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View Full Version : Merc 280 vs. Looper to 270 (or 300), where is...



Sleekster
05-19-2001, 08:44 AM
Where is the peak torque in each?

Besides all the bantering back and forth, what are the advantages and disadvantages of each?

LaveyT
05-20-2001, 06:55 AM
Good Question,I dont know if they have updated it but Land & Sea had all those charts in the front of the catolog.Im not aware of any spot on the net where these are published? Better ask BK.
p.s. There is no subsitute for cubic inches.(on Hogs)

Sleekster
05-20-2001, 06:01 PM
I'll check there. How was the ride?

LaveyT
05-20-2001, 08:08 PM
Had a good day on the water did some on the water houseboat shoping.Just couldent get waterpressure once the boat flattened out.The tape was still over the holes but when you got on it good it would drop to about three psi.At least is wasent close enough for me to make a decision to stay in it or not.There must be something going on with the angle of the water exiting the bottom of the boat.I raised the motor 3/4 of an inch and lowered the water pickup 3/4 of an inch by pluging the intake.I think I would have to plug all but the bottom intake,It just doesnt seem worth the risk of meltdown.Man Brookville is a ZOO,boats everywhere,River is up,only good water is at Brookville at 6:00 in the morning.Later

racer
05-20-2001, 11:27 PM
Peak torque on a modified OMC (not a race motor) is from 5400 to 5700 rpm,depending on compression and ports.

Instigator
05-22-2001, 07:23 AM
When I repowered my Sonic one of the reasons I went with the JohnRudes was my "feeling" that they had superior torque for pushing that much weight.
None of the manufacturers listed torque, I looked.
Euroski stopped in on his way through town last week and he has a '99 Merc 280 with a factory rev limiter set at 7800 RPM's, oh yeah- with a factory warranty!!
Guessing it to be a little weak on the torque curve though!

Bobalouie
05-22-2001, 08:53 AM
I picked up one of the 2001 Merc Racing books the other day when I was at Fishin World, and each motor had a little graph that showed the HP and Torque curves, and they were labeled by RPM on the bottom, Torque was read off the RHS of the graph and HP on the LHS. If you can get ahold of some of the new product literature, it might answer some of your questions. You should be able to have some sent to your house from the Merc website.

Bob

RocketMan
05-22-2001, 10:30 AM
Nothing will help your analysis like getting the actual dyno curves showing HP and Torque over the operating range of the engines you are comparing, but this may help.

It may be easier to obtain the HP vs. RPM curves for the various engines. If so, you can calculate the Torque curve for an engine as follows:

Torque (lb.-ft.) = (5250/RPM)x HP

Using the formula: a 280 HP Merc (280 HP at 7500 RPM) puts out approx. 196 lb.-ft. at 7500 RPM.

A 225 HP YamMerSukiRude Outboard which puts out 225 HP at 5000 RPM will have a torque output of 236.25 lb.-ft. at 5000 RPM.

For a given engine, the HP curve and Torque curves will always cross at 5250 RPM.

Have fun with your calculations,

Paul

Barney
05-22-2001, 11:29 AM
I think with your hull, your gonna be happiest with high torgue, low rpm to push your Diplomat. See lots of your hull in Havasu, not a single outboard yet.

With the 300 and a 26p Bravo 1, 1-4 people, 5-50 gal gas, makes very little difference, 80-85 on GPS.

My motor that is set up to spin is much more sensitive to weight, each passenger can slow me 2-5mph.

An OMC V-8 would sit nice with your boat.

Sleekster
05-22-2001, 02:25 PM
A couple of setbacks, most personal and some motor rebuild issues, are giving me some delay, ...........I'd like to get out on the water by this weekend and do some river testing. Maybe even some Bay testing!

Thanks to all who posted a reply. Mostly a mental exercise but, who knows, the Dark side beckons, Black Holes do have their pull.........

LaveyT
05-22-2001, 06:52 PM
Ahh young luke Sleekster,A 300X would be outstanding on our heavey boats.Instagator does not have to know!

Instigator
05-22-2001, 08:22 PM
Oh un en lightened LT, Instigator always knows.

Euroski
05-22-2001, 09:04 PM
Last season I installed the Merc 1 inch intake spacer which made a big difference. Before the hull had some porpoise around 80 just as it was airing out. But with the spacer it accelerates so fast it's no longer there. Learned this from a friend who had a Skater24 with 260's.

Sleekster
05-23-2001, 06:25 AM
Thanks Euro, but I don't understand how an intake spacer aids in reducing porposing. Can you help?

