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Thread: Weber RPM's

  1. #1
    desperado's Avatar
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    Quote Originally Posted by Bernie View Post
    You like rebuilding expensive engines ?The 150's are on the edge as it is .I would say ,Let someone else do it .Will be interested to see what the Ficht inj systems will produce above factory with their restricted capacity injectors and be able to still function in all conditions ie heat load etc .

    Bernie
    I agree the 150 engine is on the edge.

    This has nothing to do with the engine itself. It mostly has to do with the fact the engine is overpropped from the factory and is required to generate too much hp at too low rpm. EGT goes up and pistons/turbos are fried. The sled version is 140bhp at a rated 8,000rpm at 14.5psi turbo boost --- never seen a piston/turbo issue on these engines even though the EGT runs 1,600F degrees post turbo. After installing a Garrett GT25R on my Weber, the peak hp rpm increased to 8,400..... 280 hours on the engine so far and 100% reliable.... that's at 19.5psi boost.

    The turbine side of the turbo on the MSX is larger than the snowmobile counterpart... the compressor side is the same. This means the MSX has a greater rpm potential...... that being said, allowing the engine to turn higher rpm to reach peak hp is required to ensure greater engine longevity. The MPE750 is a world class engine... there is no reason other than overloading that can explain why so many of these engines have failed in the marine applications.... Let the engine spin to 7,600rpm, minimum, and enjoy. Trying to pump nearly 15psi boost at anything lower than 7,400 will kill this engine as a result of high EGT and detonation.

    About the gadget advertised that fools the MAP sensors.... ok if you have a wideband O2 controller to understand your final A/F ratio.... if you're not running 12.3:1 @ wot, and richer, don't run this sh...t on a high power/displacement turbocharged engine running on gas pump....

    my $0.02


  2. #2
    SPEED KILLS, BUT YOU GET THERE QUICKER Keddano's Avatar
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    Good info and Input,I'm sure the guys that run this motor will have a few more questions for you,Is the snowmobile and watercraft running the same injectors?

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    Rocky_Road's Avatar
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    Quote Originally Posted by desperado View Post
    I agree the 150 engine is on the edge.

    Let the engine spin to 7,600rpm, minimum, and enjoy.
    Did I read this correctly...or did you mean 7,600 MAXIMUM???

  4. #4
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by desperado View Post
    ...the engine is over-propped from the factory and is required to generate too much hp at too low rpm...
    Would a small reduction in prop pitch make a stock MSX 150 motor happier, and possibly faster?

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    desperado's Avatar
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    Quote Originally Posted by Keddano View Post
    Good info and Input,I'm sure the guys that run this motor will have a few more questions for you,Is the snowmobile and watercraft running the same injectors?
    The snowmobile version runs different injectors @ 400g/min. while both the msx110 & msx150 run smaller injectors rated at 230g/min. All Polaris/Weber engines use Bosch EV-6 high impedance injectors.... the flow volume is the only difference. The reason the snowmobile engines run higher flow injectors is because they are run at much colder air temperature.

    About the rpm.... I meant the engine should run at least 7,600 wot. Keep in mind the ECU start retarding ignition timing progressively from 7,500rpm until the 7,800 revolution limit is reached... this is part of the rev limiter operation & ignition timing map/algorythm. By running 7,600 continuous at wot, you get the benefit of slightly retarded timing for extended high load runs. Purists will say that you are not extracting all the power/potential from the engine by doing so... but engine longetivity benefits greatly with lower EGT's and reduced detonation potential at higher rpm. Another method of fighting detonation is to use colder plugs than the OEM Champions. NGK BKR9EXI iridium plugs are 2 steps colder and very robust.

    About the impeller... I believe that a pitch somewhere in the middle between the oem MSX110 and the oem MSX150 impellers is a good starting point. I have run an MSX110 upgraded to the msx150 with the stock 110 impeller: I could hit 7,800rpm on a regular basis. Although this rpm is too high, I was about 2mph slower than a stock MSX140. With slightly increased pitch and a rpm of around 7,600, the turbocharged 4 stroke should achieve a higher top speed than the 2 stroker... remains to be confirmed this summer.

  6. #6
    David
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    Hi everybody,

    Just two question: will the msx work with the FST Ecu?
    (maybe harness not good: if someone have the fst service manual to take a look)

    With the correct mod: a mechanical intake valve system.

