Summit 25% under drive pulley.

Go for it OP, I ran one for years and years without any issues. Not to mention, with aftermarket cams your idle is RAISED, so your accs are actually spinning at stock idle speeds, but when it revs they accelerate slower, which you will notice!
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To the OP under drive pulleys do offer small gains, but there are several trade offs. I don't like them personally because in the Honda world the light pulley doesn't soak up the harmonic vibrations and many people have had oil pumps shatter. Happened to a buddy of mine recently with his high dollar forged motor turbo supra. A couple hundred dollar pulley nearly wrecked his big dollar motor. They factory style pulleys are called harmonic balancers/dampers because they absorb harmonic vibrations in the crank shaft. They are able to do that because of their weight, remove the weight and you remove the harmonic balancing/dampening capability and increase harmonics in the crankshaft.
Not worth it in my opinion. But it's your car, not mine.

Last edited by 00pooterSS; Sep 20, 2017 at 05:52 PM.
Skip Cannon
15th March 2006, 01:51
A few years ago, quite a few people blew up oil pumps (and engines) - and almost all of those were running an underdrive crank pulley, like Unorthodox Racing, on a boosted engine. Speculation is that the UR underdrive lightweight crank pulleys do not include a critical harmonic damper element, and allow dangerous harmonic vibrations be transmitted to the oil pump drive, which eventually (sooner rather than later) shatters.
By any chance, were you running an aftermarket crank pulley on your boosted engine?
I think I was the first to have an oil pump shatter. There were at least 8 of us who experienced the problem. All had undampened underdrive crank pulleys and high horsepower turbo engines. It seemed to take about 2,000 miles from installation of the pulley to trashing the engine. By the time we figured it out, I was nearly 2,000 miles into a new engine, still using the underdrive pulley. I pulled the engine and inspected the oil pump. There were marks on the lobes of the G-rotor oil pump. I figured I caught it just in time.
Someone I knew inside of Mazda searched the computer records and could not find any recorded oil pump failures on any Miatas. The only oil related failure in the system at that time was from running the engine out of oil.
Prior to purchasing the pulley, Unorthodox Racing had assured me there would be no problem going from the factory pulley/harmonic dampener to their underdrive pulley without provision for harmonic dampening. They were wrong but when presented with the facts, denied the pulley was responsible, refused to take any responsibility and wouldn't even refund the price of the pulley. Some of us looked into the possibility of a class action suit but determined the company didn't have the resources to pay any judgement.
As far as the engine that is the subject of this thread, what were the symptoms of the failure? Did oil pressure go to zero, where there any unusual noises prior to complete failure?
When my engine blew at the track, it was at about 6,500 rpm and off the throttle at turn in to a series of S bends. When I fed it throttle at the apex, there was a noticable lack of power and a sound similar to an old British 4 banger with badly synchronized twin SU carbs being reved up. I looked at the oil pressure gage and it read zero so I shut off the ignition and coasted to a stop. By that time, the engine was toast.
Skip
dont do pullies. i did them, and was disappointed with the results, to put it nicely. lights were dim at a stop light, everything just about died. i only run a cd player head unit on stock speakers, so if your runnin an amp/sub or two, you will definately have problems. then to top it off, my car ran hotter, not much, but hotter to say the least. i did not notice any performance at all. dont waste your money, trust me. save it for something else, or like you said, get those sub frame connectors. thats probably one of the best mods to do. wont notice anything probably but your chasis will thank you...if it could talk....or something.
He's just one of those guys that gets loud behind a keyboard apparently. I keep the feelings out of it online, I prefer getting loud in person.
Rent free.










