Go Back   Team-BHP > Under the Hood > Technical Stuff


Reply
 
Thread Tools Search this Thread
Old 25th December 2004, 09:54   #61
Senior - BHPian
 
Gordon's Avatar
 
Join Date: Feb 2004
Location: Mumbai
Posts: 2,420
Thanked: 162 Times
Default

I'm not too sure about this, but this is what I feel.

The revs should drop considerably so that you could select the next gear during clutchless upshifts. This is to ensure that the engine is at the right speed. This is a must! Now Shan2nu says that he changes gears [WITH CLUTCH] at 4000 rpm which is very high for the next gearr. Read the capitals again "WITH CLUTCH". According to me, its the synchromesh thats allowing him to do that. Even though the engine is carrying way too much speed for that gear, the synchromesh and the clutch is always there to synchronize your engine and gearbox speeds.

I can never explain properly so LET ME TRY TO EXPLAIN SLOWLY:
You are at high rpm in 2nd gear. You press clutch and shift to the 3rd gear without dropping revs too much. While leaving the clutch for 3rd gear the clutch is not completely engaged to the flywheel, so you are not transferring ALL power at one shot to the transmission. You leave the clutch and during this process, there is low power [low rpm, maybe 2000 rpm] transferred to the gear [such low rpm is required for upshifting]. By the time you leave the clutch completely, all the power is sent to the transmission, so by this time your gear has been synchronized with the engine speed by the synchromesh.

I hope you guys have understood this and I also hope I'm right!

So the bottom point is:
  • When you upshift without clutch, the revs have to fall considerably sometimes even at 2000rpm so that you can match the upper gear.
  • When you upshift with clutch, the revs need not fall as the clutch and synchromesh will do the work.

One thing sounds obvious, you're giving more work to the clutch plate

I'm not too good at bikes. But in MotoGP, it may be the same as F1. Sequential shifting with the aid of electronics. Rider changes gear without clutch "lever", and the electronics do the rest in milisecond time.

Shan2nu has much more knowledge on technical issues than I do. I know most things to an extent.
Gordon is offline   Reply With Quote
Old 25th December 2004, 17:15   #62
Team-BHP Support
 
Rehaan's Avatar
 
Join Date: Feb 2004
Location: Bombay
Posts: 22,367
Thanked: 22,586 Times
Default

Rtech/BikerSG,

I was wondering >

Clutchless upshifting is said to be the norm for bikers in this thread... so then where does powershifting come in?? Is it a matter of choice or a matter of situation?

cya
R

ps - by powershifting i mean reaching shiftpoint RPM, holding the revvs high while disengaging the clutch, shifting, and then engaging the clutch with the throttle still held open.
Rehaan is offline   Reply With Quote
Old 27th December 2004, 14:45   #63
BHPian
 
Join Date: Oct 2004
Location: Bangalore, India
Posts: 137
Thanked: 4 Times
Default

check out the following 2 links which pretty much explains both double declutching and heel and toe. IMHO that heel and toe is best practiced along with double declutching.

http://www.tcsracing.org/doubledeclutching.htm

http://www.tcsracing.org/heelandtoe.htm

ofcourse once you master double declutching and heel and toe, people sitting next to you will will think you are tap dancing on the clutch ;-) if you want to impress someone get the whole thing right, understand the fundae and let it roll!!!
when you do it right, the engine notes sound REAL beautiful!!! of course if you mistime your second de clutch and are off on your rev matching bit, you end up screwing up your gears big time and trust me, you will hear it :-)
rahulmd is offline   Reply With Quote
Old 27th December 2004, 15:06   #64
BHPian
 
BikerSG's Avatar
 
Join Date: May 2004
Location: Chennai, INDIA
Posts: 374
Thanked: 12 Times
Default

if u dont need to use the clutch, you save time upshifting in bikes.

I dont get the point of powershifting (haven;t heard this name before) unless u want to keep the engine in the powerband, but that wont work either, as the moment u let go of the clutch after shifting, the engine speed will fall again!

RTech? Any input from u?
BikerSG is offline   Reply With Quote
Old 27th December 2004, 17:12   #65
Senior - BHPian
 
Gordon's Avatar
 
Join Date: Feb 2004
Location: Mumbai
Posts: 2,420
Thanked: 162 Times
Question is this Powershfiting?!

