First non GM block Merc.

Tail_Gunner

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#59

Originally posted by bruceb58 View Post
I think the original question was why they didn't show torque vs Hp. The thing is if you have a torque curve or a HP curve, all you need is one of them to solve for the other since all you need is torque and RPM and you solve for HP or vice versa.





Agree, but with a wheeled vehicle you can select gearing that matches peak torque for deep lugs (yes you could calc from the horsepower curve, but easy to use the torque figure if you can in fact do something with the info). With only one gear in a boat, there is no benefit in knowing Peak Torque or its RPM, because you can't "use" it. With that said Peak Torque can come into play with say a tug boat, or a commercial fishing boat dragging a huge net against a swell. But these are not conditions (except maybe a watersports tow boat) that are met normally by recreational boaters. And with the towboat, you still won't "see" peak torque" unless the RPM stops building. Like my example above, maybe with 17 skiers...

Hmmm I live in the world of retail sale's, acutally automotive I can tell you this with almost absolute certainly the more tech you throw at the masses during a buying decision the more they shut off..eye's roll back in there head...I affectionly call it the moon wobble. Now that is the last thing anyone need's when making a major purchase..it's called a off button. Let me give you a example I for one believe a marine engine should be set up to start producing torque at 1800 rpm and peak at 6000. That statement could set of a huge debate and end with many different conclusion's.....but to use one word....Horsepower... keep's it simple and clean.....

There's a expression for it and we all have heard it before..Keep It Simple Stupid..The kiss it principle.

Ohh by the way the above is strictly a opinion you milage will vary..
 
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Watermann

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^^^ Uh oh, he's a used car salesman ^^^ :lol:

I think the whole marine engine debate could be summed up pretty quickly from the comments I've read. The motor should be matched to the boat and the needs of the operator.

or.... just go get an OB, if that doesn't work go get a bigger OB and if that isn't right get two!
 

HT32BSX115

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Maybe the next IO boat I get will have a 5.7L or will get one in an upgrade. The 4.3L is no slouch when applied correctly and I had some experience with it in a S10 Blazer. This new Merc V6 has a long way to go to prove itself and I guess we'll be seeing the new owners in the IO section sooner or later.

I think Mercury can prove itself quite nicely.......They even build automotive engines too...The Corvette LT5 engine is a Mercury Marine engine....

http://articles.orlandosentinel.com/1988-09-15/topic/0070050173_1_mercury-engines-lt5
 

JustJason

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bruceb58 said:

But you do. The problem with that calculator and any other calculator is it only tells you the torque at the maximum horsepower rpm. For example. If the engine is 300hp at 5k rpms I can use that calculator and it will tell me what the torque is, at 5k rpms. But that's not what I am getting at. What I am getting at is what is the torque at 1500 rpms, 2k, 3k ect ect. Or what is peak torque, and at what rpm is peak torque?

Try and answer this question. Imagine if your not an educated boat buyer, and your looking at 2 different boats. Your primary goals are an all around family boat, you want to cruise, do some fishing, and you do want to do some tubing/wakeboarding/waterskiing with the kids/family. The boat size you decided on is a 21 foot bowrider IO.

1. Salesman A is trying to sell you a Searay boat powered by a 4.5 liter Mercrusier
2. Salesman B is trying to sell you a Regal boat powered by a 5.0 Volvo Penta

The question is, you love both boats. Which engine will better suit your needs? (even I don't know)
 
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bruceb58

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But you do. The problem with that calculator and any other calculator is it only tells you the torque at the maximum horsepower rpm.
No it doesn't. At any desired torque and RPM you calculate HP and vice versa.

If you have the HP charts of 2 engines overlayed on each other, you can see what the HP is at every given RPM. If you want to know what the HP is at 3000 RPM becuase that is where you are going to be WOT getting up on plane, then you can compare.
 

JustJason

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bruceb58 said:
No it doesn't. At any desired torque and RPM you calculate HP and vice versa.

Uhhhh... Maybe i'm misunderstanding this calculator then.

I'll use an engine I know the specs on. I have an engine that is 381 horsepower at 5600 rpms. Using that calculator, what is my peak torque? and what rpm does that peak torque develop at?
 

Tail_Gunner

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But you do. The problem with that calculator and any other calculator is it only tells you the torque at the maximum horsepower rpm. For example. If the engine is 300hp at 5k rpms I can use that calculator and it will tell me what the torque is, at 5k rpms. But that's not what I am getting at. What I am getting at is what is the torque at 1500 rpms, 2k, 3k ect ect. Or what is peak torque, and at what rpm is peak torque?

Try and answer this question. Imagine if your not an educated boat buyer, and your looking at 2 different boats. Your primary goals are an all around family boat, you want to cruise, do some fishing, and you do want to do some tubing/wakeboarding/waterskiing with the kids/family. The boat size you decided on is a 21 foot bowrider IO.

