What intake manifold?

[MasterSpoon]

Ok was bored as hell the other day and had pitbike and tools handy so had a bit of a play. Removed exhaust and cleaned up the weld inside for better flow and figured i might aswel check out the intake while I was there.

What I found was not real good. Bike is a 2008 pitpro 140XR with the 140cc motor obviously. It has a "30mm" 26 Mikuni carbie on it.
Now where the carbie mounts to the manifold has an Inside diameter of 30mm, the intake port on the head where the manifold bolts up is about 28mm. The stock manifold is about 23mm.

So my question is what will be the best manifold for this motor? like do I want to be going with a 26mm manifold as its a 26mm oval carbie and just flaring the ends to suit carbie / head? or should I be going with a 28mm manifold and just flaring the carbie end out to 30mm?

Any advice appreciated and if you have links to where i could buy one would be great.

 

[Dirtrider]

If you have a die grinder handy just take out as much alloy as you can out of the manifold. Just take care not to take to much out on the bend of the manifold. Or end up like me with a hole that needed to be patched up with metal putty.

 

[MasterSpoon]

yeah was thinking of just grinding it out but i don't think a 23mm manifold could be taken out to much so would possibly goto a 26mm manifold and grind that out but was trying to work out if i should goto 28mm or 30mm (if possible) and better still if i have to buy a new manifold if i could buy one the bigger size already.

 

[Dirtrider]

I started with a 26mm manifold and took it out to 30mm abit thin in some spots but it does the job good. I found it hard to try and get another manifold to suit a twin spar frame so i had to work with what i had.

 

[MasterSpoon]

hmm, not happy
got another manifold, 26mm puppy but the castings were a bit poor inside so took to it with grinding stones and various bits, cleaned it right up and smoothed it out a fair bit better then stock.

Went to fit it up and hmmm it doesn't fit......
My old manifold (well still current one) is a short manifold and the new one is a longer manifold.

So can I only run a short manifold or may there be something else that will fit?
the longer manifold was putting the carbie up and across and putting it into frame and fuel tank.

Note : on the side of the new manifold has written 56-2 ZL

 

[Custom]

easy bet is to make your own manifold, worked for me

 

[no_crf50_here]

now i told spoon that too, some old trampoline tube & gaffa tape - you can call it a 'custom' intake manafold...

 

[MasterSpoon]

easy bet is to make your own manifold, worked for me

care to go into detail on how you made yours?
i was thinking of trying to get a 28mm mandrel bent pipe with the bend i needed and making up flanges that basically copy the existing ones and weld them on but will be a while till i will have time to even think about that.....

 

[Custom]

mines sounds dodgy but it works, i used a bend out of a CT90 engine pipe and made the end plates out of 4mm flat mild steel. used a drill and deburrer to get the holes to the right size and 2 days to weld it all on right (day one, wrong angle..)

 

[Dirtrider]

MasterSpoon

care to go into detail on how you made yours?
i was thinking of trying to get a 28mm mandrel bent pipe with the bend i needed and making up flanges that basically copy the existing ones and weld them on but will be a while till i will have time to even think about that.....

What did you want to make it out of stainless pipe or alloy pipe. I know you can get s/s pipe ready to go with a 90 degree mandrel bend. I'm sure it had a 28mm i.d and was about 1.2 to 1.6mm wall thickness,Just would have to cut it to the size and shape you want and tig it all up. That was the stuff a was looking at when i thinking of making one. But i just took more alloy out of my old one to suit.