300X's running slower than my 300 Pro Maxs

[Eliminator22]

I have a 1999 Eliminator 22 Daytona that I purchased several years ago with a pair of 300 Pro Max motors with 20" sport master lower units (not sure what the gear ratio is on these lowers). It was equipped with the Mercury 4 blade 15 X 30 clever props. Motors were rated to run at 6100 rpm max, with those props I was turning 6300 rpm and running 98 mph gps full of fuel with 2 people in the boat. As I thought I was overreving the motors, I purchased a set of Mercury 4 blade 15 x 34 clevers and only dropped the rpms down to 6100 but now ran 109 mph on gps.

I wanted more top end, so I purchased a pair of 2005 Mercury 300X outboards with 20" sportmaster 1.62 ratio lower units. After break in, and I now have about 40 hours on the motors, I am dissapointed to be running less rpm and speed than my old 300 Pro Max motors. Running the 15 x 30" 4 blade clevers, I am now running 92 mph on GPS and pulling only 5900 rpm.

I know the 300X turn a higher rpm and are more like 330 hp vs. 300 for the PM's, so I am confused as to why I am running less rpm than with the PM's. I have not tried different props, but my thought is since both motors are 3 liters and the X should run at higher rpm, then it stands to reason that at the 6100 rpm of the old PM's, I would be running less hp at that rpm on the X and only at the higher rpm of 6800 they produce more power, but I must get to that rpm to see the hp increase. Should I be running a smaller diameter prop on the 300X motors? Or is it possible that my old 300 Promax motors with a 20" sportmaster was running a 1.75 gear ratio vs. the 1.62 of the 300X?

Another issue I should mention is that since putting on the 300X motors anytime I am running high speeds and start to turn the boat the inside motor will cut out and drop to the 3000 rpm safe mode. I need to get the boat back on the water and see what the water pressure is at top speed. Looking at the manual, water pressure should be at 10 - 12 psi at top speed and I believe I am running less than that. If that is the case, then I believe the ECU is only allowing the motor to develop 90% power, which might explain the lower rpms.

Before I start spending money on buying a bunch of props, just looking for some general opinions on what diameter and pitch people are running on a twin 300X setup.

[whipper]

Welcome to Scream and fly first off.:thumbsup: I don't know the answer to your dilemma but your in the right place to figure it out.:thumbsup: Some real experts hear will help you in the day I'm sure. I would think also though its not the props. I also sure wouldn't like the one outside motor going in safe mode at speed!:eek: The weights are pretty much the same the gears should be the same 1:62. What gear case did you have on the PM and the X is a SM I presume being 1.62? If your other gear case was a TM I think they were 1.75? If it was a SM they are he same. Is your set back and every thing else the same to? I have heard that the X gets stronger with hours but you have to big of a numbers discrepancy for that. Some one will have the answer hang in there.:thumbsup:one more thing,Have you phisicaly checked the prop shaft hight and know were you were at with the ProMax,es? Thats all I got. Later James

[Eliminator22]

Thank you for the greeting and reply.

Both the Promax and X are 20" offshore with the sportmaster lower units, I have Mercury specs on the sportmaster lowers for the X as 1.62, so I will assume the Promax to be the same gearing. Everything is the same on the boat and mounting of the motors, I removed the old Promax motors and installed the X motors with all the same mounting configuration.

I never had a problem with the Promax motors dropping down to safe mode rpm, but I do not think that the Promax motors which were not smartcraft had the failsafe mode like the X motors. I looked in the Mercury installation manual and they call out a max extreme operating mounting height of 30" from the bottom of the boat to the bottom of the transom mounting bracket. My motors are mounted with a 9" setback from the transom and a height of 31" from the bottom of the transom mounting bracket to the bottom of the hull. In addition I do have an auxiliary water pickup located in the bottom of my trim plates.

[whipper]

Ill BUMP this one so it gets front and center for ya.:thumbsup: If left to long theres so many new Posts they get left down low in the viewing.:D Hopefully someone has some more questions so ya can get this figured out. Im wondering if this has been the case with other folks also? Got some pics? You boat sounds Awsome!

[baja200merk]

90% power and the small props sounds like the issue...

are you sure the motors are mounted at the same height the promax's were?

[Riverratt]

I am going to guess that the promax had 1.75 gears and had the power to spin the 34's up. With the 1.62 you will porbably have to go down in pitch.

[baja200merk]

i dont get it cause you hear about 28ft skaters (heavier bigger boats) running in the 20s with 300x's 1.62s and 34+p seems to me it should have no problem pushin a 21 :confused:

[whipper]

i dont get it cause you hear about 28ft skaters (heavier bigger boats) running in the 20s with 300x's 1.62s and 34+p seems to me it should have no problem pushin a 21 :confused:
:iagree:Thats why its confusing hes not getting the RPM with the 30,s? He should be pulling those to the limitter with twin 300,s? That would be the sign to go up in pitch. There not making power for some reason?

[beer30]

I can hit the limiter with my 15X34 Cleaver.:) Chuck

[beer30]

:iagree:Thats why its confusing hes not getting the RPM with the 30,s? He should be pulling those to the limitter with twin 300,s? That would be the sign to go up in pitch. There not making power for some reason?

He needs to get somebody with a DDT to check spec's on both engines. Chuck

[Oz Dude]

Eliminator22 - I know how frustrating it can be when you can't get the motor(s) to rev like you know they should!