1. Salesman A is trying to sell you a Searay boat powered by a 4.5 liter Mercrusier
2. Salesman B is trying to sell you a Regal boat powered by a 5.0 Volvo Penta

The question is, you love both boats. Which engine will better suit your needs? (even I don't know)

Well Jason even guy's like you get caught in tech, so use fundamental's what are the strength's of a 5.0 gm and a 4.3 gm...the v8's power pulses are going to be smoother..the v8 will have higher and more sustainable rpm.. torque..8vs6...The 4.3 will be lighter does that offset the later...that is the question

If you accept the formula torque times RPM divided by 5,252 -- to arrive at.." horsepower"... the question your posing is what are the performance characteristics
of each engine...what do I like about each engine. In this case the new 4.3 is lighter and give's v8.. "like".. performance. For many they like that ideal clean simple and of benefit.

Now if Merc keep's the price less on the 4.3 vs 5.0 then we do move move on...Its really to bad they didn't use the variable cam timing and direct injection that would be a leap.
 
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bruceb58

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Uhhhh... Maybe i'm misunderstanding this calculator then
If you know the torque or HP at a specific RPM, you can calculate the other. The calculator just does the math for you which is actually very simple.

Back in engineering school, we had a GM engine test set up with a 5.7L engine connected to a dyno. The whole setup was given to us by GM. We had to run through a whole bunch of RPMs, measure the torque at each RPM and create graphs of HP and torque. We took measurements every 200 RPMs to create our torque graphs which we then converted to HP with the equation. The same equation is used by that calculator.
 

JustJason

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bruceb58 said:
If you know the torque or HP at a specific RPM, you can calculate the other. The calculator just does the math for you which is actually very simple.

Correct... with the key being "At a specific RPM". And that's why I had said "But you do. The problem with that calculator and any other calculator is it only tells you the torque at the maximum horsepower rpm." And the reason why I wrote that is all of the engines have a horsepower given at whatever rpm it develops peak horsepower. And that's what I was trying to get it this whole time, and that is why I had said all manufacturers should publish both HP and TQ charts with there engines. Getting back to the 4.5 liter, and this calculator. If I want to know what the torque is at 2500 rpms, which is a roundabout average towing rpm, I would have to know what the horsepower is at 2500 rpms, and then I could use that calculator and figure it out. But Mercury (and nobody else) tells you what the horsepower is at anything other than maximum. Does that make sense?

The point i'm trying to make is there are a lot of people that don't care what maximum horsepower is at peak rpm. A lot of us don't run our engines at peak rpm. Another example is theoretically, if the 5.0 makes more torque at a lower rpm than the 4.5. Then once you have punched it, got up on plane. You could then throttle back and cruise at a lower rpm while staying on plane because 1 engine makes more torque than another engine at a lower rpm. If the 4.5 doesn't have good low rpm torque, it won't have the power to stay on plane once you get there and then throttle back.
 
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doyall

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... But Mercury (and nobody else) tells you what the horsepower is at anything other than maximum. ...

Apparently you (who I believe has the most reasonable conclusions among all of the curmudgeons posting here) nor anyone of the others apparently bothered to look at the links in my post #60. Plain as day. Torque in the mid range obviously provides the desired grunt in a gasoline marine engine. Peak torque is not necessarily at WOT, irrespective of several who say so. It's time for the naysayers to put up or shut up. And the HP/torque curves throughout the RPM spectrum are listed making it easy to test the calculations.

Bottom line: torque is very important (maybe more important than HP in certain situations), where it is made is very important and Mercury should post HP/torque curves for it's new 4.5L in order for discerning buyers to be able to make a rational engine decision.
 

bruceb58

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I don't know... When it comes to marine engines, I think the OEMs need to print torque and horsepower curve charts on their sales literature.

It would be nice if they printed both but even just a HP chart will do to compare two engines...that is my point which apparently you are missing.
 

bruceb58

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Peak torque is not necessarily at WOT, irrespective of several who say so.
LOL...that's how torque is measured...at WOT. If you want to measure the torque at a specific RPM you run the engine at WOT to keep it steady at a certain RPM, load it with a dyno and measure the torque delivered.

I take it you have never used a dyno to measure torque?
 

HT32BSX115

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Correct... with the key being "At a specific RPM". And that's why I had said "But you do. The problem with that calculator and any other calculator is it only tells you the torque at the maximum horsepower rpm."

Um That's a "negative, there Tower!

The simple equation relating HP and Torque. (or Watts and Newton-Meters) Is NOT dependent on maximum HP (or Watts) of the prime mover.

It is only a simple arithmetic relationship between the two. If you have RPM and HP (or RPM & WATTS) you can calculate the torque........ at any measured RPM.

