Am I Crazy?

[theSLEEPER]

http://www.mrzperformance.com/en/parts- ... 0-28-31-v6

Or would a smaller diameter pulley OVERDRIVE??

[Money pit Beretta]

You are crazy, unless you have a hatred toward your main bearings.
3X00 is where I got my info on this. He talked me out of using mine.
I have one that has never been used and a March overdrive alternator pulley by the way.

[3X00-Modified]

When you make the Driving gear smaller then it rotates the belt less distance for each rotation there for under-driving the driven component... Think of it as a bike... When you make the front gear smaller it gets easier to pedal, the larger sprocket you use the harder it is to pedal.

The only issue with UDP's for our cars is the fact that they do not have a harmonic dampener to absorb the harmonics of our engines, Stock ones do not balance the engine in any way since our engines are internally balanced, but they most definitely act as a harmonic dampener and without that you can lessen the life of your engine/crank and timing chain/components.

I run a factory dampener on my current engine, I used to run a UDP on my old 3400 and to be honest when I saw what happened to my timing set I didn't know what to blame, the quality of the parts or the lack of a dampener and I've seen others run fine with the timing set I had so that kinda leaves one option.

As I've said to many run what you want, but don't tell me all is well without ever taking it apart to inspect what's going on inside the engine. I take my car apart once a year to check everything over, I don't just say oh its running good so all must be well... I make sure that's true.

[LOLVTEC]

I've always heard that a UDP may just eventually cause your crank seal to leak oil... I didn't know it could mess with the insides...

I've got a FFP UDP that I'm gonna use on my 3400/3500, just hope I don't run into any issues with it. Is there anyway to make one to where it has a dampener on it? I've always wondered why someone just didn't do that and sell them...

[theSLEEPER]

I don't want a UDP, this is strictly a mechanics question, but for some reason I was thinking that a larger pulley would underdrive, and I was partially right, I think...
A larger pulley will underdrive an accessory, and a smaller will underdrive a crank.

Correct?

Just didn't notice that was a crank pulley.

[3X00-Modified]

No, you’re thinking backwards... The crank is the driving component so any reference to the pulley type is referring what it will do to the components attached to it, over drive them or under drive them. You can talk in circles and try to make it sound right the other way but that’s just no how Crank pulleys are defined.

And your quote is incomplete... When referring to a Crank, a smaller pulley will under drive ALL accessories attached to the crank, not the crank itself since its the driving force, and a larger one will Overdrive them... When talking about an accessory pulley; yes a larger pulley under drives that accessory and a smaller one will overdrive it. You have to remember part of the word is DRIVE so the item being under or over driven has to be driven by something so you can't say the pully underdrives the crank when the crank is the item doing the driving...

So really you were wrong since you were questioning the function of a crank pulley... If you were questioning an accessory one then I would agree.

Also GeeTee... the only reason why some say the UDP will cause a leak is because some cheaper companies do not put a steel sleeve on the crank pulley where it touches the seal, so over time the seal will actually cause a grove to form in the aluminum and make it leak. Both MRZ and FFP did put the sleeve on the seal area so you should not have this problem, I still do not recommend using one.

The issue with a dampener is there is no way to do it and make it an underdrive, look at the size of the pulley already (stock) the rubber ring between the spoked area and the outer ring that has the belt groove is as small of a diameter as it can be due to the internal 24x crank sensor and the outer ring with the belt grooves is only about 1" thick, so if they were to make something they could only thin that out and after doing that I don't think that ring will have the right amount of dampening weight...

Its such a minimal HP gain its just not worth the damage it can cause over time.

[theSLEEPER]

No, you’re thinking backwards... The crank is the driving component so any reference to the pulley type is referring what it will do to the components attached to it, over drive them or under drive them. You can talk in circles and try to make it sound right the other way but that’s just no how Crank pulleys are defined.

And your quote is incomplete... When referring to a Crank, a smaller pulley will under drive ALL accessories attached to the crank, not the crank itself since its the driving force, and a larger one will Overdrive them... When talking about an accessory pulley; yes a larger pulley under drives that accessory and a smaller one will overdrive it. You have to remember part of the word is DRIVE so the item being under or over driven has to be driven by something so you can't say the pully underdrives the crank when the crank is the item doing the driving...

So really you were wrong since you were questioning the function of a crank pulley... If you were questioning an accessory one then I would agree.

Also GeeTee... the only reason why some say the UDP will cause a leak is because some cheaper companies do not put a steel sleeve on the crank pulley where it touches the seal, so over time the seal will actually cause a grove to form in the aluminum and make it leak. Both MRZ and FFP did put the sleeve on the seal area so you should not have this problem, I still do not recommend using one.

The issue with a dampener is there is no way to do it and make it an underdrive, look at the size of the pulley already (stock) the rubber ring between the spoked area and the outer ring that has the belt groove is as small of a diameter as it can be due to the internal 24x crank sensor and the outer ring with the belt grooves is only about 1" thick, so if they were to make something they could only thin that out and after doing that I don't think that ring will have the right amount of dampening weight...

Its such a minimal HP gain its just not worth the damage it can cause over time.

Right, gotcha. Thanks!

[woody90gtz]

I've had my UDP on my 3400 for 5 years and the factory original timing chain was still fine when I looked at it last year. This is with a stock cam, though. A more aggressive cam will wear out the timing set more quickly as Jon found out.

[3X00-Modified]

Stock cam, stock springs, Cloyes "OEM" replacement timing set.



People forget that I had these issues on a completely stock engine.

Also the con's of not running a dampener are not a myth, its proven fact... This is why I choose to not run without one.

http://www.circletrack.com/techarticles ... index.html