I don't know how many times that I've had to deal with this misconception but you gotta remember that the sidewall deformation plays a huge role in grip, too. Remember tirerack measures on different width wheels than ours.

 

Why won't it work? The conversation was about whether or not the engine will stay in VTEC rpm range after the shift. If he runs to redline in 1st, shifts to 2nd and maintains the speed he was at when he initiated the shift, the tach will tell the story. What does the speed of the shift have to do with it?

Drive Safe,
Steve R.

 

I think the tack will tell and I want to know the answer.

 

anyone going to try it?

 

Ok, here's what I got. These numbers were achieved by "normal" acceleration to redline (right at the point where it starts blinking but not at the fuel cut off point) and then shifting to the next higher gear and noting the rpm reading. By "normal," I mean I was just letting the car pick up speed like I would usually do in traffic. Throttle application was light enough that I felt nothing at the VTEC transition.

1>2 - speed, about 38 or 39 mph, tach dropped to about 5700 rpm. I say "about" because she "did not" like doing this. She wanted to GO when I shifted to 2nd. The car definitely fell below the VTEC on the 1>2 shift. Later, I did a full throttle acceleration in 1st to redline and shifted to 2nd. All I can tell you is that it only took 1/4 to 1/2 second (if that much) to get back into VTEC range so I don't consider it significant.

2>3 - speed, about 58 mph. The tach dropped to right at 5900 rpm. The car didn't try to jump ahead on me nearly as badly as it did in the 1>2 shift. Personally, I'm not going to sweat 100 rpm at this point, especially considering how fast this car accelerates in the lower three gears.

3>4 - speed, about 80 mph. The tach dropped to 6500 rpm, maybe 6600. Definitely still in VTEC.

4>5 - speed, 104 mph. Again, the tach was just over 6500 rpm and we're well within the VTEC range.

I had to shut down at this point as I was "rapidly" gaining on traffic. It wasn't a big deal but there's just too many people out tonight to try for a 5>6 shift although the one time I've pushed my car that hard a couple of weeks ago, it ended up about the same as the 3>4 and 4>5 shifts.

That's my NSSRT (not so scientific road test!)

Drive Safe,
Steve R.

 

I thought it was speculated that VTEC disengagement is different than engagement depending on the throttle position? Meaning when you shift, if you're still on the gas the VTEC won't disengage until a much lower RPM.

I thought that that is programmable in the VAFC as well?

 

you slow down significantly... and remember the tach only reads to 8000, it just flashes after that.

 

if you shift faster and let it rev more, you can stay in vtec. The stock tach is pretty slow. VTEC doesn't engage if you aren't on the throttle, btw.

 

Right, but the key is not necessarily to maintain speed during the shift, but see what speed you're going at 8000 RPM (say 58 in 2nd). Then shift. You will have slowed down slightly, but then in 3rd you can read what the engine speed is at 58 mph (depending on how much you slowed, you'd have to speed up a bit). While this isn't the most accurate way in the world (given the accuracy of the tach and speedometer amoung other things), it does answer the question that has been asked.

The question that has been brought up in this thread is about whether the gear ratios in the 04 cause you to go out of VTEC when upshifting on acceleration. There is a theoretical answer, as well as a real life answer.

Using the published gear ratios will give the theoretical answer. But there are a few assumptions:
1) No deceleration during the upshift.
2) No slippage in the clutch (it's completely in 1st, then neutral, then completely in 2nd, for example).
3) (and this assumption is very important, since I have yet to see an definitive answer) VTEC is dissengaged when the engine falls below 6000 rpms.

In this case we can calculate the from the gear ratios exactly what the engine speed should be on each upshift at redline, at rev limiter, or whatever other engine speed you choose to shift at. In fact, there is no need to convert engine speed to car velocity and then back to engine speed in the next higher gear (as several on this board have done). All you need to do is to calculate wheel speed (RPM) and then back-calculate the engine speed in the next higher gear. (If anyone is interested, I've got a spreadsheet with gear ratios for the pre04 and the 04, as I'm sure others do to. I can post some numbers.)

Doing the test that Intrepid175 did should mimic our answers from the theoretical approach, but there will be additional deviations as some (or all) of the assumptions do not hold. The numbers that Intrepid175 gave us are close (but generally higher) than the theoretical numbers, most likely because the car begins accelerating in the next higher gear before the clutch is completely engaged.

Which brings me to my final point... Even though theoretically, shifting at either redline OR EVEN rev limiter in an 04, from 1st to 2nd, or 2nd to 3rd, should drop the engine speed below 6000 RPM, typical "spirited" acceration will probably not allow the engine speed to fall below 6000 RPM. The car will accelerate while during the brief period that the clutch is slipping enough that the engine will never fall below 6000 RPM.

As to whether the car drops out of VTEC or not... I still have some questions that I hope some can answer.
1) Does VTEC disengage when you let off of the throttle above 6000 RPM?
2) Does VTEC automatically disengage when the engine drops below 6000 RPM or is there a lower transition point (say 5000 RPM)?
I'm sure I've got more...

 

Where did you find out about this? If you're not on the throttle hard enough to be accelerating that much, which I wasn't, you wouldn't "feel" the VTEC when it engaged anyway. My impression was that VTEC was rpm dependant, not throttle dependant but I could be wrong.

Just wondering?
Drive Safe,
Steve R.