B8.5 stage 2 upper pulley unitronic... cooling and cats!

[Soupnanny]

So much is said on this topic, this forum is just an amazing resource and very helpful- thank you all for your posts.... quick question, I have read stage 2 single pulley (upper) is still good idea to upgrade HX for heat soak and try avoid/mitigate cat failure... but how does heat ex work to cool air flow leaving the engine AFTER combustion and out to cats? (This is likely a dumb question... but the cat failure thing is freaking me out and considering heat ex for dd in Calgary Alberta Canadian (winter), older guy no race/track)... thanks for your insights!

[wes8398]

Go with your gut, because it's right. Anywhere you've read someone say that an HX upgrade will cool EGTs down is misinformed and/or talking out their ass. The only thing that will save your cats is either not driving it (hard) or relocating/removing them.

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[djn876]

You should be fine for a long time on just a stage 2 tune. Sure people have had bad luck, but usually that's due to an intercooler leak or something like that which causes much faster degradation. It's not like the cats just fall apart as soon as you upgrade, the biggest thing for longevity is keeping within the stock rev range. I ran stage 2, then dual pulley, then e40 for years and my cats were still overall in good shape after 5 years.

If you keep RPMs under 7k, EGTs stay quite a bit lower. If you want a lower EGT in general you will need to run methanol or ethanol as those fuels have a lower combustion/exhaust gas temperature.

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[wes8398]

You should be fine for a long time on just a stage 2 tune. Sure people have had bad luck, but usually that's due to an intercooler leak or something like that which causes much faster degradation. It's not like the cats just fall apart as soon as you upgrade, the biggest thing for longevity is keeping within the stock rev range. I ran stage 2, then dual pulley, then e40 for years and my cats were still overall in good shape after 5 years.

If you keep RPMs under 7k, EGTs stay quite a bit lower. If you want a lower EGT in general you will need to run methanol or ethanol as those fuels have a lower combustion/exhaust gas temperature.



Bit of a double-edged sword there, though, as w/m seems to be a big contributor to blower bricks/coolers failing... but yes, it does lower cylinder temps/EGTs (which is what kills cats).

Curious, what kind of driving did the car see when you were on stock cats? Ever track it? By most reports, you can kiss your cats goodbye in pretty short order - regardless of how aggressive your PR is - if you're going to be doing road course/lapping/hpde to ANY extent (which is what I'd like to get into this summer...Ugh).

[djn876]

Bit of a double-edged sword there, though, as w/m seems to be a big contributor to blower bricks/coolers failing... but yes, it does lower cylinder temps/EGTs (which is what kills cats).

Curious, what kind of driving did the car see when you were on stock cats? Ever track it? By most reports, you can kiss your cats goodbye in pretty short order - regardless of how aggressive your PR is - if you're going to be doing road course/lapping/hpde to ANY extent (which is what I'd like to get into this summer...Ugh).I have an SQ5 and no road course racing. It sees several 1/4 mile runs a year, plenty of 0-60, etc. shifting at 7400 RPM and meth only for the last couple of years. The methanol isnt spending any time on the IC for it to actually cause any corrosion. It would need to sit on the IC for an appreciable amount of time and it's diluted. I'm not worried about it causing an issue within a short period of time. It's not like the meth is injecting all of the time during normal driving.

Not sure how long people have run it before having problems, but I've been running it for about 2 years and run about 15 gallons of meth through (50-50 for most of it, 70-30 now for maybe 6 months or so).

Just was saying for the OP if you want general reliability and aren't tracking it, shift under 7k and stay on mild stage 2 tune and I'd expect the cats to be fine for a while. I agree that IAT doesn't directly cause cat failure, the impact would be the resulting timing pull that tends to make EGTs higher.

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[Soupnanny]

Thanks for the replies - I am considering mix in e85 (4-5gallons) to cool things in hotter periods... but running in mountain area so cooler and at elevation and also lane driver with only occasional freeway blast... I have only just begun to learn about using e85 (my tune is uni 93oct)... amazing the members knowledge and experience here - so grateful for your help!
Cheers!

[MSq5]

I defer to others, as I cannot get E85 here. My understanding, perhaps mistaken, is that at about 3 gals of E85 is about all that can be recommended on a 93 octane file.

[Quattro_Gang]

So much is said on this topic, this forum is just an amazing resource and very helpful- thank you all for your posts.... quick question, I have read stage 2 single pulley (upper) is still good idea to upgrade HX for heat soak and try avoid/mitigate cat failure... but how does heat ex work to cool air flow leaving the engine AFTER combustion and out to cats? (This is likely a dumb question... but the cat failure thing is freaking me out and considering heat ex for dd in Calgary Alberta Canadian (winter), older guy no race/track)... thanks for your insights!

