Cold air intake

[MCL]

I was wondering about building a cold air intake for my sterndrive boat,any issues I might run into?The gains should be far larger than on cars because on the closed engine compartment.

Boat is a glastron 20ft cuddy cabin.Engine is 4.3 vortec mercruiser alpha one,san juan full closed cooling system with 160 termostat.It has a performer intake and wooden spacer between carb and manifold.So im not too worried about fuel boiling.

Pros:more power,better fuel economy,less intake noise,backfire cant ignite any fumes.

Cons:I will need to run the bilge blower at all times,perhaps upgrade the ventilation a bit since the engine wont draw air anymore.

Thoughts?

 

[Alpheus]

Re: Cold air intake

I dont think a cold air intake would be CG approved equipment.

wooden spacer between carb and manifold.So im not too worried about fuel boiling.

I don't think anyone on this forum is worried about their fuel boiling.

These are low performance TRUCK engines. Not a Honda Civic that you can throw a bunch of bolt-on performance parts at. You can do what you want but if you use non coast guard approved upgrades and get caught during a routine inspection, or worse an accident should result from it. I would hate to be in your shoes. Good luck...

 

[dozerII]

Re: Cold air intake

I don't see how an intake system would help at all. The engine has no air plumbing ( like an auto) only a spark arrester. There is fresh air always moving through the engine compartment when the boat is moving, and the air is needed. If you were going to put one on the only thing needed would be a flexable coupler on the carb or throttle body and a staright piece of pipe coming out of the engine bay with a 180 degree bend to stop water from getting in.

 

[John_S]

Re: Cold air intake

I have seen cold air intakes on some very High-Performance boats. One on a stock V6 will not provide any noticable change. Do some test runs with engine lid vented and/or bilge air running. See how much benefit you can detect.

 

[MCL]

Re: Cold air intake

Im in Finland,we dont have cg requirements.Boats do have to pass ce requirements,but thats when they are sold as new.We also dont have multi million dollar lawsuits when something goes wrong.

In cars air is moving through the engine compartment when the car is moving,the air never really gets hot and yet they gain from CAI.Boats have closed engine compartments,they rely on the blower and engine drawing air to keep the compartment cool.A engine with a 160 termostat is 160 f as its coolest point.The oil pan,valve covers and parts that are not cooled by coolant is far hotter.

These are low performance TRUCK engines. Not a Honda Civic that you can throw a bunch of bolt-on performance parts at.

I think you got it backwards.These are low hp to displacement engines that can easily gain hp.Its much much harder to add power to a engine that is already pushing out good power for its size.I spent maybe 2 grand on my mx bike engine and added maybe 3-4hp,and it only has one cylinder.

I already have a rebuilt block,vortec heads,performer intake,600cfm 1409 carb.Im running aluminum exhaust manifolds now,but will upgrade to stainless hitek manifolds with dedicated runners in the future.Theres not much I can do to add power without going internal.

About the heat issues,a lot of boats have problems heat soaking and boiling the fuel in the carb.Using a wood spacer(insulator) keeps the carb temps down.

http://www.meanchicken.net/webmain/forum/viewtopic.php?f=36&t=2214&start=40

Is where I got my inspiration,everybody who did it noted at least a 150rpm improvement.

 

[Bondo]

Re: Cold air intake

Pros:more power,better fuel economy,less intake noise,backfire cant ignite any fumes.

Ayuh,.... Backwards or Not,... Have at it, I believe you'll be severely Disappointed...

 

[Howard Sterndrive]

Re: Cold air intake

take a back seat cushion out... there's your cold air

 

[Aloysius]

Re: Cold air intake

Are you running a stock flame arrestor, or a K&N? I picked up 200 rpms by switching..stock flame arrestors are pretty restrictive.

 

[John_S]

Re: Cold air intake

Are you running a stock flame arrestor, or a K&N? I picked up 200 rpms by switching..stock flame arrestors are pretty restrictive.

Wow! That's some increase! 200rpms would be a significant HP increase. Please provide more details on what engine/boat. I run a K&N on my 5.7L, but doubt I could tell switching to a stock type mercruiser flame arrester. Maybe 2-3hp. I suspect your stock flame arrester was plugged, but would like to hear more details. Did the change drive carb jetting changes?

