Powerhead Cowl Modifacations for Performance

[olboatman]

Would like to hear about (and pics if ya have them) some mods to cowls done for performance improvement and the theorys for them. Thanks
Gary

[racervboat]

Gary ive cut holes in the front [big ones] vents in the side,took out the rear diffuser no real gains but louvers look cool.Ran my pacecraft with mod motor and big holes in the front against tha Allison [same motor] but he was running a 1975 hood no vents at all and that hood has no cut out in the rear in the grab handle at all and we still ran the same with no bottom to top end difference ?

[FMP]

I opened up the rear top vent at the tilt grab and lower pan vent. Only noticed a difference on the hottest humid days when jetted fat but suspect better air all the tine. Top end ran out better, not a rude but still.

[racervboat]

The two motors I just mentioned one was opened up all over the other no vents in hood at all only air it got was from the pan vent and both motors were jetted the same.No significant improvement at all ?

[FMP]

You run carb covers or boxes?

[racervboat]

no covers

[FMP]

Extra air potential never hurt

[specboatops]

^ until there's a fire...

[FMP]

Sure

[specboatops]

just sayin -

[FMP]

Best to stay in bed that day

[racervboat]

best get some insurance than LOL

[FMP]

Prophylactic?
Any difference between the 85 / 140 pan vent?

[racervboat]

some were cast closed some had the bolt in plastic cover.

[spybot]

I found a few on this Forum from mid 70s till the early 80s Some are from the V8s
394770394771394772394773394774394775
I think the general consensus is as racervboat said "no real gains but louvers look cool"

[olboatman]

What I my try is to cut a hole in front of the intake(carbs) with a plate spaced in front of the hole to keep water,debris out. Then put a foam dam around the intake so all the air it gets is fresh (cool) from the outside. Makes since as this system has been used in the auto industry for yrs. I am in the process of desiging one for my V4. I also opened up the rear hole under the handle and am considering vents on the sides up front as my pan is solid and want to let the warm-hot air out. Got a lot of pics to go thru and put together soon for you guys since its been a yr ago I started this project.
Gary

[spybot]

What I my try is to cut a hole in front of the intake(carbs) with a plate spaced in front of the hole to keep water,debris out. Then put a foam dam around the intake so all the air it gets is fresh (cool) from the outside. Makes since as this system has been used in the auto industry for yrs. I am in the process of desiging one for my V4. I also opened up the rear hole under the handle and am considering vents on the sides up front as my pan is solid and want to let the warm-hot air out. Got a lot of pics to go thru and put together soon for you guys since its been a yr ago I started this project.
Gary
Looking forward to seeing what you have.

[powerabout]

When I look at those OMC cowl vents I'm thinking they would pull air out of the cowl?
I wonder if anyone ever put a modle in a wind tunnel
F1 now has sealed up cowl with hose to boat ( just like a Sea Drive, lol)

[olboatman]

When I look at those OMC cowl vents I'm thinking they would pull air out of the cowl?
I wonder if anyone ever put a modle in a wind tunnel
F1 now has sealed up cowl with hose to boat ( just like a Sea Drive, lol)

I looked at a couple F1 induction systems at the Gulfport Fl race in April. The intake hose from the cowl goes into the air scoop on the boat that has a water baffel in it to keep the water out of the mota. I am far from the first to consider ducting cool fresh air to an outboard intake!
Gary

[racervboat]

As long as its not trying to force air into the carbs as to affect the reeds from opening and closing.

[olboatman]

As long as its not trying to force air into the carbs as to affect the reeds from opening and closing.
I understand what you are sayin Ken as that is another reason for the name plate in front of the opening I cut in the cowl. I saw vents in the F1 cowls to let the pressure out! In other words we are NOT lookin for "Ram Air" as some of the muscle cars had. lol
Gary

[FORBESAUTO]

394830This is how I done my fishin cowl. Cut the front out on each side of the center support directly in front of carbs. Got the front cover off an old clam shell type cowl. Made some spacers to set the cover off the cowl some to allow air to go around. Sounds kinda like what you are wanting to do. Can't say I saw any improvement whatsoever though, other than noise.

[Hupiveneilijä]

This is how i did mine.

[AZMIDLYF]

Saw this the other day on a sponsoring S&F vendor's site and thought it was good looking:

394834

[olboatman]

This is how i did mine.
I like this too!!! When the cowl is on does it seal to the plate behind the carbs?
Gary

[racervboat]

No it does not gary but its close as you have a newer cowl,omc trying to make it look small as they could.

[Forkin' Crazy]

Here is one I modified. I kept the slots high and being cut in the angle of the cowl does create some what of a ram effect. I glassed up the rear handle because some cowls will suck in water from the spray, and I wanted it more air tight.

394839

[Forkin' Crazy]

Rear view.

