Overview

Without question, on a turbocharged vehicle, one of the single most cost effective performance improvements is the installation of a higher flowing exhaust system. This paper discusses some of the theory behind exhaust systems as well as a cost/benefit analysis of various component options. The following information was collected while researching and implementing a 3" turbo to tip exhaust systems on a 1992 Eagle Talon AWD belonging to Ryan Larsen, but should be applicable to other similar vehicles. Consider this to be a guide for putting together your own cost effective custom high performance exhaust system.

Background

 A high flowing exhaust system improves performance because it reduces the restriction of the stock exhaust and allows the spent gasses to be more easily expelled. Unlike a normally aspirated car, turbocharged engines do not need more 'back pressure' than the turbo itself provides.  Therefore, ideally, for maximum power we would want no exhaust at all.  Unfortunately, due to noise levels and environmental regulations, this is not a viable situation.  So we'll do the next best thing which is to install the largest most freely flowing exhaust we can.

However, the next issue we come across then is one of cost.  Unfortunately, full 3" turbo to tip exhaust systems (the typical big exhaust) from a well known vendor can be very costly. The better systems can run over $1100. Our objective then is to explore how we can get the most performance for the least amount of money. 

It turns out that the solution is to purchase some of our own components and utilize the services of a skilled local exhaust shop to build and install a custom exhaust. For those in Colorado, we have an arrangement with a very good shop which has successfully produced several of the systems described in this paper for members of Club DSM Colorado. Other readers across the country should be able to locate a similar shop but be advised that your best bet will be with independent shops (i.e.: not Midas, etc.)

Procedure

The first thing we have to do is familiarize ourselves with the various parts of the exhaust system.  As we go over each one, we'll look at the trade-offs involved and design our system.  Then use the checklist below to select your parts for each component and order everything. After you have assembled everything, call the shop and make an appointment to get the work done.  It is recommended that you print out this guide to take with you when you have the work done. 
NOTE! You may need to adjust your printer side margins to avoid having the right side cutoff.

The Components:

There are three main sections of the exhaust system. For cost and weight considerations we will be using aluminized piping. In areas where a lot of salt or other corrosive is used on the roadways, this may not be an appropriate material.  In those cases, stainless steel is usually the way to go but be aware that it costs more and is heavier. 

• The Downpipe: This section runs from the bottom of the O2 housing to the catalytic converter ("cat").  It is the only component with a sharp angle bend therefore it is very beneficial to construct this piece with a mandrel bend*.  In addition, the other important part of the downpipe is the flex section.  This part is needed because our transverse mounted engine will twist forward and back as it revs.  The flex section allows the engine to move but isolates and protects the rest of the exhaust from this motion.
  

  OPTIONS: There are no options to select from on the downpipe. You need to purchase all the parts listed on the checklist below.

  NOTE! Since the stock O2 housing outlet is small a 3" to 2" reducer must be used or the downpipe won't have enough room to bolt up to the O2 housing.
  

• The Cat: This component is required by law when operating your vehicle on any public street.  It's purpose is to reduce the emissions from your engine.  Unfortunately, it is also restrictive and therefore reduces your available power. There are after market so called 'high flow' cats but track results indicate that they are still power robbers. IMPORTANT: your exhaust shop cannot legally build you an exhaust system that does not include a cat. The potential fines for them and you are very steep so do not ask them to!!!  Club DSM Colorado members may obtain more information about ways to get the highest performance at the track by contacting our technical staff and requesting document R3-Aux.
  

  OPTIONS: For this component, you basically have two options; either use the stock cat or purchase a 3" high flow cat. We recommend saving money and reusing your stock cat since you have higher performance options when you're at the track.

  NOTE! If you reuse your stock cat, you'll need 3" to 2" reducers on both sides.
  

• Rear pipe, Muffler, and Tip  This section is usually referred to as a 'cat back' system as it's everything after the cat.  The rear pipe can be much more economically constructed with press bent* piping since the bends are very gentle.
  

