Modifying stock "sandwich plate" 3cyl exhaust

[Argo]

First i would like to say thanks for all the good info that has been posted at this forum :)
I have learned alot about the differenses about the 3cyl OMC engine.

To the question:

I have the -76 version of the 3cyl Johnson Stinger.

Is there anything to do to to gain som RPM and performance with modifying the stock "sandwich plate" exhaust on this engine?

I know that there is available different MOD exhaust (hustler, nydahl ) to bolt on for this for the real performance but they seem to not be available that easy :(

In this topics it is stated that cutting the "bridge" between nr 2. and 3. cylinder you can gain som RPM. Does this really help?
53137

http://www.boatracingfacts.com/forums/showthread.php?15360-1976-Evinrude-75-powerhead-and-cowls

[LakeRacer99]

I would also like details on this as well. Good photo Argo

[Bill Van Steenwyk]

I would also like details on this as well. Good photo Argo


I do not have an specific knowledge about this motor or this modification, BUT I did see a picture on this site in the last couple of days showing what was described at a modification on the "bridge" between the cylinders mentioned. Best of my recollection, it showed a place in the raised section of the bridge shown in the middle photo above that was ground away somewhat, possibly so as to allow the exhaust flow from the cylinders to mingle easier. I seem also to remember that the bridge was NOT ground away either the full depth or the full length of the bridge. Best I remember in the area of the dark spot just above the bridge in the middle photo.

Wish I could remember now on what thread I saw it but it was just a couple of days ago. Maybe one of "Fast Fred's threads or another about the 3 cyl OMC motor. Whether it is what you are looking for or will help, or hurt, I do not know.

[LittleCharger]

I do not have an specific knowledge about this motor or this modification, BUT I did see a picture on this site in the last couple of days showing what was described at a modification on the "bridge" between the cylinders mentioned. Best of my recollection, it showed a place in the raised section of the bridge shown in the middle photo above that was ground away somewhat, possibly so as to allow the exhaust flow from the cylinders to mingle easier. I seem also to remember that the bridge was NOT ground away either the full depth or the full length of the bridge. Best I remember in the area of the dark spot just above the bridge in the middle photo.

Wish I could remember now on what thread I saw it but it was just a couple of days ago. Maybe one of "Fast Fred's threads or another about the 3 cyl OMC motor. Whether it is what you are looking for or will help, or hurt, I do not know.

Here is the thread you are looking for.


http://www.boatracingfacts.com/forums/showthread.php?15360-1976-Evinrude-75-powerhead-and-cowls

[Bill Van Steenwyk]

Here is the thread you are looking for.


http://www.boatracingfacts.com/forums/showthread.php?15360-1976-Evinrude-75-powerhead-and-cowls


That's the one. After mentioning "Fast Fred" I remembered it was Smoking Joe, looked for the thread and couldn't find it. The BRF bunch is very helpful today!!

If I were Argo I would PM Joe for some suggestions about this modification and others. Seems he knows his way around a 3cyl OMC also, based on past accomplishments.

[Powerabout]

That's the one. After mentioning "Fast Fred" I remembered it was Smoking Joe, looked for the thread and couldn't find it. The BRF bunch is very helpful today!!

If I were Argo I would PM Joe for some suggestions about this modification and others. Seems he knows his way around a 3cyl OMC also, based on past accomplishments.
My guess would be that that design was to produce torque at low rpm.
Check out the photos of 31M exhaust plates and its like half a V6 merc in other words all open and straight down
You could buy the MOD 50 version from Tim
http://www.boatracingfacts.com/forums/showthread.php?13569-Racing-exhaust-for-laker-49-OMC

[Argo]

I would also like details on this as well. Good photo Argo

The photo is not mine, i think it's Tim Kurcz (let me know if you dont want me to use your photo)


Best of my recollection, it showed a place in the raised section of the bridge shown in the middle photo above that was ground away somewhat, possibly so as to allow the exhaust flow from the cylinders to mingle easier. I seem also to remember that the bridge was NOT ground away either the full depth or the full length of the bridge

Thats the main thing i was wondering with doing this modification, how much to cut and exactly where. Also should both exhaust plates respective wall's be cut?


If I were Argo I would PM Joe for some suggestions about this modification and others

I sent him a PM and asked him to answer this tread so the information get's to everyones knowledge:)


My guess would be that that design was to produce torque at low rpm.
Check out the photos of 31M exhaust plates and its like half a V6 merc in other words all open and straight down
You could buy the MOD 50 version from Tim
http://www.boatracingfacts.com/forums/showthread.php?13569-Racing-exhaust-for-laker-49-OMC

The "all open sthraight down" design would probably be the best one as it does not have any restrictions in the flow of the exhaust gases. Buying the existing kit would probably be the best alternative but the original ones seem to not be available and the custom made by Tim is abit expensive for my budget (it's probably worth the cash but still ower my budget )

[Smokin' Joe]

The modified exhaust plate came out ca. 1980. There was no measurable effect with an EP boat (6500-6900 RPM)
but Darrell Beaulier told me that on SE tunnels the motors hit a 'wall' at 7200 RPM. The cut between cyl, 2 and 3
was designed to let the motor rev higher. With the new plates 8000 RPM and more was possible. You can probably
buy the plate from SeaWay Marine as well. I recently cut one myself, then discovered too late that i
had two with the cut in my stock of parts. The 'cut' plate came on the stock OMC 60 (hp at the propshaft,
70 hp at the crank) pleasure motors, so there should be plenty available.

[David Mason]

If you are considering switching over to a Mod 50 style exhust system, Jeff Ruth makes one. We used this system on our rig last season, and it won Nationals. The price point is also considerably less than some other systems available. If you wanted to contact him, his number is 479-927-2847.

If you still want to carve out your stock exhaust, it can be done. My spare system is a stocker carved out some. Some don't believe it can be done, and that is fine. It is not as fast on top end as the Mod 50 style. But it will net you a gain.

[Detroit Whitey]

Yep it's a good mod for those of us with skinny pockets. The gain is more prevalent on the top end with a very light rig find the stocker it will have true majority of the meat cut already that helps when ya open it more. Happy cutting!!

[Argo]

Yep it's a good mod for those of us with skinny pockets. The gain is more prevalent on the top end with a very light rig find the stocker it will have true majority of the meat cut already that helps when ya open it more. Happy cutting!!

How much should i cut using the original plates? All the way down on both sides so the flow is maximal?