Power shifting??

[onsse]

Hello,

Been searching this topic, but couldn't find any.

Does anyone know what it is or have they tried it??

This guy I was talking to last weekend was telling me that its when the car's RPM hit a certain point that you just shift it with out engaging or disengaging the clutch. Its suppose to cut the shifting momentum, to maximize speed.

was i just fed bs?

~onsse

[Jack Olsen]

You were given a technique that is not good for a 915 transaxle.

[Jim Sims]

"you just shift it with out engaging or disengaging the clutch."

Try it and report back the cost of your transmission repairs in $100's ($1000's?).

[Zeke]

Has this guy ever driven a 911? I think some trannys with straight cut gears might go thru one or two shifts w/o lifting the gas pedal, but if you happened to not make the next gear, forget the cost of the tranny. The bent valves and rods would set you back several trannys worth.

[livi]

I suppose when you hit those EXACT revs......once every thousand gear changes..

[stevej37]

I have always understood "power shifting" to mean upshifting without releasing the gas pedal. Motorcycle..ok, but I would never do it with a Porsche.

[porsche930dude]

i usto shift my nissan 240sx all the time without using the clutch. just gotta match the revs. A couple times my clutch hydraulic system failed and i had to drive without it to get home Of couse that was a jap tranny. I wouldnt do it with a porsche. i doubt my 915 would allow it. And its definatly not really possible to do under hard exelleration. you have to coast and give it time to go in. Its probrobly possible at speed but it would take one hell of a driver

[fastfredracing]

I used to do it all the time in my vw bus, that transmission lasted just short of 6 months, but my buddies always got a kick out of it. I would'nt try it in a 915. Leave that for the gung ho ,he man muscle car guys. I cant imagine that it would be good for any trans.

[cab83_750]

Originally posted by porsche930dude
i... just gotta match the revs.....

I always wondered what this meant! Can someone explain?

Thanks.


BTW, lately what I have noticed is that I get smoother shifting into ANY gear if my RPM is higher than the regular 1K RPM range. I have been experimenting since I think I can afford to break the tranny. Why can I afford the rebuild?......I learned to rebuild mine thanks to this board.

[H20911]

It is not a toyota as far as shifting goes. The technogy is dated and if you want to make it last expect your shifts to take 1-2 seconds. I would suspect that you are going to be replacing that 2nd synco very soon.

[Walter_Middie]

Stevej37 has it right. Power shifting is shifting without lifting off the throttle. The clutch is still used, you just don't lift off the gas. This is a drag racing technique used on cars with strong transmissions and rear ends. When shifting from 1st to 2nd, you pre-load the gear shift lever in 1st gear by pulling back on it. The engine torque will help hold it in 1st until the clutch is just stabbed quickly, then the gear shift lever will move quickly to 2nd - you never lift off the throttle, and the clutch is only engaged momentarily. This is difficult to do if you have any sense of mechanical sympathy.

[williecoyote]

I used to do it occaisionally in my '68 911L when on a Sunday cruise. You match the revs, and she'd slide right in to gear, as long as you're not in a hurry. That car had the 901 transmission. Tried it once in my Carrera with the 915, never again, too much grinding!
I had a friend who drove his MG Midget from Raleigh, NC to Palm Springs, Ca. He lost the clutch in Albuquerqe,NM. From that point on, he would try to keep the car rolling, so that he wouldn't come to a dead stop. If the situation arose though, he would put the car in first gear, and hit the starter.

[WolfeMacleod]

I had to drive this way for several miles a couple weeks ago, when the rubber centered clutch in my 924S went kaput.

Haven't done it for years.

[rnln]

Shift without clutch? at a certain RPM, yes, not too lowed and not too high. I never done it at normal driving but when you clutch, or slave is out, it's good to know.

[trader220]

Did the guy who was talling you about it have a mullit and his car on blocks on his front lawn?

[porschefool]

Used to do it all the time in my '75 X1/9.
Thought it was cool, and when the clutch finally went out (Surprise)
it was no prob getting back home

[Dantilla]

Shifting without the clutch is not the same as power shifting!

Shifting w/o clutch is relatively easy. Just match revs. Power shifting is at full throttle. You don't match revs at full throttle.


