What kind of mileage do you guys get with your VX?

[1993CivicVX]

You guys should get gas logs for your cars.

[monroe74]

gary: "in most cases I will drive through several hundred miles with the engine never reaching any rpm above 2500"

In this regard your driving style is very similar to mine.

I just did a test in the following scenario: moderate uphill grade, 27 mph, top gear, 1000 rpm, WOT. The engine pulls smoothly, with no signs of detonation, hesitation, or unusual vibration. My weight, plus cargo, was about 230 lbs.

So I generally keep my revs very low, like you.

"at WOT you wont have lean burn"

Actually, AFR goes from lean to rich at a moderate throttle setting, way before WOT (about 25%). And if you define 'lean burn' as not just lean, but very lean, then this is only seen at very moderate throttle settings (about 10%). On the other hand, it's possible to cruise at a reasonable speed (50 or more) at such a setting. But I'm not sure that's the optimal strategy.

"I read a post on this forum where a member who had a Means of determining when lean burn was engaged"

I'm currently monitoring lean burn with a simple DMM. It's easy to do.

"he could actually climb a hill (probably a slight grade) and still stay in lean burn"

Yes, provided the conditions allow for a moderate throttle setting, which they often do. But I've come to believe that moderate throttle settings are generally not optimal.

"That was a critical factor in using a lower throttle position to try to maximise lean burn on acceleration"

My experience monitoring lean burn (defined as 'very lean') tells me that lean burn is easily achievable in steady cruising, but not generally achievable in anything we would normally call 'acceleration.' I've also come to believe that steady cruising is inferior to P&G. In other words, minimizing pumping losses has a better payoff than maximizing lean burn.

I think WOT minimizes pumping losses. I'm greatly influenced by this graph:

http://www.autospeed.com.au/cms/gall...0&a=110216&i=6

It shows that WOT improves BSFC.

I think some of our assumptions about avoiding WOT have to do with concerns about open-loop mode. But I'm starting to believe that a system with a wideband sensor doesn't have open-loop mode. Or if it does, it's less extreme than what happens on other cars, with low-resolution sensors.

"it would be interesting if we had a BFSC map for a VX"

The article I cited has a map for the Insight, which has a similar engine. The graph is interesting, although in some ways it seems to contradict the other graph I like.

"Once you have reduced the manifold vacuum to its lowest point, more throttle has no effect, except to add more fuel and basically apply full load enrichment."

Why is it reasonable to assume that the vacuum at 99% throttle is just as low as the vacuum at 100%?

"please understand this is not a criticism of any kind"

I don't take it that way at all. I greatly respect your opinion, and I appreciate the opportunity to learn something.

[monroe74]

1993: "gas logs"

I intend to, eventually, but I think I want to wait until I develop more data, and more consistency. Lately results are erratic, because I'm trying a bunch of different weird tweaks and tests, in the car and in my driving. I haven't had it very long. And I don't put on a lot of miles, right now, so it's taking a while to accumulate the data I want.

[1993CivicVX]

"27mph, 1000rpm, WOT, slight up hill"

Yeah, no, my car will not do that. I mean, it *will* do it, but it just doesn't feel at all happy. Are you telling me your car sounds/feels the same at 1000rpm, WOT, 5th gear as it does at 1300rpm, WOT, 5th gear?

[Sigifrith]

Originally Posted by monroe74

.................
I decided to look up your tire (Potenza RE92, 165/65R14) at tirerack. Your diameter is 22.5". The stock tire (165/70-13) is 22.2" (I used the Sumi HTR T4 specs). The tire that lots of folks seem to be using (175/70-13) is 22.7". So your tire is closer to stock than a 175/70-13! That surprised me. So that would explain why your speedo error is pretty small, and why 1st gear feels right (instead of feeling tall).

I was also very interested to notice how light your tire is: 13 lbs. Compared to 14 lbs. for the 165/70-13, and 15 lbs for the 175/70-13. So your tire seems to be lighter than stock! On the other hand, your wheel probably weighs a bit more. I think the VX wheel is about 8 lbs.

