[OoThomioO]

Carrying over from the thread me and elec were cluttering up, I'd like to start it here.

My argument is that the limit of exhaust size is merely sound vs gains. Whereas increasing to the next size (let us say in .25" increments) will eventually produce more sound versus gaining smaller amounts of hp, not losing hp.

Quicker the exhaust exits the turbine, the quicker spool you will see. Which means the less restriction behind the turbine, the better.

3″ Exhaust Too Big for your Turbo Mini? » PERRIN Performance Official Blog
Perrin, a huge name in the industry, also states what I'm trying to get the point across.

Please no name calling, this is not meant to anyone in particular but I want to have a serious discussion to squash this. I don't care if you rather 2.5" exhaust, it's your money do with it what you must. For the people looking to squeeze power and are already planning on getting their exhaust setup made, I urge you guys to read up before buying 2.5" piping for the "most power".

Now I will apologize for making us start over in a new thread, I guess I should have done that in the first place instead of clogging the dude's thread up : /.

 

[TheBlackBass]

In my reading on the theory of exhausts I have found that basically smaller pipes give you more exhaust velocity and will give you better low end power. Larger pipes give you more power on the higher end of the power band when trying to push more volume through. I believe this true regardless of turbo or NA. A turbo is already big restriction on exhaust gases and for best spooling the pressure difference before and after the turbine needs to be as high as possible each exhaust cycle.

With the new laws regarding fuel efficiency, car makers have pushed their designers to be more and more efficient with fuel so that there doesn't have to be many HUGE design changes such as making more cars hybrid. This is why you are seeing so many '13s coming with turbos. Our exhaust system is horrible by any means, VTs are getting 125hp/liter. But it can be better. I think for almost every purpose, a mandrel bent 2.5" exhaust with better flowing muffler would be most efficient in terms of money and gains. Yea a 3" would probably get you a few more HP but I believe you would only see that at high RPMs, the rest of the power band I don't see being different from a 2.5". IMO the most cost effective is 2.5"

As for sound. A normal NA engine will send a pulse of air through the exhaust, combined with different lengths, sizing, and restrictions you end up with the exhaust sound you hear. The more restrictions the more the pulse becomes stretched out. To make an extreme illustration if the exhaust were long enough you could reach a point where there is no longer a pulse and it would most likely just sound like air blowing through a pipe. It's an exaggeration but it illustrates the point about restrictions on the pulse of air. The less restriction the better that "pulse" is able to hold it's shape so to speak. When you increase the diameter of the exhaust this pulse widens and becomes shorter making it kind of sharp. Like a pop almost. A small diameter squeezes the pulse, elongating it and speeding it up. This also gives a different sound. A turbo is a huge restriction already so you need an exhaust that can get the air out as quickly/smoothly as possible yet can handle the volume of full boost and high RPMs. The change in air volume makes tuning the exhaust for sound on a turbo a completely different animal. What may sound great at higher RPMs could sound horrible and lower RPM, or vice versa.

All in all, I think the performance to cost the 2.5" to 3" is really just comes down to personal preference for the sound. With mandrel bent piping and as few restrictions as possible a 2.5" exhaust would handle everything the stock motor and turbo could put out. That includes tuning, raising boost, intake mods, down pipe, everything. Once you get into the realm of a larger turbo then you may want to consider a 3".

I wrote this over an hour with many interruptions. So if some of it seems disjointed I apologize. I haven't installed tons of exhausts and worked in an exhaust shop so my personal experience is limited. I'm an engineer and studied this stuff a lot in school and after so I'm looking at things from a more theoretical viewpoint.

 

[OoThomioO]

Your first paragraph isn't wrong if you think of it as being the turbo manifold/header. The turbo manifold/header is where the Exhaust Velocity and scavenging happens in turbo cars. Once the gases pass the turbine, the least amount of resistance will help the gases escape the turbine the quickest resulting in faster spool.

As far as the stock exhaust is concerned, it is restrictive as any stock exhaust is due to emission standards and cost of production. They have to please both of those worlds the best they can.

