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"K-Roll-PorscheTamer" (k-roll390) 05/08/2018 at 11:35 • Filed to: 931Lyfe, Project Car

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Making progress every week! My friend and I dialed in the ignition timing and changed the trans fluid this weekend. We took it around the block, and learned quite a few things about the car’s condition.

Let’s talk about the exhaust note first. It’s strange to me. The sound is not only better than any 944, with a more mechanical and airy sound reminiscent of older aircooled VWs and Porsches (despite being an inline water cooled engine), the turbo spool over 3000rpm is just something truly special! 

The G31 gearbox (nicknamed “snailshell”) is reportedly the strongest of all the transaxle gearboxes, used with different modifications in 924 Turbo (1979-1980 only)/Carrera GT/GTS/GTR/GTP. With a dogleg shift pattern, it has true racing pedigree, and was used in the aforementioned racecars. Unlike the later Turbo (1981-up) models that switched to the transmission that would become standard in the 944 with cone-type synchros that can handle quick shifts and speed shifting, the G31 uses Porsche’s balk ring synchros; which required and still requires slow shifting and any speed shifting results in premature wear and eventual gear grinding. Now I don’t understand the difference between cone and balk ring style synchros but the point is that those are the Achillies Heel in any Porsche gearbox with the latter.

With the trans fluid change, mine doesn’t grind as bad as previous attempts to move it but double clutching is mandatory for upshifts and downshifts, lest I truly wanna rebuild the thing right now.

Also discovered the front suspension is in desperate need of refreshing(struts, mounts, and bushings), so that’s the next project on schedule. In the meantime while waiting for parts, I’ll continue to work on the interior.

Nibby > K-Roll-PorscheTamer 05/08/2018 at 11:46

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can you make a recording of how it sounds driving around?

K-Roll-PorscheTamer > Nibby 05/08/2018 at 11:52

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I can try but I’d need a second person to hold a camera outside.

RamblinRover Luxury-Yacht > K-Roll-PorscheTamer 05/08/2018 at 11:53

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I believe it’s like this:

Interdasting. Both this and a simple ring type have a brass or similar cone clutch, but the simple ring type would (I think) not have the pre-positioning piece with the posts to do “pre-synchronization”. Since a simple ring synchro can just get bashed harder and seize quicker, it’s good for quick shifts, but this setup would be better for deliberate shifts of heavy gears that the rings would wear out faster with. The disadvantage being if you bash it, the blocker ring has to do all the synchronization and gets beaten to death.

random001 > K-Roll-PorscheTamer 05/08/2018 at 12:00

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I love your work.

Captain of the Enterprise > K-Roll-PorscheTamer 05/08/2018 at 12:36

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Cool! Sounds like it’s really coming around!

K-Roll-PorscheTamer > RamblinRover Luxury-Yacht 05/08/2018 at 13:44

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I’m still not very keen on the concept of synchros....I have no idea how they do what they do, other than knowing that it works.

RamblinRover Luxury-Yacht > K-Roll-PorscheTamer 05/08/2018 at 14:09

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Think of it as being like a stapler. You close a stapler on the two pieces of paper, then close it the extra step that pushes the staple. The synchro step is like pushing the two pieces of paper together, the “lock” step is like pushing a staple through both of them. For this to work, there have to be two parts to the motion, and the “middle” part of the system (like the lower bar of the stapler) has to move first, then stop while something moves past.

I was lucky - I got to tear down a Land Rover Series gearbox that had a big brass synchro in it and play with it with my hands. One of these:

The selector pushes the whole thing, making the spring clips push the brass cones against some steel cones... then, with a “pop”, the center assembly jumps forward and locks in its teeth. It was a great visual/tactile aid.

MM54 > K-Roll-PorscheTamer 05/08/2018 at 17:53

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Take a bottle and a tapered cork. Your hand is the gear slider (effectively the input) and the bottle is the output gear. The cork is a synchro. Twist the cork while pushing it into the opening of the bottle. You’ve just simulated a (cone) synchro.