New Bosal Catalytic Converter - How Necessary is the Old Heat Shield

[dirty_mech]

So I recently replaced the blown-out cat on my 2000 Legacy with a high quality one from Bosal.  However, I noticed the new catalytic converter bodies are shaped differently from the old catalytic converter bodies; they are round and cylinder shaped rather than an oblong, flattened shape like 1 of the 2 OEM cat bodies.  For this reason, and also because I was short on time, I didn't even attempt to transfer the OEM cat heat shield components to the new cat.

I have, however, removed them from the old cat and kept them just in case.  I wanted to ask folks here if they think I should try fitting the old cat heat shield components to the new cat.  The old cat had extended flanges and holes in those flanges to allow for installation of the heat shield components.  The new Bosal cat doesn't have those at all, but I could probably get it to fit with a bit of bending and maybe some slightly longer bolts.   It wouldn't be a perfect fit but it would be more than nothing. 

I know temperature affects how efficiently the cat works, but maybe Bosal just designed their cats such that the extra heat shielding isn't necessary?   Not seeing any advisement from the manufacturer regarding this issue.  Photos of old uninstalled cat (heat shields already removed) and new installed cat attached.

Edited May 6, 2021 by dirty_mech

[idosubaru]

Manufacturer designed it - only they would know.

If it doesn’t say and has the holes for it, that could be understood to mean they expected shields to be installed as the factory unit was.

All of this you already know. I don’t know that any of us install enough of these and follow them for 5 years to have any statistically meaningful feedback. 

If it’s not giving any check engine light snd you’re passing emissions or inspection then it’s doing it’s job at the moment at least

Edited May 6, 2021 by idosubaru

[Numbchux]

All my heat shields go in the scrap pile. All they do is rattle.

[jonathan909]

Aw... fuzzy...

[dirty_mech]

Sounds about right guys.  I'm probably just overthinking it, or being overly cautious.  If the manufacturer didn't include a heat shield or the attachments for the original one, then it probably means it's not necessary.  And I could do without any more new mystery sounds on my vehicle, so I'll just scrap them.

[Numbchux]

The mechanics at the dealership would hate putting on aftermarket cats for that exact reason, they never have provisions for heat shields. But yea, I chuck them, even with OEM cats.

[GeneralDisorder]

The heat shields are there so you don't start a brush fire when you drive over some tall dry grass and park a 750 degree cat on it. They perform basically no other function. They help keep the heat in to an extent and keep direct airflow from cooling the cats under cruise conditions but the effect of their absence doesn't seem to trip any codes if the cat's are working correctly.  

GD

[carfreak85]

5 hours ago, Numbchux said:

All they do is rattle.

Just fixed our rattles.  Parts still available, and cheap!

[Numbchux]

24 minutes ago, carfreak85 said:

Just fixed our rattles.  Parts still available, and cheap!

Here in the midwest, to completely repair, is to completely replace the exhaust system. The shields get broken, the hardware is wrecked, the mounting tabs are dissolved. Nope, rip the shields off, and weld up what's left underneath.

[idosubaru]

Same - they're scrapped when I encounter it. 

As a testament to the heat - some folks I've let fish my pond drive an impreza or low vehicle and kill about a 10 square foot area of vegetation under the car where the converter resides. In the future i'll only let them fish if they have their heat shields installed LOL  Mine are all higher off the ground Tribeca/OBW/lifted and that never happens.  

Edited May 6, 2021 by idosubaru