Bob Rawle

ok guys pics will be mailed out tomorrow evening, problems cleared up by then.

thanks

bob

pat

As Floyd has already pointed out, the main improvement from porting the headers is that it makes the manifold entry larger than the exhaust port exit. This creates a "lip" between the collector and the head, which will present a flow restriction from the collector into the head. The exit from the head is the same diameter as the collector hole, but the stud holes are larger than the studs; this allows asymmetric expansion of the collector with respect to the head, but it also means that one can "misalign" the collector onto the head, thus creating a "lip" from the head to the collector; with the collector ported, it becomes impossible to get such a lip in the normal flow direction.

Another result of porting the headers is a reduction in cabin noise. The reduction in turbulence will increase gas velocity, reducing pressure and thus also noise. It's an old trick, I ported mine a few years ago and reported the effects at the time; closely thereafter Mark, Bob and Branko ported their collectors with similar effects observed It won't magically transform the car into a fire breathing monster, but it does improve flow, I remember having to add a few percent more fuel to comensate. Bang for buck it's remarkably good Not a patch on a good set of headers though... one set needed about 25% extra fuel!

Cheers,

Pat.

Nathan L

Pat Cheers for that, makes it easy to understand.

Is getting the standard manifold off a DIY job or is it a pain in the **** ?

Floyd

iTrader: (9)

Nathan

I've done a couple now and soon to do another so I've a little experience. It really depends on the mileage of the car and the sort of treatment it's had. If it's had a hard life then there's a good chance that the heat shields will be rusted on solid. That will be your main problem so you'll need a good soak in WD40 for those bolts the night before.

It is possible to re-use the head gaskets if you remember which way they came off too. If you decide to port the intermediate joins then I'd advise new gaskets there.

Pat has a good point regarding the possible mis-match due to stud alignment.

F

harvey

iTrader: (48)

Hi Richard: What headers are you running?

ScoobyWhite

Mr. Bob Could you please send to me by mail your fotos too......

Thanks

hades

Effectively, the manifold is actually smaller than the outlet in the cylinder head, so you get a square lip which doesn't help flow. There are a few other minor issues in the mainfold, but I believe that is the biggest thing.

Scoobysport will port and fit headers for you too, although IIRC they charge more for that than David was talking.

Noise wise? It is unequal length headers that gives the characteristic burble, you lose it with equal length headers. Smoothing the flow doesn't alter the lengths.

IMHO, porting did make the burble a little less deep / boomy / resonant on my car, although it did release a little more "snarl" at higher revs and throttles. The noise suited me by seeming quieter when cruising, still sounding great when you floor it point of view.

Edit to add re: power gain. My MY02 gave very little more bhp peak power but a much wider power spread than very similar spec cars, and significantly more torque - about 10-15lbft through the 2000-3500 range. Therefore, I'd say IMHO well worthwhile difference in the real world, although it doesn't help much with figures to bandy around the pub

[Edited by hades - 2/3/2003 7:40:59 PM]