Anyone with a 2700 SC/SCR and a singe 350/5.7?

[hybris1]

I am having trouble find the right prop for my boat. It doesn't appear many have this size boat with only a 350. I don't know what cruising and top speed I should be expecting. Right now, I cruise at only 18mph at 3400rpm and my max speed is less than 30mph at 4200rpm. I have a new 300hp engine tied to a 2:1 bravo II and a 18x17 stainless prop. I have received some good input on other treads I have started but I am hoping this title may help. Ideally I would find a place that would loan me a couple of props but I have not found a place yet. Thanks.

[seapuppy]

Originally Posted by hybris1

I am having trouble find the right prop for my boat. It doesn't appear many have this size boat with only a 350. I don't know what cruising and top speed I should be expecting. Right now, I cruise at only 18mph at 3400rpm and my max speed is less than 30mph at 4200rpm. I have a new 300hp engine tied to a 2:1 bravo II and a 18x17 stainless prop. I have received some good input on other treads I have started but I am hoping this title may help. Ideally I would find a place that would loan me a couple of props but I have not found a place yet. Thanks.

it sounds like your a bit low on the wot....you should be on the hi side of 4200-4800 rpm...

your speed should be upwards of about 40 mph wot....I had the 6.2ltr engine and at wot I was hitting about 42mph.....so you should be right in that area...

SP irate:

[hybris1]

Seapuppy,

You don't happen to remember what drive ratio and prop you had on your Maxum? It may make a good comparison.

[seapuppy]

mine was the b3 drive....don't know the gears but I was spinning a 20" pitch prop...I thought that was a bit lean for the boat but the bay guys said that's what they wanted on the drive....so my numbers are going to be a bit different than yours...


SP irate:

[tglee]

Have you tried some of the “prop calculators� that are available on websites that sell props? An original 5.7 with a B2 2:1 drive would have been equipped with a 18 ¾ X 17.

[hybris1]

Yes, I believe it had a 18 3/4 x 17. I went to the prop shop Friday and told them my setup/rpm/etc and they recommended cutting down my prop 1" to increase the RPM about 200-300. They are also going to verify the profile and re-cup after they cut down the prop. I should be able to test it later this week. I also need to verify that I do have a 2:1, there is no plate on the outdrive. Does anyone know were else to get a S/N? I may just have to rotate the engine and watch the prop. It shouldn't be too bad with a 2:1 ratio.

[tglee]

The serial number tag is located on the UPPER DRIVE SHAFT HOUSING (starboard side or on the back of the housing).

[hybris1]

I had my outdrive repainted last year when I had the bottom done. I don't know if the label was removed or what. I looked on both sides of the upper outdrive and I didn't see anything. My boat is in the water so it is hard to look everywhere.

[seapuppy]

well..the 2700 with a 350 should be cruising at about 26-30 mph...your really really slow in this aspect..I could cruise at about 30 mph...4000rpm and run all day with my 6.2ltr engine....so..readline was at 5280rpm...

so...your wot for a carbed engine should be about 4200-4800rpm....which at cruise should put you at about 3800rpm...adjust your prop from there...I think your prop should be at least 19" pitch.....

SP irate:

[shrew]

I don't know that I would focus on speed regarding this, but rather RPM's. You should, theoretically be able to reach close to the MAx RPM recommended for that engine. The general (non-scientific) rule of thumb is, At Wot (Wide Open Throttle) if you are below the Max RPM range, then you're over-propped. If you're over the MAx RPM range, then you're under-propped. Neither is terribly good and can potentially harm the engine. I like to use the 50-75 percentile as an average. So if the boat MAx RPM range is 4200 -4800, then If I'm hitting 4650 at WoT, then I'm pretty good. Technically, I'd probably be happy with 4500 RPM.

Speed can be influenced by sea size/state/direction, wind, current and tides. You'll technically be going slower Kph/Mph going into a head sea or wind, then with non or a following sea for example.

I would also make sure that trim tabs are all the way up and then start slowing trimming up the outdrive watching the RPM change after each click. You will eventually hit a sweet spot. That should at least give you aball park. Consider calling US Marine. They should be able to tell you what the stock prop setup was on that year make and model a can even look at similar models from other years. Let's face it, the featrues and asthetics change from year to year, but the length, width and weight of the boat don't change THAT dramatically.

[hybris1]

Bought a new prop. I got a Solas Stainless Steel 18.25 x 19. I did the calculation and got pretty much what I wanted. My cruise speed is now 25mph (GPS) at 3500 RPM. This was my previous max speed at 4500 RPM. My old prop was slipping a lot. My WOT is 33mph at 4200 RPM. It appears to be over propped. I do like the cruise speed though. I am getting only about 20% slip versus the 42% slip I was getting before. Only about 12% at WOT. If I keep the same slip, a 17 pitch (recommend OEM) would increase my RPM 200-300 and make my cruise about 3900 RPM. This is higher than I would like but maybe better. I don't know. I am having my old prop redone with some more cup to see if that reduces the slip. I am getting pretty good at pulling the prop in the water .