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Discussion Starter · #1 ·
I have a 89 7.3 IDI I use this truck for freeway driving over mountainous terrain. What is a safe RPM range to opperate at? I need to acheve freeway speeds of 75 to 80 MPH. Is this possible with this old truck? Can I acheve higher speeds with out rapping out the RPM's by installing an aftermarket turbo? If so what turbo do you recommend? If not a turbo what mods can I do to increase speed with out running the RPM's to high?

Thanks
Stonewaters

P.S. this truck runs great its just not very efficient on the freeway....
 

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Gearing

A turbo will only get you up to speed quicker. Your engine rpm range it still limited by the motor. What you need is more highway friendly gears like in the 2.50 to 3.50 range, and overdrive or an overdrive plus a secondary overdrive like a "gear venders" or similar product. A turbo will help you pull a grade with out dropping as much speed and having to downshift. But you will have to install and monitor an EGT gauge, or risk buring up your motor!!!

For efficency slow down to 55-60 and hangout in the right lane. Been there done that!


YMMV Sean
 

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taller tires will help drop RPM's an a gear venders overdrive unit will too from all i have found out so far the idi doesnt like more than about 10 to 15lbs of boost and hypermax max a great bolt on kit for 1900bucs without doing some work like head bolts an a few other things i did see a post somewhere that had tire size an gear ratio for maximum mpg but i cant find right now ..i got an 88 CC dually 7.3 idi an im looking to get my hwy mpg up right now im running 2250rpm at 65mph with a 5speed an a 410 rearend ....everyone has told me the sweet spot for rpms on the idi is around 1600 to 1800rpm ..... im thinking about running a 19.5" wheel or maybe even a 22 or 22.5 .....i was also told the best i could possibly hope for was 20mpg an i got that driving my truck home ....so im with you if i can get 20 or better at hwy speeds it would be awsome
 
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