I am planning some mods for my new to me 2005 R52 S. From what I have read, installing a 17% pulley is the best bang for the buck. I have found praise for this mod all over this forum, but I have found very little information on the "down side" of installing this mod. Does installing a 17% pulley effect the gas mileage or engine longevity? What say you...

 

...The down side of the 17% pulley... ehr... reduced fuel mileage... but then again if you are installing the 17% pulley you are kind of thumbing your nose at Fuel efficiency anyway right? For example: dropping from 32 MPG to 28 MPG.

Additionally I would have the MOD documented so you know all the part numbers and sources for any part you had to change from stock like if you are using a different belt, belt tensioner, SC Pulley, and Crank Pulley, etc. This would allow for quick reference for replacement parts if needed.

I haven't seen any real difference in engine longevity, good maintenance will mitigate this risk.

Motor on!

 

Yeah, your MPG will probably take a hit, but if you're installing a smaller SC pulley for more power, that's probably the least of your worries.

I think the only other downside is that since you're spinning the SC faster, you may wear that component out sooner. But as JABowders said, good maintenance will go along way towards extending the life of your car all around.

 

Downsides? Not many. You will go through belts faster, but they're cheap. If you're planning to be a real track rat, where you're spending 30-40 minutes at a time banging off the rev limiter, you might consider a 15% instead, not only because of the wear, but because the effective power band of the supercharger is better with the larger pulley at the engine's limit.

 

HELIX gives good advice. If the duty cycle is heavy (i.e. on track), in addition to faster wear, the 17% will generate more heat which the stock intercooler will have a harder time dissipating, hence the 15% would be a better choice but, for normal street use, the 17% will be fine.

 

shouldn't see too big of a hit on gas mileage, yes the rpms of the SC increase, but most of the SC load come from the bypass valve being closed. there is a difference in MPG, most of the loss in MPG is using the boost associated with. I still can get 31 mpg easy on the highway at 72-75 in the summer months not running a super sticky tire. also with 55mph I can get like 34-36.


only real downside with the 17% is what helix said. if your a track rat, not the best solution.

 

For a street car the only downside is you may get a speeding ticket and hurt your face smiling.

For track use though the 15% would be a better option. If not tracking the car the 17% will give you just a little more low end on the street.

If using a 17% we do recommend changing the belt once a year just to prevent a failure.
Our kit includes the pulley, correct belt and cooler spark plugs as that is what we recommend as we have found it to be the most reliable combo.
http://www.waymotorworks.com/wmw-pulley-package.html

 

Almost invariably, anytime you spin an assembly like that faster and faster, you're increasing wear on all associated parts. More heat, more wear, less life. It's like the knucklehead VW owners who think it's a good idea to boost a baby-sized K03 turbo to 22psi.

Look at at the efficiency island for an M45 blower:

Running 17 psi on that blower puts you at 2.156 on the Y Axis. Wayyyy outside the ideal efficiency island. Now, calculating the X axis value is a bit more tricky, but I made an estimation and put it around 350m^3/Hr. The point is, too many people are too comfortable over-boosting both turbos and blowers. /Rant

 

I understand your concern. You have been given some good information on maintenance and volumetric efficiencies.


Good rule of thumb is.... you upgrade or add power of any kind to any vehicle.... Your right foot will dictate your fuel mileage.


See when we add sound and performance we tend to drive our vehicles more spirited.


Whatever you decide to do.... enjoy!

 

My initial estimation of 350m^3/Hr is grossly low, having taken a second look with more time. It's clear that these blowers are well beyond their efficiency with even a 15% pulley. To know the exact number, I need to know the diameter of our stock crank pulley. Then, with that, we know that a 15% pulley is 55mm in diameter. Using those two numbers and our engine RPM redline, we can find the drive ratio and blower RPM.

I wouldn't doubt that we're in the realm of 14,000 RPM blower speed, which puts us hilariously far out of the efficiency range for the little M45. Do yourself a favor, and graph 2.1 on the Y Axis, and 14,000+ RPM on the X Axis..... Not good. You want to be as close as possible to the small, dark blue island.

