390? engine for ...........

[rickpilgrim]

I have a 1991 Isuzu NPR that has no engine or trans. While I was at the boneyard I picked up a rebuildable 390 w/aftermarket 4bbl intake. Now the Isuzu has 4.88 gears and 31" tall tires, no other gears are available.
I'm thinking of putting the 390 in there with a C-6 but I don't know if it will take the rpm level on a day to day running, or should I look for something else engine wise? Also the stock Isuzu diesel has 368 ft/lb of torque and I'd like more than that.

 

[1985 Ford F-150]

If itll fit in there itll be turnin 3k plus on the highway.

 

[Mil1ion]

What RPM level ate you thinking ?

That engine is more efficient at lower rpm's

 

[polarbear]

It should work- there's a gas version of the NPR that runs a Chebbie 350 with an Automatic. It'll suck gas like hell won't have it though.

 

[rickpilgrim]

We are trying to make a low buck 1 ton dump truck for around town use, only need to go a few miles out for dirt, mulch etc. The F-super Duty with 7.3 we had got 11-12 doing this, 8 mpg would be good. A GM gas would be easy, but I have driven that and it's slower than the diesel one that has to be floored anytime it's loaded
But how long does the 390 last turning 34-3500 rpm? Or should I be looking for an add on OD unit?

 

[LEB Ben]

Before you thought about buying an OD unit ($2k easy), it would be cheaper to buy new axles and re-gear to get the engine operating in the sub-2500rpm range. In all honesty, I'd throw the 390 in there and run it...you may encounter some cooling problems and I'd think you'd be in the 5-6 mpg range. If you rebuild the 390 and make it fresh, I wouldn't see why it wouldn't last you an easy 150k.

 

[mtflat]

I'd try to couple it with an OD if you have to go any distances. If you use it on a limited basis, it should be ok.

 

[DNFXDLI]

Not that I really like Wiki....but regarding engine efficiency:
http://en.wikipedia.org/wiki/Engine_efficiency

 

[john112deere]

I think Tony (surewhynot) stuck a 400/C-6 combo in an NPR a few years back...

 

[SuperCab]

I think your right IIRC.

The 390 is, as ben said, gonna get oh, prolly 5mpg at that rpm under load, but it'll last as well as the chebby gasser NPRs...

 

[rickpilgrim]

I thought about changing the rear axle rather than OD. By doing that I would loose 12" rear disc brakes, 10 bolt HD rear wheels, rear abs and possibly anti sway bar. Not to mention major brake changes......
I'll try and find a add on OD unit first, or maybe find a HD manual trans to "reverse" and use in that way, or electric shifted, who knows......

 

[TexasNomad]

4.88s wow thats high dude.. Throw some 2.70 in it and she'll grow legs and run like a Watusi being cased by a lion on the high way

 

[LEB Ben]

4.88s wow thats high dude.. Throw some 2.70 in it and she'll grow legs and run like a Watusi being cased by a lion on the high way

I think he said 4.88's were the only ratio for that axle.


Had thought (which is dangerous)...why not throw some bigger tires on there to drop your rpm? Given you won't be driving on the highway, but going from a 31" tire to a 35" tire at 60mph would probably drop your 4.88's to around a 4.10 effective ratio and probably 4-600 rpm.

 

[TexasNomad]

Low gears WTF even got mad reps for that

 

[rickpilgrim]

I think he said 4.88's were the only ratio for that axle.


Had thought (which is dangerous)...why not throw some bigger tires on there to drop your rpm? Given you won't be driving on the highway, but going from a 31" tire to a 35" tire at 60mph would probably drop your 4.88's to around a 4.10 effective ratio and probably 4-600 rpm.

The problem is Isuzu used 215/80/16R tires, and the biggest that can be fit without rubbing the duals in the middle is 225/75/16 E and they are less than 1/2" apart when loaded.
So does anyone have an add on OD unit they would sell?

 

[rickpilgrim]

Got real lucky this Saturday! My sprinkler(lawn irrigation) guy who I got the NPR from called and let me know he has the "spare" rear axle for his 93 NPR with manual trans for $50 and it has 4.30 gear ratio! Seems 93 and up manual trans NPR's have 4.30 gears when equipped with the 4BT2 TI engine and I can keep everything but the ABS.
That solves half of my headache, Now are there any OD automatics that bolt to a 390 or can be adapted that are good for this?