TPI Gas Mileage (longhorn man & any others)

[cableguy0]

you have 20 inch wheels? if so more than likely those are eating more mileage than anything else. they are generally incredibly heavy compared to other wheels which means more rotating mass and unsprung weight which will kill mileage in a hurry

[Andy4639]

I did some speed and rpm checking today, here is some numbers for you. Locked in over drive.

55 mph 1500rpm's
60 mph 2000rpms
65 mph 2200rpms
Just for kicks 85mph 3000rpms

[CochinoFilipino]

Originally Posted by Andy4639

I did some speed and rpm checking today, here is some numbers for you. Locked in over drive.

55 mph 2000rpm's
60 mph 2200rpms
65 mph 2500rpms
Just for kicks 80mph 3000rpms

What numbers are you using? The online calculators are not matching those numbers?

http://www.f-body.org/gears/
http://www.700r4.com/speedoCalc/rpmcalc.shtml

OD is 0.70 ratio
http://www.700r4.com/faq/gearrat.shtml

[Andy4639]

I got a better reading this morning out on the interstate. Sorry about the other numbers. I edited the first ones.
According to this calutation I'm running over 4 grand at 70MPH, I don't think so. I don't think the thing works to good.

MPH 1:1 High Gear Trans. 4L80E Trans 700R4 Trans 2004R Trans
45 mph 3,657 2,743 2,560 2,450
50 mph 4,063 3,047 2,844 2,722
55 mph 4,470 3,352 3,129 2,995
60 mph 4,876 3,657 3,413 3,267
65 mph 5,282 3,962 3,698 3,539
70 mph 5,689 4,266 3,982 3,811
75 mph 6,095 4,571 4,266 4,084
80 mph 6,501 4,876 4,551 4,356
85 mph 6,908 5,181 4,835 4,628
90 mph 7,314 5,485 5,120 4,900
95 mph 7,720 5,790 5,404 5,173
100 mph 8,127 6,095 5,689 5,445

[CochinoFilipino]

Was wondering if Mocwon had changed out the gears and what the results were. I think my truck's guzzling gas too, and I'm only on 28"s.

[Skruffy]

Well, I don't know what the heck is wrong with my daily driver. I have a 97 C1500 with a 5.0 liter and when I'm on the highway 75-80, I only get a little over 14. Now, before I bought new tires I was getting a little over 15, but still, I don't see how my mileage could be so much less.

[68C15]

Originally Posted by Skruffy

Well, I don't know what the heck is wrong with my daily driver. I have a 97 C1500 with a 5.0 liter and when I'm on the highway 75-80, I only get a little over 14. Now, before I bought new tires I was getting a little over 15, but still, I don't see how my mileage could be so much less.

were these tests done "back to back"? a different fuel blend can make a difference. the fuel suppliers change the blend quite often. even going to a different station can make a difference.

for the record I used to have an '80 K20 with a 355, 0.120 domes, 74cc heads, Crower 00210 cam (I forget the specs), weiand stealth intake, stock HEI with Hypertech coil and both heavy springs and no vac adv., and a HIGHLY modified Holley 4776, 31-10.5-16.5 tires, 3.73 gears and a Muncie SM465 trans. I got between 17 and 18 MPG @ 75 MPH. oh, BTW, I was running 14* initial and 91 octane Amoco silver. it was a wonderful combination, at 60 I was at about 1/2" throttle and the engine just wanted to run away (if you know what I mean).

[mrein3]

I agree with everybody who thinks your speedo is off.

Without good data you can take your numbers and throw them away. They are useless.

A very simple test:
Take a hand-held GPS. If you don't own one borrow one from somebody. Turn it on and get speed over ground or what ever that particular unit calls its speed read out and get it displayed on the screen. Now go for a ride.

Here in MN most town roads are 30. Get on a town road, go until your GPS says 30 and look at your speedo. Write that down.

Here in MN most highways are 55. Get on a highway, go until your GPS says 55 and look at your speed. Write that down.

