Does it compute?
Dan,
It's not the big things, but a combination of alot of small things that gain performance. First, those aren't bad numbers for an RV4 at 8000'. Compare ground speeds or just race him and see what he is really doing. Maybe his airspeed is "self induced". My 150HP RV4 would indicate 210 mph/169 knots GS at SL, full throttle 2800 RPM when I finished tweeking it. Make sure you have fairings at all the gear intersections, flap gap seal at fuselage, tight empennage fairing, mags timed correctly, REM37BY plugs(hotter).
Having played with my RV4 for 13 years, my prop seemed to be the biggest improvement in speed along with Ram air and Electronic Ignition. When I had the 150HP 0-320, I ran a Warnke 69X70 ACS prop that just wasn't quite giving me what I thought The Bandit should be doing, so I sold it. After running my old Sterba spare (which gave OK performance), I visited Craig Catto. He wasn't making RV props at that time, but let me borrow a prop from a 160HP Glasair the owner returned. Wow, what a difference! I gained 15 knots at the top end and the whole airplane was smoother. It was a bit too much pitch for The Bandit, so me made me a new prop, his 1st 2 blade RV prop. Whack, home run! It would turn 2850 up high but that was OK by me since the MP was low.I was truing out at 165 Knots at 10,500' on 8.8 GPH. Below 5000' I could hang with any RV, any HP, except maybe Dave Anders. This with only 150HP. Your 160HP should be easily doing 165 Knots True at Altitude.
My point? After checking everything else, Catto, my brother, Catto TWO Blade. I know, everybody says his new 3 blades are better than before, but I can attest that the 2 blade on the 0-320 Rocks!
Smokey
HR2