Removal of 496HO restriction plates
 

Been following threads here and on hotboat.net and some have claimed speed increases of 1 to 3 mph by removing the "turbulator" plates between the exhaust manifold and riser. Does anyone here have any recent results, and if so are you getting the results while also running switchable exhaust and/or mufflers? I've got corsa quick and quiet plus and am wondering if I'm likely to see results with that set-up. Thanks.

Re: Removal of 496HO restriction plates
 

ttt !

Re: Removal of 496HO restriction plates
 

Well, I can see why no one will respond. If you are out of Mercury warranty I can see you wanting to do something. If you are still in warranty, I suggest to leave it alone. Another problem is that if someone says its ok to take them out, then they are liable for engine problems if something happens to your engine. Raylar has an engine kit that includes removing the plate as well as grinding the exhaust runners in the manifold to open the exhaust runners for better flow. He says this gives great benefits. I am surprised he hasnt responded as well. He would be the one to give you a HP gain I think.

Anyone else?

My .02.

John S.

Re: Removal of 496HO restriction plates
 

waiting for my gaskets to get here, will let you know what i find out.

Re: Removal of 496HO restriction plates
 

It is good for a little bit of power. When I went to Merc school last year the instructor told us that they were for colder climates and were designed to catch condensation and burn it off when the engine was run. Wne I worked at a shop in California we removed severeal sets for customers and they were pleased with the results. We did however inform them that they would not have a warranty against water reversion anymore. Im not recomending that you do it but there are some power gains to be had.

Re: Removal of 496HO restriction plates
 

When you pull the risers off to take out the plates, take the risers down to your local polishing shop and get them polished. Cost me about $50 and they look great! I'm sure the polishing made me faster as well :D

Re: Removal of 496HO restriction plates
 

The turbulator plates in between the risers and the main exhaust manifold on the Merc 496's are not to stop reversion, they are as someone else here stated to catch some of the moisture in the exhaust and burn it off because the stock engines have iron seats and steel valves that easily rust when exposed to moisture when stored, especially in the water. The problem is not encountered with our kits because our aluminum heads are equipped with special nitrided stainless valves that do not rust in the engine and our seats are also alloys that are very rust resistant. We also give our kit purchasers details on how to do some slight porting on the Merc 496 manifolds where we have been able to get them to flow much better with just small changes. We have made in excess of 550 Hp on the Merc 496 manifolds and risers with our kits and manifold mods. They are really nice parts for stock manifolds as compared to many after market manifolds who make horsepower claims based on comparisons to the old Merc "log type" exhaust manifolds. Don't be to quick to abandon them for the promise of big horsepower increases from some other manifold manufacuturers. We have tested quite a few and we know along with various headers systems how they all tend to affect power output of the 496MAGS and HO's These plates can be removed in stock 496's and because they restrict the exhaust opening diameter from 3-1/4" to just about 2-1/4" in diameter and with this restriction they have a moderate affect on the power of the engine especially above 4000 rpms. We have seen about 10 to 15 addtional horsepower at 5000rpms on the dyno and there are several boaters who have removed them and seen measurable increases in power and speed. You should not need to buy new gaskets to remove them as there are two gaskets at this flange now, one on each side of the turbulator plate. We have always found in most cases that carefull removal of these graphite coated gaskets will usually allow one to be reused, as this is all that is required when reinstalling the risers less the turbulator plates. The warranty could be a problem with Mercury if the motor is still in warranty and expierences any problems, since they may use this as a reason to dishoner the warranty, although your own Mercury dealer has some discretion here, depending on how he looks at the actual problem., ie: was it caused by this removal or was it an entirely different issue. It will always be our recommendation that you the boat and motor owner will have to decide what you choose to do to your Merc 496 package when it comes to warranty issues or not. I know our kits will not have problems with turbulator removal issues but as for stock motors, that's going to have to be based on your use conditions and your personal choice.
Just some facts and thoughts

Ray @ Raylar

Re: Removal of 496HO restriction plates
 

Thanks Ray,
I knew you could shed some light on this area.

John S.

Re: Removal of 496HO restriction plates
 

On a 454 and 502 there is a resinator in the riser. Will removal of this net you any gains also?

