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inlet valve to cylinder head port distance

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Trying to work out the resonant length of my inlet tubes.

Think I've got :


  • 45mm trumpet 
  • 112mm DHLA carb
  • 65mm VW motorsport inlet


Anyone know the distance or have  ideas how to measure the last part, side of head to inlet valve?


Think I might need much longer trumpets and plenum, or shorter trumpets to hit the high revs.





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Thinking about inserting a cable tie to closed cylinder 1 inlet valve above the carb throttle plate to find outer radius, then below throttle plate to find inner radius then use average of these

I estimate 5.5cm based on the 75mm bore and height of inlet port.


Edited by dvderlm

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But maybe I need bigger chokes.

Performance Secrets book suggests



Think that should be:


  cc 6000 --- 7000 -- 8000 -- 9000 --  10000rpm
1000 23..25, 27..29, 28..33, 30..35, 32..36
1200 27..30, 29..34, 31..36, 33..39, 36..42
1400 29..31, 30..35, 34..39, 36..42, 38..45
1600 31..32, 32..37, 36..42, 38..45, 40..48


And the Weber guide chart with hand-drawn new curve (red)) could be 33 chokes for 7000rpm. 


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Hey that's some nice info you posted there -  the Performance Secrets book sounds interesting??


My only concern is you are looking for very specific accurate dimensions off a complete operational engine, something that I'm sure you will agree, is a lot easier stripped down on a bench.

Personally I would look into whipping the inlet manifold off to get accurate measurements of the port with  a vernier caliper and it will give you a more accurate view of the distance to the valve.

I recall a Dave Vizard article for port distance you need the distance along the centre of the port.


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