Building exhaust system

[byates2]

I have a 383 stroker motor. I am running hooker headers on the engine. I want dual exhaust.

My question is would 4 inch diameter pipe be a good choice or is that too big??
Any recommendations would be very helpful.

Also any suggestions on mufflers for the best performance but nice beefy sound?
I was looking at flowmasters or glasspacks. Any suggestions??

[mmiddle]

4" is way too big unless you are just going for outlandish looks. 3" would be more than plenty for 6k rpm and above. Most run 2" - 2 1/4" for stock motors and 2 1/2" for nicely built small and big block DD's.

To give you some reference I run 5" single on a Duramax with 30 psi boost @3200rpm redline.

[byates2]

if i put pipe that is "too big" would there be a problem with not enough back pressure or is it just not necessary

[mmiddle]

Well, I know this will start an argument..... BUT, I don't subscribe to the "needing" back pressure philosophy. I believe: unrestricted air in/ unrestricted air out.
But 4" dual is just way over kill and money that could be spent else were.

I think you will be best served for a DD with 2 1/2". Save some money. 3" and larger gets real expensive fast. It is much harder to work with.

You really need to assess what your purpose for the truck is. For a DD 2 1/2" is just fine for an engine that rarely sees above 4000 rpm. Now, if you are building a street murderer that will often see above 6000 rpm you might consider 3"

Remember, as pipe diameter increases, area inside the circumference exponentially increases. A 2.5" pipe will flow significantly more than a 2.25" pipe and nearly twice as much as a 2" pipe.

[Grumpy old man]

Back pressure is needed to keep the valves cooler , go that big and start looking for replacement heads /engine etc etc etc ,absolutely no reason for exhaust that large your just not that high on the performance /HP scale .

[68 short step]

4" is stupid big on a gas engine, much less a 383, 2.5" dual would be plenty for your needs, 3" would be more then enough, with plenty of room to grow... also exhaust shops are few and far in-between

[NONHOG]

I'd take a look at this chart. Might help?

[Grumpy old man]

I think whoever made that chart sells large diameter exhaust pipe . When has anyone seen 4.5 inch pipe on a street driven ride ?

[coueshunter]

Originally Posted by Grumpy old man

I think whoever made that chart sells large diameter exhaust pipe . When has anyone seen 4.5 inch pipe on a street driven ride ?

Come on over to a couple of street performance sites and you'll awesome big exhausts

[Lattimer]

Originally Posted by Grumpy old man

I think whoever made that chart sells large diameter exhaust pipe . When has anyone seen 4.5 inch pipe on a street driven ride ?

They use 4/5/6" on diesels all the time.

[Grumpy old man]

I haven't seen many diesel 67-72 trucks and fewer running 500 hp gas at best

[Lattimer]

Originally Posted by Grumpy old man

I haven't seen many diesel 67-72 trucks and fewer running 500 hp gas at best

You said 4.5" pipe on a street driven ride. I've seen plenty that size or bigger, mostly on diesels. Hence the chart for larger pipe, and guys selling larger pipe. There are other vehicles besides 67-72 Chevy trucks ya know.

[Stu Pidd]

Engines need no back pressure. What we're looking for is the proper velocity through the exhaust system. Think of every exhaust pulse as a ball travelling through a pipe. There is a high pressure area in front of the ball, and a low pressure area behind. A properly tuned exhaust system will have a low pressure area pass by as an exhaust valve opens, helping "suck" the next exhaust pulse from that cylinder, aiding scavanging.

Pipe too small, and the system chokes itself at high rpms. Pipe too big, and all scavanging advantages disappear.

Originally Posted by Grumpy old man

Back pressure is needed to keep the valves cooler , ....

Interesting. I've never heard that before. Time to research that...

I have a race car powered by a four-cylinder engine. I started racing it with stock exhaust just to see if I liked racing, then swapped it for a three inch.
The car was noticably slower at low rpms, but gained quite a bit at high rpms. Better lap times overall, since the car stays at high rpms on the track.

Too big of an exhaust on a street-driven car/truck cuts down on low-end torque. Makes it far less fun to drive.

More is not always better.

[slowtruck]

Originally Posted by Stu Pidd

Engines need no back pressure. What we're looking for is the proper velocity through the exhaust system. Think of every exhaust pulse as a ball travelling through a pipe. There is a high pressure area in front of the ball, and a low pressure area behind. A properly tuned exhaust system will have a low pressure area pass by as an exhaust valve opens, helping "suck" the next exhaust pulse from that cylinder, aiding scavanging.

Pipe too small, and the system chokes itself at high rpms. Pipe too big, and all scavanging advantages disappear.

Well said!


2.5 with an X-pipe will support 500hp all day long.

[stepsider]

The bigger the pipe the harder to fit underneath

[Andy4639]

I'm having the 6.0 put in the truck and the motor guy said no less than 2.5" pipe. He dino tunes what he installs so I'm pretty sure he knows what he is doing. www.Hawksthirdgencamaro.com I have 2" now and will be taking it as soon as I can to have the exhaust redone. He is going to mate it to the 2" for now then after the exhaust is done we will fine tune it.
I will try and see if he will do a run with the 2" then with the 2.5" to see the differance I hope.

[suspect]

On my 383, I'm running 2.5" w/H-pipe & spintech mufflers. Spintechs are worth checking out if you want something a little different than everyone else. Really cool unique sound in my opinion.

[piecesparts]

WHEN I put my 383 in my 84 GMC, I asked the same types of questions. Here is what I learned from the guys at Flowmaster. 3" piping is too Large for an engine unless it is a big block. This also takes into account the type of driving you are going to do. If you are going to the track and the vehicle is going to be running in the upper RPM ranges for the most part of it's life, then the larger pipes can be useful. Otherwise for your 383 a 2 1/2" set of pipes would be the most optimal for your daily driving. The principal of a good exhaust system is to get proper evacuation of the exhaust gases out of your engine's cylinders, so the theory of the collapsing gases making a vacuum effect is important to the process. As exhaust gases cool they change in volume within the exhaust pipes and thus creating a negative pressure effect. If you have too large of piping, the gases will not flow smoothly and create a anti-reversionary effect and keep the cylinders from being evacuated properly. The use of a "X pipe" is also a good idea, but if that is not available, then definitely consider an "H pipe" design behind the headers to keep the flow pulses balanced and help with horsepower increases. I have been running my 2 1/2" system ever since 1996 when I built it with at first dual Flowmaster mufflers and now I have dual Magnaflow mufflers. It seems the Flowmasters did not stand up to the use as well as the stainless steel Magnaflow mufflers have. My truck has true duals on it with pipes going all the way to the tail end and it has worked well for me.

If you are planning on getting the max out of your headers, then match the system behind them to make them work at their best.

[Fitz]

Originally Posted by coueshunter

Come on over to a couple of street performance sites and you'll awesome big exhausts

Putting a 4.5 inch exhaust on a 383 is like putting lipstick on a pig.

[Fitz]

Originally Posted by Lattimer

They use 4/5/6" on diesels all the time.

On a diesel they are appropriate. Do you know why?

[byates2]

Thanks for all the replies, very helpful

[Lattimer]

Originally Posted by Fitz

On a diesel they are appropriate. Do you know why?

I presume its to allow the turbo to do its job more efficiently, but I'm not a diesel guy. Point was----the chart is relevant.

[bruin_d]

2.5" with a H or X pipe...or none...will be fine. I have dual 2.5" on my BB Suburban (402) and it does just fine. Has a ton of low end. There are as many people who think bigger is better for exhaust as there are who put way too big carbs or cams in their motors.