Max lean burn horsepower with VX engine.
 

Anybody know what the maximum horsepower produced by the VX engine in lean burn mode is? Based from the throttle position, I'm guesstimating its somewhere around 20 hp. This has been bugging me, and I'm curious to find out what my max speed in lean burn is and if is it RPM or load limited on a level highway. Been up to 80mph so far without it dropping out lean burn on a slightly downhill changing to level stretch of highway. The problem is the only 70 mph PSL roads near here are I-26 and I-85 and the closest long, flat stretches are on I-26 south of Columbia, SC. Don't want to get a ticket while trying to find the limits of lean burn.

Time for a dyno day?

What I read was lean burn was up to 2500 RPM. If memory serves me right that worked out to about 73 MPH.

regards
Mech

I'm not to sure what the max HP would be in lean burn?

What rpm are you at going 80mph?

My gear calculator says you should be around 2787rpm @ 80mph based on a VX transmission with a 22" dia.tire?

I can monitor lean burn on the SuperMID where the injector pulsewidth drops or jumps 2.0 usec as it enters or leaves lean burn when the pulsewidth reaches 6.1usec in lean burn (it jumps up to 8.0 usec as it leaves lean burn). I can also feel a sag or surge as it transisitions into or out of lean burn. Vtec-e kicks in at 2500rpm, but the pulsewidth on the MID doesn't change indicating a drop out of lean burn when it engages and I don't feel the surge that indicates it dropping out of lean burn. I haven't been able to do a long enough run at 80mph spend time trying to transistion in and out of lean burn through the 6.1usec threshhold. At 80mph the rpms are almost 2800.

One the way home this evening, I got in with a group of fast moving traffic and was able to run it up to 85mph and confirmed on the SuperMID and by the seat of the pants that I could enter and leave lean burn at that speed as I moved the throttle. It looks like, at least in my car with a Euro ECU and a D15B Vtec-e engine,that lean burn is only sensitive to the throttle position and not to RPM. Anything less than 6.1usec injector pulsewidth on a warm engine will produce lean burn. Vtec-e just kicks on at rpms over 2500 and has no effect on lean burn. I'm thinking that with a stock VX, the aerodynamic drag rises so fast that by the time you have reached 2500rpm at 73mph, the wind load is high enough to kick it out of lean burn and that's why everybody thinks when Vtec-e engages, lean burn drops out. Since that is not the case with my car, it will be interesting to find out what the terminal velocity in lean burn on a level highway will be. I'm guessing somewhere between 90 and 100mph.

Interestingly enough I was averaging 78mpg over the 5 mile stretch where I was running at speeds from 70 to 85mph. It was a section of gently rolling hills and the map shows no overall change in elevation for that stretch of highway. Now I just need to find how fast a constant 6.0usec on the SuperMID will get me on a level highway, but that will take a trip down to the Low Country and the flat roads of the coastal plains.

While down there I also need to get some mpg reading for various constant speeds and do some coastdown tests to measure my current Cd. I've made quite a number of small improvements to the car's aero since getting the Cd of 0.17 in coastdown tests 2 years ago, so my Cd may actually be less than that now.

Nice! I know the stretches of road you're talking about, ~10 miles on either side of I-95. You ought to be able to find somebody going fast enough for your needs.

I'm looking forward to seeing the results!

Makes sense to me that your lower throttle position due to lower aero drag would increase the lean burn threshold. That would explain the difference and the feeling of the surge.

I never really felt the surge, and I did not have the precise instrumentation, but I would assume your conclusion is correct. The Vtec-E was the reduced valve lift under 2500 if I remember correctly. I thought they were coordinated (the lean burn threshold and the valve actuation change) but obviously that was not the case.

It would probably happen regardless of the ECU if it was Euro or other versions.
I think my was marked AUS but that is from memory which I can't trust like I used to.

My VX was bone stock when I bought as salvage 1.5 years ago with 27,492 original miles on the ODO. I even drove it another 15 k miles on the original tires, made in March of 1993. That was spring of 2008.

regards
Mech

Glad you're having fun with that Mike :thumbup:

Don't know if you could benefit from such a thing, but I did have a device that recorded the elapsed time between ignition events on a particular cylinder via an inductive pickup. With that data and the weight of the vehicle, Cd, frontal area, ect, it would plot out a real torque curve along with hp that looked identical to a real dyno chart, and was printable. The device I found to be impressively accurate from run to run at a +/- 1.5 hp variation.

The device was great at finding that last drop of hp and shifting torque curves around as well as recording elapsed time between transient rpm changes during a pull. That was an awesome piece until I outgrew it and no longer had traction below 60 mph. The temptation to do testing in a higher gear was enough that I gave it to a friend of mine in NY to prevent possible litigation.

If you think you could use somehting like that for testing I could probably get him to ship it back for a while. You would just have to be consistent with your throttle seeing as you'd be running it at partial throttle, but it would probably give you your power reading at max leanburn

VTEC-E can engage from 2500-3300 RPMS based on what I've seen for throttle input and vehicle speed. So it would be possible to stay out of VTEC-E and still be in lean burn for quite a while on the highway.

You can always throw an LED on the Spool Solenoid (negative trigger, ECU grounds the solenoid to trigger) to see when VTEC-E engages.

Here's the Factory dyno plot and BSFC for the VX:
Green is torque, blue is BSFC
http://www.thelic.org/users/tomo/CivicVXdyno.jpg
It might help to calculate your HP at the given RPM Mike.