Cylinder volume vs compresion tuning

[wadesns]

I have often wondered how compression is accounted for while tuning and have decided to ask for others opinions. I am not sure where compression is taken into consideration while tuning. Cylinder volume is taken into consideration for in {B0104} but i cant seem to grasp the ideas for compresion. Does cylinder volume need to be adjusted when you add a 3cc piston or a -6 cc dished piston? Ideally you are changing cylinder volume right? What about shaving your heads to add compression this too is changing your volumes but there isn't a place to insert the volume for you combustion chamber?

Thanks,
..RJ..

[5.7ute]

From what I can gather B0104 is only used for the VE% calculation in the tune tool & is not used by the PCM for any fuelling or airflow calculations.
As for compression ratios do a google on DCR (Dynamic Compression Ratio) Here is where you step into the realm of professional engine builders.

[wadesns]

I must be totally confused :) doesnt the ve control your fueling? I thought that our ve tables were what tells the ecm how the engine flows so wouldn't that change almost how the entire tune works? Or is it that you are saying that cyl vol is only used for the purpose of displaying a % while using the tuning tool provided by efilive or competitors

[5.7ute]

Exactly. When the VE table is displayed as a percent there is a calculation made using B0104. While it may be close the percentages cannot be taken as gospel.

[wadesns]

ok that seems to make sense until I attempt to change b0104 and after changing its value in efilive it doesn't change my main ve {B0101} at all. If i do this same procedure using hpt the change affects the primary ve instantly. Is there a glitch in efilive? Maybe just my version? would someone else please try and see if theirs changes as well.
Thanks,
..RJ..

[5.7ute]

If you change B0104 while you are displaying the VE table in % of theoretical maximum. Save the tune,close & reopen it it will alter the data in B0101.
However if you are displaying the table in the default units,grams/cyl or grams/sec changing B0104 will not change the data on B0101.

[Redline Motorsports]

Compression is irrelevant to the PCM. All its job is too control fuel and timing. It doesn't really matter to the PCM since the objective of tuning is to correct the required tables so the PCM is not making as many corrections on its own. If you had an engine that was 11.1:1 or a motor that was 9:1, hitting a target AFR is still done the same way. This is also the same for ignition timing. Of course the values will be different depending on the airflow modeling of each and how much timing the motor likes without knock.

Make sense??:nixweiss:

Howard

[wadesns]

so there is not a need to change anything due to compression beacuse compresion is accounted for through the ve and timing tables? ie. ve accounts for airflow changes due to compression change and valve timing and the timing adjusts for change in the way fuel combusts under different compression? That is kind of what i gathered from what you said. Hope it's the right thing. Now what about the volume again. Is there any need to adjust it in the pcm if it doesnt do anything but aid us in reading a percent for ve's? if it does need to be changed should you account for piston dish or alterations or just assume it wants a volume for a flat top piston only?

Thanks,
..RJ..

[Doc]

Ditto what Howard said Plus,

In the tuning, tool under properties, Volumetric Efficiency Values;

Display in: XXXX

Change that to : default units(g*k/kPa)

Read, absorb, and live by Appendix B in the tuning tool manual.

In other words, walk like an egyptian...

No other product I know of allows you to interact with the pcm on it's level like EFI Live does.

[joecar]

Yes, the VE table is really a "temperature/pressure normalized" airmass table...

For the tunetool to treat it as a VE% table, the tunetool itself has to synthesize an artificial table using Edit->Properties->Display->Charge Temp and B0104.

The PCM wants airmass... it doesn't want compression ratio or cylinder volume.

B0104 appears to be for "documentative purposes".

[98 tigershark]

The more the compression the more the explosion and less margin of error for timing (ie detination) or unburnt fuel there for EPA and bad VE. Lower compresion is a smaller explossion and a lot less risky for detination.