394840

[racervboat]

cool dwilfong but any gains in performance?

[Hupiveneilijä]

No it does not gary but its close as you have a newer cowl,omc trying to make it look small as they could.

Yes it dont seal. There is quite a gap in every direction. Have also raised the front of cowls handle and made several holes under that plate.

[olboatman]

This is my take on fresh air.
The stock cover goes over the front hole in the cowl when running.
Sounds killer with the resignation in the box.
Think about the ex chest and how it works.
Now look up resonators and do some reading.
http://www.me.umn.edu/~hork0004/2006-01-3654.pdf
I hate reading SAE papers my self.......................LOL

This is what I'm thinkin of ..... has to be better than suckin in hot air. AirRaid and K&N say their cold air auto systems make more hp. Would need to see dyno proof BUT it makes since considering turbo intercoolers help make big hp.
Gary

[olboatman]

Here is one I modified. I kept the slots high and being cut in the angle of the cowl does create some what of a ram effect. I glassed up the rear handle because some cowls will suck in water from the spray, and I wanted it more air tight.

394839
Paul being a Finish carpenter originally(I'm finished all right) I'm curious as to what tool(s) did ya use to cut the slots. I've been usin a Fein Multi Tool to hack at mine....I did an old 25hp yrs ago (louvers) with it but I'm always lookin for better and easyer methods.
Thanks Gary

[racervboat]

Gary or a rotozip with fine blade?

[Forkin' Crazy]

Ram air is fine, unless you are directing it down the carb throats.

[spybot]

Ram air is fine, unless you are directing it down the carb throats.
So if you force air into the cowling but not down the carbs thuis is a good thing ?

[olboatman]

Yes
If the air is forced into the cowl it should not be plumbed tight to the carbs(injection) so to force open the reeds. Allowing the intake to only draw fresh air from outside the cowl is an upgrade from stock.
Gary

[spybot]

So if i add an intake like this 396716
And open up the handle at the back of the cowling like so 396717
This will allow fresh cold air but at the same time blow the hot air out
Any thoughts on this ?
the other options is to have the scoop vertical on the front facing down and have 2 slats cut just at the back of the air silencer
Thoughts please guys

[olboatman]

What you show in the two pics is where I am goin with my 140 OMC. I cut a hole in the cowl in front of the carbs, added a plate about an inch off the hole to break the air flow and keep out water. Also I opened up the hole under the rear handle that I tipped up so to act as a venturi to suck air out the rear. When I get the cowl back from the vinyl shop I'll post some pics with the rest of the project.
Gary

[racervboat]

spybot gary is not using a front plastic cover in front of carbs just like my motor.

[spybot]

spybot gary is not using a front plastic cover in front of carbs just like my motor.
So the black plastic cover that is screwed to the aluminium plate is taken off ?
That would leave the 4 barrels of the carbs left open ???396754
The plastic part is circled red. This part will be removed ?
Andy

[spybot]

What you show in the two pics is where I am goin with my 140 OMC. I cut a hole in the cowl in front of the carbs, added a plate about an inch off the hole to break the air flow and keep out water. Also I opened up the hole under the rear handle that I tipped up so to act as a venturi to suck air out the rear. When I get the cowl back from the vinyl shop I'll post some pics with the rest of the project.
Gary
Look forward to see it Gary
Andy

[racervboat]

Yes and the alum casting is cut down around the carbs except the two mounts that hold throttle and shift cables.

[spybot]

Go it. Is there any gauze or mesh over the throats or the alu thats left ?
Is it just plain ?
Andy

[racervboat]

just plain,but were not running the boat down a dirt road LOL

[spybot]

Thats true but over here at every loch we have a small fly called a midge pronounced mid-gee

https://en.wikipedia.org/wiki/Highland_midge

They are a total p.i.t.a. They attack in swarms. Not nice especially if you drive through them :eek:
They bite like hell and love the taste of blood.
I may think about some sort of gauze.
Andy

[racervboat]

Sounds like a skeeter on steroids LOL but almost all outboard motors don't have air cleaners or screens and your 85 hp sure don't so it looks like it survived the bloody critters for for 37 yrs ?

[spybot]

Fortunately i bought her 300 miles south in England Thats how hard it is to get engines in Scotland almost zero chance of getting anything above 40/50hp fishing motors.
She is in pieces now just screaming to get put back together in her new status as a 140ish sleeper :cheers:
She will be 38 and better than new this year :) Well hopefully anyway.
It can only be done with all you guys giving me pointers and advice. The whole ethos of the forum is helping each other.
Couldn't do it my self.
Andy

[racervboat]

Yeah no problem andy.

[racervboat]

You still tryin to get it done by feb 1st ?

