engines choice...90?...115?

[phantom16ft]

hi all, im new to this forum. Im from the Uk and have a phantom 16ft ex-racing boat with a tandem deck (2 seats - one infront of the other) its a great boat - 60ltr stainless fuel tank, foot throttle, transom jack, hydraulic steering, ballast tank in the frott etc.. but it had an old yam 85 on the back which gave up the ghost the other day... :(
I am now considering which engine to get but i have a low budget, most people with this hull tend to put 90hp engines on and tune them but could i get away with a v4? 115 or 130hp maybe? i can get a 1990's mercury 90 for cheap, are these tuneable? or is a yam 90 better?

look forward to you reponses, thanks

[phantom16ft]

i have also just descovered a yam 75 for sale, i hear these can be made into a 90 with bigger carbs and bigger exhaust pipes, is this right?

[David]

I don't know your boat at all, but just about any 16' boat can handle a V4, and more HP is better.

The 75 and 90 Yamaha are the same basic engine, bore/stroke. You could check the parts lists to see what components changed.

[phantom16ft]

a v4 does sound nice, would an optimax 135 be pushing it? because i have just found one of them for cheap. its 70kg heavier than the yam i had (not sure what that is in pounds) but i weigh 73kg and i have sat on the engine when the boat is in the water and it didnt go too low...

[benski]

One kilogram is equal to 2.2 lbs.

[flabum1017]

The opti will be too heavy, look around and try to find a Johnson/Evinrude V-4 bubbleback crossflow. It's a buildable motor. A looper V-4 would be a better choiceif you could find one as well. The Yam V-4 130 would be a good choice as well. I'd stay away from the three cylinder motors, the V-4's will give you better torque.

[phantom16ft]

are johnson engines reliable? They get alot of stick in the Uk for being unrelliable but there arent actaully that many around,

[Mark75H]

They are quite reliable. The early injected V6's were the problem motors once upon a time.

[phantom16ft]

ah okay, also would anyone know if a 2 stroke mercury 115 from 2004 is carbed or injected? can it be made into a 130 or 150?
As my boat is made in england many of you probably havent ever seen one, would anyone like me to post some pics?

[Mark75H]

Later inline 4's generally can not be hot rodded for more power

The Yammer 90 is a better choice

[theoldwizard]

It's all about power to weight ratio. Triples (like the Yamaha 75/90 and the old Stinger/Hustler) are hard to beat. I know some guys hear are getting good power out of old Evinrude V4s, but how much work do you want to put into it ?

If you have the cash, the new Evinrude E-TEC 90 weighs less than the new 115HO.

[benski]

What years were the bubbleback crossflow and looper V-4s made? Is there a reference bank for all this kind of jazz, and where do you find it? For the same hp class, are there any advantages/disadvantages to the Merc "Tower of Power"?

[phantom16ft]

I reckon if i get the yam i will put in a lot of work over the winter - Probably get it bored out - How much can it be bored? anyone know? (also are the cylinders cast iron lined?) then will get it ported, skim the head, new main bearings, rods, wiesco pistons, maybe bigger exhaust outlets? then put some big carbs on it, some reeds and a nice stainless prop

[theoldwizard]

I reckon if i get the yam i will put in a lot of work over the winter - Probably get it bored out - How much can it be bored? anyone know? (also are the cylinders cast iron lined?) then will get it ported, skim the head, new main bearings, rods, wiesco pistons, maybe bigger exhaust outlets? then put some big carbs on it, some reeds and a nice stainless prop
Wiseco sells piston up to 0.040 over (not that I am recommending it). Their catalog shows the 60/70 have the same bore (2.834) and the 85/90 have the same bore (3.228).

Contact the guys at Hydro Tec Marine (http://hydrotecmarine.com/) They know a lot about Yamahas and sell exhaust tuners and heads (https://www.shop.hydrotecmarine.com/categoryNavigationDocument.hg?categoryId=5).

[phantom16ft]

So what exactly is an exhaust tuner then? And what difference will the high performance head make over std head?
cheers for the help

[theoldwizard]

So what exactly is an exhaust tuner then? And what difference will the high performance head make over std head?
cheers for the help
Follow the links mate (click on the words in blue that are underlined). They got pictures ! (I suspect the head is just milled.)

Depending on what your definition of "gave up the ghost" is, that old Yamaha might be an excellent starting point. As long is no new "ventilation" in the block and the crank and some of the rods are okay, I would not be shopping for a new engine !

Start looking for a machine shop/engine builder with Yamaha experience. A 0.020 overbore, 3 new Wisecos and rings, a tuner and a shaved head and you'll be flying ! Probably under $2K if you do the tear down and assembly yourself.

You'll definitely need to re-jet the carbs so you need an experienced hand at this.

