Type IV Beetle In The Works: Intake

Hello all,

Got the intake manifold and throttle body arrangement mocked up tonight. Going to cut up the stock FI manifolds & get them welded to form a Y down to a single 60ish-mm pipe. Hope to use one of the stock TB's on each side. They have 45mm butterflies and a 59mm mouth. The intake manifold pipes have a 36mm ID, and the intake port is 34mm. I plan to smoothly radius the edges of the intake ports out to 36mm (port match).

On top of the TBs I am considering using the stock air ducts with the thermostatic air doors. They have an oval opening 82mm x 45mm, and then a nice cone down to a 40mm opening. Some sort of warm air might be helpful for cold starting? Would integrate air filters into the duct as space allows. I dunno, might work.

Pictures will be posted eventually.

Peace, Harry

Pictures at:

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Hopefully the link will work. I mocked things up in the garage and then did some calculations. It looks like things are coming together. The 45mm TBs seem like a reasonable size to supply 1000cc's (one side of the engine), and the intake runner lengths I calculated seem reasonable. Using forumlas found online I calculate that 436mm- long intake runners (from valve head to end of runner) should give a torque peak near 4000rpms. With rough measurements this is slightly shorter than those used by the factory, which makes sense.

Another formula let me calculate an ideal runner diameter of 37mm for a 2.0L engine to have a 4000rpm torque peak with a .9 volumetric efficiency. The actual runners are between 34 and 36mm. Using the actual numbers a program tells me that should support a 138 cu. in. (2.25L) engine at 4000rpm. Actual displacement 123 cu. in (2.0L). All the calcations work out close to what VW actually used, which reassures me that I'm on the right track with this.

I can give links to where I found this information.

Thanks, Harry