[spybot]

Yeah thats the plan any way. i can get her on the loch before the season starts. So i have the 2nd 3rd and 4th to try her out in the loch.
If not it will have to be tidal trials. Not too keen on that idea as its the North Sea :eek:
I have the block to strip by Tuesday to get her into the machine shop 2 hones and 2 rebores. I have to have the porting done by then. The machine guys would not entertain the porting. Dont know if its worth just getting all the pots rebored ???? I have 3 sets off each piston ie. standard .20 and .30 (job lot of Wisecos) Carbs are done Intake manifold done. Got the carson reeds from santa :) reed cages flowed. Only the cylinders to get done and the rods n piston balanced then rebuild.
Andy

Oh and the engine loom rewired :confused: Im sure it will be easy :cheers:

Andy

[spybot]

Back on topic
I will use a multi tool for the cutting of the cowl
Any thoughts on sound damping ?
All the foam is falling from inside my hood.
Andy

[racervboat]

You don't really need to balance them there pretty good from the factory its up to you.You could just do the ports round like the 140 a lot easier but if your already there grinding than go for the gusto.If your in the sea that's salt water than?

[spybot]

Yeah its salt water. Its too rough for my wee boat. She cant handle the white caps.
I keep her in a loch (fresh water) for 6 months then a trailer for the other.
I weighed the pistons and the difference between Std and +.20 is 10 grams
I figure if i have the engine stripped down this far i may as well balance her out.
Hopefully she will last another 38. My Grandkids can do the next rebuild lol
Andy

[racervboat]

Best to keep it out of the salt,to small of a boat for the ocean same goes for my boat 16ft too.

[spybot]

Yeah its just not safe. We have lost a few fishing boats and crew from the village over the years. We even have our own RNLI (Life Boat Station)
Always got to respect the sea.
Andy

[olboatman]

Back on topic
I will use a multi tool for the cutting of the cowl
Any thoughts on sound damping ?
All the foam is falling from inside my hood.
Andy
Multi tool with a fine ROUND blade works fine.....no corners to catch! Also trash the foam lining the cowl (I painted the interior of mine since I am anal as you will see and this is my "mental health project") as I like the sound!!! :eek:
;):DGary

[olboatman]

Hey Ken I started up loading pics of the project into my puter.....gettin ready FINALLY!!!!! lol ...Just waiting to get the cowl back from "Wiked Sticky"
my vinyl shop that does my signs.
Gary

[racervboat]

Gary your toooo old to have mental health issues, its not on the h20 this year your buying me and rj a round trip ticket to get that vip wet hahahahahaha

[racervboat]

sorry couldn't sleep - but the mod v-4 will be in the 80s this spring when the h20 gets soft. As you probably know working on a 15 inch 2.4 merc to put on it cause I just happen to have it for squat.But still a 1k to do it - 100 + mph should be good so im looking for an old man with mental issues to get me the time slip so I can still finish that fine bottle of whiskey I just bought .Just leave me in your will and can take of all the other fun stuff . haha Will be nice to meet up with you . Take care ken

[spybot]

Sounds like you have a blast over there :)
So its no foam then even better

[spybot]

Hey Ken I started up loading pics of the project into my puter.....gettin ready FINALLY!!!!! lol ...Just waiting to get the cowl back from "Wiked Sticky"
my vinyl shop that does my signs.
Gary

Looking forward to see this Gary
Andy

[spybot]

so im looking for an old man with mental issues to get me the time slip so I can still finish that fine bottle of whiskey I just bought .

Ken you said the magic word :cheers:

What kind is it ?
Andy

[LOSTINJ]

2.5 3.0-3.2 litre opti drop in vents I made a few years ago . They are abs vacuumed formed

[racervboat]

jim beam of course

[racervboat]

https://youtu.be/hib4n9RmFrQ?list=PL-w1scsQWbsA5AQLDQTN-CBWmaDatKRk2:cheers:way tooooo much fun andy hahaha

[olboatman]

2.5 3.0-3.2 litre opti drop in vents I made a few years ago . They are abs vacuumed formed

Did you make the abs vents to market or only for your own use.....they are sweet!!!
Gary

[AZMIDLYF]

Agree...the NACA ducts are very nice!

[spybot]

They do look good but i prefer the old fashion Scoop and side grills
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[racervboat]

:iagree:

[olboatman]

They do look good but i prefer the old fashion Scoop and side grills
397007 397006

Hey Andy....What site did you see these on? Thanks
Gary

[LOSTINJ]

I made around 20 sets , they are all gone sorry

[spybot]

On ebay uk but they come from China
I have them here and they are decent quality for little money.

https://www.ebay.co.uk/itm/2-Pcs-Mesh-Hole-Car-Hood-Fender-Air-Flow-Vent-Cover-Sticker-Black-XXXX-F5D1/322931811483?epid=1168934978&hash=item4b303c649b:g:UBIAAOSw6GJaLGSG

https://www.ebay.co.uk/itm/FP-Universal-Car-Auto-Black-Decorative-Air-Flow-Intake-Scoop-Bonnet-Vent-Cover-H/272974155881?epid=23010959319&hash=item3f8e871069:g:fBoAAOSw~QRaKoAo

