As '04 MCS is now out of warranty, I'm ready to take the plunge on a smaller pulley. I'm not interested in brands or versions, rather is it necessary to swap plugs, injectors, or flash the ECU for such an upgrade in order to ensure proper fuel mixture, etc?

Thanks in advance for the feedback

 

Everyone will say 15%, 16%, 17% pulley or combo 15+2, and 16+2 redux pulley and crank pulley, colder plugs, no need for injectors for now, and if you can attend one of Revolution Mini Works Dyno Tuning days go for that also

 

15%, 16%, 17% and 19%, all are fine on their own. 15% and 16% you don't even need a new belt (but you might as well replace it anyway while your there). 17% and 19%, you will need a smaller belt.
With a 17% and 19%, if you get a flash, you will most likely require larger injectors.

 

Change the belt while you are there.
We used the stock belt on a friends car when we put a 15% on. This last weekend we replaced the belt, one year later, and he gained 2.5 lbs of boost.
So unless your belt is brand new get a new one, they only cost about 25-30 and can make a big difference.

Sad part of this tail is we broke the tensioner tool before we could change my belt. Also a 15% with the original belt.

 

My two cents. Change the belt to the proper match for whatever you are using. Meaning if you have a 17% pulley, then get the right belt length. It is cheap insurance and a good idea to do anyway. They are generally about $20.

We do recommend plugs with the 15% and higher pulley choices. One range cooler is generally ideal.

Injectors are not beneficial unless tuned for and without the tune will reek havoc.

A tuned ECU (there are several options. Each company has their own preference) will improve AFR, and throttle response with the pulley, as well as increase torque and HP.

If we can help with any other questions, let us know! Good luck! You will love the new power!

 

I'm interested in this statement "will reek havoc" since I have installed my JCW 380's on aniticipation of getting a tune by Jan at RMW asap. What should I be watchful for until then?

 

Necessary? No. I got the pulley/belt last year and nothing else changed but the power. I'll be getting new plugs this week though, so I'll find out if I've been wasting power for the last year.



edit: Apparently the JCW injectors are smelly. Unless Adam meant 'wreak havoc'.

 

I think "havoc" is a bit of an overstatement, but the uprated injectors won't be doing a great deal (for better or worse) until the tune. Your AFRs are going to be wonky, but not dangerous for the most part. At part throttle, 380cc aren't a huge leap up and the ECU should compensate OK, but at full you'll be running super rich. My car had black crap dripping from the tips when I had the 380ccs, untuned.

On the other hand, Jan found my car, 15% w/ recently installed 380cc injectors, was running LEAN upon cold start-ups. Never would have guessed that!

 

Thanks for the info. So you think I should stay out of WOT until the tune? Dang that could be hard to do .

 

Disagree. The 15% is safe with no other mods aside from a belt (and YES, you DO need a smaller belt...see my post here: https://www.northamericanmotoring.co...33&postcount=3)

Greater than that (not sure about 15%), you do run the risk of running a bit lean toward redline (using the 17%, 19%, and 15% + 2% combos). In my mind, running the more aggressive setups MANDATES injectors as well as an even smaller belt than the 535. Hell, tuning a 15% Cooper S requires injectors...can't imagine why a more aggressive un-tuned version wouldn't.

- Matt

 

This is a little off topic, but Matt, we should start a pool to see how many more times in the next two months we tell someone to stop using the damn stock size belt on these pulley's!

On the topic of the tune, I would disagree that the 15% requires injectors. If properly tuned, larger injectors will help some...but if you're going to spend the $$$ on a custom tune, you damn well better get the injectors too

 

No joke. I think this is the third time in a less than 2 week period in which I've referenced my prior posts.

Sorry for the confusion...I was meaning to say that more than a 15% (aggressive, in my mind) mandates injectors. The 15% you're good to go, until you take away the slack that a tune does. So yeah, we're in agreement...my bad.

- Matt

 

Okay, so I read about the belt size change related to reduced pulleys. So, has anyone calculated the setup with a 15% reduced SC pulley AND a 2% oversized crank pulley? I'd be interested to know how that compares to the OEM belt length.

 

What belt size would be needed for a 19% + 4%?

 

You guys can "reverse engineer" in the manner I did. Get the diameters for the respective pulleys, and see the reduced circumference, which ends up being the amount you need to reduced your belt size by.