I would rather keep the tuning of the exhaust note out of the discussion other than the fact of overall loudness. Whereas trying to discuss how to make a car sound good or bad (in your/mine/their) opinion will be all personal preference.

I also am not stating that 2.5" is too small and I agree that with mandrel bent piping and the fewest restrictions possible will lead to getting the best out of the 2.5" system itself. But what you are doing there is removing restrictions (smaller pipe diameter is a restriction compared to bigger pipe diameter) of that pipe, the same thing I am talking about overall. The less restrictions after the turbo, the better

 

[TheBlackBass]

The less restrictions after the turbo, the better

After everything, that's all it boils to. All an engine is, is a glorified air pump. The faster you can get air into and out of the engine, the more power you will make.

 

[[email protected]]

Your first paragraph isn't wrong if you think of it as being the turbo manifold/header. The turbo manifold/header is where the Exhaust Velocity and scavenging happens in turbo cars. Once the gases pass the turbine, the least amount of resistance will help the gases escape the turbine the quickest resulting in faster spool.

As far as the stock exhaust is concerned, it is restrictive as any stock exhaust is due to emission standards and cost of production. They have to please both of those worlds the best they can.

I would rather keep the tuning of the exhaust note out of the discussion other than the fact of overall loudness. Whereas trying to discuss how to make a car sound good or bad (in your/mine/their) opinion will be all personal preference.

I also am not stating that 2.5" is too small and I agree that with mandrel bent piping and the fewest restrictions possible will lead to getting the best out of the 2.5" system itself. But what you are doing there is removing restrictions (smaller pipe diameter is a restriction compared to bigger pipe diameter) of that pipe, the same thing I am talking about overall. The less restrictions after the turbo, the better

actually most of what black bass is saying is correct, however thomio exhaust velocity is NOT dictated by the manifold/ head, and the less amount of restriction the better is true to a point.. gasses/ fluids always flow from high pressure to low pressure so you always want to keep a small amount of positive pressure in the exhaust so that way the exhaust is getting both pushed and sucked out of the exhaust however you do not want to reduce the restriction so much that the outside air has a higher pressure field then the air inside the exhaust .. the object of an exhaust is to remove the exhaust gases from the engine and dumb them to an area out of the car away from people. You want to do this as quickly as possible, that does not mean you want to get the largest exhaust you can fit on there as the gases will become stagnant in the pipes if you go too large as there is not enough velocity / air pushed by the engine to get them to exit out behind the car.. it's all a function of the length of the exhaust if you have a short little exhaust then it's not a problem to have a larger pipe on there because the air is hottest right by the engine so it will easily fill the diameter of a larger pipe as hot air is not as dense. HOWEVER on a longer pipe as the exhaust travels the length of the pipe it cools off and condenses, which means the gases will not be travelling as fast.

now i'm not saying 3" exhausts don't have their place at all however on a car thats running stock turbo there is not a need for them. There are alot of things that can be affected by running an exhaust larger then what you need decreased low end torque and a drop in MPG are 2 things that are prevalent and they are both function of the fact that the turbo can be spooling slower so it needs more engine load to help spool the turbo.

velocity is a property of the complete system and scavenging can be effected by an improper setup but is not directly related to exhaust velocity. ie you can have terrible scavenging but a proper exhaust setup due to having improper manifold runner sizes, improper runner lengths, improper collector design, improper firing order.

there are alot more things to consider then just "bigger is better" for turbo cars..like I said when i drop my car off for R&D i have no problem asking the company to make both 2.5 and 3" setups and dyno the difference. I will not deny that a 3" might make slightly more peak however it also wont make for the best car to dd either area under the curve is always much more important as far as gains go then peak is.

if we brought the VT up to closer to 300 whp then it would START to be a warranted mod however it's a ways off before it makes a overall positive gain. I run a 3" exhaust on my saturn ion, however that car pumps out around 380 whp... if your theory was correct that bigger is always better.. then I should be running at least a 3.5" exhaust.. which is not true at all.. there are cars that run 500-600 whp and are running a 3" exhaust without it effecting power output. in essense you want to keep the exhaust the smallest you can without it raising boost (this is much harder to quantify on newer cars or cars that have electronic boost solenoids as they will shoot for x psi regardless of exhaust so you might actually go too big but its possible the computer might've "compensated" by "adding boost" to keep it at the desired psi.. it really depends on how the car is tuned.. is it an engine load based setup, air flow based setup or just target command setup.