 

[Aloysius]

Re: Cold air intake

twin 302 inboards in a 24' Blackfin. I am very space limited, and the stock flame arrestors are small. Didn't change jetting, but I run non-ethanol fuel. Only noticible at full throttle.

I'm more concerned with fuel economy at cruise..3200 rpms or so. I've increased mileage from 1mpg to about 1.5 mpg by dialing in timing, props, vacuum secondary opening, and power valves in Holleys. I've got manifold vacuum gauges on my engines, btw.

 

[LAC_STS]

Re: Cold air intake

I have a K&N on my 5.7 and I didn't notice anything. My old metal flame arrestor fell apart and I found a deal on a new K&N one is the only reason I got it.

I have noticed that there is less dirt or particles or whatever it is in the carb with it on then with the old metal one.

 

[bruceb58]

Re: Cold air intake

Running a K&N or a cold air intake on a marine engine is basically worthless compared to what you have stock. A cold air intake is also worthless on an auto.

If you really want to see if there is a performance difference, remove your engine cover and spark arrestor and run it down your lake and compare. You won't be able to tell any difference.

 

[John_S]

Re: Cold air intake

twin 302 inboards in a 24' Blackfin. I am very space limited, and the stock flame arrestors are small. Didn't change jetting, but I run non-ethanol fuel. Only noticible at full throttle.

I'm more concerned with fuel economy at cruise..3200 rpms or so. I've increased mileage from 1mpg to about 1.5 mpg by dialing in timing, props, vacuum secondary opening, and power valves in Holleys. I've got manifold vacuum gauges on my engines, btw.

Thx for the feedack. I wasn't considering it was a twin engine set-up. Still seems like a very healthy increase, but not familiar with what flame arresters might have been stock on old 302's. The 90's and above Mercruisers that I am more familiar with, flow very well. The K&N does a much better job of air filtration, of course.

 

[Aloysius]

Re: Cold air intake

The newer arrestors are much better, and probably more suited to high flow requirements. The old ones were terrible..small diameter, not very tall.

At cruise, I'm pulling 6-8" vacuum. Went to a 3.5 power valve..most power valves in kits are 9-10" opening or so. 36 degrees total advance, but I don't do wide open for long.

 

[Howard Sterndrive]

Re: Cold air intake

for about $58, iboats sells the 18-7232 Sierra
3" tall.
Should be suitable for any 4 barrel with a 5" dia throat as long as there is room under the doghouse.

They also carry the tall Mallory one which I think I have. It might be 4" high?

Don't want to overlook cleaning them either. I figured bigger will extend cleaning intervals if I forget.

 

[Alpheus]

Re: Cold air intake

everybody who did it noted at least a 150rpm improvement.

WOW!!! 150 RPM's How were they able to control there boats?

That data is bogus. RPM's gains or drops can be from many different variables. Weather,humidity,air temp,water conditions. You go ahead and spend all of your time and money chasing those 150 RPM's.

 

[Howard Sterndrive]

Re: Cold air intake

who are you quoting? I don't see that...

 

[Aloysius]

Re: Cold air intake

Weather conditions do make a considerable difference in power, as does altitude. so does salt water vs. fresh water.

For larger boats, the depth of the water affects performance..a boat with 5' of draft will be slower in 10' of water than in 50' of water. Bernoulli again.

 

[45Auto]

Re: Cold air intake

For larger boats, the depth of the water affects performance..a boat with 5' of draft will be slower in 10' of water than in 50' of water. Bernoulli again.

Maybe the British don't know Bernoulli. Their ships are faster in shallow water:

The figure below shows speed/power curves for HMS Cossack for speed trials performed at the Maplin (shallow), Chesil Beach (intermediate) and Skelmorlie (deep) measured miles that clearly show the shallow water effect. In brief, a ship recording 30 knots at Maplin will only manage 28.0 at Chesil Beach and 28.5 at Skelmorlie. From this figure, you can see that the same SHP produces different results depending upon the depth of the water.

http://www.navweaps.com/index_tech/tech-091.htm

 

[Aloysius]

Re: Cold air intake

Interesting. The sportsfishermen here seem to achieve different results. Sea trials are always conducted in deep water for this reason. Planing vs. displacement hulls? I know the displacement stuff will draw more water when shallow.

Fluid mechanics and boundary value stuff can account for some weird anomalies.