I would go back to my old Statics and Dynamics textbook but it's easier to just quote Wikipedia.....

If torque and angular speed are known, using a coherent system of units (such as SI), the power may be calculated using the relationship;
ed5e6c036c8e02ff1173b4e331c8b044.png
where
44c29edb103a2872f519ad0c9a0fdaaa.png
is power,
81a69207104f00baaabd6f84cafd15a0.png
is torque, and
4d1b7b74aba3cfabd624e898d86b4602.png
is angular speed. When using other units or if the speed is in revolutions per unit time rather than radians, a conversion factor has to be included. When torque is in pound-foot units, rotational speed
dcd750ca3809748e061ec3568c291694.png
is in rpm and power is required in horsepower:
c546af195e3ac5c3af2d96a25b8b043c.png
The constant 5252 is the rounded value of (33,000 ft·lbf/min)/(2π rad/rev).
 

doyall

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LOL...that's how torque is measured...at WOT. If you want to measure the torque at a specific RPM you run the engine at WOT to keep it steady at a certain RPM, load it with a dyno and measure the torque delivered.

I take it you have never used a dyno to measure torque?

Then "peak" must have a different meaning than "maximum" ... more like "terminal" perhaps.

If an engine develops "X" pound feet of torque at 3000 RPM and "X minus 50" pound feet of torque at 5000 RPM then "peak" torque is not measured at 5000 RPM, at least not in the sense that non-engineer people would describe "peak" torque. To suggest otherwise is nonsense.
 

bruceb58

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Then "peak" must have a different meaning than "maximum" ... more like "terminal" perhaps.

If an engine develops "X" pound feet of torque at 3000 RPM and "X minus 50" pound feet of torque at 5000 RPM then "peak" torque is not measured at 5000 RPM, at least not in the sense that non-engineer people would describe "peak" torque. To suggest otherwise is nonsense.
You can have WOT and not have max RPM. All depends on the load. You are confused on what WOT means.

All the torque values that are on the charts you posted in #60 are all measure at WOT at all RPMs.
 
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JustJason

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Rick said:
The simple equation relating HP and Torque. (or Watts and Newton-Meters) Is NOT dependent on maximum HP (or Watts) of the prime mover.

It is only a simple arithmetic relationship between the two. If you have RPM and HP (or RPM & WATTS) you can calculate the torque........ at any measured RPM.

I would go back to my old Statics and Dynamics textbook but it's easier to just quote Wikipedia.....


What you wrote is not really correct. If you think it is, and if you understand what you wrote, you should be able to answer this. I have a gasoline engine. I'm not going to tell you the displacement or anything else.

It makes 381 horsepower at 5600 rpm. If you can do this, and if you understand the equations you are throwing out at me. Please tell me what peak torque is on this engine. And tell me at what rpm peak torque develops.

rick said:
If you have RPM and HP (or RPM & WATTS) you can calculate the torque........ at any measured RPM.

HP is 381, RPM is 5600. What is the engines peak torque? And what rpm does that peak torque happen?
 
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Howard Sterndrive

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So does that suggest I rebuild my carb'd 5.7 (runs fine, but getting old and tired, lots of blow-by, consuming oil) and keep it as long as possible as a collector's item, or run the 5.7 til it dies then re-power with something else?

I suspect you'll still be able to buy new replacement Crate engines for the next 20 years. That's not the production they are talking about ceasing.
 

HT32BSX115

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If an engine develops "X" pound feet of torque at 3000 RPM and "X minus 50" pound feet of torque at 5000 RPM then "peak" torque is not measured at 5000 RPM
Absolutely true. Those torque calculations are ALWAYS done at WIDE OPEN THROTTLE (for a "given" induction system) to determine where the "PEAK" torque occurs!

It would be completely meaningless if it was done at a throttle "setting" other than WOT.
 

HT32BSX115

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What you wrote is not really correct. If you think it is, and if you understand what you wrote, you should be able to answer this. I have a gasoline engine. I'm not going to tell you the displacement or anything else.

It makes 381 horsepower at 5600 rpm. If you can do this, and if you understand the equations you are throwing out at me. Please tell me what peak torque is on this engine. And tell me at what rpm peak torque develops.



HP is 381, RPM is 5600. What is the engines peak torque? And what rpm does that peak torque happen?


Well, you'll have to tell me what is not correct I guess............



The torque at 5600 RPM....... for that engine is approx 360 Lb-Ft.

Provide the measured HP from 1800-5600 RPM (measured every 50 RPM or so, ) and I'll be glad to do the arithmetic for you.

That's the only way you'll determine the "Peak" torque.

If you have information for that engine providing HP and torque and it did NOT come from an actual DYNOMOMETER test, then it's it's an estimation from a similarly built engine that WAS DYNO tested.
 
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