 

I'm not so sure I'd worry about fuel mileage as much as I'd worry about excessive tire wear.

In unofficial and undocumented studies, I have determined that there is a direct correlation to the installation of a 17% pulley and increased drive tire wear. If you have an LSD installed, the wear will be twice what one would expect. :D

 

In the end the amount of wear might be negligible. I was one of those knucklehead VW owners that chipped a 1.8t. The engine was still running strong and trouble free at 230k when a truck totaled it.

 

This really seems like some great information, I really wish I understood it. I understand the concept of an efficiency island, I just am lacking on the knowledge to read the graph.

 

I'll save you some calculations

 

if the green is the RPM of the SC, then 6000k is ideal, which would be like 5 psi of boost..... LAME

 

Just because something doesn't break, doesn't mean it was the right thing to do. That turbo is at it's peak efficiency at about half of what big name tuners like Revo and APR boost them to. It's not really debatable. The 1.8t is an inherently strong and high flowing motor (20v head) and it can take the power. The issue is that the turbo isn't made to push that kind of CFM. http://www.golfmkv.com/forums/showthread.php?p=1782738 Now I know that's a 2.0l, but the fact remains.


You can step outside the most efficient island a fair bit, but yes, peak efficiency would be at a very low boost level for the particular blower. The Miata community is fairly familiar with the Eaton M45, and there's some good tech info on Miata forums.


On the Y axis (vertical) you have the pressure ratio. To get this, you would basically take the psi which you know your blower to be running (let's say 15 psi from a 15% pulley) and add that to 1 atmosphere (14.7 psi), which gives you 29.7. From there, divide 29.7 by 1 atmosphere (14.7 psi), which gives you 2.02. Find that on the Y axis.

Then, similar to what Andy did, if you know the size of both the crank pulley and supercharger pulley, you can calculate the RPM that the supercharger will spin at. You would then find that on the X axis (green), and see where X and Y meet. For our application.....it's in outer space, and implies that the blower is far out of it's peak efficiency. On this "efficiency island map" dark blue is used to show high efficiency, but most maps are black & white, so you'd be looking for small islands as the most efficient.

Eaton has even more graphs that show how much heat is produced based on blower RPM, and how it affects power output. This is why I'm such a big supporter of spraying methanol & water directly in to the blower housing; it seals and cools the housing, both rotors, and the air inside.

http://www.alcoholinjectionsystems.c...articles_id=93

Additionally, this is why there is no debating which is more efficient: Turbos vs. Roots style Superchargers. Simply look at the maps for various turbo chargers. Even tiny ones like the VW K03 are more efficient at higher boost and CFM / RPM when compared to a small displacement blower.

 

Thanks for the lesson. I'm not always thrilled to just take someone's word that something works, but if they show show evidence like the graph, it let's me prove to myself why something either does or does not work.

Now to figure out the PSI increase for each % overdriven. Although I assume that becomes a very fluid number as boost levels would become very dynamic as RPM/load changes.

 

I'm with ya 100%. That's why I like to provide facts. There are 3 or so more charts available for the Eaton M45; I'll see if I can find them.

So, I think the pulley % decrease : boost increase relationship is fairly linear to a certain point. Most people see 1psi below the pulley reduction %. Meaning, those running a 17% pulley often see 16psi or so, 15% pulley often makes 14psi, etc. That changes at some point, but most of us run these sizes. Having said that, those with high-flow heads, aggressive cams, low compression pistons / heads, etc, will see lower boost levels due to less air resistance within the motor.

That doesn't mean lower CFM of air (quite the opposite actually), which frankly, is the more important thing to measure, but PSI became the more commonly used nomenclature due to ease of measurement. 10psi from a T25 turbo isn't the same as 10psi from a GT3071R.

 

These are what you are after? Had them saved on my computer.

Flow


Power consumption


Temp

 

Precisely.