Re: Removal of 496HO restriction plates
 

No, no such animals in the 454 - 502 packages that I know of, seems this is a 496 "exclusive" Ha!
Ray @ Raylar

Re: Removal of 496HO restriction plates
 

So in the end analysis, it would be riskier to remove them
from a boat that is slipped for the summer? As opposed to a trailered boat...in terms of the potential for rusting the valves and seats? Isn't this potential for rust exhaust stream moisture almost instantaneous on shutdown wether it's on a trailer or in a boathouse?

I'll be pulling mine off in the next couple days to facilitate the changing of exhaust tips, and have watched for your response.

10-15 HP on a dyno above 4000. Any negative effect on low RPM torque?

Re: Removal of 496HO restriction plates
 

Mercruiser does make a "Exhaust Resonator Kit" which they "strongly" recommend for all 454, 502, and 496cid engines, and can be used on other model gas engines.

The exceptions would be sterndrive models with Silent Choice, below swim platform exhaust, S-type exhaust, or mufflers that mount between the exhaust elbow and exhaust tip.

Unlike the turbulators, the purpose of the resonators is to reduce "the tuning effect" in the exhaust, which can contribute to water intrusion. And unlike the turbulators that mount between the manifold and elbow, the resonators mount in the wet exhaust hose at least 13" downstream from the elbow. The following is a direct quote from the resonator kit instruction sheet:

"The resonators help to break up the reverse pulsations, yet do not affect engine performance. In some cases, a performance increase is actually realized by using the resonators."

Dave

Re: Removal of 496HO restriction plates
 

No negative effects on rpms or torque since torque is the work of horsepower measured over time. Remember , engines are air pumps with fuel and spark, help them breathe better and they will return both torque and horsepower.The slipped boat would be more prone to moisture (condensation) than a trailer boats thats pulled up high and dry. This is the use thats probably the hardest on stock heads with stock valves. The mercury exhaust riser for the 496 has a tuned merge bell type resonater at the end under the hose connection that does a great job of reducing reversion, tuning down the reverse exhaust pulses and helpiing to extract exhaust gases in the exhust system, The Gil and Merc engineers did a damn good job with these exhausts!, could have done better, but heck they never ask me!

Ray @ Raylar

Re: Removal of 496HO restriction plates
 

As I said, they are to prevent condensation from entering the cylinders. Merc WILL NOT cover any damage cuased by reversion if you remove them though. Their purpose has nothing to do with reversion but they will void your warranty if your remove them.

Re: Removal of 496HO restriction plates
 

So is it not recommended to remove them if you have silent choice? If I do remove them and I have silent choice, will I not be able to use the silent choice at all or can it be used in moderation?

My exhaust has a pretty good downward slope...

Re: Removal of 496HO restriction plates
 

On Hotboat.net, a fellow boater running a 22 foot Donzi Classic claims to have gained 3 mph gps through the removal of the plates.

Re: Removal of 496HO restriction plates
 

How about extrude honing these stock manifolds?

Re: Removal of 496HO restriction plates
 

I removed the plates in my Carrera 257, with the 496HO, and gained approx 150-200rpm. It translated to maybe 1 mph. Nothing dramatic, but what the heck. Very easy removal, with no other modifications. I can put them back just as easy if evidence comes out that it isn't good for the motor in the long run. To remove both sides took about 1/2 hour or less.

Re: Removal of 496HO restriction plates
 

In my opinion it's a no-brainer. The risks (voided warranty/rusted valves) FAR outweigh the benefits. I would guess that removimg them might gain a little RPM/speed the first season but by the next season you would see a loss.

Dave

Re: Removal of 496HO restriction plates
 

Since these plates are for condensation boil off only then I will remove them and report the results. Think about the design of these plates. All they do is give a small shelf to catch any water dripping down the side of the exhaust risers during condensation. If you have a bunch of water come back up your exhaust (reversion) there is no way this little shelf will stop it from entering your motor. Do any motors that Merc sells with factory headers have them? I don't believe the older 454's and 502's had them and those motors seemed to have no long term effects of this condensation. To me most condensation will occur when the motor begins to heat up, all of this should be burned off quickly as the engine heats up and should not cause any corrosion problems.

Re: Removal of 496HO restriction plates
 

That was my thinking when I worked on my risers this week-end - during engine operation, I assume that there is water entering the exhaust process just above the seal between the manifold and riser. The force of the exhaust gases obviously takes care of the water assisting in the exhaust process. The plates won't stop reversion, if that's gonna happen. W/r/t condensation, I saw no evidence of rust or water on the retriction plate itself after two years of operation. Noticed another boater of hotboat reporting 3 mph gain from this past week-end.

