Cast Iron Pinto Exhaust Manifold - which to use?

[James Doulton]

I have two different cast iron manifolds for my Legerra. One is an original single outlet one (presumably a Cortina one) and the other is a twin outlet one. I am soon going to take the Legerra to a stainless steel exhaust place to get a new exhaust and I was wondering how much difference the twin pipe one is likely to make, if any. [I realise that this might be more contentious than a discussion on Brexit!]. I would expect that a twin down pipe exhaust will cost more and it will probably add to the engine bay temperature. [I won't mention heat tape] But is it worth the difference?

[Jim (across the pond) Adamek]

It probably will produce slightly more horsepower do to less constriction of the exhaust gas but you right twin exhaust pipes will be more expensive. You can wrap them if you believe that they are producing too me heat but with good venting that should not be a problem. That is why my old girl has vents on the side panels.

[Adrian Southgate]

So much depends on the attitude of the guy thats making the pipes for you James.

CMV has a single outlet '84 casting and a full stainless 1 into 2 tailpipes - I made the mistake of getting it done in two sessions and it cost me more than it should have done.

Using quite a large bore pipe with a silencer under the middle of the car is a mistake, sounds nice, quiet until you welly it but repetitive collisions with speed bumps has done it no favours and it taps on the chassis on tickover.

Given to option to 'do over' I would use the twin outlet and get the engineer to make the downpipes fit really close to the engine then continue back as a horizontal pair until just before the back axle. There is enough room for a small silencer as long as it nearly touches the last cross member. From that point I would go with a two into two silencer and then twin outlets in the bumpers like mine but thats just me. The draw back is using too large a diameter tail pipe it will rattle on the bumper You could use the same ID pipe under the car as the bore of the manifold outlet all the way back. I'll leave you to do the mathematics on the flow, capacity etc but I don't see a 'same size' pipe being detrimental.

The four branch that is going on XSC is going to use twin small bores all the way to the bumper and through it. I need to split the four branch down to descale the outside prior to wrapping it and can see an advantage to cutting off the last collector to allow this and then using two pipes all the way down, divergance being in front of the rear axle and then going up and over with silencers between the back axle and the bumper. With XSC of course I have the advantage of being able to make new supports and plan the route from above with the body off.

[Adrian Southgate]

I would now avoid the 'cortina' manifold like the plague after this happened to mine.

[Dave Adams]

The difference between the two manifolds. ...the Sierra twin pipe is better for the legerra. ..

[Big Vern]

The Ford Sierra twin cast 4 into 2 is a good performer but check carefully for cracks where the 'two pipe' bit joins the main part - Its good for 140 horse power so should meet your requirements.

[James Doulton]

Do you mean like this, BV?

I could probably get the stick welder in there but that might make it worse.