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Thread: 2.5 exhaust chest mods....
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07-16-2017, 04:23 PM #6181' HYDROSTREAM VECTOR / slightly Modified 200
before and after:http://www.screamandfly.com/showthre...inished!/page3
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07-16-2017, 06:27 PM #62
Thought your boat was 1250lbs fully rigged igged...
If I don't ask any questions, I'll never learn anything.
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07-16-2017, 07:35 PM #63
IMO A 280+260 lecktrics is hands down the best small block OB of all time.But to the point of this post,I agree fishin motors are cheep can be made to make good power,and the success or failure is up to the op! What a hoot,to get that kick in the butt feel from a motor that you built your self.
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texasvector, FORBESAUTO liked this post
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07-16-2017, 07:36 PM #64
Agreed ...they hit homerun with the 280
81' HYDROSTREAM VECTOR / slightly Modified 200
before and after:http://www.screamandfly.com/showthre...inished!/page3
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07-16-2017, 07:38 PM #6581' HYDROSTREAM VECTOR / slightly Modified 200
before and after:http://www.screamandfly.com/showthre...inished!/page3
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07-16-2017, 09:35 PM #66
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07-16-2017, 09:43 PM #67
No my junk has a 1500 dry hull only weight. I'm runnin an old heavy rascal, especially after I load it down with all my no fish catching junk! One good thing about it is at least my mota is little lighter by the time I get through cuttin on it
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07-16-2017, 10:19 PM #68
1500 lbs without a motor. You better keep porting.
If I don't ask any questions, I'll never learn anything.
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07-16-2017, 11:51 PM #69
Well I've heard plated blocks called a lot of things , but weak anywhere in the power band is not one of them .... LOL
Owning a magazine that list's fortune 500 company's and your use of the English language , I'm surprised that you mistook
Closer they can get those fishin blocks to have the same angles and volume as a 280, the closer they will be to the height of development , before Merc called it quits ..
As far as layed down short side killing torque , I aint buying it as being the single reason . Yes a large cross section will slow air speed , but more times than not it's getting to aggressive on Ex port timing that kills power across the board (no expansion chamber to shove it back in ) .
I think you'll also be pleasantly surprised that your 45* slope will tend to "loft" the column over the next guy down the line , leading to less of a contaminated charge than your 30* which while having a steeper ramp also has a flat floor leading up to your sharp overhang . Sometimes the column will straighten out enough to use the abrupt absence of the floor as a "trip" to start air tumbling . Just as it does off the back of a semi trailer . You can see where Jon Wright angled the ramp and tightened the cross section just before making the hurdle over the next port in line on the block krazy has ..
Seems like about the time I learned to "grind with a smile" ( moving the tool in one direction with light pressure at the beginning and end of the stroke with the most work being done in the middle , like the arch of a smile ) I started getting some flow bench time . Which for me , ruined just about everything I thought I knew about starting , moving and stopping a media that I cant see ...
But it sure is fun dealin with cramped fingers , grinder running in your ear , doctor using a drill to dig chips out of your eye balls and having thousands of dollars in porting tools , but needing to buy left hand carbides so you can cut both sides of the transfers without the tool bouncing out of two of the four corners ...
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07-17-2017, 05:37 AM #70Screaming And Flying!
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Yup, drill bits in the eye and driving like a one eyed pirate with a patch. Arrrr
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07-17-2017, 05:44 AM #71
Thanks for your post Chaz! I truly respect your views and feel you are one of the guys we can learn from. So many different angles and ways to look at things! Actually I was told I would be more pleased with the low end and midrange of a modified 200 on my setup than a 7- petal horn mota in general. I hope your right about the 45 degree experiment, can't wait to see how it performs. So far all the ones I've run have been on 30 and all my experiments have been in other areas. If the 45 works out well I'll go a step farther. I don't have access to a flowbench or dyno so I try to make one change at a time and evaluate how it effected performance of mota and old heavy Betha helps out in that aspect! I was surprised when I went from square exits to the large rectangle that it actually improved bottom end, and so far havnt went as far as opening up exhaust to the point where I have lost anything. ( I was expecting to gain on top and lose bottom so you never know till you try) I came to the conclusions of the angles because they almost come straight out stock and the ones I've seen on 60* where on all out drag motas, seeming to follow rpm ranges.Other than distance thing I felt it also had to do with trajectory at which exhaust hit divider plate at different velocities depending on rpm causing it to reenter next cylinder? From my results it seems after exhaust leaves port, you want to get it the heck out of there as straight and undesturbed as possible utilizing as much scavenging effect as possible. ( your right we ain't got no expansion chamber) I'm still gonna do test with shapes and angles as time passes, but one test at a time. I have been amazed how some things that's suppossed to work wasn't worth a hill a beans and how some things had an opposite effect of what you thought it would! Gos to show you have to keep an open mind.
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07-17-2017, 05:57 AM #72Screaming And Flying!
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No expansion chamber but interchest tuned pair ex pulses do rely on chest gas temp as the medium of transfer to next closing ex port. Changing temp changes travel speed and tuning effect.
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07-17-2017, 06:07 AM #73
I agree on the tuning effect, but not in a sense of pushing it back in a cylinder like an expansion chamber does, more in the scavenging effect like tuned headers, long and and shorty headers effect a four stroke motor.
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07-17-2017, 06:24 AM #74Screaming And Flying!
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Crank pin spacing in degrees and physical distance between firing order cylinders port to port at cyl sleeve.
Ex port opens , first thing to release is a high pressure pulse ahead of any spent gas. A few or more degrees of crank rotation for formation and bang it's out. The next port that is closing will except that pulse , the distance and medium gas temp effects when and quality of that pulse as well as port arrival shape. It arrives early at low rpm and later at high rpm, crank rotational speed vs travel time. At high rpm it's optimum to have it hit around 30* before ex port closing , you can't get away from it. It has the effect of pushing the fresh charge of that closing cyl back in and adds pressure.
I believe in this effect, lots of papers on it, Merc OMC , Miller WI. Was first described as a supercharging effect on cyl pressure.
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07-17-2017, 07:14 AM #75
I love ya man!! From my tinkering I do feel the most tuning takes place in chest, which is my reasoning on the angles and distances. Kinda hard to tell if it's scavanging or stuffing being effecting or both. I was leaning more to the scavenging because I'm experiencing improvements across the board by reducing backpressure. I've had a few other wild ideas to try but too scared to make the move because of mixed feelings I get about this topic, so I've so far just stayed conservative lol.
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