300 XS rpm limit

[fcalligaro]

The new 300 XS (20 inch model) has an rpm limit of 6400 rpm. Has anyone tinkered with the ECM to raise the rpm limit?? This is the only handicap of these motors¡¡¡ :confused:

[Stinky]

Lets see, power peak is at 5750. Power is down at least 5 at 6000. By 6400 its probably really dropping, -20 or so.

Now why is it you want to turn 7000 where the HP is probably down to 200 ????

Just curious.

:cool:

[fcalligaro]

Actually, the 20 inch model makes power all the way to 6400. I have these on a 28 skater and I run out of RPM´s while turning 34 X 15´s 3 blade cleavers. The 300 XS should be a bit more like the 300 X , which makes power all the way to 6800.

This all in the search for more speed... :D

[stvhelm]

on the mercury site it says 20" is 5800 to 6100 max rpm
http://mercuryracing.com/products/consumeroutboards/optimax300xs.php

[fcalligaro]

Well, you are right, that´s what it says. But the motors do pull all the way to 6400 rpm. And like it´s done with the 2.5 offshore´s, the rev limiter can be raised. I was just wondering if anyone has messed with it yet.

The 300 XS, being the last breed of the mercury racing line, should be a bit more "racing" and the only thing it lacks is RPM´s.
:D

[Propster]

The problem is far more complex than just raising the limiter. I saw a posting from a Merc engineer that there simply is not enough time to inject enough fuel after the exhaust port is closed at higher rpms. From what I understand, Merc is working on it, but it is a very complex issue. Raising the limiter may not be too difficult, the difficult part would be to keep the motor from blowing up.

[fcalligaro]

I couldn´t have said it better. I really hope the next racing engines from Merc keep up to the performance of the old muscle engines like the 300 X.

:cool:

[Stinky]

The problem is far more complex than just raising the limiter. I saw a posting from a Merc engineer that there simply is not enough time to inject enough fuel after the exhaust port is closed at higher rpms. From what I understand, Merc is working on it, but it is a very complex issue. Raising the limiter may not be too difficult, the difficult part would be to keep the motor from blowing up.

No, I think I said there is just no time to scavange the burnt charge out of the deep bowls of a DI head. Has nothing to do with time for injection.

:cool:

[Stinky]

Actually, the 20 inch model makes power all the way to 6400.

Not true. Read the graph.

Try proping to 5800 where the motor make the most power and see how fast it goes.

[fcalligaro]

Well, propping this motor on the 28 skater might require a 36 pitch prop¡¡¡. We´ll see how it goes.

Thanks for all the replies guys.:)

[AwesomeBullet]

Remember that the ECM on that motor will monitor your rpms and store them as a profile.....If you ever have a warranty issue and you are consitently running above the recomended rpm range, you could be facing an uphill battle. That computer will tattle tale on every thing that you do!

[150aintenuff]

Well, propping this motor on the 28 skater might require a 36 pitch prop¡¡¡. We´ll see how it goes.

Thanks for all the replies guys.:)
yea your point..... they are built... and if needed more will be built to occomidate it... i know there is a skater in theese woods with 250XS's that could spin 34's..... or perhaps even 35's.. and he isnt even running any adjustible jacks to eek even more speed and RPM out of it...

[Skater Doug]

Keep us posted! Going to 300 xs on my 28 as well and looking for feedback. I have heard to go with 36's. I am trying to figure out 14 3/4" or 15". Seems like from what I read they have the power to push a 15??

[fcalligaro]

Keep us posted! Going to 300 xs on my 28 as well and looking for feedback. I have heard to go with 36's. I am trying to figure out 14 3/4" or 15". Seems like from what I read they have the power to push a 15??

I tried a set of custom made 36X15 and at 6100 rpm´s and I got to 110 mph. I still have room for improvement since my motors are only at 1.5 inches above the sponsons. A mile or two an hour will be achieved raising another quarter of an inch. 34 X 15 's hit the rev limiter at 6400 rpm´s.

All tests were done light on fuel, fresh water lake, glass smooth to very mild chop water.

Hope this helps.

If anyone else has tried a different setup, please let us know.

[WATERWINGS]

I never totally understood that...........

My motor is supposed to "give out" of power between 5800 to 6000 ? (stock merc 200 2.4)..........

The fastest my boat has been was at 7200 RPM's, (95.9 GPS)

No matter what people tell me, the same prop at a higher RPM is gonna be faster.

If I propped it to only turn 5800, it would be a DOG out of the hole, and in the midrange, and I don't have miles of straight to let the monster prop finilally wind out.

If it "gives out" of power at 5800, why does it keep climbing the RPM's ?

And keeps accelerating untill the R's stop climbing??



Lets see, power peak is at 5750. Power is down at least 5 at 6000. By 6400 its probably really dropping, -20 or so.

Now why is it you want to turn 7000 where the HP is probably down to 200 ????

Just curious.

:cool:

[Stinky]

I never totally understood that...........

My motor is supposed to "give out" of power between 5800 to 6000 ? (stock merc 200 2.4)..........

The fastest my boat has been was at 7200 RPM's, (95.9 GPS)

No matter what people tell me, the same prop at a higher RPM is gonna be faster.

If I propped it to only turn 5800, it would be a DOG out of the hole, and in the midrange, and I don't have miles of straight to let the monster prop finilally wind out.

If it "gives out" of power at 5800, why does it keep climbing the RPM's ?

And keeps accelerating untill the R's stop climbing??

Do you really want to compare a 2.4L carb/efi to a 3.2L DFI. Thats like cherrys and watermelon.:rolleyes:

[150aintenuff]

Do you really want to compare a 2.4L carb/efi to a 3.2L DFI. Thats like cherrys and watermelon.:rolleyes:

good one stinky... i found that even though i can twist 7200 its faster at 62-6400 (2.4) without alot of loss at the hole shot. so i can only expect a larger bore and longer stroke to be that much faster when propped lower utilizing the torque...

[fastcat300]

maybe a stupid question, do you have 1.62 ????

[kena]

I never totally understood that...........

My motor is supposed to "give out" of power between 5800 to 6000 ? (stock merc 200 2.4)..........

The fastest my boat has been was at 7200 RPM's, (95.9 GPS)

No matter what people tell me, the same prop at a higher RPM is gonna be faster.

If I propped it to only turn 5800, it would be a DOG out of the hole, and in the midrange, and I don't have miles of straight to let the monster prop finilally wind out.

If it "gives out" of power at 5800, why does it keep climbing the RPM's ?

And keeps accelerating untill the R's stop climbing??


I agree with this post. I also have a new 300XS on my 20' Bullet Comp bassboat.

I'm no rocket scientist but:

In 1978 I bought a new 17' HydraSport bassboat and put a 235 Evinrude on it. The boat was rated for a 115. I put a homemade jackplate on it and bolted on a 26 small eared chopper and turned it 7400. The boat would run about 85 mph on a Norskog speedo. I think the motor was suppose to peter out at around 5500 rpm's but it pulled strong up to 7400. I ran the dog pee out of this rig for two years and never broke it. Granted I never ran a prop big enough to bring the rpm down to 5500 but I am not sure they even made a prop that tall back then...:p