Submitted by: Stu, Victor, George D, and Steve B.
Last updated: Wed Jan 17 1997
There are two basic ways of modifying a crossmember to accept a dual exhaust. A hard way, but probably a stronger way, and a much simpler way. I'm of the opinion that either way will work since the crossmember is not a REAL stressed member, not like the frame, but don't go too nuts modifying the crossmember. The Hard way: This method does involve removing the crossmember from your car, need to unbolt the 4 frame bolts and the trans bolts. First off, you need to estimate where you will be making the cut. I suggest installing your headers and then eyeballing where the cut will be. Then you take out the crossmember. You need to reinforce the crossmember to make up for the loss of the metal. So I used channel steel which fit over the crossmember and welded it in place. Next, I broke out the torch and referencing off the marks, cut a big, wide notch into the crossmember. Make it wide enough to make up for any mistakes you might have made. Also cut pretty deep into the crossmember, at least 1/2 way through to create a reasonable amount of room. The extra height added by the channel steel on the crossmember required a little floor pan mods, mainly jacking up the crossmember and allowing it to self clear itself fit 3" under my crossmember, so you can stuff a whole bunch of exhaust under your car. Pictures of this method can be seen on the monte homepage. There has been some email regarding the x-member the past few weeks if you want true duals on your Monte. IMHO, this should not be a problem. All you need is to find a good welder and for ~$20, he will use a combination of heating and impacting to create a C-shape in the crossmember under which the driver's side of the dual system will run. No cutting, no welding, no trans removal, no loss in strength. A 30 min. job on the hoist. Basically heat the crossmember till its nice and red and then break out BFH and pound the crossmember to gain the additional clearance. When he's done, it should look like this: ________________________________________________ rocker | ___________ | Trans panel |__________________/ \_______________| There are a slew of non emission headers for g bodies with sbc, so that shouldn't be a problem. I have used the headman and the dynomax headers. I really didn't like the headmans, but they were kinda old, so maybe they redesigned their headers. They dynomax headers I had were ceramic coated, I love the ceramic coating, makes checking the spark plugs easier. As far as true duals for g body, I can only think of Torque Tech off hand. They make some nice mandrel bent 2.5" and 3" exhaust. But any competent exhaust shop can bend you up an exhaust for the car, and can probably do the crossmember mods (the easy version). Emissions legal Cat back systems: _________________________________ To my understanding, of emissions laws, anything after the Catalytic converter doesn't need any CARB/E.O. approvals, and you can do what you want. Here's a list of mandrel bent systems for the G-body. DynoMax: 2.25" dual cat back, Aluminized mild steel, True SS exit, tailpipes polished, DynoMax turbo mufflers, P/N: 17423 Price: $230 Hooker: 2.5" Dual cat back, Non-coated mild steel, Super comp mufflers, Exits like GN, P/N: 16810 Price: $260 (Summit) ATR (Applied Technology & Research) Stainless Steel: 2.5" dual cat back, Stainless Steel with stainless core muffler wrapped with aluminized mild steel (similar to walker ultra flow). Exits like GN Price: $495 2.5" dual cat back, Stainless Steel with stainless core and external muffler. (a little quieter than the one above) Exits like GN Price: $695 3" single cat back, all Stainless Steel. Exits like GN, but only on passenger side of car. (very loud) Price: $395 Hooker: 2.5" Dual cat back, alumnized steel, Super comp mufflers, Exits like GN, P/N: 16810 Price: $260 (Summit) Torque Technology: 3" dual cat back, Aluminized mild steel, Exits like GN, Flowmaster 3 chamber mufflers Price: 471.00 Turbo City: 2.5" dual cat back Price: ?? Emissions legal Headers: _______________________ In order for headers to truly be emissions legal, they must have CARB/E.O. approval. For header manufacturers to get CARB/E.O. approval, they must have a complete system from exhaust manifold to y-pipe. All of the factory emissions equipment must remain intact and be functional, i.e.: A.I.R., heat riser valve, O2 sensor. Also, the manufacturers must do testing for *each* specific application. Only a few manufacturers have done this, and to my knowledge, Edelbrock has the only emissions legal Tubular Exhaust System for the G-body. I have heard rumors that Headman has an emissions legal system, but I'm not sure if they have a system for the G-body. Edelbrock TES (Tubular Exhaust System) CARB/E.O.