Making Up An Exhaust System

[newdean0 0]

I'm making up a downpipe to fit a magnex system to my MI but I'm forced to have the 2" magnex centre box pipe slotting inside the downpipe. I've been told that you should never create a step that is against the flow but given this is a 1mm step in a 2" diameter pipe is this really going to make a difference? I could try and file the end of the pipe to reduce the step I guess.

 

Cheers

 

Dean

[inferno 1]

never heard that before, but i can see the logic. if the smaller tube is further back, the flow of air will push the moisture into the step and rot it (its acidic and can still attack stainless). the other way round the moisture flows to the rear of the exhaust and evaporates.

 

could u use a dolly to widen the magnex bore? a short cylindrical block of steel tapered to fit in the magnex pipe, kwik fit have them and are usually pretty usefull on sundays for beer money!

 

alternativly could u get a reducer on the down pipe and shorten it a little?

[Owain1602 0]

I dont think he's refering to moisture resting in the system, but rather the flow of the system. I gather it would make a difference but what exactly are you after, is the engine something special or just standard? Dont know how good the magnex system is but some reduce flow compared to the genuine exhaust anyway so if this is the case, you would be making it worse with a reduction. No doubt there are many more qualified than me on exhausts to answer your question.

[16v205 9]

I used a cheap pattern part downpipe from my local motor factors to chop up. The downpipe fitted inside the magnex centre section just like the original. Plus I then had new material to weld and it ended up ok. Only cost around £35 for the downpipe.

 

Rich

[hengti 2]

can see the logic, but don't reckon you'd notice any difference at all - i've tried both and didn't myself

 

you'll want to be sure the magnex pipe isn't shoved all the way in to the bend in the downpipe though - i guess that might well cause a restriction if the end of the magnex pipe was sat at a bend (if that makes sense)

 

you'll also need to cut two horizontal slots into the downpipe, so that you can clamp it effectively

[Rippthrough 98]

It's not the flow restriction that's the problem, it's the pressure waves caused by the step in the system.

[newdean0 0]

Cheers for the replies - I've got a reducer now which the magnex just fits into and filed the end of the magnex so it's really sharp - hopefully this will make the step small/gradual enough not to cause any pressure wave nastiness.