Prop Selectiion

[tonyiiiafl]

I have a 1994 390 CPMY with 7.4 carb Big Blocks. The props are 22 x 22, and that is what is on the build sheet. I can hit 4000 rpm under ideal conditions, and it is not standouts, but has to build, and top speed of 29MPH. Not too shabby for a boat of this size. However, should I be hitting a higher rpm? I was wondering about maybe moving to a 22 x 21? GPH full throttle is approx 66 GPH. At 3200 I am kicking 42 GPH. Any input?

[mjk1040]

Tony, our 1998 355 AC/MY had 22x23's on it, when the spec sheet said they should be 22X22's, inquired to a 30 + ear mechanic as to why I didn't have what was spec'd the 22X22's he stated that after the build the 355 with crusader 7.4l TBI's were turning over 4400 rpm's, thus the 22X23's, one degree of added pitch to keep the rpm' at 4400 rpms, which to my understanding between 4400 & 4500 rpm's is all any gas engine manufacture wants as an engines maximum rpm. With that said and if your engine spec plate calls for a maximum rpm at full throttle in that range, I would take one degree of pitch out of your props to get to the maximum rpm's of 4400/4500.

[Midnightsun]

between 4400 & 4500 rpm's is all any gas engine manufacture wants as an engines maximum rpm.

Pretty much so talking big blocks however small blocks are different. My magnum 383 strokers were rated at 4600-5000 rpm. A standard EFI 5.7 (350) is 4400-4800 WOT spec.