Steel v. aluminum should not be an issue here. Precision honing is a thing.
what causes the 125 to be faster than a 175? whats different on the engines?
I think it’s important to note that the 175 SSE for use with SKUSA is a lot different to the 175 super shifter in the IAME cup.
That said, my observation is that the track seems to determine which has the upper hand between a KZ and a 175 SSE when they are run together. Although I’m sure class weights play a part as well.
A KZ makes more power at the higher end of its RPM range whereas the the SSE is more of a “stump puller”, delivering more power lower down. We have dyno curves on the forums comparing an SSE and a TM KZ (Same dyno) somewhere.
It’s got +25% more displacement, so the power curve should naturally be wider.