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Q&A regarding engines, turbos, and intercoolers and power upgrades
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ST165 Turbo Downpipe

Mon Aug 25, 2008 2:52 am

Has anyone ever considered using the stock cast manifold that bolts to the exhaust side of the CT26, unbolting the cat, and making a new pipe with a reducer to replace the cat? I took mine apart today and this seems like it would be a very easy/cheap/logical way to remove the first cat from the exhaust equation... I'm really thinking about trying it...
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Mon Aug 25, 2008 5:24 am

There's some examples of that on the exhaust tuning page here:


Mon Aug 25, 2008 5:51 am

Very cool. Thanks for the link!

Here is basically what I am thinking about doing except I'll retain the stock cast piece and bolt my creation to it in place of the cat...


Mon Aug 25, 2008 11:36 am

You're not the only one who thought that was a good idea. You get around the issues with the aftermarket downpipes like KO (and others) hitting the alternator fresh air duct and it might be cheaper to make. In exchange you don't have a very ideal bend coming off the turbine and also a chamber that enlarges right after the turbo decreasing exhaust gas velocity and again possibly hurting airflow slightly.


Mon Aug 25, 2008 12:36 pm

Personally I would kill to have a well-made rerouted divorced downpipe

Mon Aug 25, 2008 3:30 pm

I think I'm going to try it... A friend of mine owns an exhaust shop and can easily make all the parts I need except the flange. I designed a CNC water jet / laser cut file for that last night so it should be good to go. I'll make the first one and figure out how it works and how much it costs. If everything works out I might consider making a few more for anyone interested. I have a feeling the flange may not be cheap though.

Re: ST165 Turbo Downpipe

Sun Feb 09, 2020 4:36 pm

12-yr post revival! Lol
Did you ever get this made?!
Edit: his last visit was 2012. Prob not in the AllTrac scene now :(

Re: ST165 Turbo Downpipe

Mon Feb 10, 2020 1:49 pm


Well if it helps I have a ST165 specific catless downpipe if you are searching for one!

Re: ST165 Turbo Downpipe

Tue Feb 11, 2020 8:51 pm

Haha, back from the dead!
You have an ST165 DP with the 4-bolt flange? Sure, what make is it and can you send me a pic please?
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