reversion and intake manifolds
 

is there any correlation w/ the type of intake manifold used and reversion???

Re: reversion and intake manifolds
 

intake reversion, exhaust gas reversion, or exhaust water reversion ?

Re: reversion and intake manifolds
 

No.

Re: reversion and intake manifolds
 

Ditto, no.

Re: reversion and intake manifolds
 

I agree with No.. Unless you are going to run a supercharger.

Re: reversion and intake manifolds
 

Actually, a positive displacement supercharger can help fend of exhaust reversion. The spinning rotors seem to help stop/dampen pressure going from comb chamber to intake port.

Centrifugal blowers don't seem to have this benefit since the tb/carb throttle blades are afterwards and it does not have rotors sitting/spinning atop the the intake ports like the positive displacements.

=====================
When both valves are open the intake port, comb chamber, and exhaust are all open to each other.

So, I say Hell Yes, the intake can influence this.

=======================

I may be off in my thinking + knowledge, so let's hear more opinions.

Re: reversion and intake manifolds
 

That interesting, but he asked if the intake manifold can cause reversion, and the answer is still no.

Re: reversion and intake manifolds
 

There is definitley reversion in your intake manifold, especially in marine engines where the motor is under constant load and carb openings tend to be larger. That is why large plenum intakes are more desireable to dampen the paulses and create more top end power.

Re: reversion and intake manifolds
 

He asked IF the intake manifold caused reversion, not if there was reversion in the intake manifold.

Re: reversion and intake manifolds
 

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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

Re: reversion and intake manifolds
 

:eek: :D What does correlation have to do with an engine sucking water back through its exhaust system and into the motor (reversion)???

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.

Re: reversion and intake manifolds
 

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 :cool:

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

http://www.maxracesoftware.com/Reversion_in_Chamber.jpg

http://www.maxracesoftware.com/Rever..._Int_Ports.jpg

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.

Re: reversion and intake manifolds
 

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?

Re: reversion and intake manifolds
 

Looks like carbon in the intake port.

Re: reversion and intake manifolds
 

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.

Re: reversion and intake manifolds
 

I seem to remember someone explaining this to me at some point in time

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.

Re: reversion and intake manifolds
 

very interesting ! :eek:

Re: reversion and intake manifolds
 

Bad seal on the valve seat. Makes the rest null and void.
18 posts later :D :D :D

Re: reversion and intake manifolds
 

i was talking about the engine drawing water back in through the exhaust, i have 2 454's in the boat, i rebuilt both at the same time, but have blown the port engine twice in that timeframe, and it seems to be pulling water in at idle, with the engine idling on the shop floor you can see water being ingested into the exhaust- like a pulsation- the only difference between the 2 engines is that in one the bottom floor is drilled to connect the bottom runners to the top- bothe sides in the plenum-performer intakes, stainless exhaust, mild comp cams, 049 heads and flatops. the engines are in a 32 pachanga-the risers face forward, have aprox 3 ft of hose on them and dump into a 5 " collector that then exits aft w/ 5" hose that i have an internal flapper in that then goes out the back of the boat, i need to figure this out as i am getting tired of building engines for this thing, thanks for any help

Re: reversion and intake manifolds
 

After 22 posts, looks like you answered your own question, and validated the 'yes, it COULD' viewpoint.

Swap the intakes or plug the holes and see if it stops!

Re: reversion and intake manifolds
 

Leo,I see Jeff booted you off SW,I was going to call you for consolation but you cell is no longer working,Smitty

Re: reversion and intake manifolds
 

When was the last time that you built an engine, put it in a boat and ran that boat?

The intake itself has nothing to do with the reversion. Drilling and messing around with a stock intake "may" have. The answer to that is that the people that build and sell intakes know more than we do. Don't screw around with the stuff as it comes from them.

Re: reversion and intake manifolds
 

to answer your question, last week, i am a factory certified mercury, mercruiser, yamaha, volvo gas and diesel mechanic by trade, the 2 edelbrock performers i took in on trade on something else, one was drilled, and i didn't think anything of it, so i didn't drill it as you implied, not everyone has thousands to go buy an engine from someone, i usually build my own, i had a 115 mph allison w/ a mercury bridgeport before this and after this experience will probably go back to outboards, which seem to be more reliable

Re: reversion and intake manifolds
 

This dose bring up and interesting question, Can a Single vs Dual plane intake manifold change the pulsations on the exhaust side? I wounder if anyone has ever tested this?

Re: reversion and intake manifolds
 

My post wasn't aimed at you. It was aimed at the wantabe that had to post an "answer" when he didn't know what he was talking about.

As far as drilling the intake, its an old trick to gain some power on street and drag cars. Except for port matching and smoothing, I don't mess with the intakes too much. Edelbrock is smarter than all of us on building them.

You haven't said, but which motor is getting reversion, the one with or without the drilling?

Re: reversion and intake manifolds
 

[QUOTE=the duke]My post wasn't aimed at you. It was aimed at the wantabe that had to post an "answer" when he didn't know what he was talking about.QUOTE]

Well, I guess if you can't get your point/s across, or someone disagrees with you, next best thing is personal attacks and name calling. You a polotician, duke ? :evilb: :rolleyes:

Re: reversion and intake manifolds
 

I knew what intake tract reversion was.

