Tuning a 89 for mileage and power
 

I have a 89 D350 that I have put an intake on and straitpiped. I now average 21-23 mpg most of the time and 25-27 going 60 on the highway. I have the 5 speed getrag. I have adjusted the fuel screw for less fuel. I was wanting to boost power and maybe mileage a little. I was wondering if puting a hx35 on would hurt my mileage if I drove it the same. I am assuming I would have to readjust my fuel screw if I put a hx35 on. I was also wondering how much work it is other than putting on an intercooler. I was also wondering if putting in a 4 inch downpipe and running the exhaust out right behind the cab might help. I have also seen injectors that claim to help fuel economy and want to know if anyone has any experience with these. Most of the time I drive it like an old gramma, but occasionaly I like to toast some japcrap at a stoplight

man 20-23 is absolutly fantastic. if you are getting 25-27 on the highway in a truck that weighs 7000lbs+ someone is looking out... :humm: i get 15 driving like a grandpa in my 95 a little better in the 90 with the 5spd. that is as good as my geo tracker!!!!

but a hx35 is a great upgrade over the H1C and you can rig them up where you can run intercoolerless.

That's some great mileage! You must drive slow :w2:
Turning up your fuel shouldn't have much of an effect on mileage as long as you keep your foot out of it still.