What keeps the revs up?

"inertia of rotating assembly"
"flywheel"

 

Agreed.


Maybe its a trick question?

 

i gently blip the throttle between shifts to keep the revs matched to less shock and wear to the clutch and transaxle.

 

I just move the lever quickly!

 

Gently? Grey Poupon shifting and all that? Grind it till you find it is the mantra of all real men.

 

Agree fly wheel inertia.

Ever been to speedway and listened to sprintcars warming up in the pits...

No fly wheel just a in/out (dog) box so revs up and down are instant.

 

The governor????

 

FBB- Revs need to drop for a perfect upshift, just like they need to rise for a perfect downshift. Flywheel keeps them from dropping too much. On F1 shifters, the system actually reduces the throttle for upshifts, just like it increases it for downshifts.

Taz
Terry Phillips

 

Here's how:

http://www.youtube.com/watch?v=Orv_F2HV4gk

 

Depends on the car and fuel system.... modern injected cars tend to 'hang' and personally I hate it - its a function of emissions control and fuel management. I want motors to spin 'old school' and return to idle rpm as fast as possible when throttle off, as carb'd or early injection motors did. It really is one of the things that bugs me about modern cars!! Beyond that it is a function of rotating mass, as you know - the lighter the mass, the faster they return to base idle, which theoretically improves shift times as rotating speeds match faster in the gearbox... but you know all this stuff anyway!! I can't tell you what the exact components are that keep revs up in a modern injected car when you rev the engine or on upshifts, but I can tell you that if you rip off all the injection equipment and whack on a good old fashioned carb, the same engine will then return to base idle much quicker and arguably be a lot more fun to dirve!! (but worse on fuel economy). Personally, I want 'throttle off' response to be a return to base idle as fast as possible with no hanging if I am enjoying a spirited drive..... If I am out for a leisurely potter, I can cope with an engine hanging, but would still prefer one that retruns to base idle quickly. What are you getting at?

 

Interesting... Absolutely, upshifts should be able to gain you time - theoretically one would want an upshift to occur instantaneously and under full throttle, that serves to lose the least forward acceleration. Realistically it isn't achievable, but the closer one can get to that the faster the acceleration throught the gears will be. Then it has to be a function of how fast one can physically disengage the clutch, select the next gear, re-engage the clutch and for engine revs to descend to match gearbox rotating speeds before being able to get on the gas again. Plus add in the torque characteristics of the engine and operate within the band of max torque. As an example, it is not uncommon for modern turbocharged cars to be faster to 100 on outright acceleration in automatic gearbox trim than its manual gearbox equivalent as the autobox allows the throttle to be pinned through the gearchanges and there is no loss of boost pressure normally found at gear changes... similarly, rally cars with straight cut boxes allow for much faster and clutchless changes improving shift times and outright acceleration. It is one of the age-old problems of car design - in fact the old pre-war UK performance marques, Bentley, Lagonda and such often had a dual purpose clutch pedal - the first part of the travel disengaged the clutch, further down the travel the pedal acted on a brake band on the flywheel to retard engine revolutions and speed up the time it took to match engine rpm with gearbox rotation speed in the days prior to syncromesh - its a very clever system that takes some getting used to! (tends to find oneself stomping on the clutch and stalling the engine!). Whilst designers have clealy been battling with the problem for generations, advances in technology have overcome a lot of the difficulties - lighter rotating masses match gearbox rotation speeds faster, gearboxes have improved selecting and gearchange properties etc. so a good deal of the early probelms have been designed out. Now with double clutch gearboxes they are really starting to get somewhere - the changes on these are unbelievably good and lightning fast, way faster than a normal mainstream production engine can lose rpm. Ultimately though the holy grail is in the first line up there - instantaneous shifts under full throttle.... now it is just a question of 'how?'.

 

Usually my right foot.

 

When I was young and foolish and rode motorcycles like clutches were immortal I never let off the throttle for upshifting. Fortunately I never had enough HP and tire to flip me.

 

You mean to tell me that a motorcycle clutch isn't immortal? Heck, when I was that age I rode like I was immortal. The thought of a clutch didn't really cross my mind.

 

With a bike based gear box you don't need the clutch to up-change gears if you get the revs right all you are doing is shifting dogs, the gears are already engaged.

In my earlier years racing super karts, all you did was back off on the throttle for a split second grab the next gear and that was it.

Some times you might use the clutch on down shifts it you were going down say 2 or 3 gears at a time. I never had problems with the gearbox and never heard of any one having problems from clutchless changes.

 

Exactly... but that is in a 'proper' car. Upshifts were MUCH quicker in the race car and it was easy to upshift/downshift just as you say. Alas, the Ferrari, at least the 308, needed moire finess with stock flywheel. With an aftermarket lightenfly/clutch it was faster, yet still nowhere near that of a proper track car from my experience.

Videos of lightened fly/clutch in the 308 is th NHIS video. Have same track in the F2000 too. http://enjoythetrack.com/video/ Note that other videos with the 308 are with the stock fly/clutch.

 

+1

Sometime around the late 70's this became a requirement. Many cars built during this "transition" have a vacuum limiter on the throttlebody that keeps the revs from dropping too fast.
I've removed such devices on cars with heavy flywheels and high rotating mass, the rpms fall like a lead weight between upshifts.

On modern cars this is built into the ECU making it much harder to disable.