straight pipes

[Phil]

anyone running straight pipes?.. (no 2nd cat, no muffler juss straight 2.5 or 2.25) is it tooo loud? annoying? hows it on the highway? what are the gains like?

[doughboyr6]

pearly had a straight pipe....i think he mentioned the gains were noticeable....

if you go to mazda3forums.com there are several members there that have or had this set up....general concensus is ... GOOD...

aparantly, del of the 2nd cat frees up a lot of power on the M3, but it is also noticeable louder. The sound is mint from the clips i've herd...a lot more raw/edgy. But again, quite a bit louder.

Gains are if i remember correctly about 6-8 WHP

[Phil]

thanks alot.. i duno if its the search features or what but i cant find anything on guys running straight pipes. clips reviews stories nothing... on either of the sites. but thanks man

[Kevin@nextmod]

I had a straight pipe but i had a HKS muffler. As doughboy said, gains were noticible but it became very loud. But on the highway gaining speed was never a problem.

[3GFX]

This reminds me of a 'Sport Compact Car' article I read a few years back.

Here's my 2 cents on straight pipe. AWESOME, but its dumb for daily driving. To loud (ticket?) and the power isn't gonna be that much a differance in daily driving.

Solution? When installing a new exhaust make the cat and muffler removeable. Weld on flanges that allow you to swap out your cat for a straight pipe, a simple unbolt swap out, swap in, bolt on. That way if you track the car or something, you can have those few extra ponies at no cost!

[Gizzmo_jr]

Where can you pick up a race pipe for the 2nd cat? Or can I make one out of a 12" 2inch pipe, some flanges and my welder?

[GreyGun]

From what I understand, having SOME backpressure with these kinds of motors is to your advantage....more power. My bud lost 6hp with a straight pipe in his 2.3GT.

[Sean80]

Where can you pick up a race pipe for the 2nd cat? Or can I make one out of a 12" 2inch pipe, some flanges and my welder?

www.trubendz.com You can get a set up where the high flow cat can be swapped out with a race pipe there.

[FLIPDADY]

Don't forget to say hi to the cops for me when you get pulled over this summer.:)

Throw a muffler on the car with a high flow cat.

[Skarbro]

Don't forget to say hi to the cops for me when you get pulled over this summer.:)

Throw a muffler on the car with a high flow cat.

And also say hi to the DriveClean people when they tell you that your car fails the DriveClean test and you have to spend money to fix it! :chuckle

Ok that MIGHT not happen. But why take the risk?

[garboui]

From what I understand, having SOME backpressure with these kinds of motors is to your advantage....more power. My bud lost 6hp with a straight pipe in his 2.3GT.

Backpressure is never good in any situation unless were talking turbo between turbo and engine with stock cams. People think the the absence of backpressure from removing resonators, cats, etc. is what made them loose power. Whats probably happened with their straight pipe setup is that they lost some power at their peak but gained somewhere else in the powerband.

I have seen cases where cars are dynod before and after resonator removal and after removal there was a decrease in peak power. It sure sounded good though. Unless the exhaust is tuned to a specific rpm band through 1. having equal length hedders and 2. length and diameter, then the gains attaines from running a straight pipe setup is not going to be very aparent. The only time when having too much flow is bad is when theres negative backpressure cause by scavenging, this is because the exhaust gases will actually start pulling the fresh charge out of the cylinder before the exhaust valve(s) close. In our situartin though where the exhaust is running the length of the car this "over scavenging effect" is not likley to happen.

The reason that any backpressure is bad is the same reason why having the stock airbox and resonating chambers in is that its restrictive. If theres backpressure than not all of your exhaust gasses are being exhausted meaning less fresh charge thats able to get into the cylinder.

Now, why was peak power lost? It all has to do with resonances. On a race car the pipes are tuned to produce their peak power under given operating conditions. The formulae to derrive the optimal length of pipes is based on variables that are directly related to the speed of sound. ie. temperature, atm pressure, etc... Since exhaust comes out in pulses its actions are not unlike a normal sound wave. In a straight race pipe the objective is to have the sound wave pull the exhaust gases out of the cylinder; letting more fresh charge fill it. This is why valve overlap is important. What happens is that when the exhaust valve opens a pulse of high pressure gases(a sound wave) exits the cylinder. When this pulse reaches the open end of the pipe the bulk of the gasses just flys out the end but there is a sound wave that it reflected back up the pipe. This pulse then does the same at the cylinder head as it reflects off the exhaust port. As this pulse form the lprevious combustion cycle travels down the pipe it creates a low pressure system behind it helping it draw out the exhaust so that fresh charge can be pulled in. This is also very similar to the same principals used in the desigh of n/a induction systems.

The reaason that having equal length hedders is important is because this same phenomonen(sp?) hapens right inside the hedder the only difference being is that instead of the sound wave reflecting from an open end its reflecting from the collector. After the collector its all about flow by getting the gases to the rear w/o creating any losses. This is why some V8 guys prefer shorty hedders for their better ability to producer power in the bottom end, and some prefer longer hedders for the oppasite.

Now in our case having a free'er flowing exhaust helps this cause it avoids impeeding the flow of exhaust gasses out of the engine. Our stock manifolds are not equal length and therefore exhaust gases tend to clump up and not cause too much of a scavenging effect. Allthough there is still a pulse wave produced by this that is directly related to engine rpm. This os why we add a resonator. As it name implies it resonates. This resonating helps set up more of pure tone that has a more or less even amplitude. The big factor in this is the resonators interior volume. Different frequencies will resonate at different volumes. Because of this different resonators can be used to achieve different peaks in the power band.

The only way to truly make a straight pipe exhaust effective is to have equal length hedders which allows for scavenging to happen at the ~same rpm across all the cylinders. Also important that it allows the exhaust to exit the collector with the pulses of exhaust all leaving one behind the next. After this like i said the rest of the exhausts jub is just to get these gasses to the back of the car with minimal losses.

Sorry about the lengthy post but being the engineer type i cant just debunk a myth without explaining why it is wrong.

[majic]

ertw ;)

[GreyGun]

Thank you for your insight. Come to think of it, his car was turbo'd and had a 100shot.

[Axela3z]

wow , interesting! thanks for thatman, i cant beleive i read all that hahaha

[ArManI]

the straight pipe is a custom pipe or product associate with a catback/exhaust line? (never understand the difference between these 2 terms... oh ya i should also add "muffler" wut is the diff for all that?)

[chinsterr]

Sorry about the lengthy post but being the engineer type i cant just debunk a myth without explaining why it is wrong.

Wow, i just read all of that. ERTW muahah :P