(Sam Rayburn Reservoir Specific)
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| Name: |
LonghornBoater
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| Subject: |
4.3 ltr 190 vs. 220
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Date:
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8/20/2013 12:16:41 PM
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In a 19-20 foot bowrider, is the extra money for the 220hp MPI vs 190hp carb version of the 4.3 ltr worth the money? Is there any rational to jump to a V8? Usage will primarily be cruising with intervals of tubing for the grandchildren. This is hopefully going to be my "last" boat.
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| Name: |
CAT BOAT
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| Subject: |
4.3 ltr 190 vs. 220
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Date:
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8/20/2013 2:44:47 PM (updated 8/20/2013 3:16:34 PM)
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I have a strong opinion on that subject. Make your comparison 4.3 vs. 5.7. If you go with the larger engine, and operate it the way you say you plan to, you will use LESS fuel. You will also enjoy better performance with the larger V-8 when you need it. The larger engine will have a more aggressive propeller pitch that is measured in inches. Example, a 4.3 ltr engine will probably be equipped with a 19"pitch. A 5.7 ltr would most likely have a 23" pitch propeller. That means (provided gear ratios are the same) the 4.3ltr boat would travel 19" through the water every prop turn, and the 5.7 23 inches per turn. Now, consider this.... The 4.3 ltr is working at a higher RPM range, burning fuel while the 5.7 is operating at a much lower RPM range working less while maintaining the same speed. Here is a speed chart for comparison.
Prop pitch X RPM (_____) divided by Gear ratio X 1056 = SPEED
You must decuct a percentage for Prop slip. 8-10% for speed hulls/12-15% for heavier boats, you get the picture.
Example.
23" X 5,000 Engine RPM = 115,000
1.50 gear ratio X 1052 = 1578
115,000 divided by 1578 = 72.88 MPH. Use a slip factor of say 15% for the boat you speak of and you get 62 MPH.
Do the same calculations for the 4.3 ltr with a 19" prop and you will get the picture. However, if you run both set-ups wide ass open all day you will use MORE fuel in the 5.7 BUT you will travel a whole lot farther. I have people ask me all the time "How much fuel does your boat use"? (speaking of the Catamaran with twin engines) And the answer is "Probably less than yours". The gear ratio on performance boats are normally 1.115 to 1 and prop pitch 32-36" range.
36" X 2200 Engine RPM + 79,200.
1.15 X 1056 = 1214.40
79,200divided by 1214.40 = 65.22 Take 9% for slippage and you get 59.35 MPH. ; )
I hope this helps. Sorry for the long answer.
Respectfully,
Steve
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| Name: |
LonghornBoater
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| Subject: |
4.3 ltr 190 vs. 220
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Date:
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8/20/2013 2:50:08 PM
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Thanks as always. The answer is exactly the type of advice I was looking for.
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| Name: |
Lifer
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| Subject: |
4.3 ltr 190 vs. 220
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Date:
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8/20/2013 9:28:17 PM
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What he said. Never under power a boat. I went from a 40 to a 65hp on an old pontoon. Cut feul consumption dang near in half.
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| Name: |
GoneFishin
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| Subject: |
4.3 ltr 190 vs. 220
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Date:
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8/20/2013 10:07:35 PM
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No one ever complains about too much power.
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| Name: |
Summer Lover
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| Subject: |
Unless
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Date:
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8/21/2013 8:55:27 AM
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It is someone else who has the power...
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Unless it is attached to a boat that is either too long or too fast... at least on Lake Martin.
Crappy : )
(Just outside of Nashville)
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