drewmob

thomsbrain

As for the fuel economy question, yes having a taller overall ratio on the freeway will improve fuel economy down to the point of bogging.

As for bogging, it's easy to find information indicating how little of an issue it would be. With 10 seconds and something called Google, I pulled up a dyno chart of the stock 2.2L that shows it can produce up to 53.9 HP at 2100 RPM. It takes very roughly 20 HP to cruise at 60 MPH. So you could gear down to 2100 RPM @ 60 MPH and not even be using half of the engine's potential. The OP wanted 2.5K, so that's even easier for the engine to do.

I only saw one post in this thread from someone who actually understood the mechanics of MPG, and not surprisingly it supported the lower RPM = higher MPG reality. The foks who disagree neither understand MPG from a theoretical perspective nor have personal experience hypermiling. Not that everyone needs to be a mileage geek, but if you don't understand something don't spread your ignorance.

snakeeater

Most cars are geared from the factory to cruise at or near their peak BSFC rpm (which is usually near peak torque rpm). BSFC is fuel burn rate/horsepower. So that gearing makes sense as a good compromise between mileage and power.

If you move to taller gearing, you can improve mileage, but with the downside of reduced power. This will affect driveability, requiring more downshifting when power is needed. Of course there are limits, too low of a cruise rpm will lug or bog the engine even on flat grade, no wind, steady speed. A slightly steeper gear will avoid bogging, but you would still need to downshift every time there's a wind gust, or slight uphill section of road, or god forbid passing another car.

If you move to steeper gearing, you can increase power, but with the downside of reduced mileage. The S2000, being a sports car is normally modified towards this end of the gearing spectrum, in order to increase acceleration, since that is an important part of the sport driving experience.

Now I realize that everyone has their own individual circumstances and needs, but it is slightly unusual to think of sports cars and hypermiling in the same breath. And even stranger to consider making an expensive (semi-)permanent change to a sports car that would so negatively affect the "sports" aspect of the car's driving prowess.

rob-2

I'm just interested in what I might get.

If there was a simple way to bring the final drive down without ruining the 1-4th performance I would have done that. Thanks to all the helpful information I have ID'd the issue as two fold

1. My tires are louder then I had previously though (rated 6.4 when I normally drive a 7.8)
2. My motor noise is part of the noise, but this would be best over come with an increase in the firewall noise dampening (which there is almost none)

I believe adjusting these two, likely 2 and then 1 (I bought the car with new tires) will get me exactly what I want. I love the car and as MPG go I'm getting 25-32mpg. So I'm not in a hurry to play to improve that.

Just wanted a slightly quieter cruising experience. I realize everyone is different.

SpitfireS

snakeeater Posted on Aug 26 2009, 05:26 PM
Then howcome Honda completely missed the boat with the AP1 and the 4.10 diff?
I mean.. the 4.57 ratio is much much better.
In every way.
DD driveability, acceleration in every gear at any revs, topdown topspeed, you name it - it does it better.

chris_barry

Wow, I can't believe how much crap some people have put on this guy.

Rob, I'm also looking at putting longer legs on my S2K based race car for different reasons.

My car averages over 100mph its whole life. The only time I'm not on VTEC is under brakes and corner entry, other than that its over 7000rpm.

The problem I have is that on the long race circuits I'm running out of revs in 6th gear. I'm banging into the rev limiter which limits my top speed. Apart from the start I never use 1st or 2nd gear, and 3rd gear is too high in the rpm band mid corner. I'm stuck with a particular tyre size as the race series has control tyres so I need to make the overall gearing taller.

I'm looking at setting up a second differential unit with a 3.9 ratio which I can swap in for the long tracks. If you want to drop the cruise rpm on your car its an easy thing to check, especially if you get hold of a second diff unit so you can bolt in/out and see how you like it.

This miata web site gives the part numbers for the different ratios.

Miata diff interchanges

Good luck mate, give it a go and let us know if you like it.

snakeeater

Who knows? It could have been to meet an NVH target or an MPG target or a top speed target. Maybe durability or maintenance schedule concerns? Maybe so the test drivers never had to down shift into first gear on their test track. Could be a million different things. My theory is that, of all the gearsets then available to fit their chosen vendor's diff, the 4.10 ratio best met their goals. No one but the lead engineer on the AP1 development team could definitively answer that question, or their goals.

The 4.57 ratio may be much better in every way YOU care about. But the post after yours shows that chris wants to go faster than 150 mph on a track. In every way that matters to HIM, a 3.90 ratio would be much better.

It's a compromise, just like everything else in the design process. Every choice has its benefits, but also its own drawbacks. We make our choices with our pocketbook.

starchland

imo the ap1 had 4.10 to keep economy and reliability in check.

s2000Junky

You can effect your gear ratio through increasing your tire size as well. Of course there is a point where some other issue will arise, like handling & fitment. But this is a way to affect your gearing without getting into the expense and mechanics of your car, and if you don

MuttGrunt

Am I the only one that finds this thread over-the-top hilarious?

Guy wants to know about decreasing engine sound while improving his MPG in HIS s2000 (you know... the one he owns and paid for)

Common responses: Why would you do that / that's stupid / should have bought a Vette / that's not what the car was meant for

That's not what the car was meant for?

THAT'S NOT WHAT THE CAR WAS MEANT FOR?!?!?!?

All these people going FORCED INDUCTION in a car MEANT to be NA???
All these people lowering to a >1 inch gap between their fenders and tires??
All these people putting ugly ass over-fenders on their cars???
All these people running stretched tires and crazy camber??

But Heaven forbid a guy want to make a change to how his s2000 performs/sounds in a way that he would enjoy. And let's make sure when he comes to a huge knowledgeable s2000 community to get possible information on what it would take - he gets ridiculed.

have fun with your turbo/sc kits, ugly ass body kits, and ridiculously low set-ups that show what an S2000 was MEANT FOR

With such a wide range of tastes and mods on this site, I can't believe some of the feedback left for a guy with a legit question. To those providing intelligent, positive, well thought-out responses: props

P.S. The freeways around me have a 70MPH speed limit with a flow of traffic usually between 75-80 MPH, let alone in Texas there are 80MPH speed limits. Don't forget some states allow you to legally drive over the posted speed limit if you can prove the conditions allow for it. Quit crying over a guy driving 75-90mph