Syncro shifting, bad?

[GTO]

Last night I was testing out how to downshift smoothly and found (for instance) if I'm cruising at 70KPH in 4th, I leave the accelerator pedal where it is, engage the clutch and smoothly put it into three and release the clutch in one smooth moment I can get completely unnoticeable gear change into 3rd gear.

I’m sure its called “syncro shifting”.

Basically I want to know, if syncro shifting damages a standard WRX gear box?

Spoke to some people and I get conflicting answers, my view is that; that it’s a modern syncro tranny, since there no sudden change of load, no noise, resulting in an unnoticeable shift it should be ok?

Comments please!!!

[blah]

I do the same thing sometimes when i down shift. Usually i just wait for the car to slow down, and just slip it into gear.

[stracing]

i got reports that it hurts your tranny

so i heel toe everytime. or rev the engine to go for the lower gear when i want move a bit quicker.

[mindgam3]

When you put the clutch down, your revs will instantly drop and your crank speed wont be matching your cars speed for that particular gear. When you re-engage the clutch in a lower gear, the engine has to go from next to no revs up to many revs in a relatively short space of time which im guessing could damage the transmission but im not sure. By heel and toeing, you match the engine speed with the transmission speed so there is less of a speed difference when you re-engage the clutch.

[Vansquish]

I think you missed part of the post guys...he said he left the accelerator where it is...in other words, it was partly pressed when he put the clutch in...if that was the case, he was in essence doing the same thing as a heel-and-toe downshift, but merely left out the brake usage. In such a case it doesn't hurt your transmission except for the usual wear and tear of shifting. The more shifts you complete over the lifetime of the car, the more frequently you'll have to replace the clutch and so forth...but even that might last the whole time, my mom's got a V6 manual Ford Contour (mondeo for the rest of the world) and it's got 115,000 miles and has the original clutch.

My understanding of "synchro-shifting" (though it may well be wrong) is that in fact you leave the clutch out of the equation entirely. In a modern vehicle with synchromesh equipped transmission, you can actually upshift and downshift without using the clutch. You merely take the lever, push towards the gear you wish to be in and apply steady but not too heavy pressure. If you do it right and manage to find the right engine speed, the lever will pop right into place after the synchros match the gearbox to the engine speed. THAT is not a good thing to do, as it does do damage, however that doesnt' mean that it's not possible.

[T-Bird]

yes Syncro means that it syncronizes the speeds at the shafts and in essence makes shifting smoother but you still have to use the clutch if you plan on keeping the transmission for a while.

[jon_s]

I always understood synchro-shifting to be the same as Vanquish described.

[T-Bird]

yes that is correct but it's not all there is to the equation you have to use the clutch when you shift unless you want the damn thing to go out on you a few years down the road or sooner if you never use the clutch. when you're hauling down the road you want to use the clutch, you can leave out the clutch but not entirely and not all the time, not using the clutch is like PowerShifting. Most cars that have a manual if not all new have Syncro-Mesh Gear Boxes which makes the shifts smoother and essentially quicker. If you ever drove like a car from the 60's or later you might hear them make some grinding noises when shifting especially really old cars from before the 50's that was because you had to force the teeth to catch eachother.

[mindgam3]

When shifting normally then, would you say u had to depress the clutch fully whilst changing gear? or does it not matter how much you depress the clutch pedal as long as u do so?

[jon_s]

You don't have to fully depress the clutch. Every car is differenct, but when the clutch is disengaged then that is it. One way of finding this point is by driving along at say 30mph on a straight road. slowly depress the clutch and when the revs start to increase is the point when the clutch is out. Learn where this point is (go a little further to be sure) and you can change gear without depressing the clutch all the way.

However, when I am on a track the clutch motion happens so quick that I doubt there is any real advantage over doing the above. again this depends on the car, as mine has a relatively short distance to go through, some cars have a huge motion on the clutch, so then perhaps there is an advantage.

[Vansquish]

You only need to depress the clutch enough so that it "bites". That is the point at which the clutch meshes and the engine and transmission begin operating as a single entity. To shift, you need to go slightly beyond that point so that the two are disconnected for a moment and then let the clutch back out, if you don't do that, you're "synchro-shifting" and in essence forcing the gearchange to occur against the will of the transmission.

[Sachmo12345]

what if i put the clutch in and then rev it up and shift into a lower gear is that basically the same thing

[Vansquish]

yeah, that's just matching revs to the gears...it's perfectly allowable...the only thing you'll end up doing is burning more gas that way hehe.

