4th gear drive ratio??

To my knowledge the freeway flyer configuration is 3.80 1st, 2.06 2nd, 1.26 3rd, and a .82 4th. with a 3:88 ring and pinion. The drop off between 3rd and 4th is enormous.

 

I have the same size engine as you do and I changed up the transmission a bit and found that I really like it much better. I had a 3:44 ring and pinion put into it and changed the .82 4th to a .89. closing the huge gap between 3rd and 4th with the 3:44 making everything taller. For the bigger engines this combo seems to really work well. I'm at about 70MPH at 3000 RPMs using 24.5 inch diameter tires.

 

Here is and excellent ratio calc that takes tire diameter into the calculation.

 

http://www.et-studios.com/moto...rts/gears/gears.html

From your info, you'd have a 3.901 final drive ratio. Closest gearing to that would be a 4.375 ring and pinion and a 0.89 4th or a 4.125 r/p and 0.93 4th. The 4.125/0.93 combo was never a stock set and it would make the gearing shorter, opposite of what a "freeway flyer" is meant to do. The 4.375/0.89 was a stock combo, but it's not a "freeway flyer" either.

 

A freeway flyer would typically change 4th from 0.89 to 0.82 or from a 0.93 to 0.89 or 0.82. Though they could also change the R/P to a stock 3.88 or even a 3.44 to make all the gears taller.

 

As you mentioned, you should double check your KPH.

 

 

But if you want to calculate this yourself: http://www.currieenterprises.c...rRatioCalculator.htm

 

That will give you your overall final drive, which is simply the R/P ratio times the 4th gear ratio. If you get the two letter code of the transaxle, you can look up what it would have came with stock for ring and pinion here: http://www.shoptalkforums.com/viewtopic.php?t=113852

 

Your tire diameter is 24.5 inches. ((185 x 0.65) / 25.4) x 2 + 15

Isn't the typical 'freeway flier' transmission a 0.89 4th with a 3.88 R&P.

A 0.82 4th with a 3.88 R & P would be a terrible combination.

There is no standard. And while 3.88/0.82 would not be good, a 4.125/0.82 is only 2% taller than a 3.88/0.89.

I had a 0.82 4th with a 4.12 R & P, and I couldn't wait to get rid of it.  It may only be 2% taller, but the difference was very noticeable.

What didn't you like about it, Ron? The final drive, the longer 3rd-4th gap, or ?

I found if I didn't wind it out in 3rd the engine didn't have any pull in 4th.  I also often drove at a speed that was too high for 3rd and too low for 4th (right around 45/50 mph, if I remember correctly).

In order to use a 4.12 RP with a 0.82 you must have enough torque to make such a combo work otherwise you will hate it.

 

My engine torque is more than enough to work with that combo and it drives like a dream.

Step on the gas going 75 and you feel it willl get to 120 very quickly. Plus good MPG for a larger engine thanks to the overdrive.  The saying that "it's all in the combo" really applies here.  We read all the time about gear ratios but rarely is torque mentioned and it is a major part of the equasion from what I have been told.

For 2 liter engines and above:

 

1st: 2.80, 2nd: 2.06, 3rd: 1.26, 4th: .89 with a 3.44 Ring and Pinion. If you have a Rancho Freeway Flyer trans than this is an inexpensive modification without digging into replacing the mainshaft 1st & 2nd. Just replace the Ring and Pinion and swap out the .82 4th for a .89. It will make your 2 liter feel like a $100,000 sports car.

This is the problem with a 4 speed and an aircooled motor; the factory gear spacing is about as wide as possible given the powerband and cooling characteristics of the motor it's attached to. Making the motor bigger with a better torque curve helps, but can't totally overcome the bigger 3-4 gap when using a taller 4th gear. A taller ring and pinion (so the gear spacing stays the same) is a much better solution for those looking for higher cruising speeds. Al

The solution is a much longer 1st gear. I did replace my 1/2 mainshaft, and have a custom 3rd and Erco 4th. There's nothing cheap about it, but it's even better than stock beetle gearing with a 3.44.

 

Back in 194X, the stupidly short first gear might have been a good idea for climing the Alps with a mighty 1200 cc engine, but with a big motor it's useless for anything other than 60 ft times on the 1/4, a place where I'll happily give up a car length. For a SPORTS CAR (as opposed to a dragster) starting out with a much longer first means that the rest of the ratios can be much more closely spaces, and still end up with a nice highway gear in 4th. For 95% of the people out there, it negates the need for a 5 speed, in my humble opinion (which is correct ).

 

My final drive is a .93/3.44. I could've easily gotten away with a 3.88/3.44. It's not that hard. Rancho has an online catalog with all the Weddle and Erco gears available, and there are some good online gear ratio calculators. Plot something for a 2000 RPM drop between gears, and you'll be happy.

Stan's right; the ultimate solution for a 4 speed (with today's bigger, torquier motors) is a longer 1st gear. A new 1st-2nd gear mainshaft (and matching gears) is expensive, though, so a taller ring and pinion is a reasonable (and cheaper) solution.

It was late when I put my last post up, and I was having "issues" in the garage.

 

A couple of clarifications:

 

"For a SPORTS CAR (as opposed to a dragster) starting out with a much longer first means that the rest of the ratios can be much more closely spaced (not spaces)."

 

and:

 

"My final drive is a .93/3.44. I could've easily gotten away with a .89/3.44.(not 3.88/3.44)."

I like to cruise along at 3000 rpm at 70 mph.  To me, anything higher than that sounds like the engine is working too hard (even if, in reality, it isn't).  After a couple of hours on the road the noise starts to annoy me.  Heck, it sounds even better at 2700 rpm, but I know that's way too low for proper cooling.

I'm hoping my new 901 gearbox will allow me to cruise around 3000 rpm at 70*

 

*yes, I know 3000 rpm may be too low for proper cooling.  If the CHT increases significantly I'll install a 356 alternator pulley.

Ron-

 

In my experience (and with a 2+L engine), all the talk of needing to spin high RPMs to keep the fan speed up is a bunch of bunk. The reduced friction of the lower RPM more than offsets the fan speed thing.

 

You'll love the .89/3.44.

Ron:

 

My 901 5 speed transmission is great for cuising.  You can do 70 all day without noise and at a very comfortable rpm.

 

The only thing I don't like about it is the very short first gear.  I am sometimes tempted to start off in second, which I can do with the 2332 c.c.

 

 

With the larger motor (and it's more generous torque values) not working so hard at cruising speeds, there is less heat generated so the cooling system isn't working as hard. And less rpm's means better mileage figures. At least that's the way I've always figured it....Al

Bob, when I first starting looking for a 356 replica, back in 1999, I test drove an IM.  I had to slip the clutch a bit to get the car rolling in 1st gear, which I thought was odd.  It wasn't until after the test drive that the owner mentioned that the car had a Porsche 901 5 speed gearbox.