Hi all,

I looked through google a few times to try and find something, but it kept thinking I was searching for straight pipe results..

I'm wondering if there is a catalytic converter out there somewhere that has straight piping (instead of a bulge where the catalysts are) and what it would be referred to as.

I've never cut open a cat converter to see exactly how cells are attached to the piping, but hopefully someone here has.
Would a straight cat converter pipe be possible?

Reason that I want this is to eliminate any exhaust notes being changed by the converter.

After changing to a Berk high flow cat, the exhaust screams just before vtec engages.
Not necessarily a bad thing, but kindof hides the vtec crossover sound

Any help/opinions are appreciated

P.S. I'm aware it might not fix my 'issue', but still makes me curious...

 

If it was a straight pipe (test pipe), it wouldn't be a catalytic converter. Berk makes one.

 

I'm aware of this. I'm wondering if there is a straight piped catalytic converter, though. (a straight pipe with the catalyst cells still inside).

 

Great question, one that I've asked Gernby in the past. I think you are correct that the bulge does interrupt flow dynamics a fair bit. Gernby (and now Urge) has the best catalyst design that is incorporated into their midpipe to provide the flow dynamics and resonance you are referring to.

As far as others, the reason they bulge is to provide enough surface area to flow properly. If the catalyst was the same diameter as our mid-pipe it would be too much of a restriction. If you can't do the Gernby/Urge cat and midpipe then Berk would be the next best choice out there, it has the typical bulge but not overly large.

I've tried different exhausts and cats on my setup, and a smooth vtec transition can be a good thing. When the vtec transition point is smoothed out you could be seeing a gain in power on the low cam, where it may have been landing flat on it's face prior to the change. So the change at vtec isn't as abrubpt as the low cam power is being bumped upwards, and that is a good thing. When the vtec transition becomes more abrubt or harsh it may feel better to the butt and the brain, however a smooth vtec transition could be making more power overall. Just a theory as I've experienced that smoothing effect a few times. You really don't know until you can test different parts on a dyno though.

I ran the Berk HFC 63.5 mm with a UK modded oem exhaust and it felt like the car lost bottom end torque. I then sold the exhaust and HFC together and I ran a Mugen exhaust with the OEM cat. I have now added the Berk HFC 63.5mm to my Mugen exhaust and it feels like the bottom end is stronger. It seems like you have to get the diameters and flow right to gain max. power, but it is easy to lose power if you don't get it right.

 

I'll have to look at that one by Gernby. Does he still make them? I'll have to look when I'm home as my work pc won't load the pictures.

I've thought about my question and I've come to see that the cells actually take up volume which is why the converters bulge like they do, to let the original volume of air through. otherwise a wider pipe overall would be required which might be ok...
After all this thinking, it makes me wonder about exhaust tip catalytic converters (where the cells are visible from the exhaust tip).. It seems like it would make more sense. Especially with certain exhausts like my Q300, the actual tip of the exhaust is wider than where it meets the muffler, so it would surely make more sense to have the cells there, since restricting the very tip slightly would still have greater or at least equal to air flow as the muffler exit..

Example:


You can see in this picture too, that the muffler exit is slightly smaller than the tip exit so the catalytic converter gives very little, if any resistance.

I'm assuming the exhaust tip cats wouldn't be an option due to our car's o2 sensor/need to have them/government requirements etc..

Good to think about anyway.

 

Urge Designs is now making the Gernby pipe under license from Gernby.

I've never seen exhaust tip catalysts but that makes sense to keep the main piping the optimal size, that is cool.

 

If doing this for looks sure go for it.
If for SMOG no way that will work, the cat has to be close to the engine so it gets hot enough to work. On one of my old cars(91 Ford) it had a pre cat on each down pipe to get the exhaust hotter so the main cat will do its job right.

ROD

 

Here in Europe where pretty much all race cars needs to have a functioning cat, they all mount them as far back as possible.
I guess mostly because they will offer the least resistance there and also for them to survive at all.
Wouldn't work very good on a road car though unless you drive at WOT all the time

 

We do the same thing on our Canadian Rally Championship cars. Even the open class cars use catalytic converters as mufflers.