Isn't the stock rev limiter on the 496 engines still 5150 rpm like always? Not sure how you could be getting 5270 rpm unless you have aftermarket tune. Thinking if your tachometer is reading high that would give you the seemingly high slip numbers you are seeing.

I have whipple stage 1 on the ECU. So the rev limit is at 5450 rpm according to Whipple.

Thank you Griff!

Yes, the theoretical slip is ”only” 22% now. Wich is much better than before.
I still have the .5” spacer.

For all that you have thrown at the boat in theory and props, I would agree with Griff on installing the spacer.

If the spacer drops your slip, that is the direction to focus on.

How are you measuring MPH? GPS or pitot fed speedo?

Yes that will be for next season.
I think the spacer I have will fit standard application also and not only Sportmaster

I measure the speed with GPS

One thing that come in mind is that I dont use the trim tabs much. K-planes.

I often lets them stay at neutral position when riding. I have some automatic tab adjustments but they dont seem to work very well. I can put it in manual mode and trim up and down how I want.

I thought about it if this could cause some slip also. If I can put the trim tabs down a little bit to lift the stern from the water more, or is it more like a brake if I put them down when up on plane?

For best top speed, the Kplanes should be all the way up unless you need them to stabilize the boat

Thank you. On every top speed test I had the trim tabs all way up.