air box

[Nason]

On the air box of 40 merc it states not to exceed 3000 rpms without box , does or will it hurt the engine to run without air box? Would it be able to pull in more air without the air box? Would the jets have to be increased 1 size ?
Thanks for any help.

[Fastjeff57]

Huh? Virtually every race motor you see does not have an air box, so....

I can tell you this about one carb per cylinder motors: A standing cloud of (scary) fuel droplets will form a few inches in front of the carb at certain rpms. That "air box's" primary function is to contain that mess and prevent a nasty fire (and law suits). Silincing the intake roar is a secondary consideration.

Jeff

[Mark75H]

A standing cloud of (scary) fuel droplets will form a few inches in front of the carb at certain rpms. That "air box's" primary function is to contain that mess

very unlikely on a 2 stroke with reed valves. They are true one way check valves

[Fastjeff57]

Not so, old wise Professor of TSL (Two Stroke Lore). I've seen this happen on the 30 cube twin I built a few years ago--and I can assure you the reeds were sealing tightly--had them aart several times.

Jeff

[Mark75H]

I said UNLIKELY ... not impossible. Stuff like your Frankenstein motors are more likely than production motors :p

[Fastjeff57]

Guity as charged!

Jeff

PS: Frankenstein # 3 is running great (the external reeds triple). Trailer tested it this morning and am very pleased.

[Mark75H]

http://www.boatracingfacts.com/forums/images/icons/icon14.gif .http://www.boatracingfacts.com/forums/images/icons/icon14.gif.http://www.boatracingfacts.com/forums/images/icons/icon14.gif.

[fs5]

On the air box of 40 merc it states not to exceed 3000 rpms without box , does or will it hurt the engine to run without air box? Would it be able to pull in more air without the air box? Would the jets have to be increased 1 size ?
Thanks for any help.
mate i removed mine a few years back and i run it from low speed trauling to 6400 .i thought it was only there to keep the induction noise down.
i couldn't realy tell if i got any performance gain out of it thogh.

[Powerabout]

get the timing light out at night on a multi cylinder and you can see what happens with the fuel in the carb
Reeds may be one way valves but they have mass so momentum and harmonics as they are oscillating
The fuel and air has mass not to mention the sounds waves....

[Fastjeff57]

ight on, Powerabout!

My late friend told me of a big block Chevy he saw on a dyno. It had Hilborn injection and there was a HUGE standing wave of fuel droplets above every one of it's eight intake runners!

Just 'cause you can't see it or don't notice it, there can be a standing wave of fuel droplets in front of every carb on one carb per cylinder motors. Using one carb per TWO cylinders eliminates this due to the opposite cylinder's intake surge.

Jeff

PS: Note the rather large equalizing tube on this Yammie.

[Master Oil Racing Team]

Not that this ties in directly to reed valves and the droplets, but it is an example of some of the dynamic forces that take place within a two cycle engine. This particular incident occurred on a four cylinder opposed Konig with an external rotary valve. We were at the Pro Nationals and I was wandering the pits greeting friends the day before qualifying. Everyone was rigging up and getting their rigs ready to test. I saw Barry Anderson about to fire his off on the stands and noticed he had foam rubber shoved up inside the stinger on his pipes. Just as I was about the tell him, he fired it off. The motor went RRRUUUPPPPP....pup..pup..pup, then died, Little pieces of foam rubber were falling to the ground in front of the carbs. the foam rubber went from the stinger all the way through the engine, and when a chunk got caught by the rotary valve, the belt broke. I would have thought that the foam rubber would have been blown out the exhaust. But then no one knew either whether their had been some in the manifolds as well. I knew there were crazy things going on inside a motor with fuel, but this was a real eye opener.

[HTarver]

On the air box of 40 merc it states not to exceed 3000 rpms without box , does or will it hurt the engine to run without air box? Would it be able to pull in more air without the air box? Would the jets have to be increased 1 size ?
Thanks for any help.

Ive run these motors ever since the day they were built up until now. The first thing I do to a new mercury 3 cylinder 3 carb motor that i get is blow that air box right off the front of the motor with a 12 guage! not really but once it gets taken off, it never gets put back on. And i cant say that I see a performance gain without it, It takes alot more time and money than that.