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Old 12-09-2017, 10:15 AM
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Tom Vaught Tom Vaught is offline
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Join Date: Dec 2001
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Thank You Frank for your comments on the choke topic.

Looser converters tend to "flash" to a higher rpm. Even though it is only fractions of a second, that "delay" helps with a Double Pumper Carb's sudden Drive Mode Change to supplying WOT fuel and air to the engine. The engine has a chance to find its own acceleration rate to compensate for the sudden additional mixture change going into the engine.

With the Manual Transmission the engine and the driveline are tied together. Now the carb says I am going to make a significant change in air and fuel supplied to the engine. The problem is the driveline is trying to resist that sudden change in rpm of the components. So there is a delay in the engine's ability to digest that extra fuel and air mixture. So you get a MECHANICAL HESITATION in the performance curve. Change one component, add a torque converter and remove the clutch, and you get a whole different response from the engine.

That being said, manufacturers do not want to give up fuel economy so they came up with 'Lock-up" Converters that allow both modes.
Throttle Position Sensor detects an abrupt throttle change, converter "unlocks", rpm in engine goes up just like a old style converter, and performance is there.
After the WOT (or less) rpm change event, the Computer and TPS agree that the engine is in a mode where the "lock up" converter can be used again. If the Trans Engineer and the Engine Engineer did their jobs correctly the change is hardly felt.

That brings to mind another Drive Mode with a Manual Transmission. The time it actually takes to make the shift to the next gear.
Old days is: Acceleration Event, release the Pressure Plate from the Drive Disc, match the gears using the Trans Syncros, move to the new gear, release the clutch, accelerate at the new trans ratio.

NEW State Of the Art Manual Transmissions (and Auto Transmissions have Gears on BOTH sides of the main shaft. So now when you are accelerating in First Gear, the Computer is already setting up the gears for the Trans to be in second gear on the opposite counter-shaft gear set. So the computer releases the 1st set of clutches/gears and applies the second set of clutches/gears and the shift is made in microseconds. And as long as the TPS Sensor says we are still at WOT, it gets the next set of gears/clutches ready to make the shift.
It can do this for all 10 speeds of the transmission. This is a GM/Ford "Team Designed" Transmission in production in the new Corvette and other vehicles.

So again, Engineers can figure out how to get the best of the MANUAL TRANS features and the smoothness of the Auto Trans features.
But they are fixing a Fuel and Air Physics Problem in the engine.

Sorry for the side track as the discussion is on Holley Carburetors, not Modern EFI and TRANS Calibrations.

Tom V.

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Last edited by Tom Vaught; 12-09-2017 at 10:20 AM.