Dose anyone make a 3 inch exhaust that fits? I just blew up the motor in my 69 so it's time for a new one. But I am thinking of getting rid of the Hooker side pipes. Under car headers and exhaust out the back would be a nice change.

 

A good speed shop or muffler shop should be able to fit you up with whatever size pipes you want. I'm not sure what 3" pipes will do for you...unless you have a really strong engine you run at high rpm's you might lose a bit of low end torque due to too little back pressure and somewhat reduced scavenging.

 

You will have to have one made. The X-member will have to be changed on your 69. The tight spot is also the Rear Axel if you run 3" under it You will loose a bunch of ground clearance so you will want to tuck it up as tight as possible. Forget about useing the VB&P Dual Mount Spring they can't both be in the same place at once. I'm probably going to change mine in this area useing 3" oval Tube and gain back an inch of clearance.

 

I just had a 3" custom mandrel bent system installed. I did not have to modify the frame pass throughs or any other part of the frame, and it's not necked down anywhere. 3" Magnaflow mufflers and X-Pipe. It's sounds great linked up to the Hooker Super Comps tied to the new 555.

 

Good grief. Is this old wive's tale never going to die????

 

From Magnaflow...

PIPE DIAMETER AND PERFORMANCE

Keep in mind that the goal is to improve exhaust flow. In most cases, just changing the restrictive OEM muffler and replacing it with the same size straight-through, Wide Open Performance MagnaFlow muffler will do this job.

To reduce additional backpressure, the OEM exhaust tubing can be replaced with madrel-bent tubing of the same size or one size up from the OEM. As a general rule, you can enlarge the pipe diameter of your OEM exhaust system by 1/4- to 1/2-inch to increase your horsepower. However, any additional increase in pipe diameter is likely to decrease your performance; specifically, low end torque.

 

Let's see. Increase the pipe 1/4 to 1/2 inch, and the power goes up. Why? Less backpressure. But suddenly, reducing the backpressure even more causes a power loss? Sorry, doesn't make sense. An engine makes power by pumping air into and out of the cylinders. Restricting the output flow (by purposely increasing the backpressure) reduces the VE of the engine (a power killer!), and causes a bunch of non-power producing exhaust gas to remain in the cylinder, which then burps into the intake manifold momentarily when the intake valve opens. This reversion pulse also just screws up the carb vacuum signal.
Furthermore, the average Corvette has about five or six feet of exhaust pipe (and muffler) after the headers or exhaust manifolds. Every foot of that pipe causes a pressure drop due to wall friction, and smaller pipes have more wall area compared to volume than "big" pipes do, causing more pressure drop (more backpressure) to occur. Does anyone actually believe there is a streetable (ie: reasonably quiet) exhaust system out there that has no (or insufficient) backpressure? No, there isn't. And, if the system is that restrictive at low RPM (resulting in "needed" backpressure at low engine speeds), it's going to be significantly restrictive at high RPM. An engine in that configuration would appear to have acceptable power at low RPMs and unacceptable power at higher RPMs. It seems obvious that the bottom end was not improved, but appears relatively better due to the poor high RPM performance of the choked off engine.
I've given you physics and mechanical reasons why backpressure is undesirable. Can you please do the same explaining your position?

 

I bow to the Jedi Master.

I have seen much information over time on both sides of the issue...not just on the internet but publications...all professing to have the last and most accurate word...some written by car guys, some by techs, but all allegedly with proper knowledge.

If I'm wrong...I'm wrong. No point in denying that. What you say makes perfect sense...but so did the information in other sources, at least in the manner it was presented.

Who is correct...depends on whom you ask. I'm more than happy to accept what you say.

Have a cold on on me.


BTW - I'm another white guy clinging to my guns and religion...right on, bro!

 

What is your main reason for getting rid of the side exaust? I am highly considering it, thinking it will be the least restrictive exaust system, not mention largest primary header pipes with out custom headers(small block). I am sure noise is the big culpret.

 

Noise and leg burns can be a problem- some love them, some hate them. As for being less restrictive, unless you choose components very carefully, sidepipes can be a fair bit more restrictive than a decent under-the-car system. Then there's the fitment issue for Hooker sidepipes that's been well documented in the thread started by Lars recently. Just some things you may want to be aware of....

 

I have made my own 3" dual stainless lines.
That fits but you will loose much under the diff.
You will lose even more when you lower the car

 

69427 is 100% right.
But does this logic apply to headers. I am building new headers for my healthy 13.5:1 434 sb. 2" primaries into 3.5" merged collectors.
Too big people say. I don t think so!
What may be too big is when you install the hooker sidepipe headers on a stock 350 and expect it transform the car. 1 7/8" primaries albeit very long can t improve a stock motor.

 

Its about velocity, just like running an intake port thats too big you lose velocity( it doesnt restrict flow, but doesn't help it along either), the same happens in the exhaust. Too big and you lose the scavenging at low rpms, too small and your exhaust chokes the engine out. I think too much is made out of going too big, but definitely go bigger than smaller. Again its all part of the engine combination of cubes and the heads/cam/intake used.

 

There is not a one to one analogy of intake flow and exhaust flow. One is cool air with fuel vapor and droplets in suspension, and limited to a peak pressure drop (force) of 14.7 psi, while the exhaust is hot homogeneous gas under significant pressure (trying to resist the forward rotation of the crank). Also, the intake runner length is typically less than a foot or two, while an exhaust system can be 6-8 feet.
Apples and oranges.

 

Apples to apples. You are still trying to move a column of air dictated by a port and cam, on top of the fact the gas temps from one end to the other are significantly different( anyone know what happens to air as it cools? hint, it doesnt flow faster). On the right engine it can help, or maybe a combination thats not so optimized it can be a bandaid. If your head has a bad exhaust port, and you run a single pattern cam an exhaust thats just the right size can help scavenge while one thats too big and you just dump exhaust into pulls nothing through the engine. If what you say is true why not just run big log manifolds and not hassle with LT headers? Their is a reason LT headers of the same size work better than a shorty or mid length header even though exhaust system volume is very close to the same size.

 

Wrong. And I'll mention it again, we're talking post collector exhaust piping (NOT header pipe sizing). Please try to stay on topic, and perhaps we can then discuss the areas we may agree or disagree on.

 

Oh my. Another "engines like a little back pressure" comment. How does this stuff still keep getting repeated? I can get on board with 3" piping as over-kill for most small blocks. No need for the extra weight or cash to build them in the vast majority of cars but seriously can we all just stop repeating this crazy talk about "back pressure" as a good thing? Don't take my word for it though: If you keep trotting out the line you will find yourself openly MOCKED twice at 4:00 before testing and again after test results in the conclusion at 11:30 in the video time line. Unless running a BIG POWER BBC I wouldn't pick a 3" system simply because it's hard to fit under a C3. Yet, you still want to be sure that you're not creating exhaust back pressure. 2.5 inch fits better and is good to just about 500HP. That will get the job done for most C3s.

 

You are answering a post from 15 years ago.