Secondary cat delete

[Rigaud]

No it wasn't hearsay but based on experience from several people here. Your exhaust is measured from CFM going in and out and you need some back pressure. By going too big you lose back pressure. I did mine based on maximum cfm, max hp I could ever get out of this 1.5L N/A. Before I did mine every custom shop wanted to convince me to do 2.5"............it's more common and in stock. Been doing this for 33 years, I did my share of mistakes when I was a kid but didn't have internet or anything much like in today's world.

2-1/4" pipes 408 cfm 185hp single
2-1/2" pipes 509 cfm 232hp single

Your engine put's out 106 HP at the motor and about 89whp.

Even Jason who races these cars gave you good info. ;)

This will be my last post for info.

Cheers

[tmontague]

Fair point. Hearsay was the wrong word, it was statements given from experience of other people that either had heard it from others or just knew based on their own knowledge.

What I meant was that no one that I had read about or heard from had actually ran a 2.5" exhaust on the Yaris and actually lost torque. Now this could be because the people that ran exhausts knew better and went w/ a lower diameter.

I did a lot of reading regarding CFM's etc and even then I still found conflicting advice unfortunately. In the end I chose to go with the mechanics advice as his rationale seemed sound.

If I find that I have in fact lost some low end, then in a year or two i'll have 2.25" pipes put in and then I can better experience the difference myself. Some things I need to experience myself before I can make a confident choice on what is better suited for me.

I'll keep this thread updated as I drive more so anyone down the road doing exhaust work can read about it and help them make their own decision.

The moral of the story very well could be that people on a specific car forum will know more about the said car than an experienced multi car mechanic. Time will tell

[LTHatch]

Glad to see you went outside the normal and experimented with a larger exhaust, the impressions and feedback you provide will help other folks in the future who wonder about a larger exhaust.
How is the engine response and torque between 2-3k rpm's?
At cruising highway speeds, do you pass other cars without downshifting or with less throttle then before?
How many miles have you put on the new system and did you do a ECU reset?

[jmanous]

Can anybody comment on why loosing backpressure is bad?

I would imagine that going with a larger pipe will result into lower gas speed
at low RPM, with that been the cause of loosing some power at this band.

[tmontague]

Thanks LTHatch, even when searching other forums I hadn't read more single case where someone actually experienced loss of torque from going to big so I wanted to see for myself.

I didn't reset the ECU when the exhaust was installed, not sure I that would do anything to not as the ECU is constantly updating as you drive. No CEL has been thrown which was expected.

To answer your Q's plus a bit of an update after about 300km or so here is some more info:

I notice I have to depress the pedal down a bit more when low shifting (~2000-2300rpm) as well as when in 5th it "seems" (need more driving to confirm) that the car isn't accelerating as fast as it did after my TB and Manifold port mod.

I'm going to do some high Rev shifts today to test it out more, but so far i"ve noticed a much faster pull at higher rpm's (around 4500+). Basically it seems to get to the redline faster than it use to.

In Summary:

Potential loss of low end torque between 2000 and 2700rpm
Gain in torque from 4500+rpm
No change noticeable from 3000-4500rpm

I actually am going back to Techtune next Tuesday for 2 reasons. The first being that when I hit large bumps (going into a driveway fast) the rear axle slightly hits the exhaust and the second being to get 2.25" pipes installed.

The owner I spoke with said that he'll install 2.25" pipe over the axle as it will allow a sharper bend than the 2.5" and that there is a lot of room there for him to work with still.

He said that would also increase back pressure to help torque. I just told him I'd rather just get 2.25" throughout an d he said no problem but that it will slightly change the noise. He said it won't make it quieter but it will clean up the "dirtyness" of the noise a bit.

I'm still going to keep my resonator off for now as I do like the burble right now and my fiancée surprisingly likes it to.

Now i'll get to compare how a 2.25" pipe is like which i'm looking forward to. From doing much more reading on exhaust i've come to the understanding that it no really back pressure that you want but velocity. Going too large a pipe reduces velocity which therefore reduces exhaust scavenging.

I understand I can't get the best of both worlds (high rpm hp and low end torque) but 2.25" might be the best middle ground where 2.5" gains are minimal in th top end over 2.25" but you take a larger loss on the low end torque.

The 2.5" pipe essentially felt like I went back to stock from the torque gain I got from my DC header. It's not a large loss at all, and probably not noticeable to most people. I use my Yaris Yaris a DD so I enjoy more low end torque. I am not running my engine at 6000rpm f an hour like people who track their car do. Other than some very spirited drivind each week in the country and a handful of hard pulls, I gain more from low end torque.

I'm looking forward to seeing the difference with the 2.25" installed. That will confirm others knowledge/experience on this forum that chimed in and offered advice. I'm just curious as to how large the torque difference is.

