Need trans gearing help/comments/discussion (long)
 

I'm getting a 2.8 trans with 7500 miles and a bad bearing for cheap. I am going to pull the gears and synchro assemblies out, and drop them into my 2nd-gearless 1.8 trans.

Here's my thinking:
The 1.8 gearing is made for a 150hp motor. The 2.8 gearing is made for a 190hp motor, and I think would be better suited for a modded 1.8 (210-220hp)

Here's the question: Do I change 3rd and 4th gears as well, or leave them stock?

I feel 1st and 2nd are too short, and I like 3rd and 4th as it is. 5th gear will be taller for better cruising mpg.

So here are my options:
2.8 ratios: 3.500, 1.944, 1.300, 0.943, 0.789
Mix ratios: 3.500, 1.944, 1.429, 1.029, 0.789
1.8 ratios: 3.778, 2.176, 1.429, 1.029, 0.838

My concern is by making 2nd gear taller, and keeping 3rd the same, the shift from 2nd to 3rd will drop the RPMS less, so your RPM range for 3rd is less.
Is it better to have a shorter RPM range for a gear, or should it drop more RPMs to better use the torque range?

Here are some numbers (2.8 trans):
1st gear @ 6300 rpm = 34.2 mph
2nd gear after shift = 3500 rpm
2nd gear @ 6300 rpm = 61.7 mph
3rd gear after shift = 4200 rpm
3rd gear @ 6300 rpm = 92.2 mph
4th gear after shift = 4600 rpm
4th gear @ 6300 rpm = 127.1 mph
5th gear after shift = 5300 rpm
5th gear @ 6300 rpm = 151.9 mph

Mixed gears:
1st gear @ 6300 rpm = 34.2 mph
2nd gear after shift = 3500 rpm
2nd gear @ 6300 rpm = 61.7 mph
3rd gear after shift = 4600 rpm
3rd gear @ 6300 rpm = 83.9 mph
4th gear after shift = 4500 rpm
4th gear @ 6300 rpm = 116.5 mph
5th gear after shift = 4800 rpm
5th gear @ 6300 rpm = 151.9 mph

cruising RPM @ 70 MPH (1.8) = 3100
cruising RPM @ 70 MPH (2.8) = 2900

One last question, will a lightweight flywheel affect the decision either way?

TIA

Heres what I did:
 

I was mulling over tranny ratios for a turbo beetle and I made a chart of the ratios and then divided 2nd by 1st to come up with the ratio between them.

1.94/3.5=55%

Do that for each set of gears, and mix and match until you find the set that has the smoothest range. Generally the range will tighten as you go up the gears, such as 55% 60% 70% 75% remaining ratio. You don't want to go backwards, like 55% 60% 65% 60% that would feel funny.

Run the numbers for each kit and see.

I would imagine the guts are the same between all of the trannies (likely the same as other VW/Audi transmissions as well, for cost savings.) I doubt seriously if there is any difference between the gears in either transmission. I doubt the 2.8 gears are in any way tougher. Probably come out of the same bin.

Please remember that the final drive pinion is integral to the output shaft, so that will have to stay the 1.8T part, unless you got the R&P out of the 2.8 as well.

Good luck!

Hmm....so I get:
 

1.8: 57.6%, 65.7%, 72.0%, 81.4%
2.8: 55.5%, 66.9%, 72.5%, 83.7%
mix: 55.5%, 73.5%, 72.0%, 76.7%

Will the 73.5% to 72% feel funny? Or is it close enough it won't matter?

I've got the ETKA print outs for the upper/lower shafts and gears (If anybody wants, I can scan them). Everything is the same except the gears and input shaft. The output shaft is the same, so I won't have a problem with the pinion.

Thanks.

Looks good.
 

You won't experience a slightly larger drop between 1-2 than stock, then the rest of the ratios will feel like a wide ratio box, with similar (lower) drops between gears all around. The 2-3 and 3-4 shifts will feel about the same.

A shorter second gear might make the ratios balance out a bit better. Also a taller 4th would help. There may be other part numbers that you can scrounge for the right ratios. I think they interchange pretty freely.

My .02
 

I think your choices look pretty good with these percent drops;
.55
.73
.72
.76

But, how about
3.500
2.176 .62
1.429 .66
1.029 .72
.789 .77

Seems like a nice progression to me.

The problem is 1st and 2nd are part of the input shaft....
 

so it's either 3.778 and 2.176 or 3.5 and 1.944

Plus with the 1.944 2nd gear I can do a 0 to 60 run without having to shift to 3rd (60 in 2nd is 6900 RPM)

Is it better for the percentages to slowly increase, or be the same?
 

I'm sticking with the 2.8 1st and 2nd ratios (see post below)

If I go to a taller 4th, then the 73.5 to 72 drop gets worse, unless I change 2nd, which I can't.
4th gear is capable of 115 (@6300), and I don't think I'll be making too many redline shifts into 5th.
But I still have some doubt as to whether I should just put all the 2.8 gears in or mix them.

Well, Hell! That's a problem. I like the % to increase and definitely don't like it to jump around.