Volumetric Effeciency

by **rlees85** » Fri Sep 21, 2012 1:27 pm

Having some trouble calculating safe turbo limits. Part of the calculation is volumetric effeciency.

I am currently assuming the following:

VE = ~85% @ 2000 RPM (max torque)
VE = ~75% @ 4000 RPM

Anything inbetween is linear (ie, VE is 80% @ 3000 RPM)
Anything after is extrapolated
Anything before is just treated as 85 (not really relevent as not tuning much before 2000 RPM)

Is it safe to use assumed values for this or is it really worth while trying to figure it out from PP2000 data?

by **Relic** » Fri Sep 21, 2012 4:05 pm

You need IAT(F), MAF(lb/min), MAP(psiA) and RPM
Look at datalogs 1,2,3 in the openoffice spreadsheet file below.
VE1 is converntional based on Manifold IAT.
VE2 is based on ambient IAT for comparison as NA engines.
;)

by **rlees85** » Fri Sep 21, 2012 8:58 pm

holy crap that spreadsheet is scary!

was that data given to you or did you log it all?!

things like FMIC Temperature drop would be impossible to measure on standard equipment!

I will try and find the equation for calculating VE and try to log some data myself and see what happens. I see it is different at different air temperatures. that explains the boost limiter by air temperature map now

by **ecuedit** » Fri Sep 21, 2012 9:30 pm

rlees85 wrote:holy crap

:lol:

by **rlees85** » Fri Sep 21, 2012 9:33 pm

Just been on google and this is beginning to look like a bottomless pit...

To get VE, you need Air density,
To get air density, you need to know humidity...

I guess the only way to get solid facts is to do a series of dyno runs, at different temperatures. As I don't have a dyno this would be difficult.

How important are these values? Can estimates be used for the 2.2 Hdi?

by **Relic** » Fri Sep 21, 2012 11:58 pm

no you just need to log rpm, map, maf, and iat....thats it.
[preferably WOT low to high rpm or egr will be active]
Everything else is a calculation.
You dont need humidity for density calculation.

VE =(MAF*GAS*(RANKINE+IAT))/(MAP*(RPM/2)*INCHES)

INCHES = cubic inch dispacement
MAP = pounds/inch2 Absolute (Manifold)
MAF = pound/minute
IAT = Farenheit (Manifold)
RANKINE = 459.58 (273.1 K) absolute temperature
GAS CONSTANT = 639.6

You can rearrange the formula at will.

Air density (lb/ft3) = 1.325 * (2.03625437 * psiA) / (459.67 + IATf)

by **Relic** » Sat Sep 22, 2012 12:18 am

1.325 * (2.03625437 * 14.7) / (459.67 + 77) = 0.073902 / 0.0624 = 1.18433 kg/m3
1.325 * (2.03625437 * 14.7) / (459.67 + 68) = 0.075163 / 0.0624 = 1.20453 kg/m3

http://en.wikipedia.org/wiki/Density_of_air

by **rlees85** » Sat Sep 22, 2012 1:17 am

Thanks, thats given me something good to work with! Even google seemed to struggle with that one!! :crazy:

Relic wrote:IAT = Farenheit (Manifold)

Not sure how much of a problem it is, but with the logging software for Peugeot (pp2000) only reports IAT at the airbox, NOT the manifold where the air is likely to be much hotter. Is there a way to predict the air temp at the manifold?

by **Relic** » Sat Sep 22, 2012 2:47 pm

No...not easily.
Many MAF and MAP sensors have IAT sensor incorporated ;)
Both of mine do at least and are listed as iat1&2 in honda HDS.
Only the MAP sensor IAT (manifold) is made available to OBDII though by honda.

If you can get an OBDII cable and software to work....map maf iat and rpm are almost certainly available in all cars.
problem is map will not read above 2.55 bar as only one byte is available in the OBDII spec.
https://www.scantool.net/support/index. ... id=2&nav=0

I use obdlink usb + scanxl. BUt mainly HDS now as it can access more sensors and do hi speed datalogging too.