What should my fuel economy be with my setup?

[dds92780]

Lets hear what kind of MPG you are all getting with your setup. List the rear end ratio and transmisson type and engine. Ill start.

I have a 95 RD688S used to have a twin stick 89 R with 300 for all you classic lovers. anyways,

E7 350 Mechanical

Fuller 9 spd

442 rears 65-67 mph is top speed at 1800 rpm

The best i have gotten is 5.5 mpg but the past few days i have gotten 5.15 averaging a speed of 60mph.

The Worst i have seen is 4.4mpg and that was being loaded almost all day and going up hills.

What is the sweet spot of this engine to get the best economy? Thanks

[dds92780]

anybody?

[Lmackattack]

Sounds about the same as I get with a 285 and 6 speed direct w/4.17 rears. My buddy had a 89 R model with a Mack 350 and a 9 speed Mack with rears that could get you to 85 mph in top gear...would cruise at 65 mph at 1500-1600 rpm and thats the speed we were most at. His truck was getting 6.3-6.5 on the hi way with a gross of about 65k and 5.75 with 75k.. This was a run we did from Chicago to L.I.N.Y and back...

[MHfred]

My performance chart for my 89 E6 300 (4 valve) shows maximum economy at between 1400 and 1500 RPM but I do not know how similar your engine performance might be.

[jzack]

94 CH600

E-7 350 V-mac I w/ Blixxton upgrade

Fuller 9-speed

3.86 Mack rears

67 mph@ 1,600rpm

6.0 - 6.5 mpg winter

6.5 - 7.0 mpg summer

[dds92780]

jzack i wonder why your mpg is so much better than mine. what kind of work do you do? i have alot of stop and go at traffic lights and hills for my job because i do gravel hauling. it could also be your computer setup. I have a book that shows all the engine makes for 95 and shows that the vmac makes more hp quicker and uses less fuel spray out of the injectors the entire range whereas my mechanical pump makes gradual 350 hp and uses fuel spray as the hp goes up. I wish i had the vmac because then i could also get a blixton upgrade. I am going to be getting a new injection pump soon and wanted them to tinker with it to make it a lil more responsive and also get the fuel maps closer to the vmac. What do you all think my options would be? you cant get a blixton upgrade with a mechanical bosch pump can you?

[jzack]

jzack i wonder why your mpg is so much better than mine. what kind of work do you do? i have alot of stop and go at traffic lights and hills for my job because i do gravel hauling. it could also be your computer setup. I have a book that shows all the engine makes for 95 and shows that the vmac makes more hp quicker and uses less fuel spray out of the injectors the entire range whereas my mechanical pump makes gradual 350 hp and uses fuel spray as the hp goes up. I wish i had the vmac because then i could also get a blixton upgrade. I am going to be getting a new injection pump soon and wanted them to tinker with it to make it a lil more responsive and also get the fuel maps closer to the vmac. What do you all think my options would be? you cant get a blixton upgrade with a mechanical bosch pump can you?

I also do mostly stop and go local work. I deliver steel with a flatbed or conestoga trailer loaded with up to 6 or 7 stops per run, so I'm not grossing 80k all the time. I do have some decent idle time though as I usally let the truck run during stops. We've had several E-7 350s with 9-speeds, both mechanical and electronic, and I don't recall any of them dipping below 6mpg all that often. If I had to guess, I'd say your 442 rears probably hurt your mileage more than anything, especially if you do alot of freeway running at 65mph.. Keeping the rpms down is the key, 1,500 - 1,600rpm seems to be the sweet spot for mpg for the E-7 in my experience.

I'm not so sure about the electronic E-7 making power quicker than the mechanical. In my experience the V-macs all had a bad dead spot from 1,200-1,400rpm, where as the mechanicals pulled hard right away. Probably something to do with the electronic puff limiter because adding the blixxton would make the dead spot go away.

[dds92780]

Thanks for the response and yeah i believe that the 442 rears do make the difference in poor mileage. It could also be that i have a bad injection pump that has a miss and i would say that i have only about 320 hp right now but i do keep up with other trucks. I want to take my truck to midwest fuel injection in illinois and have them do the new pump and dyno it and hopefully they can squeeze a little more out of it? I dont want to have to change the injectors or turbo though, just get a lil more out of it and still not get hardly any smoke at all. what are the advantages of having a mechanical pump vs electronic anyways??? I don't really see an advantage anymore at this point

I will say this though, there are sometimes where if i am loaded and i take off in first gear and just about kill it from being easy on it and then floor it, it gets almost instant boost, but it usually has a delay all the time. I had my adenoid for boost checked out and it was good so im not sure why it does that sometimes? could it be that when i get my new pump it will have that kind of instant power all the time? Sorry about the long post but i just got this truck and havent ridden in any other macks before. I used to have a 89 R with 300 and twin stick and it woudl blow smoke and had more instant power so im guessing its either the pump or just that the E7 is inferior to the E6?