formula 242 prop options
 

finally got the bugs worked out of my engine, now i'm doing some testing with my propping. its a mild 454 with about 400hp and alpha drive. i've got a 19p mirage (non-plus) on the boat now and i'm getting 4300rpms at 48mph max. i did have 4 people and about 3/4 tank of fuel, so it was a bit heavy, but i still would think it should be a bit better than that. even with just me on the boat, it still only turns 4300, but not sure of the speed. i find it odd that i can't turn the engine faster with a 19p. if i try to go up in rpms, i would have to go down to a 17p, which ive never heard of with people that run bbc's in larger boats. usually its more around a 21 or 23p. the only thing i can come up with is that the drive was swapped with another drive with a higher gear ratio (other than the 1.5:1 thats supposed to be in it). i have mild timing right now too at 8* initial with 24* tb4. at 32* total, i'm very conservative with the timing, but i still wouldn't think it would gain me 4-600 rpms or any significant speed by bumping up timing 4* or so. any ideas on what might be going on with this, or something i should test or try?

Your slip is only 7% with a 1.5gr so the prop is hooked up extremely well.

Other prop testing isn't really needed untill you figure why the engine won't pull more.

Brett

yea it feels like its almost hooked up too well. it comes out of the hole great! it bites real well and planes quickly. it just feels like i can't shake it loose on the top end, and it seems like its working really hard all around. even at about 36-3800 cruise, it just feels/sounds like its working too hard. i hear the 4brl open at about 35-3600, so i know they're working correctly. like i said, i want to try to put a little more timing in it, but i doubt thats really going to make much difference. i can turn it about 3900 with normal "cruise" trim (very small and tabs down a bit), and can get it up to 43-4400 by adding more trim and pulling up the tabs. by 4400 im throwing a rooster tail and the prop is starting to slip (come out of the water).

is there a way to check the drive gear ratio? the sticker vin number on the drive is long gone (mercruiser's stupidest idea ever....really....stickers?). is there a way to count teeth on the upper or something to figure out the ratio? i really am suspecting the drive is wrong, and its messing up my propping. the previous owner of this boat has hacked everything together thus far, so anything is possible. it "looked nice" and everything "functioned" and thats about it.....shame on me....i know....

would a higher ratio like a 1.65:1, 1.84:1, etc drive from another smaller engine produce the symptoms i'm seeing?