Hi everyone,
I really need some opinions on exhaust size. My engine is as follows: ZZ4 350, AFR 190 heads, 1.5 Roller Rockers, Compucam 274.280 454/488, RPM Manifold, Holley 650 duel feed,Hooker Headers, MSD ignition, Turbo 350, TCI Sat. Special, 3:42 gears. I've been toying with a true duel 2.5 exhaust, I have 2.25 y-pipe/duel pipes/ dumping into 2.5 where the cat went (I know, I know but it was fine when the 305 was in there) into a 3" Dynomax. Can anyone suggest to me what size exhaust I need for this set-up? I've heard that Mufflex is really loud, but I'm not sure if 3" will handle this kind of power...and suggestions would be great. Thanks everyone.

 

Three inches for the pipe to the muffler, which also must have a 3 inch inlet, will be fine.

 

Mufflex also makes a 3.5 and 4 inch system. I planning on going with the four. Heard that single 3" flows a little less than dual 2.25" exhaust. Mustangs come stock with that and make a noticable amount of more power when upgradeing to 2.5" in a stock car.


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406SBC
-DART SPORTSMAN 2 HEADS
-RPM INTAKE
-750 SPEED DEMON MECH SEC. CARB
-HEDMAN HEADERS
-COMP CAM EX .507/.510

 

One 3" pipe outflows two 2.25" pipes. It's two 2.5" pipes that it just falls short of. But even that is still a debate on this board.

 

Not according to the chart on taz's page the dual 2 1/4" exhaust has more total area than the single 3" which should translate to more flow.
I used to have dual 2 1/4" than a shop that suposedly put on dual 2.5" screwd up and put on single 3". The car ran much faster with the dual 2.25's than the single 3". At the time I use to run 13.0 then went to a 13.5 with the single 3" back in the high 12's now with at tranny change and a posi diff with 3.23. Trust me dual 2.25's outflow the single 3"
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406SBC
-DART SPORTSMAN 2 HEADS
-RPM INTAKE
-750 SPEED DEMON MECH SEC. CARB
-HEDMAN HEADERS
-COMP CAM EX .507/.510

[This message has been edited by sb406camaro86 (edited August 02, 2001).]

 

So maybe a duel 2 1/2 exhaust should handle the exhaust? I just want the best/highest flow.
If I did go with a standard 3" pipe, what about y-pipe size...like I said I have 2 1/4 that flows into the 13" section of 2 1/2 into the 3".

 

Tas's chart (sorry Tas but it's true) is not accurate. He failed to subtract wall thickness from the ID of the pipe. You want the area of the ID because that is where the air flows. He also figured the volume of a cylinder at (what I figured out to be) 4" long. That is not area. That is volume. There is a difference.

The wall of exhaust pipes is (95% of the time) 1/16" thick. That's .0625".

2.25" OD pipe. Divided by two to get a radius of 1.125". Then subtract the .0625" of the wall thickness. That equals 1.0625" radius.
Then you have to square that which equals 1.129 (rounded to 1.13). Then multiply by Pi (3.14159) That equals ~3.55 square inches. Times 2 pipes is 7.1 square inches.

Now a 3" pipe has a 1.5" radius. Subtract the .0625" for the wall. That's 1.4375 radius. Squared is 2.066. Then multiply by Pi. That's 6.49 square inches.

You were right about the two 2.25" pipes having a larger area by a whopping .61 square inches. That's like a 3/4" x 3/4" square. However, running into a single pipe increases the scavenging effect, thereby increasing flow.

Just imagine two water pumps shooting water through two 2.25" pipes. IF you join them into one 3" pipe, one is gonna help the other, therefore increase the flow. It's also gonna put less strain on each of the water pumps. That's basically what happens in the exhaust pipe. It's really just simple logic. Why else would they recommend an H-pipe on true duals? It's the same concept.

 

[QUOTE]Originally posted by Sals82Z28:
[B]So maybe a duel 2 1/2 exhaust should handle the exhaust? I just want the best/highest flow.

the people that are being honest will tell you that the best flowing exhuast is true dual, and thats that. i think a lot of the people here dont like the fact of not being able to have it, and try to almost put it down to make themselves feel better about having 1 exhaust pipe. its like saying a 2 barrel is better than a 4 barrel carb because you have a 2 barrel carb intake. cumon, we all know dual exhaust flows better and is one of the best mods out there. there is simply less restriction and it sounds mean. there are arguments all the time about this but the bottom line is that if you can do it, do it: it is just a better setup to not have your exhaust converge into one pipe. i am not saying it is easy to do but it is worth it 100% as far as flow goes

 

[quote]<font face="Verdana, Arial" size="2">Originally posted by unknown_host:
[b]I couldnt have said it better. If an improvement of .6 in the 1/8 mile isnt enough to convince you. Thats what putting dual 3" on my car resulted in.

