Emi exhaust still reverting
 

Engines: Twin 509 500 HP carb'd. Crane cams Hydraulic Flat Tappet. 534/551 lift 224/236 @ .050 112 LSA .Over the last several years I had issues where the engines would seem to load up at idle while in the opened loud mode and run smooth while in the quiet mode with no loading up. That setup was with the Mercruiser silent choice and the Eddie Marine EMI-512 short SS risers.Many people told me it was reversion. Then I switched the exhaust tips to Drew marines shotgun III which then i thought cured the reversion issue because I had no loading up issues. Those spring loaded tips added back pressure to the exhaust. Little did I know it was still reverting. Last winter I removed the 2 inner exhaust manifolds to get to the starter and I noticed rust spots in every exhaust port on both motors. These heads are 2 years old. Just recently done over. So I decided to get rid of the short EMI risers and the Merc silent choice. I sent my EMI risers back to Eddie Marine and had them extended to the standard length EMI-111 which comes with the thunder series manifolds. The water comes out at the end of the pipe. I was told any big cams must have a longer than stock pipe to prevent reversion. Missing the quietness of the merc silent choice I decided to go with Gil select sound clamp on switchable mufflers. Last weekend my first test run. Gil mufflers in quiet mode. Runs smooth, sounds awesome. Gil mufflers in loud mode..Runs not so smooth, sounds loud and seems like its loading up again.Close the mufflers and it smooths out and idles fine again. Wow I'm in shock!!!..What an expense I just went through. Had 4 pipes extended and bought new switchable mufflers AND the same problems as before....HELP!!
My camshaft isn't that radical...friends of mine are running HP500's , Big blocks with a lot bigger cams than mine ..Exhaust systems like Gil, stainless marine they are all about the same in exhaust length before the transom........Any input would be appreciated

[ATTACH=CONFIG]542185[/ATTACH]

https://www.youtube.com/watch?v=MRMGLcQKbzY

We're the cams degreed when installed?

I don't know. I bought the boat with these engines. The only upgrade i did was MSD ignition and the timing is locked @ 34 degrees. Please explain why you asked about the cams being degreed?

Hmmm, dual plane intakes cut down on reversion a little too.

I'd say quite possibly, because of the mild cam (however, it does have a lot of exhaust duration) and etc, you could very well have too much initial timing.

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As far as exhaust being 'closed' having less reversion, than open, it is probably because the design of your mufflers dampens the exhaust enegy waves (back and forth) and thus not reverting. I have not seen your mufflers, but this does and can happen with some designs. Mecruiser even has an internal baffle one can install that does the same thing ie: dampens exhaust pulses.
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Are you sure it's not condensation that's not falling back in and causing the 'rust' ? Some companies use 'turbulators' that install between the riser and manifold to help catch this.

Again, I have a feeling you have too much initial timing. A motor like this will probably do better with somewhere between 16-20 initial.

BTW: other than adding water much later, Eddie Marine exhausts do not have any other safe guards against reversion like welded in dams, steps, or etc. They are just smooth with a smooth tranisition between the inner and outer pipes. Their risers don't raise up high like the late model HP 500's neither, which creates a larger rate of fall.

http://www.bullockmarine.com/mercury...500Bulldog.gif

I called Eddie Marine yesterday and they told me to send the 4 risers back and they will add a few more inches in length and also add a dam to stop the water from creeping up the pipe.

[ATTACH=CONFIG]542213[/ATTACH][ATTACH=CONFIG]542214[/ATTACH]

Thanks for your reply. I believe you are correct about the exhaust pulses. As long as there is some kind of back pressure it stops reverting. Does this look like condensation or reversion? I was told in previous posts last winter it was definitely reversion. Can't change the timing. Those msd weights and springs screw up and rust. That's why they are locked out. no moving parts for advance at all. I guess I'm going to run in closed mode at idle then open them after 1000 rpms for now.At least to the end of boating season here. Eddie marine said they would add a dam and extend them longer but it will take at least 3 weeks. Thanks

If the cams ended up getting installed a few degrees retarded it would change the valve timing events, most notably EVC ATDC. With the longer exhaust duration that it already has, this would amplify low rpm reversion pulses.

I just ordered 2 MERCRUISER EXHAUST RESONATOR KIT that is supposed to stop the reversion by changing the pulses in the exhaust. Lets see what happens

https://www.perfprotech.com/blog/art...ust-resonators interesting info

The exhaust resonators (provided with the engine package or available separately) are designed to provide increased resistance to water ingestion due to the tuning effects of the exhaust system. Quicksilver resonators are designed to break up the exhaust pulses.

