sleeper_dave

How fast should a 27 fever with a single 502 go?

I have a 1991, 27' fever with a freshly rebuilt, stock, carbureted 502. about 20 hours on it now. Fastest i've gotten out of it is 58 mph on the GPS at about 4900-5000 RPM. Is that right? I was hoping for at least 65.

What can i do to get a few more MPH out of it fairly cheap? I was thinking of swapping out the intake, maybe the carb in the spring.

What size carbs are on these stock? Block serno says it's an MPI motor, and this is not the first boat it's been in. I think this is stock 1991 running gear despite being a 1994 block. The carb has 8867 and a W on the top of it.

Rebuilt a month after i bought the boat (inside of oil pan was painted, sucked up seaweed, overheated oil, paint chipped off, sucked into oil pickup, spun #1 and #2 rod bearings). Boat previously had a supercharger (boost gauge in dash) but i'm not sure if that was on this motor ever or not.

Also, what's an extension box? Saw that mentioned on this site.

Von Bongo

Well, you should be in the mid 60's with a 502 that is 415HP. What HP are you making? 502's make a lot of different HP. If it has a carb on it then it isn't and MPI, MPI stands for Multi Port Injection.

Extension box is a box bolted between the transom and drive to set the drive back, usually raise it a bit and get the drive in clean water. Probably won't do much for you as Fountain uses a notch in the hull and that acts like an extension box.

Start by telling us what drive you have, drive ratio, prop brand & pitch and how much HP you are making.

I'd first look to see what you are running for a prop. May be under pitched.

ratman

my guess would be 171mph, did i win anything

Rookie

iTrader: (4)

Here is some info about people talking on how fast the 27 fountain is with different power.

http://www.offshoreonly.com/forums/s...d.php?t=109578

sleeper_dave

Let's see... pull out the notes...

502, according to mercruiser (checked the serial number with them) it was originally an MPI motor. Of course, it is no longer. I know it has a forged crank, 7/16" rod bolts, and forged JE pistons. Fresh bearings and rings. No idea on the HP level, i would assume somewhere in the 400 ballpark.

Drive is a bravo 1. I believe it's a 1.5 ratio. I called mercruiser and checked the serial number, but i don't have those notes in front of me right now.

Prop is a powertech, when i called them with the number they said it's a 15 1/4" diameter, 15" pitch if i read the number on the prop correctly. That doesn't sound right though, it has to be more pitch. The rep from powertech said it's more likely a 19" pitch and i just misread the 5 as a 9 at the end of the p/n. It's a 3 blade, and i just had it redone when the motor was rebuilt. They just cleaned it up and balanced it, as far as i can tell.

I'll probably replace the intake in the spring, maybe the carb too if there's a gain to be had there. But if it's already a 750 CFM carb i don't think there's much gain to be had for a NA 502. Those seem to be the two least expensive mods i can do. I got 5 mph in the quarter when i swapped the intake on my car... i don't think i'll be so lucky on the boat though.

pullmytrigger

If the guy had a blower on it before I wonder if he put in low comp blower pistons and left them in when he removed it and just installed an intake and carb.........

never heard of a powertech prop........try a Merc Mirage or Mirage Plus19 or 21 or Bravo 1 (although I think the lowest a Bravo 1 pitch goes down to is 22....if you can get one try that too)....... they are the pretty much the industry standard high performance props, shouldnt be too hard to find a prop shop to lend you one....... everyone here on the board can relate to them and their characteristics are very much known so it will make it make it much easier to sort this out.......doug

pullmytrigger

I agree with Von Bogo........definatly start with the prop

Pat McPherson

A friend of mine has a 1997 29' Fountain.
With the stock 415HP/502MagMPI she ran 64-65mph with a 24p Bravo I at 5000rpm.
I would think your boat should run about the same.
Like the others said, start with the prop...

1stfntn

2003 27' Fountain w/ 496HO (425 HP), Bravo I drive w/ 1.65 ratio and Bravo I 30P prop. Ran 71.3 on GPS with about 1 gallon of gas and a 10 pound infant driving (i.e. on the Fountain test report). Just kidding. Best I ever saw was 70 on GPS speedo, very light on fuel with only myself in the boat. Does your hull have the single step? If not, I would expect 4-5mph slower. Agree that previous owner may have lowered the compression ratio for the blower and then just slapped a carb on after yanking the blower. May be the reason for your decreased power/performance.

sleeper_dave

I'll be pretty pissed if it's got blower pistons in it. I would imagine that's something that they should have noticed when they did the rebuild. The shop i took it to subcontracted the motor to Heads Up racing, a guy named Bruce did the motor. Supposedly he's good. That's all i know.

What's the diameter on the above recommended props? the same 15.25" as the one that's on there? I'm seeing 4900-5000 RPM at WOT... is it still wise to step up in pitch? What does the power curve look like on these motors... am i coming out of the powerband up near 5k? I wouldn't mind going with a 4 blade. I've read/heard that that would provide more stern lift, which i think would help the ride at cruising speeds (right now i have to put the tabs down pretty far to smooth out the ride).

If i do a compresssion check, what kind of PSI should i be looking for if it's stock compression? Of course, i don't know what cam it has, so... Also, anyway to ID the pistons from the bottom? I still have pics of the motor with the oil pan off.

The motor does not have a step in the hull. I was expecting somewhere in the neighborhood of 65 mph when i bought the boat. I got 59 mph on the GPS before i the motor was done, 58 mph after. First time i opened it up after the rebuild i only got 53-54, so i figure it might loosen up and giv e me another mph or so. Still not 65. Wax was fresher when i got 59 out of it too.

Any ideas on how to identify the size of the carb? If the previous owner slapped a 650 on it that might have an effect. Guy i bought it off of never had a blower on it, and when he bought it he was told the motor was a new crate motor put in when the blower motor was removed. Of course, he could have been BS'ed or BS'ing (it was one or the other). I know it wasn't a new crate motor in that boat, but it may have been bought as a used or rebuilt long block and installed in this boat. At some point, someone did have the oil pan off to paint the inside.

Thanks for all the help guys.