AWIDESUPIE
08-01-2004, 09:53 AM
Original post:
I threw together a random write-up in this thread one night:
http://www.supraforums.com/forum/showthread.php?s=&threadid=185766&highlight=rev+match
The other posts are pretty darn useful too. I think this would be very helpful to some. I don't know what you would prefer to include, Shawn ... so I'll let you do your moderating and decide if you want to leave the link or copy/paste some stuff over to here. Do what ya want!
Edit for Shawn's satisfaction, per Shawn's request ... :
Having a manual transmission automobile allows you to match engine/CRANK rpm with drivetrain mph/rpm at will.
Engine rpm is obviously determined by the tach. Drivetrain speed determined by speedometer ... whether your rolling or not .. and if so .. then how fast.
Crank rpm controlled by right foot/throttle .... drivetrain speed engaged by left foot/clutch.
The closer you can match crank rpm with drivetrain rpm/speed .. the smoother/more efficient engagement becomes.
Pretty simple.
While vehicle is at rest ... drivetrain speed is ~0mph/rpm ... and engine idle is at about 650-750rpm (slow). This relationship is similar in all manual transmission vehicles .. and allows one move forward/backward (gear dependent of course) without increasing engine rpm/throttle any more than idle. Yes, if you slip the clutch slowly enough ...the car will move forward (1)... or backwards (R) .. if there isn't too mutch incline resistance from either direction ... allowing the torque to move the vehicle. If there is too much resistance .. slightly increase throttle/crank rpm to allow engine torque to overcome drivetrain resistance.
The engine only stalls if the engine bites too quickly to something that is stationary (significantly slower drivetrain). The better biting clutch one has ... or the less slip the clutch provides .. the easier it becomes to stall/slow down the engine too much.
Many clutches provide for slipping (partial biting/engagement to drivetrain before becoming fully engaged) ... allowing it to graze the drivetrain for engagement and allow some of the drivetrain and crank kinetic/potential energy to be absorbed by the other.
What this means is that if, at idle and no rolling speed (for best illustration), you slip the clutch out slowy enough to gradually engage the stationary drivetrain ... if the crank energy/power can gradually be transfered to the drivetrain ... the car will move more quickly the more the drivetrain is fully engaged by crank until 100% kinetic/potential energy is tranfered (minus loss to heat energy). Not to confuse mater anymore .. but engagement of clutch could be quicker if the car was rolling fast enough but no too fast ... just slow roll ... for crank rpm/drivetrain relationship.
Things get a bit more tricky while driving at increased speed ... but it is still the same concept. Name of the game is to get a feel of clutch bite/feel ... crank rpm ... and drivetrain speed .... and reckognize their relationships.
As long as no modifications are performed .. and motin resistance form extremem wind or inclines/declines is not affecting relationships too much .... the engine rpm in each gear will always produce the same relatoinal drivetrain speed.
This means that you should be able to determine what crank rpm in what gear will provide for smoothest engagement by observing drivetrain speed .. and you will now how to make the engagement with the clutch by getting familiar with it's particular function traits (bite hard .. slips alot ... firm/soft pedal .. etc).
If exact relation cannot be determined ... it is always better to exceed necessary engine rpm and have the clutch slip a bit or wheels spin in relation to vehicle travel direction .... rather than to have drivetrain speed exceed its relation to crank rpm ... and have the engine go into shock as it is thrown violently towards redline ... and causes vehicle speed to decrease for a split second or more ... significantly .. causing immense shock to clutch/drivetrain rigidity etc.
For instance .... 2nd gear on a r154/7mgte combination in near stock form allows around 5 through 60-65mph ... 3rd about 25-30 through 80-85mph .... 4th about 30-40 through 120-125mph ... 5th about 40-45 through top speed.
If cruising on road at about 55mph in 5th gear ... you suddenly want to pass a vehicle by accelerating as quickly as possible.
You want to be in the lowest gear that allows you to travel at your current speed .. but you also want some room to run.
55mph may be a tough decision for downshift selection in a near stock combo ... because this is very close to top of 2nd (which SHOULD provide for best pull ... ***but**) and there is pleanty of good run room for 3rd .. and it may provide the best power-band.
If you wanted 2nd .... you would have to rev to right about redline and drop/slip the clutch (depending on clutch traits) .. b/c this is the relation to crank rpm in that gear at that speed.
I would choose 3rd gear, most likely, due to better power curve (b/c let's not forget the **but** .. the stock ct26 chokes top rpm flow .. so the tip range rpm of a second gear pull would probably be a less desireable part of the power-band).
To shift into third .. at 55mph ... I would approximate engine rpm relation t be about 3000-3500rpm .. so for a safe bet I may rev to about 500rpm over my estimate and dump/slip the clutch to engage for best pull.
If during any gear engagement I chose not to match crank rpm with drivetarin speed ... and let of the gas and attempted to engage drivetrain and throttle at the same time ... or even worse throttle slightly after drivetrain engagement .. that's when violent drivetrain shock is felt. BAD for vehicle components .. bad for attempted performance.
Same relationship for all relevant crank rpm/gear/drivetrain speed ratios. Once you figure em out ... and respect the control you have.... I dont think you'll ever want to drive an automatice again .. unless it's for leisure or straightline performance.
_______
I see dejavu beginning in this thread ...
I was going to copy and past all of the posts from SF thread above that would answer these "dejavu" questions ... but you guys can just click on the link.
Make sure to read both pages. Most questions should be answered by reading the aove thread thoroughly on both pages.
