I have a 1991.5 cummins with the massive 21mm housing. It is an automatic truck and takes forever to spool. Most of my driving is on the highway and I usually have a total weight of 15k lbs or so. My main goal is to get better cruising fuel economy and to get it to spool better. I have a HX35 sitting here on a shelf, but it seems that the 12mm housing can choke the engine some with loads at speed.

 

Just separate the 12cm from the HX and get out your die grinder and start grinding away. You can probably get that 12cm pretty close to a 14cm or you can just try to find a 18cm that someone is getting rid of cheap.

 

Is the HX35 waste gated? If it is, don't worry, be happy. If it isn't, even a 14 can be small for towing.

 

Yes, it has a wastegate on it. Will the small 12mm housing hurt my fuel economy at all on the highway?

 

Only if you routinely run over 75 mph or so.

 

This is what I have on mine...there is a world of difference in the 12, and the 21. Look at the truck in my sig. The mileage shown is with a 12 housing.

Tony

 

Put the 12cm on it, You'll love it

It'll feel like another truck

 

Tony - how did your mileage change from before with the 21mm to after with the HX35? Do you have a stock converter in your transmission?

 

Its CM by the way

MM is the measurement of the compressor/turbine wheels

 

Yeah, I have no idea why I keep putting mm. Maybe I am trying to have full boost at idle...

 

My mileage has never changed. It has always been in the 20's on the hwy. The mileage in my signature is also with a flatbed on the truck. One thing I will say is going from Tucson, AZ to Mesa, AZ is going down hill. As far as I know the torque converter is stock, with 231,??? on it at this time.

Tony

 

cm 2 <-----little baby 2 raised up