thoughts on exhaust port air pump bypass
 

OK--I am at it again.
I have been looking closely at an engine in my little man cave and as I have briefy talked about before ---the exhaust ports that the airpump uses really bother me.
A lot of people that remove the air pump close these off. Is that an OK thing to do or not?
I really dont know for sure--but I do know for sure that port does move some exhaust flow.
Every engine has back pressure. With our zero overlap design we cannot take advantage of this back pressure as engines with a little overlap can. We do what we can to try and increase exhaust flow. Right?
That usuallly means headers of some design and that means in a lot of cases blocking of the aip pump access to its exhaust ports. Now whether or not that port if left open would increase flow, decrease any back pressure etc remains to be proven.
The last couple of days i have been playing with this engine. Turning it with a long handle etc. I blocked off the normal exhaust port with gorilla tape and left the air pump port open. One rotor at a time. I was surprised at the amount of flow that came out. You also have to respect the amount of carbon build up in those ports.
Next I took smoke and just pointed it toward the air pump port and watched the smoke penetrate into the exhaust port sleeve. It was coming out right next to the side seal. Ok I had looked at that before on an engine that was taken apart, but its nothing like seeing it in action. now my thought was " is it possible that space is hotter than the exhaust port sleeve due to stagnate exhaust gas that is penetrating and staying in that area? Could all that carbon buildup be affecting that area?"

Now i know on teardown that area right next to the rotor looks pretty clean, but a little ways in its not at all. I cant help but wonder if that dead space is affecting the side seals/springs?
I hate dead spaces in areas of flow.
soon I think I am going to open mine up---just for the hell of it. Add a small pipe and small muffler or get it wielded into my midpipe?
It may not make any difference, I dont know, but maybe i will sound different from everyone else!
OD

Boy, you must've been bored lately! Hahaha

I am lost OD. So are you saying blocking it off adds back pressure?

... OD ... you need to sit back and relax ....

yall know it. What the hell is wrong with me? I swear I have a life.

Closing causes backpressure?- I dont know for sure. Its a dead space. Would the exhaust be less restrictive with them open? No hard facts--- it seems to me it would and it would probably make me feel better.

My wife is about to put me on man cave restriction.

I agreed with your wife.

in fact. I think she needs to "remove" your man cave for good. lol

Lol--you are probably right but then again i would be in the house all the time...........:)

I am not giving up on this so easy!
? What does the secondary air pump do to exhaust port temps? Not exhaust gas temps--but the port?
HUHUHUHUH?
minds want to know.
i need more medicine I swear to God.

Heh - good on you OD . I must admit I have looked at those little ports and thought ..................... I wonder ....................... then ........................... NAH !

Thanks Bret----i think these things either need to be use or closed in the exhaust port itself---not just with a cover plate on the header?

No 4 cycle engine uses backpressure in a positive manner. Backpressure is always bad. A good exhaust takes advantage of acoustic tuning and the velocity of the exhaust gasses. Backpressure is a misnomer that is widely used but is always wrong.

Don't worry about that port. You won't get anymore power from hoping gasses flow through it.

ok RG answered your question, its time to take your meds OD.

interesting thought tho- whether it makes a difference of any kind to have it blocked on the inside as opposed to the outside? temp wise, seal wise, carbon wise, magic wise?

:nono: The port is there to allow air into the exhaust to warm the cat up. If you block it off, it's just that. Blocked off. There is no way for any additional back pressure to occur if it's blocked externally.
Try blowing through a straw. Air passes through it fine. Now put your finger over the end. That's whats happening to the port when you block it off.

Lol----your probably right NY and up the doseage!

I think maybe RG misinterpreted my oridginal post? I am not looking to gain power per se, although it would be nice, i am thinking that since this is a dead area in a hot zone (sort of like me at a Club Med) then it may be adding to corner/side seal problems? If air is not flowing through those areas then they cant cool down. If it is an area of hotter temps then the corneside seals are going right by it. Study after study has shown that the hotter the exhaust port the shorter the life of the side seal springs. This causes a slow reduction in power/sealing etc etc.
The immediate area behind that sleeve is nothing but air, cast iron and a bunch of carbon deposits.
When I get time (who knows) i want to add a pipe to the header hole and measure the amount of exhaust flow coming out and its temperture. That should give some indication of what is happening there?
If it can be sealed on the inside--then that means the water jacket size in that area could be
increased?
My mentioning of it possibily being a restriction is kinda out there-- i know. But any dead space in an area of flow is a restriction--maybe a very small one granted. In this case it possiblly could be a small restriction from turbulance as the exhaust pass's by? Probably not enough to even worry about. But to help explain what I am thinking, visulize a wind that blows pass an entrance to a canyon or alley? What is happening right at the entrance? Right, its pretty turbulant. Thats my picture of what may be happening concerning the exhaust flow as it passes by that area. Not to mention it has to deal with a 90degree turn at the same time!

But my main thought remains that it may be a hotspot that needs attention. If it is then how do we deal with it best--opening it or closing it from the inside?