How to calculate minimum air vent
 

A 502cid (8,2l) engine needs 2.17 US gallons (8,2liter) of air pr. 1 rpm., correct?
How do you then calculate how big the air vents need to be to not starve the engine for air?

Re: How to calculate minimum air vent
 

the volume of air is a function of the displaced volume ( as you note ) and the rpm.... as you note again... but the bottom line is simple.... if normally aspirated, you don't NEED any opening larger than the anullar opening of the throttle body/ carb (s) .. thats the choke point. however there is more to it than that.... cold inlet air and engine compartment temps are crucial to making power.... scoops into the inlet solve the cold inlet air issue... good engine bay entrance air volume and circulation in the engine bay should be accomplished at all costs...

on my top gun, i had two 2 .5 holes each side... for inlet air...or about 20 sq inches.... barely enough for the motors... i figured...

so i got two small pcs of 2x4 and set the hatch down on them such that there was now about 100 sq in opening abover the rear seat.... instant 200 revs , lower oil temps a great deal.... and i am certain the revs were NOT from better BREATHING but the fact that the intake manifold went from being about 200 degrees to ambient and the air inlet TEMP went down about 90 degrees

so i went to the local chandlery and bought some linear rail type air inlets... about 90 sq inches per side and problems solved. as far as air circulation goes... more is better

Re: How to calculate minimum air vent
 

This make sense. But what a bout a supercharged engine, how would you go about to calculate that?

Re: How to calculate minimum air vent
 

i just looked up my formulae for calculating air flow thru an orfice w/ a differential pressure . it was, as i recalled, very long with a lot of variables and keyboard characters that i don't have... but if you type that phrase into google you can see it for yourself... but again... the bottom line is... the MINIMUM you need is the the size of the annular opening that feeds the unit... that is the choke point... BUT the same principle i described earlier simply applies to a greater degree... and i would suggest to you that here is the bottomm line.

if you can conveniently run an air scoop... do it. if you can not then you get as much fresh air in and out of your engine bay as you humanly possibly can. the more you do that, the better off you will always be. always. every single solitary time.
heat is the enemy of every single componet that lives in there.

it kills your power, and it wears things out and makes them work badly.

it really is as simple as that.

Re: How to calculate minimum air vent
 

stevesxm is on the right track when he says it's the drop in temperature of engine intake air that has the benefical effect. The math is simple, when it's hot under the engine hatch the air entering the engine is less dense, therefore less power. You have to compare the absolute temperatures, (ambient versus under hatch), so you add 460 to each.

eg. (77F + 460)/(150F + 460) = 0.88

That's right ... you just lost 12% of the HP.

Now you have a choice:

- do you add air to the engine compartment and try to cool it down so that the engine gets cooler air

- or do you direct ambient air directly to the carb? (right answer)

I don't think it matters to the engine that it is 150F under the hatch, everything on the engine is water cooled. And if you do the math, (a little more complicated) you find out that it would take a huge amount of cooling air to prevent the engine compartment from rising above ambient temperature. Engines radiate a LOT of heat, 8-10% of the fuel energy is lost in this way.

Here are some numbers to put this into perspective:

engine compartment volume = 120 ft3
2 @ typical bilge blowers = 120 CFM (1 air change/min)
2 @ 450 HP engines = 1200 CFM (10 air change/min)
cooling air required to limit engine compartment to +20F
over ambient when these engines are at WOT= 12,000 CFM (100 air change/min)

This last number is based on the BTU/min radiated per HP according to the type of engine and extent of water cooling. I admit to making an educated guess of 5 BTU/min/HP.

Hood scoops, linear vents and other holes can move a lot of air, but never enough to reduce engine compartment temperature to ambient. However, if they are located immediately adjacent to the carbs, they can supply unheated ambient air directly to the engine intake.

Re: How to calculate minimum air vent
 

I am trying to get more cool air in also. Question I have is was just increasing the side vents enough? I thought about also adding a vent (Exit for heat) in the back.

The only concern I had with ducting to the carbs was water/salt getting fed directly in.