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1987 GTA 355, carbureted, TFS heads(non G2), 6-speed, McLeod clutch, 11.3:1, dual 3" flowmaster 2-chamber exhaust with NO tailpipes, 98 z-28 wheels, soon to be replacing weak 10 bolt with 12-bolt...gettin tired of breakin axles....

...Whatever turns your tires.....

 

howd you run yours?

 

Wrong. It's just not necessary. You remind me of the guys that thought EFI would never be able to produce high HP levels. Boy did they get proved wrong.

On a street motor, all that matters is average HP, and torque. Increasing flow by using two 3" pipes may be good at the strip for upper HP, but you will loose low end torque on the street. You'd have to have a very high stall speed to overcome the loss in torque.

I never said that duals were bad, I actually think they are cool as hell. But, you don't need them. Why do something you don't need to? Or do something that isn't practical?

Using a single pipe will increase the scavenging effect of the exhaust due to the increase in velocity. That will increase the flow that one bank of cylinders has on the other. Again I mention the H-pipe concept. Not only does it increase scavenging, but it also smooths out the noise coming out of the mufflers due to the smoothing of the flow. It also increases low to midrange torque, without sacrificing upper rpm HP. That is essentially what a larger single exhaust does.

twistedwedge probably saw good results because of the combo he has in the first place. Running 11.3:1 comp ratio will call for an increase in exhaust flow (not to mention the cam that he gave no specs on). But did you know that a 4.25" single has more area than two 3" pipes? Even a single 4" is within 1 square inch of two 3" pipes, AND it's less weight.

Believe what you want, but the "bigger is better" theory has been proven wrong multiple times. It doesn't always apply to everything.

EDIT: BTW, one more fact. Let's say for ex., that someone uses 1 5/8" shorty headers. Subtract 1/8' for the wall to get 1 1/2" ID on each primary tube. The area of each pipe is 1.767 sq. in. Multiply by 4 for one bank of cylinders is 7.068 sq.in. How big is the collector on 1 5/8" headers? Usually 2.5" OD or 2 3/8" ID. The area of that collector is only 4.43 sq.in. That's 2.638 sq.in. less.

Even with a 3" collector it still would be slightly more that 9/16 sq.in. SMALLER than the area of all the primaries for that bank added together. So according to your theory, the collector should be 3 1/8" OD (3" ID) as well as each exhaust pipe. That area is 7.068 sq.in. That would be a true "free flowing" exhaust system (not including bends in the pipe).

You call all the header companies and tell them how to do it, because they obviously have no idea what they're doing. OK?

[This message has been edited by AJ_92RS (edited August 05, 2001).]

 

i am not one of those bigger is better guys, but by looking at his setup it is clear that this is not a daily driver by his sig. i am not a bigger is better guy, back pressure is necessary, but how many people on this board are on here to make their cars as streetable as possible? if he had asked how he can keep his ground clearance and pass smog, i would have said single pipe. you made several valid points, however i dont believe single exhaust pertains to his question. many of us here want more horsepower, and i am a firm believer that dual exhaust with 2 2.5" pipes is the best way to go for all around street/strip performance. just look at his sig.

 

Who here has seen the movie "Road Warrior"? The car Mad Max drives is a good example of true free flowing exhaust... 8 exhaust pipes coming straight from the engine and out the sides... of course it probably wouldn't pass inspection.

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1984 Firebird - Daily driver, 305 LG4, T5 - Hurst short shifter, Edelbrock 600 CFM Performer Carb - Edelbrock Pro-Flow air filter, gutted cat, IROC 16x8 Wheels, Goodyear P215/60/R16, AIWA bargain basement (from Sears of course) CD player
Check out my ride here

Quote from my sister: "It sounds like a boat"

 

yes I know. I've been meaning to fix that as I have said before.

