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 Post subject: porsche 356 transmission
PostPosted: Tue Jun 05, 2018 5:15 pm 
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Joined: Mon May 14, 2018 3:58 pm
Posts: 5
hi all,
can someone tell me if the transmission ( 741 c/2) that is in my cabrio 356 C 1965 is the same that the one in a 356 SC of the same year
Reason for this question is that the 356 C has 75 HP,the SC 90 or 95 HP and if i drive long and fast on the highway the RPM is approx 3500 to 3700
which is high and Noisy ( in fact a 5 th gear is missing…) So is the 4 th gear " engrenage" different in the 356 C from the 356 SC .
in adding 20 to 25 HP did porsche also produce a more adapted transmission?
thanks if somebody knows
michel pitteloud geneva


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PostPosted: Tue Jun 05, 2018 6:06 pm 
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Joined: Tue May 31, 2011 10:07 pm
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Location: VT
Gear ratio's changed but I think all final drives are 1:1. There are different OD gear sets available (taller 4th gear), but obviously require complete teardown to install.

I would hate to lose the original 3-4 ratio, but with traffic cruising 80MPH these days, I would seriously consider going with a taller 4th gear if I plan to be driving long distance often (which I do).


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PostPosted: Tue Jun 05, 2018 7:36 pm 
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Location: Santa Monica, CA
Tom Conway of Carquip in Colorado used to sell a taller fourth gear. He probably still does.

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PostPosted: Tue Jun 05, 2018 7:54 pm 
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And Tom Conway gets his tall 4th gear from: 356 Enterprises!
But that is not what Pitteloud asked. The transmissions were geared the same for C and SC. In the USA, 4D, overseas, 4C.
And the final drive ratio is 4.43:1, not 1:1.

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PostPosted: Tue Jun 05, 2018 7:58 pm 
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Thanks for the info Vic! Who makes them for you?

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PostPosted: Tue Jun 05, 2018 8:11 pm 
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Joined: Fri Oct 23, 2009 7:24 pm
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Location: 30MI WEST OF PHILA
Trick question....how much lower rpm does a 912 5-speed run at 60mph than a 4-speed 912 or a US spec 356 at the same speed?

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PostPosted: Tue Jun 05, 2018 8:15 pm 
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Edwin: they are made here in Michigan.
Cliff; the same.

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PostPosted: Tue Jun 05, 2018 8:34 pm 
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Location: 30MI WEST OF PHILA
Vic Skirmants wrote:
Cliff; the same.
We have a winner!!!!! If you guys want quiet start collecting Rolls Royces. Porsches are sporting thoroughbreds that should be kept "on the boil".

Ok, I put a 10% taller ring and pinion in the 2133cc car to quiet it down a little without losing the nice spacing of the gears. I don't know if that would be a good idea for the average engine though. I do like the C forth gear as an alternative for most engines. The crazy tall 4th is not a good idea for everybody due to the big 3/4 gap. Different horses for different courses.

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PostPosted: Wed Jun 06, 2018 8:13 am 
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+1 on the "c" 4th gear.


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PostPosted: Wed Jun 06, 2018 3:11 pm 
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thanks to all of you for your replies
as i am planning to put more poweful engine in my car (approx120 to 140 HP) i ll probably study carefully to change the 4 th gear
bye
michel


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PostPosted: Wed Jun 06, 2018 3:30 pm 
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If you realty plan to increase the power to 140hp the tranny will not last to long rebuilt or not


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PostPosted: Wed Jun 06, 2018 6:49 pm 
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The trans will handle that; no problem. We put 165 through the race trannys; no problem.

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PostPosted: Thu Jun 07, 2018 9:03 am 
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Thanks for the info Vic


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PostPosted: Sun Jun 10, 2018 11:39 am 
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+1 to Vic. We have run several 150+HP Carrera 2 and 904 engines in 356's with no transmission issues.

Another +1 on the 4C gear. I changed the 4D to a 4C in my daily driver 356SC coupe with big bore kit. Great highway cruiser and better fuel mileage with no loss of drivability. The guy I sold my car to complemented the tall gear as well.


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PostPosted: Sun Jun 10, 2018 9:10 pm 
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If my gearbox ever goes apart I plan on doing the taller 4th gear. Long drives at high RPMS isn't as fun as it sounds.


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