To be honest, just save up money and upgrade your cats when you can. Eventually, if you want to make more power your cats run out quicker. In the end, you will need to replace them it's just when you will is the question. I am sure a lot of these guys on the forums have kept their car in great shape but if you bought your car from someone else who knows the status of your cats.

[Soupnanny]

Yeah good thought - I bought the car a few years old from a manager at audi dealer - it was his personal car and he swapped out frequently because of employee deal- it was about 47k km at my acquisition... now 111k km with me fully serviced and garage queen... still I take your point , gotta pay to play and simply have a budget for future costs like cats... after all it could happen even with heat ex from leak or bad luck... food for thought, thanks!

Ps my thinking is if/when cats go I would pay once to remove (or gut in place if even possible) and relocate lower for ease of service... but still learning about “test pipes” and have noise concerns...

[RoofRails]

So much is said on this topic, this forum is just an amazing resource and very helpful- thank you all for your posts.... quick question, I have read stage 2 single pulley (upper) is still good idea to upgrade HX for heat soak and try avoid/mitigate cat failure... but how does heat ex work to cool air flow leaving the engine AFTER combustion and out to cats? (This is likely a dumb question... but the cat failure thing is freaking me out and considering heat ex for dd in Calgary Alberta Canadian (winter), older guy no race/track)... thanks for your insights!In a way your not wrong. A upgraded HX will help you protect your cats by helping you to reduce timing retard. When you are hitting 180F at the top of 3rd the ECU will pull timing. This increases EGTs. No one here talks about that effect but everything I have read backs that up. Probably another silent killer of cats like coolant leaks/burn that everyone just blames on cat placement.

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[Strong Man]

So much is said on this topic, this forum is just an amazing resource and very helpful- thank you all for your posts.... quick question, I have read stage 2 single pulley (upper) is still good idea to upgrade HX for heat soak and try avoid/mitigate cat failure... but how does heat ex work to cool air flow leaving the engine AFTER combustion and out to cats? (This is likely a dumb question... but the cat failure thing is freaking me out and considering heat ex for dd in Calgary Alberta Canadian (winter), older guy no race/track)... thanks for your insights!


Man, there is NO connection between hx and egt. I’m running ST2 uni for almost 5 years - so far no issues with cats, and I like to push the car including track days etc.

[MSq5]

Man, there is NO connection between hx and egt. I’m running ST2 uni for almost 5 years - so far no issues with cats, and I like to push the car including track days etc.

See RoofRails post above you. There IS an indirect relationship based on the effect that IATs can affect timing timing pull and the effect it has on EGTs. Under load, if a tune pulls timing, as we see when the ECU pulls timing when IATs climb above a set threshold - often about 60C - and we stay in the throttle, EGTs go up. This is one more reason to control IATs and try to keep them down. The extent to which this affects EGTs seems to be related to how much timing is pulled.

Increasing the size of the HX is a known method of helping. Not only does timing pull sap power, but it can, indeed increase EGTs. Whether its enough to hurt the cats involves other variables, since the effect is cumulative.

[wes8398]

Man, there is NO connection between hx and egt. I’m running ST2 uni for almost 5 years - so far no issues with cats, and I like to push the car including track days etc.

See, THIS is the type of thing I hear that drives me CrAzY. I'm doing my clutch soon, and figure it's the best time to resolve the impending cat converter issue while I'm in there. But I'm only entertaining this because it seems I HAVE to given that I want to get into more than just Autocross. I want to get to track/lapping days ASAP, but 99% of reports out there say that cats melt (even aftermarkets like GESi and HJS) almost immediately when you drive the car like this on an aftermarket pulley ratio / tune. I'm NOT looking forward to figuring out (and paying for) test pipes, exhaust rattles, broken flex joints, downstream cats, extended rear o2's, an exhaust that sounds like complete garbage, and so on. But, I've devised my plan and put some orders in anyway... because that's what we APPARENTLY have to do. Then... THEN... posts like this come up. *throws arms up in the air* I give up.

[sepheroth86]

Timing pull will increase EGT.

Rich fuel mixture will increase EGT.

High EGT damages catalysts.

It is a delicate balancing act.

[Strong Man]

See RoofRails post above you. There IS an indirect relationship based on the effect that IATs can affect timing timing pull and the effect it has on EGTs. Under load, if a tune pulls timing, as we see when the ECU pulls timing when IATs climb above a set threshold - often about 60C - and we stay in the throttle, EGTs go up. This is one more reason to control IATs and try to keep them down. The extent to which this affects EGTs seems to be related to how much timing is pulled.