    If so: will the msx have better acceleration on lower rpm?

  7. #7
    desperado's Avatar
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    Quote Originally Posted by msxfourstroke View Post
    Hi everybody,

    Just two question: will the msx work with the FST Ecu?
    (maybe harness not good: if someone have the fst service manual to take a look)

    With the correct mod: a mechanical intake valve system.

    If so: will the msx have better acceleration on lower rpm?
    It will not work.

    The MSX runs the ME7.4.4 ECU which is the drive by wire version of the M7.4.4 ECU used in the snowmobile version.....which has a mechanical intake throttle body. The MSX has only one intake barrel which is sized much smaller than the twin barrel and much larger snowmobile version. Injector sizing would be all wrong with the stock MSX units. Also, the snowmobile ECU version incorporates features not found in the MSX... such as wideband O2 sensor reading, remote idle control and atmospheric pressure compensation for turbo boost regulation. These are the obvious... but there are many other features that differentiate the operating parameters of both ECU's.
    Last edited by desperado; 05-11-2008 at 10:49 PM.

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    David
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    Thanks for your answer: you have a lot of knowledge!

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    2&4strokepolaristech's Avatar
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    well i think you are comparing apples to oranges here. first off a snowmobile engine is loaded about 15-20% of the time and a pwc is loaded about 80-85% of the time. anything after 7500 rpm on the watercraft you are falling off peak power. watercraft have to make good torque. the programing in the ecu in the msx will hit a soft limiter at 7800 and starts to take alot of timing out of the curve after 7550. the msx 110 prop will let a 150 turn up to 7800-7900 rpm but it is worthless. you are not making any peak power there. why do you think this boat is overpropped? most msx 110/150 run anywhere from 7200-7500 rpm and the 150 makes about 15-16 psi with a overboost at 18 psi for 400 ms.

    as far as the failures lets not forget that the PWC department was the test bed for this engine just like the domestic twins were on the sleds. there were alot of things changed from the 2003-2004 msx 4 stroke to the production 2005 snowmobiles. Examples are steel waterpump gear vs plastic, revised plating process, crankshaft clearance/oil galley chamfer,oil pressure,turbo size(as you mentioned alot more lag on the PWC),no more fly by wire design,O2 sensor,overboost values,intake manifold(pwc has larger plenum for better bottom end),CPS location,oil temp operation range etc....

    the MPE 750 Engine when designed originally for the PWC would support just over 200 hp. I do not think in any way it is on the edge it is way within a safe margin.

    most problems are caused by poor fuel and owner/operator error

    many update were going to be done for 2005 but they pulled the plug!

    a sled engine is a sled engine and a PWC engine is a PWC engine.





    Quote Originally Posted by desperado View Post
    I agree the 150 engine is on the edge.

    This has nothing to do with the engine itself. It mostly has to do with the fact the engine is overpropped from the factory and is required to generate too much hp at too low rpm. EGT goes up and pistons/turbos are fried. The sled version is 140bhp at a rated 8,000rpm at 14.5psi turbo boost --- never seen a piston/turbo issue on these engines even though the EGT runs 1,600F degrees post turbo. After installing a Garrett GT25R on my Weber, the peak hp rpm increased to 8,400..... 280 hours on the engine so far and 100% reliable.... that's at 19.5psi boost.

    The turbine side of the turbo on the MSX is larger than the snowmobile counterpart... the compressor side is the same. This means the MSX has a greater rpm potential...... that being said, allowing the engine to turn higher rpm to reach peak hp is required to ensure greater engine longevity. The MPE750 is a world class engine... there is no reason other than overloading that can explain why so many of these engines have failed in the marine applications.... Let the engine spin to 7,600rpm, minimum, and enjoy. Trying to pump nearly 15psi boost at anything lower than 7,400 will kill this engine as a result of high EGT and detonation.

    About the gadget advertised that fools the MAP sensors.... ok if you have a wideband O2 controller to understand your final A/F ratio.... if you're not running 12.3:1 @ wot, and richer, don't run this sh...t on a high power/displacement turbocharged engine running on gas pump....

    my $0.02
    Last edited by 2&4strokepolaristech; 05-12-2008 at 09:01 PM.

