tomcat

Take a look at this thread. The system is being tested on a twin 496HO engine compartment with high temperatures.

http://www.offshoreonly.com/forums/s...old+air+intake

bcarpman

I thought I would need extra venting after installing a 540hp engine in a compartment made for 300. I loged the temp and pressure at the spark arrester, and found that the temp and pressure stayed close to ambient at all conditions.

If I hadn't done that first, I would have spent a lot of time creating ducts for no gain. A thermocouple to go on your multimeter and a sensitive vacuum gage are cheap.

stevesxm

i saw that thread and while interesting, i thought that cold air box arrangement average at best for a solution to the overall problem. what it does is address the throttle air intake issue and stalls the air in the engine compartment competely.

as for your temp logging, if you can keep your engine compartment at ambient at long wot runs... and i do 15 or 29 mins each way to lunch once or twice a week, that is fantastic and your system must be amazing because you are the single only example of that that i have heard of or seen. i quadrupled the area of my intakes and exhausts and use extractors and with box stock 502's i can just barely get to ambient and thats with heat shield tape around the exhaust...

JaayTeee

This spring, I built what you could call
call a "cold air box".

I have 575SCi's, I built a box that surrounded
the flame arrestors that attached to the engine hatch,
and was ducted over to the side of the boat,
where it mated to a plenum where the external vents draw air from.

Being that I just took away one of the major sources
of turning the ambient air in the engine compartment,
I added 2 4" bilge blowers on each air inlet to keep
the engine room air from becoming stagnant ( and excessively hot).

I ran these blowers off of a relay that I have one of the
hour meters trigger, so whenever the ignition is on,
the blower is drawing in outside air pushing it into the engine
compartment.

I usually run with the standard bilge blowers running,
so there will be some air movement in the engine compartment.

This spring I took a temp reading from right
inside the box, right near the flame arrestor, and another
reading from the engine compartment.

The outside air temp was 77*

Temp measured inside the box.....77*

Temp measured in the engine compartment 103*

Here's what I did notice performance wise.

I did not gain any RPM's, but before the mods,
after you would be at WOT for say over 30 seconds,
you would see the RPM's drop 100-200 RPM,
now, they don't fade away.

So, was it worth doing it ??? I think so.

Plus, it's a hell of a conversation piece.

MOBILEMERCMAN

Rebel Heart, Your open hatch idea is a good one, before you go crazy cutting holes see if you really need it. You could open your existing intakes easily without much trouble. The dump gates on transoms become nec when you have scoops and run in the 100's, with out them the engine hatches swell up and can even blow off from excessive pressure. You need air in and air out. If you want to play it all the way you could install temp gauges in and out of engine compartment to measure air temps. It's just a matter of how far you want to play it. Step one see if you need it. Good luck.
Jim

bcarpman

I ran about 10 minutes at various loads ranging from cruising to brief WOT blasts, and the temp showed 89deg max (ambient was 87). The thermocouple was taped to the mesh of the flame arrestor. I still haven't gotten it jetted right, and am still having drive issues, so I'll try the experiment again once all is 100%, but with engine temps that never go over 150 deg., and water cooled exhaust that never gets hot to the touch, there's just not much to heat up the air since it's getting pulled through by the engine.

I'm all for cold air intakes if they work, but I still haven't seen anyone say they actually went faster after all this work. You'd think the boat manufacturers would put in some pretty neat ducting if you could actually get some signifcant speed from it. (how many thousands of dollars does it cost to get a couple mph from internal mods?)

stevesxm

i don't think you are going to see ANY increase in MPH from original max. the drag numbers are so big that you would have to start taliking about 50 hp gain per side to see it on the speedo and thats unlikely to happen unless you had serious problems to start with...

in my case it was simple. i came from an industry where this sort of exercise is not only standard but where the formal engineering theory and practice are well known. only the specific execution changes.

