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Change gear ratio?

 
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After_Thought  



Joined: 08 Oct 2019
Posts: 30
Location: Hudson ohio

PostPosted: Sat Nov 28, 2020 2:16 pm    Post subject: Change gear ratio? Reply with quote

Hello, I own a 1977 porsche 924 that I've pretty much been restoring at this point. Everything under the hood has been replaced in preparation for a road trip across america next summer with a few other transaxle's.

My problem is I am the only one with a 4 speed. And sitting at 60+mph (3200rpm+) on a long road trip scares me.

I have looked a little bit into a 5 speed swap. Right now my research indicates a 1980-1982 5 speed 924 transaxle should bolt right into my car. (If I am wrong about that please let me know), this right now seems very expensive, I have to find a transaxle and then also manage to get it here to ohio.

Has anyone ever tried to change 4th gear on there 4 speed to make it more highway friendly? (Is this even possible on these cars?) If I could just take my transmission to a shop and have them but in a different 4th gear that seems like it would be the cheapest option.

Any advice on my situation would be absolutely wonderful and I thank you in advance for your help. [/list]
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Cédric  



Joined: 27 Aug 2004
Posts: 2073
Location: Sweden

PostPosted: Sat Nov 28, 2020 7:09 pm    Post subject: Reply with quote

The 5spd is an easy swap, and easily the best performance upgrade. However gearing on the top will be about the same, the gears are just tighter packed.

Either a 944 box (lots of fiddling since it have a different input shaft diameter) or put on some really large diameter wheels.
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 2102
Location: Somerset, UK

PostPosted: Sat Nov 28, 2020 7:20 pm    Post subject: Reply with quote

I sit at 3-3500rpm in a turbo for all my highway trips short or long. No problem. Being a dogleg 5 speed it’s a lot quicker than 60mph
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1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
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safe  



Joined: 18 Mar 2017
Posts: 210
Location: Sweden

PostPosted: Sun Nov 29, 2020 12:13 am    Post subject: Reply with quote

The 5 speed is better, but don't let the slightly higher rpm scare you. Its a German car they are made to endure extended high speed journeys on the autobahn.
Cruising at 4000+ is not a problem, assuming that the engine is well maintained, fuel injection is working well, the radiator and hoses, water pump and cam belt. But i wouldn't take it on any longer trips at all if those things weren't up to snuff.
You will probably get a bit better fuel mileage to at 4000.
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Porsche 924 -79 NA, under EFI and turbo conversion
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scm924s  



Joined: 22 Oct 2010
Posts: 229
Location: Gloucester UK

PostPosted: Sun Nov 29, 2020 1:38 am    Post subject: Reply with quote

I had no worries on my 4 speed Martini on motorway cruising at 70mph, but this wouldn't be doing the long distances you envisage.

Contrary to what has been posted above, I believe the 5 speed box 5th gear is higher than the direct drive of the 4 speed so top gear revs should be slightly lower.

There are variations on the final drive gearing over the years and this may be a solution

http://www.924.org/techsection/PorscheTrans1.PDF
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1984 n/a Ruby Red Metallic
1988 924S Guards red- sold
1986 924S Guards Red - sold
1984 n/a Black - sold
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1980 n/a Le Mans#2- sold
1977 Martini - sold
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