Appropriate exhaust for my car

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By now I'm sure most of you know that I have a '90 Laser RS Turbo. Since it is a turbo car, I was wondering what the appropriate size of exhaust would be. I don't have any mods done to the engine or turbo. I'm starting with exhaust.

I was thinking somewhere around 2.25" for now. Maybe 2.5". I've always heard that its best for turbo cars to have bigger exhaust. But mine isn't modded, and its also bad for cars not to have enough backpressure.

Any suggestions???:doh:

posted by  SlipKnoT

You still need to keep the velocity high enough in the exhaust pipe to stop flow seperation.

The main problem with factory turbo exhausts is usually the dump pipe. Getting this remade with radius bends and then into a bigger bore exhaust pipe usually yields tangible benefits.

Enthuisist forums usually have good advice based on trial and error.

posted by  Wally

Well I'll go register at the DSM Tuners forum and ask the same question.

posted by  SlipKnoT

Go with 2.5, but no larger. It may not be the best for the stock turbo, but it will be ready for when you switch to a bigger turbo (16g anyone? :drool: ).

posted by  PontiacFan27

The guys at told me that the best choice for a stock turbo setup would be to go with the 2.25" exhaust and downpipe with a good aftermarket manifold.

posted by  SlipKnoT

Be a bit careful with the "aftermarket manifolds". There seems to be a tendancy to build them as if they were on an aesthmatic engine. A turbine benefits from pressure differential between the inducer and exducer and basic grade 8 PVT physics tells you that if you have too much pipe surface the temperature will drop and the pressure along with it.

When you have things boogying and a CO% of 5% (AFR 12.8) you are running around 950°C exit temps with a temperature drop of something like 100°C -150°C across the turbine. This is a large TD to engine bay ambient; a large surface area of a spaghetti manifold can quickly drop the inducer temps a couple of hundred degrees, thus reducing flow through the turbine.

This car is a Mitsubishi Eclipse yes? They are something like 140kW from a 2 litre out of the box? So you want about 2.25 to 2.5" stock. Keep the dump pipe at the same size. because believe it or not transitions in pipe size do cause losses.

The problem you are going to run into is correct fueling, unless you install an aftermarket ECU .

posted by  Wally

Thanks Wally. I appreciate it. I'll do the exhaust mod as soon as I can do the ECU tune as well. :thumbs:

posted by  SlipKnoT

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