throttle load response. I read is as comparable TQ curves at a lower throttle setting.
I could be wrong..
What I would like to see is TPS versus tq at specific RPMs. Say at 2000 to 3500. It would take a brake dyno to do that.. IIRC 250s have a load sel that can fix RPM but not produce a torque number. They have an output but not calibrated.
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From: Southeast
My original post was basically stating that I had never seen any documentation along these lines. I had wondered why. It's good to see there are those who do focus on all throttle settings, not just WOT. I checked the history on my ECU (ThunderMax) and I've never even hit that since installing the unit and rarely get over 4,500 RPM! I just don't ride like that. But I DO like the way those SE 203 cams feel at part throttle!
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Joe Kucinski
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Half throttle does not make for good bragging rights.
Even with the sidecar. 22x cam and good tune on an average day just riding around the bike seldom if any sees more that 25% to 30% throttle. And i could still get a ticket most any where.
Even with the sidecar. 22x cam and good tune on an average day just riding around the bike seldom if any sees more that 25% to 30% throttle. And i could still get a ticket most any where.
I got that one.. I thought the guy was looking more for a dyno type run comparison and not an AFR sample. It's cool that check your feuling response in what I think are close to driving conditions. I would hope that all dyno operators/tuners perform some sort of validation test.
I suspect what he wants is a partial throttle load response. I read is as comparable TQ curves at a lower throttle setting.
I could be wrong..
What I would like to see is TPS versus tq at specific RPMs. Say at 2000 to 3500. It would take a brake dyno to do that.. IIRC 250s have a load sel that can fix RPM but not produce a torque number. They have an output but not calibrated.
I suspect what he wants is a partial throttle load response. I read is as comparable TQ curves at a lower throttle setting.
I could be wrong..
What I would like to see is TPS versus tq at specific RPMs. Say at 2000 to 3500. It would take a brake dyno to do that.. IIRC 250s have a load sel that can fix RPM but not produce a torque number. They have an output but not calibrated.
Generally when we are doing partial throttle runs it is to analyze what is going on with a tune from exhaust, intake, or other mods. I don't know that we have ever saved the torque and hp info on partial throttle runs. I will look.
Next time we spend some time on the dyno we will absolutely run comparisons at a fixed partial throttle position with a fixed load on the brake. That would make for some interesting comparisons.
Seems elementary now that I'm thinking about it, but had never thought of it before.
Thanks for the idea!
