Exhaust Pressure Testing

[xl_cheese]

The paper reducer was to check fitment of the following 4x3 eccentric reducer. Btw making an eccentric cone from paper is harder than it sounds. I suspect the convergent reducer on the cat is causing restriction.

Would be really cool to see what this looked like finished up under the car!

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[engineermike]

Would be really cool to see what this looked like finished up under the car!

I ran that setup a while until the cat failed. I’ve since switched to gt500 cats which have 2.75” piping stock.

 

[champamp]

Thanks Mike and everyone else who contributed to this great tread. I'm a least partially educated now although some of this is over my head. I wanted to tell you my system to get opinions. I have a '16 GT (staying NA) and 5-6 years ago I decided to upgrade. After hours on that old exhaust compilation thread, I decided on a Corsa Sport cat back with the double X. Even with my miniscule technical knowledge, I knew the small diameter remaining OEM parts couldn't be the best solution so I decided to get a pair of MAK 3" downpipes (these were their cat deletes at the time, not sure they even make them anymore) and then had a pair of GESi race cats welded into the exact OEM cat location. Didn't want LT's for emission testing reasons. Love this set up but have no idea as to any performance gains.
Can you enlighten me as to general flow / back force characteristics of this system?
I'm adding the '18 IM and airbox this spring and a Wengerd PCMtec tune. Anything special that Derel would need to know?
Thanks!

 

[K4fxd]

Exhaust is fine if you like the sound.

I'd go with a GT350 manifold and 87mm TB. Ford would not have spent the money redesigning the CMCV controls on it for the Mach/Bullits if it didn't offer a performance boost over the 18 up mani.

 

[Hammerhead13579]

This is a fantastic thread. I just read through another thread titled "strategies to keep cats from melting". Can the knowledge and testing from Lord Mike help with that particular situation as well? Blowers with stock cats and cat protection? How does the reduction in pressure after the catalytic converters affect the temperature of the cats during WOT pulls? Or the temperature change to recover after a pull?
Would I simultaneously make more power and slightly aid with the life of my catalytic converters with a 3" cat back?

 

[engineermike]

Theoretically yes, lowering backpressure should help reduce cat temps. In fact I believe the logic exists to open active exhaust if the cat temp goes too high, but I don’t recall if the logic is activated.

That said, I think the stock mustang GT and f150 cats are just too delicate to withstand the thermal shock that superchargers impose. I employed all my tricks to try to preserve my Roush f150 cats and they failed spectacularly. I really wish the aftermarket would develop bullet proof cats for us.

 

[Hammerhead13579]

Theoretically yes, lowering backpressure should help reduce cat temps. In fact I believe the logic exists to open active exhaust if the cat temp goes too high, but I don’t recall if the logic is activated.

That said, I think the stock mustang GT and f150 cats are just too delicate to withstand the thermal shock that superchargers impose. I employed all my tricks to try to preserve my Roush f150 cats and they failed spectacularly. I really wish the aftermarket would develop bullet proof cats for us.

So you found that thermal shock is the root cause of cat failure? How much damage occurs over time? It takes lots of heat cycles to noticably damage the cats, right?
I'm asking because I just had my car at the strip and plan to go back soon. Those are the longest sustained pulls the car has seen and will see, 10-11 seconds. And I definitely didn't wait for the car to fully cool last time since the track was basically empty and I was excited to get back out there and perfect my launch sequence. The car was slower (60-130) when I was "hot lapping" it vs when I let it fully cool later in the evening but, unfortunately, it seems I could have been damaging the cats too because I didn't let the car cool down between runs.

 

[engineermike]

All the research I did pointed to high cat temps degrading the effectiveness of the catalyst due to chemical changes to compounds, but the effects were over time and the result was just lack of conversion. I believe that’s what Ford is trying to prevent with cat overtemp protection. That’s not how ours are failing though. Our ceramic brick substrate is cracking and breaking. Ceramic can withstand tremendous temperatures but fail very easily when under stress. All this to conclude that uneven, rapid heating is causing stress in the ceramic which is causing cracks and breaks in my belief.

