porsche 356 transmission

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pitteloud michel
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porsche 356 transmission

#1 Post by pitteloud michel » Tue Jun 05, 2018 5:15 pm

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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Re: porsche 356 transmission

#2 Post by M Penta » Tue Jun 05, 2018 6:06 pm

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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Re: porsche 356 transmission

#3 Post by Edwin Ek » Tue Jun 05, 2018 7:36 pm

Tom Conway of Carquip in Colorado used to sell a taller fourth gear. He probably still does.
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Vic Skirmants
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Re: porsche 356 transmission

#4 Post by Vic Skirmants » Tue Jun 05, 2018 7:54 pm

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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Re: porsche 356 transmission

#5 Post by Edwin Ek » Tue Jun 05, 2018 7:58 pm

Thanks for the info Vic! Who makes them for you?
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C J Murray
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Re: porsche 356 transmission

#6 Post by C J Murray » Tue Jun 05, 2018 8:11 pm

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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Vic Skirmants
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Re: porsche 356 transmission

#7 Post by Vic Skirmants » Tue Jun 05, 2018 8:15 pm

Edwin: they are made here in Michigan.
Cliff; the same.

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Re: porsche 356 transmission

#8 Post by C J Murray » Tue Jun 05, 2018 8:34 pm

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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Re: porsche 356 transmission

#9 Post by DonCichocki » Wed Jun 06, 2018 8:13 am

+1 on the "c" 4th gear.

pitteloud michel
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Re: porsche 356 transmission

#10 Post by pitteloud michel » Wed Jun 06, 2018 3:11 pm

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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Thomas Sottile
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Re: porsche 356 transmission

#11 Post by Thomas Sottile » Wed Jun 06, 2018 3:30 pm

If you realty plan to increase the power to 140hp the tranny will not last to long rebuilt or not

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Vic Skirmants
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Re: porsche 356 transmission

#12 Post by Vic Skirmants » Wed Jun 06, 2018 6:49 pm

The trans will handle that; no problem. We put 165 through the race trannys; no problem.

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Thomas Sottile
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Re: porsche 356 transmission

#13 Post by Thomas Sottile » Thu Jun 07, 2018 9:03 am

Thanks for the info Vic

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Re: porsche 356 transmission

#14 Post by Jeff Adams » Sun Jun 10, 2018 11:39 am

+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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Re: porsche 356 transmission

#15 Post by Adam Wright » Sun Jun 10, 2018 9:10 pm

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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