Re: How to calculate minimum air vent
 

We put a data logger "spider" on the engine of a 36 skater w/ 525's - boat has big scoops on the hatches - looked like the "cold"/fresh are was blowing in on the intake - Wrong - the air was circulating was actually blowing over the top of the engine - rolling underneath and then back up to the intake - the hottest part of the engine bay was the intake and that was 28 degrees hotter than the intlet air - this air flow also changed with speed - @ 75 the temps were all pretty good - @ 100 it was terrible @ 120 it was moderating - mid range temps are important if you have detination issues

Look for a data logger for temps - also cool tool to monitor drive temps @ various speeds - header temps etc...

Unit I use is called: Datapaq " EasyTrack" Model TB0225A and has seven leads that can be used to log at one time

Re: How to calculate minimum air vent
 

Interesting that you post this. When I winterize I prop the hatch up a couple of inches, in hopes that it might allow for a little air circulation and cut down on condensation. As I was doing this at the end of last season it came to mind that, this might be a good thing to try when running as it should allow for cooler air in the engine compartment, and a few more R's. Lazy, so I didn't try proppong the hatch and running it that way this season. Your 200 RPM increase is encouraging. I have a couple of weeks left before winterizing so I'll give it a try. Just need to figure a way to prop the hatch, and keep it from blowing open/off at WOT.

Re: How to calculate minimum air vent
 

like i said... mine is hydralic so i just closed it tight on a couple small pieces of 2x4 ... quick and dirty and the answer was immediatly self evident... as for tom cats numbers, he is essentially correct in all respects... especially the air inlet temps... the one thing i think he misses or simply underestimates is the effect the inlet manifold temp has on pwer and air fuel density... and that is VERY important... now i used the word " ambient" and that was just me trying to exaggerate for clarity... my mistake... and he is right... no way on the planet you are getting the maifold to ambient... BUT if you use a scoop and seal it such that all that air goes into the intake ONLY ( as opposed to just using them as ventilators)
AND you ventilate effectively and get the manifold temps down even 40 or 50 degrees, you are absolutely going to see a significant difference in performance... especially on an efi boat that has the sensor array nec to deal with the changing parameters... on a carb boat you will find yourself re jetting substantially ill bet....

and folks.. this is a no brainer. this is " free" power and longer service life on every single boat regardless of type or application... cold inlet air is ALWAYS better... cool inlet tract is ALWAYS better... and cool FUEL is an added freebie as well... i think the way mercuriser has done that is ... well ... the weirdest and most complicated i have ever seen for a simple process.... but the bottom line is, it works as well...

Re: How to calculate minimum air vent
 

Terrific info everyone - thank you. :D

Re: How to calculate minimum air vent
 

Neat test James, especially different air flow patterns at different speeds. Ducting directly to carbs/TB is not as easy as on cars, you have to design so that water droplets are not drawn into the duct even though they came through the vent. Since water droplets are a lot bigger and heavier than air molecules, separation of the two is possible.

stevesxm: I don't doubt that a cooler intake manifold works, at least that's what Edelbrock Air Gap marketing says, I just have no numbers on it so I didn't say anything. I still think the major effect is the cooler air. I don't know how much heat the air can pick up when it passes through the intake manifold in about 0.01 second @ WOT. :D

Re: How to calculate minimum air vent
 

i don't have any real numbers either... but i have a handful of empirical data that was absolutely conclusive....

1) 2 litre , 150 hp motor that spins to 7000 rpm.... 20 laps to establish a base line... then did nothing more than comprehensively insulate the intake manifold with heavy foam and tape. avg lap time over the next 20 laps were 3/10s better on a 1.5 mile track . no significant increase in egts... just better power. took insulation off... lap time avg back to base line.

