Ive got a 29 outlaw with 7.4's. I am getting 63.5 on gps, and my tach shows 4600, but with the slip #'s my tachs obviuously wrong. Im probably turning 4800-4900 which is too much for the 7.4's.

I have a set of 25's that i was thinking about getting labbed. so if im running 4800 with 23's (mirage plus) I should drop to 4400 with 25's (mirage plus) and with labbing, that should put me at 4600-4700 right where i need to be.

this should work right?

In theory you are correct. BUT , I would first address the tachs re-baseline and make your decisions from there. The more accurate the reading the better your prop work will be.

Julie

Check your tach's.
7.4's rev limit at 4700.

My 97' 29 had 7.4's, it ran 25 mirage +'s
at 4500 rpm, speed was around 65 gps.

You may be right on the rpms, but when i did the slip calculator it comes out way to low to be accurate, and i figured the gps was correct. Maybe Im hitting the rev limiter, but its not cutting out?

I just need to put the 25's on and try it. did you spin them in or out?

Spun them out.

I found out that my tach's were off when
I tried a set of 24 Hydro. intimidators,
I would trim up, hit about 4600.....It
would fall back to about 4200, wondering
what was going on, I threw it in neutral,
ran up the throttle one at a time, slowly,
right at around 4500-4600 rpm, the rev
limiter started phasing in, both engines.

Rev limter is at 4700

Chalk up another one for those "accurate"
faria gauges.

But this time, they were reading slow