If this works, I could have saved a bunch of $$ this past month:mad:

35Fountain, the Merc resonator looks interesting, but first I would try installing some salisbury type flappers on the ends of your tips to see if this dampens the back pulses enough to tame the reversion. I have a long thread on here about reversion with a mildly cammed engine when I was running mine on a test stand, and I found that simply installing the flappers significantly cut down on the reversion. Before doing this I could hold a $20 bill in front of the tailpipe and it would suck it right out of my hand - proof positive that boats eat money! :)

It is strange how one engine with what appears to be a mild cam setup will revert, while others that seem to be more on the ragged edge run happily along without apparent problems. My suspicion is that there are a lot of boats running around out there with some degree of reversion occurring, and no one knows about it.

I have always wondered about those. They look like they would absolutely work as they appear to be just a check valve as flappers are also, just to a lesser degree. My question has always been how much of a restriction they would be. Over the years, I have come to really enjoy silent choice, but I still enjoy hi-performance engines and that can be limiting as to what you can do. It would be interesting to know what HP limits Merc claims for these, kind of like we know that the Y-pipe becomes restrictive at somewhere just over 300 HP.

If the timing chain has stretched I believe that can also retard the cam and possibly cause reversion on an engine that is on the edge.

^^^^^Up for the factual sentence of the year.....for two categories: Technical and Financial !

Being frugal I would have used a ONE dollar bill.

LOL ! So true !

I heard a rumor that the vacuum is greater when using $100's.

Teenage boy walks into the kitechen and nervously asks his parents:
"Mom/dad - Can I go to the 50¢ concert ?"

They both reply without looking :
"Sure. Here's a buck. Take your little sister."

That also applies to females. :D

I already have the external flappers on there. This problem has been with me for several years. I can tell there's a problem just by the sound of the engines upon opening the mufflers. Apparently its a problem from resonating exhaust pulses causing reversion. or is it cam overlap. Alot of Mercruiser engines have this problem
Mercury Marine part number 860222A1 RESONATOR-EXHAUST is used on the below models
454 MAG MPI BRAVO (GEN VI) GM 454 V-8 1998
454 MAG. BRAVO (GEN. V) GM 454 V-8 1996-1997
454 MAG. BRAVO MPI (GEN VI) GM 454 V-8 1996-1997
454 MAG. MPI BRAVO (GEN VI) GM 454 V-8
454 MAG. MPI HORIZON (GEN. VI) GM 454 V-8
496 MAG (Base Model)
496 MAG (H.O. Model)
496 MAG EC (Base Model)
496 MAG EC (H.O. Model)
502 MAG MPI BRAVO (GEN VI) GM 502 V-8 1998
502 MAG. MPI (GEN VI) GM 502 V-8 1996
502 MAG. MPI BRAVO (GEN VI) GM 502 V-8
7.4L BRAVO (GEN. VI) GM 454 V-8 1996-1997
7.4L BRAVO (MPI)(GEN. VI) GM 454 V-8 1998-2000
7.4L MPI MIE (L29) GEN. VI GM 454 V-8 1998-2000
8.1L INBOARD (Base)
8.1L INBOARD (Base) EC
8.1L INBOARD (H.O.)
8.1L INBOARD (H.O.) EC
8.1L TOWSPORT (Base)
8.2L Mag (Base Model)
8.2L Mag (H.O. Model)
8.2L MIE MPI (GEN. VI) GM 502 V-8

I posted a list of Mercruiser engines that these resonators are supposed to be in. How restrictive could they be....?

If we ran duals into a Y into single pipe like many Ilmore V10's, life would be better. Double amt of exhaust pulses per pipe. Would be almost like doubling the engine rpm.

Here's what they look like
[ATTACH=CONFIG]542226[/ATTACH]

[ATTACH=CONFIG]542227[/ATTACH]

B- Break
O- Out
A- Another
T- Thousand

That's not what I was referring to. I just did a search and didn't come up with anything. It seems to me Merc had a 1 way exhaust check valve, like a reed valve on 2 stroke motorcycles that mounted close to the riser.

