'86 carrera gear different gear ratios?

lvporschepilot · 12-10-2005, 08:00 AM

Hey everyone,

I noticed some time ago that my '86 goes quite a bit faster in each gear than in earlier 915 carrera's I have driven. For instance: 1st gear goes to 41 mph, 2nd to 72 mph, 3rd to 101mph while 4th and 5th remain the same as other 915 carrera's. I am using the correct tires and I am positive nothing is broken. Is this common with late '86 carrera's or with all '86's? Is my car a freak of nature? Many thanks.

John

Bill Verburg · Bill Verburg's Garage

If by earlier you mean '74 or earlier 911, then you are not imagining anything.

the internal ratios are a little different but the major chage was from 7:31 to 8:31 final drive.

That, accompanied by slightly taller tires accounts for most of the difference.

Early cars compensated for a lack of engine torque, w/ gearing.

Newer cars that are set up for track use will also generally have lower closer internal ratios but retain the taller final drive for strength.

lvporschepilot · 12-10-2005, 03:44 PM

I understand why the early cars needed different gearing for their lack of torque. I am asking why my car will do 72 mph in 2nd gear @ 6200rpm when another carrera I drove ('84) not to mention magazines I have read show 2nd gear @6200 rpm only being 67 mph. I am baffled. I have the correct size tires(bone stock) and all my instruments are fully functional. Is this just a 1986 quirck or is my tranny just different?

Bill Verburg · Bill Verburg's Garage

Here are the theoretical speeds in gears for a US Carrera w/ 25" rear tires and stock gearing @6200
37 67 94 119 150

makaio · 12-10-2005, 04:06 PM

It could be like my 86 and just have an overly optimistic speedo.

lvporschepilot · 12-10-2005, 04:14 PM

thanks very much bill. most appreciated! I am going to measure the circ. of my tires later just for kicks( not too mention it will be Sunday and I will have nadda to do).

porschenut · 12-10-2005, 05:40 PM

I don't think the tire diameter enters into it, does it? The issue is that your speedo reads 72 in 2nd gear when the book says it should read 67. The speedo sensor is in the transmission IIRC.

Aside from that, it's well known that 911 speedometers weren't even accurate when new, much less when 20 years old. Yours is just a little out of adjustment, like everyone else's.

nhromyak · nhromyak's Garage

As I recall...

'86 has the G50 transmission.

<= '85 has the 915 transmission.

I have noticed the gear differences with my friend's '86 too.

tonythetarga · 12-11-2005, 04:57 AM

negative. The 86 has a 915 and the speedo's generally display 5mph faster than the car is actually going. I had a couple of 86's and they were the same. I am sure it isn't restricted to the 86's either, the 911 speedo's were just not that accurate.
(G50 started in 87)