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Dyno Testing & Downshift

2000StreetRod

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I recently talked with a local dyno tester about future testing. He told me that normally testing is done with the transmission in direct drive. I'm concerned that I will have problems with my 5 speed automatic downshifting at full throttle unless the engine speed is above 4,000 or more rpm. I would like to know the horsepower and especially the torque at engine speeds as low as 2,500 rpm.

Has anyone had any success in obtaining reliable performance data at the low end of the torque curve?

What about the possibility of performing testing with the transmission gear selector in 2? The transmission will not upshift or downshift when 2 is selected.
 
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Spdrcer34

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But it ALSO won't be in 3rd gear when the selector is set at '2'. 3rd gear in an automatic is GENERALLY a 1:1 ratio.

If you are in 2nd gear, the numbers will be slightly skewed, as you are slightly multiplying the engine's output through the transmission.

A proper dyno operator wouldn't even do a dyno run in 2nd gear.

Dyno readings are done adding 100 to 200 RPM's per second. They do that to prevent the transmission from downshifting.

Believe me, the dyno operators have done this before, and know how to properly rev the motor to prevent the transmission from shifting.....

Ryan
 
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2000StreetRod

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But it ALSO won't be in 3rd gear when the selector is set at '2'. 3rd gear in an automatic is GENERALLY a 1:1 ratio.

If you are in 2nd gear, the numbers will be slightly skewed, as you are slightly multiplying the engine's output through the transmission.
Ryan

Thanks for the feedback Ryan.

I have the 5R55E that in the "2" selection engages 1st gear (2.47:1) and overdrive (.75:1) at the same time for a resultant 1.86:1 ratio. With my differential ratio of 3.73:1 I can start out in second with the gas pedal floored and speed up to redline (6250 rpm or 77 mph) without ever shifting. I assume that the dyno operator inputs my differential ratio and my tire diameter (28.86 inches) to compute my torque and horsepower. Why can't he just input a differential ratio of 6.94:1 (1.86 * 3.73) and pretend I was in 4th gear (1:1)?

I'm not really that interested in accurately determining my maximum horsepower. I'm more interested in making changes (air filter, throttle body, synthetic oils, etc.) and measuring the relative difference in low end torque for potential gas mileage improvements.
 
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mrboyle

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It typically depends on the dyno and knowledge of the opperator, but if they have the right equiptment it can be done. Most dyno shops only test for max torque and hp #'s and therefore don't invest in the proper software to control the dyno for "tuneing". If they have the proper software they can simulate any type of driving condition you want them to (providing they know how). Talk to the owner of the shop and explain to him exactly what you want to do. Let him know that you are trying to evaluate performance gains or loss and exactly where in the powerband you want to see the test results. If they still claim they can't do it, try to find another shop and run it past them. I know it can be done, its just going to be a matter of finding a shop that is willing to put in the extra effort to work with you.
 
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gijoecam

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Thanks for the feedback Ryan.

I have the 5R55E that in the "2" selection engages 1st gear (2.47:1) and overdrive (.75:1) at the same time for a resultant 1.86:1 ratio. With my differential ratio of 3.73:1 I can start out in second with the gas pedal floored and speed up to redline (6250 rpm or 77 mph) without ever shifting. I assume that the dyno operator inputs my differential ratio and my tire diameter (28.86 inches) to compute my torque and horsepower. Why can't he just input a differential ratio of 6.94:1 (1.86 * 3.73) and pretend I was in 4th gear (1:1)?

I'm not really that interested in accurately determining my maximum horsepower. I'm more interested in making changes (air filter, throttle body, synthetic oils, etc.) and measuring the relative difference in low end torque for potential gas mileage improvements.

What gear ratio is the torque converter, and how much does it slip at any given RPM and load?

That's why a 2nd-gear pull won't work well. Some of that power may simply be going up in heat through the trans fluid.
 
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2000StreetRod

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What gear ratio is the torque converter, and how much does it slip at any given RPM and load?