Another comparison: the Potenza has a max inflation pressure of 44. The Sumis indicate 51.

Anyway, it seems that you made a wise choice.

I'm pretty sure the VX vs HX setups are about the same weight. Higher weight wheels, but lower weight tires. I'm running 60 PSI with no problems of wear or traction.

[monroe74]

"Are you telling me your car sounds/feels the same at 1000rpm, WOT, 5th gear as it does at 1300rpm, WOT, 5th gear?"

Yes, essentially, except for the differences that are obvious and normal. 1300 rpm is about 35 mph. Things sound a bit different because you're going a bit faster, and you feel more power starting to become available. But other than that, it feels the same.

Going up that same grade, if I release the throttle (and stay in gear) and let the speed drop to about 20 mph (750 rpm), and then reapply WOT (or any throttle at all, for that matter), this is not good. I can feel immediately, in the lack of response, and in vibration, that the motor is not producing enough power to match the load I've placed on it. The speed will continue to drop, even though I'm requesting power.

But if I'm at about 1000 rpm, the motor is happy. And remember, this was going up a slight grade. On a level road, and if I dumped the 70 lbs of cargo I was carrying, the threshold moves down to maybe 800 rpm, or maybe even less.

"it [my car] just doesn't feel at all happy [in a similar situation]"

When you say not 'happy,' what's the symptom? And have you ever checked the timing? It could be something very simple, like that.

[monroe74]

"I'm pretty sure the VX vs HX setups are about the same weight."

Just to be clear, if I understand correctly, you're using the HX wheel with the Insight tire. The HX tire is 185/65-14. That tire weighs 16 lbs. Your Insight tire (165/65-14) weighs 13 lbs. So your setup is perhaps more properly called an HX/Insight setup.

Anyway, I think the HX rim is 11 lbs, vs 8 for the VX rim, so you may have increased your overall weight a little. But I have a feeling your Insight tire has especially low LRR, so that probably offsets the weight difference.

"I'm running 60 PSI with no problems of wear or traction."

Interesting. My Sumis are marked 51. I've been running them at 55, but I plan to go to 60. I'm even tempted to try 65. But first I'd like to hear that someone else got away with it!

Proportionally, your experience suggests I would be OK. The max marked on your tires is 44, I think.

[monroe74]

A few things I didn't notice until just now.

Originally Posted by R.I.D.E.

Everyone seems to be concerned about when the car is in lean burn. Couldn't that be determined by the solenoid activating that controls the closing of one intake valve. I would think that would be directly related to lean burn, since the swirl is an essential component of the lean burn mode.

You are correct that VTEC-E (what you mentioned regarding the solenoid) and lean burn are related. However, the relationship is not exactly as you described.

VTEC-E means that at low rpm, the second intake valve opens only a small amount. This provides the swirl you mentioned. And you are correct that lean burn relies on this swirl.

On the VX, the VTEC-E threshold is 2500 rpm. Above this rpm, the solenoid activates and the second intake valve opens fully. (Besides 2500 rpm, some other conditions also have to be present; e.g., the engine has to be warm.)

So lean burn does not happen over 2500 rpm. But it's important to understand that just because we're below 2500 rpm, that doesn't mean we're in lean burn. For lean burn to take place, you need to be under 2500 rpm, and you also need to be using a relatively small throttle opening.

One thing is certain, at WOT you wont have lean burn.

Correct. But the important thing to understand is that you also won't have lean burn at 75%, or 50%. I think lean burn generally goes away at any throttle position greater than 10-20%.

Without the potential for maintaining lean burn I would use 75% throttle on feedbaack fuel injection cars, to avoid open loop full load enrichment.

When you're using 75% throttle, you're definitely not in lean burn. But maybe you already know that.

Also, as far as I can tell open loop does not take place on the VX. Wideband-sensor systems generally do not need to resort to open loop. But that also might be something you already know.