porsche trans, stock VW engine...

[trevorbrady]

I know that the Porsche transmission is too high geared for the stock VW type 1 engines to cool themselves adequately, but how do the lower 4 gears compare to the stock 4 gears of a GT or 1303S gearbox? Would it be worthwhile upgrading the gearbox to Porsche 5 speed with a stock 1600 type 1 engine and restrict yourself to using just the first 4 gears? It would mean that later on when a larger engine was installed the 5th gear would come into use...
Any thoughts?

trev

[lightning bug]

What engine would you be using later? I'm using a T1 with a 915 5-speed. (not on the road yet) I don't see myself having any problems with cooling. Why don't you just add an external oil cooler? I don't know much about them, but maybe you could also add a 911 shroud. I'm not sure how the 5-speed would have an effect on cooling? Higher revs maybe? If you use only 4 gears in the Porsche 5-speed, you'll be running at higher revs anyway only being in 4th. I would say add a cooler. I don't think you'll have a problem.

[trevorbrady]

Originally posted by lightning bug

If you use only 4 gears in the Porsche 5-speed, you'll be running at higher revs anyway only being in 4th.

That's what I was wondering; is the 4th gear of the Porsche transmission higher than 4th gear of a VW transmission?
I would be worried because say you had a stock VW 1600 engine and a Porsche 901/915 transmission, geared for a much more powerful engine: You're in 5th gear and the engine is doing 1500 RPM. You gun the throttle and the engine is trying really hard to pick up some speed. Because of the low revs the fan isn't moving much air, and putting that much strain on the engine is going to generate a lot of heat, which the fan just isn't going to remove because of its low speed. I hope you follow...

As for using a Porsche fan on a stock VW engine, I reckon the volume of air moved by the fan is going to rob the stock motor of too much power, when a stock fan wouldn't.
I suppose you could use a power pulley...

The engine planned for later is still pie in the sky. Every day I change my mind from Subaru to Wasserboxer to Type4!

[trevorbrady]

just had a flash of inspiration!!
What is the stock rear tyre size of the car that the 901/915 comes out of?
Surely reducing the rolling radius of the rear wheels will lower the effective gearing of the gearbox? If the ratios are too high maybe this will bring them back down to something more reasonable?
just a thought... :)

[NYBugman1972]

I am wondering the same thing. I know its possible to put my 5-speed and stock bottom end T1 together, but if I'm going to get cooling problems, it's going to make me think twice. But, where there's a will, there's a way.

Oh, and the 901 box was used with a 165-15 tire, or a 185-70-15 radial option. My dad uses a 195-65-15 tire on his 912 (4 speed, but same final drive), and that is close to a 205-65, which is close to a 165 (stock beetle). Whew, that was a mouthful:D I'd say that if you wanted a smaller tire, go with a 205-60-15 or a 205-45-17.

Also, if your engine is stock, or close to it, you may not have to worry as much about overheating as if you had a bigger engine. What I mean is that it may take longer to reach that critical temperature. Well, once someone with experience in this particular area chimes in, we should know.

OH! Also keep in mind that the 901 box was used in the 912! Duh! Well, that means that it worked with a 90hp 4-cyl engine as well as it did with a 100+ hp 6-cyl. I dont think we have much of anything to worry about.

[kdanie]

Trevor and Mike, The trans used will have alot to do with how hot your engine will run. 901s from a 911 are taller geared than those from a 912. The 915 is geared way too tall for a stock type 1 to use 5th. With tall gears the engine runs slower, the fan turns slower reducing the volume of air available to cool the heads and cyl. The problem is the stock engine doesn't have the necessary torque to pull the taller gears at a lower RPM so you overload the engine and cook it. An external oil cooler is not the answer.
If you want a 5 speed and a stock or mild type 1 the best way to go is the 912 transaxle ('66-'68) has about a 4 to 1 final drive in 5th (same as the 912 4 speed but with close ratio gears between 1st and 5th).
If you want to run a more powerfull engine in the future you could go with a 901 from a 911 or the 911/01(used for a couple of years between the 901 and 915) or the 915 and run in 4th gear but without a gear chart for the specific trans you will run (there were many combinations of gearsets available) I can't say what RPM you would have at a specific speed. Clutchs/flywheels play a big part in this conversion, the 901 is the easier way to go. CVs/axles/stub shafts are another expensive concern, some of these transaxles use 930 size CVs and will cost another $500 or more to get the power to the wheels. Again the early 901 is the way to go.
911 fans use less HP than the stock type 1, dyno proven.
I hope this helps some.
ken