250XS but want more

[Eagle670]

Yes , i can buy a 300XS , but i cant afford it . Yamaha guys have the Phase I-III kits

But us running 250XS Mercs haven't anything like that... Drag racers and ski puller in Australia have E-techs roaring like hell, and what can we do .... buy a lightened flywheel ????

[EuropeanAM]

Try: http://www.simonmotorsports.com

[Eagle670]

Yes i now, i'm follow some treads on scream & fly with people who have get their 225 & 250 Xs upgraded + flywheel done , most of them don't see any notable gain except one who also made a 3" hole in air silencer like 300XS have....

Don, do you think a 4" trottlebody would work on a 250XS ? a complement to upgrading the ECU ? i could easily spend a couple of 1000+ dollars for 10-15 true hp.
if i get 2mph it's worth it

[EuropeanAM]

Increasing the bore of the throttle body, altering the air attenuator cover, etc. will gain NO NOTABLE increase in horspower output.

In addition- it will result in a leaner mixture, which will (in all likelihood) result is future catastrophic failure of the powerhead.

The BEST improvements on an Optimax can be found in the setup, prop selection, and working with your hull/pad area (blueprinting, weight removal or balance, etc).

Your 250XS is literally "very near" it's maximum potential... and was tuned/calibrated to provide good performance and durability on a wide array of hulls.

The "reports" you're reading about boring an opening in the air attenuator are skewed somehow.... I can tell you from "dyno testing" that even complete removal of the plastic air attentuator cover has little (if any) effect on actual propshaft horsepower.

To achieve any substantial improvement on this engine.... one would need to improve the volumetric efficiency (including the flow of air through the air runners in the block, and the natural "turbulence" created as air attempts to enter the intake ports of the sleeve). Fuel delivery would then need to be COMPLETELY recalibrated to match the new characteristics (which is a DAUNTING task, even for a couple of engineers who do it regularly).

Accomplishing this would require an alteration of the flow design (essentially more of a "cross-flow" design)... which presents additional problems on this DI (direct injected) engine, since it operates in more of a "loop-flow" fashion.

Of course... all of these "theories" require extensive amounts of time and money.... and like any "R&D" theory, will undoubtably result in some failure and disappointment during the process, as seldom does great success come on the "first" try.

[The Whip]

Peter,
You may want to talk to Rob Shaw on the Allison forum as he has a 250 pro xs and had Simon exchange his flywheel and ECU.

Manny
Allison BasSport Pro
300XS

[Todd D]

you can have the porting in your motor cleaned up and do the rest of the simon stuff and be at 320hp!

[Eagle670]

Todd , can you get me in contact with someone who have donit ?

[EuropeanAM]

<table width="90%" cellspacing=0 cellpadding=0 align=center><tr><td>Quote, originally posted by Todd D &raquo;</td></tr><tr><td class="quote">you can have the porting in your motor cleaned up and do the rest of the simon stuff and be at 320hp!</td></tr></table>

Is that Crankshaft HP or Propshaft HP, Todd?

[Todd D]

THat is crankshaft HP. The motor dyno'd at 292hp stock and the mods have increased it to 320hp on the dyno.


contact Eric Simon:

http://www.simonmotorsports.com/

[Eagle670]

Is their any formula from Crank hp &gt; Prop hp ??

[EuropeanAM]

<table width="90%" cellspacing=0 cellpadding=0 align=center><tr><td>Quote, originally posted by Eagle670 &raquo;</td></tr><tr><td class="quote">Is their any formula from Crank hp &gt; Prop hp ??</td></tr></table>

Technically, no.

However, you can get a "general" idea (on similar 3L engines) with the following:

Crankshaft Horsepower X .938 = Approximate Propshaft Horsepower

Propshaft Horspower x 1.063 = Approximate Crankshaft Horsepower

(Non-scientific formulas for approximate calculations only)

[Strokerdean]

Is the hp rating oa a stock 300xs prop shaft or crank shaft?

[EuropeanAM]

Propshaft. That's where all of the current production Mercury engines are rated (required to be within 10% of the rated horsepower).

[Eagle670]

Maby top secret info, but has mercury ever been BELOW the marked effect on cowl ?
( in optimax history )

[John Jackson]

Yes,
especially on nonperformance models. But they have been within the requried 10%.
They were especially guilty of this shortly after Brunswick Corporation bought them.(for those old enough to remember)
Don can probably provide more recent history.

[EuropeanAM]

<table width="90%" cellspacing=0 cellpadding=0 align=center><tr><td>Quote, originally posted by Eagle670 &raquo;</td></tr><tr><td class="quote">Maby top secret info, but has mercury ever been BELOW the marked effect on cowl ?
( in optimax history )

</td></tr></table>

During the Optimax series history, as a general rule: NO. Perhaps a very rare exception.... but nearly all of Mercury's 2-stroke models have historically been at the placarded horsepower (with many on the strong side of the 10% margin at time of manufacture).

Honestly, over the last 15 years or so, I can only think of one that wasn't at or above it's label (and I doubt you, or anyone on this board is running, or has one).

[John Jackson]

<table width="90%" cellspacing=0 cellpadding=0 align=center><tr><td>Quote, originally posted by EuropeanAM &raquo;</td></tr><tr><td class="quote">

During the Optimax series history, as a general rule: NO. Perhaps a very rare exception.... but nearly all of Mercury's 2-stroke models have historically been at the placarded horsepower (with many on the strong side of the 10% margin at time of manufacture).

Honestly, over the last 15 years or so, I can only think of one that wasn't at or above it's label (and I doubt you, or anyone on this board is running, or has one).


</td></tr></table>
Don,
You wouldn't be talking about the very 1st year opti, would you?

[spider1]

I thought that the 300 pro max was under the 300hp mark.

[John Jackson]

It was, but that was pre opti.