How to scan speeds faster than 158 mi/h (255km/h)?

Hi,

if I use the SAE VSS pid it works fine until the limites are reached.
If I try to rescale it in EFIlive it has the new max level but still stops at the limit, What causes this? Is it an SAE hardware limit? Can it be changed?
I can calculate the "real Speed" by using a correction factor to the RPM pid in last gear but this should be only a band aid.
At the Autobahn here in Germany I tried to do a topspeed run with our supercharged Corvette C5 and was hoping to see 200+ mi/h (320+ km/h) and so it would be really useful :notacrook: !
Anyone else already noticed this problem?

many thanks & best regards from Germany

Marco

Right click on SAE.VSS and go More Info...

Quote:

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Originally Posted by ScanTool->PIDs->SAE.VSS->More Info

Vehicle Speed Sensor {SAE.VSS}

Units: kmh
Range: 0..255 kmh

Units: mph
Range: 0..160 mph

VSS displays the vehicle's road speed if utilized by the control module strategy. Vehicle speed may be derived from a vehicle speed sensor, calculated by the PCM using other speed sensors, or obtained from the vehicle's serial data communications bus.

Reprinted with permission from SAE HS 3000/2003 © 2003 SAE International.

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This pid is 1 byte in length, so it appears that 255 (all 8 bits of the unsigned byte are 1) is the maximum value in km/h (and this converts to 160 MPH).

Quote:

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Originally Posted by Treurentner

Hi,

if I use the SAE VSS pid it works fine until the limites are reached.
If I try to rescale it in EFIlive it has the new max level but still stops at the limit, What causes this? Is it an SAE hardware limit? Can it be changed?
I can calculate the "real Speed" by using a correction factor to the RPM pid in last gear but this should be only a band aid.
At the Autobahn here in Germany I tried to do a topspeed run with our supercharged Corvette C5 and was hoping to see 200+ mi/h (320+ km/h) and so it would be really useful :notacrook: !
Anyone else already noticed this problem?

many thanks & best regards from Germany

Marco

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Yep got the same thing here, Marco.

Joecar , Thanks for the heads up .

Can you get by the max limit by creating a calculated PID using the transmission output shaft speed. I have done this to verify the speedometer accuracy and improve speed resolution.

Quote:

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Originally Posted by blandmiller

Can you get by the max limit by creating a calculated PID using the transmission output shaft speed. I have done this to verify the speedometer accuracy and improve speed resolution.

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Yes, that should work, create a calculate pid to give you road speed from TOS, which you already did.


The calc pid would calculate this:

road_speed[mph] = (tos[rpm] * tire_diameter[inch]) / (gear_ratio * 336)

.

Sorry to pull back old thread
Joe What tos speed stands for ?
for the gear ratio do you mean the rear end ratio or the selected gear ratio ?

Thanks

Trans output shaft.

TOS = trans output speed

gear ratio = trans current gear ratio x rear axle ratio

edit: correction: if you're using TOS then gear_ratio is simply just the rear axle ratio.

i wonder how op is doing driving a c5 at theese speed? just curious because i might attempt to do the same.

Quote:

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Originally Posted by joecar

Yes, that should work, create a calculate pid to give you road speed from TOS, which you already did.


The calc pid would calculate this:

road_speed[mph] = (tos[rpm] * tire_diameter[inch]) / (gear_ratio * 336)

.

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What is the "336"? Is this the gear ratio or a multiplier used on the "gear_ratio"? (so if my rear end gear ratio is 3.25, would I use 325?)
Or, if I'm interpreting correctly from previous posts, the "gear_ratio" is the currently selected gear's ratio, and the 336 is the differential gear ratio. Does a separate PID need to be created for "gear_ratio"?

Thanks