I recently swapped out my stock crank damper for an ATI super damper from Way as a preventative measure and figured I'd go for the 2% overdrive option to combine with my 15% SC pulley. Install went fine, put on a new belt and thought all was well. I'm working my way through my first full tank of fuel since the install and am getting much worse mileage, ~5mpg loss compared to before running just the 15% pulley. Granted the smaller crank pulley is adding extra losses due to spinning all the accessories faster but 5mpg seems like a lot to me. The only other thing I've noticed is some slight belt slipping (squealing) which I believe is due to using the stock JCW length which I assume is a bit long for 17% reduction. Anyone have any thoughts on the mpg loss? I haven't tried resetting the ecu or anything yet as I didn't really think that was necessary. Thanks in advance!

 

could just be the belt... your not spinning the SC enough mostly likely, computer could be throwing more gas in than necessary, ect.... issues to say the least.

get a proper belt, then try another tank of gas.

 

Hi!
MrHorsepower01

Right Now I Have 17% Pulley & 2% Crank
N' The Belt I Use Is From Napa #060539
W/ Out Any Problem.
Also I Have The Alta Tensioner Adjustable.

But Before I Was The 15% Pulley & 2% Crank.

N' I Get Good MPG. 25.7 N' City.

Maybe You Problem Is The Belt.

 

With a pulley, you have to keep your right foot in check...more power= less mpg in most cases....
Make sure you use the best octane you can get at the pump....
And yes.... It may take a tank or two of gas for the ecu to adjust...
A squeel on a new install is not good...but check with waymotorworks since they sold you the parts for the best suggested belt....

 

Thanks for the responses everyone. I ran out and grabbed a new belt from Napa after doing some research so I'll throw that on tonight and see what happens. If the squeal goes away I will run through a tank or two and see if the ECU adjust as Zippy suggested. I'll update the thread with what I find for future reference. Thanks again!

 

Yeah Broh!

That's True Take Like At Week To Get Adjust.
That Happen To Me!

But After That The Fun Is begins!

 

Could be as simple as the local gas stations have jumped the gun, and started selling winter mix fuel already. (Not sure where you're located, but that will have a profound affect on fuel economy).

We install a 1385mm belt on cars that are running a 15% up top and a 2% down low, no issues with that setup, cross reference the belt you have on there to that.

 

nkfry, I'm in NC so I would think the seasonal effects on the gas supply would be minimal. I put on a NAPA 25060535 belt last night and it appears to have stopped the squealing and looks like the tensioner is in a better spot (1 full hole showing in the tab vs. 1/2 hole showing before). I drove a short distance last night/to work this morning and the car does feel like it's running better so I'm guessing the belt was slipping to the point of causing a loss of boost. I'll run a couple tanks through and see how the mileage changes. Thanks!

 

It can also be your injectors. Depending on how extensive your modding is going to go, you definitely need to change them. With light mods (pulley, intake, exhaust, etc.) you can do JCW 380cc injectors. Add a cam and/or thumper head you can go 440cc or 550cc. Add a new and more powerful supercharger, 550cc definitely.

The stock injectors are pretty much running at max capacity, which is giving you crappy milage.


Also, a tune will really help balance things out. My friend just dyno'd and had his subie wrx pro-tuned today actually (11/12/14). Adding new injectors will definitely need a tune.

But like the others said, more power equals less mpg's, but new injectors would really help!

(i've tried to post a link from motoring alliance about injectors, but it won't let me! I'll PM you the link)

 

I had JCW pulley about 12% and then added a 2% crank pulley. I did not notice any change in gas mileage when I added the 2% pulley.

 

Quick update for anyone interested or for future reference, I have run a full tank through after replacing the belt and my fuel consumption is back at an acceptable level. I am seeing about the same mileage as I saw before I did the crank pulley, ~25-26 in-town driving, so I'm confident the belt was the issue. Thanks again for everyone's input!

 

Just so we know, what belt did you change to?

 

With just my 15% pulley I started out with the recommended belt from Way Motor Works. When I put on the crank pulley I replaced that belt with a stock JCW one which resulted in the slipping issues described above. Now I'm running a Napa 25060535 belt which appears to have solved the issue. The Napa belt is definitely shorter as it was a bit snug to get on but the car runs better and the fuel mileage is back where it should be.

 

+1
The mechanics of mpg on a mini with a pulley are pretty basic...
The car does not have the ability to change the fuel to air mixture at large throttle inputs (wot), but can use the o2 sensor to adjust the maps at light throttle and cruise....
The fuel "trims" if you look at a car with a good odb2 reader will be slightly higher....
With a 17% reduction you should be fine mixture wise unless you spend lots of time WOT, but then cavation in the water pump becomes more of an issue...
Bugger injectors with a custom tune could get you from 170-180 ish to the wheels to about 200 ish.....
Good to hear it is running great!!!

 

Excellent info Zippy, I don't hang out at redline so I felt OK running 17% net reduction, mostly just spirited back roads and the occasional WOT on-ramp pull. It definitely does feel like the car would benefit from a tune, so some injectors and a tune are definitely in my future.

 

Awesome! I plan on using the Way 15% pulley and 2% ATI damper myself. I've read great things about the NAPA 25060535 with this combo. I hope you changed your tensioner bushings (or at least checked if the stock ones were ok) as well as added a Way tensioner stop! If anything goes wrong, then that tensioner stop will stop the engine from destroying itself. For $30, it's a great investment to prevent a major dent in the wallet.

 

Actually the tensioner stop keeps the tensioner pulley from smashing itself into the crank pulley, damaging both. More than likely no damage to the motor but you are still gonna spend some money and be off the road.

 

Thanks for the correction! I knew something expensive was gonna get damaged

 

Remember added horsepower equals more fun, which in means your right foot ( gas pedal) dictates your gas mileage. Think of your driving habits before and after


Just saying.....