3" exhaust pipe

[cantbuytime]

@Comp orange. I say cut it all flush and use the stainless band clamps to connect to the headers.. If not PM me. I have a few ideas I was going to fab up for exhaust connections. I got quick release that would be sick. maybe you would be interested in fabbing it up yourself. Free is always better. LOL.

Not knocking you Aaron. I have spent more time in school then actually working in the field. Sad right?

You make valid points with the exhaust slowing down because of it cooling.. We are talking about a race car, not a street car here. I would think it can only hurt a mod motor that needs the bp or a completely bone stock pushrod car thats got no cats. yes 3" on a very mild to stock street car is overkill.. But each engine can/will respond differently to the exhaust size. Muffler design, cat design and bends in the pipe.

In fact the part that ends up hurting an engine is the primary tube size. This is were bp and flow are more important. Too big of primary pipe and it will hurt a mild to stock motor.

There is a reason when we port heads, that we open the exhaust ports more then we work the intake. Whats the point of flowing in 300cfm and only flowing out 200cfm? leaves spent gasses in the cylinder. Also going to larger diameter pipe allows the exhaust to cool quicker and slow down there for raising the back pressure.
A long time ago We built a mild 305 Chevy for a students 78 Chevy truck. I say mild, but it dyno'd 323rwhp/337rwtq through an auto. That was alot of planning and meticulous details. We put the Mufflers exactly 18" from the header collector, that alone gave him 6hp.. he ran 2.5" exhaust. Not even 2 weeks later he got T-boned and totaled the truck. So we swapped the drive train over to a 75' Chevy. The only difference was we went back with 3" exhaust..

The HP increase was almost 30RWHP , if my memory serves me correct it was about the same amount of tq picked up as well.

I have had people try to argue that Ford and Chevy V8's respond differently to exhaust, but in all reality they are basicly the same.

 

[CompOrangeSN95]

thanks for all the good information guys and correct me if im wrong but torque=acceleration horse power=top end??? As far as connecting it to the headers (which are a fucking bitch to get a hold of) I like the idea of the band clamps but I also like the idea of free haha I work as an engineer (even tho I have a degree in media and film...) and I already have it planned out, it's just a matter of getting the proper flange on the end of my H-pipe (home made) so it mounts up to the headers. All said and done I'll be able to unbolt the 2 flanges, remove 2 hangers and drop the entire exhaust in 1 piece. I'll absolutely post pictures as I get work done on it... unfortunately I can't start fabbing up anything until I get the headers... kind of have to start there haha. I like getting both sides of the story, hope there are no hard feelings.

 

[AaRoN]

:BangHead:

 

[SVTurbo 98]

I ask because a 3" exhaust will do nothing but reduce exhaust scavenging and rob power.

Prove it.

Sure thing:

First of all when it comes to modifying a car, bigger is not always better. In this case, it holds true to my point. Larger diameter exhaust piping does increase flow but decreases velocity. Velocity equals torque and flow equals horsepower (when speaking of induction and exhaust). Too large of an exhaust also reduces the scavenging effect. The general rule for a car with a 250-300 cu. in. engine making around 300HP (n/a) with dual exhaust should have a 2.5" exhaust for optimum performance and scavenging. When the piping is too big it also has more heat transfer. Meaning the exhaust gases are cooler, thus moving slower. This is the purpose of header wraps. The thermal barrier on the headers reduces the amount of escaping heat which speeds up the exhaust gases inside the header. Scavenging is important to help remove all exhaust gases from each cylinder. Without that, what's the point of the exhaust system?

Well you didn't really prove anything with that response but rather repeat what you've read on the web or read in a magazine. I was looking for tests that you have done (or someone else) that prove too big of an exhaust after the collector will hurt performance with tuning involved.

How exactly is velocity measured in an exhaust system?
What happens to exhaust gases as they cool down?
Where in the exhaust system do the gases cool down and is it farther down the system as you increase rpm?
Where is the pulse based exhaust scavenging concentrated at?

I'm really not trying to be an a*s i'm just looking for hard facts that support your claim...

Lol...I'm almost offended. First, let me tell you that this information is not something I read on the interwebz or in a car-porn magazine. I am a Ford Certified Technician and I graduated from the Universal Technical Institute with honors. If you feel you need some kind of proof of that too, I'd be happy to snap a pic of my certs.



Good for you. So you've actually done tests on 3" exhaust vs. 2 1/2" exhaust (with tuning and data logging) and can prove to us what you are saying is fact?

How exactly is velocity measured in an exhaust system? Velocity isn't really "measured" in an exhaust system. It's merely a law of physics. Think of a large diameter straw versus a small diameter straw. When you drink from a large diameter straw, you get more of what you're drinking but it doesn't go very far inside of your mouth. A smaller diameter straw moves the liquid quicker and farther into your mouth.



