How about a really fun project!

arlo · Post by **arlo** » Thu Mar 24, 2005 7:37 pm

I had a diesel rabbit in the 70's that could hit MPG's in the 50's. The type 4 lower end may be strong enough to support a small diesel. We know that 40 0r 50 HP can move a bug around OK. What if you used a real small bore for about 1.5L or so and custom made pistons to fit into the heads for about 19:1 CR. Use an OEM injection system off a rabbit or the like mounted with glow plugs into otherwise stock 1700 heads. You would probably have to do something clever with the cylinder to head seal. Diesels are so neat in ther simplisity with no ignition or fine tuned induction systems for holding a perfect air/fuel ratio.

I would think you could hit around 60 MPG in a bug and that would be very noteworthy! It would preserve the original elegant simplicity of the design and you could use stock rebuilt and OEM parts for injection and exhaust for a more economical package.

What do you think Jake, is this crazy enough that you could make it work?

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Thu Mar 24, 2005 8:03 pm

I have thought about it many times...

The issues are with expansion rates and head studs. Not even the best head studs on the market would hold that kind of cylinder pressure without snapping.

aYou'd have to Nitride the crank and use way better rod bearings than stock Bi Metals...

You could do it, but it would be far from easy to do it right

arlo · Post by **arlo** » Thu Mar 24, 2005 8:31 pm

I was thinking if you scaled the bore way down the forces involved may be managable. Lets say half or less the CC's of your 3L with not much more than twice the CR. Wouldn't the forces involved be similar? You could maybe use the 66mm crank and put sleves in 90mm cylinders. Don't get greedy on HP, just enough to push a bug like stock performance.

I was surprized that the '77 rabbit diesel appeared to get away with using the gas engine lower end if I'm not mistaken. It was reliable to. In 120K miles I only replaced a few glow plugs and did normal maintenance so I never got to look inside. It got 59 MPG on one trip when I was trying to see what I could wring out of it!

914fan. · Post by **914fan.** » Fri Mar 25, 2005 10:48 am

Diesels usually run cooler (when not pushing them) because there is no throtle so the cylinders completely fill with air each stroke. Since there is little to no fuel (less when idling) the full cylinder has a cooling effect. Or so I have been told. Look at porsche tractors. Aircooled with around 103 pistons. I think they are not nicisil (sp)

Hey what about using those heads on your 3.0
You could have a 3.0 diesel with more torque than a MAC (not the computer) Than would be fun on dyno day.
"its a vintage 3.0 VW Diesel with 8 billion pounds of torque"
The type one people would run screaming. Bring a video camara Jake. We have to see that.

What kind of studs were used on those engines? I wonder...
Wonder land beckons. I'll be back later.........

500LbGorilla · Post by **500LbGorilla** » Fri Mar 25, 2005 11:27 am

Yeah, to get 19:1 compression would be a LOT, and a 7:1 engine with about 25 pounds of boost gets an equivalent ratio of almost 19:1. It would take a lot to hold it together.

yetibone (elswhere) · Fri Mar 25, 2005 12:50 pm

Do a serch for Deutz Diesel, spfc. the FL series.

None are horizontally opposed AFAK. They go from 2 or 3 cylinders up to 12 or 16 or something, they're Diesels, and they're air cooled.

Post by **Marc** » Fri Mar 25, 2005 1:29 pm

I've owned quite a few diesels & never managed to pull down mileage quite that good in any of them. A 1600 Dasher 4-speed managed 46+ on a trip from Seattle to OKC at a steady 60-65MPH; on the return trip I opened it up to 75 wherever possible and still got over 45. A friend of mine, a retired trucker who really knew how to featherfoot a diesel could get over 55 with his 1600 Rabbit, but he also had the late 5-speed with a .7:1 high gear.
The price differential between diesel and gasoline varies widely by state; around here if you can get 25MPG on Regular the break-even point for Diesel is at about 36MPG, so they're cost-effective in that regard. My Mercedes could get that until it blew up

and I can build a few ACVW engines for what that puppy's gonna cost to go through, so when it comes to total cost-per-mile the diesel doesn't come out looking quite so good. Even Rabbit diesels get spendy to rebuild - the Brazilian pistons are about 4 times the cost of the gas version and the German are out of sight.

