Posted by Charlie on Sunday, August 05, 2001 at 3:31PM :
In Reply to: Re: 4BT not enough power posted by Dave on Saturday, August 04, 2001 at 12:38PM :
For what you intend to use the truck, you will want a 4BTA with a 6 spd, not a 5 spd, and careful attention to gearing/tire size so that rpms at 60 mph are 2000-2100 and 70 mph 2300-2450 in 6th gear. Since the NV5600's 6th is 0.73, you'd want 4.88s with 9.00R16s or 4.27s if possible (about between 4.10 and 4.56) for 7.50-16s. 5.13s or even 5.38 with 11.00R16s.
The gear ratios on the 5600 are 5.63, 3.38, 2.04, 1.39, 1.00, 0.73. This will enable easy unloaded starts in 2nd and not a huge rpm drop in 4-5 and 5-6 upshifts. If the engine is wound up to 2600 rpm then shifting up to 5th will drop it down to 1870. and the 5-6 shift will only drop to 1900 rpm.
When a wide ratio gearbox causes a drop to 14-1500 the engine would tend to lug till it gets up to 17-1800. This mainly relates to turbocharger output.
With a 6spd, which is entirely feasible due to the fact that the 6B is bolted up to the 6spd currently, the truck will be quite enjoyable to drive.
An alternative is mating a Ranger overdrive (0.73:1 OD ratio plus direct of course) between the bellhousing and an odd 5 spd called the Clark CL557, I am kicking myself for not buying a new one on Ebay last month for ~$400. Its' ratios are 6.99, 3.78, 2.12, 1.17, 1.00. This is also currently produced as the Eaton FS4205C. Note that with the overdrive the ratios are:
6.99, 3.78, 2.12, 1.55, 1.17, 1.00, 0.85, 0.73.
Super close spaced gears from 3rd on up! And double overdrive, with 1.17 splits all the way from 1.17 to 0.73. RPMs would only drop to 2200 on upshifts when at road speed. It'd be a great setup for towing, even in mountainous terrain.
The divorced transfer case is so far back in some W300s that I think especially with the short 4 cyl motor a 7" Ranger plus a 15" Eaton 5spd would fit OK. The kicker is that you'd want a GM bellhousing and a GM bolt pattern on the Eaton.
Charlie
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