New Engine Advice for 2001 20 Seacraft MA

[Bushwacker]

Originally Posted by FishStretcher

. . . With 4 strokes, one worries about burning exhaust valves at WOT if you run there for a long time. Is there a similar issue with an etec? Specifically running an etec 90 at WOT for extended periods . . .

There are NO exhaust valves to burn on a 2-stroke E-TEC! And the harder you run 'em, the more oil they get, so the only limit on time at WOT is the thickness of your wallet! Terry England's 90 hp E-TEC seems to do a fine job pushing the 19' Marshtackie stern rider loaded down with 4 divers, tanks, all their dive gear, and a big cooler full of fish!

If you want to avoid burning exhaust valves, which is the weak link on any 4-stroke engine, the best thing to do is hook a vacuum gauge to the intake manifold just downstream of the carb or throttle body and observe a cruise limit of 5 "Hg. This is about 75% of max power and is the "Max Continuous Power" rating on the Lycoming/Continental piston engines used on light aircraft. These are premium heavy duty engines that have Stellite valve seats, positive valve rotators, and exhaust valves filled with liquid sodium for improved heat transfer and better cooling. (If I was considering a 4-stroke outboard, I would definitely ask if it had this sort of heavy duty parts in it!) Most of my engineering colleagues at Pratt & Whitney who ran inboards were well aware of this limit and did not run less then 5"Hg for very long. Many of them observed a limit of 7" and could get as much as 2000 hours before needing a valve job.

One friend, who was not an engineer, ran a vacuum gauge but didn't really understand the max continuous power concept, so he just set the throttle at 5" Hg, and whatever speed that produced is what he cruised at all the time! After about 300 hours, he not only had burned exhaust valves, the heads were cracked! And this was on a 302 Ford engine, which does not have the cylinder head hot spot due to adjacent center exhaust ports like the small block Chevy, so it typically has better exhaust valve life! This guy removed the I/O and converted his 21' Wellcraft Nova to a V-6 Merc outboard!

[FishStretcher]

I was hoping that's the case! I can't use a lot more power as the boat isn't that heavy, save a mulch transom. It has small tanks and no livewell or leaning post. It does have a big t-top.

If the etec 90 is lighter than a 1999 F100 even with a 25" leg, versus my 20" that I have now then that's great
Right now only 1/4 of the time can I run WOT even with the F100, then the Etec sounds nice. I didn't check vacuum but I can't run much over 4800 RPM on my F100 which redlines at 6000 (and I can do 6000 RPM in light boat condition, 5700 loaded down). If I do run faster, I fly off the tops of waves and slam in Buzzards Bay chop.

Thanks for the verification. I think I'll add a vacuum gauge to check, and think about a repower.

[Terry England]

3500 rpms, 18.9 knots - 4 mpg......
20", 2.0 to 1 gear with 13-3/4 X 14 - 3 Blade Power-tec*
*(via Ken at Propgods)

[jdm61]

Someone posted the California ARB numbers for a few engines on that other big forum and according to them the latest Merc 115 CT and the Zuke 140 both put out 126 HP. The 20 inch Merc with the CT lower unit weighs 363, the 20 inch Zuke 394. The 25" adds 10 pounds on the Zuke. Mercury did noblest the weight of the 25" model on their website. .