My guess is Duke's a LOT SHORTER than me.

Re: reversion and intake manifolds
 

So do the rest of us. and it has nothing to do with water reversion, which is what the question is about.

Re: reversion and intake manifolds
 

As you guys all revere CFM/SB, check and see who he agrees with

Re: reversion and intake manifolds
 

Duke, buddy, I revere YOU, and Zone5 and 5325user, and FormulaFastech; you are one funny scizophenic!

Re: reversion and intake manifolds
 

I'm glad that you revere me. Glad you revere the other guys too. From what I know of Zone5/Formulafastech, he has been boating for the last 3 years with no reversion, and with a Crane 741 cam. You know, the one that is so old and outdated, that its no good anymore. As a matter of fact, my engine has an off the shelf, no reversion cam too. Has your boat motor run in the last 2 years in the water? 5325 user has twin engines, with milder cams than I have, and he has run 85 mph with them. They are "off the shelf" too. He'll hit over 110 with blowers next summer.

Re: reversion and intake manifolds
 

Re: reversion and intake manifolds
 

I assume that you are talking about the part in that thread about the 741??? Where he is talking about early intake opening on the 741 causing reversion?? I have to disagree. I am not a cam designer by any means, but these guys are. http://www.iskycams.com/techtips.php#2002
and they explain what causes reversion. Not early intake opening, and certainly not the intake manifold.

Here are 2 pictures of heads off a 502 with a 741 in it. These are not stock heads, and they are not stock exhaust. No signs of reversion
http://i109.photobucket.com/albums/n52/luzerne/741.jpg

http://i109.photobucket.com/albums/n52/luzerne/7412.jpg

Re: reversion and intake manifolds
 

Theory: The moving column of airflow through a single cylinder motor has mass and inertia. The flow starts and stops at the intake valve, and at the exhaust valve. The length and mass of the column before the intake valve pulses due to the start/stop and, at certain rpm will also be either amplified or lessened due to harmonics. These are affected by a host of factors such as column length from throttle plate to intake valve, and the port area. At some NON complimentary rpm, the oscillations within the port can cause a negative (or relatively MORE negative) pressure situation at the intake valve when it opens. In a case such as this, it will result in a less complete filling of the cylinder, or a MORE negative pressure situation during the intake downstroke of the piston. Exhaust primary pipe length will also have an effect on how the pulsing of the exhaust waves create a relatively higher or lower pressure immediately after the exhaust valve.

Depending on valve overlap and intake centerline, there *could* be a particular low rpm situation whereas the intake tuning could create a lower-than-average intake port pressure at the point of intake opening.
Depending on exhaust tuning, there *could* be a particular low rpm situation whereas the exhaust pulsing could create a higher-than-average exhaust port pressure at the point coinciding with the intake opening, while the exhaust is still held open. THIS WOULD be a situation that would indeed be more APT to result in EXHAUST reversion. This could indeed be caused in a borderline situation by a slight intake tract length change, which an intake manifold swap *could* achieve.

Note that the example above is for a single cylinder engine.
If we NOW consider a V8, we will invariably have some pulsations from other cylinder events coming into play. These could also cause the situation above, and may be more likely to occur in different manifold configurations.

A single plane intake may be swapped for a dual plane. In that situation, the intake pulses from other cylinders could cause the situation described in one or more cyliinders. Or vice versa, a dual plane to single plane could be the straw that breaks the camel's back.

Also, swapping from log exhaust manifolds to tubular shorty headers could be the factor that ends up causing reversion. Or vice versa. Or shorties to full length primaries.

As stated, each motor is a collection of 8 single cylinder motors operating in conjunction with each other, sometimes benefitting from the additional pulses, sometimes not.

So in THEORY, ANY change in intake length, area, exhaust length or area, or which cylinders are sharing a common plenum in the intake, or which exhaust primaries dump into which others and at what distance from the exhaust valve - THOSE CAN AFFECT whether a motor is "closer to reversion" or "farther from reversion" and also can change the rpm at which the most crucial point occurs.

So it is sophomoric to make a blanket statement like "there is no way an intake change can have anything to do with exhaust reversion".

REAL WORLD ANSWER THOUGH: It is mighty UNLIKELY that an intake swap will cause an otherwise dry (non exhaust reverting) motor to turn into a rusty lump. As with any significant change in hardware, though, a man is not wise to assume much of anything. Some cams are KNOWN TO BE SAFE. Some cams have a partial history of causing reversion in a few applications. A 741 is a cam that CAN be part of a reversion problem. LOTS of 741's running out there dry as a bone though. The devil is in the details....

mc

Re: reversion and intake manifolds
 

so what do you advise for a mild cam that is reversion free??? i am running very mild comp cams extreme marine cams, anyone have any experience w/ these??

Re: reversion and intake manifolds
 

Not being very specific about just WHAT you have for cams (very mild) or exhaust, I would suspect your exhuast isn't up to the task.