Stiff Clutch driveability tip
09-22-13, 08:06 AM
#1
Racing Rotary Since 1983
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iTrader: (6)
Stiff Clutch driveability tip
i often post how small our rotaries are... 80 cubic inches, 1.3 liters... primarily to raise appreciation as to the high state of tune. ducks need to be in a row.
but our motors really are SMALL
as in 13 X 13 X 13 INCHES for the shortblock.
small block means SMALL FLYWHEEL.
small flywheel means small available frictional area.
clutches are really simple despite all the marketing noise.
frictional area and spring pressure =s capacity for a given disc material.
most types of disc materials are similar.
frictional area is a constant for a single disc, double disc etc.
so we focus on spring pressure.
approx 1200 PSI for the stock setup.
most aftermarket clutches use the DAIKIN pressure plate assembly, swap in stiffer springs and paint it Tangerine or whatever.
since the stock RX7 makes 217 feet of torque but modded motors often generate 300- 450 up goes the spring pressure.... often around 2600 pounds.
down goes the driveability.
double discs, since they add additional frictional area, can often get by w around 2000.
back to driveability which is the reason for this thread.
i run a Quartermaster 8.5 inch "Rally Clutch." double disc, cerametallic, no springs. previously i have run an ACT, an Exedy Hyper Single (2605) and an Exedy Double (2000). i had to switch to the custom Quartermaster when i switched to my T56.
i was able to specify the spring pressure i wanted w the QM... 2200. i do drive the car mostly on the street.
here's the tip:
i suggest anyone running a stiff clutch, especially if it bucks on take up, warm up your engine so it is off the enrichment mode and DATALOG take up. takeup is in an area of the map that is seldom visited and often overlooked.
i was having take up problems after switching to a different ECU and finally looked at the logs to find the real problem was i was lean in the take up area. do not be afraid to throw a lot of fuel at it and you should be surprised how you have a new clutch in your car. the area of the map you are richening is generally not visited other than take up.
as always, many readers may know this, but perhaps this will be helpful to some.
it sure solved my clutch problem.
howard
but our motors really are SMALL
as in 13 X 13 X 13 INCHES for the shortblock.
small block means SMALL FLYWHEEL.
small flywheel means small available frictional area.
clutches are really simple despite all the marketing noise.
frictional area and spring pressure =s capacity for a given disc material.
most types of disc materials are similar.
frictional area is a constant for a single disc, double disc etc.
so we focus on spring pressure.
approx 1200 PSI for the stock setup.
most aftermarket clutches use the DAIKIN pressure plate assembly, swap in stiffer springs and paint it Tangerine or whatever.
since the stock RX7 makes 217 feet of torque but modded motors often generate 300- 450 up goes the spring pressure.... often around 2600 pounds.
down goes the driveability.
double discs, since they add additional frictional area, can often get by w around 2000.
back to driveability which is the reason for this thread.
i run a Quartermaster 8.5 inch "Rally Clutch." double disc, cerametallic, no springs. previously i have run an ACT, an Exedy Hyper Single (2605) and an Exedy Double (2000). i had to switch to the custom Quartermaster when i switched to my T56.
i was able to specify the spring pressure i wanted w the QM... 2200. i do drive the car mostly on the street.
here's the tip:
i suggest anyone running a stiff clutch, especially if it bucks on take up, warm up your engine so it is off the enrichment mode and DATALOG take up. takeup is in an area of the map that is seldom visited and often overlooked.
i was having take up problems after switching to a different ECU and finally looked at the logs to find the real problem was i was lean in the take up area. do not be afraid to throw a lot of fuel at it and you should be surprised how you have a new clutch in your car. the area of the map you are richening is generally not visited other than take up.
as always, many readers may know this, but perhaps this will be helpful to some.
it sure solved my clutch problem.
howard
Last edited by Howard Coleman; 10-06-13 at 11:12 AM.
09-26-13, 04:24 PM
#4
Sleepr7: it does function this way because it fires its entire displacement on every revolution, which is why it has a high power density and (presumably) why Mr. Coleman persistantly reminds readers about the rotary's challanges. (A 4-cycle piston motor, by contrast, only fires 1/2 its displacement each rev.).
So back to the clutch issue: Another thing that will help stiff or grabby clutch drive-ability is to make the entire pedal and release mechanism as stiff as possible AND reduce friction in the linkages as much as possible.
A ball or roller bearing can be added where the cleavis pin runs through the clutch pedal arm--it makes a HUGE difference in your ability to articulate the clutch, especially with a heavy plate and/or grabby discs. It also makes a heavy plate feel lighter than it is.
So back to the clutch issue: Another thing that will help stiff or grabby clutch drive-ability is to make the entire pedal and release mechanism as stiff as possible AND reduce friction in the linkages as much as possible.
A ball or roller bearing can be added where the cleavis pin runs through the clutch pedal arm--it makes a HUGE difference in your ability to articulate the clutch, especially with a heavy plate and/or grabby discs. It also makes a heavy plate feel lighter than it is.
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