Fuel Economy...

[eightyonerabbit]

okay, everyone knows that these things are capable of almost infinite mpg's, but i think we should have a thread about the most mpg's uve ever gotten... best ive gotten so far is 48mpg, but i think i might beat that with this tank of diesel...  :wink:

[Clankin-Rabbit]

Not to bust off topic here...but its slightly related to fuel economy

to my understanding...84' was the only year VW put the 4-speed in the rabbits correct?  A 4-speed would be the best, economically based tranny for getting the best MPG out of a tank of diesel over a 5-speed right?

I'm getting one hopefully this weekend..and hoping its got the 4-speed.  A manual, naturally aspirated, extremely slow diesel in a small car will be a complete blast to drive....I totally can't wait.  :lol:   It will be my first diesel and VW.

[burn_your_money]

just what the doctor ordered
http://vwdiesel.net/phpBB/viewtopic.php?t=137&highlight=

[burn_your_money]

VW used 4 speed all through out the mk1 chassis 74-84 I think

It depends what kind of driving you are doing and the gearing of the engine in the 4 vs 5 debate

[Baselyne]

5th gear lower RPM's

[burn_your_money]

I think as far as 020s go the 4A 4 speed has the lowest overall final output

[ldeikis]

I think as far as 020s go the 4A 4 speed has the lowest overall final output

How much of a difference in final drive is significant?  IE, comparing a 5 speed FF to the 4 speed 4A:

FF .71 * 3.89 = 2.762
4A .70 X 3.94 = 2.758

Is that difference significant?  If you work that out, it's less than 1 mph difference at the wheels, no?  I pulled the numbers from http://www.brokevw.com/020ratios.html and http://www.scirocco.org/gears/ and just plugged them into their calculator.

No doubt the 4A IS lower, but what does a .004 difference really mean?

Luke (getting wintertime 41mpg overall with a N/A 1.6 rabbit through aforementioned FF)

[burn_your_money]

The 4 speed weighs less, has less rotating mass and also has less resistance

I'm glad they finally added the 4A to the list

You can make a custom lower one, and also the dodge omnis (I think) used  VW tranny (4 speed) that was even lower IIRC

[eightyonerabbit]

i have an FK with a .71 5th gear... i had a GP in it, but i needed better gearing... i think i lost about 1mpg, but its not that noticable...

[Turbinepowered]

I think as far as 020s go the 4A 4 speed has the lowest overall final output

How much of a difference in final drive is significant?  IE, comparing a 5 speed FF to the 4 speed 4A:

FF .71 * 3.89 = 2.762
4A .70 X 3.94 = 2.758

Is that difference significant?  If you work that out, it's less than 1 mph difference at the wheels, no?  I pulled the numbers from http://www.brokevw.com/020ratios.html and http://www.scirocco.org/gears/ and just plugged them into their calculator.

No doubt the 4A IS lower, but what does a .004 difference really mean?

If you put the final drive from the FF into the 4A you'd have 2.723... an improvement of .039 instead of .004...

[silvertdi]

Best I've gotten was 59.6 mpg on a 800 mile trip.  I kept it at 62 mph for nearly the entire trip. Mine's an '81 with a GP 4 speed.  It even had a head gasket that was letting go.  Perhaps it was burning some antifreeze.  

[greenbert]

My ecodiesel gets about 40-42 mpg, and from what I learned the ecodiesel trans has the highest final drive.

Btw, whats an ASF trans?

[estimatd]

I am a bit naive when it comes to trans codes and gear ratios, so I'm sorry I didn't follow with most of this thread, could someone help me out with this.  I have an 81 NA with a 4spd, from what you guys are saying, it would be better to stick with the 4spd, considering I'm looking for the best mpg's?  The trans needs either to be rebuilt or replaced and I considered replacing it with a 5spd, thinking that the 5th gear would improve hwy mpg's while giving it a bit more pep down low.  Is that wrong to assume?  Also, I'm totally open to mixing and matching gears and final drives as I have someone to help me build the right setup, but is the difference negligible??

Thanks and sorry for being slow with the tranny logic! :oops:

-Charlie

[eightyonerabbit]

I am a bit naive when it comes to trans codes and gear ratios, so I'm sorry I didn't follow with most of this thread, could someone help me out with this.  I have an 81 NA with a 4spd, from what you guys are saying, it would be better to stick with the 4spd, considering I'm looking for the best mpg's?  The trans needs either to be rebuilt or replaced and I considered replacing it with a 5spd, thinking that the 5th gear would improve hwy mpg's while giving it a bit more pep down low.  Is that wrong to assume?  Also, I'm totally open to mixing and matching gears and final drives as I have someone to help me build the right setup, but is the difference negligible??

Thanks and sorry for being slow with the tranny logic! :oops:

-Charlie

well depending on your gear ratios now, u probably wont gain any fuel economy on the highway... if you have the GP tranny which is what was in my car (81 N/A), then u have a 3.89 final drive with a .71 4th gear which is about the best that you could hope for as far as highway mileage... i picked the FK tranny with the 5th gear swap so that my highway mileage would be the same, but my gearing down low would be so close that i would get instant torque as soon as i shift... basically, if you want about 2 less miles per gallon, then do the 5 speed swap with a .71 5th gear, but if you want the same MPG that you have now, just rebuild your tranny or get a GP or an FF...

sorry for dragging this post on, but i jsut couldnt help myself... i like to hear myself type...  :lol:

[estimatd]

ok thanks for the info, to keep it easy and since I'm used to driving with the 4spd, I'll probably just take your advice and rebuild it.  Basically my fuel economy sucks right now which is why I considered swapping to a 5spd, but I think there are a few other problems that need to be addressed which would help get the mpg's up.  I really think this new diesel is destroying my IP so I'll probably need to get that rebuilt soon too  :x

thanks again.
-Charlie