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dot head and carbs


nlovien

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Posted

See if you fit a dot head to something like a GSXR1100L - given the raised port roof advantage - do you need to be selective with the carbs ? i.e. does the dot head need carbs that have the float bowls at an angle to match the port or can you use the std 36 / 38mm CV's from the L ( or bandit motor)

cheers

Posted (edited)

Yep, billet tops will fix this issue or we have done another with notched frame inside, these carbs and dot head made 147bhp, so worth it for sure! 

I had them on my 750.g also same issues ,if you want to run 38,s then you will have to get carb top solution.  As for tap pingel dual outlet only way to go, with slingshot you may have to dress tap mount area dished in buy 10mm or so. 

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Edited by Fula28
  • Like 2
Posted
3 hours ago, Fula28 said:

Yep, billet tops will fix this issue or we have done another with notched frame inside, these carbs and dot head made 147bhp, so worth it for sure! 

I had them on my 750.g also same issues ,if you want to run 38,s then you will have to get carb top solution.  As for tap pingel dual outlet only way to go, with slingshot you may have to dress tap mount area dished in buy 10mm or so. 

image.jpeg

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Where did the carb tops come from? I've got the same combo for my 750f

Posted

great picture - taking what looks like the 38mm tops are almost flush with the cam cover as a guide, quick check and i'm fine for 36mm carbs but going to have frame clash with the 38's  - this could turn out to be the reason to port the std L head versus fit a dot one - or stick with the 36mm carbs, funny how decisions can be sorted by not so initially obvious things - thanks :tu

aha! even better idea, so if you're looking for that reason to go bag a set of 38mm mikuni FS smoothbores - this is it :D they will fit no bother - and they come with sloped carb tops as an added adv.

  • Like 1
Posted (edited)

I may have forgotten this but is there an advantage to the raised port or is the advantage mostly from the added compression and the cams.

If one was doing a big bore for example and high compression pistons. Would you necessarily need the dot head for anything rather than just use the cams out of it?

Edited by boilerdude
Posted

I would say the dot head has better inlet ports as well as raising the compression. If doing a big bore conversion you can normally spec the compression you want . Pic of 750L slingshot frame bandit 12 motor and carbs with dot head .

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C__Data_Users_DefApps_AppData_INTERNETEXPLORER_Temp_Saved Images_DSC00082.jpg

  • Like 1
Posted

in my limited knowledge, raising the roof on the inlets for most of the older generation engines is a good thing - especially on 4 valve heads - huge subject that requires expert knowledge versus opinion but my stab at an explanation is 

1) helps to unmask more of the valve circumference and reduces the negative impact of the turn into the valve pocket on the port low side = better flow

2) helps to promote tumble down into the bore - this tumble down works on 4 valve heads whereas swirl around the valve and across the head works on 2 valve motors

this is internet warrior info versus hard earned experience, so it could be fake news  

 

  • Like 1
  • 3 months later...
Posted

Hey I had a thought about this... What if instead of having special diaphragm caps machined. What if I was to just grind mine down and if I grind a hole in them just epoxy that shit closed when I'm done. Is that good enough or do they need to be "just so" on the inside?

Posted

Fula - what did you do to the dot head to get 147hp ?  A std dot head normally nets a handful of horses on 1100R, a lot more on B12s with cams as well. The only way I've ever managed to get BIG gains is with flowing work, often pretty subtle looking work. I'm guessing you had some head work ......147 is a good figure with standard capacity....nice !

The high entry on dot heads eases the short turn radius and helps open up the front of the valve/port - the floor at this point is eased to help this when you get a head flowed. There's a slight help with gravity too, but not like true downdraft heads.

  • Like 1
Posted (edited)

I wish I knew who to go to for master level dot head porting in eastern US. Or maybe I could take it off and send it to... somewhere. 

Edited by boilerdude
Posted

They don't need a 'special touch'! They are an engine pure and simple - what they need is someone skilled in the work, Orient Express I'd trust - they haven't won multiple racing championships by NOT knowing what works!

  • Like 1
Posted
On 6/9/2017 at 3:55 AM, Gixer1460 said:

Not unusual but tricky to avoid looking like a dogs dinner! They all MUST be air tight obviously - pin prick holes can play havoc!

I'll put red gorilla tape over the bastards and be proud. 

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