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06-20-2019, 10:56 PM #1
Drilled Exhaust - Real World Results and Weigh-In On Benefits
Guys, I want to get some real-world answers about "drilled exhaust". I've seen this done for years and while I know that noise is one downside result, is there a real benefit? I have a 20" Mercury 2.0L V6 that I'm building for myself and a later project. If I'm going to drill the exhaust, I need to do it now before I start painting.
My gut says Yes - I say this because my 2.5L Mercury V6 ProMax SS (short shaft) is the best running/performing outboard that I've ever ran. I've owned this ProMax SS for 20 years now and it's acceleration characteristics are unlike any other outboard I've ran. The transition from idle thru hole-shot has no hesitation. There is no blubbering, no hiccups, no delay that many outboards experience when "clearing" the water from the exhaust cavity. Since the SS has a huge, open hole that vents the exhaust above the cavitation plate and does not require all of it out through the gearcase and the thru-hub system, the engine is free to spin up from idle.
I know the openings wouldn't help WOT operation, but my thoughts are that they can't hurt idle and should aid (as do the reliefs) and they will help to build rpm quicker to clear the exhaust cavity when transitioning from deep in the water to on-plane.
OK, if the answer is "Go", I'll place 6 1/2" holes in the outer leg (3 on each side), but where do I drill the inner exhaust liner (shown below)? Thanks, Gordon
Last edited by Gordon02; 06-20-2019 at 10:59 PM.
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06-21-2019, 03:50 AM #2
Interesting question, hope to see a nice pro/con debate!
On my looper I experience a better off-idle accel the more exh I relieve above the gearcase, despite the fact that the prop vent holes has less and less effect the more exh is relieved...Last edited by Captain75; 06-21-2019 at 03:57 AM.
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06-21-2019, 04:46 AM #3
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tunnelmike, sonicss33 liked this post
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06-21-2019, 05:27 AM #4
Are you doing any other work/mods to motor?
MichaelLast edited by mrichartz; 06-21-2019 at 05:38 AM.
LETS GO BRANDON.... LETS GO BRANDON
Sometimes I talk to myself...then we both just laugh and laugh
'84 Checkmate Convincor
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06-21-2019, 07:01 AM #5Supporting Vendor
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Post #3 is my suggestion , while powerhead is off you have perfect opportunity to drill 5 1/2” holes at the base of your bass midsection like Mercury sent all the 260 bass mods in the early 90’s , any gains ? It would be minimum IMO but LOTS louder that once done irreversible... Think it out ...
JayJay @ JSRE
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06-21-2019, 09:25 AM #6
A lot depends on motor and it’s characteristics. I had a cust call me this morning regarding a Yamaha I just built and modified mid to relieve exhaust. He wanted to know if we could relieve more, because he noticed while taking off and the exhaust reliefs cleared the water the motor would instantly spool up, so in this application it apparently is helping. I’ve also noticed on modified carb 2.5’s, the more exhaust I relieve above water line, the better they idle without loading/puddling fuel. In long idle zones you’d have to periodically bump up accelerator to keep it from loading, much better to all but gone by allowing more exhaust out above water line.
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06-21-2019, 10:05 AM #7
Remove the liner but keep it. Drill from the top down like the 260s. All you have to do to reverse it is re-install the liner.
RockTeam Junk
No sparkling wiggles in here, only dump truck grinches.
"Screamin Heathen"
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06-21-2019, 10:53 AM #81980 Cougar 19 tunnel,90 2.4L Bridgeport EFI in middle of restoration.
1988 BAJA Sunsport 186, 96 225 Pro Max
79 12' Auminum, 95 Merc 9.9
RIP Stu
"So many idiots, so few bullets"
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06-21-2019, 12:57 PM #95000 RPM
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I will agree with above comments, my motor does idle much better with it all opened up. (260 with offshore mid, a drag racer cut of the end, and drilled holes every where) Real increased performance numbers will probably not be quantifiable in my opinion, unless other mods are made to take advantage of added breathing in the mid and top range. If it makes you feel better that the motor idles better, and you like the sound, then I could see how it would be fun, but that is about it. Most of my friends think I am stupid for taking the little step in performance, but I kinda like it
Whitney Woolard
Oregon/Washington
'96 Allison XB2003 w/Mercury 2.5 260ss
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06-21-2019, 03:53 PM #10
Guys, you've confirmed It's On! I'll get that 20" stock housing drilled over the weekend.
Thanks for the inputs and advice. I'm not after the noise, but don't mind it since I've gotten used to my 15" ProMax's 4" hole under the housing (I've had that little baffle plate removed for 20 years too). I give that above-water relief the full credit for how quickly this motor spools-up on my Allison. Never a hiccup, cough, or pause - it responds instantly and always immediate. Gordon
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06-21-2019, 04:47 PM #11
Earlier you mentioned 3 holes each side. Like Jay said the 260s had 5 each side and Mercury felt it was a good idea.
RockTeam Junk
No sparkling wiggles in here, only dump truck grinches.
"Screamin Heathen"
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06-21-2019, 05:07 PM #12
Its not a Merc, but this is my solution on my 3 litre OMC's. 3" holesaw, thru the mid and liner.
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ssv1761982, Captain75 liked this post
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06-21-2019, 05:15 PM #13
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06-21-2019, 05:17 PM #14
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06-21-2019, 06:09 PM #151980 Cougar 19 tunnel,90 2.4L Bridgeport EFI in middle of restoration.
1988 BAJA Sunsport 186, 96 225 Pro Max
79 12' Auminum, 95 Merc 9.9
RIP Stu
"So many idiots, so few bullets"
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