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Thread: Cut 3 liter exhaust?
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06-22-2017, 07:52 AM #16
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06-22-2017, 02:58 PM #176000 RPM
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06-23-2017, 07:23 AM #18
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06-23-2017, 11:28 AM #195000 RPM
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06-23-2017, 11:16 PM #20
Nice to meet ya Cali ...
Just had this discussion with a feller the other day ... !
The Porsche headers we build get checked from time to time by the big boss . he uses a seamstress tape to measure the inside and outside radius of each section of pipe . Say inside is 10" outside is 12" , that piece is 11" long ....
Finished deal better not be no mo than 1/4" diff between them all ....
Now lets look at the "header pipe length" of a 3.0L ...
Looks like 3.5 , 8 and 12 on one side and 5 , 9 and 13.5 on the other ...
Lets overlook that no two are the same and go straight to worst case ..
13.5 - 3.5 = 10 Lets get back 1" with the stagger .. and even throw in another 1" for some type of SVS intake . ( not that intake will manipulate the other side , but hey it's worth a try ) Looks like we have narrowed it down to 8" for our effort .. Soup sammich comes to mind ...
There are two aftermarket tumers for the 3.0L
One is just like a 300x in that it is cut short on both runners and the exits are smaller than the inlet side by about a third of the area .
The other actually flares at the exit , but looks just like two pieces of 4" channel iron divided by a slab of 1/2" flat ...
Both have tight , square corners ... air brakes at their finest ...
While it's true Mother Merc gave us a big cross section change on the short side .. but it's pretty comical to see the aftermarket add a second one down the line .. maybe they went to the water park and tried to make it look like the big slide ..
This Geiger piece is going on a " stick mid" 2.5 I'm in the middle of . To me it seems like it follow's the tried and trued logic of steady state header area to keep velocity up and then transition into a divergent cone with no sharp corners .
When something similar to this shows up on a 3.0 ... I'm pretty sure the results will be noticeable ...
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06-24-2017, 08:21 AM #215000 RPM
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Wow, the Geiger piece is really sweet, fully machined! What I gather is what I have always thought about two stroke outboards, very little tuning effect in the exhaust. Raced and wrenched two stroke motorcycles for many years. Now an expansion chamber is a tuned exhaust,complete science in itself. Let alone once the variable exhaust height powervalve came along. The motorcycle industry developed the two stroke along way. More power and flexability are there for the outboard. We are really uncorking the tuner to let the charge out, not so much worrying about the tune. I am really curious about that exhaust chest you have cut open. Thanks for the awesome reply.
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06-24-2017, 09:03 AM #22
I built the prototype a year ago. We are working on getting it programmed......
that tailgate looks familiar.Last edited by Todd D; 06-24-2017 at 09:07 AM.
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06-24-2017, 09:28 AM #23Supporting Member
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06-24-2017, 11:16 PM #24
lol
mine won't fit his adapter plate.
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06-25-2017, 08:37 AM #25
If your calling outboard's the Briggs+Stratton of two-stroke's ...... your right .
OMC at least took the initiative to lead a short runner directly away from the port before joining the three together in a common log . Mercury it seems went for tighter packaging .
With either , you will always have a contaminated "fresh" charge . Worse as more cylinders join in as the firing rotation moves down the log . ( btw , doesn't heat rise ) It's the nature of the layout . The best you can do is time the exhaust and make the tuner pull each cylinder down as clean as possible before you lose too much of the new charge .
In Jennings writings in both "Two stroke tuners handbook" as well as " So you want to build expansion chambers" he speaks of the two most influential parts as being the head pipe and divergent cone dimensions . Which is good for us outboard guys , since that's all we have to work with ..
I was working at a Yamaha store during the heyday of the RD 350 / Daytona 400 . I remember we sold those Torque Engineering welded up cones , which worked pretty good until Stuart Toomey / Erv Kanemoto released their mostly stamped steel pipes which flowed from section to section in a much more fluid motion .. night and day difference . At the time Kanemoto was ten years ahead of everyone else .
Then when the YZ 125's came out with boost bottle's , power jets and variable height exhaust ports , as you mentioned , changed the game again .
The only thing that separates the 300x block from every other 3.0 / 3.2 L block is that the exhaust log has the material on each side of the "speed ditch" removed .
I have an arbor I build for my mill that will reach in and get rid of most of it and some 12" tools that go in a hand grinder that will finish it up .
However ..........
If you look at a 280 block you will see that they somewhat shield each port down the line by building a roof over each port and roll the short side wayyyyy down . The only way I have found to follow their lead is to cut the back off of the block and weld where it needs material to re aim the port to where it doesn't crash onto the divider wall before finding the exit sign ..
Todd / Joe , hold the presses on making parts for ........ well , you know ...
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06-25-2017, 08:43 AM #26
P.S. I didn't mention that was Todd's tail gate , to protect the guilty by association ..
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06-25-2017, 09:47 AM #275000 RPM
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06-25-2017, 03:44 PM #28
Yes I do . They put the ditch there to try and keep velocity up during slow speed running . Makes for kind of a barrier across the port to keep the spent exhaust gasses from migrating back in the port and contaminating the fresh charge . In comparison to what they could do , it's a *&^%**(%^ Band-Aid ...
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06-25-2017, 05:36 PM #296000 RPM
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All I wanted to know is if I should cut it the mid....
Learning a lot. Probably won't do anything with it but definitely learning!
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06-25-2017, 11:10 PM #30
Ohh hey RS , welcome back to your thread ...
We adopted it when we thought you put down the grinder and just bought one already cut ..
Learning a lot. Probably won't do anything with it but definitely learning!
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