Highway flyer trans, question!

[Marc]

With 195/60-15s and a stock SSC (3.875x.93) trans the RPM is almost exactly 1000 per 20MPH, e.g. 3000@60 and 4000@80.
Same tires with a `69 (4.125x.89) box would be ~3055RPM@60.
AutoSticks have a 4.375 R&P, plus some torque converter slippage, which'd yield around 3300 or so at 60MPH.

[NextGen]

Marc I don't have a problem with someone disagreeing with me. I had a problem with Bruce.

I can deal with being wrong, actually I admit being wrong alot.

I must admit without giving you guys the correct info to go by, this is a wild goose chase.

But my car has a 500 rpm drop from the previous trans and the noise level is much lower. As for the noise level, it is from the drop of RPM, engine noise, not road, not trans.

But as I said we can drop this - there is not enough data for a true answer without taking the trans apart. Who knows what is in this tranny.
joe

[Marc]

...I asked Mike, the late Joe of Oregon Performance to make me a 74 trans. ( By the way working with that guy was a mistake). Anyway, here is what he said he was going to do, now this was 14 years ago, so lets see what I remember.

74 trans, welded 3rd and 4th gears.

Also said he was going to use some early gears because they had less teeth and were stronger. What and where they were I don't remember.

He may have made some weird ratio ( but I like it ).

If you'd mentioned this from the outset we could've saved a lot of time and bickering. It's quite likely that you do not have stock ratios, which would explain everything. If you never mentioned this to Bruce, I'd say he has an apology coming.

...there is not enough data for a true answer without taking the trans apart. Who knows what is in this tranny...

If you really want to find out you can do it by counting turns. Block the wheels and jack one rear wheel off the ground, put it in 2nd and rotate the engine clockwise to take up all the slack in the drivetrain then put a chalkmark on the tire. See how many turns of the crankshaft are required to get one turn of the wheel - should be just barely less than 4 to confirm it's a 3.875 R&P with a stock 2.06 2nd. Now repeat in 4th; if it takes just over 3-1/8 turns to get two turns of the wheel you have a .82 (bus) 4th and the mystery's solved - that'd account for a 15½% change compared to the `69 trans, just about exactly what it'd take to yield the same RPM at 70 that you used to have at 60.

[dstar]

The difference in the gear whine from the early and late trans is VERY noticable!

I have just changed out a 69 for a 76 and although I dint bother
recording the actual RPM drop, it really doesn't matter.

The NOISE difference from the gear whine is what *tells us* things are
*better*. The math says the rpms stay about the same and I agree with
that also.

Humans are VERY susceptable to noise....certain harmonics are VERY annoying!

Like my alarm clock, which I haven't heard since I bought it.
I wake up 5 minutes BEFORE it goes off, because I don't like the
SOUND it makes!

I didn't DECIDE to do it, my *subconscience* decided it didn't like the
noise and wakes me up.

Don

[Marc]

The difference in the gear whine from the early and late trans is VERY noticable!

But how do you know it's from the gears and not from the mainshaft, differential carrier, or pinion bearings? A moot point here actually, since Joe has (finally) revealed that his "1974" trans was custom-built using coarse-tooth gears...

[dstar]

*Whine* is *whine*. I'm sure you understand.....


I could give a crap which *part* is responsible FOR the whine!


69=whine
76=quieter than the 69


Hell, it COULD be that the 69 was worn out!


But it only had 98K miles on it, so I doubt it!

BUWAHAHAHAHAHAHAHAHAHAHAHAHAHA!

Don

[Plastermaster]

But as I said we can drop this - there is not enough data for a true answer without taking the trans apart. Who knows what is in this tranny.
joe

No No No! We cant drop this! Tell us the aspect ratio of your tires and we can probably figure out your gears. There are only a few R/P possible and only a few 4th that are "likely".

Dstar, you are right about the harmonics. My wifes Miata sounds has this horrible drone around 3K and seems like it is turning 5K. I keep looking for another gear. My VW at 3K and about the MPH is just relaxing itself.

Ron

[NextGen]

Yes I finally revealed my tranny may be a custom, ha.

As for Plastermaster -- Mannnnnnnnn!!! Haaaaaaaa!!! Ok I won't drop it.

