Lazy weekend afternoon..... MPG build thread #2

[FordGuy100]

Reason I was thinking 2.73 was that it was optioned in Ford trucks. My owners manual shows the towing #'s of trucks, and lists some with 2.73 rear ends.

 

[david85]

Well ideally I would get as much used parts as possible. With any luck those could be had used. As it is I know my F250 was quite drivable with 3.08s and no turbo since I had it that way for a while. Not sure how well it would do in overdrive without the turbo but generally I rarely see the boost needle move when I am in the 20+ MPG zone.

 

[Brianedwardss]

Hmm, this ought'a be an interesting build. I'm probably one of the few folks that MPG is what I'm most after. A 30 mpg diesel truck sounds like a pretty sweet deal.

I'm assuming Your '86 with 3.08's AND overdrive was mainly for MPG reasons. Between you and Gary's double overdrive setup, you guys have pushed the generally accepted limit on how high of a final gear ratio is driveable/economical. I'll be keeping a close eye on this thread, it's been awhile since I've seen a good idi mpg thread. (The psd guys have a bunch).

Also, I once drove a 2wd f150 that reportedly had 2.73 gears, and it drove fine with the tiny stock tires on it. I've always wondered what a diesel engine in that truck would've drove like.

 

[david85]

Well like I said in the OP, this is just a day dream and its unlikely that I can do much about the idea anytime soon. This is my way of having some R&R.

I think 30 MPG is possible. There was a time when I would have never believed that even 20 MPG was possible let alone 25 for that matter. And all that with 20 year old technology.....

Something's wrong with this picture, but I digress......

 

[rjjp]

Just so you know, since I've calmed down my right foot (I only see 10 lbs and black smoke half the time now, others it's 5lbs and clear) I've noticed about 2.5 mpg gain from the turbo vs non turbo around town. But I also have 4.10's so I have about 1lb going 35 and 3lbs going 60, may be different for you.

 

[david85]

Relatively speaking a turbocharger isn't all that hard to add on later. If nothing else it would be an excellent way to test what sort of difference there is - if at all. I know I never came close to 24 MPG non turbo with my F250, but I also didn't have overdrive and a locking torque converter either so my example is invalid.

I do know with more certainty that for higher engine loading, there are gains to be found but where that thresh hold is crossed is hard to say.

 

[Diesel JD]

Great minds think alike David. I've been mulling over in my head the possibility of swapping a diesel into something smaller and saving he F250 for bigger jobs and hauling stuff around. I have thought about a full sized bronco, an 80-86 or 87-91 F100 or F150, and the craziest one was a 6.9 into my brother's old Isuzu Trooper, which I am sure has never been done here. For me, it's got to be a manual transmission or nothing, but that's personal preference. I will say that after having driven DeepRoots and gonecrayzi's diesels with the ZF5, if you found it to be any effort to shift it or use the clutch, something was wrong with the setup, probably a bad TOB. I also think a turbo might not help the fuel economy too much but it probably would just be a lower emissions, higher power engine without having to do anything to the engine internally. A truck designed for in town chores and lighter work would probably be a great place to use a wastegated turbo since higher EGTs won't be an issue and you probably will find the higher boost off the line desirable. It's probably a daydream for me to, but I know I could get that Trooper really cheap, and it is a cool truck which is just begging for a diesel powerplant. As a gasser it typically gets <12 mpg, but it has been abused and neglected and has an auto and 4X4. Anyone think that kind of SUV could handle a 6.9 or does it all come down to if it physically fits or not?

 

[GOOSE]

Well like I said in the OP, this is just a day dream and its unlikely that I can do much about the idea anytime soon. This is my way of having some R&R.

I think 30 MPG is possible. There was a time when I would have never believed that even 20 MPG was possible let alone 25 for that matter. And all that with 20 year old technology.....

Something's wrong with this picture, but I digress......

Don't forget, the 6.9 was designed, prototyped and tested in the late 70's. Some of the technology is older than we think. The overdrives and locking torque converters are really the only thing that links our rigs to the 20 some year old bracket. The engine is into 30+ year old technology.

