Swapping in taller 5th gear? (09 VW "City" Golf 2.0L 8v SOHC gas)
 

Hi Folks,

I'm looking into a 5th gear swap that would drop my highway speed engine RPM's by approximately 400.
My car normally runs right on 3000 RPM @ 100km/hr when in 5th gear. This gear swap would essentially drop my RPM's to 2600 for the same 5th gear speed.

I know you guys are old hats with all this stuff, so can anybody speculate as to how much benefit this would actually be...in MPG terms? 1 MPG? 2? None?

Any of the BTDT guys have any thoughts on the matter?

Thanks,
Rem

What car do you drive? What speed do you drive? What kind of mileage do you currently get with the car?

Need moar info! :D

some cars are easier than others. S-series saturns and VW golfs can be done with the tranny in the car and ~$20 and a trip to the boneyard. Others might also be easy. It is a no-brainer for those with a 5th gear cover that you can get to in the car (and at the boneyard). Otherwise consider a tranny swap.

The wiki says 7-20% increase depending on the vehicle.

Regear for lower cruising RPM - EcoModder

Yup...09 VW Golf "City" Model, which is just a re-released version of the 2004 and earlier MK4. 2.0L 8v SOHC 4 cylinder.

My current best is 35mpg (usg) @ 60mph all hwy with cruise control.

Not sure what to expect, but I'm usually blindly optimistic;).

Rem

depends on your current ratio (5th and final). here is an article on the hows: 5th gear swap modification- lower gearing on a VW 5 speed transmission | VW TDI forum, Audi, Porsche, and Chevy Cruze diesel forum

There are gains to be had for sure, but will need more technique than cruise control to take full advantage of them.

Also the gains are manifest when combined with aerodynamic mods.

According to the code on my trans:

1st: 3.778
2nd: 2.118
3rd: 1.360
4th: 1.029
5th: 0.837
R&P: 4.235

I simply want to swap the 5th out for a TDI 5th (7.44-7.56) or pick up Euro 5th kit @ .717 ratio.

I'm not going to get into swapping the R&P...I'm not that eager...but a 5th set swap is just an afternoon in the garage. Might give it a whirl.

My question is... WHY?

Why would VW stick anything approaching a 4+ ratio in the "diff". I get that acceleration on the highway excuse, but 3k RPM's on the highway? At the speed limit no less.

Brainless.

I know, right?
This is my issue and why I want it to settle down @ hwy speeds.
A coworker of mine has the identical car and @ 75mph on the hwy, he gets only 22-23mpg compared to my 32-34 when driving @ 60mph.

In any case, I just want to get it down below 3000 RPM @ 60mph.
The 5th gear swap seems to be the easiest and most cost effective way to do it.

Maybe I'll miss the power it has in 5th now, but if the increase in MPG is decent, I don't care about the power.

I'm considering swapping in a transmission with a 3.73 final, a 3.545 1st, and a .725 5th if I can find it. The importance of this? I'd go from a 4.33 final, 3.166 1st, and a .815 5th to previously mentioned transmission. Since 4th is .969 on both, the first transmission's 4th gear is as tall as the second's 5th gear so I wouldn't lose any highway acceleration capabilities that bad.

I live in socal so I have to go up some steep grades on the freeway if I drive it more than 30 miles either way.