The 4BT Diesel Prius Project

The Prius isn’t short-listed on diesel enthusiasts’ most favored vehicles. Just mentioning the name “Prius” in a diesel crowd could get you in some trouble. Some say they aren’t as environmentally friendly as everyone thinks they are: The electricity (in the Americas) is mainly sourced from coal; the batteries could end up in a land fill where they’d then leach lead acid into the ground water. One could also argue that the long 1,000,000-mile life of a diesel beats the average battery life of only 150,000 miles (Yes, I know Toyota says they’ll last a life time, but good luck finding one with good batteries with much more than 150K miles). They also say diesel pollutes less in the manufacturing process, where six sets of batteries are used to create one Prius, not to mention that the gas engine in the Prius will probably have to be replaced three times before the vehicle ever sees 1,000,000 miles. Lastly, do they really get all that great mileage Toyota touts about? We recently put a VW TDI (NOT a hybrid) through a real world mileage test and came back with a 64-mpg highway average. Ok fine—VW cheated the EPA (see more on VW’s recent debacles on pg. 150) but the fact is the TDI got much better mileage than the Prius’ claimed 48 mpg.

As much as I may enjoy a good Prius-bashing session, that was not my intention for this article. Earlier this year, I decided to start a new project, and while it’s presented more problems than successes, it will get finished. I’m going to build a 4BT-powered Prius.

The idea for this project really did start as a joke conjured at an NHRDA event. A Prius pulled into the track (presumably on its way to a racers camp) and we all thought how funny it was to see it there surrounded by a bunch of big diesel sled pullers and purpose-built drag trucks. Sort of like a Chihuahua in a field of Pit Bulls. Someone remarked, “He should enter it in the drags!”, and the bench racing began. Ripping the engine and motor out of a Prius would offer a decent amount of room to fit a smaller diesel. But the diesel would have to be an iconic early era-esque engine though, no TDIs or Kubotas here. Nothing but the 4BT came to mind. The iconic sound, as well as the healthy aftermarket backing that would make it easy to get 500 hp out of it, helped convince me that it was a project that should be done.

Fitting the 4BT wouldn’t be the main problem, though. The real work would be in fitting a rear axle and transmission in the originally front wheel drive car. A whole transmission tunnel would have to be made (not that big of a deal) as well as fabricating and installing a 4-link rear suspension (a big deal). Also, doing all this work would then remove a large part of the Prius’ structural support, so we’d have to build some sort of frame to stop it from taco-ing at the track. Cost wouldn’t be too great since the batteries fail regularly, making it cheap and easy to get a hold of an older one in need of drivetrain work. The brainstorming quickly changed to other subjects, but I couldn’t get the image of an over-fueled, back-halved and tubbed turbo diesel Prius running 7-second passes down the track out of my head.

So six months after we came up with the idea, I’m now actively on the hunt for a cheap, non-running Prius and a 4BT out of an old bread truck. It’ll make for the perfect winter project, and I can’t wait to take it down the quarter mile, laughing all the way! DW