Nelz

I've been studying David Vizard's exhaust chapter in his Max Performance Chevy Small Blocks on a Budget book. But his article in PHR http://www.popularhotrodding.com/eng...h/viewall.html is a good summary.

I can now understand why the exhaust system sucks in our cars.

1. Poor flowing exhaust port
2. Low flowing cats.
3. 2.5" stock exhaust does not flow enough CFM
4. Restrictive muffler.

Unless you port the heads and prep the valve (in my area I was not able to find someone to perform the radius the chamber side of the exhaust valve trick found in the David Vizard Book), but if ported, a Chevy exhaust port can flow close, if not 200 cfm.

If you're going to use the stock iron manifold, port the top and sides as per the books guideline, as this will add about 15hp. There were a few other places and nuances to heed in the book about porting manifolds.

But it did recommend headers. See the sizing chart. Ideally, you need 1-5/8 or 1-3/4 diameter depending on how well your exhaust port is flowing. After this, you're looking at primary length.

Here is the problem. If you're going to go shorty's (ie. Dyno Don's, Hedman's, Hooker's) you're not getting the recommended 24-36" pipe lenght that is recommended, despite getting the pipe diameter right. I know that the Hooker Super Comp Long Tubes meet this requirement. However, they do hang pretty low for ground clearance, and you gotta do some fitment to get them around the hydraulic clutch cylinder in manual cars. But theoretically, according to Vizard, these are the "correct" pipe lengths at 24" and diameter (1-3/4) for 3rd gen Camaro's making over 375HP.

Our cars just have fitment problems for headers, so if you're using shorties, they ARE better than the stock iron manifolds as they improve flow and separate the exhaust ports thus reducing pumping losses. The collector/secondary should be 2.5" for street performance, but for motors over the 375 HP mark, a 3" collector is recommended, and preferably longer collectors, or merge collectors. This isn't always possible with what is available on the market unless you're going with custom headers.

There is a lot of debate regarding headers on the board. I'll let you read the article and books and make a decision.

As for everything behind the headers:

You need a dual cat set up.
http://www.samracing.com/HR-Oct00_pg3.html

According to S.A.M's testing with a 4th gen converter, let's assume that the stock converter does only flow 304cfm. Divide that by the magic 2.2 figure and it's only good for 138HP! A dual set up then, is only good for 276HP! Remember the 350 TPI's? They only had 245HP at most, so the dual system was ok. But what is really needed is 2 CATS that can flow for the HP you need. One example would be Vibrant's race cat that flows 578 cfm according to their catalogue. P/N 7101 fits a 2.5" inlet and 2.5" outlet. 578+578= 1156 cfm / 2.2 = 525 HP limit.

The problem is that it Y's back into 2.5" usually on the stock y-pipe. If you can have something custom made, you'd have everything exiting into a 4" set up.

What do you need for a cat back?

The Mufflex 3.5-4" system according to this:
www.exhaustvideos.com/faq/how-to-calculate-muffler-size-pipe-diameter/#easy

The 3rd Gen's were cursed with a single pipe exhaust system. As you can see, the stock 2.5" system behind the cats would only flow 509cfm and that's good for 232HP. But you if you're replacing your exhaust, go big. Mufflex makes a 3.5 and 4" system for a no loss back pressure system (from the pipe's end.)

What muffler?
Something that flows 2.2 cfm times your flywheel horsepower. So if you're up at 450HP, x 2.2 = 990 cfm. The Dynomax ultra flow series mufflers flow 1195. Good for 543HP.

The Super Turbos were great in the 80's, but only flowed around 600 cfm. Walker still lists that system in their catalogue and it's cheap. But it's not good enough for a third gen pushing more than 232HP. (The pipe diameter is the restriction. The muffler restricts at 272 HP. And their dual cat set up restrict at 355HP.)

So in summary:
-Hooker Super Comp Long tubes if making more than 375HP, otherwise 1-5/8. If you hate the ground clearance scraping sound all the time-especially on speed bumps and driving up your drive way if it's on an incline-shorties will be better than stock iron. You can debate which brand all you want. But whatever you go with:

-Dual Cat set up with vibrant or random cats that flow in the 500cfm range per cat so that you get a system that will flow past 1000cfm. You're may tear your hair out looking for a dual cat system off the shelf!

-Mufflex 3.5-4" system. You may have to trade off the drone of the pipes for performance. That's just what you have to pay.

-Dyno max Ultra Flow or any other muffler that will flow over 1000 cfm.

If you're looking at the max out of your exhaust, do it right once, or pay to do it twice!

