Hey Mike!
First, my choices for your situation if it were me, ranked in my order of preference (which you didn't ask for so just ignore)
1) Keep your U-Haul truck!!!
2) If you definitely want the Chevy, keep the existing 454 that's in it
3) Rebuild the existing 454 in the Chevy if it needs it.
With that said, I love 12V Cummins engines for the simplicity (no electronics), good power, and good reliability.
But a 454 is also good. The one in my rollback has been great. Only complaint is the fuel mileage (of course). For comparison, the 6bt (lightly modified) in my 79 K30 has as much power as my 454, but gets better mileage, and cruises steadily at a lower RPM (yes, quieter than *my* 454).
If you are thinking the 4bt will have 150hp/300tq, I would compare it to the 6.2L in my 1990 Burb. The stock C-code 6.2L (has EGR, less power than J-code) has 145hp/250tq. Here are my experiences:
weight of Burb: 6000 lbs (scaled)
4WD 1/2-ton
3.42 gears
TH700R4
235/75/15 (28.8-inch) street tires
redline (governed) 3600 rpm
The Burb does fine daily driving, but would ideally have 3.73 gears instead of 3.42. It is BY NO MEANS fast at all. But I think I'm a slow driver. I run 10mph over the speed limit, but I don't accelerate fast.
I have towed some with the Burb. A stock 350 would out-pull it easily (I am comparing to my stock 1990 K5 with TBI 350 - 200hp/300tq). But it does get the job done around here. I would never plan to tow thru western NC in my Burb in current form - it would SUCK on the big hills.
The most I ever pulled with the Burb was 6500lbs (my TJ on my trailer) to Uwharrie. The steep (but not too long) hills near Uwharrie had it dropping to 45mph, but was I having cooling issues (clutch fan was bad) so I couldn't keep the pedal down. Towing on I-40 it never dropped below 55mph on any hill, and could hold 65 on most. As a comparison, with my TBI 350, I could leave it in drive and maintain 65 on the hills.
When towing, I just leave the Burb in Drive and don't use OD at all. I run about 65mph but have the RPM to do more. That's one issue I'm glad you're looking at with the 4bt - usable (and reliable/sustainable) RPM range.
I think *most* people would NOT be happy towing with my 6.2 Burb. I was OK with it, but was planning to get a little more power (intake and exhaust) and adding a little more gear to make it work. But now I have my K30 with 6bt, so the Burb never tows over 3k.
From the 6.2L I get an avg 18.5mpg empty and a low of 12mpg pure towing when I towed the TJ to Uwharrie (other towing has been 14-16mpg). I have heard on coloradok5.com of someone with a 4bt in a Blazer getting over 25mpg empty.
So your 4bt may have 50 more lb-ft of torque than my 6.2L, and you can install a spring in the inj pump to give you 3000 or 3200 rpm. I think it would work, and if you are like me, you might be happy with it. Compare it to my experience above - hopefully with the extra torque and a little more gear the 4bt would work for you. But remember that a stock 350 TBI will be equal or better in power and have a greater RPM range.
Would I put a 4bt in my rollback or K30? No, it would not pull the kind of weight I put on them (sometimes 20k GCVW). But what would I put in my Burb if the 6.2L ever died? 4bt all the way. More power than the 6.2L and better mpg.
Keep us updated on what you decide!!!
