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[Rich B]

Hi all

I've been messing about with a variety of exhaust systems lately from both 8v and 16v cars, both cat and non-cat.

The manifold for the cat equipped system has a large heat shield just before it joins the cat, whereas the non-cat version doesn't have one. I appreciate why a cat centre box has heat shields, as cats tend to get quite hot, although not all after market cats seem to have them.

Anyone know why the manifold features heat shields on a cat car while a non-cat car doesn't have one. Surely the manifold temperatures must be similar? Also, sports manifolds for cat cars like the one made by CSC don't have any heat shieds, is this likely to cause problems?

Thanks

Rich

[Ben_nz]

Maybe it's important that the exhaust gases be as hot as possible for the cat to work effectively.. Also the cat should warm up as fast as possible after you start your car, so it can begin doing its work before your car kills too many children with smog.
I'm just guessing though.. Ain't no cat on my car, and I've never seen the heat shields you're talking about!

[john w not logged]

Hi,

My '93 16v has a cat and crossover manifold-all standard. The front heat shield is still there on the manifold- just held on with clamps as it used to slide up and down creating a horendous vibration. My only guess is that as the system goes into 'one' much further up the front of the car than a non cat system, there may be a greater concentration of heat kinda under the handbrake area. i suppose that they thought it needed protecting??

There should also be a heat shield after the cat going right round the bend to the rear box. My original and replacement 2nd hand cat, both have this missing, with no i'll effects.

john

[gritsop]

Hi,

My 33 which is cat equipped, has heat shields all way from the manifold till the cat itself.

The manifold until just before the joint with the catalyst is wrapped around with small pieces of tin; these are kept together with big hose clamps at the end of each piece.

Regarding the part of the catalyst, there are heat shields bolted on the chassis. These shields however stop at the tail of the catalyst where the pipe makes a 90 degrees turn and goes to the right where it meets the muffler joint.

I would guess that these shields play a dual role by keeping the exhaust system hot enough so that the catalyst keeps the 300 C working temperature and protecting the surrounding area from heat.

Some photos from the exhaust.





Regards,
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1991 Alfa 33 1.4 IE
2001 Alfa 147 1.6 Distinctive

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[markgp4]

blimey is that your garage floor or your front room???
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