will 3 inch exhaust be ok to weld to 2.5 " piping will it sounds ok

 

why would u want a turbo exhaust on an n/a car?

 

why not? i want to get a apex dunk muffler and i found it for 160 but turbo size

 

your going to lose HP... NA cars need some back pressure. 2.5 is really pushing it on a NA Car unless you have some major bolt ons 3" is just too big for NA. Someone want to back me up on this?


[Modified by Sushi X, 1:07 PM 5/14/2002]

 

Agreed, 2.5" is pushing it. Even with bolt-ons, 2.5 can be overkill. 3" n/a should be out of the question.

To answer the question specifically, I don't think you will have any real issues having a 2.5" exhaust system welded to a 3" muffler. Can you get me the same deal on that exhaust?

 

if all this is true... why is it that all-motor drag cars run 4-1 headers that usually end in 3" collectors and no piping. just straight headers. i know that doesnt have any back pressure.

 

That's for an all-motor drag car making its peak power from 6-9k. We are talking daily drivers here.

 

uhm, because they have way much more power than our street cars, and they normally operate in high rpm.

 

yup high end horsies come with less back pressure, but you need SOME backpressure for normal driving =P (low end torque) yeah you could just go to an exhaust shop and they could weld it on with an adapter flange. man, you won't have any low end with full 3" piping....

 

your going to lose HP... NA cars need some back pressure. 2.5 is really pushing it on a NA Car unless you have some major bolt ons 3" is just too big for NA. Someone want to back me up on this?

I had a friend of mine who tried to put a Dunk on his with 3' and it stalled numerous times.
Ric in L.A.

 

"Needing" backpressure is a myth. Any engine will perform it's best with the least backpressure. The 2.2 Liter Prelude motors generally needs about a 2.5" piping.

 

but i have 2.5 inch exhaust
just a 3 inch muffler

 

i mean i have 2.5 inch piping
soo just my muffler is bigger
soo i will be cool right

 

I'll back you up on the 3" statement but not the back pressure one.

Tell me what will happen if I place a tank that is pressurized to 10 psi gage pressure and place it in a sealed room that is at 10 psi gage pressure and then open the valve on the tank? Now what will happen if I take the same tank and put it in a room at standard atomospheric conditions?

Back pressure resists the motion of the piston and thus increases pumping losses and that is bad.

Back pressure can also cause exhaust gases to dilute the new A/F mixture coming into the cylinder and thus decreasing power and that is bad.

Back pressure reduces the pressure difference between the cylinder and the exhaust which reduces the scavenging effect and that hurts volumetric efficiency and that is bad. Volumetric efficiency is maximized when the header and exhaust system actually cause a vacuum in the exhaust port right before the exhaust valve opens to help suck the spent gases out of the chamber.

Why does a stock ITR dyno at 160whp and then after a JDM ITR header (65mm collector vs stock 50mm), a 2-1/2" cat (stock 2") and a 2-1/2" exhaust system (stock 2-1/4" with some bad bottle necks) dyno at 182 whp? I'll tell you it isn't because there's more back pressure.

SMSP - Who, like iloveracing, thought the back pressure myth was killed a while ago.

 

I stand corrected...thanks

 

well said.

 

I too thought backpressure was a big myth...so my 2.5" Custom Full Stainlesss Exhaust is good to go then. Had me worried there for a minute...

 

All n/a street driven engines need some backpressure, no backpressure at all is bad. A slight amount of backpressure is actually good (2-6psi) because it helps exhaust gas scavenging and smooths out exhaust pulese. The only case where no backpressure at all is a good this is with a turbo application.
Concerning the 3" turbo exhaust with an n/a motor, 3" would be too large of a diameter unless like the previous posts stated, your engine is built for very high RPM power.
There was a very long and detailed article in a past Sport Compact Car issue, very informative


[Modified by H22Si, 1:22 PM 5/15/2002]

 

I disagree w/ almost everyone here! I own a N/A JDM B20A w/ 3" cat-back exhaust w/ silencer. Performance was gained more than 2.25 & 2.5.

However this is my setup, it might be different on yours. I do plan on turboing later, so I'm ready now.

