Suggestions invited for the perfect set of g/box and final drive ratios

Hi All,
I have just purchased a speedster rep and am unhappy with the revs it is doing on the open road (3,400 at 100 KPH)
I would like to lower this to 2,800 approx.
The previous owner said that he had had a local firm fit a taller 4th gear, however the invoice for this work listed the ratio as 1.05, which seems to me to be a lower than standard (.89) ratio.
I have looked at some gear ratio charts and it seems that with my tyres (185/65-15) a final drive of 3.44 would give me the revs I desire on the open road.
My concern is:
Will my reconditioned 1700cc with twin Scats pull this ratio ok and
will my engine be adequately cooled at these revs ?
Thoughts ?

PS I have done a search on this topic and read the threads so please only reply if you wish to without telling me off.

Thanks

Without a dyno curve, its hard to say.....But 1700cc is a fairly small displacement, and a Speedster is "heavy" compared to my Spyder.....I run a 1915cc motor with a 3.88 final drive and 0.82 fourth.....This would be close to what you are asking for, depending on tire size and other factors....Just be aware that the leap from third to fourth is quite large......I only use 4th on very long stretches....Around town, it's 2nd and 3rd...(stop light GPs.)
Hope this helps.....(Rancho Street Pro.)

I just bought a new ProStreet transmission from KCR in California. The owner, builder there is Kevin and he is very knowledgeable on this. You might go to their website KCRtrans.com and correspond/call Kevin and pose him your question. He is one of many pro builders I'm sure, but I've just had a great experience. My new transmission is a 3.88 with an 0.89 4th and being installed next couple of weeks. My last transmission was a 4.12 with .082 4th with a 1776cc engine. I thought it had great ratios, though the 4th gear drop was a big one. I'm putting in a 2275cc stroker motor that's just being finished and needed to upgrade to handle the torque...

With out knowing what gears are in your trans, it is impossible to recommend a R&P ratio. What year is your gearbox? A 1.05 4th gear seems odd. I feel that a 3:88 R&P with a .89 would be the best for your car with the engine you describe. A 3:44 with your engine would be a dog around town, and not cool well at hi-way speeds.

Chuck--interesting post--I guess this is still on topic---I too have a 4.12 with a .082 4th, but with 136 ft pounds of torque at 3,000 rpms there is zero "drop" at all. I do 70 mph at 3,200 RPM and if I step on it, it's at 85 before you know it.

It's all in the combo, isn't it?

Jack, I had to replace the tranny anyway as it had a bad second gear synchro. Kevin recommended their beefed up version with this gearing as a good match for the torque of the new engine going in. 4:12/.82 has been a good combination for me don't get me wrong. I find I never hit 4th unless on the highway, and I think the new 3:88 will make 45-50mph in 4th gear a little easier.

I meant 45-50 in 3rd gear, but you probably already figured that out :)

Phillip:

While a dyno curve on your engine would be cool, it's not completely necessary. Remember that the goal of the transmission is to keep the engine in the power/torque band in each gear, AND to keep the fan spinning with enough air volume to keep the engine cool under all circumstances. To that end, here's what I think (my comments in Italics):

I have just purchased a speedster rep and am unhappy with the revs it is doing on the open road (3,400 at 100 KPH)

Yup, That's a tad high

I would like to lower this to 2,800 approx.

Well, for that engine, that's a tad low - 2,800 puts you towards the bottom of the power curve on an engine that likes higher revs - personally, I would like to keep it around 3,000 at 65mph, because that will provide enough fan spin to give adequate cooling, plus it won't be wanting for power and "bog" when you stomp on it in 4'th at 65mph.

The previous owner said that he had had a local firm fit a taller 4th gear, however the invoice for this work listed the ratio as 1.05, which seems to me to be a lower than standard (.89) ratio.

Yeah, that's the 4'th ratio for an original Carerra if ordered for short track racing (but those had a R&P ratio of 6:31 to make power out of smaller displacement). It looks like with the revs you're seeing, you really might have a 1.05 in there, which will give more power in 4'th, at the expense of top end.