Read this thread, have them make you a pair similar to these. These will not revert...

http://www.offshoreonly.com/forums/d...e-exhaust.html

are you running a circulation pump or crossover..thermostat? water temps makea huge differance on emis

circulation pump

you mised a ? ..oh well..installed many many many emi thunder exhaust.no issues..oh well good luck..

you have used several sets of risers on the same manifolds. were they pressure tested? it is only reversion if it is not a leak. you say fairly mild cams but they came in these engines. it is a pain but doable to degree cams in the engine compartment. you gotta hog out center of degree wheel so balancer socket fits thru.

The cam that came with these engines is a Crane 134241 going by the specs on my dyno sheet. There is 1 thing that is different. The valves intake and exhaust are longer than the stock height. I found this out when i did the heads 2 years ago. Maybe that is creating a higher lift..I don't know, that's too technical for me.The exhaust is fairly new and Eddie Marine just redid all 4 risers.. They used to be the short style and now they are the long style. As i said in previous posts ..It only reverts when the exhaust is in the open free flowing mode. It does not happen when the Gil mufflers are engaged. When the select sound mufflers are engaged it is creating back pressure in the exhaust system which in turn is stopping the reversion. I can tell this by the sound of the engines. Much smoother running even when revving from idle. BUT if i rev from idle while opened its sloppy and hesitates like it was loaded up Maybe the 2 merc resonators will be enough back pressure to stop this when in the open mode. We will soon see

To help with reverison, Make sure your idle rpm, in gear is at 750rpm or higher.

Thanks i will check the idle in gear..I also just received the merc resonators. I will put them in for a try also

Back in the 2001 era Volvo Penta with 496 had problems with water reversion because Volvo in 1999 did away with all exhaust water shutters / exhaust flapper valves. Volvo on stock apps installed check valves in the side of the risers that help a lot and for thru hull and silent choice exhaust they installed an exhaust crossover upgrade kit in which Corsa helped make part of the kit for Volvo. This crossover help a lot with water revesion.

The Volvo kit part # is 3862055 and the Volvo Service Bulletin about it in 2001 was 25-2-7 describing the problem and fix.. I can not pull any of this up to post here. maybe someone can find the info and post it. I will check with Corsa and see if they have any info about it It has worked out very well for Volvo installing the crossover kit as they do it on all their apps with thru and silent choice exhaust.

The crossover and or the check valves in the risers help equalize exhaust pulsations in which help against water reversion. It helps a lot but not 100 % plus there is other factors that comes into play with water reversion. Also too high of idle on a hot day at engine shut down can make the engine diesel / run on in which causes water version to. Just saying. You have to find that happy medium with idle rpms to help against water reversion and prevent engine run on at shut down - I say help not cure it 100 %.

My guess is that the reversion is caused by high vacuum at idle, caused by the 34 degree advance.
My engine is a 509 with 500 efi cam and intake, CMI headers and silent choice. To cure the reversion problem i have set the advance at 1 degree at idle, which gives 9 Inch hg vacuum at idle

I raised the idles to 650-700 in gear and it seemed to be better. I had the exhaust on the open position for 5 minutes idling and no load up. I'm going to install the resonators anyway and see what happens.

Interesting. High vacuum. :party-smiley-004:

1 degree advance at idle??? off of TDC how did it run?...doesn't make any sense....My timing is locked can;t be changed. There is no reversion with the mufflers in the closed position..That's because in the closed position i am adding back pressure and the back pressure is stopping the pulsations of the exhaust. Nothing to do with timing or vacuum. BTW. My vacuum is 14 with my cam. stock should be around 20 or more. 9 vacuum is low. There's your problem. You must have a large overlap cam, and silent choice means your dumping the water before the y pipe and its creeping back up the pipe. I bet it doesn't revert in the silent mode and if it still does your cam is wrong. What is the LSA and the duration @ .050

It runs OK but it is weak just of idle due to the low vacuum, It does not matter if it is weak at idle since i never accelerate hard from idle anyway.
I know the reversion is caused by the cam and the silent choice, but it is the cam and exhaust i have so the easiest and cheapest was to tamper with the ignition curve.
I bought the cam second hand and where told that it is a 500 efi cam 230*/236* @ .050 and 114* LSA.
Your vacuum is not high. I have been told that 525 efi has 14-15 at idle.

I just installed the Mercruiser Resonators today. Started up on garden hose. Open or closed position of the exhaust...very smooth revs, no hesitation. Resonators took out the low end bark sound from the exhaust. Hopefully not to quiet while cruising at 3200. we shall see. Test ride tomorrow.