Re: Porsche Sports Exhaust and gas mileage. Results

While on route to Mid Ohio on Friday, because the 401 (like an Interstate) is pretty flat and straight between London and Detroit, I decided to run a test to see if there was any difference in gas mileage between having PSE on or off. I'll explain how I tried to keep it as scientific as I could, when I reveal the answer on Friday. In the mean time. Here's the question.

What effect do you think PSE has on gas mileage? (That is, using same driving style and conditions either way)
A PSE on gives better gas mileage
B PSE off (like the stock exhaust system) gives better gas mileage
C PSE on or off, you get the same mileage

... it depends on the load you're putting on the engine.
If you are on the highway with no real loads you should get better mileage with it off.
If you're on mountain roads you should getter mileage with it on.
YMMV
Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 314,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

"A mile of highway will take you one mile. A mile of runway will take you anywhere."

I'd say on average you get better mileage with it off.

Here is my experience with PSE and gas mileage.

First. Here's what I did to eliminate as many variables that I could, like traffic, hills, wind, variations in speed etc. Having already driven 60 miles, the engine was completely warmed up.
I was on the 401 between London and Detroit, which is a straight 4 lane highway similar to US Interstates. That part of Ontario is almost like a pool table, very flat except for an occasional overpass. Traffic is very light on this 120 mile stretch, so I was able to maintain a constant speed. I know it sounds like a boring drive - and it is, which is why I decided to conduct this experiment, for something to do while on route to Ohio.

I held the car at a constant speed of 125 kph (78 mph)
Temperature in the morning was 6 C (43 F) and climbed to 10 C (50 F) by the end of this stretch.
We were driving into about a 15 - 20 mph headwind.

I decided to drive four 20 mile stretches, two with PSE on, two with PSE off. (I did not engage Sport Plus mode, as that would add another variable.) I would switch PSE off, then reset the trip computer. After a few miles, each time, it settled to a constant consumption readout which I recorded at the end of 20 miles. Then I would turn PSE on, reset the trip computer and again take a reading after 20 miles.

So, the results for each of the 20 mile segments:
1 PSE off: 9.0 liters/100 km (26.1 mpg)
2 PSE on: 8.7 liters/100 km (27.1 mpg)
3 PSE off: 9.0 liters/100 km (26.1 mpg)
4 PSE on: 8.7 liters/100 km (27.1 mpg)

So, the correct answer appears to be:
A PSE on gives better gas mileage. So not only do you get a better sound, but you save money as well.

There is of course one caveat. When you have that PSE switched on (which I always do), you just constantly want to be conducting that orchestra with a little more vim and vigour. Who wants to listen to the Symphony in Flat Six in a monotone anyway.

Just as an aside, once we crossed over into Detroit and started heading south on I-75, with heavy traffic and speeds closer to 65 - 70 mph and no longer driving into a headwind, gas mileage climbed to 29 mpg.

I infer that PSE is somehow a switchable condition?

How does it work? Do flaps open? is something by-passed?

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

Quote
grant
I infer that PSE is somehow a switchable condition?

How does it work? Do flaps open? is something by-passed?

Grant

You are correct. With the Porsche Sports Exhaust, there's a switch. Default is always PSE off. So after starting up the Boxster, I always hit the PSE button which activates a solenoid that, I believe, closes a flap to bypass most of the muffler. (I'm sure that Pedro can explain it better than I can.) I would think this causes less back pressure. I'm guessing that's where you get a bit of a freer flowing exhaust. I've never read of Porsche claiming extra HP, although most other manufacturers of sports exhausts claim all sorts of increases.

PS, Just from the sound alone, I'm sure mine gives me at least an extra 25 iHP.

So, not only does it sound good--his car's exhaust sounded nice, BTW, but it's good for your wallet , so to speak.

Quote
MikenOH
So, not only does it sound good--his car's exhaust sounded nice, BTW, but it's good for your wallet , so to speak.

Absolutely. With roughly an extra 16 miles per tank you get, it will pay for itself in no time.

In fact, with the gas you save, I'm surprised it doesn't get a government rebate because it conserves natural resources.