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This set up has got be a ball to drive. I have tuned a few 9psi Rotrexes in the 200hp range and they were fun (not fast) to drive. I imagine this car feels great with the same increasing torque curve but with 100% more.
Very nice numbers! These Rotrex SC’s love cams and compression with E85. I went a bit to mild on my cams wanting to keep some low end grunt. By the looks of it you didn’t give up anything down low (5k)
Same 11:1 CR, C30-74, E85, 9si and Dyno for comparison. I also run 2.5” exhaust but use cheap eBay header.
Cam selection is key. I played with a few cam configurations to find this was the best combo. If I were to try anything else with cams it would be more intake duration to swing the peak power to the right another 400rpm but valve wear is a convent so I’ll keep it as is. I think this winter I will try to make a header In hopes of freeing up more power. The rb unit is great but I am certain. At this power level it’s a restriction.
I would look at the 2.5” exhaust closer before taking another run at cams. I bet that’s causing the restriction up top. I kinda doubt the RB header is holding you back.
When tuning last year I fought a similar power curve (lower numbers though), turns out I left my silencer cone in the exhaust prior to tuning. Once removed she pulled all the way through the top to 298whp. Kinda shows what exhaust restriction look like on the dyno.
I’m not touching the cams I’m happy with the powerband but I think it could be improved. On the exhaust side. The idea will be to replicate an rb header with a Better merge and bigger primaries and step up to a 3 inch exhaust. I’m using Maruha cams
Which supercharger pulley were you using on the c30-94? I think 95mm gives a decent safety margin at 7200 and 95mm toes the line of overrunning the shaft speed at 7500 rpm.
I have a different crank pulley so the supercharger pulley data is irrelevant to most if not all, but it is slightly overspun and I’m aware of the repercussions of that.
just a data point I thought I’d share with you guys who might be looking into upgrading in the future
originally, I didn’t anticipate to push this much power through this engine. at this power level and at 7900rpm the crankshaft is likely flopping around. I found fretting under the caps.
Best thing is to slow the motor down a bit and put in a main stud kit. I might put billet main caps in the new engine to stop this completely.
310hp Rotrex c30-74 with e85
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