2) that same f 350 gas towing 20,000 lb trailer... 5 to 6 mpg with a hood on it.... 7-8 mpg and would go up hills like crazy with hood off it and in the trailer... made for some interesting toll booths but absolutely effective...

and on every single application where we could legally insulate or alternatively cool the intake manifolds, there was always SOME positive and measurable and repeatable result. sometimes big... which told us that the under deck temps were out of control anyway... and sometimes only minimal... which meant that we were getting good flow/ w/out drag... a tricky business... but either way... we are all on the same page here i think

my only point is that i see it easier to increase performance by NOT giving it up in the first place by virtue of inefficiency... i am working on a rear hatch assy that has two scoops that seal to a plenum permenantly mounted to the motors... and yes... i wonder about water ingestion but i figure a little bit is surviveable and the plenum will have a diffuser and a trap...

and for all you blower guys... question... why aren't you using some sort of water injection like they used on blown piston engine fighters in wwII ? i don't know a thing about it except that it was VERY effective...seems like a cheap solution to big boost detonation issues to me... especially in this day of good digital controlers...

just curious...

Re: How to calculate minimum air vent
 

Scavaging heat via negative air pressure is more effective than ramming air using scoops for a marine application - With a scoop it may in fact pack air ( you would need to use Hg guages or short pcs of string taped to the deck to prove airflow - assuming you can pack 10,000 cm, into a sealed engine bay, and the eingine only uses 1,000 cfm the stagnant air is likely to pick up heat, thereby reducing power. It is more important to get air OUT of the engine bay - ducting using the boat natrual vacuum / low pressure area behind the boat is the easiest method, this insures fresh air all the time and at huge volumes --------ok the down side - holes in the back of the boat or engine hatch are ugly, turning your scoops back ward is not cool and depending on speed you can suck exhaust fumes back into the engine bay -

Re: How to calculate minimum air vent
 

stevesxm's experiences with cooling intake are very real and very easy to get shared experiences of other builders that test what they do.

Before the airgap intakes we would take steps, and rewarded by these steps, by reducing intake manifold heat.

#1a thing to do : if cyl heads and intake manifold had heat/exhaust crossover we would block it. Reduced heat and isolating these exhaust pulses would pick up power.

#1b : using intakes with no exhaust crossovers but heads with, still using intake gaskets with blocked crossovers reduced intake heat somewhat and picked up some power.

#2 - hot oil and air from lifter galley to bottom of intake. Very real power issue. Cast iron intakes are effective, aluminum intakes highly effected !!!! Still talking about non 'airgap' intakes, we must get some sort of shield in here. GM makes one for BBC's that works with any lifter set-up, aftermarket makes them for SBC + BBC with flat tappets.

If you drag race or do a dyno run the above things don't usually show up, especially if doing normal quick runs. However, if you keep doing runs , one after another, one after another, so on and so forth, it becomes more emminent with each and every run that doesn't have a 'cool off' period in between.

Enter marine - unless a drag boat - we run our engines for minutes on end.

Heat soak does and will happen !!!!

Shhhh: we have run a few tests on non-airgap intakes running cool water under intake plenum and picked up power. Note: the power picked up was after the engine had been run for a while and manifold heat was much above ambient.

Same reason why some intercoolers don't show a power increase on some SC applications on the dyno. But if you where to heat soak the engine by running it hard for a bunch of minutes - the intercooled engine will make more hp than same engine without intercooler.

Intake manifold heat is needed for better idle/low speed effeciency only. Cold intake manifold increases chances for raw fuel puddling / clinging/etc,etc.

We all know during winter, a cold intake manifold and carb without choke is a beatch right ? Speaking of which, why do we need choke for colder air temps ? Same reason !!! Intake manifold temperature changes a lot of things going on !!!!!!

Re: How to calculate minimum air vent
 

This is a great discussion!!

I can't post any actual numbers, but I've definately noticed similar results in my auto days.

However...One thing to remember, never compare auto to marine!! Underhood temps on cars/trucks are massively different than on even the worst boats!! Cars have a much more confined underhood space, the only air comes through the hot radiator first, and they DON'T have water cooled exhaust.

It's not uncommon to see 300+ degrees underhood in a race car or tow vehicle if not properly designed.

