formula 311 sr1 rpm
 

hey guys..i purchased a 1988 311 recently..the props i believe are prob stock..23p bravo..i have the 365 hp which are around 400hp a piece with the little work that have done to them..on gps i hit 68mph at 5200 rpm...is that to high of an rpm for these motors? should i go higher in pitch? the boat planes out awesome and cruises really well also...any input would be great..thanks!!

I have an 89 311 with stock 365 mags with 23 mirage non plus props, I've seen 66.3 on GPS at 5100 rpms with a half tank of gas.

I was checking out props. Not quite sure a few mph is worth 1200 bucks. Lol

Wait till it gets hot out those rpms will come down

My boat with stock 420's and TRS drives ran 68 at 5000-5100 RPM. I wouldn't worry about spinning 365's to 5200. They have the same bottom end as the 420's, and are probably safe to 5400 or so.

I had a 1990 292 sR1 with 365's and I had both 23" pitch and 25" pitch props. I went up to 25" pitch and had the same speed at a little lower RPM, $1,000.00 down the drain. If you don't have aftermarket exhaust, I would save the $1,200.00 and put towards stainless marine exhaust or some other aftermarket system. Also, the 25's will probably hurt your hole shot a little.

I had hydro motive 24s on mine with similar power. You will cruise faster but like stated above when in gets hot revs come down.

Something doesn't seem right. Bravo 23 (really 22) props @ 5200 rpms with a top speed of 68 equals 6% slip, which is not possible. A slip number of 11-13% would be more realistic which would give you a top speed of 64 mph. What have you done to you engines over stock?

Well, they don't make odd numbered Bravo props so he likely has 24's and that gets the numbers a little closer. If you are turning 5200 light then you are almost perfect, put people, a cooler, and fuel in and that will drop down to 4900-5000,

guy i bought it from said diff pistons and cam in motors..said each motor was 400 hp..i lied about props they're quicksilver not bravo and def 23p..i had a half tank of gas 5 adults 3 kidsand against the currant on river rpm gauge on boat said 5200 and gps said 67.9...gonna stay withwhats on it..seems pretty dialed in on taking off cruising and topend

They are probably mirage or mirage plus props. I am guessing Mirage as that is what most Formulas of that time frame run. Mirage plus's are ussually labeled as such, so my lean is that you probably have Mercury Mirage.

The 23p Mirage props were from quicksilver if I am not mistaken.

I have a 89 311 bravo's and until 2010 running 365's Mags with stock 23p Mirage. I have seen speeds between 64-65mph and even on a good day she was not faster. Both mag's were spinning 5200rpm at that speed.

In 2011 the boat was repowerd to HP500's with 26p bravo's. Even now it has to be a very good day to get 72mph.

The speeds you are seeing with that load against the current amazes me.

Weird. Guy I bought it from said always between 66-68 on GPS. I didn't think that the speeds were anything great. I had a smaller boat but was faster then this one. I was more looking for a comfortable ride. I did drill holes in swim platform so I'm not sure if that makes a difference also. Maybe my GPS is off. The one thing I will boast about is how theses boats handle rough water. I was amazed how well it did in 4 footers.

another thing i read which doesnt mean much is that every extra 100 hp is roughly 3-5mph...so if my boat has 70 more hp then you that sorta makes sense