WOT speed on a '83 20' SF w/200

[VirginIslander]

Hey dljohn,
Looks like we're neighbors. I'm in Newberry and work in Gainesville.

Your numbers are kinda what I was expecting. The performance I'm experiencing is more what I would expect from a 150. My expectations are based on my 10+ year old memory of a friend's Potter 20 MA with a 150 on it. I'm still trying to figure out to what extent it's because of differences in the hull, or because I'm running this Frankenmerc on it.

I took it to P&J Marine and they stuck it on their Dyno. The torque value they gave me was 95% of the minimum for a 200, but I don't know what rpm they measured it at, so I can't calculate horsepower. If it's a linear conversion, and merc's minimum torque spec for a 200 is at 200hp, then mine is developing 190 hp.

Anyway, thanks for the input. Every extra data point helps. I'm gonna keep tweaking. BTW, how high is your motor mounted? Where is the cavitattion plate in relation to the bottom of the hull at level trim? Mine is about an inch above.
Thanks,
Dave

Max torque will be at a lower RPM than max HP.
Max torque is the RPM where the motor has the best volumetric efficiency.

Torque and HP are mathmatically related: HP equalls (torque (in #/ft) times rpm) divided by 5600.

If you look at the torque - HP plot from a dyno, you'll see they always cross at 5600 rpm. There's more ft/lbs of torque than HP up to that point, and then there's more HP than torque above that.

If the motor doesn't turn that high, then there'll always be more torque than HP.

If you're getting 95% of the torque spec for a 200, you're probably getting close enough to 95% of the minimum HP spec.

They aren't linearly related, but they're close enough for what you're figuring.

Even if you had the rpm where they measured the peak torque, it would only give you the HP at that rpm, not the max HP.

Darlene

[Blue_Heron]

Max torque will be at a lower RPM than max HP.
Max torque is the RPM where the motor has the best volumetric efficiency.

Torque and HP are mathmatically related: HP equalls (torque (in #/ft) times rpm) divided by 5600.

If you look at the torque - HP plot from a dyno, you'll see they always cross at 5600 rpm. There's more ft/lbs of torque than HP up to that point, and then there's more HP than torque above that.

If the motor doesn't turn that high, then there'll always be more torque than HP.

If you're getting 95% of the torque spec for a 200, you're probably getting close enough to 95% of the minimum HP spec.

They aren't linearly related, but they're close enough for what you're figuring.

Even if you had the rpm where they measured the peak torque, it would only give you the HP at that rpm, not the max HP.

Darlene

Thanks, Darlene,
As I understand it, the dyno they used is programmed and all they do is enter the model number for the engine they're testing, run it up to max recommended WOT rpm (5500)and see if the torque curve matches up. I don't think they calculate the max HP or do any further analysis on the numbers, but I'm just guessing. I don't know if the torque value they gave me was max torque, or torque at 5500 rpm.

I got most of what I know about the relationship between torque and HP here:

http://www.revsearch.com/dynamometer...orsepower.html

[VirginIslander]

That's a good page on HP/torque. It also made me realize I was thinking of something else when I posted 5600, it is 5252 rpm. (and it's too late to edit my original post to correct that)

Torque is usually given as the peak torque number, just as HP is given as the peak HP. Both are usually referred to at specific RPMs in knowledgable circles, but often just the HP is used in general reference.

For a "collection of black parts", you seem to have at least a reasonable facsimile of a 200 merc.


Darlene

[caper]

My '75 SF20 with a new (14 hours) Johnson 2S carbed 175 just touches 50 mph (GPS)on flat water with a light fuel load, a T-top, bottom paint, and an aluminum 14 1/2 X 19 prop.

[dljohn69]

Dave, I did not mount the engine on my boat. I will look at the cav plate the next time I am at the boat. While working on the trailer I have it in a boat house on the St Johns river. My transom is an original 20 incher and with the new saitwater series E-Tec being a 25" shaft I also run a CMC hyd jack plate. Also I do not have a T Top and I lower the bimini while running.

[ThePHNX]

"horsepower, it don't matter what color the engine is."
Shame on you Blue Heron; you obviously know better.
For one thing Horsepower ratings are as much marketing hype as engineering (and all indications are that Mercury is more of a sales organization than an engineering one)
Then there is this business of power curves where power and torque vary with engine design for any given RPM.
There are known occurrences of horsepower being overrated 20% or more by marketers so a spread of 40 HP DOWNWARD is certainly possible.
In which event would be inclined to trust Yamaha's (or just about anyone's) veracity over Mercury.
As you can tell, have gotten a pretty low opinion of Mercury Marine.

Oh, and BTW, is the cam on your FrenkenMerc engine in sync with the other volumetric components (valve lift versus area, versus open (or close) time)? Have you checked breathing?
Regards, HBH

[spareparts]

Phnx, last time i checked, 2 stroke engines don't have cams, or valves with measured lifts. As far as measured hp, most two strokes are under rated, the SAE measured hp ratings used by outboard manufactures allow 10% varriance in the claimed hp ratings. Most of the big V6 2 strokes, by all manufactures excede the ratings on the cowl. I have personally seen 225 Opti's make 245-250 hp on the dyno. I've also seen 225 fourstokes barely make the 10% under. There is no accross the board statement other than each engine has to make within 10 % of the cowl sticker when new. Right now Yamaha could sell their 150 four stroke as a 175( it makes 165-170 hp, but they decided not to because they got there but kicked when they introduced the 225 four stroke( it barely made 205hp).

[ThePHNX]

Sorry `spares' was not clear to me franken was a 2-stroke, is she?

[Bigshrimpin]

Spareparts beat me to it. PHNX - 150XR6 is a Merc 2.5L two stroke . . . Same block as the 2.5L 200hp.

all indications are that Mercury is more of a sales organization than an engineering one

That might be true today, but no outboard company put more resources into engineering, testing and research than Mercury. LakeX, Placida Test Facility, mercury racing => 1960 - 80's . . . Merc built the fastest motors around. Their props are great too. I can't comment on the new motors other than the weight of the verado But their old two stroke motors and inline motors are/were very good and strong.

Yamaha - Yamaha's 2.6L motor is one of the most reliable engines, but the block was a masterfully engineered copy of the early OMC v6. 1983 lawsuit.

[spareparts]

they closed lake X