First thread post here, new member.  A research question here....

I just recently picked up a 1990 E350 Club Wagon diesel April.  Was a former govt rig and was advertised with 252K miles but I think it is off, much lower.    Rear axle ratio is a 3.54.  The agency I got it from was the 2nd govt owner.  Found a sticker stating that the original govt owner (transit system van pool) schedualed the next oil change on 8/01 or at 155K.  Paper work stated that 2nd owner got the rig in 2002.  They stated that the first owner put the majority of the miles on it.  It would be strange if the 2nd owner only put 5-7,000 miles on it.  Then again, could someone 100K in 5 years or less?  But from what I can gather, it might be true (van was assigned to the police dept for group trips for the officers), so it wouldn't be used that much.  So, I'm guessing it has 152K miles, not the 252K.  If it is 252K, it sounds damned good.

This motor is quiet, at least compared to other IDI's I've heard (6.9's and 7.3's)  I've heard louder 7.3 IDIs, one of them is in a buddies '93 F250 4x4 E4OD 3.73.  His is loud when it first starts, then quiets down after a while and he has 130K on it (with the ATS turbo).  Another was 1 to pickup and it was loud no matter what- clatter, clatter, clatter.  This engine sounds the same when it first starts to when it's completely warmed up.

Any how, the power this thing on flat road driving is fine. (It's an IDI diesel and a 1 ton van- so I'm not expecting THAT much of performance). I'm seldom going to use it fully loaded with people and or stuff.  I'd like to put a hitch and brake controler to tow a trailer for the 'once in a blue moon' thing for local haul, less then 50 miles (better then using my F150 4.9L).  But on a recent trip, I noticed it would down shift out of OD on some hills and once out of OD, it would be fine, actually accelerate back to 70-75mph.  There wasn't enough power for the hills in OD but my buddies truck w/ the ATS never even downshifts from OD.  Granted, he has a turbo and a slighly lower (higher number wise) axle ratio- plus he's lighter by a few thousand pounds.

I'm kind of at a fork in the road so to speak.  Engine is in great shape in the van. I'm kind of thinking of installing a Hypermax turbo OR maybe a GearVendors overdrive (not sure if the version that I want is available- I heard of a OD electronics kit that actually split shifts for you- computer controlled, but I don't know if it will work on a '90 tranny).  Looking at the prices, the Hypermax turbo kit would actually be cheaper then the GV OD.  (I've been told that I should check the compression and that I shouldn't put a turbo on an engine w/ possibly 252K miles.  I don't foresee ever getting rid of this thing though.)  

I have a GV in my F150 mounted on the C6, so I am familiar with what it can do.  Install on that cost me about $600 (including drive line mod) and the GV cost me about $500-600 less then retail (at the time I looked it up last year).  Part of me eventually wants a GV OD, but no way I'm going to pay retail.

Like I said, I'd ability to climb hills w/out having to go out of OD.  I'm kind of thinking that if it had a 3.73 (but wasn't an option for that year), it would be fine in OD, maybe.  This van kind of borders a 'toy' and travel vehicle.  Oh, for those interested, it gets an avg of 14.7mpg.  On that freeway trip, flat and hills (mountain pass), I got 13.8mpg heading over and 14.7mpg heading back (was a bit softer on the throttle).

I'm leaning toward a Hypermax turbo.... opinions, comments, etc, etc.  Thanks.  

Go with the turbo AND the C-6 & GV. I have a 6.9 with that setup, we're talkin' nite & day....

Your truck downshifts because of your rear end ratio, it's a road gear, (high), as well as the heavier weight and the diesel works best in certain RPM and torque range. Your transmission has been configured to "know" what conditions require a downshift, it's performing perfectly normally.

Now, everything will get about 100% better with a turbo and a C-6 with a GV, trust me, I've had a few...