tomcat

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.

stevesxm

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...

James

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 -

SB

iTrader: (1)

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 !!!!!!

bcarpman

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.

bcarpman

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....

SB

iTrader: (1)

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.

I'll share experinces in a little bit.

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

SB

iTrader: (1)

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.

stevesxm

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

SB

iTrader: (1)

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 ?

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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.

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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 !