Two different things being discussed here. Neither one of them will insure long life of a 915 tranny.

[Quicksilver]

The only magic speed where you can slam a transmission from one gear to another is zero. At a dead stop with the engine off it works fine. The reason for different gears is because you want the engine to turn at different speeds. This supposed version of powershifting is a wives tale.

- Powershifting
As mentioned earlier powershifting is actually a technique where you leave your foot mashed to the floor on the gas while running the car through the gears while using the clutch. You need to have extremely fast syncros and/or a heavier flywheel to do this. You should also know that you are going to consume parts if you do this. You might see this in stock class drag racing where they are only going to run for a few seconds and they are used to breaking things.

-Syncroshifting
Doing this really depends on the transmission and how positive the syncros are. You do not ever want to try this with the 915's syncros. This is something for a trans with cone style (Borg Warner) syncros. The G50 has rather weak syncros for the mass of its rotating assembly so it isn't a very good candidate for syncro shifting. (that is why even a 76 Corolla will shift faster then a G50...)

Here is how it works...
Your ear knows how much the note of an engine will drop when you up shift. You take your foot off the gas enough to remove the load from the transmission so it will slip easily out of gear. You then let the rpms drop to about the point where your ear tells you the next gear should be. As you approach the correct speed you start to lightly press the shifter into the next gear. This will start to engage the syncro. (It is basically a metallic cone clutch) Because the speed isn't matched the syncro will be rotated slightly so the teeth on the syncro won't line up with the splines on the slider that actually engages the gears. Once the speed actually matches the syncro will twist around and when its teeth are aligned it will all slide together smoothly. If you can look inside a transmission it makes sense. It is kind of hard to describe with just words.

If you are good at it you can shift some transmissions like this almost forever without any damage. If you are bad at it you can spend some money! On the G50 because of the weak syncros you should only do this in an emergency and at low RPMs. Last fall I drove my 87 home from the track when the clutch pedal linkage failed. You start it in gear and shift it below 2200 rpm. When you come to a light you slide it out of gear, stop the car, and kill the motor so you can put it in first and be ready start it when the light turns green. It is the hardest car to syncro shift I have ever driven.

I had an old race car that I drove on the street that had a Muncie 4 speed in it with slotted syncros that I syncro shifted at least 20% of the time. It never had a problem for the 80,000 miles I had it. I even drove it for 2 weeks in stop and go freeway traffic with no clutch linkage at all. (very young and had no money for repairs Plus it always started on the first crank...)

It is a good technique to learn but I would never learn it in a Porsche. Go find an old Corolla.

[snbush67]

It's only to be used on rentals. Best on m-tangs.

[masraum]

Originally posted by Quicksilver

-Syncroshifting
The G50 has rather weak syncros for the mass of its rotating assembly so it isn't a very good candidate for syncro shifting. (that is why even a 76 Corolla will shift faster then a G50...)


If you are good at it you can shift some transmissions like this almost forever without any damage. If you are bad at it you can spend some money! On the G50 because of the weak syncros you should only do this in an emergency and at low RPMs. Last fall I drove my 87 home from the track when the clutch pedal linkage failed. You start it in gear and shift it below 2200 rpm. When you come to a light you slide it out of gear, stop the car, and kill the motor so you can put it in first and be ready start it when the light turns green. It is the hardest car to syncro shift I have ever driven.

Must specifically be your tranny. The G50 is considered pretty much bulletproof. In my '88 I once had the slave cyl go out across town ~40 miles. I drove home without the clutch and ended up stuck in about 2 miles of stop and go traffic on the highway due to construction. I drove home the whole way with no clutch and never shifted as low as 2200. Probably more like 3500 or 4000. Then, same car about 2 years later had one of the ears that held the clutch for shaft snap off on the way to work on morning. I finished driving to work (20 miles) and then drove home from work (30 miles) without the clutch. I thought the G50 was one of the easiest cars to shift with no clutch. I was up and downshifting. I was on a toll road, so if I downshifted to 1st I could idle through the toll booths with exact change and didn't have to come to a complete stop.

I'd think that what you said about the G50 more applies to the 915.