Re: Removal of 496HO restriction plates
 

Snap some pics while your at it. :cool:

Re: Removal of 496HO restriction plates
 

Warranty expired 2 weeks ago...Game on!

Okay, so unbolt the riser; remove this plate-a-ma-jiggy looking thing; reuse one of the two gaskets after carefully removing; re-install riser; go play. Am I missing something?

I like the polished riser idea as well. I think I read your post and saw pics of that. Think i'm gonna do the same thing as soon as I find a local polish guy...

Re: Removal of 496HO restriction plates
 

You aint gonna be able to reuse the gaskets no matter how carefull you are.

Re: Removal of 496HO restriction plates
 

I removed them two weeks ago and used two new gaskets, but could have re-used all four, they were like brand new,, about a half hour job..

Re: Removal of 496HO restriction plates
 

chris288 have you water tested since removing ?

Re: Removal of 496HO restriction plates
 

Will do. I'm waiting on my props from Houston Prop and hope to get them back this week. I might try to make some baseline runs Saturday morning then remove them and run some more. This will give me a good comparison with similar water and temp conditions. I have the gaskets ordered from Bam so hopefully they will be here in time too.

Re: Removal of 496HO restriction plates
 

Tony,, I really should have tested first then changed them at the ramp and re-tested,,, but from what I can tell I did get a consistent 1 mph more,, with 3 people and full tank of gas I was hitting 70,, usually only get around 68-69... Anyway,, I didn't like how the motor was running,, I'm thinking of putting them back in,, it was acting wierd, felt really slow one minute and then felt like a rocket,, like I said weird,, I topped the boat off with 70 gallons plus whatever I had in it at the end of last year,, so I don't know if it was the old gas or what,, it was stabalized,, but I really didn't like how the boat was acting..

Re: Removal of 496HO restriction plates
 

Okay, new gaskets....

I don't know how opening up the exhaust route a little could affect how a motor runs in a negative fashion Chris. After all isn't that how a set of after market headers work? I would suspect something else if it continues like as you said, fuel or a clogged fuel filter, etc.

Besides, to try couldn't hurt since it's so simple a task and it's done for the Raylar install. Highmark it'll be interesting to your comparison's, and just may be the deciding factor...

Re: Removal of 496HO restriction plates
 

doing mine fri nite, will let you know what happens.

Re: Removal of 496HO restriction plates
 

Rick,, my thoughts exactly,,, boat was in PA all winter getting some warranty work done... I REALLY should have run the boat first and made sure everything was A.O.K after winter storage, and then done the plates,, like you said I highly doubt one has anything to do w/ the other.. I want to get ALL the old gas out and see how she runs..

Re: Removal of 496HO restriction plates
 

Chris, man, it really sucks you did not run the motor before pulling the plates. Now you're left pondering the problem until you can get some fresh gas in there and hope that takes care of it, diagnose another problem, or put them back in. Not in any particular order either! I feel for you dude.......keep us posted.

Re: Removal of 496HO restriction plates
 

I took mine out about 2 months ago and ran the boat two times since. I also ran a new set of Hydro p5x's for the first time. All I can say is that everything ran great with no problems. I'd have to run on the lake instead of the river at wot to see if there's any gains. The props definitely gave the boat more get up and go, hopefully removing the plates had part to do with it also... :D

Re: Removal of 496HO restriction plates
 

Chris288- I'm almost willing to bet it's the old gas, let's hope so anyway... Get some fresh in there, I'm sure you'll be fine... :D

Re: Removal of 496HO restriction plates
 

Here is a quote from Ray at Raylar off the Hotboat site:

My suggestion for anyone with a stock 496 Merc engine is remove the turbulators, run 87 octane fuel and leave the rest of the motor alone until you are ready to improve the motor.

Re: Removal of 496HO restriction plates
 

got mine out last nite, took less tham 45 min,was able to use the old gasket, the top one ripped.

Re: Removal of 496HO restriction plates
 

For those of you that have removed the restrictor plates, do any of you have silent choice?

Re: Removal of 496HO restriction plates
 

I do not have silent choice...

Re: Removal of 496HO restriction plates
 

no

Re: Removal of 496HO restriction plates
 

So, any ideas then as to how a silent choice or corsa quick and quiet plus might affect either the expected performance gains or the chances of negative results on the engine?