Installed Over pipe,no more low end torque?

[RedLeader]

Originally Posted by Calum

Nameless saw more power everywhere with a 3 inch exhaust vs a 2.5 inch.

They also decided to keep the factory midpipe because there weren't enough noticeable gains by swapping it out. The factory midpipe is 2.25"


Sent from...somewhere?

[charged86]

E=SmsAlSuwaidi;942598]how do you like the sound, we are debating running it on a new frs that we just got ![/QUOTE]

Originally Posted by SmsAlSuwaidi

sound wise how is it ?

Throaty not raspy. Not too loud not too quiet

[NickFRS]

after I did my overpipe/downpipe my car was running extremely rich. Go get a tune.

[mad_sb]

Originally Posted by RedLeader

Wrong verbiage, same effect; my mistake. Loss of exhaust scavenging causing a loss of low end torque.

Also, thank you for posting the link to that article, I was looking for it earlier but couldn't remember where I'd seen it. Now I can bookmark it for later when this question inevitably comes up again.

Yeah, i read a long article a while back that i cannot find now.. it was from a guy who set out to prove back pressure is a good thing. In every single one of his tests, the opposite was proven to be true :happy0180:

Originally Posted by Calum

Nameless saw more power everywhere with a 3 inch exhaust vs a 2.5 inch.

Very true, but to be fair, that was with the prototype long tube i believe, which significantly improves flow (reduces back pressure and improves scavenging) over stock.

Originally Posted by Calum

Nameless saw more power everywhere with a 3 inch exhaust vs a 2.5 inch.

True as well, but this was with the older header design and a 2.5" front pipe. For the 3" system to work, i think it needs to be designed and run together. I think bolting a 3" header back to the stock header would not make power due to the reduced velocity (and increased pressure as a result) at the transition.

Originally Posted by Sniper2606

I have the invidia catless pipe with q300

Do you have anyway to log your AFR? If not you could use the torque app and an inexpensive obdII adapter to get a better idea of what is going on.

I felt a slight gain everywhere even with the stock catback in place but I have brzedit and had already done a tune on the stock setup before adding the front pipe.

[Mikem53]

Originally Posted by RedLeader

As with most all NA cars, the more you open the exhaust, the more low end torque you lose. Exhaust back pressure helps scavenging, which is why going to a less restrictive, wider exhaust pipe in an NA car (from the 2.25 factory to a full 2.5 with no cats, resonators, and all straight through mufflers) will gut your low end but give you a much better top end.
It IS odd that you can feel it after a single piece, but not impossible. Rumor has it that it takes a 10hp/10 ft-lb change to be noticed, but I've never tried it.

^^^ This. Some Back pressure is your friend when it comes to low end torque..

[RedLeader]

Originally Posted by Mikem53

^^^ This. Some Back pressure is your friend when it comes to low end torque..

As corrected earlier, its not the back pressure you want, its the exhaust velocity. Ideally, we'd have high velocity with no back pressure, but that's a delicate balance point.

[Mikem53]

Originally Posted by RedLeader

As corrected earlier, its not the back pressure you want, its the exhaust velocity. Ideally, we'd have high velocity with no back pressure, but that's a delicate balance point.

High velocity is the result of back pressure.. Take a garden hose for example..
A 4 inch hose will allow water to flow freely and basically just fall out.. The same water pressure in a 1/4 inch hose will shoot out with lots of pressure behind it.
It's that resistance that builds pressure.. The balance point is where you have enough resistance to create velocity, but not enough to impede flow..

[RedLeader]

Originally Posted by Mikem53

High velocity is the result of back pressure.. Take a garden hose for example..
A 4 inch hose will allow water to flow freely and basically just fall out.. The same water pressure in a 1/4 inch hose will shoot out with lots of pressure behind it.
It's that resistance that builds pressure.. The balance point is where you have enough resistance to create velocity, but not enough to impede flow..

High velocity is the result of proper exhaust pipe sizing for a given range of RPM. A wider pipe will have better velocity at higher RPM (generally) while narrower piping has good exhaust velocity at lower RPM but has too much restriction and back pressure at higher RPM.

True, a 1/4" hose would flow water faster than a 4" hose, but there's a limit to how small you can go. You don't want back pressure, you want velocity. They are related, but not co-dependent. In other words, you want the widest possible pipe that still gets sufficient velocity, while minimizing back pressure. A garden hose isn't exactly the best analogy for this system because it has a steady stream of fluid flow, while an engine, no matter how fast it is spinning, never has a 100% steady fluid flow (air is a fluid). The increased velocity of an exhaust system can help create a vacuum at the manifold and help increase exhaust scavenging. THAT is why velocity is so important. However, if you just restrict the piping to increase velocity, you also increase the back pressure which will slow the exhaust gas down, thus negating your benefits. Back pressure bad, velocity good.

[mad_sb]

Originally Posted by Mikem53

High velocity is the result of back pressure.. Take a garden hose for example..
A 4 inch hose will allow water to flow freely and basically just fall out.. The same water pressure in a 1/4 inch hose will shoot out with lots of pressure behind it.
It's that resistance that builds pressure.. The balance point is where you have enough resistance to create velocity, but not enough to impede flow..

No, it really isn't. Your saying resistance to flow increases gas velocity and that simply isn't true.

[StormTrooper]

it's not that simple....water is not compressible while exhaust gasses are. You also have to take into affect head losses and temperature do to the size of the piping. This is why exhaust is generally not just a straight 4" pipe nor does it have right angle bends or large burs(unless you bought borla headers) it's also why headers matter more than anything else in the exhaust.

*I took fluid dynamics however i was mostly hungover

[Mikem53]

Originally Posted by StormTrooper

*I took fluid dynamics however i was mostly hungover

Lol.. I understand completely.. My example wasn't a good one..
I just know that proper sizing of the exhaust matters.. and from experience.. Every time I opened up the exhaust.. Some torque was lost to upper rpm HP..
In the V8 world.. That was an equatable trade off.. I wouldn't want to lose anymore low end TQ with this car..

[Mikem53]

Originally Posted by mad_sb

No, it really isn't. Your saying resistance to flow increases gas velocity and that simply isn't true.

I am not completely wrong here.. A smaller pipe say a 2 inch pipe will cause exhaust gas velocity to increase from that of a 3 inch pipe.. Both flows before the pipe being equal.. Like blowing thru a small straw vs same pressure thru a larger one.. The small straw will have a higher velocity at exit..
Obviously there is a lot to consider when designing an exhaust system and these principles are only a small part..

[Sniper2606]

Originally Posted by SmsAlSuwaidi

how do you like the sound, we are debating running it on a new frs that we just got !

[ame="http://www.youtube.com/watch?v=PTn6_Bttt6U&list=UUwpPOt3Y2bj6Fbb2o1UiNag& index=1"]BRZ with Invidia Q300 - YouTube[/ame]

The sound is awesome

[Sniper2606]

Originally Posted by NickFRS

after I did my overpipe/downpipe my car was running extremely rich. Go get a tune.

Im getting my vortech sc kit with visconti tuned, wouldnt that be enough?