I have looked at some gear ratio charts and it seems that with my tyres (185/65-15) a final drive of 3.44 would give me the revs I desire on the open road. (Yeah, but what you want is too low for that engine.)

My concern is:
Will my reconditioned 1700cc with twin Scats pull this ratio ok?

I suspect that it'll be a little breathless at 65 in 4'th. IOW When you want to pass that big lorry, you'll have to downshift to third and shift to 4'th about halfway by. Right now, with that 1.05 4'th, it probably seems powerful enough, but going to lower revs with a .89 and 3:44 would make the engine gutless

will my engine be adequately cooled at these revs ?

No - I believe that it'll run hotter with your gearing choices.

Put these into your gear calculator and see what you think:

3:88 R&P

1'st = 3.09
2'nd = 1.76
3'rd = 1.13
4'th = .890

Those should get you nice splits between gears, keep the engine in the power band AND give adequate cooling on the highway. You may find that you prefer 3'rd gear around town, but that's OK, too. These engines were designed with revs in mind so they like 3K - 4,500

Hope this helps and I'm sure others on here can add some more to this chat.

Gordon

For those of you that have forgotten.

The rule in road racing or street driving says; Gear your vehicle from final drive down to first.

In drag racing; Gear it from first up to your maximum attainable speed in a given distance and time.

Again, street driving:
First - pick your cruising speed.

Second - have sufficient cooling (rpm) at that speed, bearing in mind da

Thanks everyone who replied.
I have decided on ratios (approx) of 3, 2,1.26, and .89 with a R/P of 3.875, and to aim for 3,000rpm at 110km/hr.

Regards,
Phillip

Sounds good, Phillip!

Now.....How about some pictures of that Apal??

Hi Gordon,
Happy to introduce self and car-see "Newbies"

Gordon, will taller 1st and 2nd gears necessitate more clutch than stock vw's put in speedies? With my 2110, 3.88 with 24.5" tires, I only get "across the street" before shifting from 1st to 2nd. Its been suggested that if I go to around 3. in first and 2. in second that I should have more clutch. Any thoughts? Thanks

Bob:

I guess the first question I might ask is at what rpm do you normally shift? Sounds like around 3,000 or lower. the second question might be "do you ride the clutch and engage slowly during a take-off??"

In regular driving, I normally run up to 4,000 - 4,500 to the shift point. For that, my gearing seems "right". I also seldom run lower than 3,000 and NEVER lower than 2,500, but that's just me. Running (for me) between 3K and 4.5K works well for the gearing I have and how I like to drive.

So, to your question, with the final ratio you mentioned up above and a 2,110 cc engine, going up a notch in 1'st and 2'nd won't hurt anything and shouldn't affect clutch actuation.

So the next question one might ask is "Will the clutch wear out sooner with a higher bottom two gears?" THAT absolutely depends on the engagement characteristics of the driver. If you tend to ride the clutch more (and a LOT of people do...) then it'll wear out faster no matter what the gear ratios are. If you get used to the gearing and "feel" and engage smartly (as in rapidly, not intelligently) then you shouldn't notice a difference.

Lastly, although not asked, is the effect of raising the ratio of 2'nd versus 3'rd - You'll now be closer together and the gap will be less so you'll pull about equally in 1'st and 2'nd, then have a much smaller gap from 2'nd to 3'rd and back to a normal gap into 4'th. Might take a little getting used to.

Hope this helps....

gn

P.S.: Clutches are funny beasts. When My dad had a bunch of school busses he had some drivers who would go through a clutch in 3-4 months, and one or two drivers who would go 2-3 YEARS on the same clutch. It's all in technique and, apparently, not a lot of people actually master it. I've always gotten well over 100,000 miles from a clutch in my personal drivers, whereas my cousin seemed to be replacing his every 6 months (same cars - '66 Mustangs, 289 3-speeds).

