DlaxMan3

I have two questions what is speed shifting vd normal shifting and how is it done, and also what is rev matching and how is this done.

spork

speed shifting i'm not familiar with but if i'm not mistaken rev matching is when u bring up the engine to a certain rpm before releasing the clutch. for example if u're going at say 30 miles per hour. Say 30 in third gear is at 2500 rpm. So you're going 30 on second gear and u switch to third.

When you push the clutch down your rpms fall to say 1000 rpm. You shift to third but before u release the clutch you rev up to 2500 rpm then release the clutch. Voila smooth shift. If you don't rev match then your car will give a jerk (how big of a jerk depends on how off your revs are) as the gears match up. So being able to rev match well entails knowing what revs your car is at at each gear and speed. Btw I made up those numbers. I don't remember what revs the car is at for 30mph on 2nd or 3rd gear. I'm not too good at it yet.

If you can rev match well, your manual transmission can be even smoother than automatics. If I got rev matching wrong correct me.

Pkskull77

Speed Shifting could mean a lot of things; I will let someone who knows exactly what you mean handle this part of the question.

Rev Matching is used when you downshift; it helps save wear and tear on your clutch. Although frequent downshifting is not really necessary, when the situation calls for a downshift you should match. Here is a brief technical explanation behind the technique; when you depress the clutch and get off the gas, the engine and the axel will start spinning at different rates. The further apart the speed of their rotation gets the worse the wear on your clutch. Your goal is to get them spinning at the same speed, thus making the shift smoother.

Here is how it's performed. Let’s say you’re on a Highway in 6th gear, and you need to reduce speed to get off the road, but you don't want to come to a complete stop. You would slowly decelerate until you got to about 48 mph, at that point you would depress the clutch, and put the car in 5th. Before letting up the clutch you would rev the engine to about 2,500 RPM’s. Then you would let the clutch go. If you get it right the shift should feel smooth, and the RPM’s should not jump up or down, instead they should stay the same for a second and then slowly decrease. You would repeat this through each gear until you reached the appropriate speed and gear. This is one of the hardest things to learn, a whole lot of trial and error involved.

If you you reverse the shift points in the manual you can usually get a smooth shift with 2,000 RPM's, the exception being between 6 and 5, I usually find you need closer to 2,500. Prehaps someone could give a more robust discription of the ideal RPM's for each gear. However this is difficult because the RPM's are proportional to your speed and gear. So perhaps trial and error is the best teacher.

mysql101

Nothing wrong with what you're saying, but if I was in 6th, doing lets say 70 mph at around 4000 rpm, and needed to slow down, I'd clutch, rev up to around 65000 rpm, flick it into 4th gear, let off the clutch in a swift motion and feel it out until the revs matched (increasing or decreasing the gas as needed) until I could let go of the clutch completely. I would do this process and brake as needed. Once you get the hang of it, the exact rev doesn't matter, you'll be able to sense how far to press the gas pedal.

Going to a complete stop I just put it into neutral and brake. Some people advise against this, but it only takes a split second to get going again.

grnrx_8

Probably the same thing, but I grew up calling it double clutching... I used to have a '72 Triumph TR-6 and that was the only way it would down shift because the synchro hubs in the tranmission were shot, so it's 2nd nature now. Takes a little practice but once you get it down, your clutch will be happier... and besides it's great just to hear that engine rev up

9100RPM

In OZ that's called adouble shuffle. Try it with heel and toe and you might learn to drive smoothly and quickly without damaging gearbox or clutch..smooth, be smooth, you go faster and your passengers feel comfortable too. 9100RPM

mitchmiller

yesyesyes just be smooth

Gord96BRG

Nope - what people have described so far is just rev-matching. Think about it - they press and release the clutch once, not twice.

For a double-clutch downshift, say from 3rd gear at 3000 rpm to 2nd gear (where the engine would be turning at 4500 rpm) (rpm figures not exact, for illustrative purposes only!):
- in 3rd gear at 3000 rpm, press in clutch, let off throttle
- move shifter to neutral
- release clutch, blip throttle to raise revs to just over 4500 rpm
- press in clutch, move shifter to 2nd gear
- release clutch

Done properly, a double-clutch (notice the clutch was pressed twice?) downshift takes maybe 0.1 seconds longer to perform than a rev-matched downshift, ie very quick. The difference is that the throttle blip with the clutch released in neutral is used to spin up the gearbox shafts to the speed needed for engaging the lower gear, so that the synchronizers have very little or no work to do. That eliminates wear on the synchronizers - and yes, gearbox synchros do wear out. If you don't release the clutch in neutral, then you're just rev-matching. That makes for an equally smooth downshift as far as the rest of the drivetrain is concerned, but doesn't reduce gearbox synchro wear.

There are a few previous threads discussing this - a search for "double clutch" should turn them up.

Regards,
Gordon

KAuss

Speed shifting can either be shifting really fast, or "power shift" which is keeping your foot on the gas pedal at all times while clutching into the upper gear and releasing it to friction to smooth out your shift... Most of the time this will result in a slight chirp of the tire... Definately NOT mechanically sound to do this, and only done if you want the best up shift times possible...

Rev matching is a lot smoother for regular driving... Heel toe is better reserved for the track or multiple gear down shifts... I don't know about the RX-8 and its gearing, but for normal piston engine close ratio 6s... It's really hard to brake and rev at the same time under normal throttle operation... Usually you'll over rev if you only want to downshift one gear... However it's a god send when you use heel toe for say a 4 > 2 right hand turn...

It's generally better to over rev your downshifts than under rev... Better to eat clutch than to drag your engine... Still with practice, you'll hit it every time...

Edit: Sorry for biring up the old posts, but since no one chimed in on the "speed shift" thing, I just thought I'd fill in...