That's why a 2nd-gear pull won't work well. Some of that power may simply be going up in heat through the trans fluid.

Mark at Stable Performance easily worked around the downshift problem in 4th gear (1:1) but encountered another problem I didn't anticipate. Apparently my Sport PCM has a speed limiter at 105 mph. The engine was still accelerating well until around 5200 rpm (as I recall) but would not exceed it. The engine pulled strong to 6000 rpm in the lower gears. So I'll have to scale my 2nd gear pulls to the 4th gear limited range horespower/torque data we obtained.

I don't know what my torque converter ratio is. Mark could tell from the second gear pulls that I have a locking torque converter and where (at what rpm) it locked up during the runs.

Have any of you encountered a speed limiter on your vehicle? If so, do you know how to defeat it?
 
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hunterdan

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The way to get around the speed limiter is through a custom tune. Also, there is no actual ratio in the torque converter.

Dan
 
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2000StreetRod

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The way to get around the speed limiter is through a custom tune.
Dan

Thanks Dan,

I heard some chuckles from the drag strip guys who came by Mark's shop while my Sport was on the dyno. Seeing an Explorer on the dyno was a first for them. Below are photos of my Sport strapped down after several pulls.
dynofrt.JPG

The fans are to prevent overheating. You may notice the ATF leak on the floor from the radiator cooler.
dynorear.JPG

I assume that a "custom tune" entails pulling the PCM, removing a nonvolatile memory chip from the PCM, reprogramming the chip and then reinstalling everything. It's too bad there's no way to reprogram via the diagnostic port. Is there a single data entry for max speed or is it derived by the PCM based on a combination of several parameters? As I recall, 105 mph in 4th occurs after max horsepower. I wonder if the same limit occurs in 5th gear. That's something to try the next time on the dyno.
 
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gijoecam

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The 105 limit is due to the max safe driveline and tire speeds. That's as fast as Ford ever figured the Explorer should go, so that's where they set the limiter. The tires are the biggest issue... there aren't too many SUV tires rated for the weight that'll also be rated for speeds in excess of 100mph. Not a whole lotta need there either. I personally wouldn't recommend exceeding the tire or the truck's max speed limits. That's just asking for trouble.

And yes, the limiter applies in 5th as well.
 
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Turdle

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Thanks Dan,

I heard some chuckles from the drag strip guys who came by Mark's shop while my Sport was on the dyno. Seeing an Explorer on the dyno was a first for them.

I assume that a "custom tune" entails pulling the PCM, removing a nonvolatile memory chip from the PCM, reprogramming the chip and then reinstalling everything. It's too bad there's no way to reprogram via the diagnostic port. Is there a single data entry for max speed or is it derived by the PCM based on a combination of several parameters? As I recall, 105 mph in 4th occurs after max horsepower. I wonder if the same limit occurs in 5th gear. That's something to try the next time on the dyno.

Tuning is done through the diagnostic port.

Get ahold of James, ( jah81592) our resident tuner.

www.hensonperformance.com
 
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hunterdan

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Almost all tuners now flash the computers via the OBDII port. Just check out superchips and see what they have to offer, especially from James at henson performance.
 
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2000StreetRod

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The 105 limit is due to the max safe driveline and tire speeds. That's as fast as Ford ever figured the Explorer should go, so that's where they set the limiter. The tires are the biggest issue... there aren't too many SUV tires rated for the weight that'll also be rated for speeds in excess of 100mph. Not a whole lotta need there either. I personally wouldn't recommend exceeding the tire or the truck's max speed limits. That's just asking for trouble.

And yes, the limiter applies in 5th as well.

One reason I bought the BF Goodrich Long Trail T/A Tour tires is they are T rated (good for sustained speeds up to 118 mph dependent on tire pressure). The dyno runs are less than 10 seconds above 100 mph.

Thanks for the info on speed limit in 5th.
 
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dennit469

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One reason I bought the BF Goodrich Long Trail T/A Tour tires is they are T rated (good for sustained speeds up to 118 mph dependent on tire pressure). The dyno runs are less than 10 seconds above 100 mph.

