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Possible to run catless dp but with cat in place of resonator with o2 extension to lower under-hood temps?

danbfree

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#1
Is it crazy to think that by moving the catalysts from the DP (run catless dp) to a high flow race cat converter in place of the stock resonator with an O2 with extension cable or something? Or not worth all the trouble for minimal temp reduction?
 

Krug

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#2
Not worth it, and would likely just cause you more headaches.

Proper function of a catalyst relies on retaining temperature in order to burn the emissions. In fact, the O2 sensors rely on this temperature as well but they are typically self-heating. The usual upstream placement of the catalyst near the engine is deliberate, to allow the catalyst(s) to heat up quickly, retain heat, and lower emissions more effectively. If you relocate the catalyst further downstream you'll likely interfere with its operation - not catastrophically, but in a way that would make it slower to reach nominal temperature and possibly trigger a code by causing the ECU to think that it's functioning below the expected efficiency threshold. Furthermore, depending on where you were to place the catalyst you may end up with more heat transferring into the floorpan or baking something that shouldn't be exposed to that much heat.

Basically, if you're THAT worried about temperatures from your catalyst you'd be better off just improving your cooling system, running catless and/or getting that section of your exhaust ceramic coated to trap more of the heat inside the exhaust itself.
 
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danbfree

danbfree

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Thread Starter #3
Not worth it, and would likely just cause you more headaches.

Proper function of a catalyst relies on retaining temperature in order to burn the emissions. In fact, the O2 sensors rely on this temperature as well but they are typically self-heating. The usual upstream placement of the catalyst near the engine is deliberate, to allow the catalyst(s) to heat up quickly, retain heat, and lower emissions more effectively. If you relocate the catalyst further downstream you'll likely interfere with its operation - not catastrophically, but in a way that would make it slower to reach nominal temperature and possibly trigger a code by causing the ECU to think that it's functioning below the expected efficiency threshold. Furthermore, depending on where you were to place the catalyst you may end up with more heat transferring into the floorpan or baking something that shouldn't be exposed to that much heat.

Basically, if you're THAT worried about temperatures from your catalyst you'd be better off just improving your cooling system, running catless and/or getting that section of your exhaust ceramic coated to trap more of the heat inside the exhaust itself.
Again, fantastic information from you! Thanks, that all makes perfect sense, sounds like literally ceramic coating the stock DP would be far easier with less headaches for about the same desired results.
 

Krug

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#4
I should also add a slightly tangential bit that the catalyst can actually aid in spool and exhaust flow, and moving the catalyst downstream could turn it into more of a restriction and negatively impact performance. Modern catalysts (and high-flow cats especially) are not like the old chokingly restrictive catalysts of yore. They're actually quite efficient for flow. Some testing done with the FiST that I vaguely recall actually showed that running a catalyst improved spool versus running catless. Some attribute this to "backpressure" being desirable, but I highly doubt this is the case and think that it is a misnomer born from misinterpretation of outdated automotive wisdom (exhaust that was too free-flowing could burn up your exhaust valves, before metallurgy improved) and buzzwordiness.

It's more likely that the catalyst functions to increase laminar flow by maintaining exhaust gas temperatures and eliminating turbulence. Heat equals energy, and hotter gases move more quickly, right? Also consider that the FiST downpipe has what is basically a 90-degree bend right off the turbo. You've got these exhaust gases exiting the turbine, tumbling around, and being forced through a bend. Now add the cooling effect of these gases passing through the downpipe without being further burned/heated by a catalyst or having the flow corrected by the catalyst cells, and you have a recipe for increased pressure/mass/turbulence that the engine has to work harder to push against! This is also why larger exhaust diameters are not necessarily better, as the increased volume can result in the same effect. It's for these reasons that I earnestly believe that if anyone is intent on running catless with the FiST they should absolutely invest in having their downpipe and at least some of the upstream portion of their exhaust system wrapped or ceramic coated to trap that energy inside the exhaust and increase flow.

I've spoken to some of the engineers at my workplace that deal with exhaust systems about these kinds of things, and proper exhaust tuning via balancing harmonics, flow, and other factors is almost as much an art as it is a science.
 
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danbfree

danbfree

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Thread Starter #5
Very well said. I've always known that our factory exhaust is quite efficient. Seriously thanks for taking the time to provide so much of these details, it all makes sense. It's kind of crazy, on the Facebook groups people try to insist the stock DP is restrictive, they just don't get it. Dizzy makes the same ~315whp with an e20 tune on an x47r with a 100% stock exhaust, the same as those running 3" straight piped.
 

