Water reversion
 

When they say water reversion with HP500's are we talking about the exhaust manifold(GIL) cooling water getting back into the engine or is it water from outside the exhaust pipe that makes its way into the engine? It is said that the cam lobe centerline has alot to do with this reversion...true? If this subject has been already been beatened to death sorry I've been busy............gofast

Reversion means that water is being sucked into the motor from the exhaust. This can be caused by too much cam overlap, too much duration, too short of a riser, etc...

A lobe separation angle between 104-108 will allow it to happen. A LSA between 109-112 might allow some water so mercruiser has suggested on their high per. engines that after extended periods of idling, the engine should be revved up a few times before it is shut off to clear any water.It is generally accepted that 109 degrees is the best LSA in a marine engine, but may have slightly too rough an idle for some boaters.:)

Water reversion has to do with overlap. Period.

A combination of duration and lobe separation contributes to overlap.

The closer the lobe separation the sooner hp/torque will peak and drop off. A wider separation will allow hp/torque to spread over a broader portion of the rpm range of the cam.

It depends on your engine and what you want to accomplish for a recommended lsa.

The amount of overlap you can handle depends on the exhaust you have.

Most engine builders like to stay with a 112-114 lsa for marine use. The tighter the lsa the rougher the idle creating the need for a higher idle speed in turn creating more of problem maneuvering in the marina and clutch wear.
I have read that a 109 lsa is used for optimum hp for a high performance engines but to my knowlege even the Merc 575's don't use that tight of an angle.

DAVE

Dave F,

So the cam overlap allows water to that is in THE EXHAUST to go back in the motor?

How does a taller riser prevent this?

I know basically what reversion is but I am unclear to exactly HOW IT HAPPENS.

Thanks

Cam overlap means that for a short while, both valves are open at the same time. This happens when the piston is beginning its' intake stroke. For a small amount of time ( cam overlap ) the exhaust valve is still open. This causes a suction or a backwards pulse in the exhaust. It is that pulse or suction that can cause water to revert back into the cylinders. The longer the riser, thus the further back water mixes with exhaust, the less chance you have of getting reversion. The larger the overlap, which means the more duration and/or the tighter the lobe seperation, the more reversion will occur.

That makes sense. So, when the say "longer" riser they really mean "taller" meaning the water is mixed farther away from the cylinder.

This must be why the don't recommend using silent choice with big cams? Because silent choise usually has a short riser?

Thanks

you have it right BH... You can still use fairly big cams but the overlap and duration are restricted as is the resulting HP. According to the guys at nickersons, they are using a roller with over .585 lift with silent choice.

The carbed HP500's had a problem with reversion and the gil exhaust. That's proably why they are now using the cmi's. The factory fix was to raise the idle to a higher level to reduce the chances of reversion. The next step was to go to a higher riser or dry tails. If you do have reversion problems, then check your valve springs. Apparently these springs had a tendancy to rust and break. The service replacement is the new HP500efi spring. I believe that it's being made by crane. Either way, if you have more than 250 hours on the stock springs, they should be swapped out.

Simply put, the further towards the transom you can get your water to enter the tail pipe the better.

I ran a Crane roller 236/244 112 .610/.632 with CMI's that are the same as what's on the 500 efi's. The water entered the tail pipes approx. 3-4 inches from the transom. No problems.

The reason they still got reversion in the Gils is because they're just a slightly improved Merc design. They have dividers inside that help separate exhaust pulses but not much more than that.
It is also true that they had problems with the valve springs. I do believe that they changed to the Comp cams double spring.

The best set up would be a "dry" setup. The pipes are still water jacketed but the water never mixes with the exhaust gas. The water is expelled through it's own pipe.
With that set up you could run any cam you wanted to.

DAVE

Million dollar question
 

Thanks everyone for the lesson. Like I said, I always new what reversion was, I just didn't know exactly how it happen. So now the million dollar question.

How do you know if reversion is occuring?

Detonation, high oil temps, loose spark plugs, tuliped valves, rust on plugs, blown holes in piston(s) and finally... meltdown.

BT

Don't forget when the tulip of the valves snap off after getting cold water dripped on them..

Blue Thunder:

I've seen reversion causing rust on valvetrain and bores & perhaps in extreme case hurt valves or completely hydraulicing a motor. How would it cause detonation, increased oil temp and blown pistons (I'm assuming that both of these are a result of detonation).

Water injection has been used for years to control excessive cyl temps & detonation. How is water creating detonation?