The more I work on this truck, the more it reminds me of the 390 fe motor that was in my '74 F100, simple, powerful and little to no emissions crap. Oh and for digressing, My 390 passed 1996 emissions standards with nothing more than a PCV valve, points and a 2 barrel carb, and got 15mpg's. Boy haven't the gassers come a long way,,,,,,NOT!!!!

Getting back onto the subject, did anyone see the orange rig in this months Diesel Power? 30 mpg right there. He did it with an 80-86 pickup. Why only a picture of the truck and no details? I know were headed in the right direction fuel economy wise.

 

[12clip]

That's a nice old F150. I have an '85 that's almost the same but is 4wd and still has the fuel injected 302. I know this doesn't help your cause but my F150 gets anywhere between 15-20mpg (imperial). I don't drive it enough to do much accurate calculations, but it is very respectable. It is also the old mechanic lock-up AOD, 3.55 gears, stock fuel injection, with an O2 sensor that I haven't even got around to hooking up as these old ones with the one wire O2's didn't seem to do much. It does have shorty headers and dual exhaust. The timing has been bumped up to 14 degrees and doesn't ping.

I have 31x10.50/15's right now and will be putting 33x12.50/15's right away and hope the mileage doesn't take too much of a hit. Anyway enough about that as this is not what you are after.

I think 2.73's in the 8.8 is the simplest/cheapset setup. Many Mustang 5.0L came with 2.73's in the late 80's early 90's and were swapped out for something like a 3.55. If you know anyone with such a car they may have 2.73's lying around. I may still have my set from my Mustang, but I'm not sure if they would be rusted a bit by now.

These gears with a ZF5 or E4OD would give a good setup for cruising in OD and towing in direct.

I don't think you will have much luck getting a load range E 15" tire, so I would probably look into a set of 16" wheels. You could then easily get a taller tire if you want a little higher gear ratio than what the 2.73's give.

 

[david85]

The idea was to keep the tires fairly small. What size is normally used on the dually trucks? Was it something like 225/75/16? That could do the trick maybe.

In fairness, I never cruised this F150 at 55 MPH. Always at, or above 70 or as fast as that poor 302 could manage. Going from my diesel to that F150 is a night and day difference. The F150 does ok of you pin the throttle and wind it out but its still pretty slow with almost no bottom end. Thought about putting headers in it but never bothered.

Hey Goose, do you have a link to that article?

 

[GOOSE]

http://www.forgottendiesels.com/6.9_ford.html

There is a bit of the history segment, is that what you are looking for?

 

[GOOSE]

The truck is an orange 2wd said to be owned by Jason Aziza. He is running with no ac, manual steering and has most of the grille blocked off. There also looks to be plexiglass smoothing the headlights/ turn signals and the pic shows his mirrors folded in.

Its on page 164 of Novembers Diesel power.

 

[12clip]

245/75r16 came on 7700 F-150's and would work well. 225/75r16 are also easy to get a load range E tire as well.

Not to go on and on about the 302 but I could never understand why people would put the carb setup on. It had no where near the low end torque that the long runner EFI manifold gave.

 

[david85]

245/75r16 came on 7700 F-150's and would work well. 225/75r16 are also easy to get a load range E tire as well.

Not to go on and on about the 302 but I could never understand why people would put the carb setup on. It had no where near the low end torque that the long runner EFI manifold gave.

The propane setup uses an impco 425 mixer carb so the EFI lower and upper manifold has to be replaced with an older style carb manifold. Mine uses a 4 barrel spread bore which seems to help a little at higher RPMs. The engine was also converted to the older duraspark 2 ignition system. It runs well for what it is but the price of propane has been tracking in areas that its just not worth burning it anymore. Cost per mile is now the same as gasoline but the range is lower and fuel harder to find. I absolutely hate having to rely on full service stations to fill up. As it is, the truck only has about a 200-250 mile range for average driving.

Never driven a comparable stock EFI 5.0 of the same era so I can't really compare.

For a time I even thought about putting a 390 in the truck or maybe a 351 rollercam. But deep down I know neither will give me the over all performance of a diesel.

 

[icanfixall]

All precups now are the same item. They are marked too so if your changing them don't worry about getting something differant. Some wil probably tell you they are selling you "something special" when they really aren't....