Not saying it won't make a difference on a boat, I'm sure it will, just not as much as on a F-150 towing a boat up the rockies.

Re: How to calculate minimum air vent
 

Anyone know how much various manifolds will effect not only power, but also Idle quality and cruise economy?

Which is a better insulator, an air gap aluminum, or a traditional marine iron manifold?

If you took a stock 454 with a low rise iron manifold and exhaust cross-over, and added an air gap manifold without exhaust crossover, how much idle quality and cruise economy would you loose? (assuming you re-jetted properly) Would it be noticeable?

I know most of you aren't real worried about idle quality and fuel economy, but it's a "system" thing. If you loose idle quality from the manifold design it means that ultimately you have to run a milder cam, etc....

Re: How to calculate minimum air vent
 

Yes, I do. Cold weather/ hot weather.....cold air/ hot air is part of our year in the upper Northeast.

I get to deal with frozen water to 80° F water temps and -20°F to + 100°F air temps. :( It's all good though but does make you do a dance at times. :D

I'll share experinces in a little bit.

BTW: I, too, think this is a fantastic discussion.

Re: How to calculate minimum air vent
 

Ok, with boats, we typically use them air temp of 60°F + and same for water temp.

Start up and idling is fine. Let engine start at fast idle around 900 or so rpm for a minute or so. Aluminum intake will warm up and idle better quicker than an iron intake will. But, iron will still be fine in quick time.

Now, winter driving with a hp engine in your car/truck....well, things can get interesting !!! If car/truck is regularly used I would suggest using one closed / one open intake gasket heat riser if using intake/head with crossover.

I, as many I've known, will take out their Victor Jr , Dart, Brodix intaked and aft headed engines that have no crossover's at all in sub freezing temperatures. A good 3,4,5 minute warm up is needed before you drive off. Even with a loose converter, these may belch and choke from such a 'lean' mixture. Speaking of which, the carbs will usually need a good jump in jet size, a little more accelrator pump shot - all dependant on what the temp was when last tuned.

Tuning is a huge factor with this !!! Both my boat motors (one sbc and one BBC) have no added heat and start with the turn of the key and no carb pump shot, if you can believe that ! That's in 70-80+ degree weather. As it dips under 50 I might have to give them 1/4 throttle jab - once or twice. I keep them running and imm bring idle to 900 or so rpm until temp starts to move and test if it will hold idle fine.

Yes, intake heat (vs stone cold) will give you a bit better fuel economy, but in boats we deal with warmer weather so there really isn't much difference. You are probably losing more gph due to your driving style and tune. :D

Re: How to calculate minimum air vent
 

thats what makes efi so good. it gives you a range of temps to work with and adjusts to suit.... but we are no longer talking apples and apples.... the bottom line is that it is unlikely you are using your boat in 40 deg weather... and if you are your motor is making great power... the discussion is what happens when thiongs get too hot.... and that is a negative ALWAYS... the trick is when your boat is in the bay at 100 deg ambient and 150 under the deck to make it THINK its 40 degrees out... not really of course ... but as cool as possible. there is absolutely no downside to this at all. if you really believe an extra min or two of warm up is a valid trade off for the other 99.9 % running time ... well ... i guess thats what you believe... but the numbers will always prove you wrong

Re: How to calculate minimum air vent
 

I was with you until this point.

My answer was to cover all the temp variables I could from the questions I was asked.

In our weather extremes, it is nice to have EFI so we can start our VEHICLES from inside, behind the windows.

In the temps our boats are subjected to, EFI's advantage is negated 95% of the time.

Anyway - that is another discussion - we are having one on air inlet temp engine compartment temp.

Speaking of EFI - don't these manifolds have more of a heat soak issue when dry (as in MPI) then carb'd or tbi's ? :D

===========================

Tomcat - as far as all the air russing in thru the intake I totally understand what you are saying. I always think about the same and then remind myself about all the experiences of removing intake manifold heat making more power. Therefore, I don't do the math - I follow the results.

