914-4 vs 914-6 gear ratios

[jtf914]

I know we have exhausted the tailshifter/sideshifter conversion questions on this board, but I couldn't find an answer to this in the archives.

Is the gear ratio different for a factory -6 vs -4?

I am starting to collect parts for a sideshift conversion, and I was wondering if the gear ratio was different between the -6 and the -4. Basically, am I better off converting my tailshifter to a sideshift and maintaining the current gear ratio, or should I just use a complete sideshift unit because the gear ratio is pretty much the same?

I know the complete switch is easier; I'm just trying to weigh all my options before I start buying parts.

Thanks,
Justin

[Joe Bob]

Yes, the /6 trans gear ratioss are different from the /4 transmissions.

The /4 trans are the same no matter if they are original side shifter or tail shifter. BTW, you can take a good tail shifter trans and convert it to a side shifter. It involves parts from the side shifter and they can be transplanted, then you can use it in a side shifter car 73 and up.....or on an early car that has all the side shifter linkage in the interior, tunnel and engine mount where the bar goes thru the hole in the engine mount.....

[red-beard]

First, the ratios:

914-4 914-6
11:34 11:34 1st
18:34 18:32 2nd
23:29 23:28 3rd
27:25 27:25 4th
31:22 29:22 5th
ring and pinion gear: 7:32 (Same on both)

If you notice, they are not _that_ different. Plenty of people do the six conversion everyday and keep their original tranny. It is certainly easier to switch trannies than to rebuild one (I'm rebuilding an original 6 tranny right now!).

But, if you're going to do the conversion, you need everything! The shift console, all the linkages and rods and the tranny. You will need to "straigthen" the shift rod. A recent post on trannies has pictures of someone cutting and welding in a straight peice on the shift rod so it doesn't hit the heat exchangers on the 6.

If you don't change the shift console, your car will end up like my 1971 914-4, which has the shift pattern mirrored (5th&4th are where Rev&1st should be!).

James

[Jim Chambers]

2nd, 3rd and 5th are different. Go to http://members.rennlist.com/chuxter/901&915ratios.htm
for more very exact specs. including the letter designations for the various gear options.

[Dave at Pelican Parts]

According to Jon Lowe, PCA's 914 Tech expert, you do not want to run 914-4 gears in a 914-6. The -4 top gear is too tall, and the -6 will not turn enough revs at standard freeway speeds. This can evidently lead to overheating because the fan pumps less air at lower RPMs than at higher ones.

No experience with it myself, just passing along Jon's past comments.

--DD

[jtf914]

Thanks guys, this is exactly what I was looking for.

Justin

[J P Stein]

What Jon Lowe says is undoubtly true for a stock 914/6. For non CW usage, shorter tires take care of the low rpms problem when using a 4 trans....throws the speedo into disaray, however.
I run about 3200 rpms @ 65 mph using 225 X 50 X 15s.

We perversion......er.... conversion types don't have to worry bout originality, thank God. There are a whole pee pot full of tricks
to keep a 911 motor cool in a 914. Under 160 hp (or so), all are either cheep or free. Above 160 hp, the price of "cool" goes up.