Guys I thought I would throw in a picture of my motors and a question since this thread did start about HP500 reversion. I was wondering with the merc risers if reversion would still be much of a issue? I do have a different cam it's a Crane 168731 and yes I did change the springs they are now Comp Cams double that have a normal seat pressure instead of the 170+ pounds I used to have:rolleyes:
I have never seen any evidence of it like steam out the exhaust or rust in the valve trane.

The best way to tell is to run the motor, idle it for a while and then shut it down. Take the exhaust off and look in the port. If you see water, you have a problem.

CCperf... water would take space in the combustion chamber thus increasing the effective compresion ratio of your mixture. Too high a compression and you get detonation/heat. Too much heat on the piston may first show up as high oil temps. I have an engine on a pallet in my garage with the loss of exhaust valve head checkmate454 mentioned. This was due to what I described above.

BT :cool:

Hey BT:

I'm not busting your balls I'm just trying to learn soemthing here.
I don't doubt that a valve head may snap or tulip due to thermal shock(cold water on hot valve) or overheating. But I'm confused. Are you suggesting that both conditions are happening simotaniosly. How can a cylinder be so hot as to burn pistons and valves and also be taking on fresh cool water at the same time? Its either hot or cold, not both. Although I guess this could take place after the motor is run hard and you then go to idle I can see the water damaging the valve which would in turn impede the efficiency of exhaust gases out that would increase cyl & oil temps.

Did this occur at idle speeds or at cruise speed. even if a motor reverts like niagra falls at idle, it most likely goes away at speed. If this is at idle and detonation was so catostraphic as to cause this damage would you not hear the rattling and or wash out plugs due to excessive water?

CC.. If you suck in a small amount of water through the exhaust valve, then it closes, you have effectively increased your compression ratio, because the water takes up space in the combustion chamber. Lets just says it take up enough volume to create a compression ratio of 20:1. What octane fuel would you need to prevent detonation with a 20:1 compression ratio?

In my case I never heard any pinging. Probably due to open exhaust. I'm sure it was happening. I was at about 4500rpm when it blew. I think what happens is as the exhaust valve looses its seal due to tuliping, the suction of water increases and things go bad in a hurry. I had been having an oil temp problem on this motor before it blew up. I don't think there is a hole in the piston... but I haven't tore into it yet to see. That will be my winter job, if nothing else lets loose in the mean time. I think holes in the piston are more often caused be a lean condition over a longer period of time. Remember... all this is just my .02.

And lastly... stop bustin my balls!! :D

BT :cool:

Get the new issue of Hot Rod mag. Good article explaining the basics of cam design.

Dan

LOL,

Sorry Blue Thunder I just can't buy that one. Static & effective CR are two differant animals. If your valvers were as bad as you said, what water was there was likely squeezed right past them. Additionally, you're accounting for some unknown amount of water increasing the effective CR, yet this "water" would also have several other effects on the combustion process:

1) cool the mixture, effectively canceling or eliminating preignition / detonation

2) increase the perceived octain of you fuel, also countering detonation effects. (this has been done in big turbo application for 20 some years)

3) Most importantly - you are NOT encountering "reversion" at 4500 rpm. Once you reach a certain rpm say 1500 - 2000 ish, the exhaust gases are no longer being pulled backwards. If you were getting water in that cylinder at 4500 RPM it was coming from a leaking exhaust / manifold riser gasket or crack, leaking head gasket, cracked head / block, etc., etc,

Or quite possibly you just had a failed exh valve. Was it Inconel or good stainless or just std junk GM stuff. How many hours? I think you'll learn more when you tear that motor down. Thats my .02 cents...

Yes you are right CC.... failed exhaust manifold causing water infiltration. This makes the water mixture in the exhaust closer to the valves and caused reversion of fluid into the cylinders. I had an unknown valve composition, so they may have started tuliping as well. I believed this to be causing what I said....detonation. There were other strange things about this motor. High valve spring tension (unknown exact values) are one. That may have also started the malay.

Reversion is an interpretive word CC. The amount of reversion on an engine with a cam sporting a low LSA is often controlled by how far away from the valves the water mixes with the exh gas in the manifold. If the gas/water mixes sooner in the manifold due to reasons other than LSA, and gets sucked into the engine, it is still reversion. Just a different variable changing. I guess I am missing your point entirely. Seems simple to me.

If you think an uncontrolled amount of water in your combustion chamber is going to cool the chamber, you went to a different school of hard knocks than I. Pressure creates heat no matter how you slice it. More pressure creates more heat. Whether you choose to call that type of heat "detonation" or not is up to you. It has the same result either way. Your points 1 and 2 are incorrect with uncontrolled amounts of fluid mix in the chamber. Pressure creates HEAT!!! That is what I was suggesting.