i looked at the boat when i got it and said to myself, " this can't possibly be right... 850 hp in what is effectively a sealed 75 or 100 cubic ft space with 4 giant exhaust pipes ( albeit water cooled but not cold or ambient by any stretch of the imagination) and the motors BREATHING this air... all fed by 4 - 2 1/2 holes and existing thru only 2 of the same...

so once everything else was all sorted out i went and ran it as fast as it would go... and repeatably , in very good conditions it was 65 mph at 5000 rpm all gps all within such a small degree of difference as to be statistically meaningless. the other significant observation was the inability of the oil temp to stabilize.

so i open the engine cover and the intake manifold had to be 150 degrees and the heat was unbelieveable...

so... i take two pieces of 2x4 and drop the hatch on it so i now have a 240 sq inch opening on the leaing edge and the sides rough the same...

same test...

66 mph over and over 5050 or so revs... BUT it got there in half the time and would stay there as long as i wanted and the oil temp got to 220 and never moved beyond.

and when i open the hatch all the way... everything is just warm to the touch.

its not magic or mythology. its thermodynamics and execution specific to your application.

the simple fact is that if you are ignoring this issue or not dealing with it you are simply driving a boat that is both slower than it could be and wearing everything out faster than it has to.

the air going into the intake needs to be ambient. the engine compartment needs to be ambient in all conditions. anything other than that is a mistake to some degree.

tomcat

I am not saying that you shouldn't ventilate the engine compartment, but it isn't practical to ventilate it down to ambient. I did a rough calculation using some data from emergency generators in small rooms and scaled it up for a 400 HP engine. I too was thinking of adding bilge blowers. In a nutshell the results were something like this:

bilge blower - 60 CFM
engine needs - 600 CFM
heat removal needs - 6000 CFM

So instead of trying to get 12,000 CFM to flow through a twin engine compartment, let's get 600 CFM of ambient air for each engine and get whatever we can for heat in the compartment. It' wont matter if the air in the compartment goes to 150F, the engine, oil and water are that hot anyway. As long as the combustion air is ambient you're ahead.

We will post results including scan tool datalogging when complete.

stevesxm

your math makes no sense at all and your premise is simply wrong. it is not how many cfm you move as a total number. it is how often you can exchange the air after it reaches saturation temp. with nothing other than your bilge blower at 60 cfm, you would completely change the air in engine compartment every minute and a half or so... and that is ignoring the existing hard vents. that is barely good enough as long as the hard vents can supply the motor AND the exits allow 60 cfm OUT.

your premise that ambient air into a 150 degree manifold is somehow fixing the problem is absolutely absurd.

you can rationalize all you want but that doesn't change what the truth is.

articfriends

Here is a twist on this subject and little of my own recent testing for anyone interested in the idea of running a innercooler on a naturally aspirated enigne. I recently spent alot of extra time and money when I dynoed my motor to set up a complete fuel map/ecu program so that I could run it N/A or blown by simply removing the blower belt (procharger mounted like a accesory),swapping ecu's,map sensors and removing the blower discharge to innercooler piping. So I can run my motor N/A or switch to blown in 10 minutes. My innercooler is mounted approx 10" from the throttle body and is connected by a 3.5" tube, I have often wondered if a N/A motor would benefit from running with a innercooler pre-cooling the intake air charge. I made a bell mouth to smooth the transition of air flow into the innercooler. After several testing sessions I can tell you in my application the added restriction of the innercooler made less power then pulling hot engine compt air directly into the throttle body,there was a 100-200 drop when running the innercooler vs not running it,the test was easy enough and now I know it doesn't work but at least I tried and got to see. I did not have a merc scan tool to see what my intake air temp sensor was reading but the fact I lost 100-200 rpm's and 2 mph told me enough.
I do like the idea of ventilating the engine compt better on my boat but I have yet to come up with a workable solution as my boat has no place above the rub rail that is flat or uniform to mount any extra venting,any ideas? (2000 Baja 272),Smitty

You would never believe it if you saw it but I made my bell mouth from a pvc 3 x 4" adapter