Less than 1psi under those conditions. Your backpressure will be much higher at full throttle/high rpm. Even then you still wouldn't get more than one psi. 6psi at 3k rpm with no load is really bad. Both of them are bad but one is worse which is why you have a big difference in fuel trim between b1 and b2. You need to fix this problem first. No matter what else you do it's never going to run right with the exhaust restricted so much. You did a b25 to b30 swap right? I think the converters are the same (verify p/n on realoem.com) so maybe you can use the 325 cats.

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Thank you Randy for the response. I was hoping maybe only one was bad since the other one was less restrictions but I had a feeling that both are cloged.

Now I debate if I should use the headers from my other 325 running bmw to pass the smog and punch out the cloged one's and use them with out cats.

The only thing I'm not sure is will I need to flush the dme to euro tune to eliminate back o2 sensors or there is a way to do it with out that.

My other option will be to buy used once but locly people want 300 for them and when I paid 250 for b30 complete engine it's hard to justify spending that much just for the headers.

(I just found out ms45 can't be r lashed with euro tune.... forget that)

Looks I got two option drive with check engine light or get used oem headers.


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B30 can use B25 headers

 

B30 and b25 are the same and I found from a BMW tech guy that was selling B30 zhp parts that they all interchange including zhp option bolt on. Just I'm not having luck finding replacement headers for a reasonable price.
If anyone has them in San Diego LA are let me know

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Where I'm at people are asking around $300 for oem headers????
I got a b30 complete engine at a local pick a part for $205 out the door so it sounds crazy to me to be spending $300 for just the headers with cats. I have a b25 engine for sale less than I'm asking less....

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I'm my are people are asking $300 for oem headers????
I got a b30 complete engine at a local pick a part for $205 out the door so it sounds crazy to me to be spending 150% more for the headers with cats.

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Probably cause it's $2,000 new from factory and contains expensive metals such as plantium

 

Most likely that's why, I'll try lkq and see if they sell me headers for $35 each. (If they don't notice they have hiding cat in there . I tried to do that one but they noticed o2 sensor wires and I had to unbolt them of off the b25 engine I was buying.

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Yup it's illegal for used cats to be sold in Cali

 

What about the cats from the 2.5? Are they good?

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What about the cats from the 2.5? Are they good?

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I'll give a week and if I can't find them for under 200 I'll swap them with other car I have and I'll have 2 years to find good set so I don't have to be doing this every 2 years.

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I end up going with aftermarket headers and no more back pressure problems.

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My previous post was written with the assumption that aftermarket headers mean catless performance type. If you got aftermarket converters then don't worry about it for now but definitely remember my tip when you get a catalytic converter code in the future. Aftermarket cats don't satisfy the dme for too long but the oe parts price for a pair is more than many e46's are worth now so options suck.

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https://www.ebay.com/p/Spark-Plug-G...0%26rvr_id%3D1579481545780%26rvr_ts%3D3f0c5f931640a866a3524d2fffffdc0d&thm=1000

Get these (2 packs of 2) doorman 42009. Drill out two with a 1/2" drill and leave two unmodified. Screw a drilled one onto a downstream o2 sensor and then screw an undrilled one onto the end of the drilled one. Reinstall the o2 sensor with the spacers into the exhaust system and repeat for the other downstream o2 sensor. The anti foulers partially isolate the o2 sensors from the exhaust system which slows down and smooths out the signal. This will fool the dme by simulating the effect of a functioning catalytic converter. As long as the sensor and spacer stack fits without clearance issues, this will keep the converter codes (p0420+p0430) away. Again this is ONLY for the downstream o2 sensors after the catalytic converters. Most auto parts stores should have these in stock. How does your car run now that it can breathe? I bet it is a night and day difference in performance.

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In answer to the original question - throttle opening (load) matters just as much as RPM with regard to the pressure you will see in the exhaust manifold.

Pressure readings above old*catalyst. (140k mi and failing due to excessive oil consumption)
Idle ***8211; needle rattles at around 1 psig
Light load stoplight cruising up to 2500 RPM - 1-2 psig
Heavy foot between stoplights ***8211; up to 7 psig
WOT at 3000 RPM ***8211; easily pegs the needle at 10 psig

Pressure readings above new*BMW catalyst
Idle ***8211; needle rattles at around 0 psig
Light load stoplight cruising up to 2500 RPM ***8211; 0.5 ***8211; 1 psig
Heavy foot between stoplights ***8211; up to 3 psig
WOT at 5000 RPM ***8211; 4 psig

I bought one BMW catalyst and one new Magnaflow (California legal) catalyst to compare them.
They cost about the same, and the BMW unit looks better heat shielded and fits slightly better.
They perform exactly the same so far (+100k miles)