1) EFI cars running faster with iced down intake manifolds
(I have not tried this on a boat - I don't drag race them)

2) Boats running faster with intake valley trays, blocked off exhaust crossover, manifolds with raised plenums, etc,etc.

Boats require power - lots of steady power, especially when we run them hard. Even if temps are consistent, the BTU's are much more then a low load counterpart.

We want the combustion chamber warm enough so it doesn't make fuel re-liquify but we want the intake relatively cool and the air inlet as cold as possible.

A master of horsepower is routinely quoted that to make max horsepower he wants to be no higher than 120 degrees engine temp...at all costs.

==================================

Just so people know that don't know me - I'm not out here to be 'right' so don't take I'm pushing that way. I'm here to throw everything on the table that I have experienced, heard from others, etc,etc and walk away from these discussions feeling like I learned something new or atleast something new to try.

I love ideas / experiences bounced around. Absolutely love it.

Let's here more !

Re: How to calculate minimum air vent
 

SB, so are you saying type of manifold/exhaust heat, etc. won't make much of an idle quality difference once the engine is warmed up? If that's the case then I can see why we wouldn't care. It's not like we jump in our boats for a quick run to the mini-market. I can't remember the last time I didn't let the engine warm up.

So which do you think is better for keeping heat out of the intake, an iron manifold or an air gap aluminum? Dennis Moore says in his book that the better iron manifolds flow pretty good, and you don't have corrosion issues.

Not to change the topic, but I've read several places that even in fresh water, you need to change the manifold ever couple years if you run aluminum. Is this true?

Re: How to calculate minimum air vent
 

Okay, I'm with you now. I read this as something different. Reading your post #9 this AM (with a clear / coffee filled blood system) made it clear to me.

You are correct and I am with you 100%. I though we got onto a different page, but we haven't. :D

Cool air intake and cool intake manifold is what we need to strive for to make air going into cyl head..........cool. :D

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Oil temp greatly effects intake manifold temp's. We cannot forget this. Main reason why we need lifter valley trays and raised plenums to keep plenum + runners as cool as possible.

Also means we have to watch oil temp for this reason also.

Re: How to calculate minimum air vent
 

I ran a aluminum intake on my last boat for 8 years in freshwater,I took it off the motor after selling boat without a motor and a buddy is STILL running it on his race car today,Smitty

Re: How to calculate minimum air vent
 

An 'air gap' cast iron intake. :eek:

Well, since we don't have these available, the 'air gap' aluminum intakes.

Aluminum intakes in fresh water typically corrode first at t-stat housing flange and coolant passages at the head mating (when using cast iron heads) locations.

On my lake I check t-stat flange each time it get's winterized. If it is pretty corroded and ready to leak here, manifold comes off to further inspect other areas.

On my SBC I do personally use the Bowtie cast iron intake w/1204 Fel pro intake gaskets that block off the heat/exhaust crossover. This intake also comes OE with sheild riveted underneath it in lifter valley side. See - GM even knows the deal.

Yes, there is some HP in a set of intake gaskets...for some applications. This is one of them.

Re: How to calculate minimum air vent
 

remember folks... air gap...no air gap ...diff materials make no dif what so ever if the assy is sitting in stagnant air... the temps are reduced by FLOW over the surface area... FLOW... air MOVEMENT.... which is where we started all this..... and my point was and still remains... there is never too much air moving thru the engine compartment on a boat...do what you have to do to keep the water out but the more air in/air out that happens the better off you are going to be in ANY apples to apples comparison.

and i would fundementally disagree w/ the notion that efi is a " one trick pony" efi allows abosutely flawless mixture control w/ 3 dimensional mapping over every relative parameter at a high sample rate... as opposed to a carb which is only slightly better than sitting there pouring gas out of a dixie cup into the intake manifold... there is absolutely no comparison at all at any flow rate... any horsepower or any application at all.

i was offered two 454 carb motors FREE for my boat... and i BOUGHT two 502 efi.... and i haven't regretted it for an instant.

