Inquirering mind

[--GQ--]

It seems to me everytime i'm in the shower, ideas just hit me. Got out of the shower 1/2 an hour ago. Here is the latest. My 4 cyclinders M3 is capable of producing 250 hp and 190 lbs. of torque. A 4 cyclinders boat engine on the other hand can do no more than 135 hp. Thats almost half less. What gives. Can anyone answer this?

 

[MRS]

Re: Inquirering mind

If you have enough money and time you can do anything you want

 

[QC]

Re: Inquirering mind

Yes. Your M3 a) turns more RPM which if all other things are equal results in more bhp b) is electronically controlled c) has overhead cams and 4 valves = more air = more fuel = more power c) the M3 is a 6 cyl, but that doesn't really matter, but I thought I would point that out . . . d) the 135 is at the prop, the M3 is rated at the flywheel. e) the 135 bhp 4 banger is rated to run at 135 bhp 100% of the time if desired (not necessarily good, but it can do it) f) the 135 is carbureted, the M3 is fuel injected etc. etc.<br /><br />The best thing to remember is nobody ever promised that every engine puts out the maximum horsepower that is possible They are all tweaked for something; longevity, cost, fuel, performance or whatever the engineers are trying to do with that iteration. You should have stayed in the shower longer . . .

 

[--GQ--]

Re: Inquirering mind

Quietcat, I think we've met before on a different topic at a different time. You my "mentor" seems to have an answer to my every question (confusing it may be ). Braces yourself i'm sure to have more.<br /><br />Having said that, why not just transfers car engine components to marine engines and water proof it? A marine engine is no more exposed to water since its incased or sits in an engine compartment than a car engine in a car driving thru rain/snow.<br /><br />Don't you hate it when an answer leads to a question? Let me know when to shut up.<br /><br />First Generation M3 = 4 cyclinders

 

[QC]

Re: Inquirering mind

What year M3? I figured I would get in trouble on that one . . .<br /><br />There are corrosion issues with aluminum in marine engines. I believe you will see more of it in the future. There are many here that understand that issue better than I do. Anyway, if I had it my way we would be using VW 1.8Ts in boats along with a CVT tranny, but for now it is mostly cast iron engines of American origin.<br /><br />Yes, I recall posting on something you asked before. Don't recall for sure, but I think it was your 18' Chap that you wanted to pull the thermo out of. Yes? No? Please tell me you din't do it if that was you . . .

 

[Dunaruna]

Re: Inquirering mind

The first generation M3 (E30) was a 2.3L 195HP - 1986.<br /><br />HP didn't reach 238 until the evo3 in 1990, that was a 2.5L.

 

[--GQ--]

Re: Inquirering mind

mine is super charged stage III. i use to race..... older now <br /><br />evo III is european spec...<br /><br /><br />the dealer has it. they are still working on it. i bought the darn thing 2 months ago; half the time sitting at the chap dealer. so amy problems

 

[Dunaruna]

Re: Inquirering mind

Was it factory blown?

 

[--GQ--]

Re: Inquirering mind

in the US...1988-1991....no 1996<br /><br />i'm not sure. the tach was set wrong, the speedo tube has a kink. (dealer had no clue. fixed my self), temp. gauage reads 220 degrees.<br /><br />Hmmm this reminds me of AOL except for the time delay

 

[trog100]

Re: Inquirering mind

GQ your mistake is to think that max horse power for a given engine size is the common goal.. it isnt always..<br /><br />two ways of getting more power from an engine.. one is to make it rev faster the other is to simply increase the capacity.. the old four banger boat engine only puts out 135 hp cos thats all the makers want it to.. it neatly fits in a power rating/sales slot that kinda starts at 5 hp and goes up in tidy increments to 300 hp roughly..<br /><br />its also an ancient 40 year old cast iron block/head engine that was made in the days when 45 hp per litre was considered okay.. its also pretty much a straight import from a street car of forty years ago.. <br /><br />your M3 belongs in a different era completely where 45 hp per litre would be laffed of the planet.. he he he<br /><br />the old cast iron boat engines put out plenty of bottom end grunt (boats dont have gearboxes) and there are 250 hp cast iron boat engines they just come in bigger capacities.. <br /><br />there is also no real competive reason like there is in cars for boat makers to enter the BHP per litre race.. if they want more power they just bung in a bigger but similar engine..<br /><br />gm make a commerical version of the old 3.0l engine its rated at about 90 hp and at only 3000 rpm.. pretty much the same engine just aimed at a different market.. over the years there have no doubt been much more powerfull race tuned versions of basically the same engine bunging out as much power as your M3..<br /><br />its horses for courses so they say..<br /><br />as to your last question.. thats exactly what they did.. transfer car parts to boats.. only it was done forty years ago and they aint seen any reason to change em much ever since.. he he.. <br /><br />trog

 

[aggiedave98]

Re: Inquirering mind

I'm not an expert, so please refute if I'm wrong, but... (and I just posted a question on this topic...)<br /><br /><br />the M3 is 190ft-lbs, but the 3.0L mercruiser is 178 ft lbs... not that different... the torque is closely related to displacement... the HP is related to things like RPM, etc.<br /><br />Not an expert on all the things that give you HP, but wanted to point out torque is not that far off...<br /><br /><br />LET ME ASK THIS... does the fact that a marine engine exhaust goes into the water (and therefore is restrictive??) make a difference??

