Can exhaust size be too big? [Archive] - Chevy Nova Forum

: Can exhaust size be too big?


mihc45
27th-February-2010, 11:23 PM
hello, i have a 350 with a mild cam, long tubes and not too much more. when i bought the car a year ago the guy put on dual 3in exhaust with a h pipe and flow master 40 series dumped at the axle..

The car is way too loud in the car and i was wondering if im loosing trq with the 3 inch pipes, and or how much my mpg is being affected not that i care about that too much?

Thanks

Longroofer
28th-February-2010, 12:16 AM
Yes, it is possible for exhaust piping to be too large. When the pipe diameter increases, the exhaust gas velocity decreases and can be detrimental to engine performance. As you are aware, another drawback of tubing that is too large, is increased noise. There was an article, I believe in Chevy Hi Performance, where they covered this with dyno tests a while back. Personally, I wouldn't use 3" on anything less than a serious effort engine with 400 cid or more.

tnblkc230wz
28th-February-2010, 12:28 AM
You can probably drop down to a 2.25 inch system with no problems and it will be quieter.

Necro
28th-February-2010, 08:48 AM
2 1/4 to 2 1/2 is the largest i would do on a mild small block,400 hp or less.
also the headers size is important, i dont know what you have but 1 5/8 for most street engines is fine.

mihc45
28th-February-2010, 09:58 AM
So do you think i would notice a differnce in power by stepping down to a smaller pipe?

cichliddan
28th-February-2010, 10:28 AM
You should do what you want. Yes if you close it up a bit you might be happier.:cool:

mihc45
28th-February-2010, 12:27 PM
i do have 1 5/8 headers, does the collector size matter? mine are 3 in

cichliddan
28th-February-2010, 12:54 PM
your headers seem to me to be a good size. Its the rest of the exhaust that could be smaller. If you want it to be quieter and maybe a little more torque on the bottom end. Go with a more restrictive system. You might lose power in the end though.
:cool:

1969SS454
28th-February-2010, 07:40 PM
Not trying to hijack the thread, but how does a more restrictive exhaust build torque? Open headers must really kill the torque than.

Bipolar4U
28th-February-2010, 08:57 PM
Not trying to hijack the thread, but how does a more restrictive exhaust build torque? Open headers must really kill the torque than.

If my understanding is correct, exhaust pipes that are too large reduce the velocity of the exhaust gasses passing through the exhaust system. In doing so they diminish the emptying out or "scavenging" effect in the cylinder.

Doing that lessens the amount of useable cylinder space for the incoming charge. Less gas removed dimishes the amount of the incoming charge. The incoming charge more effeciently fills the cylinder if there is a vacume caused by rapidly flowing exhaust gases. In turn, that encourages high intake velocities at low rpm's which are the key to bottom end torque.

I believe that's the theory but I'll glady defer to those who are better equipped to explain the phenomenon.

marks1972
2nd-March-2010, 12:13 AM
How about a 415 SBC with 485 Hp and 545 torque, would 3" be a good choice, or would 2-1/2" be sufficient?

Thanks

fossilrunner
2nd-March-2010, 12:38 AM
i would say yes 3" would be a good choice for that motor.

JRouche
2nd-March-2010, 03:04 AM
My thinking is the header tubes will influence the torque and HP much more than the exhaust tube size. The length of the primary tubes and the diameter of them. And Im just thinking here, not a solid theory. But longer primary tubes can help with torque if the tubes are too large for the engine.

For an example. On a 350ci that is pretty stock, between 300 and 400hp a long tube header with say 1-5/8" dia primary tubes is a pretty good match. Dumping into 3" collectors.

Sometimes the full length headers wont fit. So we use a short header. I think a short header will accomplish a similar scavenging with a smaller tube dia for the primary tubes and then they will benefit with a smaller collector tube. Say 2.5".

But really, the diff between a 2.5" or 3" exhaust after the collector is minimal.

What I like? If its a long tube header, with smallish tubes (2-5/8" or smaller) on a 350ci then a 3" exhaust is fine. I think a 2.5" exhaust is fine also. If its a short tube header with smaller primaries then a 2.5" or 2.25" exhaust will help.

On a stockish (300-400hp) 350ci the worst you can do is primaries of 1-3/4" dumping into a 3" exhaust.

Oh, and for the noise. Toss the flow masters, they will be loud, they are supposed to be, thats what they market to, guys with stock sounding cars that wants some noise. JR

mihc45
2nd-March-2010, 08:17 AM
Thanks alot! yeah i was planning on getting rid of the flowmasters, i was just waiting to see if i was changing the pipe size.

76 SS
2nd-March-2010, 08:41 AM
Just add some 2.5 tail pipes to your existing system with clamps, then you can open it up when you want.

Rroxon7
2nd-March-2010, 12:27 PM
I ended up getting the Summit 2 1/2 in. duel exhaust and Heddman Hedders on my 327.. sounds and works great..

taz3
2nd-March-2010, 12:43 PM
I run a 2.5 Magnaflow with a mild 396 060 over and love it. After reading their dyno info, bigger isn't always better and smaller is easier on the wallet!

Nova_Guy
2nd-March-2010, 02:44 PM
This a friend of mines shop and the guidelines he uses.

http://www.fabshopheaders.com/header-facts.html

http://www.fabshopheaders.com/header-sizing.html

$Piker
2nd-March-2010, 10:02 PM
I have long tubes 3in collector, reduced down to 2.5in, H-piped, back to the 40 series flowmasters then 3in welded on the exits of the flowmasters and dumped in the stock-ish location..

Sounds awesome on 327

mihc45
17th-March-2010, 06:51 PM
Well im bout to take the car through inspection and i decided im going to buy a new exhaust sooner then i thought.
Im going to go with the summit kit but cant decide between these two:
http://www.summitracing.com/parts/SUM-680100/
or
http://www.summitracing.com/parts/SUM-680101/


Should i got with the 2.25 or 2.50? its a mostly stock 350, i want more trq and quieter so should i go with the 2.25?

Dan_Lebherz
17th-March-2010, 07:01 PM
Go with the 2.5".
You really could try tailpipes too b/4 changing the whole system.
Going from 3" with Flowmasters dumping b/4 the rear axles to just adding 2.5" tailpipe out the back will make a huge difference.

tnblkc230wz
17th-March-2010, 08:47 PM
Well im bout to take the car through inspection and i decided im going to buy a new exhaust sooner then i thought.
Im going to go with the summit kit but cant decide between these two:
http://www.summitracing.com/parts/SUM-680100/
or
http://www.summitracing.com/parts/SUM-680101/


Should i got with the 2.25 or 2.50? its a mostly stock 350, i want more trq and quieter so should i go with the 2.25?

If you don't plan any major power upgrades and you want quiet, then I'd go 2.25 inch.

mihc45
17th-March-2010, 09:50 PM
yeah nothing big power rise. i might actually go to a smaller cam and smaller stall just to make the car more street friendly and fun to drive.

slickman
18th-March-2010, 11:31 AM
For what its worth, I installed a set of Hooker Super Comps (Along with throttle body fuel injection) and also have 3 inch exhaust as well. Have not noticed any deference on the low end but did notice it will hit the higher RPM's easier now.

My setup
ZZ4
LT4 hot cam
Scorpions roller rockers
Edelbrock Air Gap
Retrotek Fuel injection (750)
Hooker Super Comps
Pipes Stainless Steel 3 inch exhaust

Other info
Richmond Super Street 5 speed
3:73 posi with Eaton and Mozer's