The end result should look pretty cool. By the time i add then fair them onto the cowl.
Andy

[racervboat]

gary ebay usa just type in car vent hood scoop,side vent and so on and they all come up as andy linked

[mn808gade]

mite want to ck out "frogskins",used on sleds in deep snow,see thru-lets air in-but waterproof-th

[olboatman]

mite want to ck out "frogskins",used on sleds in deep snow,see thru-lets air in-but waterproof-th
Great site! These would be perfect for cowl rear vents that get wet due to the "station wagon effect". I may just use one or two!
Gary

[spybot]

Great site! These would be perfect for cowl rear vents that get wet due to the "station wagon effect". I may just use one or two!
Gary
They seem good but unfortunately only available in the US as with many great products.
Just means us Scots have to come up with our own take on things.
Heyho necessity is the mother of invention
But will there be that much water drawn in the rear cut out?
Shouldn't the flow through the front scoop and across the top of the motor be enough to keep the water out ?
Are we not over thinking this ?
Remember the "Frog Skin" If used on the rear of the cowl will have to work in reveres.
This is only my views on them,

[Forkin' Crazy]

Paul being a Finish carpenter originally(I'm finished all right) I'm curious as to what tool(s) did ya use to cut the slots. I've been usin a Fein Multi Tool to hack at mine....I did an old 25hp yrs ago (louvers) with it but I'm always lookin for better and easyer methods.
Thanks Gary

Roughed it with a small pneumatic reciprocating saw, then used a paint paddled wrapped with sand paper to finish it off.


So if you force air into the cowling but not down the carbs thuis is a good thing ?

It can cause problems with fuel metering. An even pressure is better.

[spybot]

It can cause problems with fuel metering. An even pressure is better.

On your build Paul was it only the front that allowed air in ?
Did this have the even pressure you are talking about ?

[olboatman]

They seem good but unfortunately only available in the US as with many great products.
Just means us Scots have to come up with our own take on things.
Heyho necessity is the mother of invention
But will there be that much water drawn in the rear cut out?
Shouldn't the flow through the front scoop and across the top of the motor be enough to keep the water out ?
Are we not over thinking this ?
Remember the "Frog Skin" If used on the rear of the cowl will have to work in reveres.
This is only my views on them,
I think if you set up a rear vent like a venturi (air flowing at a higher speed) you shouldn't have any water backin up thru it. I am tipping up my handle over the rear vent to try to flow air by it.
Gary

[spybot]

I think if you set up a rear vent like a venturi (air flowing at a higher speed) you shouldn't have any water backin up thru it. I am tipping up my handle over the rear vent to try to flow air by it.
Gary
I get the venturi idea air moving in through the front vent out the back will create a venturi but the hole must be narrower at the rear. I dont get the tipping up of the handle ????
Andy

[Markus]

From what I remember, there was an B&WB article where John Tiger Jr first added a Brucato SVS to a 3 liter Mercury and gained 1 mph top speed.

Then he added some spacers to lift up the air intake section in the top back of the the cowl up an inch or so to increase air flow to the engine. The boat gained another 3 mph top speed from that.

(All numbers are as far as I can remember from an article many years ago)

[olboatman]

I get the venturi idea air moving in through the front vent out the back will create a venturi but the hole must be narrower at the rear. I dont get the tipping up of the handle ????
Andy
Andy check out the first pic on post # 23.....you will see what I mean.
Gary

[phillnjack]

This is not my hood but deserves to be seen.

A nice set of vents I saw on a forum, the guy is from the states who owns this, I think its realy cool.
this only works on evinrude though :p


.

397355397354397352397353

[spybot]

Andy check out the first pic on post # 23.....you will see what I mean.
Gary

Is this the part you will raise up ?
I think i get the idea but if you have a front vent will that not allow flow straight over the motor pulling the air through ?397387

[olboatman]

It should complement the front vent or intake hole.
Gary

[akuczera]

So is there any real savings in a fishing cowl vs. alien or 2.5 drag? Other than weight?

[phillnjack]

a vent at the front that is not a ram air vent and a vent on the side will not make it pressurised.
what your after is air that is cooler and free to get in if needed.
you dont want anything to pull air out or that could create a vacuum effect and make it a negative, you are not after cooling the motor with cold air, just
wanting nice fresh air for the carbs to use when they want it.
this is why some older simple 2 strokes had the little plate 1 inch away from the front of the carb, to stop the ram effect. too much air can be as bad as too little.

just my opinion

[spybot]

Think we can get a more exact figure using this
http://www.engineering.com/calculators/airflow.htm

Andy