JR VPAC

[iranman]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by JRCivic:
... the VPAC is also boost and hrottle position sensitive in that it will only engage VTEC when you are aggressively accelerating. Otherwise, it simply stays on the low cam lobes.
<HR></BLOCKQUOTE>

I think schwett was attempting to quote this passage, but anyway....

Also, not to be Mr. Technicality, but how the hell can the VPAC be sensitive to boost if it only receives TPS inputs?

I have the VPAC, and I can tell that the radical cams engage at part-throttle and do so pretty much when positive pressure is created. I assume JR took the mechanical characteristics of the bypass valve into consideration when determining what TP setting would engage VTEC.

So, by what JRCivic is saying, the V-AFC engages VTEC from RPM inputs only? What about it's own TPS inputs? Are they only for the designation of narrow- and high-throttle fuel settings?
[please excuse my obvious lack of knowledge of the Apexi unit]


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'98 White Supercharged Prelude
My JRSC Site
Tampa Prelude Mailing List

[JRCivic]

Sorry for being too general...

The VPAC alone will only turn the VTEC hi-cam on/off based on two inputs: rpm and throttle position.

However, when coupled with the JR BTC, it also becomes boost sensitive AND it overides the retard settings inside the BTC under WOT.

As for the V-AFC operation... I am not very experienced tuning them either, but I can tell you that the VTEC operation is merely rpm driven... you have a hi-lobe engagement rpm and a lower rpm setting for the switch back to the low-lobes. The TPS and MAP connections are used to modify these readings to "trick" the stock ECU into the fuel changes that you have set.

I hope this helps to clarify a bit.

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'93 Civic Si H/B with B18C1, JRSC @ 8psi
Best 1320: 12.68 at 110 mph

[iranman]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by JRCivic:
Sorry for being too general...<HR></BLOCKQUOTE>

Bah! Don't worry about it!

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by JRCivic:
However, when coupled with the JR BTC, it also becomes boost sensitive AND it overides the retard settings inside the BTC under WOT.
<HR></BLOCKQUOTE>

Ah. I have a beef with this statement. From my discussion with JR, I've found that JR states that the fuel/timing maps under the radical cams are for a more 'loaded' system, unlike the normal cams. Thus, there is a lesser need for retarding the ignition timing.

Fair enough. If Honda programs the VTEC maps under the premise of being under a "higher load," then it makes sense to advance the timing little bit. After all, the BTC ain't perfect.

However, using my OBDII scanner (www.obd-2.com), I've seen data that points to the contrary. I was under the impression that the ignition timing would be modified from the newly set VTEC point up until redline. The results speak for themselves:



Tests were performed on a somewhat cool night in third gear. On the 'stock' setting, the VTEC point on the VPAC was cranked up all the way to the max.

I must add that this data isn't entirely accurate. Due to the design of the scanner, monitoring two parameters simultaneously does not mean that those two data values are retrieved at the same time. In fact, the readings are NOT taken simulataneously; the reading for the second parameter takes places during the delay between two values of the first parameter.

For example, here is a basic snapshot of values:

As you can tell, there's a slight time difference between the two parameters. Since I couldn't find a way to plot rpm vs. data point & ignition timing vs. data point, somehow extrapolate a curve that shows the exact relationship between timing and rpm, I just directly plotted Ignition Timing vs. Engine RPM.

Furthermore, it is noted that the BTC does it's job by modifying the ICM signal. Thus, the signal is modifed after it leaves the ECU, lending me to wonder how the hell differences in ignitition timing would be picked up by the scanner, unless somehow these outputs made it to the OBDII data connector AFTER the BTC (but I highly doubt that).

I can rule out statistical deviation due to the presence of changes of greater than 1-2? over the span of 200-300RPMS, as well as the fact that other users (namely schwett) have also datalogged differences in ignition timing (see his post below).

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'98 White Supercharged Prelude
My JRSC Site
Tampa Prelude Mailing List

[This message has been edited by iranman (edited November 12, 2001).]

[JRCivic]

It does not change any of the stock ECU timing values... the VPAC simply "bypasses" the boost retard knob under WOT when connected to a JR BTC... thus, it allows the full timing that you have set on the crank... whatever that value may be. In effect, the BTC now becomes a product that helps fight part throttle tip-in detonation by retarding timing in the mid rpm range and under part throttle boost.

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'93 Civic Si H/B with B18C1, JRSC @ 8psi
Best 1320: 12.68 at 110 mph