 

[Mak3fit]

Hey guys, what would you all think about doing this? just wondering if there would be any benefit in flow or tone if i do this along with the resonated x pipe.

So im thinking of getting a true x pipe to connect at the top where the long tube headers meet and then add the jones maxflow x pipe right after it leading into the catback(exhaust will be 3 inch all the way through).

Is this worth doing as in would there be any benefit in flow or tone because theres a true x pipe before it goes into the resonator or should i just connect my long tube headers with only the resonated x pipe?

Im not boosted, just building a e85 fbo N/A semi track/street autocross car.

 

[Hammerhead13579]

Hey guys, what would you all think about doing this? just wondering if there would be any benefit in flow or tone if i do this along with the resonated x pipe.

So im thinking of getting a true x pipe to connect at the top where the long tube headers meet and then add the jones maxflow x pipe right after it leading into the catback(exhaust will be 3 inch all the way through).

Is this worth doing as in would there be any benefit in flow or tone because theres a true x pipe before it goes into the resonator or should i just connect my long tube headers with only the resonated x pipe?

Im not boosted, just building a e85 fbo N/A semi track/street autocross car.

Since you aren't boosted I say just go with whatever you think might sound good. If you got rid of the manifold/cat restriction and the OEM resonator restriction then everything else at 3" is sort of overkill. I don't think there will be much of a pressure difference or power difference so just focus on sound

 

[xr4x4ti]

Hey guys, what would you all think about doing this? just wondering if there would be any benefit in flow or tone if i do this along with the resonated x pipe.

So im thinking of getting a true x pipe to connect at the top where the long tube headers meet and then add the jones maxflow x pipe right after it leading into the catback(exhaust will be 3 inch all the way through).

Is this worth doing as in would there be any benefit in flow or tone because theres a true x pipe before it goes into the resonator or should i just connect my long tube headers with only the resonated x pipe?

Im not boosted, just building a e85 fbo N/A semi track/street autocross car.

I don't see the point, the muffler already has an "X" inside of it.

 

[DougS550]

Are upgraded mid-pipes available for use with the stock cats?



With a PD blower the airflow is a function of the blower size, speed, and inlet conditions. Therefore, changes in exhaust pressure can not change the air flow rate, unlike NA, centrif, and turbos. If we leave the tune alone, the reduction in pumping losses is the sole source of gains. A pumping loss improvement of 4 psi is as follows:

power = work / time
work = force x distance
power = force x distance / time
power = 4 x 3.66^2 x 3.1416 / 4 x 3.65 x 4 x 7400 / 12 / 60 / 550 = 11.5 hp



Sure didn’t, but I wouldn’t expect much change. It would require another gauge setup since the inferred manifold pressure doesn’t know what’s going on with the exhaust.

Mike: I run the 1-7/8" LTH headers and a 3" Borla Cat back (No Cats). I was thinking would I gain benefit if I cut the 2-1/4" end of the connector pipe and weld a 3" in its place? Just wondering

 

[K4fxd]

I run the 1-7/8" LTH headers and a 3" Borla Cat back (No Cats). I was thinking would I gain benefit if I cut the 2-1/4" end of the connector pipe and weld a 3" in its place? Just wondering

Yes, that 2-1/4 piece is a huge choke point.

 

[DougS550]

Yes, that 2-1/4 piece is a huge choke point.

I ordered 3" 304 stainless pipe 15 minutes ago. I think it makes no sense to have a set of headers and then restrict the outlet to 2.25" and then push high boost. Plus, the added restriction to my engine would definitely, negatively impact my engine performance as well as the danger by raising cylinder temps causing misfires/knock etc which isn't good for the engine longevity/reliability to say the least. Later

 

[Mak3fit]

I don't see the point, the muffler already has an "X" inside of it.

Was kind of thinking it might minimize the loss from the resonator since the setup would have an unresonated "x pass" before it and could sound different as well.

I dunno just throwing ideas out there, not the brightest when it comes to this car stuff

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