4.3 L merc I/O perf on Seafari

[rhody98]

McGillicuddy recently requested the 1969 Boating article on the Seafari. With the boating season over in RI ("pulled" is the term recently coined in one of the posts), Gilly's request prompted me to re-read.

The performance #'s for the seafari with a 140 hp, 4 cyl sterndrive can be summarized from the article (pg 80) as follows:
1500 rpm, 6.1 mph, 3.9 mpg
2500 rpm, 19.2 mph, 5.3 mpg
3000 rpm, 26.5 mph, 5 mpg
3500 rpm, 31.9 mph, 4.4 mpg
4400 rpm, 39.6 mph, 3.8 mpg

I have a 4.3 L V6. In very good condition. Based on GPS my speed vs rpm is very similar to the numbers reported in the article, except I top out at low 40's at 4400 max rpm. I don't have fuel use gauge but based on my mileage vs fill-ups I believe my gas consumption does not differ substantially from the #'s in the article either....perhaps I am under 5 mpg. This is with a mirage 19p, 2 persons, full tank, top down.

Motor sounds great, very dependable over 50 hrs this summer and I am not a speed demon. But very curious why the performance on my 6 cyl is same as that reported for 4cyl, while adding 200 lbs in weight?????

[McGillicuddy]

Rhody,
Pretty impressive numbers. I would guess your numbers are comparable due to the greater hp engine engine not having to work as hard to push the load. Figure if you have the 190 hp 4.3 you're getting at least an extra 50 hp and if you have the 220 hp model you have that much more hp, plus fuel injection, which likely lends itself to better economy. Especially with an efficient hull design. If the engine is running "relaxed", I'm betting it gets better economy. Don't know if there is any truth to this guess but it sounds about right.

[rhody98]

Its the 190 hp model. Very marginally better performance, if at all, and probably slightly lower fuel economy vs the 4 cyl, which makes me think my engine is not tuned properly. If so I suspect the ignition system.

WOT is 4400 rpm so I dont think the prop is a problem.

There may be no problem at all and I am simply proof that there is no advantage of the V6 over the inline 4 on the seafari.

[McGillicuddy]

Rhody here's some merc performance numbers from their website
http://www.mercurymarine.com/look_de...ecks&mercV6=14

With the exception of running 400 rpm below ideal, it sounds like you're getting nice performance.
If you were thinking you might get better numbers than the 4-cyl consider this thought. Your added weight is farther aft. It may be giving you a hair more bow rise causing you to push a little more water. Also, if you have the 15-1/4" dia prop it to may be pushing more water than a smaller wheel of greater pitch, maybe slightly reducing your rpm from that ideal 4800... Remember - I really don't know squat about this stuff - just been thinking about my own wheel a lot. That being said, I wonder if a smaller 4-blade wheel with similar pitch wouldn't lift your stern a bit & squeeze just a little more out of her.

[3rdday]

That 4.3 is bulletproof great engine, hard to kill them!

[rhody98]

Thanks Gilly, yes the stern could use a lift and for that reason I too was interested in the recent discussions on the 4 blade props. My main interest is best performance at 3000 rpm.