I've seen threads asking about how a 15% pulley affects mileage, but no one had a good answer. It was usually, "Well, I drive faster now, so I can't compare."

So if you have a 15% pulley and the on-board computer, I have a request:

What is your MPG at a steady 70 mph in 6th gear?

The reason I ask is that I want to see if you get better highway mileage by adding more power with a pulley. Make sense, or am I crazy?

(Obviously how quickly you get up to 70mph has a greater impact on overall mileage. I'm trying to take that out of the equation by getting the instant MPG from the OBC.)

Thanks!

 

Actually I don't know if you are or aren't! but I was only given two choices.

If you think what the car is doing, it has to do a certain amount of work to move the car at a constant speed. This work is air resistance, tire rolling resistance, internal friction, and motor efficiency. Sinc the motor is going at a fixed RPM, cars with pulleys will probably run slightly less open TBs such that there's the same air density in the intake. Then the ECU sqirts a the same amount of gas, and the car makes the right power for the conditions. Also, this light load may well have the by-pass open, running little or no boost.

There are a bunch of competing issues in gas mileage as driven, and depending on how you drive, you will definantly get better or worse or the same milage!

Matt

 

On my 2005 MCS automatic with a 17% pulley, Alta intake and MTH standard software my on board computer showed 32.5 to 33.5 MPG in sixth gear at 70 MPH (cruise control on and air conditioning off).

At the time I got these readings my hand-calculated mileage was about 0.5 MPG higher than the on board computer calculated it.

I've also found that my in town gas mileage did not suffer at all with the 17% pulley. It may have even gone up a tad.

/gary

 

I have a 15+2 set up with Miltek catback and went back to the factory airbox (service time coming up). I wanted to see for myself how gas mileage was affected so decided to take an average over 15 days driving (25 mile commute each way to work) To try and account for variations in traffic/ driving conditions etc.) also trying to account for wind resistance weather differences etc. by recording on days where weather was similar. That's easier here in San Diego where it is Sunny and 60s-70s most every day

Anyway, I didn't try to completely control my driving style and I have to say, as the mods have been added I have noticed a significant increase in foot density...

To make a long story short I'll summarize my statistically insignificant study... No mods completely stock... Overall average was 28.5 mpg. Daily range from 28-29.5mpg.
Mods as listed above Overall average 28.4mpg Daily range from 27.5mpg to 29.5mpg

I have had days where gas mileage has been much worse (those were FUN days!!! ) but my real life average wasn't really any different with or without mods. Take this for what its worth... Now that I've shared my completely subjective study I'm going to go have a margarita in honor of quatro de Mayo

 

It's difficult to find a stretch of freeway on my commute where the road is flat for very long, but I think I was getting 38-40 MPG at 70 mph in 6th (my car has no performance mods, except for my wind-cheating shorty antenna). Even my lowest MPG was above what gmcdonnell is reporting.

04SDMini's experiment answers my overall question as well as anyone probably can - on a typical commuting schedule, a pulley won't have much of an effect on MPG (positive or negative). My San Diego commute is 20 miles each way, and I'm in the same MPG range as you are, with a rare peak of 30 MPG during the holidays when there isn't any stop-and-go traffic on my route.

Thanks, all.

 

Holy crap, 38-40?!?!?!? Man, I got a lemon.

 

If you see a blue w/black roof mini on your way into work, don't forget the secret mini hand wave

 

My inclination is that my mileage (even at a steady 70 mph) has dropped slightly. I will have a definative answer by monday as I'm taking the Mini to the Catskills this weekend and have tracked mileage for this trip pre-pulley.

Richard

 

Don't think it's either improved or worsened since all my mods, but on the way to the Dragon, I kept your question in mind, and held it steady at 70 for an hour on 81. Granted, some up-and-down sections w/elevation, but I averaged 35.1 mpg over the hour. Mods in my sig (the MTH file is the 'tuner' by the way).

 

I too kept your question in mind on my first post-pulley trip to the Catskills this weekend. Mileage seems to be essentially unchanged after adding the pulley, GIAC ECU map and Helix CAI.

Richard

 

The bypass valve is acutated by vacuum. So a 70, light throttle, it will be open. So the manifold pressure is down, and the SC is pretty much free-wheelin.

I'm all for testing something, but make sure the test you want to run has a chance of measureing something useful!

Matt

 

Thanks everybody for checking, even if it was a futile study!

 

This is so good to hear! With gas prices were thier at I am happy to hear that after I mod my car it will still be good on gas

 

My MCSa with a CAI and 15% pulley did 30mpg on a recent trip. Long driving @ about 70mph.

 

I was watching this 2 weeks ago. I was on a straight, flat freeway for about 20 miles on California I10 going from Ontario to San Bernardino.

I pulled over to the slow lane, set cruise control to 70 and watched the ongoing mpg on my OBC, got 39 to 42 mpg.

Then I slowed down to 55 and, sweating bullets as the semis passed me like I was standing still, found I was getting worse mpg, about 35 to 38. I don't know why about that, I guess I may have slipped out of the jet stream...

 

But most people don't drive to get a certain amount of accelleration and don't have the presence of mind to rollback on the throttle because they're accellerating too fast.

Many people just mash the gas to get going from a dead stop, or to merge onto the freeway, etc. With fullblown Wide Open Throttle, at any given RPM the supercharger is spinning faster in a pulley'd car than a stock car. A faster spinning s/c means more air is being compressed. The TMAP sensor on the intake manifold will pick up on the fact that there's more air going into the cylinders and sends that info along to the ECU. The ECU will perk up as say, "hey, more boost, more fuel is needed". Now when WOT, the ECU not's going by what the O2 sensor is telling it. So it won't do any realtime feedback to get the A/F adjusted optimally. This is open loop mode. So, in effect and in summary, the ECU will at WOT in a given RPM and gear, pump in more fuel into a pulley'd car than in a stock car. Hence why with pulley'd cars many drivers will get lower fuel economy that in a non-pulley'd car

 

but the original poster asked for MPG readings at a STEADY 70 MPH..... SO WOT maps have nothing to do with it. If the SC is spinning faster, the TB will just close more.....

Matt