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

[blackS2]

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

Youre right... dropping the boost Level down approx. 0.2 - 0.3 bar the issues were solved but thats not acceptable for this size of charger

The tuner can't be blamed because the car has been built up by myself... ...and I know that there is a hardware problem... and it seems to be that the only difference between my car an the other GT30 - GT35 cars he mapped is my exhaust system...

...so I'm going to change this first and we'll see...

maybe this is a possible single cat --> http://www.hjs-motorsport.de/download/h_90950050.pdf

[JP]

I've got a GT30R with .63 backhousing.

Exhaust system 3" downpipe, into 3" sports cat similar to your link, straight 3" pipe 1.8m long into straight through muffler small s bend into 3" straight through back box.

Got to 1.5bar (470hp) and the internals of the cat found themselves being pulled out of the backbox by use of long nose pliers. EGT's at this point where 840 celsius measured at the cylinderhead in the exhaust manifold runner on a 6th gear redline using a cast manifold with ceramic coating.

So although temperatures where not high the pressure in downpipe was too great for the cat.

I've hit 980's and 990's before on a 5th gear dyno pull at 2+bar or 1st to 6th pull on a straight to redline of the clocks. But this is quite clearly down to the .63 backhousing.

Where abouts are you measuring the EGT's from as this will give an indication where the problem lies. Also what is the cylinderhead specification and the cam profile? As these all have an influence on the EGT's.

[blackS2]

I've got a GT30R with .63 backhousing.

Exhaust system 3" downpipe, into 3" sports cat similar to your link, straight 3" pipe 1.8m long into straight through muffler small s bend into 3" straight through back box.

Got to 1.5bar (470hp) and the internals of the cat found themselves being pulled out of the backbox by use of long nose pliers. EGT's at this point where 840 celsius measured at the cylinderhead in the exhaust manifold runner on a 6th gear redline using a cast manifold with ceramic coating.

So although temperatures where not high the pressure in downpipe was too great for the cat.

I've hit 980's and 990's before on a 5th gear dyno pull at 2+bar or 1st to 6th pull on a straight to redline of the clocks. But this is quite clearly down to the .63 backhousing.

Where abouts are you measuring the EGT's from as this will give an indication where the problem lies. Also what is the cylinderhead specification and the cam profile? As these all have an influence on the EGT's.

Cams are 7A inlet and 7A outlet at OEM timing... EGT measured at manifold to turbocharger flange...

[GazzaG60]

let us know how the cat fairs. its a question ive been asking myself too.

im straight thru and only seeing about 780c

[JP]

Realistically it looks like the cat is the problem from that info.

Unless you are trying to run 2+bar on a stock head? As the port velocities on the exhaust runners will be far too high causing sonic choke and a rapid increase in EGT's irrespective of manifold, downpipe and cat. Remember there is no point having a highflowing setup if the part before it is the bottleneck causing the low Volumetric Efficiency of the engine.

This becomes more significant on your cam set up from the greater overlap. As some of the boost pressure is not retained in the combustion chamber, instead it is forced straight into the exhaust. The end result being that the turbo may for example have to create 2.2bar at the compressor to sustain 2bar of positive pressure in the intake manifold instead of 2.1bar like it would on a cam profile of less overlap.
This means higher intake charge temperatures, more timing retard and ultimately higher EGT's.

[GazzaG60]

good point on balance there RWD

[blackS2]

Realistically it looks like the cat is the problem from that info.

Unless you are trying to run 2+bar on a stock head? As the port velocities on the exhaust runners will be far too high causing sonic choke and a rapid increase in EGT's irrespective of manifold, downpipe and cat. Remember there is no point having a highflowing setup if the part before it is the bottleneck causing the low Volumetric Efficiency of the engine.

This becomes more significant on your cam set up from the greater overlap. As some of the boost pressure is not retained in the combustion chamber, instead it is forced straight into the exhaust. The end result being that the turbo may for example have to create 2.2bar at the compressor to sustain 2bar of positive pressure in the intake manifold instead of 2.1bar like it would on a cam profile of less overlap.
This means higher intake charge temperatures, more timing retard and ultimately higher EGT's.

Stock Head - but that should not be a problem - we have cars here with stock head running over 600hp...

7A cams have no overlap at 1mm lift... inlet close is 6 deg after OT...

When you have cams with overlap, the problem at high revs and high boost would not be forcing boost straight trough the exhaust cause in turbo applications the backpressure before the turbine is higher then the boost pressure (at WOT/redline)...

our max intake temp was 65deg

[JP]

Just had a look at the 7A profile, quite surprising would have thought a smaller lobe separation for a naturally aspirated motor but your right no overlap at 1mm. So this won't be your cause.

As for higher backpressures in exhaust system than boost then you have got a problem. If running 2bar boost you should not exceed 1bar in exhaust system otherwise you have a restriction. Which will cause high EGT's.

As for intake temperatures of 65 Degrees I assume you had ambient temperatures exceeding 30celsius? Otherwise again I would look at the intercooler/pipework setup.

But going back to the original question in your thread, looks like running a cat is going to restrict you running reliably over 500hp from the information provided.

