Re: difference in 115 and 140 crossflow
OK, here's a thought -- dont get too hung up on horsepower numbers. I'm not sure how much everybody knows about how a dyno is run -- and I'm talking a real read-out dyno, not just a water break for loading -- but you can "make" a dyno read out in a great variance on the same motor.<br /><br />Then keep in mind the NMMA's allowable tolerances. Also remember that before the early to mid 80's the NMMA didn't really enforce those rules all that closely. Thru the 60's and 70's a lot was determined on the race course.<br /><br />Anyway, lets look at torque rather than hp. The difference between a V4 cf with a flat back exhaust and one with a bubble is minimal in the rpm range we're talking about. Even between the 85/90 small port style and the 115/140 larger port style. <br /><br />Since 1979 all V4 cf's have the same bore, stroke, gear ratio, ignition, crank, rods, piston, intake, mid section (there are some variances between years but not between hp's in the same year) and general carb configuration. <br /><br />This is why a lot of times we see someone go to a lot of expense to upgrade from a 90 or 115 (flat back) to a 140 style bubble back and they're very disappointed. Again, in the rpm range around 5600. <br /><br />However we do see an advantage in the bubble back exhaust after 6300-6500 rpm. But that's not where the average V4 cf is set at. <br /><br />Horsepower is an OK guideline but torque is where its at. A stock 120 looper will always out run, out pull and out perform even the healthiest 140 crossflow.
I like your way of thinking.