Oh, and Second to None...hope you know that the 19% already puts the outside the M45's ideal efficiency...factor in the 4%, and all you'll be doing is making more heat, overspinning your alternator, and overspinning your water pump. All that adds up to shortened life for the affected components. Unless you've added all that already, that is, in which case my point is moot.

- Matt

 

Gee, I was hoping for the answer was already determined. Not only will I have to measure the OEM and 2% crank, I'll have estimate the percentage of contact the belt actually has. Maybe this spring when the wheel wells are off for spring cleaning.

Thanks anyway!

 

Yeah, sorry about that. I even checked the Bentley manual, obviously in vain. Didn't think I had seen part dimensions in there before, but I had to re-confirm.

As far as the belt wrap, I don't think it needs to be too precise. If you're off a couple fractions of an inch, no biggie. The tensioner will fix any minor discrepancies. My issue in my original post regarding belt sizes was the chart of belt sizes people reference, with the assumption that the stock belt or JCW is the correct size for the 15%. Essentially what you're looking for is for the tensioner to be in the correct (original) position.

- Matt

 

Ok going back to the injectors. The issue involves at idle and part throttle AFR. The ECU (un modded) doesn't understand that the car is running larger injectors. So with each pulse more fuel is being distributed than anticipated. In closed loop (WOT) not so much of a concern. It is the around town, day to day stuff where it is going to be an issue. Best to install the injectors at the same time the ECU is upgraded. Otherwise, just literally pissing away fuel needlessly.

 

Ok, thanks. I was worried that I was going to detonate my engine . And yes I see a drop in MPG, but I saw that after I did my first mod . Can't keep my right foot off the throttle .

 

Get a 15% pulley, correct belt, JCW 380s and a RMW tune but no crank pulley.

 

I installed a 15% pulley, and I changed my tensioner and my belt to a Gatorback, because I had some belt slippage, even with a JCW belt. But now all is fine, and it runs like a champ.

 

15% pulley with +2% crank pulley. JCW belt with no slippage

 

Alta has on their site the belt sizes for the pullies and crank pullies.




I installed the 19% need to put the right belt on. It came with the 060539, I need the 060535 belt. i picked it up and now need to install it. I put out 18psi with this pulley and wrong belt combo. Should get a couple more psi with the correct belt.

As far as power, it comes on quick, very quick. Just casual driving, you can hear the blower whine.

 

That chart has been proven by several members here to be inaccurate through both simple driving experience and through dyno testing. Not all of our cars are the same and no offense to ALTA to providing this chart, but it needs to be updated.

I'm not sure what the proper part number is of the top of my head for your 19%, but the 060535 is what a lot of us are using for the 15% pulley with great success. verveabsolut might chime in here in a bit adn might know the right NAPA part#.

BTW, my 15% was noticeably slipping above 5000 RPM.

 

LOL, it just keeps going...

The 19% needs a belt about an inch to inch and a quarter shorter than stock...that would put this belt around there:

Item#: NBH25060532
http://www.napaonline.com/MasterPage...t+-+Serpentine
Features & Benefits:For Replacing Original Belts on Serpentine Drives & Other V-Ribbed Applications. Designed for Smaller Dia. Pulleys
Backside Idlers & Use w/ or w/o Automatic Tensioners. Eliminates Belt Noise
Reduce
Imperial Length:53.835" (1367mm)
Top Width:.807" (20mm)
# of Ribs:6
Angle Degree:40 Degrees

That belt seems to be about right for a 19%...think my calculations are correct using my original posts method (see here: https://www.northamericanmotoring.com/forums/showpost.php?p=1946733&postcount=3). The belt listed above is .437 of an inch shorter than what I run for the 15% (the 535). Meets up fairly close, a bit tighter, than the ~.3inch difference between the 15% and 19% in circumference. Ideally there would be a belt a smidge longer; 1370-1371mm. I couldn't find it my incrementing numbers on NAPA's site, maybe Gatorback might be an option?

In all honesty, the 535 might not be that bad for the 19%...tensioner won't be out of range, but it won't be in the ideal position either. No biggie I suppose in this case. After all, these are minute differences. The tensioner can, and will, take up the slack (to an extent...).

My concerns, like I've stated before, were with the idea that the stock belt or JCW belt were short enough for the 15% or more. Hell no.

- Matt