[blackS2]

Just had a look at the 7A profile, quite surprising would have thought a smaller lobe separation for a naturally aspirated motor but your right no overlap at 1mm. So this won't be your cause.

As for higher backpressures in exhaust system than boost then you have got a problem. If running 2bar boost you should not exceed 1bar in exhaust system otherwise you have a restriction. Which will cause high EGT's.

As for intake temperatures of 65 Degrees I assume you had ambient temperatures exceeding 30celsius? Otherwise again I would look at the intercooler/pipework setup.

But going back to the original question in your thread, looks like running a cat is going to restrict you running reliably over 500hp from the information provided.

yes 65 deg at summer outside 28deg

If running 2bar boost you should not exceed 1bar in exhaust system otherwise you have a restriction.

IMHO thats impossible if you mean the pressure in exhaust manifold... you will allways hit the boost pressure with exhaust manifold pressure at turbo application...

just have a look at the IMSA S2 engine -->

Test # 3, KKK 3476(equal to Turbonetic T66), and #16 exhaust housing and E85 fuel 110 octane


r/min, PS, Nm, AFR, Boost, Backpressure, EGT,
3000 085 188 13,74 0,10 0,05 761
3500 095 190 13,70 0,20 0,10 768
4000 186 279 13,33 0,60 0,39 789
4500 221 314 13,43 0,79 0,50 794
5000 291 384 13,22 1,09 0,77 798
5500 467 561 12,94 1,88 1,57 824
6000 602 714 12,93 2,10 1,89 850
6500 663 730 13,20 2,00 2,00 872
7000 689 706 13,24 2,00 2,00 895
7500 705 675 12,82 1,90 2,10 912
8000 701 635 12,69 1,88 2,20 902
8500 700 630 12,95 1,85 2,20 896

[JP]

^^^ I've not played with E85 before so can't tell how the characteristics change relative to normal Super unleaded. Purely because you can throw a lot more ignition timing at it which will effect the EGT's

But looking at those figures I can only imagine that the exit of the turbo must be glowing see through! Either the hotside is too small flow wise for the top end or the wastegate is too small which can be seen the way the figures drop of due to the exhaust backpressure exceeding intake pressure.

For example, assuming there is no further restriction further down the exhaust system, running an oversized wastegate is a way to resolve such an issue by bleeding of excess exhaust gases once peak boost has been achieved. This will reduce backpressure in the system and allow the figures to keep climbing within the allowable cam profile range without throwing EGT's through the roof or affecting low down boost response. Realistically if the system is matched you should be able to hold peak boost to redline keeping a flat boost curve.
Below is a low boost plot at 1.5 Bar running Shell V Power, highest recorded EGT was 767celsius at 7800rpm. Low backpressure from a well matched system meant very high VE figures giving a smooth powercurve for a GT4094R on a 2ltr spooling peak boost by 4800rpm just as the engine comes on cam on a 1.06 backhousing and a 60mm wastegate. (T66 = approx a GT42 as reference)



Sometime in the next month it will be run up on Q16 racefuel (116 Octane) which should have the same timing characteristics to E85 at which point I will see if the boost curve can be held flat to redline at 2-2.5bar after which I can make a further comment on the backpressure pre turbo with reference to the above IMSA figures.
We haven't decided what the car is going to be run at boost wise yet but the efficiency island of the compressor is between 1.6 to 2.5bar, obviously the minute the boost tails of and cannot be held to redline we know we are in the same scenario as the IMSA figures above.

As a rule of thumb I normally look at where a cam makes peak power, then choose the boost level and hotside size that is appropriate in order to hold intake manifold pressure till a couple of 100rpm past peak power. As there is no point reving past that point.

If you get into a situation where the backpressure is too great EGT's go through the roof as the spend exhaust gases can't efficiently exit the combustion chamber. This results in less fresh air entering the combustion chamber from the intake side to burn the fuel of the next combustion cycle, resulting in a much hotter burn that escalates into ridiculously high EGT's.

I see this happen all the time on remapped RS4 engines where the high port velocities of the stock cylinderhead exhaust ports result in sonic choke preventing the combustion chamber scavenging efficiently. End result being very high EGT's, as much as 1050celsius at times.
Take the same engine leave the intake ports alone, same exhaust and turbo setup and just port the exhaust ports on the head (correctly obviously) and those EGT's can drop below 950 by eliminating sonic choke in the head. Along with the added benefit of improved top end torque and hp figures.

Again as many appear to have no issues with stock S2 heads aiming for the same power figures as you are seeking and the only difference being no cat. One can only assume on your setup that indeed it is the cat that is the restriction causing the high backpressure for your desired boost targets.

[porkkis]

you will allways hit the boost pressure with exhaust manifold pressure at turbo application

I have to disagree.

[blackS2]

@RWD19T thx for explanation

@porkkis why??

[porkkis]

Why not?

It's not a compressed air system where the last part of the exhaust system acts as a restrictor causing the pressure in the whole system. Using mild cams and a big turbine side turbo may easily lead to a situation where exhaust manifold pressure is less than boost.