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reversion and intake manifolds

Old 10-23-2006, 09:51 PM
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Default Re: reversion and intake manifolds

Originally Posted by racinfever
To clear things up, heres the definition of correlation. Making my response relative. I think one of us has misunderstood the meaning of correlation.

n 1: a reciprocal relation between two or more things
What does correlation have to do with an engine sucking water back through its exhaust system and into the motor (reversion)???
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Old 10-23-2006, 10:23 PM
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Default Re: reversion and intake manifolds

I'm sorry Duke but I don't see where the original post indicated anything about exhaust reversion. From what I can tell, you are assuming he means that!! Correct me if I'm wrong! Better yet, could we get the question rephrased. At this time, I'm thinking this is one I shouldn't have gotten involved in but there is a lot of interesting information out there relative to ( intake) reversion and how it effects performance.
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Old 10-23-2006, 10:34 PM
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Default Re: reversion and intake manifolds

Originally Posted by racinfever
I don't see where the original post indicated anything about exhaust reversion. From what I can tell, you are assuming he means that!! .
Thats how I'm reading it. I've never heard reversion described as anything else in the boating world. If we want to talk about the air charge, and exhaust gas being expelled, and fresh air pulled in, etc etc, then of course the intake manifold has something to do with it. I've just never heard that called reversion
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Old 10-24-2006, 06:33 AM
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Default Re: reversion and intake manifolds

Here's the issue, and thus why I asked on Post #2 what kind of reversion.

Reversion is reverse flow. So, in an engine we have intake and exhaust reversion. Now, in the marine world, many speak of reversion as water coming back into motor. This is fine, but should always be stated as exhaust water reversion or ect

On the intake side this happens as the intake valve is closing since the piston is rising to TDC for compression stroke. So, this is one form of intake reversion. I think this is the type RacinFever is talking about

Also on the intake side, during overlap ( intake opening + exhaust closing), we have the piston approaching TDC . A slow, lazy intake port may not have ability to overcome residual exhaust psi present in exhaust port and/or comb chamber. A sow moving 'lazy' exhaust will also contribute to this.

You ever see a 'dirty' intake bowl or port ? It does happen - it shouldn't - but mismatched parts, valve events, etc,etc leads to this.

Here's good evidence of intake reversion during overlap (when exhaust gas actually makes it past intake valve and into intake port) from a running engine




Last edited by SB; 10-24-2006 at 06:40 AM.
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Old 10-24-2006, 06:36 AM
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Default Re: reversion and intake manifolds

Anyway - I'm not out to blow this whole thing out of the water. It was a vague statement since most think that 'reversion' is only exhaust water coming back to combustion chamber. Not by fault of author since most only talk about this form - but fault of all of us not talking and distinguishing about all forms of reversion ie: back flow.

There are many other reversion events in a 4 cycle engine and I still believe that the intake manifold design can influence reversion - reversion during overlap and reversion when piston approaching TDC during IVC (intake valve closing.)

Just something to think about.

Last edited by SB; 10-24-2006 at 06:39 AM.
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Old 10-24-2006, 09:48 PM
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Default Re: reversion and intake manifolds

Originally Posted by SB
Here's good evidence of intake reversion during overlap (when exhaust gas actually makes it past intake valve and into intake port) from a running engine
This is a good picture of an intake valve with a bad seat/lousy seal.

What does this picture have to do with the original question about the intake manifold?
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Old 10-24-2006, 09:52 PM
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Default Re: reversion and intake manifolds

Looks like carbon in the intake port.
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Old 10-25-2006, 06:32 AM
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Default Re: reversion and intake manifolds

Originally Posted by Kidnova
Looks like carbon in the intake port.
Yes it is. Notice how it goes all the way up the the entrance of the heads intake port.

Now why would I post a pic of a damaged seat or bad valve seal on this discussion ?

Anyway - when dealing with a stock typpe motor with stock cyl heads, stock cam, etc,etc, Duke is correct that swapping an intake will not likely cause intake/exhaust reversion.

But, when we start touching things we have to be careful in what heads / what porting / what camshaft / what intake manifold we use and how we modify them.

Combustion gases getting into the intake tract is not as uncommon as some people would think.
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Old 10-25-2006, 07:41 AM
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Cool Re: reversion and intake manifolds

Originally Posted by SB
Yes it is. Notice how it goes all the way up the the entrance of the heads intake port.

Combustion gases getting into the intake tract is not as uncommon as some people would think.
I seem to remember someone explaining this to me at some point in time
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Old 10-25-2006, 09:12 AM
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Default Re: reversion and intake manifolds

Theoretically an intake could have some effect on reversion in the exhaust. One of the things that an intake can do is change flow velocity of the intake charge-the speed at which the A/F mixture moves through the engine. In some applications this velocity can alter both the combustion cycle and the exhaust cycle. This can be critical at idle when most reversion occurs in boat motors. If you went with a larger plenum/port intake on an engine that was on the edge of reversion, the resulting loss of flow velocity could increase the chance of reversion in the engine.
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