_____
continued ...
I threw together a random write-up in this thread one night:
http://www.supraforums.com/forum/showthread.php?s=&threadid=185766&highlight=rev+match
The other posts are pretty darn useful too. I think this would be very helpful to some. I don't know what you would prefer to include, Shawn ... so I'll let you do your moderating and decide if you want to leave the link or copy/paste some stuff over to here. Do what ya want!
Edit for Shawn's satisfaction, per Shawn's request ... :
Having a manual transmission automobile allows you to match engine/CRANK rpm with drivetrain mph/rpm at will.
Engine rpm is obviously determined by the tach. Drivetrain speed determined by speedometer ... whether your rolling or not .. and if so .. then how fast.
Crank rpm controlled by right foot/throttle .... drivetrain speed engaged by left foot/clutch.
The closer you can match crank rpm with drivetrain rpm/speed .. the smoother/more efficient engagement becomes.
Pretty simple.
While vehicle is at rest ... drivetrain speed is ~0mph/rpm ... and engine idle is at about 650-750rpm (slow). This relationship is similar in all manual transmission vehicles .. and allows one move forward/backward (gear dependent of course) without increasing engine rpm/throttle any more than idle. Yes, if you slip the clutch slowly enough ...the car will move forward (1)... or backwards (R) .. if there isn't too mutch incline resistance from either direction ... allowing the torque to move the vehicle. If there is too much resistance .. slightly increase throttle/crank rpm to allow engine torque to overcome drivetrain resistance.
The engine only stalls if the engine bites too quickly to something that is stationary (significantly slower drivetrain). The better biting clutch one has ... or the less slip the clutch provides .. the easier it becomes to stall/slow down the engine too much.
Many clutches provide for slipping (partial biting/engagement to drivetrain before becoming fully engaged) ... allowing it to graze the drivetrain for engagement and allow some of the drivetrain and crank kinetic/potential energy to be absorbed by the other.
What this means is that if, at idle and no rolling speed (for best illustration), you slip the clutch out slowy enough to gradually engage the stationary drivetrain ... if the crank energy/power can gradually be transfered to the drivetrain ... the car will move more quickly the more the drivetrain is fully engaged by crank until 100% kinetic/potential energy is tranfered (minus loss to heat energy). Not to confuse mater anymore .. but engagement of clutch could be quicker if the car was rolling fast enough but no too fast ... just slow roll ... for crank rpm/drivetrain relationship.
Things get a bit more tricky while driving at increased speed ... but it is still the same concept. Name of the game is to get a feel of clutch bite/feel ... crank rpm ... and drivetrain speed .... and reckognize their relationships.
As long as no modifications are performed .. and motin resistance form extremem wind or inclines/declines is not affecting relationships too much .... the engine rpm in each gear will always produce the same relatoinal drivetrain speed.
This means that you should be able to determine what crank rpm in what gear will provide for smoothest engagement by observing drivetrain speed .. and you will now how to make the engagement with the clutch by getting familiar with it's particular function traits (bite hard .. slips alot ... firm/soft pedal .. etc).
If exact relation cannot be determined ... it is always better to exceed necessary engine rpm and have the clutch slip a bit or wheels spin in relation to vehicle travel direction .... rather than to have drivetrain speed exceed its relation to crank rpm ... and have the engine go into shock as it is thrown violently towards redline ... and causes vehicle speed to decrease for a split second or more ... significantly .. causing immense shock to clutch/drivetrain rigidity etc.
For instance .... 2nd gear on a r154/7mgte combination in near stock form allows around 5 through 60-65mph ... 3rd about 25-30 through 80-85mph .... 4th about 30-40 through 120-125mph ... 5th about 40-45 through top speed.
If cruising on road at about 55mph in 5th gear ... you suddenly want to pass a vehicle by accelerating as quickly as possible.
You want to be in the lowest gear that allows you to travel at your current speed .. but you also want some room to run.
55mph may be a tough decision for downshift selection in a near stock combo ... because this is very close to top of 2nd (which SHOULD provide for best pull ... ***but**) and there is pleanty of good run room for 3rd .. and it may provide the best power-band.
If you wanted 2nd .... you would have to rev to right about redline and drop/slip the clutch (depending on clutch traits) .. b/c this is the relation to crank rpm in that gear at that speed.
I would choose 3rd gear, most likely, due to better power curve (b/c let's not forget the **but** .. the stock ct26 chokes top rpm flow .. so the tip range rpm of a second gear pull would probably be a less desireable part of the power-band).
To shift into third .. at 55mph ... I would approximate engine rpm relation t be about 3000-3500rpm .. so for a safe bet I may rev to about 500rpm over my estimate and dump/slip the clutch to engage for best pull.
If during any gear engagement I chose not to match crank rpm with drivetarin speed ... and let of the gas and attempted to engage drivetrain and throttle at the same time ... or even worse throttle slightly after drivetrain engagement .. that's when violent drivetrain shock is felt. BAD for vehicle components .. bad for attempted performance.
Same relationship for all relevant crank rpm/gear/drivetrain speed ratios. Once you figure em out ... and respect the control you have.... I dont think you'll ever want to drive an automatice again .. unless it's for leisure or straightline performance.
_______
I see dejavu beginning in this thread ...
I was going to copy and past all of the posts from SF thread above that would answer these "dejavu" questions ... but you guys can just click on the link.
Make sure to read both pages. Most questions should be answered by reading the aove thread thoroughly on both pages.
_____
continued ...