As I'm rebuilding this looper, I realized that the air flow through the intake could not be more like the Colorado River, going this way, then that, then....... Mad EFI was a lot more sane to go the direct route. I should take another gander at the performance gains. But the old, how fast you want to go is directly linear to how much you gonna spend.

So is the merc intake path too efficient? By being too short? More hang time for the air/gas/oil mix was needed?

Barney, I agree I'll need the most torque I can get. does this little 3.0 looper have it to give?

LT, if I end up w/ a 300, merc X, or tweek this little looper, or go to the V8, it would be nice to do a little motor testing/contrasting....Kinda like prop testing...

I'll bring the cherry picker!

Rickracer
05-23-2001, 07:25 AM
A JohnRude Looper V-8 should round out that combo nicely, theoretically speaking. And if you should decide that there isn't enough horsepower there already, it isn't that hard to find way more in that motor. Like Barney, this is just my opinion, I could be wrong. But if I had a big enough boat to safely put one on, I would have had one long ago.

RocketMan
05-23-2001, 01:58 PM
Bobalouie is correct, the 2001 Merc high perf product brochures show the HP and Torque curves for almost all their HP engines. Hopefully the marketing department didn't screw too much with the hard data, just to draw pretty pictures in their brochures! They did try to disguise the HP curve for the 300X by showing "% of propshaft HP" vs. RPM. They show the 300X compared to the old ProMax 300 and do not show the Torque curves for either motor. With some quality calculator or EXCEL spreadsheet time you can generate approx. torque curves for the big ProMax's using the formula I posted above.

From the brochure, it looks like the torque peak of a 2.5/280 is approx. 250 lb-ft at 5000 RPM. The motor develops at least 200 lb-ft of torque from 3500-7000 RPM.

The 300, by my quick calculations, makes more than 250 lb-ft of torque across it's operating range and appears to have a double torque peak hitting approx. 290 lb-ft at 1500 and approx. 335 lb-ft at 4000 RPM.

REPEAT AFTER ME > "THERE IS NO SUBSTITUTE FOR CUBIC INCHES"!

Maybe somebody from inside Mercury, who just happens to see this thread, can supply us with the actual numerical data. Then we can really do some number crunching and draw our own curves!

Someone might also be able to dig out the numbers for the "other" brands.

Paul

Euroski
05-23-2001, 04:05 PM
Not sure how old you are but here goes. Remember in the hot rod days you just built a Chevy SB or BB. Politically let's include ford, and all the others(lol)! For the most part adding a hi-rise intake or under carb spacer usually didn't add any more power but helped the motors be more efficient by making the air have less turbulence. Now on the Merc, the air goes this route- air horn, reeds, spacer, engine crankcase. The spacer gives the air a chance to straighten up after leaving the reeds before the injectors spray the gas. As for stopping the porpoise... the engine revs so fast the boat spends very little time in the speed range where the porpoise would start. Maybe JSRE could give a better explanation! I think I said it made a world of difference on my friends Skater 24 with 2-260's!

Instigator
05-23-2001, 04:41 PM
I read everything technical I can get my hands on,car and boat and a lot of knowledgeable people say that its the torque not the horsepower that wins races.
Seems to be especially true with the car drag racers. Have seen cases for example in cam shaft testing where one cam made more peak HP's but less torque and there for ran a slower E.T.
It's been my experience that the more weight you're pushing, the more torque you want.(dah)
How about this, two identical boats, weights, set up etc.
Both boats have the same peak HP's but one has a higher torque peak than the other, what would happen??
Would they run the same top end speed but the boat with the torque advantage out accelerates the other???
When my boss was a current world champion in Pro O/B with the Koenigs, he swore by lake testing and not dyno sheets.
He said they had many instances during engine development where the dyno showed more HP's but the boat slowed down.
That was also running ovals though, and you needed a pretty broad "power" curve.
I still have a hard time believing that on a light fast boat, HP's are not where it's at!
I also wonder about the formulas of converting HP's to torque. Anybody ever done the formulas and overlayed them on a dyno pull???
Seems like typically peak torque is somewhere around 75-80% of the rpm of peak HP's???
O.K., now my brain is smoking!

