Yamaha engine mods.

[SKIFFY123]

Hello everybody,
New to the forum not boating. I have a 90 hp yamaha that I would like to get a few more hp out of. I can not go to a bigger motor because of weight. What can i do. I have it propped right.

Never souped up an outbourd just v8 car motors any help or direction would be appreciated.
thanks

[SKIFFY123]

great forum

[Mark75H]

I looked up the weight of the 90 and some other motors. There are other motors within 60 pounds of the 90 that make much more power. If 60 pounds is that critical, 90 is probably all you should be using anyway.

[SKIFFY123]

what motors are within 60 lbs? I looked when I purchased the yamaha. everything was way heavier. Are you refering to some of the old school motors?

[Mark75H]

Yepyep

[SKIFFY123]

alrighty then. lay some models on me.

[David]

You should start with set up before motor mods or re-powering. I say that, but I had great success putting a faster boat under the same motor. Some boats just aren't made to go fast.

Promax 225, 350 lb
For my money, as good as it gets, power to weight. The 2.5's have more power, but at the cost of regular re-ringing, and more expensive fuel.

OMC V6 Eagle (150-175 60 degree), 370 lb
OMC looper V4 90 degree 365 lb
OMC looper V4 60 degree 319 lb
OMC cross flow V4, 301 lb
Any random V6 Merc 'fishing' motor is a round 400 lb

90 Yamaha = 256 lb

[Mark75H]

Those are all so much heavier than the Yammer I don't think they are in the running.

Inline 6 Mercs come in around 300 and go up to 155 hp

[SKIFFY123]

are those the mercs from the early '80's ? This is going on a javilin 17 ft bass boat that is set up for cruising.

[David]

Yup, I'd forgotten about inline 6s as they are old. Not a ton more power than a crossflow V4, but maybe easier to prop.

What's the boat?

[Mark75H]

Yup, I'd forgotten about inline 6s as they are old. Not a ton more power than a crossflow V4, but maybe easier to prop.

The old crossflow V-4s were about the same weight ... probably another very good motor to consider for the weight.

Another reason to consider the V-4 crossflow ... they are kicking I-6 butt in the "Trihull" race class limited to 99ci motors. The I-6's have been the radar shootout winners for top speed on the Trihulls, but the V-4's dominate on the circle.



javilin 17 ft bass boat that is set up for cruising On that boat, for that application ... just leave the 90 stock and enjoy

[DoktorC]

The old crossflow V-4s were about the same weight ... probably another very good motor to consider for the weight.

Another reason to consider the V-4 crossflow ... they are kicking I-6 butt in the "Trihull" race class limited to 99ci motors. The I-6's have been the radar shootout winners for top speed on the Trihulls, but the V-4's dominate on the circle.


On that boat, for that application ... just leave the 90 stock and enjoy

What's an old ProV115 weigh? Then you get all the yamaha goodness AND keep your rigging.

[Mark75H]

What's an old ProV115 weigh? Then you get all the yamaha goodness AND keep your rigging.

My book says about 360 ... 100 more than the 90

[Markus]

The Yamaha 90 can certainly be modified. There was a thread here not long ago from a Norwegian guy with one on a Hydrolift offshore boat.

I don't know whom to talk to in the US, though. Maybe Hydrotec...

[SKIFFY123]

IF I keep the yammy I do not want to keep it stock that is for sure. Stock is to plain.

[Jason Johnson]

What hull are you running, My 90 yammi runs 70.5mph on GPS on a 14' Allison. 26p merc cleaver "worked" 58-5900rpm.

I am in the process of building a very modified 90. Light flywheel, big carbs, TDR reeds and mod. cages, ported (and finger ported) block, light pistons pins and rods, custom tuner, 13" midsection, LWP, AND IT WILL BE FINISHED REAL SOON.

A 90 yammi is to me the best engine in that range, parts are abundant, easy to work on and modify, takes mods well, ecttt......I LOVE MY YAMMIS, I own ten and I'm still buying em.

[David]

I still think
1. start with set up before modifying the motor
2. easier to buy a bigger motor than to modify a motor
Just about any 17' hull can handle a V4

[Jason Johnson]

Just went back and caught the 17' Javalin, yes step up to a V4, 130 Yammi be a good choice.

