GageBrand

I have a 1985 Iroc Z28 5.0 TPI. It has a one in two out magnaflow muffler on it but its old, I want to re do the whole exhaust and I have a few questions, I want to put new magnaflow headers and mufflers but how difficult is it to install a dual exhaust set up on this body style? I'm not sure if I want to throw cattylic converters on there, I've heard ill get more power without them and a more louder aggressive sound, is that true?

1MeanZ

iTrader: (9)

This has been covered 1.2 gajillion times. Do a search.

A true dual setup will have to be custom fabricated.

Properly sized catalytic converters will not have a measurable impact on power, you should keep them.

Yes it will be much louder without them depending on which muffler you run.

killer777

If you run true duals without cats it'll be too loud in a lot of cases. Depending on the muffler ^. Use the cats, use an appropriate muffler and run 2 1/2 to 2 1/4 inch pipe. 3s are too big and bulky and aren't needed until you reach like 550 hp. Run them straight back and dump them before the rear axle with turn downs or use an x pipe design. Will have to be custom work, they don't make kits for our cars as 1meanz said.

dmccain

iTrader: (2)

Just go with a single 3in exhaust it will be perfect. Jegs has a 3in catback exhaust system for like $259. As for cat converters if it doesn't have to pass a smog test id trash em. They get old, they stop up.

GageBrand

I don't have to get emissions for it where I live

1MeanZ

iTrader: (9)

Catalytic converters don't just randomly plug up these days, they can live a very long life if cared for properly. They go bad because of a poorly running engine in nearly every case.

I'd still run converters. Keeps the car reasonably quiet, removes the stink and bad smell, and technically it's illegal to remove them.

bbc632

Almost everything is illegal now days anyway.

GageBrand

Its not illegal in my state to have them removed since my car isn't required for emissions, I'm not looking for quite though I'm looking for a loud aggressive sound

1MeanZ

iTrader: (9)

Disabling an emissions control device on a registered car used on public roads is a federal offense as far as I know, your state has nothing to do with it. I'm not trying to be the smog police, just want to get the correct info out there.

If you want loud and aggressive then you can go with cats only, or muffler only, or neither...

Ozz1967

iTrader: (4)

1MeanZ has it right.

It's technically a federal offense to remove any of the factory emissions equipment from the vehicle so I will in no way approve of doing so.

That said, it's your car.

Getting a true dual around a 700R is a difficult thing to do. Some people get shorties and route a true dual down the factory locations. I've seen this done several times. If you look up in the sticky threads you'll see the picture thread. Look it over. If you run long tubes you will lose quite a bit of ground clearance.

A 3" single loses only about 5cfm of flow to a true dual 2.5" set up. Unless your running 400+hp or trying to dig .001's in a drag set up, it's really not worth it imo.

midias

You could always copy this y pipe I made and just not merge it or put an X pipe where the merger is

GageBrand

Thank you for the input, ill do some more research and decide what I want to put on it!

ASE doc

Look at the stickies. The dual exhaust photo collection has pictures of a dual 2.5" system that goes over the axle and exits in the stock locations. It was custom(by owner) made using mandrel bent pipe. It uses chambered mufflers which produce a very aggressive sound. Think Flowmasters on steroids.
I'm going to build a system just like that but with dual 3" to fit my 406 which is coming soon. I haven't run catalyst for 16 years. I think the feds have more important things on their minds than my car. If you're engine is stock, the cat won't make any real difference and will last several years with the engine in good tune. If you go with a radical engine build, it will eat cats no matter how well you tune it. It's the overlap from a big cam that does it.

ASE doc

Midias, I like your y-pipe. I've been thinking about building my own head pipes to go from the shorty headers to the x-pipe. You have shown me that it can be done.

midias

Thanks, it was a labor of love that is for sure and I made it for a friend. It was my first attempt at making my own Y pipe from scratch. The couplers made it a lot easier to get everything aligned and get clearance.

