From a lot of experience building actual racing engines, building winning race cars and building winning and reliable race cars I can tell you that a solid hub underdrive pulley is not likely to cause engine failure in a modern mildly modified 4 cylinder engine.

My qualifications are that I was an engineer at TRD many years ago, I was an OEM engineer at Nissan spending the last several years working on the Nismo project and am now a motorsports engineering consultant. I have been an automotive and motorsports engineer for 20 years. I also happen to be a consultant for the Jackson Dawson team.

On a relatively under stressed near stock motor like the TC with bolt ons or low amounts of boost like what we will be running and I suspect what most of the people on this forum probably run, an underdrive pulley will not have any life threatening consiqunces for your motors. The factory pulley with a twin ring damper is primarily for wide band NVH (noise vibration harshness) suppression from the engine and driveline. Removing the damper and replacing it with a solid hub underdrive pulley will cause additional NVH but not harm the engine.

The engineering reasons are that an inline 4 cylinder engine has a short stiff strong crank with a relativly high natural frequency. The dangerous second harmonic that can cause damage occurs at an rpm that this sort of engine will never see, in the area of 9500 rpm.

Now the stock harmonic balancer is not tuned for attenuation at this sort of rpm either so the argument is somewhat of a moot point.

Now 4 cylinders that are pushing the limit with lots of revs, wimpy cranks, super long strokes, lots of boost and dwelling in the upper rpm ranges for long periods of time can benifit from a damper designed to deal with this sort of operation but our engine is not like this due to rules contraints and probably very few people with this motor on this forum push the envelope that hard.

The tC engine has a strong and stiff bottom end that is overbuilt if anything for our intended use. It has an internaly balanced crankshaft, It has a chain driven oil pump which is less like to break due to torsional vibration like the more common crank snout driven georotor type found on Honda and Nissan motors. Nothing is going to happen, not even in our road raced tC. Road racing is much more punishing on an engine than other motorsports. The engine is subjected to run times lasting anywhere from 20 to 45 minutes with the engine always in the upper ranges of its rpm limit. One race weekend is the equivelent of hundreds of 1/4 mile passes.

Some engines like the Nissan SR20 have to have an underdrive pulley to live at all under race conditions as the water pump cavitates at a low rpm. All SE-R Cup cars and probably most professional drift S chassis cars run an underdrive pulley. I can tell you that SE-R Cup cars are very reliable with engines lasting several seasons sometimes. The one in my car has lasted about 2.5 seasons and is still going strong. My personal 529 whp turbo SE-R has an underdrive pulley. I don't know of an SR engine that has failed due to a pulley. I know several guys that have had them for 200,000 miles.

The same goes for the VG, VQ, QR and GA engines. Many World Challange race cars use underdrive pulleys.

Is an underdrive pulley harmless to all engines? No it is not. Inline six cylinders when modified way past the simple bolt on stages will probably have problems. These engines reach critical harmonics at lower rpm due to the length of the crankshaft, this is in the 7500 rpm range, an rpm often reached by a performance engine. Now a BPU Supra or other mildly modded inline six will most likely be fine but one subjected to high rpm for long periods of time with lots of boost will probably suffer. In this case , the stock balancer is probably not adiquate either. In my experiance with I-6 Nissan RB engines the oil pump inner gear cracks first due to crank whip. For serious I-6 motors I use ATI or Fisher dampers. Crazy stroked out B series Honda motors with strokes approaching 100 mm will also crack their oil pump gears and racing Nissan KA motors crack blocks. These motors need to have the revs limited, dry sumps and other special prep to deal with vibration in extreme full race use in very highly modified form. American V8 engines are often externally balanced and it is critical not to use a solid hub pulley not designed for this application or damage to the engine will result.

Our tC engine and most people's here have motors that do not fall into the above category. Rest assured that your engine will not blow up and die or have a reduced life in street and even racing use with these parts. Will you notice more noise from the drivetrain and front end accessories, yes possibly.

I would bet that every "expert" that tells you otherwise here has little personal practical experiance with the subject.