Any benefit of drilling holes through the mid section for the exhaust outlets?

[spybot]

I have seen a few engines with the exhaust gases coming through holes drilled in the mid section.
Is there any benefit from this ??
I thought the engine needs back pressure from the exhaust to work properly.
Any thoughts on this ???

 

[Auxlarry]

What engine are you referring to?

 

[spybot]

Outboads

 

[tomhath]

If you're talking about modifications done by the owner rather than coming that way from the factory you're correct, there is no benefit. But some people think louder means more power. And some people think louder makes them cool.

 

[Faztbullet]

All they are good for is to make noise and draw attention if you run factory RPM's an tuner. They will give you a little better holeshot as the exhaust doesn't have to push all the water out of exhaust can and can spin up a lil faster. Most people that have them think the noise makes them faster!!!

 

[gm280]

Any time somebody wants to modify their OB to make it more powerful, that is a sign that they need a large engine. Without proper tuning capabilities, anything you do is merely guess work and could actually decrease the output. If you knew how to install a tune port exhaust system you could get more power, but that also means higher RPMs. And if the crank, connecting rod and bearings are not beefed up as well, you could be looking for an interesting engine disassembly, and not the kind where you use wrenches either. JMHO

 

[Joe Reeves]

All of the above are spot on! Don't even think about it.

 

[spybot]

Thanks for the info
I was curious to why and now my curiosity will no more.
I just couldn't understand why they were doing it. I know you need back pressure but i was thinking do they have a tuned pipe ect ect.

 

[Joe Reeves]

Thanks for the info
I was curious to why and now my curiosity will no more.
I just couldn't understand why they were doing it. I know you need back pressure but i was thinking do they have a tuned pipe ect ect.

That practice is common with the group who spend thousands souping up a stock powerhead(s), installing specialty designed lower units, etc, ie having three or more of their high powered engine on the back of a 25' ocean going racer model. They found it necessary to have those loud sounding exhaust relief holes available to rid the engine of the immense powerful exhaust backup pressure build up so as to escape the bogging down action of the powerhead.

 

[V153]

Well Faz evidently people think noise makes everything faster, even scooters ... Yo Joe it's also common practice for those who scrounge up parts for a couple hundred here and there and do their homework before putting something together. My mid already had the holes CAST in with tubes through, not drilled. So I left it as is ... Yeah it's a lil louder flat out but this pig comes outa the hole like a rocket. And it's certainly no louder than the freakin thru-hull I/O's. (Which I take great pride in blowing many of them off ...)

www.youtube.com/watch?v=yi6g8If1kOQ

 

[flyingscott]

Don't mistake aftermarket parts that have been designed by people from companies that spend a lot of money designing these systems. Yes they are louder but they work with the motor and that is the difference between a person who just cut holes in there motor and the proper parts.

 

[V153]

Any time somebody wants to modify their OB to make it more powerful, that is a sign that they need a large engine. Without proper tuning capabilities, anything you do is merely guess work and could actually decrease the output. If you knew how to install a tune port exhaust system you could get more power, but that also means higher RPMs. And if the crank, connecting rod and bearings are not beefed up as well, you could be looking for an interesting engine disassembly, and not the kind where you use wrenches either. JMHO

Key is to only do ONE thing/"mod" at a time. (I know it's hard.) Then test/verify results.

Fwiw many motors are based on the same platform. HP is gained or lost via fuel intake, compression, and exhaust tuning. So it's not fair to say you "need a larger engine" if/when it's possible to upgrade yours, w/factory parts.

Jmo

 

[gm280]

Key is to only do ONE thing/"mod" at a time. (I know it's hard.) Then test/verify results.

Fwiw many motors are based on the same platform. HP is gained or lost via fuel intake, compression, and exhaust tuning. So it's not fair to say you "need a larger engine" if/when it's possible to upgrade yours, w/factory parts.

Jmo

J153, I honestly know what you are saying. However, IF any manufacturer could simply build more RELIABLE HP in any of their engines with factory bolt on type parts, they would do that and offer it as a HO version. But the key word here is RELIABLE.

I use to fly R/C airplanes with 2-cycle engines, not that much different then most OB, in their designs. And the only way you could make more HP was to add on a turned port exhaust system. And if you bought such a turn post system, it was built for that engine and factory set to give the highest RPM you could possibly make from that setup. Some installed pressurized fuel systems, but as finicky as they were, you had to constantly be adjust things because of the change in daily temps and humidity.

So hopping up any outboard engine is tricky at best and you risk the option of buying another engine if you royally screw up the engine. Port intake and exhaust timing is an option, buy you really need some special testing equipment to see how port timing changes works. And it is so easy to destroy an engine's power head casing if you make a mistake. JMHO

 

[V153]

Don't mistake aftermarket parts that have been designed by people from companies that spend a lot of money designing these systems.

Zactly.

 

[V153]

We're purty sure that mid on mine's genuine OMC "Second Effort" chit. Everybody that looks at it agrees the casting/tooling's original. Yet nobody'll commit, on camera, that it is indeed second effort. I need "closure". Please help ...

 

[V153]

J153, I honestly know what you are saying. However, IF any manufacturer could simply build more RELIABLE HP in any of their engines with factory bolt on type parts, they would do that and offer it as a HO version.

They do do that. But they also de-tune the same block(s) to lower hp.

On boat motors I mean ...

 

[Faztbullet]

Never seen Second Effort offer a midsection for sale in any of their catalogues'....most likey someones idea and good heliarcing welding. Had a customer add the S/S tubes off a handicap had rail on V-6 Merc mid right below the cowl..looked cool and sounded nice.

 

[jimmbo]

Fwiw many motors are based on the same platform. HP is gained or lost via fuel intake, compression, and exhaust tuning. So it's not fair to say you "need a larger engine" if/when it's possible to upgrade yours, w/factory parts.

Jmo

What most people don't realize about "many motors are based on the same platform. HP is gained or lost via fuel intake, compression, and exhaust tuning".
The lower HP models usually provide the best Hole Shot, and the higher HP models while having a higher top end actually have poorer acceleration, and often less than smooth operation at low speeds.
Some engine lines like the post 1978 OMC V4 crossflow 90hp can be, with some machining and/or parts be made into a crossflow 115 or 140. The crossflow 115 came be made into a 140. As mentioned, OMC Second Effort with specialty parts can make these engine produce even more power, but they would only be of any use on a racing hull

So for most pleasure boating, a bigger engine is often the best solution to get more performance

 

[V153]

Yes of course "there's no replacement for displacement". However I do think we're talking about Xflows so ... there's a lot of room for improvement to be made with the lower hp models.

 

[jimmbo]

However I do think we're talking about Xflows so ....

So was I