53mph at what RPM?

No clue, neither tach was working correctly, somewhere around 4800-5000 if I were to guess

i have a pair of 25 mirage plus that i ran on my 30 scarab w/ trs drives
they track straight are balanced, never been welded, have no reconditioning stamps, and are for sale 400 bucks, plus shipping

[ATTACH=CONFIG]558101[/ATTACH][ATTACH=CONFIG]558102[/ATTACH]

Well that's between 17% and 20% slippage if they are a true 21" pitch. A bit too much for a Mirage prop so there must be a problem. Guessing you already checked carbs are wide open at full throttle and timing is on the money (good tune up). Could be the trannies if your props slightly spin in neutral (clutch packs warped) or just tired motors/heavy boat.

His tachs aren't working.

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I could not imagine propping a boat without having working tachs.

I wish you woulda posted that about 4 hours ago, I just gave a guy my word Id spend 500 on his props, same as yours. Thanks for the offer though!

Ive gotten the tach problem figured out, just haven't had it back in the water since the repair.

Ive read several posts on the 30' scarab hull with TRS drives and the consensus was that the 25p was the perfect prop. Props don't spin very much at idle out of the water, trannies seem to be holding up. The three blade 21s that are on there have been labbed, but are in pretty bad shape, looks like the PO used them as a depth finder more than for propulsion. Were gonna try the 25's and see what they do, in the meantime we're gonna send these 21's off the be trued (if that's possible)

I couldnt spin 25s on my magnum sport with the 280 trs which is a more powerful small block, and lighter boat. Again you need to get the necessary items working correctly before i would spend a dime on props. trim-tachs then props

So then let me ask this, mind you I'm undoubtedly the most ignorant person on this forum, but at what rpm do you spin your motors at WOT?