[mindgam3]

You don't have to fully depress the clutch. Every car is differenct, but when the clutch is disengaged then that is it. One way of finding this point is by driving along at say 30mph on a straight road. slowly depress the clutch and when the revs start to increase is the point when the clutch is out. Learn where this point is (go a little further to be sure) and you can change gear without depressing the clutch all the way.

However, when I am on a track the clutch motion happens so quick that I doubt there is any real advantage over doing the above. again this depends on the car, as mine has a relatively short distance to go through, some cars have a huge motion on the clutch, so then perhaps there is an advantage.

hehe thats what i thought, thanks for confirming that though ;)

[mit5005]

yes that is correct but it's not all there is to the equation you have to use the clutch when you shift unless you want the damn thing to go out on you a few years down the road or sooner if you never use the clutch. when you're hauling down the road you want to use the clutch, you can leave out the clutch but not entirely and not all the time, not using the clutch is like PowerShifting. Most cars that have a manual if not all new have Syncro-Mesh Gear Boxes which makes the shifts smoother and essentially quicker. If you ever drove like a car from the 60's or later you might hear them make some grinding noises when shifting especially really old cars from before the 50's that was because you had to force the teeth to catch eachother.

I have always heard that if you have an old car that doesn't have a synchronized trans, it is best to double clutch. Am I right?

[T-Bird]

yeah it works on an older car but it's not the end of the world if you don't

[SFDMALEX]

Well I dont see how it would be smooth if you just leave the throttle in the same position. Yes it would be smoother then not throtteling at all, but you need to blip the throttle because the next gear will need higher RPM in order to trully syncronyze your shift.

You still hear the engine struggle for few RPMs if you dont blip.

Anyway thats all for competative driving.....

[GTO]

Thanks for comments guys !

Vansquish thanks its exactly the answer(s) I need :)

I was going to practice heel-and-toe downshifting later on but didn't realise that I was doing a derivative of it! :lol:

I googled "synchro-shifting" and got exactly what you said, its no technique I'm not willing to try, prehaps on a rental though :lol:

T-Bird you mentioned PowerShifting, is that aslso called flat shifting? (leaving the gas on during shifting, while the clutch is engauged)?

[blah]

yeah, that's just matching revs to the gears...it's perfectly allowable...the only thing you'll end up doing is burning more gas that way hehe.

This more describes the method i use. I wear shoe size 13 1/2 so heel n toe is alittle difficult to even try to do.

[Vansquish]

LOL...Well you know what they say about guys who wear big shoes right?


(They have big feet)


As for the shifting, glad to be of help hehe, and as for the flat shifting, yeah, that's basically what powershifting is...it can make a significant improvement in acceleration times, but shortens the life of the transmission quite a bit, as in essence you're doing several full throttle clutch drops each time you do it.

[jakaracman]

T-Bird you mentioned PowerShifting, is that aslso called flat shifting? (leaving the gas on during shifting, while the clutch is engauged)?
Exactly. And it doesn't hurt the car (excep the clutch wear a bit until you're shifting fast enough) if you dont do it from 1. to 2. gear, and try to do it at the moment you hit the rev limiter ...

[T-Bird]

T-Bird you mentioned PowerShifting, is that aslso called flat shifting? (leaving the gas on during shifting, while the clutch is engauged)?
Exactly. And it doesn't hurt the car (excep the clutch wear a bit until you're shifting fast enough) if you dont do it from 1. to 2. gear, and try to do it at the moment you hit the rev limiter ...

it CAN hurt the car it can screw up your car if you do it wrong or at the wrong RPM like stated it's essentially dropping the clutch everytime you shift. hell some people don't even use the clutch when they do it either because they don't want to or they forget and that will fuck up your tranny and engine.

[SFDMALEX]

PowerShifting will fuck up your car. No matter how fast you work you the clutch you will still hit the limiter. Hitting the limiter= major wear and tear on the engine.

[Vansquish]

PowerShifting will fuck up your car. No matter how fast you work you the clutch you will still hit the limiter. Hitting the limiter= major wear and tear on the engine.

You won't necessarily bonk into the rev limiter depending on where in the RPM range you make your shift, but it will definetely cause serious clutch and transmission wear any and EVERY time you do it. Like I said before, it is essentially a high RPM clutch drop EVERY time you shift.

