VE and load

[cesar]

I have street tuned several turbo japanese vehicles and decided to transfer to the domestic world. I am a seasoned reader, and have some calibration books in my repertoire as well as some physics books as I am currently attending a university for an engineering degree. But in one of the books I have by Greg Banish, which should be a known guy in this forum I am assuming, there is a statement and reads as follows:
" For example, one may choose to test going from 2,000 RPM and 50 kPa to 2,000 RPM and 70 kPa. This simple tip-in event is typical of a normal traffic event in the vehicle"

I have never been so profoundly curious over this statement until today, hence me signing up to ask this. As far as I know there is a linear form equation when kpa and rpm are charted in the y and x axis respectively. The line has a positive slope.

The question is this: "How can someone be at steady state in 2000 rpm at one point and have 50 kPa or 50% load, and then at the same time magically increase the load without accelerating or doing any TPS changes?"

Correct me if I am wrong as I am not the best in tuning, but if the data plot forms a linear graph then how can 2000 rpm have TWO values of 50 kpa and 70 kpa?

Is this done in a mustang dyno, chassis dyno where the bearings increase kinetic friction and thus create more load on the engine? something in the lines of " a truck at 2000 rpm with no trailer will be in the 50 kpa cell, and a truck with a trailer attached will be in the 70 kpa cell at 2000 rpm"

is that how it works?





BY THE WAY, why does the HPtuners software measure MAP positive across the board? is it magnitude only? because 100 kPa at 7000 rpm would be so much "boost" in the intake manifold. I am assuming anything under 100 kpa is a negative value which in this case has only magnitude and is reported as positive pressure instead of vacuum.

[Bill@HPTuners]

100kpa is 0psi of positive boost pressure...

[2xLS1]

Where in Banish's statement does he say there in no change in TPS? A tip in event is a change in TPS.

[cesar]

100kpa is 0psi of positive boost pressure...

according to the conversion measurements

14.5037738 psi = 100 kPa

I am aware 100 kPa=100 % VE in NA engines, anything after 100% and 100 kPa is positive MAP pressure.

but in the hptuners software, that is not the case.

How is it determined that 100 kPa or n/m^2 inside the intake manifold is the same 0 psi in the manifold? thanks in advance


Also, 2xLs1 of course a tip in has to increase TPS signal. My concern is how do you magically change the load on a car while keeping the car steady at 2000 rpm? is that done through a chassis dyno?

[Bill@HPTuners]

which is atmospheric pressure.

[Chris@HPTuners]

MAP is Manifold Absolute Pressure - absolute meaning referenced to 0 (perfect vacuum) not refernced to atmospheric pressure which is around 101kPa unless you live in the mountains.

VE and MAP are not the same thing. VE refers to the engines volumetric efficiency in pumping air. Even if MAP is 100kpa (atmospheric meaning there is little loss in the throttle or air filter) the engines VE at it's current RPM might be much less like 70%. Depending on camshaft, cylidner head, etc.

To tune the car at various MAP (load) points at a constant RPM you need a load based dyno that can hold the engine RPM fixed. Or search for a long uphill road

[twinturbo]

Greg was talking about tip in with throttle opening. Adds more load, more kpa. Many of the import tuning software uses different units of measure, but once you get used to KPA, which is the unit all domestic OEM's use, it will make better sense to you. I see others using PSI in aftermarket controllers, and IMO, KPA makes more sense to me, and I use those units, if an option.

As far as increasing load(KPA) with no throttle change, yes, that would be a hill or other load factor. With the loaded dynos, you can create that event as well, and is useful for your steady state tuning.

The areas I defined for myself years ago are:

Idle (no load, no load w/ a/c, same in gear)
Steady State at different load and rpm points
WOT up the range
Transitions (mainly tip in and positive throttle delta change)

I like to isolate these so as not to skew my numbers, and I also like to see constant repeatability and average on each.

Think of KPA as:

-0 is 30 inches of vacuum, 50 is 15", and 90-105 as zero inches of vacuum

-KPA is 0% load , and 90-105KPA is 100% load. Boost is over 100% load, with 14.7psi being around 200KPA

-I have seen Zero inches of vacuum range from 100-105 at sea level, to 95-97 at 1200 feet above sea level. Key on, engine off will show you what your zero is for where you are.

-14.7 psi is actual atmospheric pressure, FYI, but refenced as Zero for the most part in GUI's.

-Keep it simple for you.

Jim

[cesar]

thank all of you guys, I fully understand now since it is referenced to '0'

awesome info