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Posts: 3508
Location: Elk River, Minnesota | Hi everyone...
This is just a question out of curiosity more than anything. I have been looking at different motor brochures and am curious as to if a V4 engine gives up a bit of power as a comparable inline cylinder styled engine at all. I have been curious about this for a while based upon previous experiences (not apples to apples but the same basic physical aspects taking place) with the older ford 4.9 inline 6 as compared to the ford V8 (5.2 or 5.3?) They both had about the same power, but the inline had better fuel efficiency.
Please help me figure this if you will...I am not sure if this is correct or not:
But...when the cylinders of an inline engine fire, will they or will they not have more downward force on the camshaft per cylinder as compared to a v style engine that may have more or less cid and a possible extra cylinder?
Also, how does the compression ratio affect horsepower to compare engine wise? I have noticed that different engines have a different compression ratio, so this is interesting to me as well.
Thanks
Steve |
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Posts: 152
| Muskies confuse me, engines I know. First thing is a V configuration is more compact and better ballanced than a inline. The V four will vibrate less. Tourqe is what moves a vehicle, horsepower is a byproduct of tourqe. The longer the stroke, the more tourqe an engine has at a lower r.p.m., but will not safely rev as high as a short stroke. Two engines can have the same horsepower rating and be of the same displacement, yet one will get a boat on plane faster. The one that makes tourqe at a lower r.p.m. is the one that gets you up sooner. 4,700 ft. per second is considered maximum safe piston speed(This is not r.p.m., but how many feet the piston travels in the cylinder per second) and after that bearings start to come apart. The venerable Ford 300 cbic inch straight 6 was a stump puller becouse of it's long stroke and small bore. It made power at low r.p.m.. There are three types of engine configurations, square, where the bore and stroke are the same (4 inch bore and 4 inch stroke), over square(4.5 inch bore and 3.5 stroke), and under square(3.5 inch bore and 4.5 inch stroke). Todays engines most comonly are square or oversquare. Harleys are still undersquare. My 93 incher is 3 5/8x4 1/2. Higher compression makes more power, but can also cause detonation with low octane fuel. A bathtub combustion chamber can handle more compression than a hemi becouse it burns the fuel more efficiently and evenly. Higher octane fuel is no more powerful than low octane, it simply burns slower to allow more advance of timing and higher compression. When oil is added to gas it lowers the octane. I have tried to keep this simple and I won't go into two stroke limitations becouse of the intake and exoust ports or camshaft lifts, duration and timing. Let alone reversion waves, CV carbs and fuel injection. Bottom line is a V engine is a better design and if two engines have the same power and one has a significantly larger displacement, the one with the larger displacement is not working as hard and will have a longer life, all things being equal like having the same power at the same r.p.m., Later |
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Posts: 3508
Location: Elk River, Minnesota | This is very interesting!!
See...here the curiosity in me working. I have recently purchased a yamaha 2 stroke 90 hp (inline 3 cyl) with 69.6 cid. I purchased this based on it's compact design, price, and reliability with which I am extremely happy with. I did notice, though, that the Johnson 2 stroke 90 hp has a 60 degree v-4 with 105 cid. Given that I will rarely load my boat down, the extra weight of the V4 just did not fit the bill...and if a smaller motor can create that much power to me seems like a good sell (power to weight and design). But...how is it that yamaha can create so much power with that inline with such significantly smaller cid than the comparable johnson in a v4? I know the extra cid will get me out of the water faster, but would it be safe to assume that the compression ratio in the yamaha is higher, thus creating the power that would be equivalent to the johnson?
Steve
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Posts: 152
| Without knowing the bore and stroke of each engine I can only guess. The Yamaha could have a more oversquare engine that lets it rev higher. The more times a piston goes up and down per minute, the more often it is getting fuel into the cylinder. As I stated before, 4,700 ft, per second is maximum safe piston speed. A Harley is on the edge at seven grand where a Yamaha crotch rocket is able to pull twelve grand before it reaches the 4,700 ft. per sec.. The Harley makes a ton more power below six grand, but looses the peak power battle becouse the Yamaha can rev higher and pack more fuel in. Other factors are the compression and what type of carburation are used. A two stroke uses the placement of the intake and exaust ports in the cylinder to control the power band. It is very hard to get a two stroke to make good power from low to high r.p.m. becouse of the limitations of the port placement. A larger displacement would overcome a lot of these problems. You could still have 90 hp and better low end power with a larger displacement like the Johnson. With outboards this is not generally a problem becouse we are most often running at half to full throttle. Exaust tuning is critical in two strokes for maximum power and to determine the powerbands characteristics. That gets into ultra sonic waves that scavange buned gas and help bring fresh gas in. I would like to see Dyno printouts on each of these engines. When I lived in the South West the 300 ford six was used to run irrigation pumps and they would last longer than any V-8 with a larger displacement. The only thing better was the old Moline engines, but it got to the point you couldn't get them. Inline three's balance pretty well, I have a inline three Merc and it is very smooth. It's good to have choices! Is this a great country or what! Later |
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Posts: 459
Location: New Baden IL | Wow,
I though all you knew about was sandwiches, coffe, and smokes!
Rod |
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Posts: 152
| Mr. 2Rodknocker, I wish I would have let your mom cut my ponytail off! |
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