JTS Racing
05-23-2001, 05:51 PM
Instigator,,,,,,your right and wrong. In the cars, pullers, and "most" other forms of land racing, and lets leave out Formula 1/CART, torque is where its at. In the liquid quarter, torque can be a bad thing. Only hulls like hydros and tunnels are capable of handling the higher torque engines. Top Fuel Hydros will run slower trap speeds than a Top Alky Hydro, but at .5+ sec's faster ET's.:) A buddy of mine had a bad ass Alky/OMC on an Ally. To try and keep it under 9500 rpm, he "tried" to run a 30 pitch prop. It was at the edge of undriveable at launch. The torque of the engine along with the tall pitch laid it on its side extremely hard. Droping to a more realistic 24 gave great acceleration, but ran out of steam on the big end. This thing was a speed demon at tha lake though. The advantage I see Mercs having in this case is the higher torque comes on at mid-range after the hull has had a better chance of setting, and the higher rpm capability for faster speeds at the end.

Technology and guru's are finding more ways each year to harness the torque factor and apply it to H2O. I know there are some strong OMC's and one Yammie out there with shifters. Maybe even a 300X??? If they ever get um ta work, and running the liquid quarter stays around, then things could get even more interesting in the years to come. :cool:

Rickracer
05-23-2001, 06:57 PM
only if you can use it efficiently. Back when I was street racing, I did everything I could to move the torque curve up beyond the range that caused a lot of tire smoke. I often got beat out of the hole, but almost nobody passed me once I got rolling. I used to love to race big blocks, because by the time they got hooked up, I was nearly at the finish line. It helped having a small block that would turn 8000 rpms.

racer
05-23-2001, 09:17 PM
Ran a stock 250 ocean pro on the dyno and peak torque was at 4800

Sleekster
05-23-2001, 09:53 PM
But I'm hanging on.

OK, so I can understand the higher RPM thing on a lighter hull like my 'ol V-King (even though I only ran OMC's), and the Cubic inches yeilds higher torque right? So on my pig of a family bow-rider-want-to-be-a-fast hull I need greater torque to get it going. Then a V8 appears (theoretically) to be the power plant of choice.

How do you move the torque up the line? In hydrodynamics, drag requires more power, but how can a two stroke V8 have it's peak or mutiple peaks moved? Rickracer, you deserve props for making a small block spin 8k. Can you do that w' my '93 Ford conversion?

Darn, I can't see the post's...

Euro, yeah I remember the flow-thing now, so I gotta ask, why did OMC put so many turn in the air/gas flow? I guess that is why the '97's were changed. My '96 (newly bolted -on intake) is old technology.

rickracer, can you get me a price on the '97 intakes? I'd like to see one. But more than that I'd like to clean-up the flow.


Hydro, So is it that the torque on a lighter hull peaks too fast or peaks too steep that makes it less desirable than the higher spinning motor?

Racer, now I know you have Instigator's attention. What was the peak Rtorque at 4800 r's? Did it have hang time?

Rocketman, OK "There is no substitute for cubic inches" so why not a V8?

Rickracer, yes, I've been looking at the V8's and Mark S. even e-med about one on Ebay, but the cards need a lttle more shuffling to bring one home. Mercman's selling the Monty V8 had me drooling, but it wasn't in the cards, yet. I have a couple of V6 loopers, can I duct tape some together and get........

JTS Racing
05-23-2001, 10:46 PM
No dude,,,your jus getting yo feet wet:)

What I ment was that some small light hulls don't respond well to high torque output at the lower rpm level.

Torque is of value. It is what does the work. HP is a relation of torque and rpm.

Want to get in over yo head??? Get into Port Timing, Combustion chamber design, Peek cyl pressure, Max cyl pressure, Timing at target rpm and fuel mixtures. Then alter those with NOS or Nitro introduction.

Stir it up jus a little more. How do carbs draft? Someone explain venturie size to engine ratio, mixing tube size and location, vent jets, and do velocity stacks really work?? What happens if I space the carbs away from the reeds or get them closer??

Why do fuel injection systems fire and entire bank or companion at the same time? Wouldn't it be better if each injector was fired with proper timing for that cylinder and able to set the mixture from that individual injector??

