GermanLook Forums  

Go Back   GermanLook Forums > Technical Section > Transmissions

Reply
 
Thread Tools Display Modes
  #1  
Old August 28th 2002, 08:19
trevorbrady's Avatar
trevorbrady trevorbrady is offline
Registered User
 
Join Date: Jul 2002
Location: Kilkenny, Ireland
Posts: 144
porsche trans, stock VW engine...

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
Reply With Quote
  #2  
Old August 28th 2002, 17:49
lightning bug's Avatar
lightning bug lightning bug is offline
Registered User
 
Join Date: Jul 2002
Location: Philadelphia, Pennsylvania USA
Posts: 462
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.
__________________
Julian
'74 Super

"If you are under control you're going too slow" - Parnelli Jones

Last edited by lightning bug; August 28th 2002 at 17:53.
Reply With Quote
  #3  
Old August 29th 2002, 03:57
trevorbrady's Avatar
trevorbrady trevorbrady is offline
Registered User
 
Join Date: Jul 2002
Location: Kilkenny, Ireland
Posts: 144
Quote:
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!

Last edited by trevorbrady; August 29th 2002 at 04:03.
Reply With Quote
  #4  
Old August 29th 2002, 06:12
trevorbrady's Avatar
trevorbrady trevorbrady is offline
Registered User
 
Join Date: Jul 2002
Location: Kilkenny, Ireland
Posts: 144
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...

Last edited by trevorbrady; August 29th 2002 at 06:25.
Reply With Quote
  #5  
Old August 29th 2002, 07:57
NYBugman1972's Avatar
NYBugman1972 NYBugman1972 is offline
Registered User
 
Join Date: Jul 2002
Location: Brooklyn, NY
Posts: 365
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 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.
__________________
Mike Serrone

'08 GTI DSG :: 1980 911 SC Track Car
1972 1302 German Looker - dearly missed

///BrooklynAutoRennen
Reply With Quote
  #6  
Old August 29th 2002, 15:37
kdanie kdanie is offline
Registered User
 
Join Date: Aug 2002
Location: Petaluma CA
Posts: 358
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
Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 12:38.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
© www.GermanLook.net 2002-2017. All Rights Reserved