Anomaly: Shift points change with boost level

[John Larkin]

After a big thanks to Lee Thompson taking several hours to log some DS files riding shotgun with me, we noticed something. My shift points with street gas (94 + alky) @ 18psi boost WOT were around 4900, hitting 5000 occasionally. With race chip, C16 and 20psi boost, they went to 5250. My governor is modified to the point of the small weight looking like swiss cheese to lighten it; the intention was to raise shift points. The small weight is also pinned for the spring, necessitating most of the lightening to compensate for the pin. I'm happy with the 5250 since that seems to be the optimal shift point for most folks, but the question remains: why higher with boost? Is it due to engine load? Lee said he's noticed it before also. Just looking for a reasonable theory and perhaps shake out a potential problem if one exists.

[chris718]

this a very simple question for me to answer in my head but may not be immediately comprehensible by those reading it the first time .anyhow this is my explanation based on what i have seen when adding boost ,more n20 ,or ignition timing.follow closely.without changing the governor or tv cable adjustment our theoretical gn running with 15 lbs of boost will shift 1/2 at 5000rpms and at 40 mphour .now, we crank up the boost to 20 lbs.now our theoretical gn is running with 20 lbs of boost and the 1/2 shift happens at 5200 RPMS AND 40 MPHOUR.see whats happening?by adding boost we are increasing the torque delivered to the convertor therefore the speed bias between the engine slightly increases allowing the engine to drive the turbine with a higher rpm .generally the stator multplies torque on initial acceleration and gives added leverage to the engine/flywheel to rotate the convertor pump half.this in turn multiplies twisting force ratio at the input shaft .at increased speeds attained at the flyweel and insude the convertor the stator ovverruns and the main factors at work are convertor pump verses convertor turbine .these two are what is at work in the extra 200 rpms we are seeing on the tachometer on our theoretical gn.obviously yours is a real world example .anyhow you can see that the mphour gear changes occur is controlled only by output shaft/governor rpm and tv setting not input torque created by the engine .correct me if im wrong.i would love to hear other opinions on this other than my own.www.ckperformance.com

[chris718]

i would really like other opinions on this.i thought there would be more of an interest in this post but guess iwas wrong.chris.

[TurboBob]

Ya going to Bowling Green, Chris?

I'll spend some time debating converters with ya.

I do agree with your post, tho. With more torque he's pushing through the converter more (more RPM) even though his shiftpoint MPH is the same (governor)

His 9x11 is all done multiplying torque at that point, he's just working with coupling efficiency there.

Bob

[John Larkin]

Thanks for the replies. Is there anything to do other than manually shift it to get consistency regardless of load? I wonder how high it will shift at 25 psi. I'm a trans idiot.

[WE4]

Very correct!
In fact what it is telling you is converter effecientcy. We have a hard time explaning cause it is a little "backwards" than what one would believe. But Chris explained it as well as anyone could have without going into a whole nother debate about converter effeiceintcy. <<<( How the hell do you spell this word correctly)
But basically the more "fluid coupled" the converter is the higher the shift point can be.
Here is another thought....... that may not be the whole cause but part of and in conjunction with what was mentioned above,......Temp of oil discharged from converter can effect even more and that is.....Remember a converter under load is a big heat pump.

More heat is generated at stall under load. Both mainline and other required pressures decrease due to tempeture rising under the stall or load incurred under heavy boost. So in theory the oil thins enough to not have the "power" or "properties" to function shift valves, tv oil and/or gov pressure.( To some degree, not like it fails just slightly , lets say, late.) Also, by the time you reach same mph under more boost , the more G forces are incurred and filter can be uncovering or starving for oil return due to how much oil a quality converter will move and it cannot scavenge back to pan fast enough.

So in turn 3 or 4 factors can effect and/or cause this symptom.

Honestly.... This is exactly where we noticed the tractor hydrulic fluid and deeper pans, dramatically effected these exact symptoms. Temp was lower and viscosity was better, improving mainline pressure stability , in turn making the shift points more consistant.
Try it Chris, see if you notice any difference. Even if you just try one fluid vs another, see if you get a change. Sometimes, believe it or not, add a quart of 20-50 or 30 w motor oil to trans ATF and lube properties and viscosity properties will improve. You will see this by more stable line ptressures throughout tempature rise.

Whatcha think ?
Agree, disagree? Chris? Opinions?


Bruce
WE4

[chris718]

no im not going to bowling green ,but i wish i were.john at 25 the increase probably wouldnt be another 200 rpms ,BUT.........why dont you do some testing and let us know .you may start at w/ever boost level add 5 ,and 5 again and report .i bet this would be interesting.i suspect increases at the second step would be minimal rpm gain ,but cant be sure ,lets see.i cant say that viscosity of oil and windage isnt a factor because it is but in my thinking these are the results of the increased rpm available at the input shaft when adding boost.think of it like cause and effect.oil temperature certainly effects consistency and launch rpm in a bracket car.www.ckperformance.com

[chris718]

what do you think john?

[John Larkin]

LOL, what can I say? I guess I gotta get the car fired up and crank up the boost. I do see the theory in a vague sort of way. Almost like the converter is spinning the fluid out of itself faster than it can fill up since the engine is torquing up more quickly. This causes it take more time to fill to create the line pressure necessary to make the shift. More time would equal more RPM. Just my take on it all. Am I way off base or just beating around the same bush in a different way?

[chris718]

john you may want to reread the post .its tuff to understand .yes you are off base but thats ok .i dont mean it in a bad way.i am going to find the info you post very useful however and it is a very important subject that you have placed before all of us.i am always happy to learn something new and now is our chance.thanks www.ckperformance.com

[MeanBuicks]

Originally posted by WE4
effeiceintcy. <<<( How the hell do you spell this word correctly)

In Miss'ippi, it's efishnsee.

[John Larkin]

Not a problem Chris; learning is good. I've tried twice to write a reply with a question. These are the most simple ones:

How similar is the torque converter to a turbo? They both have a power side and an output side that are linked but the TC has a stator in the center to transmit it's power through (a fluid link rather than a shaft in the turbo). Are the pump and stator the only parts of the TC that have splines to connect themselves to the trans input shaft? Where is the stator one-way clutch in relation to the pump and turbine?

I just can't get the relationship established between pump/stator and turbine/stator. I won't throw the lock up pressure plate into the equation since it's a variable at this point.

Maybe I've diverted the point of the thread but I think knowing the relationships of the TC internals will give insight into what really goes on.

[chris718]

john ill get to this tomorrow.extrremely busy.