[aeneas]

Hi,
I think Markus means my engine... It is a Yamaha 90 mod. I think you can contact Fast Fred on this forum (http://forums.screamandfly.com/forums/showthread.php?t=55871&highlight=hydrolift) - he has given some interesting input... Hydrotec absolutely!

I think you should keep your engine - they respond well to tuning and there are parts out there. I have Hydrotecs High Performance head and tuning pipe and off coarse so much more... Pictures with labbed Winrace Cleaver 14x25...

http://www.boatlife.se/forum/uploads/monthly_05_2008/post-2893-1211145474.jpg
Bob's Big Foot single hose nose cone
http://www.boatlife.se/forum/uploads/monthly_05_2008/post-2893-1211145772.jpg
Engine block bored, ported, finger ported, shaved/planed with 2x oversize Yamaha pistons lightened/balanced on rods.
Hydrotec High Performance head adjusted to the planed block...
Carbs bored/taken up to maximum with 44mm Keihin FCR velocity stacks...
Jets changed from 160 to 175.
Hydrotec High Performance exhaust pipe.
Fiber reeds.
http://www.boatlife.se/forum/uploads/monthly_05_2008/post-2893-1211145966.jpg
A good pull from 4000rpm to 6800...
http://www.fendern.se/propeller/uploads/post-3459-1211405907.jpg
Hydrolift T-17 - 24 degree V with a pad.
http://www.boatlife.se/forum/uploads/monthly_05_2008/post-2893-1211145876.jpg

wbr aeneas

[SKIFFY123]

What kind of speed are you getting from that set up? One reason for keeping the 90 is fuel cost. Who makes that lower unit and prop?

[aeneas]

What kind of speed are you getting from that set up? One reason for keeping the 90 is fuel cost. Who makes that lower unit and prop?

With two people and about 40litres of fuel on board just under 70mph on the first testrun. Will do over 70...

Very good thinking! It is an economical engine.

The lower unit is a nose cone from Bob's Machine shop (http://www.bobsmachine.com/). I think they can put it together for you. Mine is put together like racing lower with shims etc. The propeller is a Norwegian Winrace (http://www.winracepropellers.no/) Cleaver 14x25 racing prop (USD 1700/NOK 8125;- you can deduct the VAT 25%). You fill in a form with specs and wanted performance and they make it for you... Top stuff! (If you order it's for Offshore 1,3litre...)

I think you should contact Fast Fred! He could tune your engine proper... If he does other engines than racing...

I heard of a Yamaha 90 taken up to over 160hp here in Norway... That was too much - didn't last. But 130-140hp should be ok with reliability. Over 130 and you will need other carbs etc.

[SKIFFY123]

I am stoked about my little yammy. I did some home work before buying it. I just did not realize the potential for making that kind of horse power! I just need contacts and or web link to get the ball rolling/prop turning.

[aeneas]

I could give you three names to really serious racing tuning people here in Norway. In the US I would absolutly contact Fast Fred (http://forums.screamandfly.com/forums/member.php?u=4365) or Hydrotec (http://www.yamaha-rebuild.com/phasekits.htm).

Good luck!

[Jason Johnson]

Skiffy if you want one already done, there is one on central to north Fl. 15 inch mid, LWP, Build power head, lil motor hauls butt. Actually the whole rig is for sale. it runs low 80s with the top end prop.

If you want to build yours I will help also if you want. I am almost finish with my new one. Light flywheel, TDR reeds, Jay smith lightened rods, wiesco pistons / pins, built tuner, 13 inch mid, bobs low water pickup, milled & rechambered head, ported & finger ported block, bored carbs. This thing shoud roll pretty hard, HP don't know, but my stock 90 ran 70 on the Alli, and this one will replace it.

[SKIFFY123]

The sad part is the motor i have is a 1999 and was just rebuilt 5 months ago. Maybe sell mine and look for one already built up. I live in central fl. what hull is the on the one in north fl? do you know what he is asking for just the motor?

[aeneas]

Skiffy if you want one already done, there is one on central to north Fl. 15 inch mid, LWP, Build power head, lil motor hauls butt. Actually the whole rig is for sale. it runs low 80s with the top end prop.

