Needed a set of pipes to allow the 383 destined for my GTA to exhale easily. shorty headers(I'm planning to make my own next winter) 2.5" pipes to the dual 2.5" converters. Flowmaster merge collector and single 3.5" the rest of the way out through the massive Magnaflow muffler. All 16ga mild steel tubing. the front half is welded in the pix the back half is just tacked. Will be pulling it all to finish welding tonight. The head pipes are bolted together before and after the cats. There is an OEM late model GM truck hanger attached to the Spohn T56 cross member. The rest of the system uses the stock hangers and has a slip joint over the axle so I can take it off easily if needed. The purpose here is to be quiet but not kill power. We'll see if I've met that goal in a few weeks.

 

 

Very nicely done. have you run it since the install? I'm sure it'll sound amazing. How much room over the axle?

 

That looks Awesome!!
Are those Hooker 2460 Headers?

 

Engine is not done yet so I have not tried it out. I slid the muffler over the tail pipe on my Tahoe (that has cats but no muffler) and it sounds good but I'm sure the whole system on the car will sound different. Over the axle I've got about 1/4" or so, you can see it in the pix above, it's not much but the exhaust is hung well and quite stable so I doubt it will hit anywhere. I can grab the tail pipe and shake the exhaust all around and it doesnt rattle anywhere so I'm nearly certain it will be fine on the street.

This sounds really bad, but I'm not sure what headers they are. I got them used from my dad, who got them used a while back. I got them long before the 383 was planned, there were originally going on my stock L98. I'm just using them because they are what I have. I'm going to make new ones next winter I think. Anyway, I thought they were the 2460s, but the primaries are 1.5" ID which is smaller than what Hooker offers as far as I know. That said I think they might be Flowtech units. Again, I'm just using them becasue it's what I had, I'll change to something else later. Right now I'm just trying to finish the build without totally killing my budget.

 

Very clean and nicely run. Great job!

 

looks good. I like the hidden outlet... not trying to brag. Ground clearance looks great. Hopefully the 16 ga+cats+big muffler makes it quet for DD use.

 

With the car on the ground the tip should be hidden but not dump the exhaust onto the paint either. The whole rear section will be painted black so the muffler and everything will hide.

Lowest spot for ground clearance is right before it turns up to go over the axle. It is 2" below the rear control arm attachment point. It is the best I could do, there just isn't much room to cram a 3.5" pipe in there. If it becomes a problem I may splice a section of oval piping in there.

At idle and low load I think it will be quiet. At WOT I'm sure it will make noise but thats OK. I am worried about drone on the highway but hopefully 6th gear is tall enough that it wont be a problem.

 

I love that exhaust, Mine is run very similar. I have longtubes that Y right after the trans crossmember into a 3.5" over the axle. Mine is not custom however it is a mufflex kit from the cat back with a single in single out spintech muffler. I prefer the look, or lack of, of the 3.5" slash cut exhaust tip. I think our cars look better without exhaust tips showing. There is just no body line back there to compliment tips.

 

Looks very similar to the exhaust I had on my '83, up to the flowmaster y, but I had 3" (for a while straight back that I really liked, and then an ultraflow welded which I thought was a little quiet). I seriously doubt that the 2 2.5" cats will flow more than a single 3", so I doubt that the 3.5" was worth the effort.

The one surprising thing I found with mine was that a brace between the 2 sides in front of the cats made a difference wrt vibration, but I welded a crossover in there and was very surprised to find that not only did it sound better/smoother, but it actually went faster at the track.

 

Not sure where you get your info but 2.5" duals certainly outflow a single 3" pipe, I have no idea why dual 2.5" cats wouldn't flow more than a single 3" one. I also ran dual cats because it will be quieter than using only 1 cat. 2.5" duals are good for about 513hp, single 3.5" is said to be good for 503hp. This engine should make around 480hp. I wouldn't even consider running a single 3" setup on anything making more than around 375hp. I think the 3.5" was well worth it.

Are you saying you put a crossover before the cats on a single setup and it picked up power?

 

it was exactly the same layout as yours, and I added a crossover before the dual cats, roughly where the 2 pipes run parallel to the rocker and added power.

Ignoring everything else, 2 x 2.5" has about the same surface area as 1 x 3.5", BUT:

1. Your 2.5" sections are MUCH more restrictive than your 3.5" section, every bend adds to the restriction and your 2.5" sections bend around a bit where your 3.5" section it mostly straight
2. yea, everyone says modern cat designs aren't much of a restriction, but noone will say that they flow the same as a straight pipe
3. exhaust gas takes up less volume as it cools, and it's significantly cooler where it exits then at the headers. your 2.5" pipes are flowing much more volume than your 3.5".

this all adds up to a situation that I'd bet that you'd see no difference in overall flow if you used a 2.5-3" y, and possibly even a 2.5" tailpipe after the muffler

 

I think you both have to look at the CFM ratings of the cats to get the right answer. A single cat that flows 400 cfm vs. 2 cats that combined flow 800 cfm. I'd take 2 cats over 1 any day. The 2.2 factor mentioned by David Vizard to create a no loss exhaust system is the worry. 400/2.2 = 181 HP. x 2 = 363 HP before you'll see a restriction.

 

Very nice job!

 

Here is what the exhaust looks like exiting the car since I didn't get pix of that during mock up.

 

I love it!! Looks great and is it somewhat quiet with the Magnaflow? PN For that muffler?

 

unless you're at WOT it is nearly as quiet as stock, and at WOT it's just a throaty muscle car sound.

Don't remember the PN for the muffler but it's giant. It is 3.5" in and out and the body is 24" long, 11" wide and 6" thick.

 

That is a killer looking set up, bet it's going to sound good. I do like the tucked tip.

 

Now that is an exhaust to be proud of! Kudos!

 

Looks good man. What bends did you need for the single 3.5"?

 

thanks to whoever posted this!

 

Not sure what you are asking, but I just used standard 3.5" mandrel bends. I don't remember the radius off the top of my head, 6" or so if I had to guess, 18ga wall.