As for the pressure wave termination box on a third gen---if you figure it out, let me know. I think the cats will do a good enough job and that there will be no more room left.

I almost considered the Walker stock replacement system, until I realized that I would pay again to upgrade the system later. It's not a bad system as long as you realize that it limits power to 232HP (which was good enough for the stock LB9.)

InfernalVortex

iTrader: (4)

Ive got a single 3.5 exhaust over the axle (From long tubes even) and Ive got no drone at all. It is LOUD, but there's no drone like with my old flowmaster 80. I run a straight through Dynatech Split Flow muffler, very similar to a Borla XR-1. Very loud, wouldn't necessarily recommend it if you like to drive around neighborhoods in the wee hours of the morning. I'd probably go with a 3.5 inch Aerochamber muffler if I had to do it agian, probably wouldnt sound as awesome, but it would be less loud I think.

Also, Hookers seem to be a bit of a pain to install, but they fit around the T5 slave cylinder just fine. Hedmans wont fit around a T5 slave cylinder without mods. Hedmans sit up a lot higher in the car, also. Both clear a T56.

abray1

I have 2210s into dual 3 into a 4 system into a spintech 4-3-3 muffler and it sounds great with no drone at all. It made over 400hp on Ed Wrights dyno.

Nelz

I was at a trade show yesterday and Vibrant was one of the exhibitors. I asked them about part number 7101 and they said that it doesn't last that more than a year in high performance vehicles and tried to up sell me on their "new" OBD II catalytic convertors that go for over $300 for 1 convertor. (Although in the Vibrant Catalogue there is a warning that an overly rich A/F of 11:5 or lower or operating temperature exceeding 1200 F will cause premature failure of the cat.) They suggested part number 7830 their new GESi cat. (It only comes with a 3" or 4" inlet/outlet and runs for $300+ each vs. $100 each for their OBD I part number 7101) which is rated for 500-800HP. However it doesn't have the cfm numbers on them, so I'm unable to verify their claimed HP loads. Also, with a 3" inlet/outlet, if the claim is true, then I suppose you could run this into a single cat system. Anyone able to perform a flow test?

Keep in mind, the Cats are the first restriction in your exhaust as the stock cat flowed in the 300 cfm range, which divided by 2.2 is good for 136 HP. When your cat dies, switch to a higher flowing cat and a dual set up. Unless someone can really find flow numbers for the GESi cats.

Update:
So I went to talk to the reps again and they said their new cats also flow 500 cfm+. The main difference is that the material inside the new more expensive cats are welded onto the inside of the metal body of the cat, thus preventing blow out. Their old model, along with other manufacturers including magnaflow, the core is attached to a membrane to allow the catalyst inside to flex. And that is what causes the core to blow out. The membrane doesn't stay attached to the housing of the convertor.

1bdbrd

iTrader: (1)

What about running a dual setup similar to the Bassani duals that 4th gens run?

Nelz

Well if you look at that exhaust cfm link, you'd have your answer.

Mike's 87

Im running a 87 IROC with a 383 stroker 10.25:1 compression with a TPI and 30#.injectors a march underdrive polished billet pulley system. also running eddlebrock tpi headers EMISSIONS.EQUIPMENT BYPASSED/REMOVED except walker cat. 3" exhaust to transverse muffler (series 80 dynomax) with 2 1/4" 2 1/2" outlets. motor dyno'd with carbs at 425hp before headers pulleys k&n and tpi. thinking of eliminating cat abduction running straight from headers to long.pipe to back. ANY.THOUGHTS.???? SUGGESTIONS?? also thinking.of a flowmaster super 40 to replace.80 series.

prossi

well my thoughts on eliminating cat abduction is that their owners will probably appreciate it...now if you can stop all those pesky dog abductions

Mike's 87

Ok prosi you got me lol auto correct with word prediction on cell phone strikes again.

Mike's 87

Insert AND instead of ABDUCTION lol

Nelz

Well since we all have to breathe, I wouldn't get rid of your cats. But its up to you. Vibrant does make a cheap and expensive cat that will flow enough as long as you are running a dual cat set up. Take your pick on cats. The 3" pipe is not big enough for a no loss system above 339HP. I wouldn't go with a flow master, but would go with a walker ultra flow as I know the cfm. You're on your own looking up flow master cfm numbers. Because the flow master reps won't give me a straight answer on flow numbers for their mufflers.

BlackenedBird

iTrader: (5)

I've had this for awhile & forget where it came from. Use & trust the info at your own discretion.....