The V8 Owners Forum -

Hi guys, I've just ported the rover heads (basicaly port mached to the gaskets) but is there any need to port the offy manifold or are they optimised already?

Jono

Which Offy manifold have you got? If its the dual port one then I suspect that the ports are made to the same size as the standard Rover head ports. The best thing would be to measure them.

I have just been chatting to V8 Dev about the dual port manifold, they recon that they have seen a loss of 30 BHP on their dyno with this manifold when comparing it to an Eddy Performer 180!

(The Eddy's ports are only the standard size to but it can be port matched with files, burrs etc)

Hi
I would leave the manifold alone, matching the ports to the gasket takes them out far to far in that region and causes the flow to stall just before the pushrod area which is the big restriction. If you leave the manifold untouched you may avoid this flow stalling happening, but I think it is only a hope. I don't know how many times this has been posted on here about not matching to the gasket on the rover heads . . .
It is only done on very highly tuned big valve race heads, and only then when the pushrod area has been worked by fitting thin wall steel sleeves. It is the valve insert area that needs the work, and the pushrod area. The port mating area is already too big for anything less than stage 3 (large valve) heads. The aim in re shaping the port is to have a constant taper from the back of the area behind the port to the carburetor venturi of about 7% area per inch traveled toward the venturi, if you can't achieve this because of some restriction the one thing to avoid is the port going from narrow to wide to narrow, which unfortunatly is exactly what you have created here by opening the mating face to the gasket.
Best regards
Mike
Sorry to rant but it is more than a little frustrating. . .

It's the Offenhauser 360 manifold
I supose to keep things all equal and flowing as they should I could open up the inlet track on the manifold the same amount as the heads, or would that be a pointless exercise?

The reason I did the heads to the gasket was I read in a few places on the net that the port entrance area of the head drasticaly reduced the flow, but matching it to the gasket took them a little less flow area than the start of the inlet track.

Not to worry if this causes a negative affect as I have a spair set I can swap for in the garage!

Jono

Jono FD3 wrote:It's the Offenhauser 360 manifold

Good!

This is the manifold I have got...... not in my hands yet, but being picked up over the weekend all going well!!

Manifold and Holley 390cfm carb, total of £100 and £20 for my mate to go and pick it up for me