From past "knowledge" and after a little thinking this is what I made of Powershifting in cars

Powershifting
- Powershifting is done using the clutch. In this process, you keep the accelerator pedal pinned down almost all the time. While upshifting, the accelerator pedal is down and the throttle is wide open, you put the car into neutral just before you reach the shift point and at the same time disengage clutch completely, shift to the next gear and then release clutch. You do not need to redline or change at way too high rpms. You have to shift gears just before you would "normally"* shift. I guess the tires would squeal everytime you change to a higher gear. And I also feel that this kind of stuff can wear out your clutch plate and nor is it good for your gearbox.

* normally as in when you normally shift gears with clutch

Quote:
Originally Posted by Rehaan
Is it a matter of choice or a matter of situation?
What did you mean by this??!
Rehaan you were talking about bikes, right? I have no idea about powershifting in bikes.

Quote:
Originally Posted by BikerSG
the engine speed will fall again
BikerSG, I know you are talking about bikes too. Anyways, I would like to know why would engine speed drop during powershifting?
Gordon is offline   Reply With Quote
Old 27th December 2004, 17:19   #66
BHPian
 
BikerSG's Avatar
 
Join Date: May 2004
Location: Chennai, INDIA
Posts: 374
Thanked: 12 Times
Default

engine speed has to fall during upshfting! thats the idea behind having gears.

when doing 100kph in 3rd gear at say 5,000 revs (example only), when u shift to 4th gear, engine speed will drop to maybe 3,000 revs but speed remains same at 100kph.

When downshifting, its the opposite - as in revs increase, thats why the need to blip.

I hope I've explained it well!
BikerSG is offline   Reply With Quote
Old 27th December 2004, 17:45   #67
Senior - BHPian
 
Gordon's Avatar
 
Join Date: Feb 2004
Location: Mumbai
Posts: 2,420
Thanked: 162 Times
Exclamation

This I know [COLOR=DarkOrange][and I hope you're talking about clutchless shifting][/COLOR], and this happens because you let go off throttle and it is very good because engine speeds must fall to match the appropriate higher gear.

BUT!

here you do not let go off the throttle, you keep it open all throughout the upshift. Logically, the engine speed will remain the same.

Does anyone have any idea on Powershifting in Bikes??!

[THIS POST IS ABOUT BIKES]
Gordon is offline   Reply With Quote
Old 27th December 2004, 20:20   #68
Team-BHP Support
 
Rehaan's Avatar
 
Join Date: Feb 2004
Location: Bombay
Posts: 22,367
Thanked: 22,586 Times
Default

Quote:
Originally Posted by BikerSG
I dont get the point of powershifting (haven;t heard this name before) unless u want to keep the engine in the powerband, but that wont work either, as the moment u let go of the clutch after shifting, the engine speed will fall again!
Hey guys,

The point of powershifting is to keep the engine in its powerband, and keep the drop in the revvs minimal.

Naturally the engine speed will fall after u change gears with powershifting, however there will be more power transfered than if you clutch-shifted normally. (im not gona get into clutchless here).
Think about it, when you launch a car from a standstill @2000RPM, the revvs will drop a bit as the clutch makes contact and then begin to rise again.
Whereas if you launched a car from a standstill @4000RPM the revvs would drop as well, however more power would be transfered, and the car would accelerate faster.
Exactly the same principle applies with powershifting.

cya
R

Last edited by Rehaan : 27th December 2004 at 20:21.
Rehaan is offline   Reply With Quote
Old 28th December 2004, 17:10   #69
BHPian
 
BikerSG's Avatar
 
Join Date: May 2004
Location: Chennai, INDIA
Posts: 374
Thanked: 12 Times
Default

there are 2 moving discs (engine side and gear side) with different speeds.

we cannot say that by keeping throttle fully open, engine speed will not drop and gear speed will increase faster than normal to meet the engine speed! Both have to meet somewhere in the middle. Exactly in the middle or not is dependent on time taken (and maybe other factors).

And upshifting is to be treated differently than downshifting.

For the gear speed to drop, there is more than one way - braking and engine braking. But for the gear speed to increase, there is only engine!

