As many on here already know, I have swapped ECU's so that I have a 2001 ECU in my 2004 MY S2k. The theory is, the 01's run leaner and therefore afford the 2004 owner with slightly more torque/horsepower. This fact has actually been proven a number of times, running against other 01-05 S2k's. The car does pull on any non-SC S2k, from my experiences so far, which has been pretty cool.

However, lately my gas mileage has been, well, unusually high. I can't believe this myself, but the numbers and the multiple situations have me really wondering if the leaner mix is giving me more HP and more MPG!

For instance...

About a month ago, I was at Mid Ohio for a NASA track day with SoundZero and we filled up right before the event, at Sunoco. After we both did a full day of track driving (same number of heats and minutes on track, essentially), we headed out for home. Andy informed me that he was about empty (a few bars left). I looked at my gauge and saw I still had a little more than a 1/4 of a tank. I did not think much of it and wrote it off to driving style.
This weekend, I met up with Andy, Chase, and Scott to head up to Jon's GTG, in West Lake. They had all filled up that morning and I was running late so, I had to make due with about 3/4 of a tank, figuring I would fill up once we got up there. As it turned out, I ended up driving up there, doing about an hour cruise with everyone around Cleveland. After the air show, Chase and I took off back to Columbus. About 15 miles outside Cleveland, we both filled up. Chase said he had about 3 bars left. I checked and had 2 bars left! This is after I started with about a 1/4 tank less and drove the same route at the same pace!
At this point, I stared to wonder if I was getting some abnormal gas mileage. So, I said to Chase "let's fill up, drive back to Columbus and immediately get off the highway and fill up again, checking the gallons used". Our drive back was not an easy drive, with numerous speed fluctions in traffic and our pace was spirited. Anyway, I get back to Powell and fill up at the Mobil station. I check my mileage and had run about 115 miles since the last fill-up. The car only took 3.2 gallons!
That is 36 MPG!

I need to do a few more trips to check this repeatedly, but the number of times I have noticed comparitively better mileage is hard to ignore.

 

I believe it. This is equivalent to 43.23 miles per IMPERIAL gallon. My best when my MY'00 was completely stock was 39.9 (miles/IMP gal.) over a distance of 300 miles.
Over a short distance like what you did will not be as accurate as if you drove under the same conditions for nearly a tankful. I'd be interested to see what you get over a tankful.
This has got to be one of the most fuel efficient sports cars in this class.

 

What are you doing to prevent over-rev with the 2.0 ECU?

I hope your motor lasts.

Edit: BTW, the latest Consumer Reports has a thing on how cars aren't meeting their EPA gas mileage ratings. They have tested 303 cars and only 10% have gotten as good or better than their EPA rating -- the 2000 S2000 was one of them.

 

Gary please keep us informed on this I wonder if the powers that be at the corprate level new this, if there wouldn't be more changes for 2006?

 

Gary that is interesting. Please keep us posted.

 

I've already told Gary he's shortening his engine life. You guys should know by now how tightly Honda optimizes things. Sure there's always more power to be had with the factory tuning but at what cost.....

 

I hear what you are saying and knowing it, I have been careful with watching the tach during WOT acceleration, shifting about where I used to shift, 8200 RPM-8300 RPM. Rarely does the car see anything in the 8300-8500 RPM range and doubt the car has ever seen 9000 RPM. I don't plan on taking it there and I don't drive the car at high RPM levels often. Most my driving is around town with normal RPM levels.

I can't imagine what I am doing is any harder on a motor than running at the track all day at 8000-8200 RPM, in an S2000 with a stock ECU. For the occasional stint in the high RPM range, I would suspect the wear and tear would take place over a long period of time. Educate us, if I am seeing this wrong.

As for my longterm plans for keeping it, I am not sure either way. Of course, I want to have the engine torn down and checked out by Ganely, before deciding.

I'll keep everyone posted.

 

Why can't you believe it? The engine runs leaner, which means it's using less fuel for a given amount of air. And being that an engine is an limited displacement air pump, there's not going to be an increase in air flow by leaning the motor out.

You should get better mileage running lean, though the significance of the difference might worry me a bit. If the engine is running under stoich you could be creating some unfavorable burn conditions. Keep good gas in it, watch your plugs, etc.

 

I understand about running leaner.

Before the ECU, the best I did was 31 MPG, all highway.

After the ECU, I have 36 MPG, all highway, which surprised me that an S2000 would get mid 30's.

 

Have you gotten your car on a dyno since the change? I'd be curious to see the resultant A/F and power curves.