If you want to build yours I will help also if you want. I am almost finish with my new one. Light flywheel, TDR reeds, Jay smith lightened rods, wiesco pistons / pins, built tuner, 13 inch mid, bobs low water pickup, milled & rechambered head, ported & finger ported block, bored carbs. This thing shoud roll pretty hard, HP don't know, but my stock 90 ran 70 on the Alli, and this one will replace it.

Have you got any pics of your engine? What boat are you running it on? What's an Alli?

SKIFFY123, what boat have you got?

[Jason Johnson]

14' Allison, I love my boat

[aeneas]

More pics please!

That must kick rear parts with a tuned Yamaha 90 on it! :)

[Jason Johnson]

This pic was not at speed, this one I was slowing down mabey about 60 at best. When I install the mod 90, I will have a professional come take pics.

[Roflhat]

Anyone got a link to velocity stacks to fit yam 90 carbs?
Cheers

[Markus]

Velocity stacks are pretty, but will not make the engine run better...

[powerabout]

Velocity stacks are pretty, but will not make the engine run better...
they will certainly alter the way the carbs work perhaps only smooth out the airflow that removing the silence base caused to be not as good as it was with it?

[Roflhat]

If you tune your engine to suit once the stacks are on they will make a difference, admittedly not a huge one but every little helps

[Mark75H]

they will certainly alter the way the carbs work perhaps only smooth out the airflow that removing the silence base caused to be not as good as it was with it?

Sometimes, but not always

[Markus]

Never seen or heard of anyone making gains with velocity stacks on a Yamaha.

[powerabout]

basic cfd, air flow into a sharp cut off pipe is poor compared to the same pipe with a bellmouth but a bellmouth is not a velocity stack.

[Cougarman46]

Hi,
I think Markus means my engine... It is a Yamaha 90 mod. I think you can contact Fast Fred on this forum (http://forums.screamandfly.com/forums/showthread.php?t=55871&highlight=hydrolift) - he has given some interesting input... Hydrotec absolutely!

I think you should keep your engine - they respond well to tuning and there are parts out there. I have Hydrotecs High Performance head and tuning pipe and off coarse so much more... Pictures with labbed Winrace Cleaver 14x25...

http://www.boatlife.se/forum/uploads/monthly_05_2008/post-2893-1211145474.jpg
Bob's Big Foot single hose nose cone
http://www.boatlife.se/forum/uploads/monthly_05_2008/post-2893-1211145772.jpg
Engine block bored, ported, finger ported, shaved/planed with 2x oversize Yamaha pistons lightened/balanced on rods.
Hydrotec High Performance head adjusted to the planed block...
Carbs bored/taken up to maximum with 44mm Keihin FCR velocity stacks...
Jets changed from 160 to 175.
Hydrotec High Performance exhaust pipe.
Fiber reeds.
http://www.boatlife.se/forum/uploads/monthly_05_2008/post-2893-1211145966.jpg
A good pull from 4000rpm to 6800...
http://www.fendern.se/propeller/uploads/post-3459-1211405907.jpg
Hydrolift T-17 - 24 degree V with a pad.
http://www.boatlife.se/forum/uploads/monthly_05_2008/post-2893-1211145876.jpg

wbr aeneas

Nice set up

[PanRonnie]

benefits of a properly shaped bell

[phillnjack]

back in this topic it says about fuel consumption....
well you cannot mod an engine and get power gains and not be adding more fuel, for example if you get 9 gallons and hour from a 90 then hit it up to
have it pumping out 120hp it will use around the same amount of fuel as the normal 120, there is just no way you get more power without getting stung.

so economy of the motor is never a concern, if it is then leave it alone or you will be crying at the fuel pump.

[Mark75H]

back in this topic it says about fuel consumption....
well you cannot mod an engine and get power gains and not be adding more fuel, for example if you get 9 gallons and hour from a 90 then hit it up to
have it pumping out 120hp it will use around the same amount of fuel as the normal 120, there is just no way you get more power without getting stung.

so economy of the motor is never a concern, if it is then leave it alone or you will be crying at the fuel pump.

Generally true at the 90/120 increment, but at smaller increments there are ways to get more power from the same amount of fuel.