I have been reading the MPG threads this afternoon and I was curious with all the different mods that everybody has done or not done, various gear ratio's, standard or auto, ect. ect.
What are the Egts, and boost pressures and RPM's???
I'm thinking that these bits of info tell how the various engines out there are utilizing the fuel and converting it to energy to get the miles right?
With my project in progress i am looking for both power and the best fuel economy, and toying with axle gearing, tire size, and whatever i can cut off this tank to save some weight
Your input is greatly appriciated

 

If you were looking for economy, you should have left the VE pump on there. Beat the P7100 any time in MPGs. Power is another story.

My best guess would be to get the fuelling that you want from the pump, some Mahc1-1.5ish injectors, and play with timing specs. I'd say you'd do well to get 20mpg from that tank. More like 18hwy.

I'd look for some 3.54 or 3.42 gears.

I have gotten as high as 23mpg with a 91 dually, nonIC, EGT of around 700cruise, 3-5psi boost on the flat, with 4.10 gears and a Getrag.

Current rig runs 750deg at 75mph, 8psi boost, and 2100rpm. Curb weight of 7200#. 3.54 gears and Getrag.

Daniel

 

In a recent trip from Portland OR to Meridian ID for a dyno event - about 850 miles round trip I saw 22.45 MPG at a steady 70 MPH - this is typical for my truck. On the dyno I put down 394/865 on #2 and 441/889 with W/M. With my NV4500HD - running in 5th my tach shows about 1800 RPMs. Rear gears are 3.54s and cruise egts are 700 to 900 - with 950 running Cabage Hill at 70 mph.

I've always felt that your best mileage control factor is your right foot.

Bob

 

To shed some light on things I understand that with the VE pump would give me better fuel milage than the p-pump; However,,,, Like most I want to have my cake and eat it too yea i want high HP and great fuel milage and i think that with the proper gearing/tire size and pressure on the go-pedel I can attain the most out of my application!
being a aircraft turbine mechanic the temps,pressure's and torques will give good understanding of the Engines power and efficency...

 

What mileage do you get out of your 89 with G/V overdrive. If it is auto it probably has the 3.07 axle ratio. With overdrive i was wondering what kind of mileage you could get out of a 1st gen. My idea was a low gear manual tranny with a G/V to get the RPMs way down on the flat highway. I am between using 3.42 GM gears or going with my old 3.07. I got 23mpg on the highway in my 90 D250 auto without any overdrive and 3.07 gears. I know duals seems to really make the milage plummet.

 

Well my 89 w/ G/V is my wifes truck, I am building a 91.5 CTD engine to put in my 88GMC, and it has the a518 tranny, and I don't have a predetermined MPG that i want (well actually 20 would be great however i am a little smarter than that) cause i really am more into a good running truck with the power I need when i want it and if I get good fuel economy (16-18) while doing this i think it would be a great thing....

 

Just a side note I just didn't want to highjack other threads that were dealing with this issue, I was just curious what people were running on their cockpit instruments and see how that all relates to fuel economy, along with gearing and tire sizes..
And thanks for all the input

 

[QUOTE=chevummins;1701345]What mileage do you get out of your 89 with G/V overdrive. If it is auto it probably has the 3.07 axle ratio. With overdrive i was wondering what kind of mileage you could get out of a 1st gen.

Sorry about the last post I went back and reread your post and realized i didn't anwser your question so to reply about fuel milage on my 89 i don't know because the speedometer is broke and i do alot of around town driving so hard to keep track of milage... to add to the anwser my 91.5 I/C CTD when i brought it back from Kelso Wa. to roseburg or. I was at about 21 mpg with 33X12.5 rear tires and the 518A also has 3.56 gears..
hope this helps... I am looking for a speedo for the 89 so i can track fuel milage better, I do notice that when cruising about 2100 rpm and turn on the G/V OD the RPM's drop and speed increases' however my tach and speedo both are inop. so exact #'s right now are unkown..

 

I really wish there was something for giving a straight fuel mileage reading for these trucks. Really, it shouldn't be too complicated, you just have to measure the fuel going into the engine and the distance the vehicle's moving. I always heard that in-car MPG readouts were a joke, but the one in my '03 Ram was absolutely dead-on all the time. I could figure out my mileage in any condition, on the spot.

 

89 non ic
22 mpg @ 70 mph
2100 rpm
600* egt
4 lb boost
354 rear
getrag 5th=.75 to 1
32" tall tire

 

I still have to mess with the pump but I have been getting bad fuel economy that last couple tanks around 16mpg with a 5sp and 4:10's at 65 I cannot figure out what is wrong.

 

I used to think that I got poor economy till i tracked my speed with a gps, and found that my speedo was reading slow,,,,
I also ran 10 miles on the interstate and saw that i logged about 8 miles,,,,, Speedo fixed now. Before you start banging your head, Trust the mile markers on the interstate, check the odo compared to them.
Peter.

 

That's not very easy with a mechanical fuel system. Most of the fuel that goes into the injection pump goes back to the tank through the return line, either directly or via the injector drain.

 

Machinos- have you had your injecors checked? If they are popping low, it will affect dynamic timing and atomoization. It isnt too expensive to have done, and the truck will normally pay for itself in fuel savings if the sticks are too far out of spec.

Daniel

 

That is a good idea, I will do that tomorrow. You said speedo fixed how did you fix it? Is there an adjustment of some sort?