Part throttle torque

[stony]

I've heard of it, and experienced it, but is part throttle torque a quantifiable item? Am I right to assume that it results from the creation of a high V/E at certain throttle angles, varying of course with RPM, plenum volume, intake runner length and valve/cam geometry?
Do any of you "Dyno Gurus" have any insight?

Or am I on glue?X-)

 

[atroader]

it all makes sense-- I know what you are talkin about.
The only way to really describe it though would be on a dyno or to approximate power outputs based on air fuel effiency at those part throttle times and compare to a full throttle dyno graph- so might as well use a dyno for part throttle. most of the volume and flow rates are dependent on rpm alone (excluding other immediate factors) if you can plot flow rates along with fuel effiency/rpm at a certain throttle and compare-- you might find times when part throttle torques would be reached.

 

[carnage]

Yes there is part throttle torque. I don't know how to quantify it. it has to do with having a higher intake velocity that results in a slightly higer VE. Holley's websight hints at it when mentioning on the carb selection guidelines that you will usually be happier with a carb that is to small rather than one that is to big, because the smaller carb will give quicker acceleration.(whitch I translate to mean more tourque.) This is also why dual plenum maifolds boost low end torque, because they cause an increase in the velocity of the intake gas.

 

[Marquis]

Part Throttle torque IS a qantifiable term. Automotive manufacturers used a fraction of the full load BMEP of that engine to quantify this amount. For instance ,internally GM like to use 2 bar BMEP, 2000 rpm, or Ford like to use 2.62 bar ,1500 rpm and quantities such as BSFC ( break specific fuel consumption) and such like are measured and quoted internally. Alternatively part load conditions are specifed by quoting a certain amount of manifold depression ( manifold vaccuum with the throttle only partially open)

"Am I right to
assume that it results from the creation of a high V/E at certain throttle angles"

It would be wrong to assume anything like this really. I've have NEVER ever seen a boost in VE as the throttle is shut or closed over having it open.

"Yes there is part throttle torque. I don't know how to quantify it. it has to do with having a higher
intake velocity that results in a slightly higer VE."

Higher gas velocities AT the throttle DO NOT boost torque. If for nothing else these velocities would totally loose momentum by the time they reached the intake ports. By closing off the throttle all you're doing is increasing the restriction. If what is said was true, this would be the same as there being a boost in performance of a car when the throttle was only partially pressed down, only to be lost when the gas pedal was pressed down further!

"Holley's websight hints at it when mentioning on
the carb selection guidelines that you will usually be happier with a carb that is to small rather
than one that is to big, because the smaller carb will give quicker acceleration.(whitch I translate
to mean more tourque.)"



Now higher Gas velocities in the port or intake runners-this is something quite different and to do with full load intake ram tuning frequency: THIS is the phenomenon that you perhaps refer to when you talk of smaller carbs/choke sizes on an engine. "Quicker acceleration"? Perhaps you mean throttle response? This is different to actual torque but can be related: It IS possible to have a high torque engine with very poor throttle response and vice versa. I need not go into all the parameters that effect it unless there is a request for it, but one of the factors is how small the throttled voulme is -the volume between the intake valve and where the throttle is itself.

"This is also why dual plenum maifolds boost low end torque, because they
cause an increase in the velocity of the intake gas."

Again, another totally different phenomenon which has nothing to do with gas velocity. Twin plenum and "tuning valves" on intake manifolds work by changing the resonant properties of the intake system as a "container" when the natural frequency of this set up matches the forcing frequency ( in this case the piston ) a resonace condition is met and VE can be booted over a narrow rev band. This works particularly well on V6 engines and not so well on V8 (cruciform crank type) engines -andeven then must involve special connectivity. Examples of a cruciform crank V8 which uses a resonant tuning flap are the Posche 928 S4 and a few Ford truck. V6 applications are numerous.