[phantom16ft]

im quite experianced with tuning small 2 stroke racing motorbikes 125's and 250's so i have mechanical knowledge just not quite specific to boat engines, my old 85 is absolutely knackered, its thrown a rod and its an early 1980's model which has dodgy electrics and alot of corrosion in the water channels, im currently looking at a decent yam 75 to work on though, so if i get the carbs off a 90 could i bore out the venturi 3mm or so then re-jet? or is there a bigger carb upgrade? A 0.020 overbore would give me how much extra cc? cheers guys
EDIT: just worked out a 54cc increase, would this make much difference? I would prefer the 0.040 overbore 108cc increase, im power terms, roughly how much increase should i expect with mods?

[theoldwizard]

How fast you go only depends on how much money you have in your pocket !

Find a good Yamaha 85/90 triple and you'll go faster with less upgrades.

[Mark75H]

just worked out a 54cc increase, would this make much difference? I would prefer the 0.040 overbore 108cc increase, im power terms, roughly how much increase should i expect with mods?

That will give you no increase that you will notice

[phantom16ft]

That will give you no increase that you will notice

so is there any point in boring out the block then?

[Mark75H]

Nope.

[phantom16ft]

but surely with other mods it would help to have more cc?

[benski]

Volume is volume. Milling the head will increase the CR, and reduce the cc's of your motor. You will probably be ahead if you just stick with a 90 and spend some hours getting it set up, as referenced above. Run good, clean premium gas (@ 8 plus dollars a gallon US!) synthetic lube and oil and relax..Just my.02 US cents worth..

[mike bryan]

milling the head will reduce the cc's of the combustion chamber but not affect the cc displacement of the engine.

[theoldwizard]

Volume is volume. Milling the head will increase the CR, and reduce the cc's of your motor. You will probably be ahead if you just stick with a 90 and spend some hours getting it set up, as referenced above. Run good, clean premium gas (@ 8 plus dollars a gallon US!) synthetic lube and oil and relax..Just my.02 US cents worth..
:iagree:

[benski]

michael b:
If the bore and stroke remain the same, and the cc's of the combustion chamber are reduced, isn't that a decrease in the total volume of the engine, or am I mistaken somewhere? Please help. Maybe the head volume isn't calculated in engine displacement..I don't know.

[theoldwizard]

michael b:
If the bore and stroke remain the same, and the cc's of the combustion chamber are reduced, isn't that a decrease in the total volume of the engine, or am I mistaken somewhere?
Technically you are correct.


Maybe the head volume isn't calculated in engine displacement.
The volume of the head is constant and is not included in the "swept volume" of a cylinder. "swept volume" x number of cylinders = displacement

[mike bryan]

last statement is correct.changing head cc only affects compression ratio.

[JP Love]

90 Merc is a good engine too .... Reliability... Good to do lot hours. Simple like the Yamaha.. J-P Love

[theoldwizard]

90 Merc is a good engine too .... Reliability... Good to do lot hours. Simple like the Yamaha.. J-P Love
What year Merc are you referring to ? 2S or 4S ?

[phantom16ft]

Volume is volume. Milling the head will increase the CR, and reduce the cc's of your motor. You will probably be ahead if you just stick with a 90 and spend some hours getting it set up, as referenced above. Run good, clean premium gas (@ 8 plus dollars a gallon US!) synthetic lube and oil and relax..Just my.02 US cents worth..


do you mean synthetic gear lube? i was looking to maybe boost from 90hp to 100hp or maybe higher, should this be possible? and which mods are needed?

[theoldwizard]

do you mean synthetic gear lube? i was looking to maybe boost from 90hp to 100hp or maybe higher, should this be possible? and which mods are needed?
To make that kind of power you will definitely need a milled heads (which means premium fuel, minimum) and an exhaust tuner. Synthetic gear lube should be worth a couple of horses.

[phantom16ft]

so, keep the cc stock, milled head, exhaust tuner, bore out the carb a few mm and rejet how much hp (roughly) would you estimate i would have?
what squish would i be after? (mm)

[JP Love]

Tree cylinders since 1987 are all good engines 75 to 90HP Merc... The 115 more displacement in 1994 reliable but like fuel no good on cruise speed... The 90 Mercury between 3000-4200 rpm do best millage there.. the 115 same at 3000 to 5000.. Love fuel.. I have a new one 1993 and sale in the second summer for that. J-P Love

[phantom16ft]

For 100 - 115 hp out of a yam 90 would i need to rebuild the bottom end if the engine is in fairly good nick? (pistons and rods + rebore) also is nikasil plating in the cylinder advantageous in any way? (all my bikes have nikasil plated barrels) And can i port it myself? (DIY job) or does it need to be done professionally on a flowbench? (bearing in mind i have no porting experience as my bikes barrels all get sent off but as i live in the UK i dont think anyone ports boat motors that i know of.... cheers for all the help guys