Hey Gordon, with your monster motor I'm surprised you don't have a ton of speeding tickets shifting that beast at 4500 rpm. :-)

Gordon, I normally shift somewhere between 32 to 3600 rpms. In 1st gear that takes me to about 18 to 19 mph. I can wind higher but not with increase in speed. 2nd gear to about 35mph or so.Ist gear barely gets me "across the street". transmission guys around here suggest the answer is to change the main shaft to 3.10 in 1st, down from 3.88, and to 1.96 in 2nd, down from 2.06. I like 3rd and 4th. At around 3100 revs I'm at near 70 mph.Not at all a racer, but I do enjoy carving the foothill roads above Clovis.

I try not to ride the clutch. Good reminder though. Been driving a stick since I was a kid, So I know the difference. But very little experience with these cars. Its been suggested that if I go to 3.1 1st then I may want to look at a stronger clutch. Sure appreciate you sharing your experience with me. Please don't hesitate if this doesn't make sense. Thanks

Bob

Bob:

If you're running a stock VW tranny with stock gearing, then 1'st is quite a stump puller.

Listen to your local tranny guys and go with a 3-3.09 for 1'st. While you have it out, spring for a Kennedy 1700 pound clutch and you'll be fine IMHO.

gn

Ron: Only one "ticket" (a warning , actually) in ten years.

Gordon:
Thanks for the help

Bob:

I re-read your post and I honestly believe you're shifting too low. There's nothing wrong in running the revs up to or slightly past 4K. In fact, that'll kep you in the power band of that engine.

Think of it this way: Sure, the engine makes a little power between 2K - 3K, but the carbs and cam and flow all start to really come on at 3K rpm. To confirm that, just look at any of the "dyno" graphs occasionally shown on here and you'll see the kink in the power curve around 3K.

So....If you're shifting at 3,200 (just getting into the power band), then you drop way down into the low 2K's and drop out of the power band, so it has to grunt a bit (it may even lug, if conditions are right) to get you back up just into the band and THEN you immediately shift and the process starts over again. The engine never gets a chance to work easier.

If, on the other hand, you get well into the band, say, at 4,000 or so before you shift, then you drop down to 3,200 but are still well into the power band (that comes on at 3K, remember?) and the engine has to work a lot less. Sure, it's reving higher, but so what?? It's working easier and placing less stress on the moving parts, like the crank bearings. I've only heard of one of these engines dieing from over-reving once, and that was from a severely missed shift in a race when the driver was constantly shifting at 5,200-6K and never going below 4K. These engines can take the revs, especially the higher performance versions some people have, but they really don't like the low end below the power band. That tends to pound the bearings and wear them out earlier.

I think this shifting lower in the power band is a North American thing, brought on by automatic transmissions and V8's. When you go to Europe and elsewhere, people are cranking their engines higher than us all the time. The techs at the Porsche factories regularly run around the parking lots cranked to 4K, too.

It would be interesting to get Larry's or Jake's opinion on this, too.

Gordon is right. I cruise mine around 2500, really put the foot in it above 3K though. My redline is set at 6500, and I take it there often, but not too often. Anything above 6K in a non-blueprinted counterbalanced crank motor is going to get an early retirement of the engine! (My engine is balanced and blueprinted)

Torque rises sharply until 3K, then is flat all the way to 6K. HP just rises to 6500. My engine loves 3-6K, sounds good there too. Really loud exhaust resonance at 3500, right around the torque peak.

1956 Speedster gear ratios:

1st 3.09
2nd 1.76
3rd 1.23
4th .089
Final drive 4.28

1972 VW Karmann Ghia (and most other VW gear boxes)

1st 3.80
2nd 2.06
3rd 1.26
4th 0.89
Final drive 4.13

If you'll notice, the main difference is in first and second gears. That is what made the Porsche more responsive. Starting out doesn't require changing gears as fast and the closeness of the ratios doesn't leave much of a lag.

VW designed its ratios for the old 36hp engines and all around driving, not sports car use. They never changed them. That's why they don't really work well except to pull stumps or empress your friends of never needing to press the accelerator....just idle away.

If your only looking to cruse at a lower rpm, then change the final drive. Personally, I would be looking for more responsive (better ratios) driving from first through fourth.