EGT issue. How much Power can be "pushed" trough one single 100 CPI Cat?

[blackS2]

Hi,

after getting some issues with EGTs in 5/6 Gear at redline we started to explore the reason for this behaviour...

Its an compression dropped ABY with GT35R and 0.82 A/R...

we have no issuses to get the mixture rich enough.... so the fuel supply should not be the problem...

...we measured the exhaust backpressure after turbine and it was rising up to 450-500 mbar... that is a lot...

the mounted exhaust system is a 3" downpipe splitted Y like OEM ABY to 2 x 2,5" with 2 x 100 CPI cat and joined to single 3" behind the cats...

...after that - straight trough 3" with 2 mufflers - Coupe

...so after reading the forum I'm asking for any experiences with engines over 500/550 hp using one single 100 CPI catalytic converter without EGT issues...??

cause I'm planing to replace the 2 cat system with single 100cpi /76 cat to solve the EGT issue??

[porkkis]

I think you left the most important out - how much the exhaust temp actually is ? What exhaust manifold are you using?

Your exhaust pipe pressure is definitely on the high side.

[Bram]

I would think a single 3" pipe is too small for that turbo. Do you have the WG pipe separated like a dump tube already?

[blackS2]

I think you left the most important out - how much the exhaust temp actually is ? What exhaust manifold are you using?

Your exhaust pipe pressure is definitely on the high side.

exhaust temp is usually rising round about 950 C on WOT 2/3/4/5 but sometimes especially on Autobahn 5/6 we hit 980,990 - I don't like that... ...and we are around 10.0 -10.5 AFR

the exhaust manifold ist not the problem... it is the FURANS tubular version with T3 flange...


...ps wastgate is not separated and 3" should be enough because I know people with no issuses at 3" 600hp... but they are not using a cat... so no comparison...

sparks are BOSCH F3CS

[a4kquattro]

exhaust temp is usually rising round about 950 C on WOT 2/3/4/5 but sometimes especially on Autobahn 5/6 we hit 980,990 - I don't like that... ...and we are around 10.0 -10.5 AFR

the exhaust manifold ist not the problem... it is the FURANS tubular version with T3 flange...


...ps wastgate is not separated and 3" should be enough because I know people with no issuses at 3" 600hp... but they are not using a cat... so no comparison...

sparks are BOSCH F3CS

how much spark advance......? 980/990c is indeed no good.

[a4kquattro]

also, as a simple diagnostic I'd consider unbolting the exhaust aft of the downpipe and going for a test run to see if your EGT situation resolves itself. if so, you're on the right track that it is a back pressure problem. If not, ignition timing.

[porkkis]

I'd be quite comfortable with 980C using a cast iron manifold if the afr would be ok. As the car has a tubular manifold and is running overly rich so clearly something needs to be done.

Ok, maybe autobahns do change things a bit as you are able to have longer runs...

[a4kquattro]

I'd be quite comfortable with 980C using a cast iron manifold if the afr would be ok. As the car has a tubular manifold and is running overly rich so clearly something needs to be done.

Ok, maybe autobahns do change things a bit as you are able to have longer runs...

Precisely. 990c *will* melt the motor if sustained for any length of time. I agree, you can probably get away with briefly touching that kind of EGT like in a drag run, nothing more.

[blackS2]

also, as a simple diagnostic I'd consider unbolting the exhaust aft of the downpipe and going for a test run to see if your EGT situation resolves itself. if so, you're on the right track that it is a back pressure problem. If not, ignition timing.

...thats the way we are planing to do but it's not solving the problem if it's caused by backpressure - I can't drive without exhaust and I won't drive without cat

...ignition timing is surely not the issue I belive - because it is done and checked twice by one of the most capable 20VT tuners in germany... ...the timing maps are quite mild...

...ignition timing could only be an issue if there is something wrong with ignition hardware... ...but I think in this case there should be ignition interrupts - but the car runs like hell...

[GazzaG60]

...thats the way we are planing to do but it's not solving the problem if it's caused by backpressure - I can't drive without exhaust and I won't drive without cat

...ignition timing is surely not the issue I belive - because it is done and checked twice by one of the most capable 20VT tuners in germany... ...the timing maps are quite mild...

...ignition timing could only be an issue if there is something wrong with ignition hardware... ...but I think in this case there should be ignition interrupts - but the car runs like hell...

is the ignition timing quite mild or too mild?

just because they have been put on a pedistool as a great tuner it doesn't mean a thing. i recollect a certaint tuner with a certain basemap and it burned a hole in a ported header. good job the header was too thin or it would have been a sob story.

[EspenW]

...thats the way we are planing to do but it's not solving the problem if it's caused by backpressure - I can't drive without exhaust and I won't drive without cat

...ignition timing is surely not the issue I belive - because it is done and checked twice by one of the most capable 20VT tuners in germany... ...the timing maps are quite mild...

...ignition timing could only be an issue if there is something wrong with ignition hardware... ...but I think in this case there should be ignition interrupts - but the car runs like hell...

An ignition map that is too mild might be the cause. Late ignition means the combustion process happens later in the power stroke, causing more heat to exit the exhaust ports rather than being absorbed by head/piston/block.

[blackS2]

An ignition map that is too mild might be the cause. Late ignition means the combustion process happens later in the power stroke, causing more heat to exit the exhaust ports rather than being absorbed by head/piston/block.

Yes, I know... a had a conversation with him about that a few days ago, while we checked the maps driving on the Autobahn with EVC OLS emulator... ...he knows the correct timing - that is for sure... ...so there must be another reason...

[GazzaG60]

if he knows for sure that timing is not the cause he must have a good knowledge of other items so surely knows this. has timing been increased with a set of det cans to deturmine and prove there is no EGT drop?

if you dont want to test the back pressure theory by removing the cats im sure we may be a little stuck for suggestions. id have my money, presuming the the timing is good as you say it is that its the cats not flowing.

[blackS2]

if you dont want to test the back pressure theory by removing the cats im sure we may be a little stuck for suggestions. id have my money, presuming the the timing is good as you say it is that its the cats not flowing.

he has done so many S2 here - from chiptuning up to over 700hp - I belive he knows his job...

we will test the backpressure theorie first... so we will replace the twin cat system by a single 3" pipe...

...but after that I am interested if one single 100cpi cat is able to do the job... ...so I'm really interested if somebody has a car above 500hp with one single 100cpi cat... ...thats the topic...

[porkkis]

If I were you, I'd measure the exhaust pressure from the EM collector. Just replace your exhaust temp sensor with a hose fitting etc. It can be quite tricky to measure as the flow usually causes fluctuations but you're able to get a picture of the matter.

The tuner may have done everything he can except taking the boost down if the hardware simply can't support the boost levels that cause problems. There is no tuner that can map a car with fundamental problem in engine hardware. Your problem is very probably simply too high back pressure.
Btw who is he, the tuner? He can't be blamed so I can't see it as a secret. I'm just curious who is regarded as one of the most capable