Amongst the information you provided, when looking at your various combinations (old and new) another thing that really stood out was how much the slip changed between motors. With your old setup, your theoretical prop slip was between 3 & 4% on both props. Under your new setup, that has grown to 11% - something else isn't right there...

Just another thing for you to put in the pot with the rest of the info.

Oz

[bigbore]

And does'nt make sense,maybe gear ratio,swap lower's.:cool:

[Lost In Space]

do both throttle plates go 100% open?

[H.M.]

the probem that you are having is low water presure. the pro max motors dont have a gardian mood so thats why it never happend to them. the 300x motors will shut down if it gets to 10psi. you need to lower your motors or go to external water pick ups. also the 4 blade props have more stern lift that creates lower water presure as well 3 blades would problely help your problem too. At 40-50mph you should have aleast 15psi. good luck.
Chris

[notritejohn]

I am running twin 300x on a 32 Skater with 14 1/2" diameter 32 pitch and it will go to 6800 rpm at exactly 100 mph and my sportmaster ratio is 1:62

[2scoops]

I think i would try running the same props at the same engine height as a baseline and work from there. Rest assured the X motors will stomp the Promaxs on the same playing field and beyond!

[Eliminator22]

Thanks to all for your feedback and ideas. I'm gonna address some of the points/questions you guys have.

The motors are definitely sitting exactly the same as my old motors, nothing had changed.

When not getting full rpms, one of the first things I checked was that the throttle plates were indeed opening to 100%.

When I first bought the boat, I created a spreadsheet to input pitch, rpm, and gps speed with various percentage of slip. With the old motors and new motors I am running 11% slip on the 30 pitch props and on the old motors 10% slip with the 34's, but haven't tried the 34's on the new motors.

One thing I forgot to mention is that when I first bought the new X's, I wasted the gears in the lower unit and had put one of my lowers from my old motors on, thus I know that both the old and new motors are running the 1.62 gears as I have a split throttle and they both motors run the same rpm when equal throttle amount is applied to each.

notritejohn, interesting to read you are running a 32 foot skater with 14.5 x 32 props and turning 6800 that must be a much heavier boat then mine and you are able to turn the high rpms. I was waiting to see a reply from someone to see what type of props they are running on a twin 300x setup. Are they cleavers, what brand and also how many blade?

I went to Parker this weekend for the first trip of the season. Was with my fiancee the whole time on the boat so running high speeds wasn't always in the cards. I set the smartcraft gauges to default in water pressure mode and at low speeds 50 and below I was running like 6 psi, when I went beyond 70, the pressure increased to about 12 psi, but at no point could I get the water pressure above that. Manual says at WOT, pressure should be a minimum of 10 -12 psi, so that tells me I should easily be seeing way more pressure. I trimmed the motors alittle higher this weekend then normal, and I was able to crank them up to a solid 7000 rpm which makes no sense at all the trimming them higher I should have lowered the water pressure even more. Wow, these motors sure seem like the power really starts to come on in the higher rpm band! I also watched my water pressure as I would make turns going 50 mph or so and found that the water pressure would drop to like 2 psi at times. So, clearly I have a serious low water pressure issue that I need to address. I have external pickups that are located on my trim tabs, but, the trim tabs are mounted on the high part or the tunnels, so once I'm at speed those pickups should be completely out of the water. That is how it was setup when I bought the boat and I think the solution is much longer pickup tubes that would extend below the water line of the bottom of the sponsons.

I read in the manual that with the guardian system if it senses low water pressure/high water temp it can back the motor power down to as low as 4%. Does anyone know how it does this, ie, timing retard, rich fuel mixture? Running the low water pressure, I'm wondering if the fuel mixture gets enriched, cause sure seems like these motors just eat the fuel.

I would like to post pics of the boat and the trim plates/pickup tubes, but can't figure out how to do so. I have the pics on the computer in personal files, but not on a website. Can someone instruct me how to post pics?

One other question: Since I put these motors on, the port motor keeps getting low on oil in the oil tank mounted ont the engine, it drops the level down about 2 inches, but never lower than that and then of course it trips the low oil warning which drops power output to 95%. I can't figure out why the level won't drop lower than that, but also can't figure out why it drops at all. Any ideas?

[hydrostream1]

I would talk to eric simon,he is the 3.0L guru,he has played with these setups.He can also reprogram the ecu`s,I would give him a call.

[Tague]

There are a few things that I would try. First of all when I was racing and removed motors or touched anything I would always measure it again to make sure nothing moved. Take a level and get the running surface in front of the lower unit level. Then put the level on the cav plate of the lower unit and make it match the bottom. Take a drywall square and see how far up each motor is and make them equal on both sides, I would talk to eliminator to get the correct x dimention as a starting point and ask them about the remote pickups. I have seen 4mph increases with a 1/16" movement, and i've seen water pressure die with the same movement. Adjust the tie bar so the motors are perfectly straight. This gives you a starting point. When you trim in or out even a little it can greatly effect the water pressure. Run the boat and don't touch the trim buttons at all and try both sets of props. Pin the throttles and record, rpm, speed, water pressure.

If you have to low water pressure you will have to go down a little, try 1/8" And do it to both sides and not just one. Try to make both side equal.

If you have good water pressure and no rpm's then you need to go up 1/8".

It may sound funny but sometimes if you raise the motors you can gain water pressure because you wony need all the trim to get the speed and rpms's.

feel free to give me a call if you have any questions

Tague
954-648-1896

[Dd24skater]

Are the impellers OK ?