Re: How to calculate minimum air vent
 

Perfectly stated :D

Re: How to calculate minimum air vent
 

Pretty much true. I did not get into the temp transfer rates and such between cast iron and aluminum.

Cast iron takes longer to heat up and longer to cool down. Aluminum transfers temp quicker.

If you run long enough, the cast iron will get as hot as the aluminum. To cool it down, you'll have to wait longer with the cast iron.

Any hoosey :D , as stevesxm is heavily promoting, we must concern ourselves with removing heat and quantity / quality / and direction of airflow must be attacked and made as effecient as possible. The better you do at this, the more reward you'll get.

Now on the EFI thing......well.....that's a whole 'nother subject matter, unless we are still talking about air temperature vs design + materials.

Re: How to calculate minimum air vent
 

I totally agree with what's said in your 1st paragraph....nuts and bolts/common sense.

However I am curious about your statements on carb/efi. As far as efi is concerned, it is a good "turn key" thing for the general boating public, as the computer will automatically make adjustments relative to elevation, heat, humidity, etc. and allow the engine to run well, under most any circumstances. I have read, and have been told by respected sources that a well tuned carb, tuned for a certain elevation and or temperature range, will out perform, produce more hp, than efi. Reason being, generally a carb breaks up the fuel/air mixture better than efi therefore allowing for a better mix in the combustion chamber. i.e. roughly said, efi provides very fine droplets into the combustion chamber, where well tuned carb provides a finer "mist" into the combustion chamber.

One more thing....Lawn mower = Dixie cup. BB = coffee can :D

Just trying to learn something here :confused:

Re: How to calculate minimum air vent
 

Just a thought, but I'm thinking you can always make more power thru other avenues so with that in mind, big hp (blown or NA) motors with well mannered EFI is always going to come out on top for us pleasure boaters; especially for us Rocky Mountain guys who go from 0-6500 feet on a regular basis) Again, just thinking out loud :drink:

This thread comes at great time and I as well am learning here. After a Diacom run with my twin 496HOs stuffed into a small area I learned that my intake air temps are 145-148 with outside air temps in the upper 80's.
This has prompted me to look at some cold air intakes on my setup. These will be plumbed with minimal pressure loss (thanks to help from Tom) and intake only outside air.

Keep the good info flowing :evilb:

Later,
Dave

Re: How to calculate minimum air vent
 

Isn't boat EFI kind of a simplistic version of real EFI (meaning it doesn't use as many parameters)? I see just about everybody w/ a carbed 502 making 600 horsepower when upgrading. I've yet to see better than 530-550 horsepower with the Mercruser 502 EFI system. Why is that?

Re: How to calculate minimum air vent
 

Intake manifold... :cool:

Re: How to calculate minimum air vent
 

I am amazed by the effect of intake manifold heat being reported. My theory says there is very little time and limited surface area for this heat transfer to take place but I am willing to accept the facts as borne out by your experience. Thanks everybody, now I have to change my theory. :rolleyes:

On the subject of cold air intakes, Dave and I have been bouncing this around for a while. Yes, there can be a big increase in air density if you do it right, but you have to be careful that you don't lose most of that gain by restricting air flow into the engine with the piping.

One reason air intake kits work on cars is that car engines have restrictive piping. Do a better job of designing the pipe and you "should" see a gain. But on your boat's EFI engine there is no pipe and no restriction. No matter what you do, a cold air intake on a boat is going to add restriction. Design and testing is the way to reduce this restriction to a minimum. I'm thinking here about boats with no hood scoops. If you have scoops, it is a great idea to seal them to the flame arrester somehow as mentioned above.

This is the design that I am testing on the flow bench next week. Baseline will be the bare throttle body, then throttle body with stock flame arrester, then this layout. I will also test with a water resistant filter wrap.

This is the minimum amount of piping and elbows needed to get the air filter under the gunnels where you can get the first stab at the ambient air entering the vents. I am hoping that Dave will be the guinea pig! :D

Re: How to calculate minimum air vent
 

Kind of getting a bit off topic here, but I thought I'd add a bit of experience to the EFI vs. Carb discussion.

