Overdrive pulley for thunderbolt Blower: would it work?

[Ohio_Man]

I was discussing with my dad how Thunderbolts are supercharged (Like Detroit 2 strokes and Hot rods) And this raised the question of if the supercharger on the Thunderbolt would accept an overdrive pulley (smaller pulley to make the blower spin faster). Assuming the motor driving the blower would take the additional load (or if you had a bigger motor) would there be an increase in performance or would there be an unseen factor making this not worth the venture? I know Eaton superchargers (M90 and 112) will take overdrives as well as Detroit blowers.

Has anyone on this site with a thunderbolt ever played with the pulley ratio?

[OHIO Desperado]

You need to be careful with doing this and if you are considering it, you need to be reasonable with the change. Those roots blowers were designed and balanced for a certain RPM range. A blower on a car / truck engine was designed to be run at a varying rate as the engine was sped up and slowed down as well. A blower for use with an electric motor was setup for a single operating RPM. I wouldn't go more than a 10 % overdrive due to this. SO the next question is WHY? Are you trying to make it louder or change the pitch?? More air is more sound. Pitch is the speed of the chopper. So not sure why you would want it louder for a hobby siren.

[Ohio_Man]

You need to be careful with doing this and if you are considering it, you need to be reasonable with the change. Those roots blowers were designed and balanced for a certain RPM range. A blower on a car / truck engine was designed to be run at a varying rate as the engine was sped up and slowed down as well. A blower for use with an electric motor was setup for a single operating RPM. I wouldn't go more than a 10 % overdrive due to this. SO the next question is WHY? Are you trying to make it louder or change the pitch?? More air is more sound. Pitch is the speed of the chopper. So not sure why you would want it louder for a hobby siren.

I don't have a thunderbolt so I can't test it, I'm just wondering if it works. I know a 4M (the common blower) produces 250CFM on it's stock pulley, the 5M (Very rare) 350 and the 6M 300.

If a 4m spun 10% faster it would move 10% more air and since 10% of 250 is 25 it would move 275 CFM in theory, not quite the 6M's 300 but pretty close.

Speaking of, If a 6M spun 10% faster it would move 10% more air, and since 10% of 300 is 30 that would be 330 CFM, not quite a 5M but still more air than stock.

Now I know what you're thinking and I already did the math.10 percent of 350 is 35, so 350+35= 385CFM. So if you wanted to build a killer Thunderbolt a 5M blower with 10% overdrive will throw out 385 CFM.

Compensating for the load (if the stock blower motor won't take it) would be a soft starter (dedicated soft starter or star delta for 3 phase sirens) or a bigger motor. Keep in mind if someone were to do this I'd keep an eye on amps and temps during the first run.

But as to why I posted this, I was wondering if anyone else had done It. I can't since I lack a thunderbolt and the funds to buy one and a space and power hookup for it.

But in theory would this improve performance? I know a 5m is a heavily desired blower and 6m's are pretty popular too. This is all on paper, I haven't factored in real world testing.

Does anyone know the pulley ratio for a thunderbolt's Various blowers?

[TrainsAndSirens1]

I remember long time ago that Tboltmanaic ran his Thunderbolt 1003 (5M?) blower using a lawnmower's blade pulley and the blower worked.

[AcousticTheory]

You can run a Roots blower pretty fast if you have a powerful enough motor, but you will run into one of two things: 1) the motor overheating from being asked to supply too much power (excessive slip), or 2) the blower overheating from internal recirculation (or overheating the drive end bearings). If the blower overheats, it can seize, and while it may return to normal operation upon cooling, if you do this multiple times it can permanently reduce the maximum pressure the blower can produce, because the overheated rotors will mill small amounts of material from the casing before the whole thing stalls, and that will create a larger recirculation path. At this point the damage to the blower is permanent.