1988 r690 speed ?’s

[66rmack 81]

I’m looking at a 88 R-690 tri axle dump it has a em6-300L with a 2070 trans and 5:73 gears. Everything about the truck is perfect for wat I want except the top speed of 59mph. I have another 89 Mack that has 4:42 gears if I put those carriers in would it sacrifice too much power? I don’t mind being under powered but I don’t want it to struggle to go. Or is there another route I could go? I really need it to go 65mph. Could I get away with 24 talls and turning it up to 2400rpm? Thank you all for your help in advance! I know this ? Has been brought up mor than once in here.  Pick for reference. 

[tjc transport 1,278]

I would go with 24's and turn up the pump.

[66rmack 81]

So I did some figures and it looks like the 2070 has a final drive of .60 and 41'' tire with 2100rpms off the engine and 5:73 final drive ratio gives it a top speed of 74.53 mph so I guess I need to go drive it. The salesman told me it would go 58 on the flat according to his gps. I am going to go look at it friday afternoon I will report back, Anybody have a rough idea what its worth? Its very solid the bed is beat up no major oil leaks unknown mileage decent tires but getting ready for brakes. 

[JoeH 432]

The em6-300L is governed at like 1750 rpms. It won't do 2100 rpms unless you're going down hill. We bought an 88 2 years ago, still assembling a truck body for it so we haven't had it on the road yet to know how it drives.

[Lmackattack 1,073]

a 300L is a low RPM motor that has a max loaded rpm of 1750. you can pull the pump and have it re-calibrated to 2100 RPM. for a few $100 bills....it will then be a 70+mph truck. and it will drive better than that junk 1750 spec..   you will burn more fuel but it will drive like it should