Sekred

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#6
I run a Catless DP with a 200 Cell Cat fitted where the resonator would usually sit. I running a BT with a blanket and wrapped SS manifold. My under bonnets are low, well below a stock turbo setup. No problems with a CEL but the vehicle runs a tune disabling the PID for catalyst efficiency.
 

Krug

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#7
Interesting! I wonder if a code would trigger without the tune suppressing it (could show that the catalyst is or isn't operating as it should) and how your spool characteristics compare to a stock placement catalyst. Does your locality require emissions testing? I'm also interested in what portion of the lower temperatures is due to the wrap and turbo blanket.

Either way, sounds like a nice setup!
 
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danbfree

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I run a Catless DP with a 200 Cell Cat fitted where the resonator would usually sit. I running a BT with a blanket and wrapped SS manifold. My under bonnets are low, well below a stock turbo setup. No problems with a CEL but the vehicle runs a tune disabling the PID for catalyst efficiency.
Thanks for sharing mate, cool to see someone actually has done this so my thought wasn't so crazy after all, and you did it the right way with wrapped turbo and manifold!
 

Sekred

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#9
I use to run a Catted CPE down pipe on the stock turbo. It would trigger a CEL after about 40 minutes of driving depending on conditions, highway or traffic so I think its very sensitive. My runs ok, no smell once it warms up. I would suggest theres no problem reaching light off temperature for the catalytic converter where its fitted.
 
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danbfree

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I use to run a Catted CPE down pipe on the stock turbo. It would trigger a CEL after about 40 minutes of driving depending on conditions, highway or traffic so I think its very sensitive. My runs ok, no smell once it warms up. I would suggest theres no problem reaching light off temperature for the catalytic converter where its fitted.
How did you hook up the O2 sensor and what tune did you have? From what I understand, whether you go catted high flow or catless, you either need to do a defouler spacer on the O2 or have it turned off in your tune... Anyway, I was assuming from the start I'd have to do this if I moved the catalyst further back with either an extension to an O2 sensor or just have it turned off in my tune anyway, but thanks for confirming your experience. After seeing more and more how the stock exhaust is so not restrictive pretty much at all, I don't think I'm going to bother with any more exhaust mods at all at this point.
 

Krug

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#11
I would still recommend wrapping/coating your exhaust if you ever have the inclination. If you ever swap your turbo, that would be the perfect time to do so. Get a turbo blanket, too! Besides less heat being radiated from the exhaust/turbo, there absolutely are some performance benefits to doing so.

Not exactly related to this thread, but this has reminded me of the recent exhaust replacement I helped a friend with, on his R53 Cooper S. Besides the Borla catback system we installed, he had also selected long tubular headers that included a resonator that was more-or-less the same size and shape as the catalyst, but placed just slightly further back. I thought it was rather cheeky that they included a resonator like that. If nobody knew any better, it'd look like that portion was a stock system.
 
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danbfree

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Thread Starter #12
I would still recommend wrapping/coating your exhaust if you ever have the inclination. If you ever swap your turbo, that would be the perfect time to do so. Get a turbo blanket, too! Besides less heat being radiated from the exhaust/turbo, there absolutely are some performance benefits to doing so.

Not exactly related to this thread, but this has reminded me of the recent exhaust replacement I helped a friend with, on his R53 Cooper S. Besides the Borla catback system we installed, he had also selected long tubular headers that included a resonator that was more-or-less the same size and shape as the catalyst, but placed just slightly further back. I thought it was rather cheeky that they included a resonator like that. If nobody knew any better, it'd look like that portion was a stock system.
Great idea! If I do end up doing the turbo upgrade I'll ceramic coat the DP and ported manifold for sure...
 

Sekred

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#13
How did you hook up the O2 sensor and what tune did you have? From what I understand, whether you go catted high flow or catless, you either need to do a defouler spacer on the O2 or have it turned off in your tune... Anyway, I was assuming from the start I'd have to do this if I moved the catalyst further back with either an extension to an O2 sensor or just have it turned off in my tune anyway, but thanks for confirming your experience. After seeing more and more how the stock exhaust is so not restrictive pretty much at all, I don't think I'm going to bother with any more exhaust mods at all at this point.
The O2 sensors were in the same place as the OEM down pipe, no tune at the time.
 
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danbfree

danbfree

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Thread Starter #14
The O2 sensors were in the same place as the OEM down pipe, no tune at the time.
OK, that totally makes sense then, if you used a defouler spacer along with high flow cats then you may not have triggered a CEL at all even without a tune.
 


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