TwinTurbo.NET: Nissan 300ZX forum - Exhaust leak - downpipe divider
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Subject Exhaust leak - downpipe divider
Posted by Woodnutz (PA) on October 10, 2023 at 10:00 AM
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Message For a while, I've been chasing an idle issue. Once warm, I would get a noticable, but not extreme, bounce in RPM. A boost leak test revealed several that needed addressed, but once that was done, I still had the same idle bounce between 700-800, at worst.

I connected with the Haltech software to dig into it further and saw that my AFRs for each bank were about 1.0 different from each other. Needing to shift gears a little, I decided to chase a rattle that I had noticed as I was messing with the injector settings (a rougher idle brought out the rattle). I climbed under the car and found this pretty much right away:

Rattle near turbo

Of course, I freak out a little and go cry in the corner, thinking the turbo is shot - initial thought was contact between turbine/compressor and housing. After gathering myself, I asked a couple friends their opinion - one of which was maybe it's an exhaust leak. This made sense, given the difference in AFRs. EIther way, driver side downpipe has to come off... fun.

I pulled the downpipe and heard a rattle as I turned it over. Threw me for a bit until I saw this:

Downpipes divider bolt

The one bolt was hanging on by maybe one thread. With the thru holes on the downpipe flange, it's an easy path for a leak. Here's what it looked like when tightened down:

Downpipes divider bolt

I'm as confident as I can be that I found the leak, but this also means the passenger pipe needs to come off, too. Bernie noted that the divider is there to help with spool on smaller turbos, but can cause spiking in larger ones. I do like the quick spool, but I'm debating leaving them in or taking them out and sealing the holes. Anyone else have any opinions on those dividers on OEM turbos? Bernie also mentioned using longer bolts, as the current ones don't engage all the threads in the hole (this is my most likely course of action), but I'd still like to hear anything y'all would have to share.

- Aaron

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