[tmontague]

Originally Posted by jmanous

Can anybody comment on why loosing backpressure is bad?

I would imagine that going with a larger pipe will result into lower gas speed
at low RPM, with that been the cause of loosing some power at this band.

Here's my take on it after a ton of reading from various viewpoints:

You don't want back pressure as this would slow down exhaust scavenging. Back pressure is often a misused term. You want exhaust velocity, this is what creates negative pressure and "pulls" or scavenges exhaust gases out of the engine.

Velocity is changed with diameter shape/size. Too narrow a pipe and back pressure increases which leads to slow exhaust velocity and poor scavenging and therefore a hindrance on performance. Too large a diameter and you also lower exhaust velocity even though there is little resistance to to exhaust gases to exit.

Think of a large hose with water flowing through like a garden hose. Assuming that the power of the water being pushed through the hose is always the same the only change in speed of the water comes from the diameter of the hose. The same amount of water will exit (unless the hose becomes way too small) but too large a hose and the water slows down. Too small and you reduce the amount of water that can exit. The right size is one that causes the water to increase it's speed (velocity) without being restrictive.

The reason why at high revs this is less of an issue is because the engine is pushing exhaust gases out at a much higher rate. In the water example above that would be equivalent to turning up the power of water being pushed through the hose. In that case a large diameter hose is less of an issue, but a low water power the velocity slows and it becomes problematic.

This is why Ferrari and a few others have variable exhaust so at low rpm's the exhaust is switched to a smaller diameter to keep velocity high. At high rpm's the exhaust is switched to a larger diameter to allow the increase of exhaust gases to escape but also keep the velocity high.

These variable systems are expensive so if you are going with a custom exhaust a middle ground is ideal. If you are building a track car a larger diameter straight pipe type would be good since you spend most of the time at high rpm's. For a higher performing DD you still want some low end torque so a larger than stock pipe that is still small enough to create a high velocity at lower rpm's is ideal.

I'm sure other's have varying opinions on this but the above is what I've come to conclude after reading through various experienced individuals opinions.

[jmanous]

Variable diameter? Wow... this is probably more expensive than a new yaris...

[Redbat01]

I would not worry about the difference between 2.25 and 2.5 inch diameter pipes if the engine is otherwise stock. A mandrel-bent 2.25 inch diameter pipe should flow just fine for anything up to 150 horsepower, maybe more. There are charts on the internet, based on scientific formulas, that deal with this issue.

The decrease in restriction associated with a 2.5 inch diameter pipe is negligible at this horsepower range. In other words, you'd accomplish nothing but hanging more metal underneath your car. Now, if you're running a twin-turbo 200 horsepower monster motor in your Yaris, that's another story!

[tmontague]

I'm also putting the stock resonator back on when I get my 2.25" pipe installed. Due to loosing the dirty sound I don't want to have to deal with the potential rasp I hate. Plus it is a little loud as of now and I'm thinking it'll get annoying in a couple months.

The stock resonator is straight through and won't restrict and with the larger pipes plus aftermarket turbo muffler the noise should still be loud enough minus the potential rasp.

[tmontague]

ad my Yaris up on ramps today to install my DIY splitter. Took a look at the exhaust. All welds are very good, bends are crushed bends not mandrel. They don't have the waves in the bends but they are still crush bent.

I am going to go down to 2.25" this Tuesday but I am stuck between a couple options:

1.Just simply swap out 2.5" to 2.25", I'm worried about reducing the dirtiness of the sound and it turning into a clean raspy sound which I don't want

2. Switching the 2.5" pipe to 2.25" and add the resonator back in (not the 2nd cat). This will reduce the potential raspiness but how much sound will I lose?

I really like the sounds now (I'll post sounds clips soon) but the mechanic stated that with the smaller pipes it won't quiet down but it will clean the sound up a bit. The sound is fairly loud and at the limit of my tolerance, but it has a nice burble to it. If it has any more rasp to it than I wouldn't like it. That is what my worry is with not adding the resonator back in.

Anyone have any experience when an aftermarket muffler, larger than stock pipes and either a resonator delete or with it still installed? Curious to the differences.

[20104dr]

I have a 2010 sedan with 2nd cat out. The piping is replaced with 2 1/4" from 1st cat to a 2 1/4 inlet/ 2" outlet flowmaster muffler. No resonator. Sounds good at lower rpms but at 4500-6000 rpms sounds kinda a tinie but its a 4bahger with 106hp. I also have a header and k&n air ram. At first, I took off both cats but the sound was just insane.

[tmontague]

Thanks for the input. I'm going to see if you can use a straight through muffler or a high flow resonator instead of the stock resonator. It should give me the best of both worlds.

My exhaust has slightly increased in noise this past week so i'm going to have to put something back in to quiet it down slightly an remove the slight rasp that occasionally happens.

