Understanding what kPa is for tuning

[rbabos]

Load is higher at the 1/2 throttle 100 kpa.
Ron

[Tsani]

Well, on question 2, I was leaning towards higher, but just couldn't get around the idea of a fixed rpm-throttle- dealie with a load change...till hotrod brought up a real worls situation. And BTW, MAF is the other sensor I was thinking about.

As far as Q3,
No difference, 100 is 100 is 100 if all we are talking about is pressure. But if we are now including other things, I am with rbabos on this one.

[Scotty]

Question #3

What is the difference if the manifold measures 100 kPa at 1/2 throttle or 100 kPa at WOT in sea level conditions? Sea Level conditions means a Baro reading of 100 kPa for this case.

Difference in what? .................... 100 kpa is 100 kpa  no matter what the throttle position

[Jeffd]

i am voting with rabos  in order to be a 100kpa at 1/2 throttle must be under high load.

[thumpn]

Absolutely nothing as long as it reads 100% it doesent matter whether the throttle blade is at 50% or 100% the manifold is at atmospheric pressue

[hotroadking]

Or the engine isn't running at all 100 at sea level presuming that is the pressure
of the atmosphere at sea level and at 1/2 and wot would nothing be happening ie
the pistons are not moving and valves not opening changing pressure.


Isn't the MAP actually measuring the drop in pressure?  Can Pressure increase
above the max pressure out side the engine in the atmosphere ie if it's 100 KPa outside
the engine, wouldn't that be the max you could have?

[Steve Cole]

Tsani has got it! When you measure Absolute pressure it is what it is. If it's 50 kPa at 25 % throttle or 50 kPa at 50% throttle it doesn't matter, just the same as if it's 100 kPa at 20% throttle or 100 kPa at 100% throttle the pressure is what it is.

Question #4

So if your tuning a VE table @ 1500 RPM that is in RPM and TPS, what is the difference going to be if you reach 100 kPa at 40% TPS all the way out to 100% TPS? Again in sea level conditions

[hotroadking]

Apparently - None..

[thumpn]

I would say nothing would change the motor is all ready atmopheric so the is no inprovmemnt. The motor isn't capable of of any more. I think

[glens]

BINGO, MAYOR is a winner! The MAP will increase as soon as the load changes when throttle position is held constant and RPM stays fixed.

I'd like to see a load change where both the throttle blade and engine speed remain constant.  I don't think it can be done.  If you've got a load change, in order to maintain RPM the throttle is going to have to move, and in order to maintain throttle the RPM is going to change.

Question #3

What is the difference if the manifold measures 100 kPa at 1/2 throttle or 100 kPa at WOT in sea level conditions? Sea Level conditions means a Baro reading of 100 kPa for this case.

No difference.  The engine is taking as much air as it can and it ain't fast enough to overcome what the atmosphere can push through the throttle plate.  Now if the engine speed is different between the two conditions that's another matter in terms of what'll become fuel requirements.  If the engine's the same speed both ways, no fuel difference.

[mayor]

Question #4

So if your tuning a VE table @ 1500 RPM that is in RPM and TPS, what is the difference going to be if you reach 100 kPa at 40% TPS all the way out to 100% TPS? Again in sea level conditions

so, if a bike reaches 100 kpa at 1700 rpm at say 28% throttle...we can assume that the pressure can not go up, but is the amount of air traveling through the heads linear regardless of the increased throttle? what if your bike is capable of reaching greater than 100 kPa, due to increased cylinder fill abilities? 

[glens]

Question #4

So if your tuning a VE table @ 1500 RPM that is in RPM and TPS, what is the difference going to be if you reach 100 kPa at 40% TPS all the way out to 100% TPS? Again in sea level conditions

No difference.  All the table cells to the right of 40% are redundant in this particular case.

[Steve Cole]

Question #4

So if your tuning a VE table @ 1500 RPM that is in RPM and TPS, what is the difference going to be if you reach 100 kPa at 40% TPS all the way out to 100% TPS? Again in sea level conditions

so, if a bike reaches 100 kpa at 1700 rpm at say 28% throttle...we can assume that the pressure can not go up, but is the amount of air traveling through the heads linear regardless of the increased throttle? what if your bike is capable of reaching greater than 100 kPa, due to increased cylinder fill abilities?

There is always if's, and's or butt's but you need to first understand the basics. So I'm working in theory first and will get to real world after you can get your head around the basics. Now as far as getting better than 100 kPa it isn't going to happen as the head/port cannot push the air in. All it can do is restrict it less!

[glens]

what if your bike is capable of reaching greater than 100 kPa, due to increased cylinder fill abilities?

