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250 Griffon Build

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  • #16
    250 Griff exhaust...can be improved

    Good idea - and sure it can be improved - it was an early pre-computer modelling empirical design improvement on the challenger exhaust...........and has that slightly ugly sharp turn at end of the header and overly long diffuser and short body ...... I have made a different replacement for my 250 Griff ...and it improves - but the stock one is better than you would think !! Drop me a PM if you are interested and I will dig out my cone dimensions ...also note that by doing in 1mm steel ...the exhaust is considerably lighter than stock

    I also computer modelled the QUB exhaust - of Dr Blair fame - and interestingly that one is very close to what my modelling sw recommended!!....the exhaust gas flow theory has not changed since 1972!
    Cheers Kim

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    • #17
      Kim, actually I suspected that the stock pipe is pretty good. With that in mind I will be building my new pipe very similar to stock. I hope to eliminate that odd join angle at the end of the header though. I don't want anything drastically different yet with out actually even running the engine. I want to have a good stockish baseline to start with. I would be interested to see a picture of the pipe you built though. I don't do 3D modeling but I am drawing mine up in autocad. I was a mechanical designer up until a few years ago but never seemed to get the time to learn solidworks although I do have the program. Anyway I will hopefully get cracking on the pipe this week somtime.
      Last edited by johnu; 11/02/2015, 04:55 AM.

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      • #18
        Got my tank painted today Came out pretty good, this is the good side, I had a slight issue with the Greeves decal on the other side but still not too bad. Before and after pics.
        Attached Files

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        • #19
          Exhaust Drawing

          Hi Johnu...

          Have you ever looked at the software for designing motorcycle exhaust systems, there is one I purchased several years ago called Cone Layout
          www.pulserate.com you can download a free 21 day trial and have a look at it.

          Regards
          Sean

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          • #20
            Originally posted by Sean Bowers View Post
            Hi Johnu...

            Have you ever looked at the software for designing motorcycle exhaust systems, there is one I purchased several years ago called Cone Layout
            www.pulserate.com you can download a free 21 day trial and have a look at it.

            Regards
            Sean
            Thanks Sean. Yes I have a program for exhaust design which I used on a Suzuki T500 project and it worked out great. Right now though I am going to stick to close to stock just because of the simple fact that I have never run this bike before. I would like to have a known baseline to start off with before I start modifying. Did that cone layout work well for you? I tried the free trial and ended up with a serious virus on my computer (may have been something else that caused that though).

            Cheers,
            John.

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            • #21
              Exhaust Drawing

              Hi Johnu
              I purchased the software a couple of years ago and did not experience any issues with either virus or in using the program, but to be honest I have not used the program in anger as yet.
              But what I did do as a trial was to put all the dimensions in to fabricate a megaphone for my BSA C15s and I found the beauty of this was to print out each template on card, cut out the various shapes and make a mock up.
              I was able to offer the model up to the machine and check out the fitment which looked quite good.
              Regards
              Sean

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              • #22
                Sean,
                Yes I always make up card board cones first and tape them together to check fitment. The exhaust program I use gives you the pipe as a straight layout so I just cut the cones into sections at various angles (mostly 10degrees) then start rotating them to form the shape I need. Not very scientific I know but it works well. I develop the cone patterns on autocad. I might try that Cone Layout again as it would save me a lot of time on the development of the templates.

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                • #23
                  I couldn't just leave the tank sitting on the bench after painting so I did a quick mock up
                  Attached Files

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                  • #24
                    Hi johnu
                    that looks as though it is going to be a beut, love the blue.
                    Sorry to be pedant, but can you not change the side pull throttle for a more period piece.

                    Colin

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                    • #25
                      Originally posted by cray View Post
                      Hi johnu
                      that looks as though it is going to be a beut, love the blue.
                      Sorry to be pedant, but can you not change the side pull throttle for a more period piece.

                      Colin
                      Thanks Colin!
                      Regarding the throttle I specifically changed it to the side pull as this bike will be raced. I am not building the bike to sit and look at. My dad is going to give me grief when he sees that I am not building it stock as well There will be other parts of the bike that will not be factory such as alloy rims and I am building my own expansion chamber. I will probably install modern bars and levers also. When I'm done racing the bike it would be easy to change back to stock (aside from the rims).

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                      • #26
                        Good for you . Build it how you want it ..... As long as your racing it
                        When you are racing u need a bike you can trust and have confidence in .
                        Good luck with the rest of the build. Can't wait to see some action shots !

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                        • #27
                          Originally posted by johnu View Post
                          Thanks Colin!
                          Regarding the throttle I specifically changed it to the side pull as this bike will be raced. I am not building the bike to sit and look at. My dad is going to give me grief when he sees that I am not building it stock as well There will be other parts of the bike that will not be factory such as alloy rims and I am building my own expansion chamber. I will probably install modern bars and levers also. When I'm done racing the bike it would be easy to change back to stock (aside from the rims).
                          Have to agree with you to some extent with the throttle, they are better,(I have one on my pathfinder ) but the loop of throttle cable flapping away when on full chat does look nice
                          Look forward to seeing the complete bike, good luck with your rebuild.

                          Colin

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                          • #28
                            Originally posted by cray View Post
                            Have to agree with you to some extent with the throttle, they are better,(I have one on my pathfinder ) but the loop of throttle cable flapping away when on full chat does look nice
                            Look forward to seeing the complete bike, good luck with your rebuild.

                            Colin
                            Thanks Colin

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                            • #29
                              Griffon pipe ready to roll
                              Attached Files

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                              • #30
                                Been so busy with work for the last few months that the Greeves had to take a back seat. However I do have a small update, I have formed the cones and tacked most of them for the exhaust. I also made my own version of the original header clamp as shown in the pictures below.
                                Attached Files

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