Cummins 4B-T aka..”The Paint Shaker”

We regularly get emails from customers wanting more information about the 4B-T cummins (B3.9) engines. Unfortunately, we dont really have any place to send them for comprehensive, real-world factual data. Most of the information online is from companies “selling” 4B-T conversions so what is available is highly biased and factually inaccurate. So, we put together a little fact-checker list.

Top 10 Dumbest Engine Swaps

A few years back, JP Magazine did an article entitled ” Top 10 Dumbest Engine Swaps” and the little “pain shaker” 4B-T made the list. (FYI we did NOT write this)

Taken from JP Magazine article…

“But again, the noise, vibration, and fumes from one of these little paint shakers will be enough to push most Jeep owners over the edge of the nearest cliff. Plus, they weigh a little more than an all-iron big-block. They sound good on paper, but when you’ve lived with one of these conversions for a little while the buzzing and belching can really test the temperament of some drivers.”

Source: http://www.jpmagazine.com/techarticles/engine/154_1006_top_10_dumbest_jeep_engine_swaps_ever/viewall.html#ixzz2Inm6gkue

Why is it called “the Paint Shaker”?

The 4B-T engine was developed by Cummins for use in off-highway stationary generator sets and large heavy-duty delivery vans. They were considered large displacement 4 cylinders touting “1 liter per cylinder” displacement. This was a big deal back in the 1980′s when they were designed. Most passenger vehicle diesel engines are internally balanced which minimizes vibration and internal engine wear.  The B3.9 4B-T Cummins engines are not internally balanced. Due to the large displacement and long stroke, and not having an internal balancing mechanism, the 4B-T shakes far more than your average engine. To combat this issue, the aftermarket tried to develop a liquid-filled engine mount to absorb some of the extreme vibration. Again, the issue is that the engines were not internally balanced.  Cummins did sell an add-on balance shaft module for the 4B-T cummins engines. These add-on modules have several technical drawbacks when using in a passenger vehicle application. First, they were designed to be operated at a constant RPM and are limited to 1,900 RPM’s. They were also expensive at +$2,000, and extremely bulky (requiring the use of a huge oil pan assembly) which makes fitment in a passenger vehicle engine compartment literally impossible.

30 mpg?

This is probably the most disingenuous  aspect of the 4B-T engine swap. We see 4B-T swap companies touting all sorts of astronomical fuel economy numbers online. However, with fuel consumption data from Cummins’ own website and a calculator, one can easily see that these mpg numbers are wildly inflated and completely impractical when combined with reality-based calculations.

Here we see a data sheet from Cummins:

4BTA3.9G4

We’ll be as generous as physically possible and assume you’re only using the engine at 25% load. Creating only 30 hp in the process, we use approximately 1.8 gallons of fuel. A simple equation can be formulated here. Let’s assume a vehicle was traveling at a speed of 60 miles per hour at 25% load spinning 1,500 rpm, you would  travel 60 miles and consume 1.8 gallons of fuel or  30 miles per gallon right? Amazing!  Now, when this figure is applied to a passenger vehicle, the math goes all fuzzy.  At 1500 rpms, your transmission’s final drive ratio physically cannot spin the tires at 60 miles per hour! So, you have to speed up the engine to achieve that speed. Once you do that, look what happens to your fuel consumption.

 

So, these figures that you see companies touting online are based on a VERY generous use of a calculator  and not taking into account real world application data in order to make their engines look as efficient as possible. Aerodynamics, larger tires, parasitic loads like alternators, a/c compressors etc, and power steering were not included in the original Cummins consumption tests as the application was different. These engine swap companies do this to sell conversions…plain and simple.

Our approach?

We get emails from some “interesting” folks wanting to argue about “our approach” to diesel converions and how much they love the 4B-T Cummins engines in their mom’s station wagon, Bronco, etc. Well, the fact is that “our approach” is not really “our” approach at all; it’s Jeep’s or Toyotas. We ONLY install factory powertrains found in the OEM vehicles in other countries. So, whether you like or dislike our product really boils down to if you want a fully integrated, no compromises, daily driver that is designed and built by the same company that built your vehicle. Shoe-horning a bread truck engine into your vehicle (while technically possible) rarely translates into the type of product a professional company wants to stand behind.