Yeah, that sounds pretty rough - even worse than last time. If you're iffy on the app, mph is always a good indicator of power as it eliminates a lot of the noise that can cause ET to vary. You could pick two points on the street about 1/4 mile apart (per the odometer), do a couple runs, note the mph, then come back and do it again once you've made changes.

If you suspect anything in the exhaust stream, I still think its worthwhile to cut a spot or two to add flanges in. For ease of working on it long term, you really need a flange somewhere anyways, so you may as well use it to your advantage here and do it in places strategic to your investigation.


Im still a bit concerned about single digit timing too. Your AFR sounds good and you've got good boost. Assuming you cant find any maintenance issues, I wonder if the crazy low timing is killing power. Do you have race gas available locally? If so, I'd think about dumping in half a tank when empty, doubling that WOT timing, and see what it feels like. No doubt more timing will make more power, so it should feel a bit faster, but if it suddenly feels like a rocket ship from a timing tweak only, then you know you need to do something to get those timing numbers back up to something more reasonable.

I've honestly never went that low on timing, so I wonder if you're getting an inverse side to the curve. On the top end, when you start getting 20+, the power gains go to near zero with each degree added. I'm wondering if those power losses with each degree removed start to get exponentially worse when you start getting that low? Total speculation, but it's the only thing I've seen in your data that's odd.

 

I installed a zzp 3" downpipe with cat and then had my ignition control module go out. While I was diagnosing what went wrong, I had about two or three loud afterfires go through the cat caused by the fuel not being burned, and they absolutely destroyed the thing. Like huge chunks falling out of it. So if you have detonation that carries into the exhaust, it could definitely destroy the cat.

Link

 

Hm good info, thank you. I also had to drive the thing 30ish miles with one of the sparkplugs completely burnt out, so there was definitely some fuel getting into the cat, I wonder if that premptively killed it.

 

Get under the car and give the cat a good shake, or hit it with a hammer. If you hear rattling, its completely shot.

 

It's certainly possible. The reaction inside a cat gets very hot just running on the small amounts of stuff that make it through combustion. I cant imagine how hot it could get dumping raw fuel and oxygen into it, but it seems feasible to get it well above it's designed operating temperature.

I still advocate the sawzall method.

 

Alright well update, the cat seemed to be fine. I have yet to go out and do some pulls and check timing and knock, but the old cat looked okay and it doesn't feel any different just driving around town. I'm wondering if I shouldn't just pay the $80ish for a couple dyno pulls at my local shop and see what numbers I make.

 

That's disappointing to hear!

$80 for a couple runs really isnt that bad TBH. If nothing else it gives you another data point to work from.

Out of curiosity, have you done a compression test lately on the cylinders? Just trying to spitball ideas on why performance could be lacking on an otherwise seemingly fine engine.

I do still think the next step needs to be getting that timing up somehow - either a slightly larger pulley or a couple more mods to at least get it solidly in the double digits.

 

Ran a compression test, luckily the engine passed. The readings for each cylinder were

1. 170psi
2. 165psi
3. 178psi
4. 165psi
5. 175psi
6. 176psi

Cylinder 4, the one I was most worried about, did take a bit more cranking than the others to get above 160psi, but it got there. Unless someone thinks otherwise, I don't think compression issue are at fault here. My next step honestly is probably to cut out the spiral louvered core glasspack and weld in a real resonator. I've got one ordered from Vibrant, hopefully it does the trick.

 

Yeah, you're spot on, those numbers are fine.

 

Alright well I finally got around to hacking out the louvered core glasspack that I had as a resonator. Did some runs today in the summer heat and I was able to bump my timing up to 11-12°. Keeping in mind that its mid 90s right now and my IAT is at 120-130F, compared to previously which was in the winter with IATs more like 70-80F, does this sound like my issue was the glasspack all along? Hacking it out definitely allowed me to bump timing up some, my question now is if I am still having an issue somewhere else, or is 11-12° of advance fairly normal for a hot summer day.