gearbox ratios

I am thinking of a new gearbox for the wife's build as 40 years of Thai mechanics can pretty well guarantee that the oil has never been changed. By the time I get the parts imported and buy the jig to set the box, I may as well just import a rebuilt box and be done with it.

I am not sure that the stock gear ratio is ideal for the Speedster application using a VW motor
What is the collective wisdom re close ratio 3-4th gears?
3.88 R&P VS a high 4th?
Any other combos?

Seems to me the best set up would be a 3.88 with the close ratio 3/4th gear set, but I would appreciate some input from those who know before I shell out the cash for a new box

3:88 R&P

310. 1st
193. 2nd
121. 3rd
082. 4th

I would suggest making a note of the various roads you drive, the road speed and the engine speed. I'm running a .89 fourth gear on a 3.88 R & P and I spend lots of miles in 3rd gear just to keep the revs up. With a .82 fourth gear, your highway revs would be even lower than mine.

If that doesn't bother you - have at it.

I'd die for a 5 speed, but that's another thread.

I live in Chiangmai, Northern Thailand and the roads are generally crappy, narrow, winding, and mountainous with the odd elephant thrown in. In the city there is a developed ring road system, and the main highways are not too bad with speeds of 120 Kph.

I have never seen a speed limit sign, and there is no radar in the North, so the locals drive like Buddha is protecting them and do what they damm well please without warning or reason. 120 Kph not withstanding, there is always some cretin who will make the left hand turn of faith onto the road without looking, or simply park in the lane to visit his favourite noodle stand on the opposite side of the road.

Sounds like the suggested ratios will be a bit too high for me.

i miss Chiangmai. had a great time visiting there a few years back. Friendly people, Fantastic food and cheap cheap cheap.

i did an eco tour with a very small group of us (6) and the guide came across the super bright green snake - picks it up and puts it in his bag for a pet.

R&P 4.120 w/ 25" tall rear tires
1st- 3.78
2nd- 2.06
3rd- 1.26
4th- 0.821

Don't forget to take into consideration your motor's torque / hp.
This is part of the formula in choosing the right tranny as well as final drive ratio to keep the fan moving fast enough to cool the motor properly cooled... ~Alan

The original Porsche Speedster gear and final drive ratios were:

4.28/1 Final drive

3.09 1st gear
1.76 2nd gear
1.23 3rd gear
0.89 4th gear


VW Karman Ghia (and most Type 1 gearboxes):

4.13/1 Final drive

3.80 1st gear
2.06 2nd gear
1.26 3rd gear
0.89 4th gear

Anyone who has driven an original Porsche gearbox and VW back to back will tell you that the VW 'jumps' off the line, but runs out of steam quickly. The Porsche is much smoother through the gears as they are much closer. Perhaps, I'm not using the correct words, but if you have driven a Porsche and VW, you will know the difference right away. If I could have my choice, I would change the VW first two gears to follow the Porsche and smile all the way.

I have bought a 3.88 R&P but have to go with whatever transmission gears available in Thailand.

1st and 2nd are the same at 3.80 and 2.06 but I have a choice of 3rd and 4th:
3rd at 1.32 or 1.26
4th at .89 or .93

Tyre height is yet to be determined and again limited to what I can buy. Heights range from 667, 645, 634, 621, 615, 577mm.
577mm or 22.71 inches is the preferred compound but is a 195/50
In all cases but 615mm (24.21 inch) I need to run 6 inch rims which dictates some wheel work.

Engine is a 2332, Engle 120 cam, 35 x 40 valves in stock heads ported by me. I know I can use better heads, but TIT (This Is Thailand)and good heads are 1800 USD

What thinks the group on gears and tyres?

i traveled from sattahip to bangkok on R&R in 1969 and that was the roughest, potholed road, narrow and it was awful. i dont see how a speedy could do it. a 4wd would be more appropriate. and i dont have to tell u that their drivers dont use brakes, only the horn.

Roads have improved somewhat since 69, however the drivers are terrible.

With our lightened chassis and rare loading of R passenger/cargo space, the stock
1st ( &2nd ?) gear ratio could be changed.
When i remember, I sometimes start off in 2nd.

However potholes/ruts might require less speed !!

Changing out 1st and second gear with more appropriate ratios is something I recommend. I have done it on 2 different cars, using a 2.58 first, 1.86 second,1.26 3rd, and 0.93 fourth. My current transmission is a 3.44 R&P and the next one will be 3.88 instead. The 3.44 is overkill. I am running 205x50x15 tires....

