Looking for your opinions on what modifications I can do to add hp and torque while maintaining fuel efficiency.

I'm just getting into the 12 valve Cummins world with 1991.5 d350.

Thanks in advance for your help.

 

Get the air flowing in and exhaust flowing out like 4 inch exhaust n air filter upgrades.

 

I was really impressed when i installed the denny t fuel pin and the 366 gov. spring. it really bought the beast out in my truck

 

Every power mod I ever did to my truck also brought better economy - 16cm^2 housing, afc and starwheel, full load screw 2 turns past the collar. I gained 1-2mpg and tons of power vs. stock.

 

Until you get into really big injectors efficiency will be mostly related to your right foot. There are several mods which really help drivability (exhaust housing, 3600 rpm gov. spring, 4" exhaust and BHAF) and tuning (see the sticky at the top of the thread page) which give a mild HP increase with out hurting economy and as furios70 said might even help. Automatic trucks benefit from a torque converter change as well.

It will help if we know what transmission you have and what gears.

 

Thanks everyone for the help. I look forward tO modding.

It's an automatic. I will get details on the rear end ratio.