 

[Aries86]

wow thats pretty interesting, i was expecting at least a little low and loss but it was like a constant gain. makes me wanna go put together a 3" exhaust lol
i could see how different engines would react differently though. maybe hondas just like 3"
i would love to see an eco motor do the same thing that they did with the different exhaust and mods

 

[snail powered]

I was running 2.5 from dp back on my turbo civic. My buddie kept telling me to go 3 inch. With the 2.5 i made 220 whp and 170 tq on a 1.6 single cam honda on 8 psi. I finally went 3 inch from dp back and made 16 more whp and 20 pounds more of tq. It flows better in my book. Now it was a tad laggie it was at full spool at 4300 rpms and reved to 7500 rpm. But we do have fwd cars so the little lag made it to where it wasent blowing the tires off instantly and she spun a tad in second it was a very fun car.

 

[Turbosocks]

again.. on a turbo, there is no 'too big' you want the least restriction possible after the turbo, period...

Yeah, you can waste money going too big because you aren't flowing enough to get gains from a big 4" exhaust but it isn't going to be bad.

Also, pipe sizing matters just as much as the design.. If you made a 5" system of loops, bends and mufflers then it can flow like crap

http://www.turbosocks.com/Turbo_Exhaust_theory.pdf

 

[mwil028]

hey socks are you the friend or the engineer?

 

[Turbosocks]

haha

this is just a copy of an article I found online. I wanted to preserve it, so I uploaded it to my website so it would live forever!!

 

[mwil028]

haha

this is just a copy of an article I found online. I wanted to preserve it, so I uploaded it to my website so it would live forever!!

Ah thank god u aren't the engineer. I would have to hate you. Lol.( Sorry engineers.)

 

[Turbosocks]

I am an engineer of sorts, just not Mechanical. I am working in the Civil field.. Weird huh? Working in the Civil field while running Turbosocks on the side.. makes plenty of sense

 

[mwil028]

Civil!! even worse lol Im a property manager and do alot of construction. I do alot of work with Civil and Mechanical engineers. They tend to make my projects hell. lol

 

[Cinderblock7881]

This is a can of worms I am surprised someone wanted open. I am no engineer, and hvae only ever home built one exhaust, but Having dealt with race cars, and drag cars most of my life, there must be some credit in the fact that the land speed cars, or high hp cars just straight dump the exhaust from a turbo as soon as possible, out as big of an outlet as possible lol. We have seen the dyno numbers for a 2.5" system, and a 3 inch system, and the 3 showed slight gains all around if I remember right. Sure they were on two different cars so you can argue that fact. But I am sure I am not the only one who has seen the pics of that Magnaflow system for sale, and the SS pipes on that thing are gold as Fuuu or even near blue in some bends, meaning this system carries plenty of heat all the way to the rear, and still catches some restriction in the bends of a 2.5" system.

pale yellow 290 straw yellow 340 dark yellow 370 brown 390 purple brown 420 dark purple 450 blue 540 dark blue 600
here is another chart.

That is a chart that I found stating what temp SS changes at. so the exhaust is staying pretty hot still, plenty enough on a 2.5 to evacuate to a low pressure area.

 

[tjmath13]

I have 1 3/4 primary long tube headers with 3" collectors and a full 3" exhaust on my NA truck. Works perfectly for being NA. I have a friend with the same truck that he added a 76mm turbo to. He has a 5" DP that is straight piped and dumped behind the cab of the truck. