Re-Power w/ new Suzuki 90...

Fr. Frank · #1 01-12-2011, 09:53 AM

Providing you're running the ADI electronic ignition, you're going to get marginally better performance from the Merc, than you are from the Suzuki. The Merc also weighs 50 lbs less at 296 lbs. The downside is that the Merc can use 30-40% more fuel, and that mixed two-stroke fuel costs more than the straight gas for the Suzuki, too.

That being said, the inline 6 cylinder "Tower of Power" motor is far and away my favorite outboard motor. With the right Boysen reeds, ported pistons, right carbs and jetting and free exhaust, the 89ci/1450cc liter 115 Mercury can produce 200 hp, and do it reliably. You just can never run it between 6500 and 7000 rpms. 9000 is okay, but run it at 6800 and it will self-destruct from harmonics. (I used to run a 1500XS 150 hp at 80+ mph on my 14'10" Cacci Craft, which was a Checkmate V-mate copy. The boat was named "Kamikaze Express")

Tim "Bigshrimpin" posted some amazing test results from Land n Sea from these motors a few years ago, including taking the big displacement version (the 99ci/1600cc 140/150 hp) and making it produce 240 hp at 9200 rpms.

povertysucks · #2 01-13-2011, 12:24 AM

Yea, I guess I really can't go wrong with either choice. I mean one is super light for a 4 stroke, packs a punch for it's size, and has an awesome name to back it up. The other is a great performer, just a tad bit of a gas guzzler. Nothings perfect eh?

-Brad

McGillicuddy · #3 01-13-2011, 01:12 AM

I run an '83 blue band Merc 115 on a 20' Seafari. I'm not sure what blue/red signifies maybe salt vs fresh or 20 vs 25" shaft?

At any rate I get best performance with a 15p Black Max prop. 36mph@5500 rpm 2 mpg.
Best economy comes @3750-4200 rpm getting 2.5 mpg at 23 to 27 mph. Fine motor but I'd swap it for a dfi 2S or that Zuke in a heartbeat if I had the extra $8K.

It would easily double my range and likely come close to tripling it. That is huge on tuna excursions.

Etec 90 is about 325 lbs and probably gets better economy than the Zuke throughout the rpm band... I understand the desire for a 4 stroke and that Zuke is the best of the lot, but check out that etec 90... and compare boat performance tests... I think you'll be surprised by what you find...

povertysucks · #4 01-14-2011, 12:29 AM

I actually forgot about the Etec 90 lol. I will have to ponder that thought too. But for now, I think the ol' Merc' will do just fine.
Mcgillicudy- so you'd say your merc is alright on gas?

McGillicuddy · #5 01-14-2011, 04:56 AM

It does ok considering its got three carbs.

It sucks gas at low speed so if you're planning on idling a lot or slow trolling get kicker motor.

I really like the smooth, even, seemingly effortless performance of the motor. The inherent balance of an inline 6 motor has a lot to do with that. But the right prop is the key to performance. My $50 13-3/4 x 15p Black Diamond aluminum prop bested 3 other props I tested in in top speed, economy, and grip but most clearly on the hole shot. Using some online calculators I'm getting about 7% slip (WOT)which I think is very good for an old design right out of the box. It gets out of the hole and on plane immediately. It cruises around 2.3-2.5 mpg measured by gps/navman inline fuel meter.

The sooner you get on plane the better with these hulls. The Etec has a huge advantage at low speed only burning what it needs. I've seen reports citing 26 mpg on a 20' hull (not a SeaCraft) @ 700rpm. Same for the Zuke 90 but keep in mind 7 or 8k will buy a lot of fuel.

Here are my results:
Quicksilver Black Diamond 13.75x15 Al
RPM SPEED MPG GPH
1000 4.10 1.80 2.28
1500 6.40 1.74 3.68
2000 7.30 1.50 4.87
3000 17.70 2.20 8.05
3500 21.00 2.30 9.13
4000 23.60 2.40 9.83
4250 26.50 2.45 10.82
4500 29.00 2.50 11.60
5000 31.00 2.40 12.92
5500 35.90 2.10 17.10

You'll notice a big gap where I just couldn't run at 2500 RPM. Just past 2K rpm it would bust up on plane and the motor would simultaneously rev up and haul out... I couldn't control its desire to get on plane.

Enjoy your new setup!

povertysucks · #6 01-15-2011, 02:18 PM

Very nice report. I have the same prop on my boat now. It's very hard for me to fathom almost 10 gallons an hour when your just cruising lol. I only have a 30-40 gallon tank I believe. I'm gonna be burning alloott of it.
Brad

Fr. Frank · #7 01-15-2011, 07:45 PM

Quote:

You'll notice a big gap where I just couldn't run at 2500 RPM. Just past 2K rpm it would bust up on plane and the motor would simultaneously rev up and haul out... I couldn't control its desire to get on plane.

Every motor does that. That because as soon as the boat gets on plane, it takes a lot less hp to maintain that planing action. It may take 60% power to get on plane, but then only 40% to stay on plane. So at 50% power it won't plane off, and at 60%, you've got half again as much power as you need to stay on plane.

The question is, can you extremely carefully throttle back to 2500 rpms without falling off plane?

eggsuckindog · #8 01-16-2011, 09:23 PM

Just some quick numbers
$8000

@ $3 per gal = 2600 gals

66 tanks of fuel

@ 2 mpg = 5200mi

thats alot of boat riding - just say'in

FishStretcher · #9 01-23-2011, 11:41 AM

There is a 150 hp tower of power for sale locally, and the thought has me interested. But I don't think I need to replace a 86 Yamaha with a 74 Merc.

Quote:

Providing you're running the ADI electronic ignition, you're going to get marginally better performance from the Merc, than you are from the Suzuki. The Merc also weighs 50 lbs less at 296 lbs. The downside is that the Merc can use 30-40% more fuel, and that mixed two-stroke fuel costs more than the straight gas for the Suzuki, too.

That being said, the inline 6 cylinder "Tower of Power" motor is far and away my favorite outboard motor. With the right Boysen reeds, ported pistons, right carbs and jetting and free exhaust, the 89ci/1450cc liter 115 Mercury can produce 200 hp, and do it reliably. You just can never run it between 6500 and 7000 rpms. 9000 is okay, but run it at 6800 and it will self-destruct from harmonics. (I used to run a 1500XS 150 hp at 80+ mph on my 14'10" Cacci Craft, which was a Checkmate V-mate copy. The boat was named "Kamikaze Express")

Tim "Bigshrimpin" posted some amazing test results from Land n Sea from these motors a few years ago, including taking the big displacement version (the 99ci/1600cc 140/150 hp) and making it produce 240 hp at 9200 rpms.