When racing engines started surviving blasts up to 10,000 RPM, it became a requirement to have an inlet runner under about 10". So even a Weber or Delorto bolted right to the cylinder head became a bit too long.

 

Going to the slide throttle (Lucas) allows for a shorter tuned length and a pure tube, with no throttle shaft and butterfly in the flow.

 

Not strange at all that the Lucas units have a Weber bolt pattern and gasket shape.

At the same time Lucas came up with a high pressure mechanical injection (about 95 PSI) that works great and tunes by lifting a plunger and turning it to a different position. Even I could do it.

 

I never encountered the poor idle advertised in some locations. My factory Pport modified by Mandeville, to the point that a child could reach into the chamber through the intake, idled like a street engine. 

We drove it to the false grid with no difficulty. The Bridge ported side port engines must be towed around with little tractors. Neither has any power below 2,000 RPM but the side port pops and farts, and stalls and gets carb fires and is a general pain to deal with. Just never a factor with the Pport. 

 

When you are building runners 18-24 inchesl long it just seems a shame to spend so much time on a slide throttle. The Lucas piece is well thought out. Hardened slide with rows of bearing rollers supporting the slide. It never hangs up no matter the load on it. 

 

Lynn E. Hanover