Increasing the size of the HX is a known method of helping. Not only does timing pull sap power, but it can, indeed increase EGTs. Whether its enough to hurt the cats involves other variables, since the effect is cumulative.

Let’s stop talking about theories because theories I know too. Give EGT numbers with and without hx?

[wes8398]

Let’s stop talking about theories because theories I know too. Give EGT numbers with and without hx?

It actually IS fact that timing pull = significant EGT increase. So yes, indirectly, lower IAT's do impact EGT's. It's not just a theory at this point. But I think it's misleading to say that getting a heat exchanger will help keep your EGTs down. Besides a few outliers such as yourself, the fact of the matter is that our EGT's cause cats to fail in the OEM location when you're dealing with increased boost pressures, tunes that don't care about cat health, track/HPDE use, and so on. I'd LOVE to know why people like you get away with it, but nobody can answer that question without just guessing - there are too many variables at play. In the end, go ahead and consider yourself lucky. I'd be very curious to see a bore scope make its way into your o2 bung and give us a look at the engine side of your cats though. How often do you track? How long are your heats? Do you run cool-down laps or anything? What's your pulley ratio and supporting modifications?

[MSq5]

Let’s stop talking about theories because theories I know too. Give EGT numbers with and without hx?

There is a published Society of Automotive Engineers journal article on this principle. There is absolutely no doubt that timing pull under load causes EGT rise, even as low as half load. That's why we try hard to keep IATs below the point where the tune starts to pull time. There are too many variables to give hard numbers, as the stage tune, the quality of fuel, the pulley ratio, the tuner's choices for AFR, timing, injector band width (spray duration and pressure) and boost all vary. Failure for us is multi-factorial - high up cat placement, high EGTs from increased power from aftermarket tunes and higher pulley ratios, and climbing IATs triggering timing pull. We should be aware of all of this and address the variables we can while balancing power and risk. The best solution may yet to be found. Keeping IATs in check is part of it. Going catless when we can or moving tbe cats downstream may be the best choice.

https://i.postimg.cc/VvjqCHzS/8-C6-C39-AB-D30-B-4236-9447-121-D585-E8904.png

[Izzyz28]

Just face reality, your CATS are most likely going to melt or blow out at some point. Everyone gets lucky right up to the day it happens to them. You can do whatever you want to reduce EGT and try to "save" them, but it's a battle you will likely lose. In the end, what's the point of spending all the time and money modding one of these cars just to baby it around? Either run it till they pop and figure things out then, install test pipes now, or buy a different car. Everybody is going to come in here with their story about 5 years of track use on DP with stock CATS, and and the next guy will be bone stock with 30K on the clock and the CATS are trash. Both of mine went within 2 weeks of each other, 10K of DP on a 35K mile car, no long pulls or beating the dogshit out of it.

Edit: And please dont listen to anyone who says "single pulley and tune" should be "safe" for the CATS, it simply doesn't matter. A bone stock car can and does destroy them. Mod the hell out of it and enjoy it.

[sacandagaD]

Soooooo, getting back to the OP's original question about whether or not to upgrade cooling. Can everyone agree, that adding HX is not going to be the savior of his cats, but rather an option that could help prolong them a bit, but there is no guarantee, so if it makes him feel good, then do it?

[01northernS4]

Man, there is NO connection between hx and egt. I’m running ST2 uni for almost 5 years - so far no issues with cats, and I like to push the car including track days etc.


I'd LOVE to know why people like you [Strong Man] get away with it

I think Strong Man may be on to something but not with regards to the hx and egt correlation... his tune, like mine (Unitronic), is uber conservative, safe and probably the most thoroughly tested overall from this perspective, imho... at the expense of a little less power overall and timing... for me on a daily driven vehicle - I can live with that compromise.

I've said this time and again on the forums, I've personally yet to see a Unitronic cat failure on a car that wasn't totally thrashed and here we have strong man tracking with no ill effects on... Unitronic.

I agree with wes8398, I'd love to see Strong Man's cats through the 02 bung hole... I may do it myself one day for shits and giggles.

If anybody can share a Unitronic cat failure on this engine, please do as I'm curious.

Again just my 2c.



...Or it could just be because Strong Man and I drive S5's lol [rolleyes]

[wes8398]

I think Strong Man may be on to something but not with regards to the hx and egt correlation... his tune, like mine (Unitronic), is uber conservative, safe and probably the most thoroughly tested overall from this perspective, imho... at the expense of a little less power overall and timing... for me on a daily driven vehicle - I can live with that compromise.

