RB25 pulleys

[siksII]

not being technical at all here.

but i just took my friends 300zxtt for a spin, he just fitted a lightweight underdrive pulley kit.. the main pulley is 800g compared to the original 8kg.. and it DEFINETLY accelerated heaps harder.. reved faster. made the whole car feel lighter, as if the engine had less of a job to do.

[Busky2k]

Hmmm funny. I gave GFB a call about their crank pulleys and belt sizes the other day concerning my SR20. Anyways, after that I asked them why they dont make pulleys for the RB. They plainly stated that it ruins the bearings and that they 'learned the hard way'.

Food for thought...

[Guest RedLineGTR]

"ruins the bearings" thats interesting anyone have some more info on that???

[Busky2k]

Give them a call i guess. I remember a few days ago i was reading about a H22A honda using a pulley, and after 40,000ks, a teardown was performed. It was found that the main bearing #1 was completely hammered compared to main bearing #5. I'll try and dig it up.

Also alot of WRXs seem to have trouble with pulleys, as it causes the CAS to go whacked at 6000rpm. Sounds like nasty vibrations are responsible, and this is on a short crank EJ20.. Tonnes more info on NASIOC.

[Ryno]

This is the email Reply I got from Brett turner at Go Fast Bits:

Hi Ryan,

We don't do a pulley for the RB series engine, because they rely on the harmonic balancer. Without it, the oil pump will fail and therefore the engine will shortly after if it is not stopped in time, which is unfortunate because there would be a significant gain to be had by removing the extremely heavy factory pulley.

Regards,

Brett Turner

Engineer/Technical Sales

Go Fast Bits

+612 9569 7648

www.gofastbits.com.au

[GTRgeoff]

Perhaps if they were to satisfy us with underdriven/lightened pulleys and forgo the balancer we would be happy?

Thanks for the great discussion guys. Heaps more interesting than the weapons engineering I'm stuck with now.

[Sydneykid]

Hi guys, we have been running lightweight pulleys on race engines for years (not RB's, yet) without any signs of these bearing issues. Since they have all been very tightly balanced, maybe this is why we have no problems.

This of course doesn't not fix any harmonic problems, but I can't see how that would be an issue with RB20/25/26 's. But RB30's, because of their longer stroke, may be an issue.

I am about to test a set of lightweight pulley's on an RB31DET on the engine dyno in the next few weeks, so that will be interesting to see if there are any vibrations. They show up readily on the engine dyno as it has sensors mounted in the bed.

Interesting thread...........

[predator]

hmm... torsional vibration and whatever else aside.. if people are really keen on reducing the rotational mass.. wouldn't a more simple solution to cut a few items out of the equation?

Wouldn't simply just removing the belt to the aircon compressor (and you may as well remove the compressor at the same time to save that 10kg or so), removing the engine fan, replacing that with a thermo fan, and putting in an electric water pump (craig davies, etc) give you similar results in terms of reduced rotational mass? Ok, maybe its not as simple, but same end results(??)

http://www.fordmuscle.com/archives/2000/08...ump/index.shtml - is an interesting article..

p.s. has anybody run a craig davies pump in their RB? What were the results like? Its about $600 for the kit.

[Busky2k]

predator, I dont think ppl wanna forgo AC. And besides, you loose almost no power to the compressor anyway when its not operating! And the fan is viscous coupling, so you'd only loose coupla hp you wouldnt feel at best (unless its fully locked due to being fooked or ur engine is running hot)

Also ~80% of the gain from a pulley is actually removing the weight from it, and the rest is from underdriving the accessories!

[Duncan]

the AC stops drawing power at WOT so there should be little gain.

....and it means it gets bloody hot when u are running flat out for an hour or 2 in NT

[predator]

I'd agree that off the aircon off is barely making a difference.. my physics isn't great but wouldn't *any* friction on the pulley caused by the belt would cause some loss? Even if is not actively spinning?? But anyhow, the aircon wasn't the main factor, as like above, you'd get the same effect just by turning it off (simple)

However the fan would have to place some noticeable placing draw?? and like wise the waterpump must be placing draw?? as again (physics knowledge not great) isn't any device running off that pulley system effectively creating an increase in rotational mass?? it works as "one" system, rather than simply a weight of an individual component??

as you can see with the question marks I have absolutely no idea, but I'm just keen to find out why/why not :-)

[Sydneykid]

Hi predator, I have already completely removed the A/C and the viscous fan has been replaced with an electric one. Based on other results I have seen, an electric water pump is not on my list. I have also replaced the standard flywheel and clutch with an OS Giken twin plate. So pulleys are next on the list of rotating things to lighten.

[Guest RedLineGTR]

Sorry to be abit off the topic but is it worth getting a electric fan installed and do they last long?? and do they keep the temps at stock levels if you get the same size fan.

[Ryno]

You are right Predator, the water pump does draw power from the engine... but if we could get our hand on a light weight crankshaft pulley, it would be easier, and less expensive.

Out of interest, Issue 40 of "High Performance Imports" (GTR Special No. 4) - has an add on page 11 for a super light weight crankshaft pulley for the RB26DETT, by Power Enterprise. I wonder if they make one for the RB25DET?

[predator]

Trust/Greddy makes a set of pulleys, all *bar* the the main crank (I assume for the risk/perceived risk of the balancing issues discussed).. Favourites nengun have them for approximately $300: http://www.nengun.com/product_info.php?cPa...4694af6628dcbea

I guess the main one everybody has been talking about is the main crank pulley, however I feeling trust would have invested a bit to see whether it was safe enough to reliably put on a stock balanced RB engine and the answer was no. For fitment, I assume they are same across RB25 and RB26, seeing as everything around this "area" is pretty much transferable (water pump, timing belt, ex. and inlet cam gears, even the cam cover)

[benm]

hrmm I wonder how much fitting would cost ???

[EnricoPalazzo]

diy

[Guest RedLineGTR]

anyone wanna test them on thier car

[GTRgeoff]

RedLine you gonna donate them?

[the phantom]

Hi Sydneykid,

Curious to hear about the results of your rotating mass reduction experiments. Have you produced any sort of measurable results thus far? I guess in racing it all matters, but I was just wondering if you have been able to deduce how much power was being sapped by the heavy pulleys experimentally? Also, I dont understand how the state of engine balance, i.e. dynamic balance of the crank, and static balance of rods/pistons etc, has anything to do with the harmonic balancer. I was under the impression that its task was to reduce torsional oscillations, not moments produced by dynamic imbalances which lead to crank bending perpendicular to its axis. Do you think you'll get an accurate representation of torsional effect without the use of an encoder device on the crank snout? Interesting...