Quote:
Originally Posted by RedReplicant
I was hoping to get down to about 300whp, but clearly I was overly optimistic.
Same dyno, same fuel, 90mm pulley, and a small tune tweak from CSG.
Not sure what to do at this point short of paying CSG to do a flat tune, I need to be making about 300 peak and I want to keep the ethanol for safety on track.
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I presume the tune tweak from CSG was tweaking the ignition timing or richening up the AFR a bit. The problem with trying to de-tune it may be getting to a point where the loss of fuel efficiency and/or other reliability issues from running too rich (E.G. fouling plugs, cylinder wall washing from excess fuel causing ring wear / poor sealing, etc.) outweigh the specific power goal.
I also don't think adding exhaust restriction is a great way to go because of the added strain on components upstream from that restriction with boost. If anything, maybe a restrictor plate on the intake side (at the throttle body or somewhere along that path) might be a better way to go.
That's what they used to do on the WRC cars (and possibly still do?) and in many various touring car series to limit peak power to a specific output while still getting the most low-mid range power.
Other than that, maybe a 95-ish mm diameter larger pulley for slightly less boost? Not sure if that would have to be a custom job or not, as I have no idea what other pulleys are available from Harrop. That would then allow the tune to be "maxed out" and efficient, but keep power levels within your desired range.
EDIT: just saw that dropping from 85 to 90mm only gave you a 5 whp drop, so probably an even larger pulley than 95mm would be needed...100 or 105mm? You'd then be dropping way out of the efficiency range of the blower, probably. Could be that an intake restrictor plate may be the better way to go.