Speedo and MPG check - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**Fbks_Cruiser** · 05-30-2018, 05:20 PM

It seemed like my speedometer was off a bit. I decided to check it and the odometer as well as true MPG by running a GPS for a tank of gas.

Turns out the speedometer/odometer is off by about 10% (indicates faster than true speed). When GPS speed was showing 55 mph, speedometer was at about 60-61 mph. Odometer also registered about 10% too many miles.

MPG check with true GPS miles was 11 mpg in mixed town and highway driving.

Here is my setup:

1972 GMC K2500
350/350TH/NP205
4:10 gears (per previous owner, I haven't checked but seems reasonable)
235/85R16 tires
HEI distributor set to 8* base
"RV" cam (per previous owner, I don't know the specs but seems fairly mild)
Weiand 8004 intake
Edelbrock 1406 carb with one step richer than stock metering rods

05-30-2018, 05:20 PM	#1
Fbks_Cruiser Senior Member Join Date: Apr 2016 Location: Fairbanks, AK Posts: 334	K2500 Speedo and MPG check with GPS It seemed like my speedometer was off a bit. I decided to check it and the odometer as well as true MPG by running a GPS for a tank of gas. Turns out the speedometer/odometer is off by about 10% (indicates faster than true speed). When GPS speed was showing 55 mph, speedometer was at about 60-61 mph. Odometer also registered about 10% too many miles. MPG check with true GPS miles was 11 mpg in mixed town and highway driving. Here is my setup: 1972 GMC K2500 350/350TH/NP205 4:10 gears (per previous owner, I haven't checked but seems reasonable) 235/85R16 tires HEI distributor set to 8* base "RV" cam (per previous owner, I don't know the specs but seems fairly mild) Weiand 8004 intake Edelbrock 1406 carb with one step richer than stock metering rods __________________ 1972 GMC K2500 Super Custom Matt Last edited by Fbks_Cruiser; 05-30-2018 at 08:34 PM.



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