Thanks for the info on speed limit in 5th.

mine is governed at 110? we have the same exact same car but different colors haha
 
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jah81592

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If you are going to dyno a stock vehicle I would pull the vehicle in 3rd gear (not a 1:1) but still you can get your #'s. If the vehicle is being tuned you (the tuner) can go into the shift schedules to prevent downshifts. I do this all the time on my dyno. I always (if possible) start my pulls at 2000-2500 rpm. This gives me a better average power increase, rather than starting at 3500-4000. You will find your SOHC will be done anywhere around 5500-5800 rpm. Where are you located at? If you are near Alabama I would be happy to tune and pull the truck on my dyno.-j
 
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gijoecam

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One reason I bought the BF Goodrich Long Trail T/A Tour tires is they are T rated (good for sustained speeds up to 118 mph dependent on tire pressure). The dyno runs are less than 10 seconds above 100 mph.

Thanks for the info on speed limit in 5th.

Since it got bumped....

So did you also check that the wheels, driveshaft, (and front halfshafts if applicable) are also rated for the higher speeds? What about the chassis dynamics at those speeds?

Tires alone do not limit the safe speed of the vehicle.
 
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2000StreetRod

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....

So did you also check that the wheels, driveshaft, (and front halfshafts if applicable) are also rated for the higher speeds? What about the chassis dynamics at those speeds?

Tires alone do not limit the safe speed of the vehicle.

You're right that there is a lot more than tire ratings involved when going fast. That is why the only time my Sport goes fast is when it's strapped down on the dyno.
 
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2000StreetRod

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If you are going to dyno a stock vehicle I would pull the vehicle in 3rd gear (not a 1:1) but still you can get your #'s. If the vehicle is being tuned you (the tuner) can go into the shift schedules to prevent downshifts. I do this all the time on my dyno. I always (if possible) start my pulls at 2000-2500 rpm. This gives me a better average power increase, rather than starting at 3500-4000. You will find your SOHC will be done anywhere around 5500-5800 rpm. Where are you located at? If you are near Alabama I would be happy to tune and pull the truck on my dyno.-j

I established my baseline using two different pulls. The first one is a time to speed in "D" from wheels stopped. It measures shift performance as well as engine performance.

The second pull is in "2" for maximum power. I realize the number may differ from a standard pull in direct drive but it is quick and repeatable. I'm mainly interested in performance differences due to mods instead of absolute numbers.

I live in Greenville, SC and there is a dyno about 5 miles from my house but thanks for the offer. By the way, I'm the one who e-mailed you about custom tunes for my mods and buying an SCT SF3. You can read about my 75mm throttle body http://http://www.explorerforum.com/forums/showthread.php?t=249607

and my MAFSAmp http://http://www.explorerforum.com/forums/showthread.php?t=249266
on this forum. Currently I'm involved with adding engine and transmission oil filters and coolers http://http://www.explorerforum.com/forums/showthread.php?t=247990. My purchase of an SF3 is on hold until after I purchase an Accusump.
 
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2000StreetRod

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Dynojet vs Dyno-Scan

Tomorrow I'm scheduled to receive my Dyno-Scan software and hardware for Windows. I've been reading the user's manual I downloaded and learned it supports acceleration testing similar to performing pulls on a dynamometer. The setup parameters include frontal area and coefficient of drag. I'm looking forward to my first Dyno-Scan test and to comparing the results to my past Dynojet results. The test will be in "2" to avoid speed limit violations.
 
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SB98UKexplorer

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this is a great thread, im also on similier line of tuning mine up, would you happen to have the dyno print outs so i could compare with mine? ill post them up here when i get the photo copier working.
 
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wpurple

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When I had my Mountaineer dyno'd, the dyno tech kept it in 3rd...he was able to get it to a speed and rpm where it would not downshift at WOT, plus my tune removed the speed limiter.

I would agree with the above that a good dyno tech knows how to work the vehicles that are automatics.
 
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