Inliners International Forums General Discussion Hi Performance offenhauser for 250 design theory

Anybody know the theory behind the design of the offenhauser intake manifold. the end corners seem to be really square and not nice smooth rounds like other manifolds. I'm thinking of port filling the corners inside to make a nice round transition.

I think if you could recon-tour the short turn on the Offy intake you would benefit more.

A longer more gentle turn would allow the air/fuel mixture to follow the short turn & feed the # 2 & # 5 cylinders a bit better.

By having a long gentle radius the air has an easier time to follow a gentle turn.
In turn it should increase airflow.
Just like having a long short turn radius in the intake port, it will increase airflow allowing the air to come into the combustion chamber throughout the whole diameter of the intake valve, & not the majority of the long turn radius.

The long turn radius still gets the majority of airflow, but having a good short turn radius helps tremendously for improved short turn radius flow.

For a turbocharged app, I would think it would show an improvement also.

Stock for stock, (turbo charged APP), I think a OFFY intake would work better because of the sharp 90 degree turn, most of the air/fuel will go to the outboard sides, but I think by all the air/fuel hitting that wall hard, it might break up the flow & possibly feed more air/fuel to the #'s 2 & 5 cylinders, just a thought anyways.

I think this intake is better than the Offy or Clifford.
http://www.ebay.com/itm/161462168269?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

But, I have not seen any back to back dyno/track or street racing comparisions.

MBHD

It is done that way also on the OEM intakes. It helps maintain velocity and airspeed for the long runners to the end ports. Its done that way intentionally. Filing the corners will only reduce the runner cross section further and probably have the opposite results from what you are seeking.

Actually if you compare the OEM intakes, they have a broad curved outer elbow. where as the Offenhauser has a dog leg where part of it actually extends past the corner and then reverses back to the intake port.
http://img2.uploadhouse.com/fileuploads/2986/2986738a4598106d9aa750b449baaec13c9341c.jpg

http://static.summitracing.com/global/images/prod/large/OFY-5416.jpg

maybe it has something to do with intake pulses and reflection from one end to the other. because as the firing order goes
1 5 3 6 2 4 the air-fuel flow direction is going back and forth from one end to the other.