[mit5005]

Correct me if I am wrong, but it doesn't seem power shifting would give you an advantage over regular shifting during a race. I mean, you are still disengaging the engine from the drivetrain, so you are still losing power during that time.

[T-Bird]

well although Nascar is a crappy sport they don't even use their Clutches during races they just slam it through the gears and leave it at the top until they pit then they use the clutch and when they speed up again no Clutch maybe other sports use this technique but I doubt it since Nascar is like the only one they go in a circle and still use a Manual.
Why you ask? because they rebuild the tranny after every race.

I must say it's still not as bad as neutral dropping in an Automatic Transmission

[Vansquish]

CART and IRL still use proper clutched manual transmissions without electro-hydraulic operation for the clutch. In order to get going, they do use the clutch, but once on the move, it really isn't necessary...straight-cut gearboxes help in that respect and all that is required for a shift is a throttle lift during the shift in order to help the gears mesh properly. Again, the engine and transmission is rebuilt after every event, so it's certainly not helping with wear-and-tear of the mechanicals.

[mit5005]

Actually, I have seen CART races many times, and you are partly right. But they don't need to do throttle lift because when they shift, the car automatically disengages the trottle so the drivers don't have to do it themselves. And the shifter is like an SMG style gearbox in the E46 M3, you just push forward and back for shifts. It does have a clutch pedal though, which is used for starting up, but the straight cut gears (as you said) allow shifting w/o the pressing the clutch. I wonder if you can get straight cut gears in a streetable car. :?: That would be fun.

[T-Bird]

you can get them for like muscle cars and stuff they call them powerglides you just slam it forward through the gears and back to downshift. but you have to push it into eachgear it's not an Electronic thing.

[mit5005]

Yea the powerglide is a Chevy 2 speed automatic transmission but you do have to shift it yourself. A lot of drag racers use that transmission. My dad was thinkin of getting one for our 69 mach 1 drag car, but I don't like the idea of chevy parts in our Ford.

[T-Bird]

get a B&M powerglide they have them with more gears now and they don't say Chevy anywhere on them :wink:
Like the Chevy guys using Ford 9 inchers on their cars.

[mit5005]

get a B&M powerglide they have them with more gears now and they don't say Chevy anywhere on them :wink:
Like the Chevy guys using Ford 9 inchers on their cars.

I haven't heard of those yet. Definitely something I have to look up. I mean our C6 is good but it soaks up more hp than a powerglide does.

[T-Bird]

Yeah B&M makes some good shit, sadly their website is somewhat vaque on some details.

[SFDMALEX]

Correct me if I am wrong, but it doesn't seem power shifting would give you an advantage over regular shifting during a race. I mean, you are still disengaging the engine from the drivetrain, so you are still losing power during that time.

Power shifting is this:

Your in 3rd at the redline or what ever. You shift to 4th just by pressing the clutch and moving the gear lever to the right slot with your foot FLAT on the thottle.

During the time that tranny is disconected from the engine with your foot on the floor your engine will hit the limiter and bounce. Hitting the limiter is not healthy.

In a race drivers have a very different strategy. They never rev the engine high. They have good 500rpm in reserver because if they drove a 3 hour race at the redline the engine would blow up after an hour or so. Im talking FIA GT here. So going to the redline while powershifting has zero advantages.


Lastly power shifting has no real advantage. If you properly lift you will change gear faster. If you would try to power shift on a non syncro transmission you would never change gear.

When you shift you up, the revs required for the next gear are lower then the gear that you are in. Depending on the gearing, but usualy in a race car(GT) lets say 3rd and 2nd are very close together. So if you want to shift from 2nd to 3rd you will theoreticaly need to drop about 800rpm from the redline in order to get the next gear up. That gear being 3rd if you are switching from 2nd.

The bottom line is that power shifting has zero advantages. Its just a fast way for inexperianced drivers(ricers) to switch gears fast on a syncro 'box.

[Vansquish]

SFDMALEX wrote:

The bottom line is that power shifting has zero advantages. Its just a fast way for inexperianced drivers(ricers) to switch gears fast on a syncro 'box.


That's not entirely true actually...consider a standing start acceleration run...in order to get the best off-the-line performance, you don't drop the clutch from the highest point in the rev range, nor do you normally accelerate from idle speed...then consider what would happen if you didn't have a flywheel on the engine, so when you pressed the clutch on a one-two upshift, the revs fell to idle speed...then you popped the gear in place and started running again...not the fastest way to go.

I'm trying to explain what I'm thinking, but having a little trouble expressing myself hehe.

