//// TDI Prius ////

You would have a better chance of building a rocket and starting a colony on Pluto. Now to the seriousness of it:

You would invest more money into this than it would take to buy a brand new delivery vehicle. Everything from a complete fuel system change out to all the sensor inputs for the hybrid control. It would take a mountain of cash, and even then probably wouldn't work. A Prius drivetrain is nowhere even related to a normal vehicle when it comes to transaxle/engine/HV system/Hybrid control/ sensor interaction, etc. It's an engineering marvel and is definitely not conducive to modifications. At all....

and just to put it out there, the electric motor is rated for 295 ft-lbs of torque from 0 to 1200 rpm.. If I remember correctly, isn't that more than most TDIs?

 

i think it's brilliant. will be following your retro mod, all the best!

 

If you're good at welding and skilled at eliminating error codes by fooling the computers it'd be fun to see you succeed. But you're literally going have to remove the entire wiring harness, fuel and exhaust system, almost all the dash electronics and not have a back seat because the battery pack would replace it.

 

Wow, that’s ambitious!

I’m a firm believer that you can do anything you like (in the automotive context) if you hose enough money, calendar squares and sweat into it.

A few observations:

• This will not save any money. This is the kind of thing an experienced mechanic does when he/she wants to show off. You could drive it 200k miles and never earn back what the fab work & ECU coding is going to cost.
• Getting measurements and diagrams from the internet will help, but it’s no substitute for popping out your own engine and taking your own measurements. Most transplants require multiple test fits anyway- it’s normal to try to fit the engine in there a few times before you find all the problems and come up with solutions to each of them. Don’t think for a second that this will be done in a week. I’ve been the helper on a few budget-limited transplant projects. They all required months of both-cars-taken-apart downtime, and those were old low-tech cars. If we hadn’t been required to work on other stuff for income maybe we could have done it in 2 weeks.
• The 1.9 TDI seems to wear a lot of accessories on its nose, and is consequently shifted towards the center of the engine bay in its native applications. You can’t get away with that in the Prius, need room for the longer hybrid transmission. Granted you aren’t going to need a few of those accessories anyway. You’re starting with a tight fit given that the TDI block needs to be a bit longer for its timing gallery.
• Some states have restrictions on engine swaps, and the general rule of thumb is that the new engine must be same or later model-year than the original, for emissions purposes.
• I recall that a Prius engine redline is rather low- maybe 4000RPM? Will the TDI be properly useful if you somehow get it to obey the Toyota hybrid ECU and thus stay under that limit?
• I expect you’ll need to create an interposer ECU that interacts with the TDI on one end and then with the Hybrid ECU on the other. That’s going to be a big challenge- how to map various conditions and behaviors so that the Toyota stuff isn’t constantly thinking there’s an error even though the VW is operating normally.
• Prius engines have trick valvetrains to reduce compression during startup, to make in-flight restarts less jarring. That would be a tall order. So I would anticipate whippty-thud-BANG starts. All the time.
• Extra torque from the engine is problematic, for proper operation of the Toyota CVT there needs to be an appropriate counter-torque created by the electric drive. You can theoretically reprogram the Toyota stuff to use some extra mustard, but it might be a better fit with one of the larger hybrids like the Camry or Highlander- they have bigger batteries capable of supplying more of that backing torque. Probably better just to have your interposer ECU restrict the output of the VW and then lie to the hybrid ECU.
• A 2006 Prius is going to have hybrid battery trouble soon. Plan on a few grand extra to deal with that.

 

Look at what a Hybrid transaxle hopes to solve, and you will realize why there are no diesel hybrids.

The Prius engine is an Atkinson cycle engine, very good efficiency, but no low end torque and very limited high end RPMs. (Gen 1 4500 RPMS, Gen 2 5000 RPMs, Gen3 5200 RPMs)

The Diesel will have great low end torque but be hard to start. It will change RPMs slowly.

The transaxle adds both horsepower and torque the the engine, an electric motor has maximum torque at 0 RPMs. The electric motor loses torque with RPM, many gas engines gain torque with RPM. Diesels torque peak is often under 2000 RPM. So a diesel Hybrid would have gobs of low end torque but no top end at all.

Motor/Generator1 is sized to start a 1.8 litre gas engine. Starting a similar size Diesel would take a larger M/G1. (I am guessing this is a $4000 problem)

As a rule, Diesel engines are started less frequently than Hybrid engines. There tend to be more steps and it tends to be a longer process. All the timing of starting the engine would need to be reprogrammed. (I am guessing this is a $100,000 problem. Read this: How to Start a Diesel Truck: 5 Steps (with Pictures) - wikiHow)

As a reliability issue, the Prius does not fire the spark plugs until the gas engine is up to speed. As the diesel has no spark plugs, you would need some other method to get the engine up to speed before firing (not injecting fuel?)

There is a reason almost all hybrids use Atkinson cycle engines, the weaknesses of the engine are complemented by the strengths of the Transaxle. (The is similar to the fact that almost all diesels are turbocharged, the strengths and weaknesses play into each other)

1) I think the design difficulties will be overwhelming. 2) I do not think the results would be efficient. 3) I would be happy to be proved wrong.

Atkinson cycle - Wikipedia

 

60 MPG is rather common from the latest generation. How is "better" defined in your regard?

Don't forget about emissions either. A repurposed diesel in a junk titled vehicle may not get approved for road registration.

 

How about modifying a Jetta hybrid?

 

Mercedes sells Diesel hybrids at europe.
They sure have to have quite different program for keeping diesel engine at right temps, start it, run it correct rpms etc.

Installing diesel engine to Prius would need quite bit programming to multiple ecus i believe.

But hell, i wanna see this project to finish!

 

Awesome summary, and I agree on all points.

 

The Atkinson cycle reduces compression ratio versus expansion ratio, but a Diesel requires high compression to fire the charge. I do not think you can reduce it.

 

Would be easier to put that TDI engine in your Jetta wagon and get a junk yard engine for the Prius.

 

Gen IIs are $50 on up for the whole engine

 

A blown engine should never be the death of a Prius. Those engines have a relatively easy life.

The death of many are due to failures of the HV battery, inverter, and ABS actuator/pump. They leave behind many viable used engines.

If you're even thinking about this crazy swap, you have enough ambition to replace the engine.

 

Where do you find engines at this price point? My searches yield $200 or higher with local pickup that's far from me. I'm in the Washington DC metro area.

I wonder if there is any kind of hobby that can make use of these cheap plentiful engines.

 

There was a guy on ecomodder who put one in an mr2

2005 Prius engine into 1986 MR2: mk1 1nzfxe Prius swap (gas only) - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com

 

hi andy, how's it going?