exhaust manifold porting?

[Dale .D]

Hi from the great white North.Doing some work on my 71 opel intake & exhaust manifolds.I'm planning on doing some minor porting of the intake.I'm wondering if there's any advantage to be made from any porting or grinding away any roughness in the exhaust manifold. Couldn't find any threads on this!.Also I was wondering if it is normal to have 3 stacked gaskets between the intake & exhaust manifolds.I've ordered 1 . this was where there was a leak? I'm getting the manifolds resurfaced & the exhaust plated.just want to do all the right things the first time. Any advise would be great . Thanks eh!

[RallyBob]

There's nothing to port. The stock manifold is already *bigger* than the stock exhaust ports. Making it bigger will serve no purpose other than wasting your time!

Opels respond primarily to intake work, I'd concentrate on that first.

[Dale .D]

Thanks Bob.I guess thats why there's no threads on the subject.Just doing the mild street porting on the intake . Any Ideas on the multiple stacked gaskets between the manifolds.Is that normal?Maybe it's an bolt alighnment issue for the intake & exhaust.

[hrcollinsjr]

Some of the gasket sets I've used have three gaskets for the intake to exhaust seal, a soft AL one and two thin gaskets to be used in conjunction with each other. Is this what you have?

Harold

[GTJIM]

With the stock Opel cast iron exhaust manifold it is desirable to keep the different sizes at the transition faces - head/manifold; manifold/down-tubes and even at each joint after that.
These 'steps' form what is known as 'reversion dams' which help stabilise the flow of exhaust gases away from the valve.
The stock exhaust manifold (and also the 'Sprint' one) are carefully designed on the 'interference' principle of exhaust scavenging - completely different to the principles behind the four tube header.
This type of manifold works over a larger rev range and has far less of an effect at specific revs - thus smoothing the torque curve and extending peak torque over a wider rev range. Near perfect for the street motor!