1994 Maxum 2700 SCR - Bravo 2 Prop Size?

[1994Maxum2700SCR]

Hey guys!
I have a 1994 Maxum 2700 SCR with a 7.4L merc bravo 2, I just purchased it a few days ago and I know something is wrong with it (I assume the prop pitch is wrong)
I'm topped out at about 3200 RPM and am barely pushing 20mph (and it is sucking gas like no other).
I'm not sure what size prop is on it now (i think the previous owner said 21" pitch but i could be wrong - haven't had the chance to pull it out of the water).
(The previous owner also blew the old lower unit because he forgot the thrust washer and it ate the prop, he gave me the old lower unit and old prop, the old prop has a 19" pitch.)
There is a brand new lower unit on the maxum now and what i believe to be a 21" prop. do you have any insight for what could be the correct prop size? or perhaps the solution to this low rpm, gas guzzling, sluggish problem? These props cost like $400 - $600 so I'm trying to get the right size once lol.
To top it all off, i blew the starter today and i realized its not a high torque starter so that was on its way out anyway i researched online and think i need an ARCO 30470 starter but I'm not 100% on anything, if someone could double check that also for me it'd be greatly appreciated.

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Thanks for your help,
- Joe

[seapuppy]

welcome to the zoo joe.....I answered your im too me....as for the starter parts no....I'd get the hin # and the engine # and call your local bayliner dealer and he can get you a marine grade starter...be sure it's marine grade ........


SP

[ImRich]

I have a 1990 SCR-2700 with a 7.4L Bravo engine. It also has a Bravo 2 stern drive with a 2.00:1 gear ratio.

My current prop is about a 18x23 3 blade aluminum (i'm not sure if it's an 18.5x23 or 18.75x23).

If you want to check your gear ratio, call Mercruiser with the serial numbers of your engine and outdrive. They can look up what the gear ratio is/was.

I say is/was, because if your lower unit was replaced, perhaps they put in a different gear ratio? This will affect what prop to use.

[1994Maxum2700SCR]

Hey guys, I just wanted to keep everyone updated in case they have the same problem. I spoke to a propeller expert and they assured me that my low wot problem is due to the wrong prop pitch.
I ordered a 18 3/4" x 17" pitch Stainless steel prop (rated for boats 27' - 34' long and 5900-8700 lbs). Since the boat's dry weight is about 6,500 lbs, it seems fitting. The propeller people also said that if i went from the 21" pitch (currently on boat) to a 19" pitch that it would be much better but i would still not be reaching the rated rpms. for every 1 inch pitch, they said is equivalent to about 300 RPMs. so with the 17" pitch i should be gaining about 1,200 RPMs which should put me at about 4,400 RPM. The boat is rated for 4,200 - 4,800 RPM. The prop is being ordered and I will install as soon as i get it. I will keep everyone posted if interested.

[ImRich]

I know I'm new here and to the Maxum, but I would be sure to check that your engine is working properly before trying a 19 inch pitch prop.

Why? See this previous thread of mine: http://www.maxumownersclub.com/forum...rive-questions

When I had my first test ride of my SCR-2700, with the 7.4L, Bravo 2 with 2.00:1 gear ratio, I couldn't get over 11 MPH (measured by GPS) and the WOT was low!

Later tests and the engine started running better. The dealer rebuilt the carburator and found that the timing of the distributor was off a couple of degrees. Now I get good speed and WOT with the 23inch pich prop. Before this, I was about to try to purchase a 19 inch pitch prop myself.

Be sure to let us know what you find in the end!

[1994Maxum2700SCR]

Hey Rich,
I really hope its just my timing. I have a quick question for you. when you had a low WOT and were going 11mph, were you also burning up a ton of gas? right now i'm literally burning like 70 gallons in about an hour at full speed and im probably moving about 20mph (rough estimate, no gps yet and speedo is broken at the moment). Engine seems to be running strong. I read your forum post a while ago and saw that you said you were hitting 4,000 rpm at wot and going 11mph, im only hitting 3200 rpm at wot. that's why im leaning more towards the prop as the culprit. im gonna take your advise though and check the carbs/timing tomorrow morning and see what im working with. worst case scenario, i'll have an extra prop. the 17" pitch may not get me up to 40mph but it should put me to plane really fast since its a wider diameter (fingers crossed).
I hope i get this problem licked soon, kinda just wana get out and enjoy the season.
the boat's name fits haha,
We'll Sea...

