Throttle body size

[John Slade]

I'm fabricating an intake system for my 13B turbo. I'll be using the cast manifold and runners from Lamar and building my own plenum using my fancy new TIG welder. The recommended throttle body is from a Mustang 5.0, but I'm not sure what size to get. I've had suggestions ranging from 65mm to 75mm. Any thoughts?

[Dave Clifford]

Wish I had known that last month John. Last summer I came across a retired Ford engineer who designed fuel delivery systems. He always aquired one or two he had helped on when they went into production. He retired a couple years ago and was moving. He sold them to me at his garage sale dirt cheap. I auctioned the last three off last month on Ebay for $49.00 @. I had two for the 5.0 Mustang, a 65mm and the 75mm H.O. Brand new. Bolt on, plug in and go.

[Aaron]

Usually you want to keep your inlet velocity lower than 300 ft/sec (reference: Corky Bell)

non-turbo (assuming flow of 450 cfm )

450 cfm/(300 ft/s * 60 s/min)=.025 sq ft area required

 

turbo (assuming 600 cfm)

600 cfm/(300 ft/s * 60 s/min)=.033 sq ft required

 

65mm=.0357 sq feet area

75mm=.0475 sq feet area

 

It looks like the 65mm is big enough even under the turbo load. If you go too big, part throttle suffers greatly, and it would be embarrasing to stall out on the taxiway

[John Slade]

Scary. There's a theory for almost everything. Thanks Aaron.