Mercruiser 165 inline 6 torque curve.

[kilowatts]

Hi Guys:

I'm a big fan of the MCM 165 inline 6 engines having rebuilt several over the last little while. Does anyone know where I could get a torque graph for a stock engine? Searched but no result. Many thanks in advance:

kilowatts

 

[Don S]

Re: Mercruiser 165 inline 6 torque curve.

Mercruiser has never published torque specs for any of their engines....... Never.

 

[QC]

Re: Mercruiser 165 inline 6 torque curve.

The reason is that "peak" torque curves don't matter much to marine applications despite a lot of misunderstood comments.

One way to prove this is to ask, "What would you do with a torque curve in a marine application if you had it?"

 

[dan t.]

Re: Mercruiser 165 inline 6 torque curve.

If you know your cam specs you can figure it out pretty close with the Dyno 2000 engine simulator program. It is acually a lot of fun to play with, try changing a few things and see what you get. It calculates both HP and torque.

 

[Don S]

Re: Mercruiser 165 inline 6 torque curve.

f you know your cam specs

Merc also doesn't publish it's cam specs.

 

[HTownws6]

Re: Mercruiser 165 inline 6 torque curve.

I'm a drag racer so I love this kinda stuff. I've got the Comp Cams cam selection software on my computer, so I ran the numbers. It spits out a stock replacement cam for the inline 250, a 240 duration cam with these specs:

Here is the graph:

Range of the cam was 500 to 4000 rpm.

Max power: 163.7 hp @ 4000 rpm, avg power: 37.7 hp

Max torque: 242.2 ft-lbs @ 3000 rpm, avg tq: 67.2 ft-lbs

I tried 1 or 2 grinds bigger than this cam, but really didn't gain any power or torque without doing a bunch of other stuff (bigger carb, more efficient exhaust).

From what I have read, these marine motors are difficult to mod and get any usable results from...

 

[Silvertip]

Re: Mercruiser 165 inline 6 torque curve.

Marine engines are no more difficult to modify than their automotive equivalent. The difference however is in a marine application you can't use the power gains. Power modifications just moves the HP and Torque curves around (normally higher up the rpm band). 6500 rpm on a marine motor doesn't help you much when trying to get a heavy boat out of the hole. Land based vehicles have transmissions with multiple gear ratios available. Boats have two gears (forward and reverse). Stick a NASCAR motor in your family truckster and then try and start out in high gear. Shucks, a NASCAR car can't hardly get out of the pits unless you wind it up to 7 grand and dump the clutch to get the wheels spinning.

 

[HTownws6]

Re: Mercruiser 165 inline 6 torque curve.

The difference however is in a marine application you can't use the power gains.

That is what I meant to say. Drag racing requires alot of power at high rpm. Most marine applications need torque down low. I think the inline 6 is a great motor for this. A torque monster considering the size of the motor. More torque can be had with these motors with a bigger cam, but not without some intake/exhaust changes also. That was the point I was trying to make.

 

[kilowatts]

Re: Mercruiser 165 inline 6 torque curve.

Hi Guys:

Thanks for all your advice and your comments. I have no intention of trying to increase performance on my engines as I'm quite happy with their characteristics. I've always had the idea that the 165 is the ideal engine for back yard marine guys like me as they are simple,powerful, reliable and cheap. Not having a background in mechanics of any kind I always wondered why they seemed so good and I assumed the torque curve graph would explain it.

HTown: Many thanks for your help and the graph. Sadly, I don't really understand it very well, for example which line is torque and which is HP? Is the graph set up for a standard spec Chevy 250CID inline 6 from a truck? Would you mind expanding a bit please? Many thanks in advance.

kilowatts

 

[HTownws6]

Re: Mercruiser 165 inline 6 torque curve.

No problem. The green line is the torque, and the red line is the hp. This graph is just from the cam selection software. It is of a
250" Inline 6 chevy engine.Its not actually a graph of a dyno pull, but just a simulated pull using the software. But I suspect that it probably isn't far off. My experience with these cam selection software is they are pretty darn accurate. I'd love to know how they calculate all that. But as you can see, the torque peaks very fast, then the hp follows but drops off very fast also after about 4000 rpms.

 

[kilowatts]

Re: Mercruiser 165 inline 6 torque curve.

Hi Guys:

Thanks for your help HTown. It's really good of you to produce the graph and then explain it, I appreciate it very much.

kilowatts

 

[kilowatts]

Re: Mercruiser 165 inline 6 torque curve.

Hi Guys:

Further thoughts on the torque curve:

My boat is a Grew/Slickcraft SS215. According to others on this site it has excellent sea keeping abilities and has one of the best handling hulls available for a small boat. I live on the BC coast and use the boat in the local lakes, the Fraser River and the ocean about equally. Although the boat has the excellent qualities already attributed, it's limited by it's size to about a true 1.5 to 2 foot chop to handle comfortably. In other words, I can only go WOT (4200rpm) when the water is somewhat calm or risk damaging either my kidneys or the boat or both. Generally, I run at 2500 to 3500 rpm which gives me a speed of 22 to 26 mph (GPS), this gives me a reasonably comfortable ride in a medium chop as above.
Correct me if I'm wrong but, given the torque specs provided above by HTown isn't the 165 engine perfectly suited for my uses? From my reading the power and torque bands are exactly where I run most of the time. Further, the engine runs at around 6GPH at this rate.
Please let me know your thoughts as I have no experience with automotive/marine technical specs regarding engines.

kilowatts

 

[Don S]

Re: Mercruiser 165 inline 6 torque curve.

as I have no experience with automotive/marine technical specs regarding engines.

Then don't mess with what you have. Looking at an automotive chart tells you nothing about what it will do in a boat.
Might want to do a search on "Reversion" from having too much valve overlap, and how it sucks water back in from the exhaust and into the cylinders. Too many automotive cam experts have no clue what it is or how damaging it is to an engine.

 

[kilowatts]

Re: Mercruiser 165 inline 6 torque curve.

Hi Guys:

Thanks for the comments, Don. As I said earlier I have no intention in changing anything as I am delighted with the engine and merely wanted to learn more about it. The interpretation of the torque curve data is really the question here and not whether or not it should or could be improved. I think I'm understanding it but I'm not certain.

kilowatts