1988 sr1 272 prop question
 

88 272sr1 with the twin special mpi 320 hp 5.7 l. "Factory high performance" and bravo 1.5 ratio. I bought it a year ago and love it. Im wondering if anyone KNOWS what props it came with when new?
Currently i have 23p at 4800rpm 64..gps. Also with the 23's it snaps on plane no problem. But at 4800 its lugging the motors because..........
These motors are supposed to run at 5400 rpm. i have 21 p to try should get me up to that.

ok here i am answering my own question so those of you who are curios.
I called Formula tech line
206.724.1413 and gave them my HIN and he looked at the build sheet and sent me a copy. he said my boat went out with 23's then we discussed the logic of it and he said at the time formula was more concerned with safety and reliability and prop tuning was up to owner/dealer. He agreed with me that possibly going to the 21's would make more sense.

They would certainly get you up closer to the 5400 mark.

yeah I hope so. maybe more speed if that gets me more HP.... well see

If you get 5400 and your slip stays at 8 the calculator says 66

I had the same boat also 1988 but with 350 MPIs and acceleration was great with 23 mirages but maxed out 45-4600. I always felt the boat hit 60 but didn't want to get beyond it. The engines had no issues getting to top speed quickly. I question if the hull design is set up to run much over 60? Then again you have a little more power.

Heres the deal, try the 21s, but you might find they spin higher rpms for the same or less speed. And then you lose cruising speed with the small pitch. I bet on a dyno those motors are done a 48-5k

whay would you say that on a dyno done at 4800-5000?

Meaning their peak power pretty much flat lines above 5k

mine says 5400. i thought that meant peak output is 5400 and below or above that generally means less than peak, like 4800 is 600 rpms less than 5400