I've said this time and again on the forums, I've personally yet to see a Unitronic cat failure on a car that wasn't totally thrashed and here we have strong man tracking with no ill effects on... Unitronic.

I agree with wes8398, I'd love to see Strong Man's cats through the 02 bung hole... I may do it myself one day for shits and giggles.

If anybody can share a Unitronic cat failure on this engine, please do as I'm curious.

Again just my 2c.



...Or it could just be because Strong Man and I drive S5's lol [rolleyes]

There definitely seems to be a common thread amongst those who aren't having converter issues being tuned with Unitronic. It's too bad their specific approach to their tuning isn't public knowledge; along with all the other tuners. Tony and Chris from EPL are my guys, and they're usually pretty damn good with answering questions. I wonder if they'd broach the topic of why they think Unitronic tunes are easier on cats. BUT - in the same breath - I'd also venture a guess that Unitronic is probably one of the least popular "big name" tunes for this platform. They're big with us Canadians because, well, they're Canadian. But compared to 034, APR, and IE; I'm going to say their share of the market is pretty small. Probably similar or smaller than EPL's. This means their sample size is also significantly smaller. So we could just be playing a numbers game here, rather than making an accurate inference. On the topic of EPL, I will say that I've had many conversations with Tony and/or Chris about my converter's health. I've been assured a number of times that they have plenty of customers who - to the best of their knowledge - are running stock cats, EPL software, and tracking (road course) their cars without issues. I believe EPL has a name for being "conservative" too; so maybe there's something to that... I'd love to compare timing tables, etc between the "aggressive" tuners and the others.

[Soupnanny]

Thanks for all the posts folks! I really do appreciate hearing people’s experiences... there are so many variables but still some good thoughts to consider... the heat exchanger seems like it might just be a good thing for the over all health of the car and really not that bad for cost (merc racing).... I have also been told by a tuner or two that the stock air intake is likely okay (again I am not into s/c whine, do not track or race... only odd spirited drive on weekends...)... maybe I am “working backwards” but I am getting uni stage 2 + upper pulley today along with oil and dsg service... going from stock so hoping to blow my hair back... will consider iat and/or heat ex in the future... but I do agree with the wisdom here that there are many variables and drive hard along with more boost likely to cause or at least worsen cat wear... I am rolling the dice and saving the couch coins for future work! Cheers all!

[MSq5]

There definitely seems to be a common thread amongst those who aren't having converter issues being tuned with Unitronic. It's too bad their specific approach to their tuning isn't public knowledge; along with all the other tuners. Tony and Chris from EPL are my guys, and they're usually pretty damn good with answering questions. I wonder if they'd broach the topic of why they think Unitronic tunes are easier on cats. BUT - in the same breath - I'd also venture a guess that Unitronic is probably one of the least popular "big name" tunes for this platform. They're big with us Canadians because, well, they're Canadian. But compared to 034, APR, and IE; I'm going to say their share of the market is pretty small. Probably similar or smaller than EPL's. This means their sample size is also significantly smaller. So we could just be playing a numbers game here, rather than making an accurate inference. On the topic of EPL, I will say that I've had many conversations with Tony and/or Chris about my converter's health. I've been assured a number of times that they have plenty of customers who - to the best of their knowledge - are running stock cats, EPL software, and tracking (road course) their cars without issues. I believe EPL has a name for being "conservative" too; so maybe there's something to that... I'd love to compare timing tables, etc between the "aggressive" tuners and the others.

I may have said this earlier (it is in my signature). I'm EPL Stage 2 dual pulley, 3.247 ratio, Merc HX, and with 7,000 rpm upshift TCU tune. Still on stock cats - full stock exhaust. I don't road course the car, but have several hundred hard launches, full quarter mile Dragy runs, long highway pulls up to 130. There may be something to a somewhat more conservative ECU tune.

I'm going to scope my cats. I got a low efficiency code on bank 2 a few weeks ago, but cleaned the rear sensor on that cat and the code has not recurred. Probably just a matter of time, though, as guys blow cats on stock tune, too.