Even if powershifting is good for times, it is extremely bad for ur clutch!

More info soon!
BikerSG is offline   Reply With Quote
Old 28th December 2004, 19:08   #70
Team-BHP Support
 
Rehaan's Avatar
 
Join Date: Feb 2004
Location: Bombay
Posts: 22,367
Thanked: 22,586 Times
Default

Quote:
Originally Posted by BikerSG
we cannot say that by keeping throttle fully open, engine speed will not drop and gear speed will increase faster than normal to meet the engine speed! Both have to meet somewhere in the middle.
Ofcourse engine speed will drop, however it WILL be better in terms of acceleration than if you match revvs perfectly, then engage the clutch and then open throttle fully.

And yes its bad for the clutch...but this is racing that we are talking about... they dont care about clutch wear, they care about 0.1second.

cya
R
Rehaan is offline   Reply With Quote
Old 29th December 2004, 11:41   #71
Team-BHP Support
 
Rtech's Avatar
 
Join Date: Apr 2004
Location: Bombay
Posts: 5,769
Thanked: 212 Times
Default

hey guys...stupid phone lines were down...grrr! Will post on this as soon as I get a decent connection.

till then....


Rt
Rtech is offline   Reply With Quote
Old 29th December 2004, 11:47   #72
BHPian
 
BikerSG's Avatar
 
Join Date: May 2004
Location: Chennai, INDIA
Posts: 374
Thanked: 12 Times
Default

when i tried this out yesterday in my sonata, i could see that the engine revs did drop a bit (but not as much as they would have fallen if I had taken foot off the throttle) but the full power of the engine is not transferred to the wheels as the clutch intervenes until the gear speed comes up to the level of the engine speed!

Whats the point in keeping the engine in the powerband if all the power is not being shifted to the wheels? Has anybody tried taking times?

As far as I know, it is best to pull out the clutch as fast as possible and then squeeze the throttle for best results!
BikerSG is offline   Reply With Quote
Old 29th December 2004, 11:49   #73
BHPian
 
BikerSG's Avatar
 
Join Date: May 2004
Location: Chennai, INDIA
Posts: 374
Thanked: 12 Times
Default

and rehaan, in the case of upshifting, there is no need to do anything to match revs perfectly! it happens automatically when u take ur foot off the throttle!

only downshifting requires blip of the throttle to get engine speed up to match gear speed.
BikerSG is offline   Reply With Quote
Old 29th December 2004, 15:26   #74
Team-BHP Support
 
Rtech's Avatar
 
Join Date: Apr 2004
Location: Bombay
Posts: 5,769
Thanked: 212 Times
Default

guys, powershifting on a bike is the norm in most racing series. Motogp, superbikes etc all have mechanisms that allow the rider to powershift. Basically all it does is allow the rider to upshift without letting up on the throttle.

However, the clutch is never, i repeat NEVER used while powershifting.

On a car, well, I'm thinking out aloud here, but the descriptions given above are basically describing the method of double declutching, where you shift into neutral, rev the engine and pop it in the next gear. Done mostly on older cars to make for an easier shift.

As far as modern cars go, unless fitted with a powershift mechanism similar to what the GP bikes use, it will be quicker, smoother and overall much better to just shift up int eh regular manner, just quicker. If the revs are dropping too much between shifts, you need to work on your shifting technique!

Rt

Last edited by Rtech : 29th December 2004 at 15:28.
Rtech is offline   Reply With Quote
Old 1st January 2005, 01:09   #75
BANNED
 
Join Date: Nov 2004
Location: Mumbai
Posts: 124
Thanked: 0 Times
Default

well can u tell me wats the exact procedure from first i should revv n shift to second or shift thru neutral no touchin cluth??
fasbond1412 is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Acceleration at low gears zen-ith Technical Stuff 8 4th July 2006 20:57
Problem with Siena gears & clutch satish_appasani Technical Stuff 11 10th June 2006 20:51
Why is this forum called "Shifting Gears"? aalaap Shifting gears 2 11th October 2004 13:42


All times are GMT +5.5. The time now is 06:38.

Copyright 2000 - 2017, Team-BHP.com
Proudly powered by E2E Networks