-Joe

[ImRich]

I don't know the fuel consumption as this was during the first check out ride. But I would guess that the fuel consumption was high. I noticed at the time that I went from 3000 to 4000 RPM and it only changed the speed by 1 mph! (from 10 to 11 MPH). I also couldn't get the boat on plane at the time.

[1994Maxum2700SCR]

Installed the new starter yesterday, engine was still having trouble starting. I checked the plugs, gas in all cylinders. the #4 cylinder also had some water in it (uh oh). I checked compression in all the cylinders (1 plug at a time at cold engine) and found that my compression for all cylinders was pretty consistent at around 120psi. However, the #4 cylinder only had compression at 90psi (it was also having trouble holding the compression as the meter slowly dipped down during the test). There was no spark coming from 1 plug that i tested (possibly more than 1), so I replaced all of the spark plugs. cranked the engine and noticed that my carburetor is dumping a ton of gas in it. disconnected the fuel line and manually got it started finally. took the boat for a test spin with the new plugs. at wot i was hitting only 2600 rpm, at 3/4 throttle it jumped back up to 3000 rpm, at 1/2 throttle it brought me to idle at about 1000 rpm. im not sure if it was because the fuel filter was affected from when i disconnected the fuel lines but i was in a hurry to go to work so i couldnt risk getting stuck on the water. I ordered a reman carb from a reliable place and will be installing that this week along with the 17pitch prop. I am pretty certain that there is an underlying problem at play here, but i dont want to be pulling the engine at the beginning of the season unless absolutely necessary.

Here's a little history on this boat, the guy i bought it from got it after it had been sitting for 2 years. he put New plugs, wires, cap rotor, alternator, propeller 21pitch ,risers, belts, zinks, boots and hydraulic lines,The bravo 2 unit is new with receeipt '04-30-12', 3 new batteries, Trim tabs work.

when i picked up the boat i drove it for a 5 hour transport on the water and it performed pretty well with no sputtering, just rpms never passed 3200 and i was topping out at about 15-20mph.
I also touched the risers yesterday when we had it running, the port side was cool as a cucumber but the starboard side was much warmer.
From my experience, the manifolds should probably be changed. i hope the block isnt cracked, and im hoping the heads arent cracked either.
water is not spitting out of any spark plug ports, just enough is noticed when pulling the plugs out.
When i checked the oil, there was a small amount of water in there as well (condensation?) or leak?

any help is greatly appreciated, slowly losing my sanity lol

- Joe

[ImRich]

Seems like you have some work to do:

Rebuild carb
find out why #4 cylinder has water and lower compression (probably one and the same reason, if your lucky, it's just a head gasket).
Get it running properly.

After the above is fixed, then check your WOT and prop size.

[1994Maxum2700SCR]

Hey guys, I finally found time to mess with the engine. I've decided I'm going to get the carbs rebuilt, heads redone, and new manifolds (risers also if bad - previous owner said risers were new, we'll see).
pulling boat out of the water in 2 days hopefully and gonna have in back in the water within 2 weeks. I'll let you know if we get the problems licked. I wish I hadn't put down a deposit on the 17" pitch prop because im starting to think the rpm problem is compression related and not prop related.

We'll Sea...
-Joe

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[ss3964spd]

Good luck with it Joe, let us know how it goes.

[1994Maxum2700SCR]

Started taking the engine apart today and bad news... water in the block.
I pulled the engine, after a long ordeal and a few gray hairs later it was out of the boat (old fork lift and nerve racking dilemmas) so i decided that I'm gonna just buy a re-manufactured long block engine.
My dad used to send his engines to a local guy to get his rebuilt but he's not the greatest.
I found these 2 websites and I'm not sure if anyone has ever dealt with them but I'm looking to order a new engine from somewhere tomorrow (trying to get this boat back in the water asap).
I don't know what places build good marine engines so any input is appreciated.

Engine is a 1994 Mercruiser 7.4L (454 big block) - non vortec, carburetor, single rear seal, external fuel pump

One place bores them out more also to "give them more HP and Torque and use less gas" - thoughts on them? stay away or go for it?

here are the 2 sites i looked at:

http://usaboatmotor.com/home/remanufactured-boat-motors
BBB REVIEW: http://www.bbb.org/wyoming/business-...er-wy-46012500


http://usenginesinc.com/Marine-Engin...ne-Engine.html
BBB REVIEW: http://www.bbb.org/western-washingto...kent-wa-511160

What do you guys think I should do? This boat is bleeding me dry lol so I don't want to waste money, trying to get things done right.

Thanks,
- Joe

[ImRich]

Wow, good luck! You'll have a new engine when you are done!