Diesel needs time to burn. Short strokes and short rods are counter-indicated. Look at the specs on those Rabbit engines: Bore was 76.5mm (they used a different block than the gas engines of the same displacement, basically like the ones in the 79.5-bore engines so the cylinder walls would be thick enough) and the stroke was 80mm for a displacement of 1471cc.
When they bumped them up to 1588cc they left the bore alone and stroked them further to 86.4mm (unlike the gas 1588 which was 79.5x80).
The compression ratio on the 1500 was about 23½:1 on the 1600, around 22:1...a healthy one will pump 500+psi on a cranking compression test. A "prechamber" diesel needs this kind of C.R., if you were to go with a direct injection system you could bring that down some, maybe 18:1 - still a bunch.
914fan, it's the very fact that diesels have no throttle plates that allows them to run - if they didn't get a full charge of air regardless of the pedal position, there wouldn't be enough heat generating from compressing it to get the fuel to light. Compare the size of the radiator in a diesel Rabbit to the one in the gas model....which one do you think has more heat to dissipate? Sure the diesel will run cool at idle, but when you ask it to get some work done that'll change - and the range of the thermal cycling makes things even worse for the head studs if you go air-cooled. The Rabbits used 11.5mm head bolts, later upped to 12.5mm, and still had more than their share of failures - cracked IRON blocks were commonplace, I shudder to think how a stock aluminum case would hold up.

Yes you can build an aircooled diesel, there're plenty of purpose-built ones out there as examples - but starting with a Type IV would be a tough (and not very sensible) way to go about it.

HAM Inc · Post by **HAM Inc** » Fri Mar 25, 2005 2:59 pm

I don't think the heads have the meat to handle the thermal requirements. Aluminum diesel heads are out there, but I don't think it's the right material for the application.
I believe that the gas mileagemaster engine Jake and I are developing will fill the need for a fuel effecient aircooled alternative. With Jakes programmable F.I. I believe the design has a chance to meet modern emmisions requirements as well, if fitted with a catalytic converter. (But who's going to want to do that?!)
The end result will be efficient, reasonably powerful, and very reliable. Should cost pennies/mile to operate, and be fun to drive too.

Post by **Piledriver** » Fri Mar 25, 2005 4:34 pm

The Deutz 903 (air/oil cooled diesel) cylinders fit a T4 stud pattern, and the heads might as well...
The heads are oil cooled. Jugs are air cooled.

Used jugs (they don't rebore them) 100mm cost ~$20 ea, used heads go for ~$100, as they are rebuildable. You would need 4.
(From a US Deutz rebuilder, I posted contact info somewhere on forums)

The jugs are WAY too long and would have to be turned down.

raygreenwood · Post by **raygreenwood** » Fri Mar 25, 2005 5:58 pm

Marc beat meto it. The rabbit diesel blocks were differnt in more than a handful of areas, thickness, ribbing, oil passages. They were generally wanted for high performance. They are stronger than the gas engine blocks.
Jake is also correct. Have you ever taken a look at the standard rabbit head bolts? The diesels are even larger and stronger if memory serves.

Now...if smeone created a complete casting...say a siamesed head and cylinder assembly....wherin first the cylinders bores are roughed in, then cast iron cylinders shrunk in that aluminum casting...kinda like a biral...but not quite...then the combustion chambers finished....through the cylinders via CNC milling....and the whole mess....sandwiched together with complete...head to head....long...fat...bolts.......its doable. Ray

Post by **Piledriver** » Fri Mar 25, 2005 6:11 pm

HAM or Jake, feel free to elaborate on your "mileage master" project.

I pretty certain that's approximately where I'm headed, I'm still just debating if it will be T4 or wasser based. Each has certain advantages...

I was looking at having Endyn in Ft Worth do something interesting, but before I commit, I'm curious where you are.

A 4000 lb Jetta TDI can get >60MPG, easily. Turbocharging a diesel makes it MORE efficient.

My 81 Rabbit got ~45 MPG combined pretty much regardless how I drove it, but it wasn't a turbo or common rail injected.

arlo · Post by **arlo** » Fri Mar 25, 2005 6:30 pm

How about bolting it together like the way Ray suggested but form the one piece head and cylinder assembly by welding unfinished nickies to the modified type 4 heads then inserting iron liners. The heads would be stronger, cooler and more evenly cooled once joined to the aluminium cylinders and now maybe strong enough. I would think the bolts could be made as strong as they need to be. You could experiment with the liner ID to find the largest bore that would hold together.

arlo · Post by **arlo** » Sat Mar 26, 2005 5:47 am

On second thought, I don't like the long bolt idea at all... too much offset between the left and right cylinders.

Instead, leave a flange on the base of the billet cylinders, weld them to the heads and bolt them to the block through the flange with an array of many moderate sized studs just like aircraft engines.

raygreenwood · Post by **raygreenwood** » Sat Mar 26, 2005 3:27 pm

Good idea arlo. Or...make a plate type flange with cylinder cut-outs...that is about 1/4" thick steel...as a base plate....with the 8 big fat rods welded to it.....that goes on the inside of the block...with the rods poking out through holes where the threads are now. Ray

Ephry73 · Post by **Ephry73** » Mon Mar 28, 2005 11:39 am

Then again, an alcohol engine will give you twice the horsepower and half the mileage. If you work it right, you can start making your own moonshine at a lot cheaper you can buy gas for and still kick some serious butt on the streets.

Ephry