 

What engines need is low backpressure, but high exhaust stream velocity. A fast-moving but free-flowing gas column in the exhaust helps create a rarefaction or a negative pressure wave behind the exhaust valve as it opens. This vacuum helps scavenge the cylinder of exhaust gas faster and more throughly with less pumping losses. An exhaust pipe that is too big in diameter has low backpressure but lower velocity. The low velocity reduces the effectiveness of this scavenging effect, which has the greatest impact on low-end torque.
Low backpressure and high exhaust stream velocity can be achieved by running straight-through free-flowing mufflers and small pipe diameters. The only two exceptions to this are turbocharged engines and engines optimized for large amounts of nitrous oxide. Both of these devices vastly increase the exhaust gas volume and simply need larger pipe to get rid of it all.
Some stock mufflers and exhaust systemshave up to 18psi of choking, power-robbing backpressure. In direct contrast, a well-designed, high-performance street exhaust system typically has about 2-6psi of backpressure. For an interesting comparison, an un-muffled straight pipe on a "real racecar" usually has 1-3psi of backpressure.

 

1,500cc - 2,000cc = 2-inch
2,100cc - 2,500cc = 2.25-inch
2,600cc - 3,000cc = 2.5-inch

 

ah yes... taken straight from the pages of SCC.

or maybe they took it straight from the pages of H-T


[Modified by exaccord, 12:31 PM 5/15/2002]

 

It's good to see that you are coming around a bit from your first post. Now, I'm not sure if the above words are yours or SCC, but if they are SCC's then they should be quoted as such.

Some basics here, an exhaust system needs to exhaust the header while the header exhausts the cylinders. Flow happens when there is a difference in pressure between 2 points. The greater the difference the greater the flow. Our system is very dynamic and it can't be designed to yield the best possible output for a given engine at every rpm through the operating range. Compromises are and will (unless $ and packaging are no objects) always have to be made.

Where do you want the bulk of the power to be? Low, mid or high rpms. 4-1 headers can be designed to kick the butts of standard 4-2-1s in the low range and 4-2-1s can be designed to kill standard 4-1s in the high end. Exhaust systems can be done in the same way. Will a free flowing 2" system give more low end power versus a 2-1/2" system because it has more back pressure? No, it does it because the gases at traveling at a higher velocity at a given rpm then in a 2-1/2" system and they have more energy and "should" be able to help the header scanvenge better in the low range. And the 2" system can still have little to no back pressure depending on the rpm. But as engine speed is increased, so will flow and you get to a point where it becomes work for the engine to move the gases and the down stream pressures of the exhaust system rise and power falls. But this range happens to be in an area where performance will shine for a larger system. So, I'm back to the question where do you want the bulk of the power to be?

When we tested my header and cat back system on an ITR, the power actually dropped when we ran open header. This happened because the energy from the exhaust flow was discipated into the atmosphere and not used to extract gases from the header and not because the back pressure dropped below 2-6psi. But remember this was only on a dyno and a dyno is at best just another tool. At speed there may be a low pressure area right at the collector of an open header and then power would be increased since the engine would see a greater difference in pressure between the intake manifold and this helpful low pressure spot.

So, at least we both agree that we want a low pressure area at the exhaust valve right before it opens. But if you can do this while keeping the downstream pressure near 0, you will be able to inject more gas flow into the system before you start to build downstream pressure and increase pumping losses.

Intake manifold runners can actually see pressure spikes when the exhaust and intake charge flows are so high and efficient because there is so much momentum in the intake charge that it "piles" up in the runner and port as the intake valve slams shut. This obviously can help with volumetric efficiency if there is still pressure in the runner when the valve starts to open again.

Now the above discussion pertains to 4 cycle engines, most of this goes out the window when you bring in 2 cycle engines.

 

From Sport Compact Car.......like I stated. Nice info though!


[Modified by H22Si, 5:42 PM 5/15/2002]

 

Hmm maybe you read SCC you read the letter from the guy that prove the entire SCC article wrong then? He had dyno proof that 2.5 inch was better than 2.25 as in the stated ranges put out by SCC...