I don't know anything about these companies, but I'm not sure how more HP means less fuel consumption. It just doesn't make sense to me. Engines need fuel to make HP, they bore them out to allow for more fuel to burn, which means more HP.

Perhaps someone else can educate us on how a larger bore means less fuel consumption.

Seeing that I may be in the same situation someday (with my 1990 vintage engine/boat), I want to know how your 'project' turns out. I think my first replacement will be my complete 1990 Bravo 2 outdrive. The company that says better fuel economy also says a 7 year warranty, and that sounds attractive.

[pascavone]

did you do a compression test on the old engine? sometimes its just the head leaking water thru the manifolds.

I'd call around a few local marine mechanics to get a local opinion.

a 7 year limited warranty gives them plenty of "outs" to blame things on other existing conditions.

Meaning, for $3,500 engine they know who to blame a engine failure on the installer.

I'd go cheap and spend some money on the transom seals since the engine out.

here's a craigslist find for comparison.

don't put more money in the thing then is worth.....

2 mercruiser 454 v8 big block chevy marine motors neg TRADE OBO REDUCE - $3175

http://newyork.craigslist.org/brk/boa/3099411043.html

[ss3964spd]

Joe,

When a rebuilder bores out the cylinders it's because they have to; the cylinders are probably too worn, or are tappered, from years of use and if the builder were to simply install new rings in the old bores (after a light hone) they probably won't seal well. How worn the cylinders are determines how much they need to be bored. A pretty standard over bore is .030 which, on a 454 CI block, would result in 460 CI's. A 6 CI increase is very slight and one would need a dyno to see the HP difference because you'd never be able to feel the difference. But the more you bore the cylinders the thinner the side walls become - possibly compromising the block so most rebuilders will only over bore the minimum needed to clean up the cylinders; could be .010 or .020 over. Basically, there is very little HP/Tq gain from over-boring. The big HP/Tq gains come from better breathing cylinder heads and more agressive camshafts.

Actually yes, you can increase HP and also see an improvement in MPG but it's a pretty tight balance. If you install a low HP engine in a heavy vehicle you'll spend so much time at high RPM's and close to WOT that it will use a ton of fuel. Install a higher HP engine in the same vehicle and the engine spends far less time at high RPM and WOT. The key, however, is torque (not HP) and what the torque curve looks like through the RPM range.

All that said, what you really need to be careful of is that you outdrive will be able to handle the extra power. Going with more HP/Tq will mean nothing if it shreads the drive.

Dan

[seapuppy]

might consider michiganmotorz.com....they are well known and can build up a long block pretty much to your spec.....

SP

[1994Maxum2700SCR]

Originally Posted by pascavone

did you do a compression test on the old engine? sometimes its just the head leaking water thru the manifolds.

I'd call around a few local marine mechanics to get a local opinion.

a 7 year limited warranty gives them plenty of "outs" to blame things on other existing conditions.

Meaning, for $3,500 engine they know who to blame a engine failure on the installer.

I'd go cheap and spend some money on the transom seals since the engine out.

here's a craigslist find for comparison.

don't put more money in the thing then is worth.....

2 mercruiser 454 v8 big block chevy marine motors neg TRADE OBO REDUCE - $3175

http://newyork.craigslist.org/brk/boa/3099411043.html

Hey Pascavone, yea compression was 120 on 3 cylinders on one side, 1 cylinder has 90 and was leaking (also had water in it). the other side of the engine was about 110 all around.
Originally i was going to do the heads, gaskets, manifolds, risers done but when i got deeper into the engine, it seemed like I'd be wasting my money. the oil was all milky white gunk - salt water got in. to be on the safe side the engine really should be rebuilt. (previous owner said it sat for 2 years)
I decided to order from http://usaboatmotor.com/home/remanufactured-boat-motors
and since they don't need my old block, I'll have the time to rebuild that one as a spare.
I'll let you guys know how their engines are in case anyone is interested. I should have it in my boat within a week or 2.
I got a price from a local rebuilder and he said $2,900 to rebuilt my engine. (figured $400 is worth keeping the old block).
I asked about how they hone their engines also and they said that they do not surpass 0.040 over.
454/7.4L 73-95 330 HP V8, All Non-Vortec, Boat Motor $3,295

We'll Sea...
- Joe

[1994Maxum2700SCR]

here's a little update:

pulled the old engine
water in the block
bought new remanufactured engine (arrived yesterday)
got to the Y-pipe and 1 flapper is missing, the other was stuck open (explains the water in the block problem)
purchased new flappers (better new age design) and Y-pipe gasket,
re-installing Y-pipe today and assembling the new engine with the valve covers/tin