i had this Nova 5 years ago. never pushed it hard. friend i sold it to built it up and saw 63 MPH at 5200 RPM's. i am pretty sure they are stock 260 Merc ignition systems. do they have rev limiters? and at what RPM?

I would double check those numbers, if running 23 pitch like wellcraft put on them from the factory you are at 17% slip which is pretty high for a boat with twins.

Factory numbers by radar were 63 mph at 4600 rpms with the 23 pitch cleavers. (about 6%slip)

Which in turn seems unrealisticly low. 10-12% is about where you want ot be and should expect to be.

boat currently has 1 23 mirage and 1 21 mirage. he mighta been using those as he had a prop stolen. i have picked up another 23 mirage. anyway, does anyone know if 260 mercs had rev limiters? or did they use the inherent lack of balls as a rev limiter? or is it lack of irony?

Even with the few kinks I am trying to work out, according to the merc prop calc tool, I am at 7% slip running SS 21p 4 blade(same boat as OP). Speed from GPS.

But I do agree that 6% slip on cleavers is optomistic, but...... I have two magazine articles on the boat from the original owner that state top speed as 62mph in one magazine and 63 in the other. It seems that they+ tested the same boat, at least based on the color scheme, and equipment package of the boats in the article.

What year 260s?

I have '87 vintage 350 mags.

If there are rev limiters, I've never hit 'em!

And I've been to 5400, briefly.

My thought is that the gun hasn't been as precise as gps is today and the cleavers can be a tad higher than 23" maybe. Heck, just look at the new articles and see the diff. Tachs back then were also a bit off from time to time, they still are. If your prop is burried, yes you can run 7%. Also remember that stock props have slight variations. It might be 23.25+" and merc has a tendency to get weird with their pitch now and then. The Maxies are higher than stamped, the B1s are about an inch lower ect. Problem is, you can't really do a precise calculation untill you scan the prop and know exactly what it is. Back then with the cleavers, it's anyones guess. But yes, you are probably not off if you are between 7-8%. That is possible and pretty good, maybe even a tad low.

No rev limiters on Merc black engines that have TB IV ignitions.

Thanks Griff that's good to know, it's the same box I have.