The bad news is the 1st and second gears are EXPENSIVE.....approaches $1000 just for the gear set alone.....

The 3.88 R&P will make 1st and 2nd higher compared to my stock 4.375 but a new 1-2 mainshaft gear set is not available, doubles in cost by the time I import it, and out of the question.

I am limited to changing 3 and 4th as described and would appreciate suggestions on what gears to use as it is off to the transmission builder tomorrow. That is if his shop passes my inspection, has the tools, and does not work on a dirt floor. If not then I will give it a go myself using an old case for the setting jig

On further thought re tyres, the shortest size is a 50 series so not really suitable to this classic bodied Speedster.

Your springs/shocks betta be rite. Shorter tyres = less bounce.
You're sayin 60 or 65 profile tyres arent generally available in SE Asia ??

I hope they're not Vietnam surplus!

I too am right in the middle of this tranny gear issue and have learned (I believe) that Joe Soltis has it mailed with his numbers posted earlier.

I understand that a 3.88 r&P with a .082 4th gear will yield much too high geraring and you will spend a LOT of time in 3rd---even at some highway speeds. And the less hp & torque your engine produces, the more this is true.

In my preoect; new engine & tranny, I will have what Joe posted; 4.12 R & P with a .082 4th. I don't know about a type I but a type 4 will benefit from this making a 5-speed teans unnecessary.

With the higher gearing I'd be looking at 2,000 rpms at 60---an exaggeration but it makes the point.

I always thought the 3.88 "Freeway Flyer" was the holy grail and with 50 hp to the wheels and a stock 4th gear maybe it was, but now with my own new combo it's 4.12 and .082.

Jack,

You may want to re-check your numbers. I just ran the tranny calculator with a 4.12 R&P and 0.82 final gear. With 25" tires you would have to run 2,729 rpm to make 60 mph and with a 3.88 R&P you could do it at 2,570 rpm. At 2,000 rpm the best you could do is about 47 mph.

Rich

Rich---thank you for this---I'll check into this. My car is not here so I can't measure the tire height but it's the standare VW bug 165/15

--do you know how high that is? 25" seems low. Thanks---Jack

Jack's tire is 25.8" tall fully inflated and loaded. His gearing will be optimum for his driving speeds and the engine I have created for him.

GEAR SELECTION CALCULATOR
http://www.et-studios.com/motorsports/gears/gears.html

I said that 2000 rpm for 60 was an exaggeration---and it sure was.

Using the calculator I get 45 mph at 2,000 and 68 at 3,000.

Seems like I used to see about 3,600 at 70 so it's a very good reduction in engine speed, noise, wear and tear with better mpg.
The chart gives me 114 mph at 5,000 rpms and red line might be as high as 7,000, which on a graph results in 136 mph!!

Not with my butt in it! But it should be a hoss at normal highway speeds when passing or entering highways and at 70 mph and just 3,100 rpms the engine is just loafing which is the whole idea.

Nice calculator---thanks.

About that 7000 RPM in high gear, not many performance vehicles are geared to pull redline in top gear. Most vehicles are geared to pull redline in the lower gears only, but not the top gear - unless you are heading for Bonneville!

If 7000 RPM is the redline of an engine, I'd guess that the car would be geared to pull maybe 5500 to 6000 RPM in top gear. I've always heard the you should gear a car to cruise in high gear at, or near, your torque peak to achieve max mileage. And max highway mileage is the purpose for high gear. Anybody?

As speed increases the aero wall gets harder to overcome and more power is needed to push beyond it.. We hold 7 Land Speed records and I have learned all about that! Even my Wife is an LSR racer!

The Bugatti Veyron only needs 250HP to go the first 100+ MPH, but it needs 730 more HP to reach 250 MPH.

The faster you go, the harder it is to go fast.

Boat racers know all about that drag factor. You have an 80 MPH boat. You double the horsepower. You get a 90 MPH boat with twice the fuel consumption!

Still undecided on 3rd gear ratio and a bit confused on which ratio will reduce the spread between 3-4

Have decided on a 3.88 R&P as this is what I have and the 4.12 is just not available locally.
Am also leaning toward a .93 4th with the 3.88.

What to use for 3rd - 1.26 or 1.32?
Engine is a mild 2332, street driven, with little freeway use: mostly mountains, country roads, and in town