Unorthodox Racing Engine Pulleys
Engine Pulleys - Quick Access:
Engine Pulleys - Description
Besides bottom-end internal balance, the flywheel has the greatest effect on engine longevity
[source: Advanced Engine Technology, written by Heinz Heisler]. Toyota uses the term, "dual-mode damper" for the
crankshaft pulley. It's effects on the crankshaft are twofold- the dual-mode dampers' inner ring counteracts
torsional vibration, while the outer ring counteracts bending vibration. Inner/Outer rings, hence the 'dual-mode'
terminology [source: Toyota Engine Technology]. Perhaps of some significance w/regard to the dual-mode damper, is
mention of design parameters meant to deal specifically w/400Hz harmonics. Whether or not the Supra [or any] flywheel
is likely to serve this specific function, could not be found in the literature mentioned. The aforementioned
frequency [400Hz] is quite possibly the resonant frequency of the engine, so that aspect of vibration attenuation
could be surmised as simple noise reduction- this a best guess on my part only.
Both sources indicate that the flywheel's mass is partially responsible for less of the torsional/bending vibrations
experienced in the crankshaft; much more so in the Heisler writeup. IE, the resultant attenuation of crankshaft
harmonics is the result of collaboration between the two devices.
The Unorthodox Racing underdrive crank pulley [UD pulley] does not have any means of vibration dampening.
So, why in the world would I opt to remove the dual-mode damper in favor of the undampened Unorthodox Racing product?
Easy. I did the mod before I knew all of the facts, & once installed, I figured I'd play the odds & see if
any of the known drawbacks to the setup would rear their ugly heads. What attracted me to the mod in the 1st place was
loss of rotational mass, which is undeniable at ~8.9 lbs. I wasn't too thrilled about underdriving, but the nominal
15% reduction has not proven to be detrimental from a charging system standpoint.
Here's a kicker for you. While I was cruising the Web, I found that TRD made undampened aluminum crankshaft pulleys
for their race cars. Regardless of what any of the other findings indicate, this is a pretty compelling argument for
the folks who stand by this mod. I still have no opinion one way or the other, from a technical standpoint; but I can
offer what real-world experience I've had using the undampened pulley thus far.
So far, the bottom-end of my 7M-GTE has about 42,000 miles on it utilizing the UD pulley, & it's still running
strong & noise-free to this point. So many factors are involved here, it's really tough to say if the UD pulley
has done, or will do any damage. The disassembly this engine will receive in the future will tell the story. If I note
no unusual wear patterns on the bottom-end, I will conclude that vibration attenuation of the stock crank pulley to
be geared more toward noise attenuation, rather than addressing crankshaft distortion per the many technical write-ups
that I've read since doing the mod.
Enough on the UD pulley. The accessory pulleys were also replaced, yielding some pretty decent rotational mass weight
savings as well:
That amounts to over 1 3/4 lbs of rotational mass less than the original pulley sets; above & beyond the ~8.9 lbs
reduction offered by the UD pulley. Please note that the accessory pulleys are not underdriven, & are made to
OEM-spec diameters. I've found no documented negative bias or drawbacks to using these pulleys.
The build-quality of all the pieces is 1st rate, all beautifully CNC machined & anodized. In the looks department,
they definitely rate a 10. In the performance category, this particular mod (as a collective), provided a noticeably
*freer-revving* motor, & the results were well within expectations.
The infamous Unorthodox Racing underdrive crank pulley & the undersized belts to run it.
Underdrive Crank Pulley Installation Instructions
Dave Mobley authored a modder's viewpoint of the installation at SupraCentral. Here's the link:
Dave listed Kelly-Springfield belts in his write-up. Since I noticed those part #s don't match up to the CarQuest #s I used, I've listed them below as an additional reference. These #s match the commonly found Gates brand part #s.
The Unorthodox Racing accessory pulley set.
L to R: Power Steering, Water Pump, & Alternator.
Another view of the Unorthodox Racing accessory pulley set.
L to R: Alternator, Power Steering, & Water Pump.
Accessory Pulleys Install Photos
Unorthodox Racing accessory pulleys installed, pic #1.
Unorthodox Racing accessory pulleys installed, pic #2.
Unorthodox Racing accessory pulleys installed, pic #3.
I guess we now know TRD's take on crankshaft distortion.
More views of the TRD aluminum crank pulley. L-R: Top, Belt-section, & Bottom.
These photos were contributed by Shane from Australia. He sold the pulley due to it not having a provision for AC.