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Thread: 2.5 exhaust chest mods....
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11-23-2017, 03:16 PM #106Screaming And Flying!
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Can you compare that to a SST 120?
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11-23-2017, 03:47 PM #107
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11-23-2017, 04:36 PM #108Screaming And Flying!
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118* , 92.7* +/-2*
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11-23-2017, 05:02 PM #109
That's 124 degrees duration on the transfers with only 25.3 blowdown. Hmmm.
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11-23-2017, 05:20 PM #110Screaming And Flying!
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Isn't that +/-3* for the boost from 118*?
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11-23-2017, 06:26 PM #111
guys the sst 120 specks loaded in a program show a 178 deg total ex timing 130 deg total transfer timing and 128 deg boost timing that is a 25.1 deg blow down timing.
It also has 6 to 1 trap CR.
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11-23-2017, 06:48 PM #112Screaming And Flying!
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What does it spin, 8500? I like that motor
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11-23-2017, 07:31 PM #113
look at the port lay out. It is a 3 port intake system. the intake port timings are sky high. WHY????
Time area.................
there are only 3 ports so you have to leave them open to get flow into the cylinder.
The timing per say is not the thing you look at. but what the timing gives you the port open longer.
Limiting the ex is what controls the HP out put on the eng. now give it 190 ex and it would be a true beast.
Remember this is 40 year old 2 stroke tec. Things have change just a little in 40 years in port design.
I am almost tempted to do a 130/ 190 eng on this next build. Those # are a truly powerful eng combo.Last edited by dwilfong; 11-23-2017 at 07:35 PM.
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Krazymaan liked this post
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04-19-2018, 08:48 PM #114
Welp don't wanna speak too soon, but got the idle time in on the ole big chested hussie with the more laid back ramps and super wide exhaust ports in sleeve. Took it down to the river for some easy riding. And from what I can tell without crowding it, don't think I lost any low end torque, may have even gained some, runs cleaner and smoother at lower cruising rpms around 3k,(and a little rich still and yet and heavy on oil) and certainly feels stronger above 3 k. I hit it one time while on trailer to try and clean it out a tad setting idle and all but shoved my F-250 up the ramp and flashed about 5 k and no telling how hard it would have went up if I didn't let out, didn't show any signs of laying down. Definitely stronger in that aspect. Had no problem jumping on plane with part throttle on the old barge. I'll keep ya posted on how it does once fully broken in and can test with some more definant info. But so far I am pleased at what I see. If really turns out to be a real runner, I may do a build thread on it. But if it's a flop, we'll just pretend it never happened.
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08-18-2018, 06:11 PM #115
Welp been busy as a one legged man in a butt kicking contest. Haven’t had a lot of time to mess with boat. Just know getting break in period done and gotta go back to work on the jetting. The last mota was happy with .092 mains and .052 idles. The .092 was the largest mains I had, so started with same jetting. This mota was pig rich at idle and anywhere at part throttle when checking it on break in, so dropped idles to .054 and still need to lean it out some more. Thinking it’ll be around .060 to clear it up, so not wanting near as much fuel at idle and part throttle. Plan was to jump on it wot and shut key off at 6500 and check mains before I let her spoil on up. Well the hussy kit 6800 before I got the key off and was pulling like mad. Pulled the plugs and they looked like I just took em out the box, lean as all get up. So the trend of her sipping fuel went out the window at wot and turned into a gasaholic. Putting some .096 in her and do the same scenario and see where we at ( hope she ain’t wantin no more fuel than that, but if she does, I’ll give her what she wants ) Being the last mota would only turn this set up 7200 at the load I was runnin, I think she’s gonna go by how fast it was pullin headed toward the 7k mark and bottom end very close to other motor and midrange is definitely stronger. Maybe in the next month or so I’ll get it ironed out and keep the one interested posted how it does
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texasvector liked this post
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08-18-2018, 06:22 PM #116
Sounds fantastic. I'm very interested in your jetting size. What carbs are you running?
If I don't ask any questions, I'll never learn anything.
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08-18-2018, 06:37 PM #117
Wh20’s with opened up bowls. I’m thinking the big difference in what the motors are wanting as far as jetting is going from 4 petal to a 7 petal. I’m thinking the 4 petal had better velocity at idle requiring more fuel and being part throttle is a blend of mains and idles it stayed rich. Once I went to wot on the 7 petal motor that’s when with ability to move more air showed up and the need for much more fuel. The two motors have the same port timing, but different angles, widths, chest and openings are the same except for angle increase at bottom of each cylinder port pocket.
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08-19-2018, 12:58 PM #118
Hey forbes ,mite be rookie question but wh20s with opened bowls? Can u tell me about this?
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08-19-2018, 01:46 PM #119
The area of the bowls are pretty small on the wh’s and don’t hold much fuel. I remove as much material as I can, mainly on the pedestal in the center of the bowl. The pedestal looks like a mushroom when done. This increases the volume significantly. In the beginning I thought this was what was making the new mota run richer from the extra pressure on main jets from the added fuel volume. I also opened the seats up to flow more fuel, not sure if it really needs all that, but figured if ain’t gonna hurt and could possibly save me a mota on long hard runs.
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Merc 2.5 thanked for this post
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08-19-2018, 10:41 PM #120
Adding bowl volume makes no difference if you can't fill them.
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