Manifold Cones

[chrispitman]

Got my manifolds off at present and in the process of de catting, can anybody here give me some advise on these reversal cones that are fitted to some exhausts. What benifits do they offer and are they really needed. Would like to find out as going to get the manifols ceramic coated.

[victormeldrew]

I have decatted pipes without the cones and you do get a metallic ringing not unlike tappet noise from the front of the car - exhaust gasses expanding and pinging about in the cat chambers apparently. Apart from the benefits in gas flow, the anti-reversal cones are supposed to stop that bag of spanners sound when the cats are removed. They'd need to be fitted before you get the ceramic coating done, obviously!

[clive f]

you need some steel formed to make the cone, about 100mm diameter at one end , tapering down to about 60 to 65mm diameter at the other end, and about 150mm long, have these welded in where you cut the manifold, usually around the welded seam just after where the 4 pipes converge into the 4 "pipe, making sure you mark it all up properly so as to realign it all afterwards, when you weld it back together again!

Edited by clive f on Tuesday 10th April 11:59

[2Munkys]

Still got my old NRV manifolds in the shed. I think the job costs around £200 these days', maybe a little more. They give the car a nice sound without being loud, but their function is to increase torque.

[simonb9]

Am I right in saying then that if you want to get the pre-cats out you have to cut the end of the manifolds, remove the pre-cats and then weld them back up again ?? I take it that the pre-cats must be a life long product then as I wouldn't have thought garages would like to go to the length of cuting/welding when the pre-cats need replacing ??

[crazycraig]

You shouldn't need to cut and weld unless they're really stuck I guess.

He's a link to a topic I begun about precats.

www.pistonheads.co.uk/gassing/topic.asp?p=3&f=13&t=228906&h=0

[chrispitman]

You can beat out the cats in the manifolds without cutting welding etc. Have done one still got one to go, did take a couple of hours to do.

[spend]

victormeldrew said:

I have decatted pipes without the cones and you do get a metallic ringing not unlike tappet noise from the front of the car - exhaust gasses expanding and pinging about in the cat chambers apparently. Apart from the benefits in gas flow, the anti-reversal cones are supposed to stop that bag of spanners sound when the cats are removed.

Cant say I notice any of those sounds, but I havent had Phils catalogue of calamaties either (his chassis number must be 131313) . I certainly wouldnt bother with cones...

Dave

[chrispitman]

MAIN CAT Removal - What can be gained by removing the main CAT, ie do you get more power also dose it get alot louder. I do understand that you have to put a CAT in to get through MOT.

[spend]

It's too Fin loud.... Just seems to rev a little more freely to me, but you can throw fuel down the exhaust. Mine is 430 which to all reports has different sound to other models tho....

Dave

[that daddy]

I have the precats removed and it does soung ringy but with the HC cam it sounds like a cammie small blocki like it.

[Bomber Denton]

The point of the non-reversal cones is that the gases exit the head at one angle then take a sharp (about 30 degree) as they enter the manifold restricting flow. The cone in the manifold creates a venturi which pulls the gases around the bend rather than just letting them bounce.

Speak to Tim at ACT, he can supply you with more information, exchange manifolds, ARP bolts (essential) and should you wish and also ceramic coating.

ACT tel. [phone]

[clive f]

simonb9 said:

Am I right in saying then that if you want to get the pre-cats out you have to cut the end of the manifolds, remove the pre-cats and then weld them back up again ?? I take it that the pre-cats must be a life long product then as I wouldn't have thought garages would like to go to the length of cuting/welding when the pre-cats need replacing ??

only if you are going to do the job properly and fit a pair of cones in.

[Nuggs]

clive f said:

simonb9 said:

Am I right in saying then that if you want to get the pre-cats out you have to cut the end of the manifolds, remove the pre-cats and then weld them back up again ?? I take it that the pre-cats must be a life long product then as I wouldn't have thought garages would like to go to the length of cuting/welding when the pre-cats need replacing ??

only if you are going to do the job properly and fit a pair of cones in.

The advice given to me by 'those wot know' was that you don't need the cones for a 400...

Edited by Nuggs on Tuesday 10th April 15:38

[GreenV8S]

Bomber Denton said:

The point of the non-reversal cones is that the gases exit the head at one angle then take a sharp (about 30 degree) as they enter the manifold restricting flow. The cone in the manifold creates a venturi which pulls the gases around the bend rather than just letting them bounce.

I don't think there's any venturi effect at all, the cones just act as a 'one way valve' for pressure waves in the exhaust. Pulses coming from the engine pass through with minimal restriction, pulses coming back are partially reflected by the cone.