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Discussion Starter #1 (Edited by Moderator)
I've read in Bob's post that it is good to open the exhaust from 1 5/8 to 2";, but is anything larger than that beneficial? I have used a 3"; stainless set up from Thermal Research with a Jackson Racing cat on my Miata that helped the car breathe. The system has a nice "throaty" sound unlike the typical "rice" buzz or boom and has lasted longer than the car. Are there stainless systems for the Opel?
 
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Discussion Starter #2 (Edited by Moderator)
Do you mean on a stock 1.9 litre? I'd stay away from anything larger than 2" if that's the case. In fact, a 2" system will sustain 140-150 hp no problem, while a stock Opel 1.9 is 65-85 hp depending on the year. I use a 2.5" system on a 224 hp racing Opel 2.2 litre....it's all it needs. I also use a 2.5" system on my friend's 2.5 litre engine, again it is more than enough. Going to 3" is WAYY too much for anything without a turbo. Turbos need lots more airflow out the exhaust, backpressure is a bad thing for proper turbo operation. Normally aspirated engines don't need backpressure either, however they require higher exhaust gas velocity than a turbo or the powerband will be narrow and peaky. Not the thing for the street.

For stainless systems for your Opel, you're on your own. You'll have to have one built from scratch. Expect to pay $500 to $800 to have one custom built from 304 or 316 stainless. Stay away from 400 series stainless, it's barely better than mild steel in terms of corrosion resistance in my experience.

RallyBob
 

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