Basically when you do a flat shift (powershift...etc...whatever you wish to call it) you're dropping the clutch from the redline each time you change gears...the difference between this and a standing start, redline-clutch drop is that the tires in effect have more grip...so that extra torque and power that is generally available higher in the rev range tries to act on the drive mechanism for the car. It DOES increase performance in acceleration tests because even if that extra power mostly goes to waste, some of it does find its way to the ground.

The best example of this in action is something I read a few years ago in Motortrend (I think it was MT at any rate it was some American auto mag). They had been testing the 405bhp Corvette ZR1 and couldn't get beyond the 5-secoind barrier in 0-60mph performance tests and Chevy had quoted the time as 4.9 or 4.7 or something like that. MT called Chevy, Chevy subsequently sent a test driver out and he "showed them how". He flat shifted each shift, and sure enough, the times were right on par with what the Corvette was claimed to be able to do.

In other words, flat-shifting does work, it can improve performance times, but it is severely detrimental to the internals of the engine and transmission, not to mention the rest of the drivetrain.

[SFDMALEX]

I agree with you. But I still think that a lighting fast lift (one we cant do :lol: ) will change gear faster then a flat shift. Just because of the fact that the next gear need lower rpm.

[coombsie66]

^^ Dude, actuall shift time has nothing to do with whether its a flat shift, or if you are lifting to rev match for the next ratio, the shift time is the time that the positive drive through the drivetrain is disengaged, flat shifting will cause the clutch to slip when you change gear into the next ratio, untill the revs are at the applicable level for that next gear ratio, so by flat shifting, you are actually transfering the increased inertia of the flywheel and engine parts (that are being overrevved compared to the gear that you have changed into) to the road, via the slippage of the clutch. So there is no difference in 'shift time' between a flat shift or normal shift if the clutch is disengaged for the same amount of time!
Flat shifting (as has been said does increase acceleration) and the FIA GT porsches sit on the friggin limiter all day long! They were on the limiters at the start of the LEMANS 24 hrs!!!!! They are so reliable they can withstand slamming the rev and pit lane speed limiter all the time.

And, the nascars and other racecars speculated about do clutchless gearchanges due to them having dog box's theh synchro's have massive teeth compared to the smaller road car syncros. This is why the race car boxes are soo noisy when they are idling or searching for 1st gear in the pits!

[SFDMALEX]

coombsie66- In FIA GT they dont flat shift :wink: All cars(most) are equiped with software that lifts for them. All they do is keep their foot flat. Some of the cheaper teams have a switch on their gear lever to cut the throttle when they shift.

And being on the subject of fast shifts you would think that in F1 they want to achieve the fastestest shifts no? Well tell me one time when you dont hear the throttle lifting when they upshift :wink:

[Vansquish]

As far as the rev-limiter is concerned, the reason it's in place is to prevent engine damage, so in all likelihood, if you're sitting on the limiter all day, you'll likely end up with a perfectly serviceable engine at the end of the day, the only problem is that because of the higher engine speeds there's just a bit more wear and tear associated with it. Overrevving is something that is far more dangerous, as at that point you're actually approaching the physical limits of the engine internals.

[coombsie66]

coombsie66- In FIA GT they dont flat shift :wink: All cars(most) are equiped with software that lifts for them. All they do is keep their foot flat. Some of the cheaper teams have a switch on their gear lever to cut the throttle when they shift.

And being on the subject of fast shifts you would think that in F1 they want to achieve the fastestest shifts no? Well tell me one time when you dont hear the throttle lifting when they upshift :wink:

In the FIA morgan its a dog box, so you lift as you change gear, without use of the clutch (on the way up). And yes most have software that 'lifts' for them, but this is all integrated into what are pretty much automated sequential boxes (or are in the porsche GT3 RSR's i have seen).
And how are you gunna hear if the throttle is lifted in an F1 car!? They: 1. have such low mass flywheels/clutch etc that you wouldnt hear wether there was a lift, or that was the engine just being slowed to the speed relevent to the new rato.
2. Are pretty much a completely different ball game compared to the normal shifting debate we are having here.

All i am saying is that shift 'speed' is surely just the amount of time that the clutch is disengaged juring the shift, which is mutually exclusive from wether the shift is being done with the throttle flat or with a lift!?!
And yes flat shifting is detrimental to the longevity of the vehicles drivetrain, but u have to admit it increases the acceleration of the vehicle!?!?! :|