Alfa Romeo Forum - View Single Post - Porting Manifold and bigger downpipe on JTD

Mark_JTD · 15-02-2008

Hi there, my car is in a standard state at the moment(156 2.4JTDm 175) and the tuning bug has hit me after 2 weeks ownership!! I've searched for info on this and can't find anything, apologies if I've missed it though. Before I get a remap and BMC CDA with a superspint exhaust & de-cat, I wanted to get other bits out of the way to hopefully really make good use of the re-map.

My other car is a Fiat Coupe 20VT with 300bhp & about 270lb/ft and I was wondering if any of the mods would be beneficial to be carried out on my newly aquired Alfa.

I'd imagine porting the exhaust manifold to be fairly straight forward(if required & after removal) as I did this on my Fiat. The main reason for doing this is that the manifold itself has smaller holes going into it than the head, so you just match the manifold gasket holes to those on the manifold(as the gasket are the same size diameter as the head). Purely by doing this gave me better spool up and I was able to produce the same power on the RR with 0.2bar less boost.

So I suppose the question is, does anyone know if the manifold entry holes are smaller than the head holes which creates a lip and then allow the exhaust gases to disappear quicker with the lip(manifold) being ground away?

The other thing I was going to ask about is are there bigger downpipes available than standard, to again get rid of the gases quicker?! If so, where from? I've got a 2.75" manifold on my Fiat which was made by Hayward & Scott. Anyone know the diameter of the standard downpipe?

Thanks in advance,

Mark

15-02-2008	#1 (Post Link)
Mark_JTD Club Member Club Member Number: 323 Join Date: Feb 2008 Location: Nr Salisbury, Wilts Posts: 188 Member car: 156 2.4 JTDm 20v Veloce	Porting Manifold and bigger downpipe on JTD Hi there, my car is in a standard state at the moment(156 2.4JTDm 175) and the tuning bug has hit me after 2 weeks ownership!! I've searched for info on this and can't find anything, apologies if I've missed it though. Before I get a remap and BMC CDA with a superspint exhaust & de-cat, I wanted to get other bits out of the way to hopefully really make good use of the re-map. My other car is a Fiat Coupe 20VT with 300bhp & about 270lb/ft and I was wondering if any of the mods would be beneficial to be carried out on my newly aquired Alfa. I'd imagine porting the exhaust manifold to be fairly straight forward(if required & after removal) as I did this on my Fiat. The main reason for doing this is that the manifold itself has smaller holes going into it than the head, so you just match the manifold gasket holes to those on the manifold(as the gasket are the same size diameter as the head). Purely by doing this gave me better spool up and I was able to produce the same power on the RR with 0.2bar less boost. So I suppose the question is, does anyone know if the manifold entry holes are smaller than the head holes which creates a lip and then allow the exhaust gases to disappear quicker with the lip(manifold) being ground away? The other thing I was going to ask about is are there bigger downpipes available than standard, to again get rid of the gases quicker?! If so, where from? I've got a 2.75" manifold on my Fiat which was made by Hayward & Scott. Anyone know the diameter of the standard downpipe? Thanks in advance, Mark Alfa 156 2.4JTDm Veloce 175 - soon to be mapped Last edited by Mark_JTD : 15-02-2008 at 13:24.