Here in MN the freeways out of the Cities are 70. Get on a freeway, go until your GPS says 70 and look at your speedo. Write that down.

Of course don't do this in rush hour traffic. It would be better to have a co-pilot to be holding and looking at the GPS and recording data.

I just did this with my daily drivers. A 1994 Ford Escort and a 2004 Ford Explorer. Both of them are 2mph slow on the speedo. My truck, th350 with speedo cable hooked up to the transfer case, 373 rear end gears, stock height tires is dead nuts on. I get 13 driving like a grandpa and not towing the boat. I get 8.5-9 pulling my boat around the state.

Every GPS made today is at least as accurate relatively speaking as the cop's radar gun. WAY more accurate than the cop's uncalibrated radar gun. You should know your speedo's characteristics whether you record your gas mileage or not.

If you are out there claiming 18+ mpg in one of these old trucks, and haven't compared your speedo to a GPS speed read out, I don't believe you. I'm not calling anybody a liar, I just don't believe data that hasn't been proved correct. 18-20 is a really tough number to reach with a vehicle like this. It isn't impossible. Just not probable.

Oh, and when you get this data, you may find out your mileage really isn't that bad. Your speedo (and odometer) may be off by 10 or 20 percent. If you are recording 12-14, and your speedo is off by 20 percent, you may be getting 14-17 which is about all I'd expect out of a pick-up. Of course it may be 20 percent high and you are getting 10-12 mpg.

Hooking up the lock-up clutch in the converter is a no-brainer. I won't even address that subject. Get that working.

[Skruffy]

Originally Posted by 68C15

were these tests done "back to back"? a different fuel blend can make a difference. the fuel suppliers change the blend quite often. even going to a different station can make a difference.

for the record I used to have an '80 K20 with a 355, 0.120 domes, 74cc heads, Crower 00210 cam (I forget the specs), weiand stealth intake, stock HEI with Hypertech coil and both heavy springs and no vac adv., and a HIGHLY modified Holley 4776, 31-10.5-16.5 tires, 3.73 gears and a Muncie SM465 trans. I got between 17 and 18 MPG @ 75 MPH. oh, BTW, I was running 14* initial and 91 octane Amoco silver. it was a wonderful combination, at 60 I was at about 1/2" throttle and the engine just wanted to run away (if you know what I mean).

Well, I don't know about back-to-back, but over the same trip over the last year it has been the same. The only time it changed was when I changed tires. When I'm on the interstate it seems to be turning about 2K RPMs.

[barraza]

A few comments about mileage

To be accurate, you must only pay attention to the odometer, because the speedo can be accurate and the odometer off. Check the odometer against the mile markers on the interstate over a good distance, and do it more than once in case some got moved. I found my trucks odometer to be less than 1% off over 100 miles while the speedometer was off about 8%.

Lockup is a must!! The engine is turning near the stall speed of the torque convertor for a lot of your driving and is very inefficient and creating a lot of heat. Very bad for mileage and the tranny will not live a long life in that configuration.

These trucks will never get good mileage at 70 plus mph. They are aerodynamic pigs.

As a reference point, I had a MarkVII lincoln that had a trip computer that gave instant and interval mileages and I had double checked its accuracy. A sick parent necessitated monthly 2400 mile trips and I got ample opportunity to stare at that screen and watch mileage. Even in a relatively aero car, the diference between 60 and 70 was a 10% decrease in mileage. That lincoln would get 32 mpg at 60 with a gutless 302. Headwinds, hills, and even getting off and on the interstate could be seen on that computer. It is hard to come to conclusions with out good data.

[grayw0lf]

& here I am with my sad 305 getting only 12mpg. Then again my '70 is pulling a boat at 65mph & turning 3900rpm.

[vtblazer]

Your running the same rpm @ 70 mph as my Duramx diesel, doesn't seem like it would work so good for best mpg with a gas motor.