Centri supercharger cat choices?

[Jjmoberg]

So i have read the whole 14 pages of the protect your cats thread. But its a bit difficult to know what the right thing actually is to do. Theres a lot of high level talk in that thread and guys saying no cats is the only way and guys saying factory cats may be best. GESI cats are ok. GESI cats are not ok.

Bottom line if I am gonna have Wengerd tune my car and run either an ESS G3 Mach 1 kit or a Vortech beefcake kit, at 8.5 ish psi and shooting for 700 hp on 93, then WTH am i supposed to for cats? This wont be a race car. Its just a fun weekend and evening toy that i will not be getting too crazy with.

I do want my lady to enjoy time in it, so headers and no cats is probably not gonna happen for sound reasons. Id like to run some sort of cat anyway for rasp reasons. Id like more flow than stock and not too much more volume.

I feel like my use is unlikely to melt a cat at 5000 miles a year tops. So i was considering the MAK pipes with the GESI UHO cats that are supposed to be good to 850hp each. Seems some here dont like those cats but i know they are popular in the BMW/Toyota crowd in active autowerks downpipes. Some of those guys are doing 750 crank. Though i realize thats turbo and different heat wise.

Thoughts?

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[schmeky]

My stock cats are fine after 7.5K boosted miles at roughly 750 crank with a centri.

 

[K4fxd]

I'd get a set of GT500 cats and be done with it. Ford tested these to 750 at least and probably 900.

 

[engineermike]

Oem uses ceramic substrate because of its high heat tolerance. However, it can crack if it heats too quickly. I really want to try a set of stock gt500 cats but they are super expensive. Short of that a lot of it is in the tuning. Most tuners will neuter the cat protect because it hurts power output. The Roush phase 2 strategy runs really rich at wot which delays cat protect but also sacrifices power. But people don’t like the Roush tune and they replace it with something that runs leaner. Personally I tend to copy the Roush idea and run it rich before cot. Keep in mind the gt500 typically goes into cot about 2 seconds after going wot. That’s part of why they live.

 

[Jjmoberg]

Thats good to hear. I would guess 700 whp would be about 800 crank or just a bit over that. I would like to think that just using my car for cruising around and some occasional fun blasts, that most any stock or high quality cat would be ok. But its hard to say. Honestly my tip 2 choices are leave the stockers and manifolds alone cause its easiest, or LTH 1 7/8 headers w/ their GESI EcoF cats.

Though it is unclear exactly which GESI cats those are…

 

[K4fxd]

I'd keep the stock cats and manifolds, which are pretty good, and make sure your tuner leaves the cat protection on.

 

[Jjmoberg]

Oem uses ceramic substrate because of its high heat tolerance. However, it can crack if it heats too quickly. I really want to try a set of stock gt500 cats but they are super expensive. Short of that a lot of it is in the tuning. Most tuners will neuter the cat protect because it hurts power output. The Roush phase 2 strategy runs really rich at wot which delays cat protect but also sacrifices power. But people don’t like the Roush tune and they replace it with something that runs leaner. Personally I tend to copy the Roush idea and run it rich before cot. Keep in mind the gt500 typically goes into cot about 2 seconds after going wot. That’s part of why they live.

I read where you considering the GT500 cats and changing your tuning strategy. I suppose I can talk to Wengerd about it when the time comes.

Its concerning that some have blown out the factory ceramic cats too.

I would bet the HJS cat pipes from Fabspeed can take the abuse. Unclear how easily those would bolt up. But i cant imagine its much worse than having to weld in the flange for the MAK pipe on the one side.

And the MAK pipe offers the GESI UHO and UHO+ as an option

 

[engineermike]

Maybe Wengard knows a ton about protecting cats, but most tuners generally don't spend much time concerning themselves with that. There's a lot to it when you add the supercharger because the PCM EGT model scales have to be extended and populated, plus EGT offsets as a function of cam angles. The cat temp model won't be super accurate to begin with. Then you have to adjust the COT trigger and min lambda, and make them work best with the WOT PE curve. The tuner actually has to choose between making more power before COT, but then have it kick in sooner, vs sacrificing power initially but delaying COT. One might be better on the dyno but the other faster at the track or on the street.

I've spent (wasted?) a ton of time reading and logging data, including EGT and mid-bed thermocouples, and observing the effects of load, timing, lambda, etc.

Virtually all aftermarket cats use a metal substrate because it's simpler to produce and easier to obtain. Metal has the advantage of holding up well to rapid heat-up. However, metal does not hold up to high temps very well. I have logged some interesting things regarding cat temp. After going WOT, the cat temp starts to stabilize. Once you let out, the cat temp stays high or heats up even more, for a couple of minutes. If you go WOT again, then the cat temp goes even higher. I believe these situations will hurt the metal substrate aftermarket cats more than ceramic.

The ceramic cats like stock will hold up to high temps better than metal. However, the ceramic doesn't do well in rapid heat-up scenarios. If you let them cool down between dyno pulls, then do a pull without letting the cat warm up (even though the engine is still up to temp), then they can crack. The tuner needs to ensure the PE enrichment rate is set very high so EGT doesn't spike when going WOT. I've inspected a "failed" stock cat where a crack had formed right in the center and allowed exhaust gas to bypass and go straight to the downstream O2 sensor. Other than the crack, the element looked perfect after quite a bit of abuse.

Now that I think about it, I think I'm going to change my tune to command more fuel in the mid-range that should slow down the rapid heat-up at WOT.

 

[Jjmoberg]

Wow you know a lot about this stuff. I will talk to him about it when it come time to tune.

I guess one good thing about the stock cats if if they fail they break, and dont likely clog your exhaust completely and blow up your engine.

Given that, I think i will stick with stock cats, and try to get a very safe tune done. Then i will remove the passenger side cat for inspection each winter. I will replace it with something if it blows.

Id like to think that only 8 psi of boost and the way i intend to use the car will lead to long cat life.

 

[engineermike]

If you’re really only running 8.5 psi on good 93 and it’s centrif, the stock cats have a good chance - particularly if you can get a lot of timing into it. If wengard can optimize the gdi system and run it on the rich side, you should be able to run 20+ deg of timing which will cool the egt.

 

[Jjmoberg]

If i go ESS, I am planning on running the 8 psi @ 7200 rpm rated pulley, and taking shift points no higher than 7700. I would imagine that will see 8.5 to 9 psi depending on DA. A Sunoco with 93 opened a few months ago about 5 miles from my house. So that will be my go to station.

 

[Jjmoberg]

I do wonder if the Fabspeed GT500 HJS cat pipes would be an option. Id like to have a backup plan thats not catless, if my stockers take a dump.

They cant be much harder to fit then the cat delete pipes from MAK or 2M. Those HJS cats live on Mclarens making 900hp on stage 2 tunes. I would bet they are making 26-28 pounds of boost. Cause they are 20 psi stock and adding 175 whp or more.

 

[engineermike]

Careful comparing anything turbo. Turbochargers turn exhaust heat into work, thereby robbing heat from the exhaust stream so the cats experience much cooler temps.

 

[Jjmoberg]

I had read where you talked about that. I figured 26 psi still would get pretty hot though. Its interesting how much harder it is to deal with superchargers heat wise.

Those are only a 200 cell cat as well.

 

[engineermike]

I didn’t install thermocouples but I did review a stock ecoboost cat temp log and it’s like it barely wanted to budge and wouldn’t go over 900 deg f. Conversely, a stock mustang gt will hit 1400+ quickly and supercharger will pass up 1600 in a hurry with the wrong tune. Gt500 hits 1650 in 2 seconds at wot. Turbos help the cats out a ton!

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