Since I worked for GM for 17 years, and had access to all the best equipment available, I always ran EFI in all of my home projects as well. I've put EFI on race cars, motorcycles, street robs, supercharged, turbo, NA, nitrous, etc. I've worked on speed density, mass flow, open loop, closed loop, and even some mechnical FI (no electrons :) You get the point.

Yes, a properly mapped out EFI system can do things no carb could ever do. Weather and altitude correction, cold start, etc.. EFI is also generally less of a compromise if engineered properly. Since the walls of the manifold are "dry" (TBI or a carb is"wet") you don't have to worry about fuel puddling, and hence can design the manifold purely for airflow without worrying about what it does to the air/fuel mixture. This is HUGE, and cannot be underestimated.

EFI is also essential when working with turbo's or blow through superchargers. I wouldn't even think of trying to do a turbo/carb setup. I tried that once...never again!!

HOWEVER.....It's very easy to get lost in an EFI calibration. yes, you have control over everything, and sometimes it's next to impossible to figure out what part of the calibration is giving you headaches. Yes Merc EFI is tremendously simpler than automotive EFI, but they still have many engineers working many months to produce a good cal.

Also, many people have spent many years developing carbs and their respective intakes to the point where they work pretty darn well. Amazingly well actually. I'll be the first to admit that although some of my home based efi manifolds have done everything I wanted them to, and made more power in a more civilized package than a carb ever could, I've built a couple that couldn't be saved regardless of how much dyno time I spent on them.

Yes, if I was going to build my ultimate "spare no expense" boat motor it'd have EFI, but even with all my experience, after rebuilding my "454/330 on roids" this winter, I'll toss on a dual plane manifold and carb...Just too easy, and I know bunch of crazy electrons won't keep me off the lake in June 07. :)

Re: How to calculate minimum air vent
 

I didn't mean to throw the thread OT, or hijack it with my efi/carb post. It is definitely a subject for another thread.

Air ventilation is the topic here, and I find it very interesting and informative.

Re: How to calculate minimum air vent
 

I'm in :evilb: :evilb:

(I'll be measuring my exact front clearance this weekend)

Re: How to calculate minimum air vent
 

Tomcat - I believe a huge potential source for figuring out piping to your inlet could be Doug from BG ie: Rumrunner.

They deal with this in drag racing applications all the time. What makes 'sense' sometimes can make you fall behind and vice versa.

Biggest things I can add is:

1) Do not put outside opening in a low psi area. Use some small dry pieces/straps of paper / ribbons or etc that will move with airflow. A good example as many that sit in the back seat of a boat can attest to - their hair usually blows forward towards the driver. Many vortices, and air flow reversals going on.

2) What may not be restrictive in a 10 second 'pull' may be restrictive ocer 30 seconds, a minute, 10 minutes, etc,etc. A vacuum guage tapped in different places will give you the headsup here. A temp guage will also help - some intake pipes can transmit heat pretty well also.

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BTW: This subject of heat may or may not make a decided difference in everyon'es applications. Not one engine compartment / engine build is likely to be like the next persons. A lot of variables here.

But, the more heat you are subjected to, the bigger the difference will be when reducing it.

I'm glad to see all the interest with this subject.

I hope we can have more discussions like this one on other topics as time goes on.

It's a lot of fun. :D

Re: How to calculate minimum air vent
 

Outerwears ? They work pretty good in 4x4's and snowmobiles - I'll attest to that ! Blurp, blurp. :D

Just make sure it does have the water resistant treating - I believe they carry different materials.

Re: How to calculate minimum air vent
 

Yes, this is the best part of the tech section, thrashing a good topic.

Thanks for the suggestions. It seems to me that a lot of new boats have the engines squeezed in pretty tight and vents are part of the styling and may not move enough air. The design so far just gets the filter to the gunnels; how well the vents work in that area is still a question. Ask Dave what he may have to do on his boat.

One thing that EFI does is allow data logging. Anybody with a 496 should be able to check their MAT by borrowing a Mercury scan tool.