I took the MP/Cat Conv. off last month and replaced it with a Main Cat that had less than 30K miles. Kept the DP on.

Average city MPG with Mid pipe/Hi-Performance Magnaflow Cat Converter was 15.0. Average highway MPG with MP was 22.0

Average city MPG with stock Main-Cat is now 20.4. Pretty good number I think.

Fuel Octane: 93
Reman with 28.5K current miles. (Installed on 01/01)

PROS: Main Cat has added 5.4 mpg in city driving. Dbs much, much lower. Although still loud at WOT. Pretty pleasant over 3K rpm. Don't have any mpg numbers for highway driving, but I intent to take her out of town tomorrow. Hope I can approach 28mpg.

CONS: Notable HP loss (10-20?) at WOT.

But car still has great top-end speed. Had her up to 152 MPH last week with a little more to give

Just thought I'd share the info with y'all.

 

There is NO way that adding a restriction to the exhaust nets a fuel mileage increase, let alone of the order of magnitude you are claiming. Sorry, but you either miscalculated it or there is something else responsible for the change.

 

I was wondering about those numbers too. Shouldn't less restriction = better fule economy?

 

WAY!!!. I've been documenting MPG since acquiring the FD in 05/03. The numbers are accurate.

 

i dont know about this one

why do you think when a manufacturer puts out a car, it has the most restrictive exhaust ever? to pass emissions and at the same time get better fuel economy..

 

I second that notation. At first I thought it was hard to believe, but you also got to take in account the fact of running less boost (less full tossed in engine) with a more restrictive exhaust.

What I would question more and what to know is how are you getting such a high MPG in the city? Whats your driving habits, setup, etc..... Fill us in, any ting to squeeze a few more mpg is gold!

 

In general, restriction wastes fuel. But there are a lot of other things going with engine control systems, etc. that could negate the savings.

I do find it hard to believe that you got >20 MPG in city driving with this car. What is your method for measuring MPG?

-Max

 

I would think that more restriction = less boost = less fuel = better MPG

 

No, I don't believe they are. There is no way someone is getting over 3 mpg better than the EPA estimate for city driving, not in this car.

Wrong. Less boost = less fuel = better mpg. You can boost the same pressure level with both setups. In that instance, the car with less restriction will get better fuel economy. Besides, the only way to even get CLOSE to 20 mpg in city driving would be to NEVER boost. In which case the midpipe car wins again.

It's simple physics.

 

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Perhaps not too much stop and go driving in my city like in bigger venues? Also, I rarely boost above 4psi. I usually excellerate up to speed limit (30mph) from a complete stop without boosting above 2psi. I have a pretty light foot. The car can cruise a steady 80mph (at 3K rpm) pulling a 12 vacuum.

 

LOL!. You're arguing a moot point. The numbers are real. What's your city MPG??

 

At what rated Octane did EPA conduct it's test to obtain data??

 

the best MPG I've ever gotten HIGHWAY, hardly boosting if ever, (DP and catback) was 24mpg... going between 70-80mph... (on the way to Mid-Ohio Sportscar Course)...

I'm really amazed that you're hitting over 20mpg city, though... taking it really easy, the best I've seen city is about 19mpg...

when just driving normally, though, we're talking about 17mpg....

 

I'm still curious about your method for calculating MPG. Perhaps there is some issue with the method that is skewing the results. Please describe your method.

If I could get 15 MPG city, I'd be pretty happy. Or bored.

-Max

 

Agreed

 

Me too. Remember that FDNewbie' method was to note the position of the gas gauge and divide that by the maximum capacity of 20 gallons. Then again, he had all of his tires inflated to the maximum recommended pressure on the sidewall...

 

I'm bored much of the time

Method: I ALWAYS fill with ten (10) gallons and wait till low fuel light comes on. I mark mileage on my trip odometer and devide by ten. Since the Main-Cat install I've been averaging 204 miles per 10 gallons of 93 octane fuel. I was averaging 150 miles per 10 gallons when the MP/ hi-perf cat was on.

But I will add (just realized) that I installed new rubber all around (Dunlop FM901 P235/ZR40-17s) at the same time I installed the main-cat. Hmmmmm??.

The new tires are the same size as the old (Yoko A520's) ones.

 

If those Dunlops are different in any way from the tires you had previously, that will skew the results.

 

Definitely a softer, quiter ride. Grips like a ***** though

 

What I meant was whether you had the exact same Dunlops on your car previously...

 

I had Yoko A520s. Different tire manufacturer, but same size.

 

What ECU? Airpump?

 

The problem there is that there is no "size standard" among the tire manufacturers. One maker's "P235/ZR40-17" may be slightly different in diameter than another (yes, it's small, but that can make a big difference in rpm per miles traveled). Just because they have the same size designation doesn't mean that they're exactly the same size.

 

Try filling the tank until the pump kicks out by itself (do not top off), zero your odometer, drive for awhile, and then fill up until the pump kicks out by itself again. Divide the number of miles shown on your odometer by the number of gallons shown on the pump and you've got your average (assuming your tires are approximately stock diameter).

The gas gauge and sensor are not incredibly accurate. It's far more accurate to let the gas pump do the calculating of how much fuel has been consumed.

 

Stock ECU. Disconnected Air Pump. Also, I never let the AWS rev the engine at cold start-up. I bump it and let the engine idle into operating temp before the car is driven.