  10. #10
    desperado's Avatar
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    Quote Originally Posted by 4strokepolaristech View Post
    well i think you are comparing apples to oranges here. first off a snowmobile engine is loaded about 15-20% of the time and a pwc is loaded about 80-85% of the time. anything after 7500 rpm on the watercraft you are falling off peak power. watercraft have to make good torque. the programing in the ecu in the msx will hit a soft limiter at 7800 and starts to take alot of timing out of the curve after 7550. the msx 110 prop will let a 150 turn up to 7800-7900 rpm but it is worthless. you are not making any peak power there. why do you think this boat is overpropped? most msx 110/150 run anywhere from 7200-7500 rpm and the 150 makes about 15-16 psi with a overboost at 18 psi for 400 ms.

    as far as the failures lets not forget that the PWC department was the test bed for this engine just like the domestic twins were on the sleds. there were alot of things changed from the 2003-2004 msx 4 stroke to the production 2005 snowmobiles. Examples are steel waterpump gear vs plastic, revised plating process, crankshaft clearance/oil galley chamfer,oil pressure,turbo size(as you mentioned alot more lag on the PWC),no more fly by wire design,O2 sensor,overboost values,intake manifold(larger plenum for better bottom end),CPS location,oil temp operation range etc....

    the MPE 750 Engine when designed originally for the PWC would support just over 200 hp. I do not think in any way it is on the edge it is way within a safe margin.

    most problems are caused by poor fuel and owner/operator error

    many update were going to be done for 2005 but they pulled the plug!

    a sled engine is a sled engine and a PWC engine is a PWC engine.
    Jay,

    I highly respect your knowledge and expertise and appreciate your extensive experience on Weber engines. However, I have to say you are making erronous statements above.

    First, it is totally wrong and misleading to say that a snowmobile engine is loaded about 15%-20% of the time. These engines are coupled to variable ratio clutches that force rpm operation to be within the peak torque curve over 80% of the time while the vehicule is running at anything over 30mph. Fast pace trail riding at 50mph to 70mph will require energy consumption by the rate of around 25-30lb/hr fuel which equates to around 80bhp with a volumetric efficiency of around 90. This is far from your 15-20%.... more like 60%. Mathematical models using the Crouch formula for determing marine prop loading shows there is an exponential relationship between required bhp and prop shaft rpm... marine powerplant engineers always design for 75-80% of peak bhp for continuous fast cruise operation which does not translates into a linear relationship to rpm because of the exponential power curve.... this would put the Weber at around 6,800 fast cruise.

    Second, you mention that above 7,500 you fall off peak.... I know all about that. If you take the time to read my previous post carefully, you will note that I already made comments to that regard. I even stated that purists would oppose such a strategy pointing to the fact that maximum engine potential could not be used. My whole point was about engine longevity... not absolute performance.

    Fact: the MSX PWC has been the least successful combination ever for the Weber MPE750.... this raises legitimate questions. Although it has been good business for many Polaris dealerships, numerous customers have been disapointed by their short lived powerplant.

    I agree fuel quality plays a major role in ensuring greater reliability by helping fight detonation... however, this is a mass production powerplant sold to the general public.... most other PWC's out there are not as sensitive to fuel quality and don't grenade within few hours of operation -- why could this ever be an excuse for the Weber? I'll say it again: get the rpm to 7,600 and benefit from 1-) a slightly retarded ignition timing, 2-) lower EGT's due to less engine load, 3-) decreased fuel mixture burn cycle time.....

    Third, it is not resonnable to state the Weber could support 200bhp. This means the engine would be pumping 266bhp/liter.... a comparable 3 liter engine would produce 800bhp........ this is F1 racing engine territory and beyond! A proven mathematical model suggests that to achieve 200bhp from the Weber engine you would require 36psi turbo boost at 7,400rpm. This is based on a 90% volumetric efficiency, 65% compressor efficiency, 75% intercooler efficiency and an ambient air temperature of 80F degrees. At that level, the engine would consume 260cfm air and the intake air charge would be 167F degrees............ sorry: that's impossible and the top end of the MPE750 can't support that from a technical standpoint.

    Anyway..... again, I really respect your input and expertise on this board and I don't want to sound like I'm arguing. All I meant to say was...... give the engine a few more rpm's to help it live longer..... or run on the edge and hope your fuel is always fresh!

    Regards.
    Last edited by desperado; 05-12-2008 at 09:47 PM.

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