Installed Over pipe,no more low end torque?
 

I recently installed the FT86 over pipe on my brz matching it with the q300 and catless pipe, right away ive noticed that i lost the nice low rpm torque the car used to have, i did noticed the car pulling better on 4th, 5th,6th gear which i enjoy but im trying to figure out where the low end torque went?

Thanks

That's interesting you say that. Do you have any other mods? It's common that most bolt on mods are geared toward the higher end of the rev band, but to be able to actually "feel" the loss is surprising.

Did you disconnect the battery for any reason? The ECU may be in it's learning phase, which can feel sluggish.

^^^^What he said. I've seen several posts here describing what you have experienced until they either:
a. reset the ECU via disconnecting the batter
b. giving the ECU time to "re-learn" on its own

Keep us posted on how it turns out!!!

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.

I'll give the ecu more time to understand, don't wanna restart ecu and have my radio settings all jack up again

Hopefully once I installed the vortech sc kit I can get that torque back

This is an old myth. The reason larger exhausts often loose low end torque is because of reduced velocity which hurts scavenging, back-pressure does not help scavenging it hurts it.

http://www.gomog.com/allmorgan/exhaustbackpressure.html

OP, i certainly did not notice a loss in torque when i installed my nameless over / front pipe. My guess is you may be running a little richer than before but i don't know what front pipe you have.

I have the invidia catless pipe with q300

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.

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

I have the same with sniper but with motiv overpipe. My car had the same feel. Give the car same time to react and adapt

I agree your AFR is probably a bit rich now. Its time for a tune :)

sound wise how is it ?

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?

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

Throaty not raspy. Not too loud not too quiet

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

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:

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.

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.


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.

^^^ 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.

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.

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

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

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..

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..

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

The sound is awesome

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

Sounded good at idle, similar to a Nameless axleback but when it picked up there was nothing much there. Lots of air and a little bit of attitude trying to get out but without much success.

i honestly felt a minor decrease in low end with the overpipe. with the ecutek tune it all feels better / more smooth now.

How restrictive is the OEM over pipe anyways? I can't imagine getting much of a gain given it's compact compartment to fit in.

[quote]A picture is easier to understand some times.
It would be if I could post it!!!!!!
[IMG]http://*************/forum/attachments/f16/5596d1372715617-nameless-performance-exhaust-image.jpg[/IMG]

you lost power at low rpm to install frontpipe decated resonated envidia?

we have low end torque?

Compared to an RX-8 or Miata, yes :lol:

The stock AVCS valve timing is tuned for much higher resistance and back-pressure. The ECU adjusts the A/F ratios automatically, (learning), but it doesn't adjust the valve timing, so when you change the resistance of the intake or the exhaust flow you need to re-tune the valve timing to compensate.
I use an OpenFlash Tablet and RomRaider software to adjust the tuning on my car, and it never ceases to amaze me how much difference tiny changes can make. The OFT off-the-shelf tunes for stage 1 and stage 2 have changes to the AVCS tables because stage 2 tunes are for cars with headers and less restriction in the exhaust.
You haven't mentioned any header. Are you still using the OEM header on your car? If you're not planning on getting a tune, or an OFT right away, I've just reinstalled my catted front pipe and immediately noticed how much more low-end torque I got back. I also average about 2 MPG better overall.
The best mileage and performance is still going to be with proper intake and exhaust valve timing and an unrestricted intake/exhaust, but I just haven't learned how to properly adjust the AVCS tables yet, so I put the OEM Catted front-pipe back on to temporarily give me better torque and mileage.

I changed only the rear muffler (top speed axleback) and apexi of substitution with oem air box .... necessary adjustment to your comment?

install the envy frontpipe thought silenced without catalyst .... this change would need the setting you said?

Thank you very much!

I also have the top speed axleback. Changing that alone reduces back-pressure, but still barely within the tolerance of the stock tune. When you also removed the restriction of the Catted front-pipe, you went outside the efficiency range in the stock ECU. The OEM ECU is setup for restricted airflow of both the intake and exhaust. You changed both the intake and exhaust restrictions when you replaced the air filter, muffler, front-pipe, and over-pipe. A good tune will bring the ECU back into the efficiency range, producing better power, torque, and mileage.

frontpipe not even install. I'm thinking about it, just frontpipe without overpipe.
Frontpipe + axleback ..... ecu reprogramming necesary?

very thanks for your responses