Any Guesses??

[ck7684]

I've got full travel on my cable now, but still cant seem to get past 4800 RPM. Playing with the trim I was able to get to 66 MPH.
BTW, when crusing at a steady 3500 RPM, my GPS seemed to take forever to get up to speed. It seemed to update faster in my car (different day). Anybody have their GPS update really slowly? I'm wondering if I didnt have a good signal. I was running out of lake pretty fast also. (I only have about 1/4 mile of usable water on the lake I was on, which is close to home) I'm sure I was maxed out by then though...
Any input?

[79cobrajet]

Just curious to see what what you all think my speed is. I havent had a speedo or GPS in yet to find out...
My boat is a 16ft 1979 GMC CobraJet, Berk "F" pump with an "A" impeller. Pump was just rebuilt using an Ultimate wear ring from HTP. Engine is a fairly stout 468 BBC...
I have touched 5300 RPMs briefly, but for discussion sake, let's say @ 5000 RPM.
Years ago, with the stock engine, worn pump (not sure how worn, but used condition) and 3 people on board, a handheld GPS said 70 MPH as top speed (not sure what RPM)
Any guesses???:idea:

my speedo doesnt work either but I has similar case , first day out , low gas and basically empty for a wet test and she ripped that little like it was a puddle 4200 rpm and quickly too, took her out to river and it seemed to get more and more sluggish (although the engine was revving up fast) it just never quite hit 4k on rpm but was hitting 3800... I later foumd water logging in the lowest level of the boat, just enough to make her fat , heavy and lazy!
Probably doesnt have much to do with yours but just thought it is good to mention... By the way ...
I was wondering if you had ever gotten any useful info on the GMC CobraJet boat... I have a 1979 , 16 1/2 ft. that I just got and I am having one heck of a time locating info on this desighn.