Technical Stuff

The best engine for your Puma...

Of course, this is something I realised just a bit too late. Hindsight is a wonderful thing. When I got my Puma, it had a 1600 Type III engine, which was fairly tired. Instead of rebuilding that engine, I replaced it with a stock 1700 Fuel Injected Type IV engine from a Variant. Type IV engines are strong, and perform well. They're also bloody heavy. IMHO too heavy for a Puma. (Dave Williams' Engine Weight/Size FYI gives Type I: 200 - 250 lb (91 - 114 kg), Type IV: 311 lb (141 kg) -- call it a 96 lb / 44 kg difference.)

So, why the 1500 and not the 1600? Again, IMHO, VW stretched the engine beyond it's capability with the 1600. The 1600 was not nearly as reliable as the 1500, which is why VW then redesigned the engine totally to get the Type IV 1700 (which they stretched to 1800 and then to 2000).

On the other hand, I could be wrong. And for now, I'm sticking with the Type IV engine. I will try to move as much weight as far forward as possible, but apart from the battery there's not much that can move, is there?

Of course, I have seen a Puma with a Ford 3L V6 in the back. Apart from it being waaay unbalanced, and overheating chronically, there was nothing wrong with it...

The best Type IV engine for your Puma...

Type IV pulleys

Mating a Type IV engine to a Type I gearbox

Firstly, you need the later type gearbox, where the release bearing slides on a tube around the gearbox input shaft. All flat VW engines share the same basic engine/gearbox interface, but for various complicated reasons the Type I release bearing won't reach the Type IV pressure plate if you don't make an adaptor. The adaptor is made from two release bearing cups welded together. Or you could use a spacer, of course.

Secondly, and most importantly, the Type IV gearbox input shaft is 18mm longer than the Type I equivalent. (The Type I pilot bearing is located in the nut holding the flywheel to the crank, while the Type IV pilot bearing is located in the crankshaft itself. The Porsche 914 also uses the Type IV engine, but the pilot bearing is located in the flywheel.) I found the hard way (terrible vibration) that the pilot bearing has to be relocated if you're fitting a Type IV engine to a Beetle.

Oil temperature sender

There are a number of places to fit an oil temperature sender to a Type IV engine, some of them bad, some of them better.

If you google, you will find the term "taco plate". This plate puts the oil temperature sender in the sump, which is not a bad location for it, although there are concerns about the air under the car cooling the sender down (if you don't have the correct cover plate), or the oil in the sump forming hot and cold spots and you measuring the cold spot. But this was used on the Porsche so it can't be too bad. As far as I can see it locates the sender in the flow to the oil pump. If you're using the right sender, with a long nose. (Note : the picture is confusing, that's the cover plate over the taco plate in picture 111)

When I got the Puma, it had a pipe running from the stock oil pressure sender location to a T fitting with the pressure sender on the one side and the temperature sender on the other (this was still on the Type III engine, but it's equally bad on the Type IV). The oil doesn't go anywhere, so you don't have any idea what the oil temperature is. I thought of using the pressure sender location for the oil temperature, and relocating the oil pressure sender, but it's on the input side of the oil cooler so it has no real benefits.

For a while, I had the sender in the middle of the stock plate where the "taco plate" would go. This is a dead spot, and doesn't work.

After this, I moved the sender to the oil filler hole, thinking that it was the airflow cooling the sender down. Not true, I was still measuring the same dead spot, also a bad idea.

If you know of a way of measuring the oil temperature after the cooler, without relocating the cooler, please let me know.

Dipstick tube

The Variant dipstick tube and oil filler pipe runs down the back of the engine and into the case at the bottom right hand side. This gets in the way.

On the busses, the filler is in the breather, and the dipstick next to it. It's relatively easy to drill a hole, swage a brass pipe into the hole, and fit a dipstick. The old oil fill location then needs a blanking plate.

I had a piece of 3/8 brass tube left over from when I replaced the Rand-Lover's dipstick tube. It mikes at 9.54mm, so a 9.5mm drill will probably do the trick.

Building a "freeway flyer" gearbox

As you can imagine, a 1700 VW engine has more than enough torque to keep a light little car like a Puma going. And as such, the top speed is only limited by the engine revs, and keeping the engine revs down is good for the engine. So, a higher top gear would be nice.

I composed a table of the standard VW gear ratios which can be summarised (for swing-axle, Type I) as follows:

You'll see that there are three basic models, and of these, the 3.875 R&P gives the lowest ratio in fourth gear (3.604). This will of course give you the highest top speed for a given engine speed, assuming that your engine has the torque required.

If you want to increase the top speed for the given engine revs, you need to lower the total ratio even more.

One way would be to change the R&P (if you have an "AC" box with 0.89 fourth and 4.125 R&P, and you changed to a 3.875 R&P, your new ratio would be 3.449, a six percent improvement over what you had, and a 4 percent improvement over the "AT" box). Of course a similar result is obtained by using an "AT" box and fitting an 0.89 fourth gear set).

The good news is that you can do even better than this. The early (swing axle + reduction box) Type II VWs had an 0.82 fourth gear (23/28 teeth), which gives a ratio of 3.178 in the "AT" box, an 11.8% improvement.

But, can we willy-nilly swap out gears between different gearboxes like this? It seems that we can, with a few catches.

1. Split window busses (swing axle) had keyed mainshafts, bay window busses had splined mainshafts. I've heard that the 3.88 main shaft is splined, although CIP sells keyed 3.88 R & P sets -- more here when I pull my gearbox apart and learn something...

2. You get coarse tooth and fine tooth gears, apparently the fine tooth gears are quieter, and the coarse tooth gears are stronger.

Other technical articles

• Armand Botha on building a large Type IV engine

Links

Type IV

• Type 4 Engine Technical Articles.
• T-4 Upright Conversion on a budget.
• DTM Upright Cooling for your Type IV.

Gearbox (Transmission for USAnians :-)

• VW Transmission Diagrams with part numbers.

Handling

• Improving your Beetle's handling.

EFI and CDI

• Links
• KitCarlson Programmable EFI for flat four engines.

Exhaust

• 4:2:1 tuned exhaust calculator at Mez Porting.

General

• Technical article collection.