poormxdad

Gents,

My Rotrex C30-74 has gone through most of the family of 6 bolt/7 rib pulleys. It's got a 75mm pulley on it now. The only 6 bolt/70mm pulley I can find has 8 ribs. Will there be any issues? It's Sunday, and I don't expect a response from the vendor soon...

Thanks,

highroller101

Mx- what rpm are you running?

im in the process of upgrading my c30-74 w/95mm pulley to a c30-84 (just a compressor housing swap) and a 75mm pulley. TDR wanted me to use a 72mm pulley but I rev to 7200rpm and the 72s limit is 7000rpm. 70 I believe is a 6700rpm limit.. or is your plan to over-spin the Rotrex? If you’re chasing more power you might look into the -84 conversion, simple and cheap. I think all of the parts were roughly $400.

poormxdad

I did some math this morning and believe you are correct. If I assume the pulley diameter for the Rotrex on the Fluidampr crank pulley is 5.25", the 70mm pulley would overspin the supercharger.

Do you have a link to the compressor housing swap?

Thanks,

highroller101

Just call track dog, they will sell you the compressor housing and the air intake housing and filter. I think it’s 6 bolts to do the swap.

out of curiosity… what boost pressure do you see? Power level?

im hoping that my upgrades take me from 177 to 225. TDR said the rule of thumb is 1psi/5mm on pulley size and each psi is worth 8-12hp. So I’m hoping to gain 5 psi and 50hp…

rascal

My real world experience was more like 2psi per 5mm, though 8-12 hp per psi was still valid.
I went from 95mm pulley to 105mm pulley and psi dropped from 8 to 4 and whp went from 210 to 165.

I guess part of that is relativity. 5mm out of 105mm is 4.7% whereas 5mm out of 75mm is 6.6% so almost 50% more

poormxdad

With the C30-74 and 75mm pulley, I usually see about 9.7 - 9.8 psi boost on track. On a really good day, I've actually hit 10 psi. I believe she's putting down about 225 rwhp, but I haven't had her on a dyno in a while.

highroller101

I see 7-8psi at redline. I’m hoping for 12psi with the 75mm. But more than anything just trying to stay in front of these Miata’s with built engines putting down 180-200 and better aero than me (for now, I have 9LR bits ready to go).