4.12 or 3.88 irs is there much difference

Discuss VW transaxles and transmissions. Gearheads wanted!

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Marc
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Post by Marc » Wed Nov 16, 2005 1:09 pm

I'd probably do better if that was the case...

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Post by 500LbGorilla » Wed Nov 16, 2005 1:33 pm

Note to self: never touch Marc's KB.

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Post by raygreenwood » Wed Nov 16, 2005 7:03 pm

I really gotta know where you found that graphic of that poor bastard self destructing on his keyboard...thats a hoot! Ray

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Re: 4.12 or 3.88 irs is there much difference

Post by stimey » Sat Mar 04, 2017 2:04 pm

Guys I don't get the math. If the transmission was exactly 1:1 in 4th . Would it not take ~4 turns of the input shaft to turn the output flange ( wheel) once with a 3.88 or a 4.12? How do you come up with around 7 or 8. Would that not be the figure for 2nd gear. 2.06. I am really confused. I just put in a new tranny and was trying to verify the r/p and these numbers don't work. I get about 7.25 turns of input shaft to 1 turn of the wheel in second. Does the differential come in to play?
Thanks Lee

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Re: 4.12 or 3.88 irs is there much difference

Post by Bruce2 » Sun Mar 05, 2017 5:20 am

stimey wrote:
Sat Mar 04, 2017 2:04 pm
If the transmission was exactly 1:1 in 4th .
There's no point in asking this. 4th is never 1:1.

Put the trans in 2nd then count input shaft turns needed for one full turn of BOTH tires. If you have a dragging brake that stops one wheel, then put that wheel on the ground to completely stop it. Now count the number of turns of the input shaft to make the remaining wheel in the air turn 2 revolutions.
8 turns = 3.88
8.5 turns = 4.12
9 turns = 4.37

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Re: 4.12 or 3.88 irs is there much difference

Post by stimey » Sun Mar 05, 2017 7:19 am

I was just trying to simplify the math by saying 1 to 1. I stll don't understand why I am looking for 2 revolutions of the tire. I have already tried what you said. It took 7.5 turns on the input for 1 turn of the tire. Which to me.. Divided by 2.06 for second comes out to 3.42 which seems impossible. No big deal just trying to understand it in my head.

Think I understand it. The differential is the reason for 2 turns of the unlocked wheel.
Lee

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Re: 4.12 or 3.88 irs is there much difference

Post by Bruce2 » Tue Mar 07, 2017 1:47 am

There is an aftermarket 3.44:1 R&P.

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Re: 4.12 or 3.88 irs is there much difference

Post by Piledriver » Tue Mar 07, 2017 2:27 am

Bruce2 wrote:
Tue Mar 07, 2017 1:47 am
There is an aftermarket 3.44:1 R&P.
Is there any way to get it surface hardened so it will last in regular use?
(the std 3.44 R&P heat treat is IIRC for drag racing, tough not hard)
I, for one, regularly embrace our new robot overlords, as I am the guy fixing the robots...

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Re: 4.12 or 3.88 irs is there much difference

Post by Bruce2 » Wed Mar 08, 2017 1:46 am

The gearboxes I build with 3.44s are exclusively street cars that never go drag racing. My customer has been installing them in his builds for at least 15 years. I've never heard him say he had one worn out. Yours is the first claim I've heard that they won't last.The R&Ps my customer uses are made in the USA by US Gear. There may be a China manufacturer out there making them too, I don't know.

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Re: 4.12 or 3.88 irs is there much difference

Post by Piledriver » Wed Mar 08, 2017 3:22 am

Cool, glad to be misinformed about that, I thought I read that in this forum.

The 3.44s are usually used with a std close 3/4 ratio setup for even spacing?

I must confess, I'm still looking for an automatic in order to have a reliable trans that can take significant power without costing $10K, I'm dubious anybodies T1 trans or even 091 based setup would live long with the 2.5L thats going together now... Have even considered a Subaru trans.
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Re: 4.12 or 3.88 irs is there much difference

Post by Bruce2 » Thu Mar 09, 2017 2:17 am

Piledriver wrote:
Wed Mar 08, 2017 3:22 am
The 3.44s are usually used with a std close 3/4 ratio setup for even spacing?
Not the ones I build. My builds all get stock gears. 3.78, 2.06, 1.26, .89. My customer hasn't had a buyer who wants extra tall gears, so I haven't built a 3.44 with a .82 4th yet.
The speedster crowd likes tall gears, and when a watercooled engine is used, you don't need to worry about having enough rpms to cool the engine. Last summer I had a chance to drive one of my gearboxes in a Speedster with a 2.5 liter turbo Subaru engine. 110mph......in 3rd gear!

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