Different EGT between sections
 

Hi guys,

Looking for some suggestions what can be the cause of such difference in exhaust temperature between sections .

1st (front) section is above 1000 C / 1800F
2nd (rear) section is about 850 C / 1500 F

Above is rough figures at open throttle and roughly 0,7 Bar / 10 psi.

the sensors are pre turbo, 1 per section.

Its a 13B-Rew swapped rx8. Single Turbo. I did the engine break in and started to push up the boost and such difference between sections has stopped us from ECU tuning further.
The temperature sensors are not faulty, I have changed to a bigger A/R on the turbo (from 0.82 to 0.90) and switched to waste gate dumping outside, but none of this has helped.


Iam using the BHR coils (D585 I believe they are called).
Full function eng: blocked off primaries, Xssive lim with ID 1700 cc on the sides, and ID 1050cc in the middle

So far my next suspicion is something wrong with the injectors.

Any input would be appreciated.

could you have mixed up injectors?
have you tried swapping sensors front to back?

Pulled out the fuel injectors and had them tested this weekend. they are working fine.

they only idea left is that maybe one of the wastegates (on the front section) is not opening fully or not functioning correctly.

Swap your probes and check your depth and length from the exhaust ports to see if the problem persists. There are a lot of variables that could make it do such a thing.

yes I have swapped them around and even bought a 3rd probe, to check if one was faulty. Seems it is not the probes.

how do lower plugs compare?

didn't catch you fully. what do you mean ?

"Reading" plugs is the oldschool way of making sure all "cylinders" are running the same AFR.

Google "reading plugs".

As far as your EGT issue - make sure each probe is same distance from port and same angle of entry into the manifold (so tip of probe where thermal junction is has same distance from port).

And of course compression test engine.

I did dual EGT in my modded S5 TII cast manifold.
Probes were same distance to port, but front runner is a straight velocity stack to the turbo and the rear is a tortured 90 degree bend then straight and another 90 degree bend. I had a divided 60mm wastegate instead of stock IWG.

It ran cooler on the straight shot port at lean cruise, but would even out quickly once under load with wastegate open.

:icon_tup:

lean afr? retarded timing?

The spark plugs I haven't cheeked yet, will probably buy new ones and take a look how the old ones compare.

The AFR is on the rich side. The difference is EGT is only when you are flooring it and going under full boost. When cruising there is no significant difference . This is a rebuilt motor, on a half bridge port, the compression is slightly shy of 7.0


some pictures of the manifold
https://cimg6.ibsrv.net/gimg/www.rx7...47dfba3e6.jpeg
https://cimg7.ibsrv.net/gimg/www.rx7...312e0e330.jpeg

Finally took the plugs out, the plugs are carbon fouled, nonetheless i went to test them on a stand under(above) 10 Bar/ 145 psi, they were firing and spark looked ok.
Iam running 9's EQP all around.

i already bought and installed new ones, but seeing that the stand showed the plugs are working and there is spark - maybe the problem was not in the plugs?

maybe stuck wastegate ?
 

My other concern is hooking up the waste gates like this, I have seen people suggesting to hook them up parallel but also some suggest that hooking them up in a series (as in photo) also works . any input ? By looking at the photo the Waste gate on the left side that is where the high EGT are - and iam thinking the WG is not functioning properly because of such hook up arrangement.



https://cimg1.ibsrv.net/gimg/www.rx7...7b2e17860.jpeg

try switching the wastegates around

I'm running a similar setup in my swapped RX8 and I rarely see over 800C. That's with a 0.91 AR Borg S360 running between 0.85 and 1 bar of boost. AFR in the low 11s at full boost on 10% ethanol 93 pump gas.
I have a short runner exhaust manifold with EGT probes about an inch from the port flange. The independent wastegates are routed back into a 3" exhaust. The boost solenoid plumbed as shown above.
I am also running D585 coils and saw some latency I had to cal out. Double check your timing at a few higher RPM points. Swapping wastegates as mentioned is a good idea. I would also swap secondary injectors between rotors since you said it is only an issue under high load. I'm assuming you are running staged secondaries. Bench testing won't catch a possible heat related issue.