Static CR is your base measure and relates directly to the effective CR with a given fluid/vapor concentration, within a given system (ie. engine). Change any variable (increase the fluid/vapor volume) and you create more heat. More heat creates all bad things mentioned.

Have you learned enough yet? :D

BT :cool:

WOW.......This one is getting deep. I am going to let you 2 guys argue this one out. Interesting reading from where I am sitting!!:D

Hey BT:

I guess were going to have to agree to disagree on a couple things and I may need some more schooling.

First, to say that any pre-mixing of water is reversion is a little mis-leading. Were arguing semantics. I think you would agree that the condition Black Hawk was referring to was the traditional definition of reversion, i.e. water was being pulled back into the cylinder as a result of ineffective manifolds or cam lobe center choices, etc. You now acknowledge that your situation was reversion as a result of a water "leak". In my school, A water leak is completely different than a reversion issue. A leak is merely equipment failure. You can't tune for it. Changing valve springs, valves, cams or installing 10 foot tail pipes is not going to correct that problem.. If you’re mixing water any closer than say a stock Merc manifold or a Gil manifold as a result of a bad gasket or crack that is a "leak". That leak will likely occur at any rpm as where traditional "reversion" is an idle type situation hence you test for it at idle and the so-called Merc fix of increased idle.

As for CR, I agree that any obstacle in the chamber has the potential to increase pressure and or heat. But you must also recognize that adding 20 or 50cc of cold water is much different than adding 20 or 50cc of piston dome or decreasing the chamber by that amount. Also water in a cylinder with a narrow lobe centerline with questionable valve seal is not the same either. Hell for that matter you can build a motor with a static CR upwards of 10 to 1 that runs on pump gas given the right cam choice. If you think you had a marine motor taking on water in such severe heat & detonation that it snapped a valve head off then I doubt anyone can convince you otherwise. Perhaps you know best.

Thanks

Actually CC, the original question was "what is reversion". Technically, reversion is "when something goes back to where it came from"... in our conversation this thing was cooling water. In low LSA instances and internal leaks in the manifolds, water can get sucked back into the engine. This is at least an iterpretation of reversion.

Our conversation, symantics aside, was more focused around the affects of reversion on the internal operation of an engine. If I read you description correctly of the ill effects of reversion, you said valve train rust and hydraulic lock. Now I've never heard of hydraulic lock in a reversion case. Reversion in our definition only occurs when an engine is running. I suppose hyd lock happens in a running engine in extreme cases... maybe even did in my case. The other item, valve train rust... well rust is a static kinda thing as well, so I still haven't learned a different way than I proposed, on how reversion is bad to a running engine.

I guess you are saying reversion is good on low LSA grind marine engines because the reversion of water helps super chill the fuel charge? Well CC, we will have to agree to disagree on that one too. I would say in this case, you clearly know best.

BT :cool:

Your missing the point BT. In that the initial post was as follows:

When they say water reversion with HP500's are we talking about the exhaust manifold(GIL) cooling water getting back into the engine or is it water from outside the exhaust pipe that makes its way into the engine? It is said that the cam lobe centerline has alot to do with this reversion...true? If this subject has been already been beatened to death sorry I've been busy............gofast

And the subsequent definition was as follows:

Reversion means that water is being sucked into the motor from the exhaust. This can be caused by too much cam overlap, too much duration, too short of a riser, etc...

I made the assumption you were referring to "reversion" resulting from a cam issue as in the case of a HP-500 or an equivelant cam situation. Therefore your detonation and valve issues seemed rather extreme.

Also what I meant about your definition of reversion was rather that I thought it was too all inclusive. Sure, any water "reverting" back into the motor could be considered "reversion". By the same token, one squirting a garden hose in the exhaust would also be classified as reversion. In the context of the initial post I think all would agree that reversion would be defined by any water being being sucked into the cylinder as a result of intake/exh pulses. Assuming the mixing is done as it was intended at least aft the riser.

Whereas in your application it appears water was leaking before the mix, perhaps in the manifold or in the riser gasket. Therefore the water was falling or leaking into the cyl, not being sucked back from the tailpipes as in the case of a normal reversion. Normal being at least as far back as a stock Merc set-up. I don't care what cam/lobe center you choose there isn't one in existance that will prevent water from getting in your cylinder in the situation you described, even if it were dry tail pipes.

Hopefully that makes a little more sense.

that would be over the transom headers right .

no. Plenty of dry pipes that exit through the transom.

just so you’re aware this thread is just shy of 2 decades old. Feel free to start a new thread with your questions if you need to….