#D-215-1: LG4 engine, Non-coated, P/N: 6878 Price: $305 LG4 engine, Ceramic coated P/N: 7978 Price: $475 L69 engine, Non-coated, P/N: 6879 Price: $335 L69 engine, Ceramic coated P/N: 7979 Price: $505 Mufflers: And now the forever asked questions about mufflers. Generally, Montes take an offset/offset configuration. There are a huge amount of mufflers which can fit the car. But the question that everyone has concerns the Flowmaster and the Dynomax Super Turbo mufflers. First off, there are many things which effect the sound and volume of the exhaust. Most important are probably cubic inches, cam, headers, exhaust size, converter, and tailpipes besides the muffler itself. Any changes of these will make an effect on the sound and volume of the exhaust. But the muffler probably does play the biggest role in the tone of the car. Flowmaster 2 chamber vs. 3 chamber: Yes, Flowmasters are louder than the stock exhaust, but generally speaking the 3 chamber mufflers are streetable while the 2 chamber ones are pretty loud, so you might want to think about that before you go that route. As a side, in a test of mufflers done by a Ford magazine, they didn't find very much power difference between the 2 chambers and the 3 chambers, the difference mainly comes on the very top end. Contrary to popular belief, they are affordable, should be around $50 a piece if you order from a major mail order place. To characterize the sound of Flowmaster, I would say they sound very much like open headers, just quieter. They have a certain crackle to them, like open exhaust. Flowmaster work on the baffled system, so there is no fiberglass to blow out. So, they should sound the same the day you put them on to years down the road. Dynomax Super Turbo: The dynomax has a different sound from the Flowmaster, they tend to have a deeper, more muffled tone. Hard to describe, but I would characterize them as being more refined, less crackly than the Flowmasters. Beware, when you first put them on, they will be pretty quiet. But since they are fiberglass filled, the will get louder the more you use the car. These mufflers tend to be cheaper, around $30 from the mail order shops. Exhaust Size: The stock monte exhaust is 2". But the stock design monte exhaust comes together into one cat and then splits into two pipes. This is not the most conductive to making lots of power, but probably must be retained to pass emissions. So generally speaking, for a stock monte, 2" may be more than enough. But if you're getting a new system, you might as well step up in size, since they allow you make more power later. But remember, the y pipe is still the choke point no matter how big you make the exhaust. But don't let that scare you, people have used the y pipe with dual 3" exhaust and still made tons of power. My rule of thumb is at minimum, get a 2.25" or 2.5" exhaust. I tend to lean towards the 2.5" since there usually isn't a big price difference. 2.5" on a stock 305 might be kinda large, but you might as well. For true dual exhaust, I would suggest 2.5" when you get near the 300 hp level. 3" when you get around 400 hp. These are general rules, I had a dual 3" on a motor making around 350 hp. I didn't notice too much of a loss on low end, but then it was geared to eliminate low end problem. I still made a ton of low end. Catalytic Converters: For those who need to run, or at least pretend to run cats, there are a variety of options. The simplest thing to do if your cat goes bad (or even if it doesn't) is to hollow it out. Cats are made up or certain rare metals, platinum, palladium, etc. (which is why they're so expensive) on a ceramic honeycomb. The most common cause for the cat to go bad is an over rich condition. So if you're tuning a carb on a car with a cat, be careful about running it too rich. Also, if your o2 sensor goes bad, the motor will often go rich, which may end up killing the cat. Going rich will cause the substrate material to melt and end up clogging up the ceramic honeycomb and generally causing a large amount of back pressure. Also, physically hitting the cat can cause it to break. So watch it when you ramble speed bumps and other might spot opportunities. Federal law says you can't change your working cat unless its gone bad or you have at least 50k miles on it. If you cat does go bad, these are the symptoms: If you bang on the bottom of the cat or if you floor it, you may hear some rattling of chunks inside it. Unexplained loss of power is a good one. Especially if you floor it and it feels like there is a boat anchor tied to your rear, the engine will labor to make rpm's and it will just run like crap. Rotten egg (sulfur) odor. Not necessarily a bad cat, but if it is consistent, it is bad. The exhaust note will change, the engine temps will go up. Also, the cat gets very hot. The passenger side floor around the cat would get very hot. Its pretty easy to breakup and take it out, broomstick should work. Remember to take out the broken chunks after you're done. Remember, running no cats on an originally cat equipped car is only legal for off road applications. For those who would like to keep a working cat, Summit Racing sells a hi flow cat which people have used and liked. Its a PFP brand and should be able to be had for under $100. Call for specific part numbers. If you have a 3" system, Random Technologies makes a real high flow 3" cat; supposedly the least restrictive on the market. Not too much more restrictive than a straight pipe. It's $200 though.