  The muffler will be the largest source of control on how your exhaust sounds (tone and volume).  The more power you create at WOT, the louder your exhaust will be. Since our objective is to improve power as much as possible, we recommend what's called a 'straight through' muffler design which is exactly what it sounds like; no baffles or other restrictions.  You can always trade maximum power output for a more restrictive muffler design though which will have the side effect of being quieter. We prefer to just lift our right foot a little when we want to generate a little less noise :-) 

  The tip is the final part of your exhaust system. It is really more of an aesthetic preference than anything else. Be aware that the larger your tip, the more ridiculous your car will look to most people. Costs can vary greatly with this component too so you can save yourself quite a bit by going with something a little more subtle.  About the only performance issue is that you will want a tip that is a little larger than the output of the muffler so we recommend 4". 

  OPTIONS: There are muffler and tip options for this component. We recommend the magnaflow muffler that Ken's carries as it performs well and only costs $99. You'll do best to purchase your own tip.

*Mandrel bent pipe is one in which the cross sectional area remains constant around a bend radius whereas in a pressbent pipe a bend will compress the cross section somewhat depending on the degree of the bend and the technique used to bend it. 

Select and Order Your Components

Recommended vendor item you order 
Optional vendor item you order 
Shop item, welding, etc.
R = Recommended combination
O = Optional combination

Component		Item	Source & P/N	Price
Downpipe		2" flange for O2 housing & reducer, 3" flange for Cat, welding	Shop	100.00
		3" mandrel bend	Jeg's (289-42323)	21.99
		3" Flex section	Alamo Motorsports (362N)	49.95
Cat	R	Reuse stock cat, two reducers, 3" flange both sides, welding	Shop	30.00
	O	3" high flow cat	Jeg's (289-15147)	139.99
		3" flange both sides, welding	Shop	20.00
Catback	R	3" rear pipe, flange to cat, welding	Shop	50.00
		3" Magnaflow muffler	Shop	99.00
		Hedman chrome tip	Jeg's (500-17162)	25.99
	O	3" rear pipe, flange to cat	shop	50.00
		Dynomax Ultraflow 6" round, stainless,  3" in/out	Jeg's (289-17296)	109.99
		Other tip you supply	various	?

So if you go with the recommended system (3" turbo to tip), the total price is $376.93 + tax. A pretty nice price considering what you're getting!  Also, another cost saving tip: the mandrel bend for the down pipe is a 'U-bend'. You can get two DPs from the one bend so if you team up with someone else, you can save yourself another $10! 

The Shop

We have made arrangements and maintain a working relationship with a very good shop up here in Northern Colorado...

Ken's Muffler Shop
1219 N. College Ave.
Fort Collins, CO 80524
Phone:  (970) 484-6001

Use mapquest to get directions and a map to the shop. Our main contact there is a guy  by the name of "Toad".  He is quite the craftsman and does first class  work. Keep in mind that Toad is doing us a favor and treat him and his shop with the class that our club is based on. Call him and set up an appointment to get your work done only after you have all your parts in your possession.  It will work best if you can have your work done during a weekday although they may be able to get you in on the weekend. 

Make sure you go over everything with him up front. Let him know what parts you got on your own and which ones you are getting from the shop. Be aware that their stock will vary and they may be temporarily out of some items. 

Lastly, although we have set this up as a club deal, it is your responsibility to reach the final agreement on the price for the work that you have done there.  Obviously there are numerous options beyond what I've outlined above and therefore quite a wide range of costs depending on the exact system . I cannot be responsible for misunderstandings or pricing mistakes. Just like any transaction though, you can avoid most all problems if you're clear about what work you want done.

Several Club DSM Colorado members have already taken advantage of this deal and are well satisfied with the results. So get on board and find out just how much more performance your DSM has locked inside just waiting to be unleashed!

Copyright 2001, by SteveTek Inc. 
Please direct any and all correspondence regarding this document to engineering_staff@stevetek.com