 

[trog100]

Re: Inquirering mind

not a lot with a lowly tuned four stroke boat engine.. aggiedave.. higher revving two strokes are more subject to restrictive exhausts.. and the more u tweak an engine to gain more revs and top end power the more it matters.. <br /><br />torque is just another way of measuring low end (rpm) usable horse power.. to be usefull without constant gear changing an engine has to have a wide power band.. to be able to open the throttle at say 2000 rpm before u start to accelerate the engine needs to have good power down there before its gonna do its business and whoosh off..<br /><br />power quoted at the top end is power u never use.. torque is what provides the get up and go.. its torque that gets u to that top end power quickly..<br /><br />u could marry a higher revving more powerfull (modern) type car engine to a boat.. especially a closed cooling one.. but it would need different gear ratios (a complete re-design drive) and a variable pitch prop to be of much use..<br /><br />power gained from useing large capacity but lowly tuned and revving cast iron engines provides that wide power band that keeps it all simple and cheap and does the job with plenty of bottom end torgue (horse power where u need it) to provide good acceleration without the need for variable gears or fancy variable pitch props..<br /><br />mind u a variable pitch prop while not being practical in some ways would certainly improve the systems we use at the moment.. <br /><br />trog

 

[QC]

Re: Inquirering mind

Originally posted by trog100:<br /> mind u a variable pitch prop while not being practical in some ways would certainly improve the systems we use at the moment..

And reduce the dependence on high peak torque values. Another way to do this is with a Continuously Variable Transmission (CVT). Also, if there is no need to "jump" on plane, high peak torque is meaningless in a marine engine. Prop load curves are fairly linear, so if you slowly gain RPM as you do with large boats i.e. run it up 500 RPM at a time and patiently wait to get on plane, then again the low-end high torque value never comes into play. This in no way disputes most of trog's post, but helps clarify maybe . . .

 

[Richard Petersen]

Re: Inquirering mind

I think the biggest difference is that most boat engines have a VERY flat torque curve from 1200 rpm's up to about 3200 rpm's. This is needed to get the boat up over the low speed bow wave and then accelerate to top end. Most boats have one speed in foward, so torque rules over peak HP. Standard boat engines can not produce constant flat torque curves and high peak HP. Has not been done by Mercruiser yet.

 

[QC]

Re: Inquirering mind

Originally posted by cyclops2:<br /> I think the biggest difference is that most boat engines have a VERY flat torque curve

Not true. Marine engines have very similar peak torque values to their automotive relatives (not talking about 2 strokes). You are correct that a high torque value helps you climb the bow wave to get on plane faster, but this requires a STEEP curve, not a flat one. A flat one is what I describe when discussing the prop load curve. If you bump the engine up say 100 RPM at a time the high peak torque value (big curve not flat) never comes into play. Trust me, a flat torque "curve" is the oppostie of what you describe. bhp=torquexRPM/5252. Stare at it, it is the whole story. "Flat" torque curve gives you straight line bhp linear with RPM. NO peak where you say it is needed. Period.

 

[trog100]

Re: Inquirering mind

yes if u only want to get up to speed slowly and then stay there (the majority of boats) none of it matters that much.. in a car it matters a lot and it does in a "speed boat" specially one used for water sports..<br /><br />just for interest.. bunging a blower (super not turbo) on one of these ancient cast iron lumps would make them go somewhat better..<br /><br />u would probably have to lower the compression ratio some way but otherwise i cant see any real problems.. <br /><br />there just hasnt been the market incentive to keep boating technology up to date.. and cheap US gas prices hasnt helped.. the new compressed diesels are the first real attempt to move into the modern world.. again not popular (yet) in the US but they are everywhere else..<br /><br />i also think fire hazard wise.. super charging as opposed to turbo chargeing makes a lot more sense in a boat.. shame they aint going this way.. turbo is more "fashionable".. <br /><br />its the US market demand that governs all this.. the rest of the world suffers cos we dont get the cheap gas.. just the way it is.. <br /><br />trog

 

[QC]

Re: Inquirering mind

Originally posted by trog100:<br /> in a car it matters a lot and it does in a "speed boat" specially one used for water sports.

It being torque, I agree, unless you have a CVT, then it's benefits decline . . .<br /><br />

Originally posted by trog100:<br /> turbo is more "fashionable"..

and more efficient. Follow the diesels, they are designed around commercial needs i.e. efficiency. I agree about your comments on the US market holding back some technology for pleasure and personal. Again, look to the commercial applications, we understand that

 

[SeaRay24Sorrento]

Re: Inquirering mind

I would think the Mazda rotary engine from the late 80's stacked with four cylinders vs. the normal two in an RX-7 would be an incredible setup w/ FWC. Lots of power and HIGH RPM! Any body seen an application in a boat such as that??

 

[Bondo]

Re: Inquirering mind

Lots of power and HIGH RPM!

Just How Fast are you going to Spin It,..???....<br /><br />Outdrives start Disintergrating a little over 5500rpms.............<br /><br />That's WHY most of this discussion is a Moot Point,..........<br />Most of the little motors you're talking about Don't make their Advertized HP till it's Reved Way Passed the Usable rpm Range of All the Drives that Most of Us are using............. <br /><br />In other words,........<br />Horsepower is a Mathematical result of the equation that's based on Torque,+ RPMs,.............<br /><br />A 3.0l Mercruiser could build 300hp,...............<br />If you Could spin it 12,000RPMs or so..........

 

[QC]

Re: Inquirering mind

Originally posted by Bondo:<br /> Outdrives start Disintergrating a little over 5500rpms.............

That's why you need the CVT Any output speed at any input speed (within reason).