Reply With QuoteI have not used an underdrive crank pulley, though I know TedtheRed has on a Mini. He might have some input on this.
Underdrive aluminum crank pulleys
The above is a quote from the GRM build blog that Andy Hollis wrote for his STS2 Miata. That is a pretty big endorsement for adding a lightweight underdrive crank pulley to my [now] STS2 car....our second quickie performance improvement was to install a lightweight underdrive pulley. This helps out in three ways. First, it reduces the power loss through rotational inertia the same way a lightweight flywheel does. Second, the smaller diameter spins the accessories (water pump and alternator) slower, reducing the parasitic power loss. And finally, it takes weight off the nose of the car. The results of our install were dramatic. So much so, that we'd recommend this enhancement early on in the development of any STS2 car. It's cheap and it works.
Has anybody installed one of these and do you have any comments?
Do you have any pulley recommendations? 1.6 pulleys are hard to find, but I have found two:
http://www.indigospeed.com/GTPullies.html
http://www.rsaperformance.com/unrapoulstli10.html
I have not used an underdrive crank pulley, though I know TedtheRed has on a Mini. He might have some input on this.
I'm interested. Keep me advised as a tech day might be in order. I have a three car garage that could be used for a double your fun day. I do have an small air compressor with tools.
Bobby
RED RULES!
90 Miata, 04 Rubicon, 05 Boxster
Stripe Das Sape
We are leading the world to democracy by example.
Someone correct me if I'm wrong. But should you also change your harmonic balancer/stabalizer with this so that the pulley won't vibrate causing it to damage your motor?
Blah blah blah!
I have been running one for about 4 or 5 years now. I can't attest to it's benefits because I put a lightweight flywheel on at the same time. The stock pulley weighed 56.4 oz. vs. the underdrive pulley (UR) at 14.6 oz. One thing to watch out for is the bolt length may have to be shortened when you put replace the stock unit.
What's left of a '96 Miata with stock clutch.
My car exceeds my driving ability. That's the only possible explanation.
I have an UD pulley on my current miata (indigo) and had an ebay one on my red '96. I could tell a difference in power gain in the top end. When my red miata was mostly stock, it didn't like to rev smoothly and quickly to redline. It would die off around 6K. After the UD pulley was on, it pulled smoothly to redline. Same goes for my '93 subaru legacy. I only had an intake on it and the UD pulley made a huge difference.
There is alot of argument about how an UD pulley puts tensile stress on the end of the crank and what not, but I don't see how that would be any worse than a crank overlay pulley for a Supercharger with an additional belt.
Last edited by johnwag; 11-27-2008 at 12:17 AM.
every serious STS and STS2 competitor has an underdrive pulley
part is monkey-see-monkey-do, but there is a performance advantage
I can't tell you how much, but when you have a little over 100hp, it doesn't take much improvement to be worthwhile
the one on both of my cars is no longer produced (Unorthodox Racing) so if you can find one that is good quality elsewhere, it will be worth it
2009 MX-5 STR and track toy
2003 Z06 -- Not a Miata, but 3200# and 400 RWHP is fun
OTM -- 2012 Sierra, 2016 Impala (Appliances)
Be sure to order a colored one. They are much faster. I have the slower silver type.
What's left of a '96 Miata with stock clutch.
My car exceeds my driving ability. That's the only possible explanation.
I have ordered one. Thanks, all.
You get the pink one? I hear those are the fastest.Originally Posted by jrj512
Have you tried Track Dog Racing? Link - http://www.trackdogracing.com/
When you call the kid who answers the phone is going to do a hard sell on you buying a set of RB Sway Bar Brace Kit Hardware, but once you can get him to focus he may be able to help!
I don't remember mine being too tough to install, but I think it took a few stabs to find the right belt size.
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