I used

Parts list

1. 6 @ 2.5" 90 degree bends
2. 2 @ 2.5" 45 degree bends
3. 1 @ 3" 45 degree bends
4. 5 @ 2.5" to 2.5" couplers.
5. Flowmaster Y250300 Collector

Here is the build thread.

https://www.thirdgen.org/forums/exha...al-y-pipe.html

GageBrand

I'm going to go with magnaflows, what headers would you all recommend, I'm stumped on what ones would be good and go good with a dual magnaflow setup

midias

Seems like a lot of extra work for a 305 and no gain over a 3" single like the magnaflow.

ASE doc

It is alot of effort and will be more exhaust than the 305 will want. If you build it right though, it will work great with a larger engine down the road. The best headers would be made from stainless tube so they last and have thick flanges so they don't waste gaskets. I would recommend SLP, like I have, but it looks like they don't offer headers for the third gen anymore. Might be worth calling them to find out for sure.

ASE doc

Another option I just thought of is Dyno Don. He makes a good set of headers.

1MeanZ

iTrader: (9)

Dyno Don headers all the way. Great fit and quality. If you are looking to buy your last set of headers ever, buy these. Might even find a used set on the classifieds. I wouldn't be afraid of a used set at all, these are hands down the best shorty headers you can buy for these cars.

killer777

Doug's headers are really sturdy and constructed well, they fit like a glove and the price doesn't drain your wallet.

chad87sc

If anyone can can find dyno don headers I would like them asap.

midias

Try sending a PM to dyno don

chad87sc

Just did that

ASE doc

Don't mean to take this thread off topic but since we're talking about dual exhaust, I just went back to the Classic Chambered website and their sights and sounds page. Those are great sounding mufflers. Like I said before, think Flowmaster on steroids.

One cool thing about Classic Chambered is their American made and not that expensive. I definitely feel good about using them in the new dual system I'll be building this summer.

firechicken_3

iTrader: (4)

For a street driven car that you want to be easily worked on true dual is not worth it.. I have had it for about 4 years now, its loud and with a healthy engine and cam it sounds amazing. I used 18 inch 3 chamber mufflers from sweet thunder exhaust, same thing as classic chambered exhaust. Very raw and sharp when you get after it.

I have longtubes and a t56 it is the absolute easiest combo to do true dual with. There is no room for the exhaust to move it has to be hung so tightly that keeping it off the body is next to impossible, the driveshaft will hit the exhaust when the suspension droops to that means no more 2 post hoists or letting the rear axle hang while you have stands under the subframe.

I have broken my hangers numerous times and dealt with the pipes banging on the car and rubbing and rattling. With a shift in my interests to taking longer trips and weekends away with the car, I am currently going back to 3 inch single to a crossflow muffler.

ASE doc

Hi firechicken_3, Is your dual system 2.5" or 3"? Any photos?

I can see what you mean about things being tight. Looking at my own plans, there will be definite interference concerns where the pipes run along by the driveline. Also, ground clearance is going to be tight under the rear seat area of the floor pan. I'm considering forming an indentation in that area to make room for the RH tube.

I can make it fit okay, but it might very well mean no more racking the car on the two post. Not without first removing the exhaust. With the right fittings installed, the mid and tail sections can be removed in a few minutes. At the shop now I have a flat rack and a two post. I can remove the mid and tail sections on the flat rack then move the car to the two post.

It will certainly make repairs, where the two post is required, more time consuming in the future.

firechicken_3

iTrader: (4)

It is/was 2.5 inch. body diameter on the mufflers was i believe 3/3.5. I don't know if i ever took pics of it but if i did i probably posted it here somewhere.

I came together under the tailshaft ran side by side mufflers were just ahead of turn up over the axle mounted to a bolt under the passenger rear seat. tied together ina couple places to keep them from banging around. after the turn up i used butt joint band clamps to make a seperation point and then finished out with various bends to a long stainless tip on each side. It truly is a huge pain to work on. It was a pain to remove exhaust to work on things.

All that said its in a pile and my new stuff is partially mocked up waiting on correct factory type hangers and a bend that i didnt realize i needed to replace until i found that the hanger had ripped a hole in it.