[Strong Man]

There is a published Society of Automotive Engineers journal article on this principle. There is absolutely no doubt that timing pull under load causes EGT rise, even as low as half load. That's why we try hard to keep IATs below the point where the tune starts to pull time. There are too many variables to give hard numbers, as the stage tune, the quality of fuel, the pulley ratio, the tuner's choices for AFR, timing, injector band width (spray duration and pressure) and boost all vary. Failure for us is multi-factorial - high up cat placement, high EGTs from increased power from aftermarket tunes and higher pulley ratios, and climbing IATs triggering timing pull. We should be aware of all of this and address the variables we can while balancing power and risk. The best solution may yet to be found. Keeping IATs in check is part of it. Going catless when we can or moving tbe cats downstream may be the best choice.

https://i.postimg.cc/VvjqCHzS/8-C6-C39-AB-D30-B-4236-9447-121-D585-E8904.png


Sorry for the delay :) I was busy of kicking ass some BMW, Mustang and a few heavily tuned A5 :)

Finally, someone has replayed with some numbers BUT I didn't ask for the numbers just because I don't know them ...quite opposite ... I do measured/monitored EGT a while ago by using P3 and I still remember numbers before and after hx has been installed...Now...IN THE VERY HOT DAYS, when out-temp was around +35 degrees cel (welcome to Canada :) ) without hx IAT was about 55-60 degrees and EGT 980 up to 1100...now with hx, same conditions IAT is about 40-55 degrees and EGT 950 up to 1050 (checked just yesterday!)

and you're saying under load in max 150!!!! degrees cel (but in average it's half of it) is going to make huge effect on CATS?! Sorry, I personally don't believe in it.

[Strong Man]

I think Strong Man may be on to something but not with regards to the hx and egt correlation... his tune, like mine (Unitronic), is uber conservative, safe and probably the most thoroughly tested overall from this perspective, imho... at the expense of a little less power overall and timing... for me on a daily driven vehicle - I can live with that compromise.

I've said this time and again on the forums, I've personally yet to see a Unitronic cat failure on a car that wasn't totally thrashed and here we have strong man tracking with no ill effects on... Unitronic.





BINGO! Unitronic is running very long test cycles in their pretty big lab/dyno stand before they release any software.





...Or it could just be because Strong Man and I drive S5's lol [rolleyes]

LOL

[MSq5]

Sorry for the delay :) I was busy of kicking ass some BMW, Mustang and a few heavily tuned A5 :)

Finally, someone has replayed with some numbers BUT I didn't ask for the numbers just because I don't know them ...quite opposite ... I do measured/monitored EGT a while ago by using P3 and I still remember numbers before and after hx has been installed...Now...IN THE VERY HOT DAYS, when out-temp was around +35 degrees cel (welcome to Canada :) ) without hx IAT was about 55-60 degrees and EGT 980 up to 1100...now with hx, same conditions IAT is about 40-55 degrees and EGT 950 up to 1050 (checked just yesterday!)

and you're saying under load in max 150!!!! degrees cel (but in average it's half of it) is going to make huge effect on CATS?! Sorry, I personally don't believe in it.

We cannot monitor EGTs. There is no thermocouple in the exhaust manifold or in cat on either side. It is a calculated value taken from other sensors based on an algorithm, that may or may not be accurate. It may predict delta but may not reflect absolute values.

What we do know is that timing pull does raise EGTs as a matter of physics. The SAE study shows that. Even on a small 1 liter low powered normally aspirated engine, and we know the real EGT threshold in which cats start failing.

And, we know that our cats are about as close to the exhaust manifolds as humanly possible, and prone to fail even on stock tune when pushed hard. The accumulated data points to the risk increasing with engine power upgrades and full throttle, especially when rpm is also increased in TCU tunes.

[01northernS4]

We cannot monitor EGTs. There is no thermocouple in the exhaust manifold or in catvon either side. It is a calculated value taken from other sensors based on an algorithm, that may or may not be accurate. It may predict delta but may not reflect absolute values.

What we do know is that timing pull does raise EGTs as a matter of physics. The SAE study shows that. Even on a small 1 liter low powered normally aspirated engine, and we know the real EGT threshold in which cats start failing.

And, we know that our cats are about as close to the exhaust manifolds as humanly possible, and prone to fail even on stock tune when pushed hard. The accumulated data points to the risk increasing with engine power upgrades and full throttle, especially when rpm is also increased in TCU tunes.

good points, MSq5

to add to this discussion, the main reason I went with Unitronic was upon reading bhvrdr Mike's many very informative and helpful posts and noticed he had a wicked fast car with no cat problems on any of his b8/8.5s. At one point iirc he had the fastest B8/8.5 on 93 octane tune... this struck a cord with me and I was sold.

strong man also makes a good point about Unitronic running very long test cycles before they release anything... maybe we are seeing the fruits of that approach now with no cat failures I personally know of... I hope I didn't just jinx myself, lol

joking aside we have a number of Unitronic members running strong, thoroughly enjoying the car (I know I do) with no failures to report... if anybody knows of one, please post