Are H pipes necessary/desireable?

[Lolvoguy]

On the BMW in my sig, the cat has finally developed some holes. Considering this car has a dual setup, the cat seems to be the only place the exhaust from each manifold "meets".
After the cat and all the way to the tail pipes, I have a dual setup.
The exhaust setup is:
Engine>>dual exh manifolds>>single cat>> rusty-looking OEM muffler

Considering cats are not required where I live, I'm thinking of getting a pair of resonators (cherry bomb or equivalent) in place.

The setup would look like:
Engine>>dual exh manifolds>>dual resonators/"cherry bombs">> single dual in, dual out performance Stromung exhaust.

Is this possible?
I'd like to purchase everything before-hand (with the exception of additional piping, fasteners etc), and take it all to a reputable exhaust shop to do the work.

thanks in advance

 

[knerml]

What about the O2 sensor?

 

[Lolvoguy]

Originally Posted by knerml
What about the O2 sensor?

Oh yes, that's just after the dual exh manifolds.

 

[555]

I'd keep same design but make everything bigger. Two resonators where one is sufficient will add weight and absorb more heat from the system and may slow down exhaust gases. Let me say I'm not a scientist. Usually H or X pipes are designed with exhaust pulses in mind. Have you checked out a BMW site?

 

[ecotourist]

You might improve things or make them worse. I'd replace like with like.

 

[Linctex]

To be COMPLETELY honest, the single system (when sized right) will provide better torque and fuel economy in all the usual driving RPM ranges.

Duals are really only best at the very, very top RPM's

You have the potential to really mess with your computer's thought processes doing this.

 

[Lolvoguy]

Originally Posted by 555
I'd keep same design but make everything bigger. Two resonators where one is sufficient will add weight and absorb more heat from the system and may slow down exhaust gases. Let me say I'm not a scientist. Usually H or X pipes are designed with exhaust pulses in mind. Have you checked out a BMW site?

The piping I have on the stock setup is 1.75 inches each. I was planning on running a set of small resonators that would be similar in size to the OEM pipes.
So I don't think weight would be much of an issue, as the resonators would be small. Combined would probably be smaller than the stock cat.
I am not interested in increasing pipe diameter, I'm more interested if the flow will be adequate.

Yes, there's so many differing opinions on those sites. Especially since these cars are older, and many do engine swaps, so they aren't even running the stock engine displacement/cylinder count.

Originally Posted by ecotourist
You might improve things or make them worse. I'd replace like with like.

Yes, that's what I'm attempting to do. As mentioned above, I don't want to increase pipe size, just get rid of the cat.
But if I need the flow by having a box (cat) to balance the exhausts out, I'd like to know ahead of time so I can plan accordingly.


Originally Posted by Linctex
To be COMPLETELY honest, the single system (when sized right) will provide better torque and fuel economy in all the usual driving RPM ranges.

Duals are really only best at the very, very top RPM's

You have the potential to really mess with your computer's thought processes doing this.

True.

Despite being computerized, this car is very old tech. There's several threads on the internet of people running all sorts of exhaust setups and it working easily.
I just want to ensure that I'm not overlooking something important.

 

[Linctex]

Originally Posted by Lolvoguy
I don't want to increase pipe size, just get rid of the cat.
But if I need the flow by having a box (cat) to balance the exhausts out, I'd like to know ahead of time so I can plan accordingly.
.


Just go to an DECENT exhaust shop and have them build a good "Y" to suit your needs.

 

[ragtoplvr]

Avoid glass packs with a louvered core, they are very restrictive. Perforated pipe is way better. Those nasty louvers are a no go.

Chambered mufflers can be pretty good. No packing to burn out.

No brands, been a long time since I modified a car.

My motorcycle is my performance fix.

Rod

 

[ecotourist]

Originally Posted by Lolvoguy
I don't want to increase pipe size, just get rid of the cat.

If you aren't having problems with it, why replace the cat? It's actually doing something.

Doesn't your emissions system compare exhaust oxygen levels before and after the cat? Not so easy if you don't have a cat.

 

[Lolvoguy]

Originally Posted by ecotourist
Originally Posted by Lolvoguy
I don't want to increase pipe size, just get rid of the cat.

If you aren't having problems with it, why replace the cat? It's actually doing something.

Doesn't your emissions system compare exhaust oxygen levels before and after the cat? Not so easy if you don't have a cat.

The cat is rusty and has holes. It's 31 years old.
No, these old BMW;s only have one o2 sensor before the cat.

 

[Lolvoguy]

Originally Posted by ragtoplvr
Avoid glass packs with a louvered core, they are very restrictive. Perforated pipe is way better. Those nasty louvers are a no go.

Chambered mufflers can be pretty good. No packing to burn out.

No brands, been a long time since I modified a car.

My motorcycle is my performance fix.

Rod

This is very good advice! Thank you!
I've noticed quite a few have louvers, and just like oil louvered oil filters, they should be avoided

Seems like I have my work cut out for me!
Need to find a chambered resonator/muffler that'll fit where the cat was.
Shouldn't be too hard to find something online....should it?

Now that you mention it, I found this:
https://www.amazon.ca/Magnaflow-125...RID=AXVENBXY0P30DQR66C0G#customerReviews
It has the chambers, as well as the size that's comparable to the stock cat.
Also would alleviate the need to add in an H or X pipe section.