I'm getting it done Tuesday so i'll let you all know the difference.

I miss the torque that I had before so going to 2.25" again and adding a resonator should help increase exhaust velocity again.

[tmontague]

New exhaust being installed tomorrow. Here is a link to a short video I took of the current exhaust set up. The revs are only to about 4500rpm as the car was cold at the time. Also because it was cold you'll briefly notice the higher idle.

https://youtu.be/fdX8bSedH50

*that not my girlish laugh in the video, it's the camera woman's ;)

I love the sound, but the loss of torque isn't worth it and it gets slightly annoying when it sounds loud at light 2500rpm shifts when i'm just cruising.

Current set up:
2.5" pipe straight to turbo muffler.
Secondary cat an resonator delete.

I'll post after tomorrow with the new set up sound.

[jmanous]

So is the low-end torque loss really noticeable? If so why not going back to 2" which
is stated as the optimal for the hp range?

In a previous post it was stated that the CFM when going from 2.1/4 -> 2.1/2 change
substantial, is it possible to have similar problems with the 2.1/4?

Sounds awesome though - although might be a little loud for a DD.

[tmontague]

It's not that noticeable to the point that is affects drivability. However, because I am pretty sensitive to changes in my Yaris I have noticed it when I am driving more conservatively and trying to low shift around 2,000-2200rpm. I feel that I now need to shift as at least 2500rpm to get a decent pull. This could also be that I'm used to accelerating a bit harder the past few months so when I do low shift I feel that it lacks torque and not necessarily due to the exhaust.

It seems to have essentially canceled out my torque gain with the header I installed. I'm going to 2.25" as I really like the high Rev gains I got from a 2.5" pipe. A 2.25" with a resonator installed back in should not cause any loss in top end just like the 2.5", but it should improve exhaust velocity and gain me back most of the torque.

I feel it should be the best of both worlds. Plus the pipes are crushed bent (not the wavy type) and the sharp bend above the axle could create a narrow restriction so I feel the 2.25" is ideal. On top of that a resonator will also help a bit with the low end.

Without a variable exhaust you have to be willing to give up a bit of one end to gain in the other. Now that being said this can be minimized by using an optimal diameter pipe and set up, but there may still be slight losses.

I'll let you know what I notice

[tmontague]

At Techtune waiting for exhaust work to be done. They had a 2.25" fin type resonator for an extra $100 but I decided to save the cash and go with the stock resonator which is a perforated type and 1.8" straight through.

The perforated type should keep the noise still some what higher but stil reducing the sharpness an raspiness. It alsoo will flow better than the fine type so it was a win/win for me.

[tmontague]

Alright, got my exhaust completed and have driven about 30km highway and about 2km city. Here is the sound clip, you can compare it to the one I posted above
https://youtu.be/Hqhis-4LDpI

So now i'm at the following:
Secondary cat delete, stock resonator is still there with 2.25" mandrel bent tubing down to an aftermarket turbo muffler.

Sound from my point of view as a driver is much much quieter. At first I was a little dissapointed with how quiet it became. No drone at any highway speed what so ever which was kind of annoying me before I changed the exhaust. As a DD it would've got annoying pretty quick.

No longer really loud at low rpm, but is still loud at high rpm. Although in the cabin it's never very loud, it's actually surprising how loud it still is outside the car but not obnoxious and not bad at low revs.

Stil has a low tone to it an most importantly my torque is back! Now when cruising @80km/h in 5th , don't have to shift down to 4th fo it to accelerate as quickly to 100km/h.

Still pulls fairly hard at high rpm, but maybe not at hard as before. I'll need more time with it to determine for sure. Seems to be getting slightly louder a I drive it, which is expected an a good thing.

Tech tune did a great job again and actually didn't charge me at all. I gave them some cash anyway for their time/parts as I know it'll pay off when ever I go back there.

I'm very happy with it, i'll likely be painting it black this weekend to help it hold up longer as it's aluminum.

Eveything is welded except for the muffler attatchment to the pipe after it comes over the axle to themuffler. This makes it easy to remove t paint. Just unbolt the exhaust donut gasket after the header, unbolt the uclamp that attaches it to the muffler and drop the exhaust.

I'll update with any tone changes and further performance changes. All in all very pleased with the exhaust and happy to deal with the shop I chose to go with.

[invader166]

Awesome feedback on this thread!! Thanks tmontague!!

Knowing all this, I've personally decided that my next exhaust job (once I save enough money) will be to replace the mid-section with a new Magnaflow unit.

http://m.ebay.com/itm/Magnaflow-Dire...962?nav=SEARCH

I honestly want to just stay as legal as I can but still have a slight performance benefit. Plus, both my header and muffler are stainless so I'd like to have it all the same material.