phelpsa
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| posted on 24/5/07 at 06:40 PM |
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Bike Carb Manifold
I'm usually a BEC boy... plus this isnt for a locost but you lot know everything 
Would this manifold design be okay (its for a 1360cc Pug 205 and GSXR carbs)?:
The main bit that concerns me is that the centre pipes do not reach all the way to the carbs, should they bend around to meet the carb flat? Also,
does the length of the pipes make any difference other than to throttle response?
Adam
[Edited on 24-5-07 by phelpsa]
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flak monkey
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| posted on 24/5/07 at 06:46 PM |
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Chop the ends of the two centre tubes off at the proper angle so they do meet the carbs flat, problem solved surely?
Ideally you want all the runners the same length, but a bit of variation aint going to make a lot of difference.
Sera
http://www.motosera.com
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phelpsa
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| posted on 24/5/07 at 06:48 PM |
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quote:
Originally posted by flak monkey
Chop the ends of the two centre tubes off at the proper angle so they do meet the carbs flat, problem solved surely?
Ideally you want all the runners the same length, but a bit of variation aint going to make a lot of difference.
But then I'll end up with an oval end meeting the circular entrance of the carb, which wouldn't be great?
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westf27
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| posted on 24/5/07 at 06:51 PM |
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you need a smooth curve ideally with no steps between tube and what looks like silicone rubber tube.Gas flow has trouble thro'angles/corners
etc.Someone else will be along shortly who may be able to help more and yes the inlet length can affect torque I believe.
[Edited on 24/5/07 by westf27]
555
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phelpsa
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| posted on 24/5/07 at 06:54 PM |
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So ideally there wants to be a nice curve on those centre pipes. Will be a bit more tricky but there we go!
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flak monkey
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| posted on 24/5/07 at 06:57 PM |
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Ideally yes. How much power is the engine making and what state of tune is it in?
You are right you would get an oval end if you cut the ends at an angle. But you already have this at the engine end anyway.
You could leave it as it is and use angled or slightly longer tubes to connect the carbs.
If its only being mildly tuned then its not worth the effort IMO.
Longer runners spread the torque over a wider rev range, shorter ones give a higher peak bhp but the useable range is smaller.
David
Sera
http://www.motosera.com
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indykid
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| posted on 24/5/07 at 06:57 PM |
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since you're going to have to weld the stubs onto the flange, why not put the dog leg in the runner rather the join between runner and carb?
you'll then be able to mitre the tube and get matching elliptical ends to weld together.
still won't be ideal for gas flow, but neither is your original design. it will make the assembly a bit more likely to stay assembled though.
tom
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MikeRJ
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| posted on 24/5/07 at 07:00 PM |
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If you don't want to respace the GSXR bodies, then the center tubes idealy should have an S bend to match up to the ports and the TB's
correctly.
The design as shown won't flow very well with those sharp angles.
Much better to re-space all the TB's so they match the ports if they are separate TB's, or if they are the later type then just space the
left and right bank to give the best match in runner lengths and angles.
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phelpsa
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| posted on 24/5/07 at 07:04 PM |
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It'll be running hopefully around 120bhp or so.
Thanks for the help chaps  Anyone know anymore about how the manifold length affects torque etc?
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westf27
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| posted on 24/5/07 at 07:05 PM |
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something like this would help smooth off inside with a die grinder
 
Rescued attachment Untitled.jpg
555
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flak monkey
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| posted on 24/5/07 at 07:07 PM |
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quote:
Originally posted by phelpsa
It'll be running hopefully around 120bhp or so.
Thanks for the help chaps Anyone know anymore about how the manifold length affects torque etc?
Re-read my second post.
Sera
http://www.motosera.com
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jacko
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| posted on 24/5/07 at 07:27 PM |
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Phelpsa have a look in my photo archive under zx9r carbs there is some photos of how i did the manifold
Graham
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matt_claydon
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| posted on 24/5/07 at 07:36 PM |
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Why not respace the carbs and go for something like this? Still have angled joints but the angles are halved and the runners are now equal
lengths
 
Rescued attachment Carbs.gif
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takumi
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| posted on 24/5/07 at 07:42 PM |
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the only problem you have with this manifold design, is the carb on the far left (pic) might hit the top rear engine mount.
I made a manifold of that design (equal runner), for a Saxo with the same engine and it fouled the top engine mount about 15-20mm.. worth checking
before you start anywork..
RobinHood 2B 2.0i pinto, Keihin 38mm Carbs, lightened flywheel, O'Mori remote filter kit, 10 row oil cooler. Modified head, 10.2cr, special
valves FR22 cam, 4- 1 header.
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Bob C
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| posted on 25/5/07 at 11:49 AM |
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everyon'e worried about the dog leg runner/carb - there's also one runner/head with (ostensibly) exactly the same amount of gas
passing.......
Bob
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MikeRJ
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| posted on 25/5/07 at 03:41 PM |
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quote:
Originally posted by Bob C
everyon'e worried about the dog leg runner/carb - there's also one runner/head with (ostensibly) exactly the same amount of gas
passing.......
Bob
Not quite sure I understand, could you explain a bit further?
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Memphis Twin
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| posted on 25/5/07 at 04:02 PM |
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Adam,
You need nice lazy S bends for the inner two runners. Or get them re-spaced so that all runners are straight. Gasflow doesn't do corners.
Cheers Chris.
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Bob C
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| posted on 25/5/07 at 09:51 PM |
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quote:Originally posted by Bob C
everyon'e worried about the dog leg runner/carb - there's also one runner/head with (ostensibly) exactly the same amount of gas
passing.......
Bob
Not quite sure I understand, could you explain a bit further?
OK I didn't mean dog leg - it's just a bend, I was just pointing out that smoothing in the carb to runner joint while leaving the runner
to head joint as a sharp bend seems a bit daft ;^)
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MikeRJ
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| posted on 25/5/07 at 10:57 PM |
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quote:
Originally posted by Bob C
OK I didn't mean dog leg - it's just a bend, I was just pointing out that smoothing in the carb to runner joint while leaving the runner
to head joint as a sharp bend seems a bit daft ;^)
Oh right, I totaly agree. Sharp angles in manifolds are generally not a sign of good design.
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