Now it gets fun:eek:

Jus had ta do dat;)

Instigator
05-23-2001, 11:19 PM
This one started in French and did'nt get translated very well either!
I want a dyno for my B.day (Fri.), a half dozen mule motors, a die grinder, some carbide burrs, a shoe box full of jets, a pot of coffee and a pack of No DOZE!
One thing I learned a long time ago is that when you change one facet in the tuning of a motor (i.e. port timing, compression etc) you cannot accurately measure the change until all other factors are adjusted (jetting, ign timing)accordingly.
I got side tracked off of my FrankenRude project while I screwed my roached 250 back together, but I'm ready to go back and finish porting so I can send the block out.
I'm not ashamed to admit that I'm scared silly to finish porting! Built a bunch of motors that looked fast on the work bench!!!
Difference between 2 strokes and 4's ?? Want to change port size and timing on a 4?? Change the cam and valves. Want to do the same to a 2 stroke?? Throw away the block and start again!
You start studying the damn things and you see why so many people think it's a "Black Art"!
Keep thinking those Land & Sea dynos are'nt that expensive??
Racer, you said you dyno'd a 250 Ocean pro and torque peaked at 4800??? I believe it after seeing how much is left in those things!! Where did HP's peak?? I'd guess about 5500 going by the seat of my pants??
Too bad my motors are '99's and not allowed to be modified in any way. LEGALLY! They are both coming down this fall for some EPA/GW approved updating!!



[Edited by Instigator on 05-23-2001 at 11:34 PM]

racer
05-24-2001, 12:33 AM
Instigator, Peak Hp was at 5700 and held pretty consistent until 6300 where it started to drop off at a faster rate. Reading taken on a superflow with windyn thru a 10 inch dia X 48 inch long muffler. Stock jets and Egt`s all between 1120 and 1160, timing at 18 degrees. Airbox intact.

Instigator
05-24-2001, 06:44 AM
Thank you! I know mine pull hard to 6K, and I'm happy to hear that they pull to 6300 before dropping off. More R's than I expected.
With stock airbox, jetting and timing too! HUMMH?
The manual says that I can run low octane fuel which I have been. In stock configuration do you think I would see anything with higher octane fuel??
Also the manual says to run oil with the fuel if you're going to beat on the motors. After I just fried one motor I have started doing this, do you agree?
Thanx Racer!
Instigator

Sleekster
05-24-2001, 07:32 AM
OK, my feet are wet. But I'm still in the game.

So Racer, if the 250 pulls to 6300, then wouldn't Instigator be smart to prop to that point? Or on the only-for-top-end goal, would propping above that yeild any good (more speed)? Or is that when the turn in turnkey stops?

I guess on my modified looper, I have to lake test or get it dyno-ed. my 225 modified to 265 or so, still leaves me w/ trial and error, with less of the latter I hope.

JTS Racing
05-24-2001, 12:37 PM
It's been a while since I've had much time to be on the board. Jus had to do that for a little fun.;)

Your in the same question that should be #1. Were does an engine produce it's most power??? I've seen guys have tricked 2.5 HP's that were on Bullets, Allys, Norris Crafts, etc...take them off because they were tired of the no storage, fast bass platforms. Traded or sold the boat and put their engine on a new limo like Stratos, Javlin, Triton,,etc,,,and blow the engine within a month. And still can't figure out what happened. ""It turned this Alabama Cut 28 just fine before, but its a dog now...Something must be wrong with the engine"...lol

The first thing most good engine builders will ask is,"What are you going to put it on?" The heavier hulls require the torque at lower rpms. Everybody, almost, wants to go a little faster. Simple things like cages, reeds and opening the exhaust can kill hole shot on a 21' Stratos. Put on a small pitch and launch it, turn the rpm up a little more and start having stator, triger and charging problems. But guess what....They ain't going any faster on top end!! Light hulls that don't take a lot to get um on top can have the torque band raised up the rpm level to allow spinning a tall wheel at 8000 or so for all out top end.

One question....lots of different answers.:rolleyes: But those are what makes the engines and builders get better. :cool:

Bobalouie
05-24-2001, 03:58 PM
The reason most engines batch fire injectors is because there is only one coil. The distributor does the switching mechanically and is not controlled by the ecm. The ECM is programmed with one coil driver and 2 injector drivers, because there wasnt much use for the flexability to control each injector individually. I guess it came down to the fact that since they could not use the flexability, why add cost and complexity to a product that could not make good use of it. Most engines that use multiple coils, like the new GM truck 5.3L and 8.1L control the injectors individually since they had to write software to control each coil individually anyway and it can use the complexity to control things, like knock.

Bob

jim jesella
05-24-2001, 09:58 PM
Hey Sleek I know you are a die hard OMC fan, so why don't you buy John W (mercmans) V 8 .You will NOT go wrong. It is a GREAT motor. I just bought his SVS and it was perfect, just like he said. He is Honest. jimmy

Sleekster
05-24-2001, 10:02 PM
Thanks Jim, guess my true colors are too easy to see, blue or white.

Last I heard the motor was sold.

I e-ed him though.....had me looking hard.