My tires are 195 60 15's

[Marc]

..My tires are 195 60 15's

Like I said earlier, 60MPH would be approximately 3000RPM with that tire (~3500@70) if the trans was a stock SSC (3.875x.93). If you have a bus 4th in there it'd be around 3085@70.
Obviously we must assume that your tach and speedo are both accurate - for example, if you have the same size tire up front your speedo will be reading about 5% optimistic and 70 indicated would only be 66.7 actual (~2940RPM with a bus 4th, ~3335RPM with a .93).

[NextGen]

Marc you may have hit it on the head about the bus 4th and like I said 195's all around, they are large tires.

If my car was not blocked by a mountain of snow I would take it out and do a digital photo of the tach and Speedo.

But that sounds like the logical answer. I did not know you could use a bus 4th. My car reminds me of my 914 because after getting out of third, 4th starts putting out power at 65mph. At times I don't know if I should be in 3rd or 4th.

Too bad I had a bad experiance with the Builder or I would call. Especially since my 3rd synco never was working at it's best from day one. But having to wait so long for the trans, I just settled. NY to Wash. is too damn far.

Joe

[Marc]

...195's all around, they are large tires....

Wider, but about 5% smaller in diameter than the stock 165-15s are.
http://www.miata.net/garage/tirecalc.html
165-15s are about 82 aspect ratio, but 80 is close enough to use for comparison. Right now I'm running 185/70-14s on the front (they're virtually identical in diameter to 195/60-15s so I've got that 5% speedo error) and tall 165-15 studded tires on the rear. That puts me at ~3300 at an indicated 70MPH (actual 66.7) and that's about the tallest I'd ever want to gear a bug with a stock Type I motor. I've only got a 1600SP in it, fortunately for me the gap between 3rd and 4th is fairly small with the .93 4th and I can drop down to 3rd without slowing if it starts bogging on an incline - 2750 in 4th is about 3725 in 3rd.
I've got another trans that was built for a baja pulling 28" rear tires - it has a 4.375 R&P and a 1.32 3rd/.82 4th, great for zipping around town as a 3-speed and still cruising comfortably at 70+. The 3/4 gap on that one feels like you're driving a 5-speed with no 4th (in fact, it works out almost identical to a Rabbit GTI 5-speed as far as RPM per MPH). With a big enough engine it works well enough, but with a stocker you end up climbing mountain passes in 3rd at 45MPH because it can't pull 4th - with that one, 2750 in 4th is ~4425 in 3rd, a little much for a stocker.

[Plastermaster]

According to Tireracks site a 195/60 turns 858 times per mile. The closest I can come up with using common ratios: 3.44 X .82 = 2420rpm at the engine. This does not take into consideration speedo not being calibrated to your non stock tires. However that is not going to throw it off too much. I doubt you actually have 3.44 rp and a .82 4th, but who knows? 2500 rpm at 6o MPH is very tall gearing however it is arrived at.

I just remembered, if I am correct, wasn't there a bus tranny that used a .72 4th a 4.12 with a .72 would get you close???

Ron

[NextGen]

The weird thing about this is I thought it was normal after at least 13 years with the trans in the car.

Keep in mind my engine is a meek lightly worked 2.0 with concave pistons , 2.0 crank and rods and 1700 heads. Yet it loves speeds above 65. At 85 it starts to feel a bit unconfortable. But I have had it over 100. Not that I like to go above 80 in it, due to the car not being made for those speeds. It is set up as a highway car, dropped frontend, 4 wheel discs, front and rear antisway bars, KYB gas adjust shocks. Handles excellent. But it's not a low slung roadster so I watch out. After wiping out 90 feet of guard rail a telephone pole and a mail box in a 914 I crashed on a mountain. I have learned a few things about staying alive. It took 2 years to build after finding it in a South Bronx heated garage after 8 years of storage.

[Bobby74]

As was hinted at on the final posts... The noise difference is due to the teeth count AND the tooth pitch.

A 1974 and later SSC tranny with stock gearing has VERY fine 3rd and 4th gears. The teeth only engage about 1/8 inch! This is why trans builders use the more coarse early gears. They are much stronger. Later gears run quiet, but I wouldn't use them for more than 100HP.

-Bobby

[Bobby74]

Also, don't mean to bash anyone, but Mikey Locicero isn't known for being the most honest person. He is kinda like Vince, only he's done more for the hobby.