bcarpman

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?

SB

iTrader: (1)

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.

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

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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.

articfriends

iTrader: (1)

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

SB

iTrader: (1)

An 'air gap' cast iron intake.

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.

stevesxm

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.

Nordicflame

iTrader: (4)

Perfectly stated

SB

iTrader: (1)

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 , 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.

Kidnova

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

Just trying to learn something here

Nordicflame

iTrader: (4)

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

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

Later,
Dave

BGIII

iTrader: (3)

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?