[vuu16v]

I'm gathering parts for my tranny rebuild and need to decide on a 3.90 or 4.25 r&p. Most of my autocross experiences have been all second gear courses. I want to stay closer to the sweet spot without being a moron and forcing myself to shift into third because I've gone too low on the r&p. It comes down to not wanting to get the 3.90 and seeing little to no results or getting the 4.25 and shifting into third and just moving my no torque problem up one gear for 500 bucks.

The trans will get a lightened/balanced flywheel, quaiffe, new r&p and fourth gear cog if necessary.

 

[RiskMan]

Re: 3.90 r&p or 4.25 for autocross?? (1sweet16v)

1sweet16v, correct me if I'm wrong, but isn't the stock final drive 3.67? Moving up to a 3.90 is going to move you up the rpm range already. Our experience here last year was that we were most often at the top of second gear on the courses here. You really don't want to shift unless you have to! Second gear is where you want to be, working between 3500 and 6500 rpm.
What class are you planning on running?

 

[vuu16v]

Re: 3.90 r&p or 4.25 for autocross?? (RiskMan)

quote:[HR][/HR] Moving up to a 3.90 is going to move you up the rpm range already. Our experience here last year was that we were most often at the top of second gear on the courses here. You really don't want to shift unless you have to! Second gear is where you want to be, working between 3500 and 6500 rpm.
What class are you planning on running? [HR][/HR]​

I should have been more clear. I'm now coming out of tight corners @ 2500-3500 rpm's, which is too low. I want a lower r&p w/out going so low that I end up where I'm at already, only in third as opposed to second. I want to hit the "meat" of second.

 

[a2vwnick]

Re: 3.90 r&p or 4.25 for autocross?? (1sweet16v)

It depends on the size of the course. It seems that you have a pretty tight course and your not able to stay in the rev range. The 3.9 or 4.25 will help you there, but if the course also as places where now you are getting upwards of 6000, you are going to have to shift, which means downshifting later... you get the idea.

 

[VWzealot]

Re: 3.90 r&p or 4.25 for autocross?? (1sweet16v)

quote:[HR][/HR] and fourth gear cog if necessary. [HR][/HR]​

you will need it

 

[AntoineJo]

Re: 3.90 r&p or 4.25 for autocross?? (duff_man2000)

4.25 is the best IMO, thats if you only auto-x with that car, otherwise you will need 6 gears to travel on the highway. Check out scirroco.org for calculating gears...

 

[VWzealot]

Re: 3.90 r&p or 4.25 for autocross?? (duff_man2000)

quote:[HR][/HR]
purdy!....s'all clean and what not....[HR][/HR]​

nah. the new gears where purdy

 

[vuu16v]

Re: 3.90 r&p or 4.25 for autocross?? (ajothy)

quote:[HR][/HR]4.25 is the best IMO, thats if you only auto-x with that car, otherwise you will need 6 gears to travel on the highway. [HR][/HR]​

or a .71 5th!!

 

[VWzealot]

Re: 3.90 r&p or 4.25 for autocross?? (1sweet16v)

or better yet a .71 6th

.

 

[AntoineJo]

Re: 3.90 r&p or 4.25 for autocross?? (1sweet16v)

4.25 with a 6th. The only way to go if you don't want to compromise. Otherwise 3.89 or 3.94 and a tall 5th is the way to go IMO. I like top speed, and I like short ratios.

 

[vuu16v]

Re: 3.90 r&p or 4.25 for autocross?? (ajothy)

I agree but how often do I need to be in the powerband going from 4th to 5th. Now that's racing!

 

[AntoineJo]

Re: 3.90 r&p or 4.25 for autocross?? (1sweet16v)

Only you can answer that. Myslef, I decided to opt for a very long .71 5th considering my R&P will be 3.89 only. That was driven by cost because of a good deal on the parts needed to build that custom 2Y tranny. I hardly ever drive on the highway and when I do its long trips so I'd rather save on gas. I know that if I get into a race though, I will happily downshift to 4th and pull it hard enough to get near the power sweet spot when upshifiting to 5th. That shift is crucial, 4th to 5th, in highway battles and I can't tell right now how effective my setup will be... I fear that I will get distanced in low 5th... depending on who the customer is.

 

[rockin16v]

Re: 3.90 r&p or 4.25 for autocross?? (ajothy)

quote:[HR][/HR]4.25 with a 6th. The only way to go if you don't want to compromise. Otherwise 3.89 or 3.94 and a tall 5th is the way to go IMO. I like top speed, and I like short ratios.[HR][/HR]​

hell ya bro http://****************.com/smile/emthup.gif http://****************.com/smile/emthup.gif
i just installed a 3.94 (not 3.9) Ring and pinion, close ratio 1-4, and a 0.71 5th.

quote:[HR][/HR]I agree but how often do I need to be in the powerband going from 4th to 5th. Now that's racing!
[HR][/HR]​

i feel the same way you do 1sweet16v about the power band from 4th to 5th
pulls like mad on the street, but highway...goooood gas mileage. aside from a 6th gear (cough.. cough.. vwzealot), this is the best option IMO too.
edit: add url http://cars.vwsport.com/gears/index.html


[Modified by rockin16v, 5:31 PM 2-12-2002]