bus gearing

regis101 · Post by **regis101** » Tue Feb 04, 2003 5:57 pm

Greetings. Wotking on a 67 split. Going to keep the reduction boxes for a while. Cruising speed is about 55. I have been told that changing to a 3.88 will get some mph. Question is how much? Just trying to get to a comfy 65 with 75 being tops. Along those lines, if I can get to 75, how much HP should I plan on having to carry the bus. I'm thinkin about a hundred? I'd like the cruise rpm to be around 3200-3500. Topping out at 5k. Any help or thoughts about the gearing? Thanks, Regis

amskeptic · Post by **amskeptic** » Tue Feb 04, 2003 6:48 pm

I won't get into the particulars of ratios with you, reduction boxes ruin all the numbers I have stored in my head for the bay window buses. What I would like to share with you, is some of the thinking that went into VW's working out of gear and axle ratios. VW purposely designed their engines to cruise at the horsepower peak, not just for top gear, but for hill pulls. The ratios they selected were designed to allow you to pull that long hill at 4,400rpm in third gear with no protest from the engine, then when you shift into fourth, they deposit you square in the middle of the torque peak for the next gear up. This allows you linear acceleration. Check out any modern van with overdrive and torque converter lock-ups that hunt and shift all over the place, the engine is too frisky in the lower gear and dead in higher gear, and you will see how much easier VW made it by ensuring that the engine's output was carefully built up from 0through75mph. If you want a highway cruiser, make sure that you know your particular engine's horsepower and torque peaks. Your individual gear ratios work in-concert with the rear axle ratio.
There is more math than I can get into here, to make sure that you have the power you want for the speed you want. Consider carefully the work your engine will be doing at your selected cruising speed, if your rpms are too slow (because you wanted an engine that didn't sound like it was being flogged back there for example) you could be plagued with overheating and lousy gas mileage. If you get too tall of a rear axle ratio without closing the gap between third and fourth, you could end up rowing the gear shift maddeningly in the Rockies, because third is too short and fourth is too tall.
The factory engineers were a smart bunch.
I'd recommend that you look at late model Vanagon ratios as a start. If you get your engine up to 100hp, with peak torque around 3,000-3,200rpm, and horsepower around 4,200-4,500rpm, the Vanagon ratios should give you good driveability and highway cooling, but, like all VW Bus owners do, expect that your engine will be turning over pretty quickly.
Your math will be divided by your reduction ratios, of course.
Colin

regis101 · Post by **regis101** » Tue Feb 04, 2003 8:10 pm

Very good reply. Easy to read and understand. You seem to know the angle of my question and stated what I wanted to hear. I will indeed reference the vanagon ratios and using the 1.26 for the reduction boxes be able to calculate a final ratio. I can compare this to the 67's numbers. I'm not trying to reinvent something but rather enhance and/or accept what I have. Thanks, Regis

regis101 · Post by **regis101** » Tue Feb 04, 2003 8:18 pm

Our 78 westy comes to mind when comparing how it drives to your Rocky mountain point. We can cruise right along at 60 or so until we hit the Sierras. Then it's cruising at 55 downhill and shifting to third doing 5o-55 uphill. For just having 67 HP, this thing carries itself along nicely as long as I respect it for what it is. Its all in the gearing. Kudos to you

JK · Post by JK » Wed Feb 05, 2003 6:28 am

I have a 67 with 3.88 bus trans in it. 215/75/15 rears. I'm running a spare 1600 in it right now. Pretty gutless on hills, but better than I expected. It runs good with a 2L T1, better with a 2L T4. I run an external cooler too. The 3.88 gearing will up the temps some. With 2L engines I can cruise up to 80. 60mph is 3000. 70 is 3500 I think. 75 about 3800, 80 4000 rpm. I don't cruise my engines above that. Most hills don't really affect the speed using the T4 engine. I run a Rancho trans with HD sideplate, superdiff, Berg poormans posi just in case.

Pillow · Post by **Pillow** » Wed Feb 05, 2003 8:18 am

This might help, here are the normal '66 ratios:

1st: 3.8
2nd: 2.06
3rd: 1.217
4th: 0.82
RGB: 1.38
R&P: 4.37*
* For '67 some of them had a 4.10? R&P which made them a little faster anyway.

There are loads of calculators out there so have fun playing with the numbers

I know I did! Arg. Tire size plays a huge role as well, 215/75/R14-15 will fit and help a lot over the little stock units

Just be very careful of the 3rd to 4th drop with the taller R&P. And be realistic on how fast you need to go.

... On mine I have planned for 3500RPM at 4th to be about 72MPH. Yes, I need to finish a big motor to even push it.

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Adrian Pillow
'66 VW Westfalia
'79 Porsche 911 SC - FS
VolkSport Kafer Gruppe

Post by **Marc** » Wed Feb 05, 2003 8:58 am

Note that going from a 4.375:1 R&P to a 3.875:1 is a 12% change and that most 3.88 trannies have a .93 4th (you need a double sideplate box to convert to swingaxle, so you might find one from a late `Ghia that's 3.88/.89). Compared to your stock bus 4th, that's an 11 to 13% change the other way so you'd be going taller in all gears except 4th. Tightens up the spread between 3rd and 4th nicely so you don't have to slow as much to shift to 3rd, but if you want to make any real difference in 4th-gear RPM beyond what you can do with tire size you'll need a custom-made trans.

biggraham · Post by **biggraham** » Wed Feb 05, 2003 5:05 pm

I just swapped a set of Kadrons and $100 for a freeway tranny, I figured there's no point in installing idfs and 044s just to overrev my motor to sit at 60 mph, I'll let you know how it works out.

Pillow · Post by **Pillow** » Thu Feb 06, 2003 9:01 am

Correction on the RGB ratio for big nut: 1.24

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Adrian Pillow
'66 VW Westfalia
'79 Porsche 911 SC - FS
VolkSport Kafer Gruppe