For a track car that needed mufflers due to regulations I would do something similar again but not go all the way out. Otherwise I am going to a 3 inch single and a flow tech afterburner crossflow with factory style tailpipes. I'm not a fan of bling anyways fit and function are my thing. Another issue is the lack of an easy place to put a proper cross over or balance tube.. I believe my engine is happier being able to scavenge side to side.

ASE doc

V engines don't like exhaust imbalance. I plan on using an X-pipe, mounted where the cat originally was. It seems that there will be room there for it. The more I think about it, the more I consider just going with dual 2.5". From what I understand, dual 2.5" will support 550hp. My 406 should make right at 550 if we can get my heads to flow 280cfm. However, if I end up going with different heads down the road, I could pass 600hp and then I would want the dual 3". Single 3" supports 350hp before it becomes restrictive. I'm already past that by a bit. I expect that freeing up the exhaust will increase the upper end of my torque curve noticeably, but I'll have to wait and see.

Honestly though, when I finally do get the funds together to build the 406 and the new intake to make 550hp, I will probably be done with the engine, in which case dual 2.5" will be plenty. Either that, or I'll be soon divorced and have to live in my car when my wife throws my *** out for all the money I spend on my car.

From the sound of it, my design will be a little different than what you have, due to the headers. I'm running SLP 1 3/4 shorties so that both head pipes come back on the passenger side. This makes it a little easier to follow the factory routing and by sandwiching the two pipes tight together, I think I can make it fit.

There is a photo set of a system like this in the sticky "Third Gen dual exhaust photo collection". Unfortunately, the link in the first post of that sticky just links to some useless advertisements, but the link in the second post by Willie links to the photo set of his dual 2.5" system. I can see where there may be some interference when hoisting the car on a two post, but it would be minimal.

I was thinking originally of having butt connections at the rear axle for removing the tail section if needed. I don't have an in tank fuel pump but I do still have the sending unit in the tank that may need service someday. Now, after reading your posts, I'm thinking about adding connectors right after the X-pipe as well so that the mid pipes and tail pipes can both be removed without cutting.

Willie used a quick disconnect at his axle made from a slip joint with flat steel brackets welded on each side of the joint, fastened together with bolts. This design would come apart super easy but I'm afraid it might also leak just a little. I'm thinking of band clamp butt connections for goods sealing with straps like Willie used to hold the butt joints in place. I have seen problems in the past with the butt joints and band clamps slipping.

firechicken_3

iTrader: (4)

I remember seeing the system you mention in that thread, it was very well done. Since you are using shorties and swinging through the original cat location then yeah you should have room to drop an x pipe in there and then bring the pipes tight together. You will still have no drive shaft access unless you intend to modify the floor beneath the rear seat to run pipes and mufflers.

A hint for you of what long tubes, duals and those chambered mufflers might sound like with the xe274, my engine is right on 10.5-1 compression so it helps it pop a bit.

This is idle only, roughly 750-800rpm

ASE doc

Beautiful music buddy! I run the ZZX cam from TPIS in my 355. It's 290/290 @.006. 240/240 @ .050 with .373 lobe lift on int. and exh., which converts to .560 lift at the valves. So the sound should be similar.

That is a very nice, b*d *ss sounding car. I do understand though why you want to change the exhaust. I've built cars for people before that ended up being too much trouble. It's exciting for a while, then you have to live with what you built. That's the nice thing about fab work, it can always be redone.

My car is lowered 1.5" so ground clearance, even with the single 3" is already tight in the rear seat bucket area. Adding another 3" pipe will definitely require modification to the floor pan. I'm thinking now about what I'm going to do there. I really don't know if I want to modify the floor, even though I rarely have rear seat passengers. It would only take a little indent, made with a section of 4" pipe and a floor jack, to make the needed clearance, but I just don't know if I want to do that. I guess as long as there is no cutting or welding done to the body, it can always be put back the way it was later. But I hate mess with the body.

If I just go with dual 2.5", it will make things much easier. The more I think about it, the more I'm leaning that way. Especially if I take steps to make the mid pipes easy to detach for undercar service, it won't be nearly as much trouble down the road. I highly doubt I'll ever get to the place where I'll need anymore than dual 2.5" exhaust.