How are your phenomenal cylinder fill abilities ever going to be able to increase the air pressure outside of the manifold?

[Tsani]

Question #4

So if your tuning a VE table @ 1500 RPM that is in RPM and TPS, what is the difference going to be if you reach 100 kPa at 40% TPS all the way out to 100% TPS? Again in sea level conditions
[/quote]

Well if the RPM is staying the same but the throttle plate is changing, it would seem to me that there will lees restriction and the pressure would decrease.

[mayor]

what if your bike is capable of reaching greater than 100 kPa, due to increased cylinder fill abilities?

How are your phenomenal cylinder fill abilities ever going to be able to increase the air pressure outside of the manifold?

simple Glen, not all bikes are stock.    How do you think that one build of a certain cubic inch might out produce another by 15 ft-lbs?  that's all based on cylinder fill...it literally is like putting 6 lb's of crap in a 5 lb bag.  I have seen bikes pull 107 kPa, and I'm sure that's not a record...and I'm at 1,000 asl.   

[Steve Cole]

Question #4

So if your tuning a VE table @ 1500 RPM that is in RPM and TPS, what is the difference going to be if you reach 100 kPa at 40% TPS all the way out to 100% TPS? Again in sea level conditions

Well if the RPM is staying the same but the throttle plate is changing, it would seem to me that there will lees restriction and the pressure would decrease.

One you reach the point where the manifold reach's atmospheric pressure there is no more air entering the cylinder unless there is something pushing it in like a supercharger or turbo charger. So as you've learned 100 kPa is 100 kPa and your not getting any more regardless if the throttle is at 40% or 100%!

[Tsani]

Mayor, that is milli bars correct?
The other day we were at 30 inches mercury which is 102 kPa which is 1020 mb. I am at 68 ft asl.

[Tsani]

One you reach the point where the manifold reach's atmospheric pressure there is no more air entering the cylinder unless there is something pushing it in like a supercharger or turbo charger. So as you've learned 100 kPa is 100 kPa and your not getting any more regardless if the throttle is at 40% or 100%!

In theory, correct?

[Steve Cole]

As the weather changes your going to have number changes so that is why for this discussion I've called out sea level as 100 kPa. Here at the shop we see 102 - 103 kPa most of the winter months when it cold out, but the principal is the same. Whatever the Baro reading is, that is the best your going to get.

[mayor]

on reply #19 on this thread is a screen shot showing 33 inHG:
http://harleytechtalk.com/htt/index.php/topic,45734.0.html

so, how would the 100 kPa limit work with a bike that hits over 110 kPa?     I guess we could assume that a hi pressure area was around during this run.   

[Tsani]

I got cha on that Steve. Max is max unless aided. However the opposite is not true and comes into play in an engine. Carburators rely on it. So I assume so do EFI systems in a manner of speaking. But I will wait. As on of my old instructors used to say"For all you guys with time in the field, shut up, I have to teach this a certain way!"

[akjeff]

Seems to me that if you have 100k/Pa(basically atmospheric ppressure) at 40% throttle, the only way you can maintain that same pressure at 100% throttle, is for the volume of air to increase? That being the engine increasing in RPM in order to move the increasing mass of air?

Jeff

[hotroadking]

so the MAP is really only measuring the decrease in potential pressure

[glens]

what if your bike is capable of reaching greater than 100 kPa, due to increased cylinder fill abilities?

How are your phenomenal cylinder fill abilities ever going to be able to increase the air pressure outside of the manifold?

simple Glen, not all bikes are stock.    How do you think that one build of a certain cubic inch might out produce another by 15 ft-lbs?  that's all based on cylinder fill...it literally is like putting 6 lb's of crap in a 5 lb bag.  I have seen bikes pull 107 kPa, and I'm sure that's not a record...and I'm at 1,000 asl.   

Don't listen to Jim.  I never said or implied that all bikes are stock.  He's the one that keeps trying to make it seem that's what I'm saying.

Okay, so do you believe that reading in the screenshot?  It's only for informational purposes as the TMax uses that sensor for nothing otherwise, right? 

The only way I can envision a good-cylinder-filling arrangement could possibly cause a MAP sensor to go above atmospheric pressure would be to get the column of air moving so fast, then slam the door shut on it at the intake valve.  The mass of air might still be moving into the intake, hit the dead end, and get packed in by the tail of the column.  This is theory only, but if the MAP sensor was polled at just the right time it might capture a smidgen above atmospheric.

Maybe a long-overlap cam with exhaust anomalies could slightly pressurize the manifold, too.

Neither of those possibilities are what I would consider to be beneficial to the engine's running characteristics, though.