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-Tas
'89 Formula WS-6

305, TBI, auto, 14x3 chrome flat based open element with K&N, Milodon 160* thermo, functional Formula hood, cross-flow Flowmaster, '99z28 rear pipes and tips....

To be installed eventually far far far into the future: Yours if the price is right and I don't have to ship :
Hooker 1-5/8" 50 state legal headers, Dynomax 3" I pipe (PN 44063 and 43248), Catco 3" cat, and injector spacer.

Super GRK_Taz World
F-Body Dual Exaust
EFI & Intake Options
AOL IM: superGRtaz

 

I had this exhaust setup on the same cubic inch motor last year with only 10:1 compression. My cam is .510 .525 lift 232/242 duration @.050. By no means a big cam... When my friend went from the factory setup on his 94 z-28 to dual 2.5 inch his car picked up .4 in the 1/8. The best he could get with the stock type exhaust with gutted cat, and ported LT-1 heads was 8.20's-8.30's in the 1/8. Needless to say he was a little dissapointed. After the duals were installed he ran a 7.88. Then, he ditched the shorty headers and went with the super comps and a straighter 3" setup. He also installed a cam about the same specs as mine, just a little more lift. His car then netted a 11.98 in the 1/4 @117mph. Maybe his car was a fluke too? The more I think about how messed up the flow must be in a stock y-pipe exhaust system the more I shake my head. Maybe this is why the corvettes run so much better than the f-bodies stock vs stock?

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1987 GTA 355, carbureted, TFS heads(non G2), 6-speed, McLeod clutch, 11.3:1, dual 3" flowmaster 2-chamber exhaust with NO tailpipes, 98 z-28 wheels, soon to be replacing weak 10 bolt with 12-bolt...gettin tired of breakin axles....

...Whatever turns your tires.....

 

Look people, it's not as difficult as y'all are makin' it....

It's all about simple air flow. Streeters notwithstanding, if you have a single pipe that flows as much air as 2 smaller ones, you're getting the same job done.

If you feel that 2 - 2.5" pipes are better than a single 4", fine. Physics will disagree with you, but hey, it's YOUR car.

My point is that you're playing an optimization game here. Obviously, the larger it is, and the straighter it is, the better it flows. BUT, how much is really required? Perfectly straight dual 4" pipes should outflow any of you. Do you need that? Hell no.

So, since we know you don't need that large, do the math, and figure out what you DO need. You will probably find that you can get away with a few bends if the pipes are larger. You may find that you can get away with smaller pipes if they're straighter. You may also find that both do the exact same thing.

My car isn't a drag car, but I run with around 500hp and run it between 4000-7500 rpm on most courses. I run shorty headers, 2-3" pipes that Y into a single 4". It does just fine for me.

 

3" nooone should get 3"+ unless they are putting out 350hp at the rear.

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1990 G92 5spd LB9 - 3.42 80,000 miles

Accel Ignition/Wires (8.8mm), Advanced Timing, TB Bypass, Ported and Gasket Matched Plenum, Synthetic Motor Oil, 160 Thermo, TPIS Airfoil, K&N Air Filters, Centerforce I Pressure Plate and Clutch, Edelbrock TES Headers, Dual Cats, Edelbrock RPM Series Catback, Homemade Ram Air, Bosch +4 Platinum Plugs

14.4 @ 94mph w/2.0622 60ft (w/o headers and catback)

14.426 @ 96.19mph w/2.167 60ft(w/headers and catback)

Also newly modded w/o track times:

Holley AFPR, Underdrive Pulleys, KYB Shocks and Struts, Crane Ignition

 

Check out my post on the Tech/general engine board --> "HP/exhaust size chart" it covers both dual & single pipe sizes per HP.

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91 B4C 305 TPI - SOON TO BE 383
TREMEC 5-SP, STOCK 1-BOLT REAREAND w/342 GEARS, K&N, AIRFOIL
EDELBROCK HEADERS, DUAL CAT TO HOMEMADE Y-PIPE & 3.5" SINGLE PIPE W/ FLOWMASTER, CRANK PULLEY, MSD, FUEL PRESS REG, COWL HOOD, WELD WHEELS
14.1@ 98MPH
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OTHER RIDE
67 CAMARO - STREET CAR, BIG BLOCK, PUMP GAS
350TH w/ATI 10", 12-BOLT w/373 GEARS
10.94@124.13 ON MOTOR - ET-STREETs w/MUFFLERS