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12-24-2017, 01:22 PM #181
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powerabout thanked for this post
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12-24-2017, 01:43 PM #182
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"A couple months ago , I had a guy with a box stock 225 efi ( late model Motorola) trade in a flywheel , inner can , 6 pedal rubber reed blocks and a set of 73 cc heads .
He took home a 13 lb flywheel , cut and cleaned out can like the one above , striped , flattened and tumble polished reed blocks with shortened stops and Carson reeds. He wanted to run 89 to 91 octane fuel , so I did a set of 65 cc heads for him .
He put just that stuff on his open fisherman boat . He called me about a week later and said it was 7 mph faster than it was before.
The whole deal with the 300 ign is it has a coupe more degree's of WOT timing which helps it accelerate harder and a little higher secondary rev limiter.
The idea of a 250 fuel box is these things run blubbery fat , so the lower HP fuel curve actually clean's some of that up . It also has the soft limiter which starts dumping extra fuel back in (nice right ) at high RPM . I never really saw much gain from the computer thing , the porting is so mild , that they quit pulling way before the "benefits" show up ...
Reed blocks look like this ..."
The 73 and 63cc heads have a pretty wide chamber ...
Anything less than 65 cc I like to just weld up the chambers and mill them back out to whatever size we're lookin for .
This set is pretty tight but works well with a big exhaust port ..
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12-24-2017, 02:09 PM #183
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Please add/correct where necessary:
the tuner, the side attached to the adaptor plate is the smaller diameter thus has the effect of the Divergent section. As you follow the tuner down into the can cavity, it's diameter gets larger.
The resonance bounces off of the lower portion of the driveshaft housing which is smaller in diameter (Convergent section), shoots back up the tuner, up through the exhaust chest cavity of the block and pushes back the fresh fuel mixture back into the exhaust port.
here's a pic of an adaptor plate and a tuner. Notice the cone shape of the tuner.
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powerabout liked this post
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12-24-2017, 02:27 PM #184
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What happens when we cut down a 20" mid to a 15" mid?
Theoretically, the power curve will also be altered because we "detuned" the outboard's "Tuned Exhaust system" ?
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12-24-2017, 04:01 PM #1857000 RPM
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Another opinion is that those are not "tuners", they are diffusers. And the divergent cone thinking is just sales talk or wishful thinking. The "diffuser" opinion suggests they do next to nothing except ease the transition into the can.
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noli liked this post
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12-25-2017, 04:06 AM #186
While this will definitely Aumentato il pane di dimensioni cestello ......>
1. very dry ricottaIn this application , we will "settle" for ....
2. granulated sugar
3. vanilla
4. Chocolate chips
5. Cannoli shells
1. header
2. convergent cone
3. belly
4. divergent cone
5. stinger
#2 ) Can someone explain the function of each component ?
#3 ) Can someone name the two basic components of an outboards exhaust ?
#4 ) Can someone explain the function of each component ?
#5 ) Can someone identify any overlapping functions of these components ?
However there are some that feel that there are some expansion chamber like benefits to be had from log plugging or partial stuffing . This really only works if the exhaust is arranged in a fashion where there are three evenly spaced headers in the shape of a trident. And even then , it's minimal at best .The OMC arrangement comes close , and in the "stacked" Mercury seems to be more of a determent than an asset .
Pretty simple in design and rudimentary application . The major issues that come up seem to be rooted in the use of terms that that are non applicable , or have other meanings .
Case in point :
Another opinion is that those are not "tuners", they are diffusers. And the divergent cone thinking is just sales talk or wishful thinking. The "diffuser" opinion suggests they do next to nothing except ease the transition into the can.
( and have been saying so for month's now )
The problem is : "Divergent" is a description of a shape !
I.E. (Drawing apart from a common point )
"Diffuser" : A passage that decelerates a stream of gas or liquid from a high to a low velocity .
# 6 ) Anyone care to guess the most common shape of most diffuser's ?
Just kidding ....
Please refer to the original exhaust document for further information .. >
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noli, powerabout liked this post
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12-30-2017, 02:43 PM #187I CAN ALWAYS MAKE ANOTHER DOLLAR, BUT I CANNOT MAKE ANOTHER DAY
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12-30-2017, 03:15 PM #188
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That picture explains why V6 outboards can't have a tuned exhaust unless every cylinder has its own exhaust system with expansion chamber in each?
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12-31-2017, 02:20 AM #189Screaming And Flying!
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Yet 3cyl and v6 outboards can make 2hp/ci pretty easily
Not so easy on any other combination so thats saying 3 cyl in one exhaust does have a tuning advantage
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12-31-2017, 06:22 AM #190
I don't think they are saying it's not tuned, just not in the same way and as effective as an expansion chamber tuned exhaust is. I feel the outboard exhaust system does a pretty good job on the scavanging part of tuning. On the stuffing part there's a lot to be desired. I feel you get a small amount and not nearly as efficient of stuffing from the initial pressure wave of the next in line fired cylinder that can somewhat stuff the closing exhaust of the previously fired cylinder. Only problem is with 3 cylinders there is no equal pairs or all equal lengths to work effectively. And cylinders 5 and 6 are the ones that get left out and have no correctly timed means of stuffing, therefore get the most issues. This is why it's so important to close the door at the right time to prevent from loosing much of your fresh charge. This is also the reason you will notice that most Outboard's run less blowdown degrees between the exhaust and transfers than a well tuned expansion chamber motor would for the same rpm range, because there is not an efficient way to put it back in. JMO
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12-31-2017, 06:46 AM #191Screaming And Flying!
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The problem with 3cyl...?
Yet they work better than any other combination in an outboard.
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12-31-2017, 08:36 AM #192
If we are relying on cylinders to stuff each other, without equal lengths how's it gonna work efficiently? Somebody is gonna have to have a longer trip to make.
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12-31-2017, 08:56 AM #193Screaming And Flying!
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12-31-2017, 09:12 AM #194
Yes, but think it's more to do with the spacing in crank degrees between cylinders to make the little that is there work at all. Also remember the tuning used in a tuned style exhaust is using the "sound" wave. There is not enough distance for this type of tuning in the chest, they are simply using the exhaust pressure wave, which is much slower and sloppy causing it to be inconsistent as far as a stuffing method. And at higher rpm levels really goes to crap, which is why on the hipo motors the chest no longer has the "ditch", because at that level it's useless.
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12-31-2017, 09:24 AM #195
I just got off the phone with the president . I got him to sign an executive order squashing the "no child left behind" laws ....
Since we all (should) know by now that between , expanding exhaust pressure , a piston carrying ( flywheel effect ) momentum pushing the spent charge out a relatively large hole and a conduit that provides a scavenging effect .
It becomes easy to see that emptying the cylinder is easy compared to having only 14.7 psi of atmospheric pressure to start the process of filling it .
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