Say what? Well if you can't measure the velocity in the exhaust how do you know if it is flowing correctly...
btw i prefer a big straw over a little one when I'm thirsty...just sayin

What happens to exhaust gases as they cool down? As exhaust gases cool, they slow down. Think about what happens when the you are running and exhale slower. Takes you longer to catch your breath. Right?



I'm not following you. What does this have to do with exhaust diameter? What is physically happening to the exhaust to make it slow down is what I'm asking you.

Where in the exhaust system do the gases cool down and is it farther down the system as you increase rpm? Gases begin to cool almost immediately. Not by a significant amount and yes, it is always further down the exhaust system that they cool the most. A larger exhaust system (more surface area) will cool the gases more quickly.



Do you have any technical data to support how it would affect performance? What is the correct temperature for optimum "velocity" in an exhaust system? And what is the temperature difference between a 2 1/2" system vs. a 3" system in a 300rwhp car?

Where is the pulse based exhaust scavenging concentrated at? The scavenging depends on the entire exhaust system (pipe diameter and length, header design, muffler design, back pressure, etc.).



wrong.

An exhaust system has to be matched to an engine. Do you think that manufacturers just pull pipe sizes, lengths, bends and muffler designs out of a hat and say " that looks good"? It's all engineered based on formulas. Formulas which I'd be happy to share with the SN95 community and if you still feel this is all "stuff I read on the internet".


Manufacturers aren't worried about performance as much as emissions and controlling the sound of their engines.

If you're going to preach something you should be able to prove it.

 

[SVTurbo 98]

thanks for all the good information guys and correct me if im wrong but torque=acceleration horse power=top end??? As far as connecting it to the headers (which are a f*cking b*tch to get a hold of) I like the idea of the band clamps but I also like the idea of free haha I work as an engineer (even tho I have a degree in media and film...) and I already have it planned out, it's just a matter of getting the proper flange on the end of my H-pipe (home made) so it mounts up to the headers. All said and done I'll be able to unbolt the 2 flanges, remove 2 hangers and drop the entire exhaust in 1 piece. I'll absolutely post pictures as I get work done on it... unfortunately I can't start fabbing up anything until I get the headers... kind of have to start there haha. I like getting both sides of the story, hope there are no hard feelings.

acceleration is rpm vs. time

horsepower is a measurement between torque and rpm....peak torque can happen high or low in the rpm band depending on the setup, etc....but horsepower is always going to exceed torque at 5252 rpm..

I always thought about torque as the force to get you where you're going and horsepower as the distance you went...or something like that...

v band clamps are nice and easy to work with but can be expensive...

 

[cantbuytime]

Here are some things we have done here and there for guys who want a quick disconnect for their race cars.

We welded 3" threaded pipe to the collector and then a piece to the exhaust pipe. Instead of a rubber ring he had cut down a 3" exhaust donut. Thats been 4 years and he has never had problems with it. He drives it on the street alot too.

Here is a set of headers that a guy had built for his project. This is just reference pic.

 

[MustangChris]

just for the record.

my older brother (certified mechanical engineer) told me, pretty much verbadum (sp?) what Aaron posted in his first post.

i did not ask for "proof" or "evidence" or "test results" as he is my older, engineering, brother.. . . (No need to question him)

i do not blame you for asking aaron for info, since we are all retards on the internet, but i 100% back aaron on this subject, as i have it from good authority that what he is saying is fact.

 

[SVTurbo 98]

just for the record.

my older brother (certified mechanical engineer) told me, pretty much verbadum (sp?) what Aaron posted in his first post.

i did not ask for "proof" or "evidence" or "test results" as he is my older, engineering, brother.. . . (No need to question him)

i do not blame you for asking aaron for info, since we are all retards on the internet, but i 100% back aaron on this subject, as i have it from good authority that what he is saying is fact.

See that's the problem...People who are new to this hobby and trying to learn will read his first post and assume he is correct, even though he can't prove his claims. Then they will answer someone else's question with the info they gathered from him, and so on. But when they are asked detailed information about what is actually happening, they are lost.

I'm not knocking Aaron at all because there's countless others that do the same thing...but I feel like if you're going to try to teach something to someone, you should have a high about of experience, knowledge and data to support your claims. Mostly because if someone is trying to learn, they will understand why it is the way it is instead of just taking your word for it.

 

[cantbuytime]

There are alot more factors to the exhaust flow then just size of the pipe and engine CI.(stated once already)

He will be fine with the 3". Its only going to be some(if any)low end tq loss and about 10HP difference.(if any)

If you were building a custom exhaust, the headers should be the main focus.

Further down the exhaust the mufflers and cats have more effect then the pipe diameter. After the H-pipe or x pipe the exhaust pipe diameter really doesnt matter.

 

[CompOrangeSN95]

Thanks again for all the info, I'll have the headers tomorrow, I'm not to worried about scavenging as the car won't often be under 3.5k rpm, If there is a loss in power, so be it. Bottom line is this motor with 2.5 or 3" exhaust will run 100x better then the motor I took out.