Gearboxes - got to be easier than last discussions

[Ron Earp]

I noticed that early 240z cars had four speeds. My JH is a four speed, and I'm having a hell of a time getting a five speed from anyone.

Does anyone run a four speed? How do they do? My ratios would be horrible I think, but just looking to see if anyone else does it as well? Or, do folks not race the early 4 speeds and do a later model with a 5 speed?

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Ron
http://www.gt40s.com
Lotus Turbo Esprit
BMW E36 M3
RF GT40 Replica
Jensen-Healey: IT prep progressing!

[Geo]

240Zs should only have a 4-speed since that is all they came with. Did the JH (as classified) ever come with a 5-speed?


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George Roffe
Houston, TX
84 944 ITS car under construction
92 ITS Sentra SE-R occasionally borrowed
http://www.nissport.com

[JeffYoung]

yep, in 75

[Geo]

Originally posted by JeffYoung:
yep, in 75

Show me a 75 240Z and I'll show you an illegal car. The 240Z was only produced until 73.

[edit]: Or do you mean the JH? Of so, go ahead and install one!

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George Roffe
Houston, TX
84 944 ITS car under construction
92 ITS Sentra SE-R occasionally borrowed
http://www.nissport.com

[This message has been edited by Geo (edited September 23, 2004).]

[Ron Earp]

The 5 speed JH is definitely legal, I was just wondering if anyone ever ran 4 speed boxes at all, or, rather, were forced to?

R

[Eric Parham]

Not my personal experience, but I understand that 4-speeds are sometimes run for one or more of the following reasons:

1) reduce weight
2) reduce rotating inertia
3) reduce friction
4) reduce cost or complexity
5) take advantage of shift-linkage geometry for 3-4 which is often less awkward than 4-5.

For example, I've heard that some ITC VWs run the 4-speed with a taller R&P instead of the 5-speed with a shorter one and find it quicker at both NHIS and/or Lime Rock. In that particular case, I believe that the 5-speed has the same ratios as the 4, except for a closer 5th tacked on (and an optionally shorter 3rd for the 4-speed).

Keep in mind that we really only use two gears at most tracks, most of the time. So some would say "why lug around the extras?"!

[Ron Earp]

Here is what I have:

4 Speed Ratios Speed Difference
3.12 42.28
1.99 66.29 24.0
1.30 101.87 35.5
1.00 131.92 30.0

5 Speed Ratios Speed Difference
3.37 39.17
2.16 61.07 21.9
1.58 83.49 22.4
1.24 106.30 22.8
1.00 131.92 25.6

The 5 speed is just dang hard to find. Twice I've entered into deals to buy a used one from someone to have it fizzle. I have two four speeds however, and they are reported to be MUCH stronger since they were made by Chysler and served duty in much heavier cars.

What does anyone think about the ratios, henious?

Ron

[This message has been edited by rlearp (edited September 23, 2004).]

[BMW RACER]

Didn't the Jensen-Squeely use a Getrag (same as BMW) at some point?

[JeffYoung]

Yes, that is the '75 model I was referring to above. It had a 5-speed Getrag box that lots of people we talked to said is rather weak.

Ron, looking at those ratios again, it just looks like 2-3 is too long. At VIR, you spend a lot of time accelerating from say 70 to 110 or so. Looks like that is all going to be third gear, and with a peaky four cylinder, you are going to be starting way low on the tach in 3rd.

I know availability is an issue, but I'd go Getrag if you can. Was that box used in a BMW from the mid-70s? If so, maybe you can find and use one.

Jeff

[Ron Earp]

I'll check and find out. Getting a 5 speed from a JH Preservationist is not easy. These are the same people that paid me $114 for two sun visors, remember? Now that "feature" of the JH is NOT working in my favor on a gear box.

Ron

[dickita15]

ron
i would plan to build the car with the 4 speed and keep looking for a deal a 5 speed. the top gear ratios are the same so this will not hold up the build. find out the top speed for a ITS car at the tracks you are going to run and pick you rear end gear from that as low (or high numericaly as possible). it remains to be seen if the power band will be to narrow with this gear box.
when you set your cam timing go for a wide power band
dick patullo

[Knestis]

Take a look at Gear Crasher gear charting software from DaveSport...

http://www.davesport.com/cgi-bin/davesport...t/software.html

It's pretty slick.

K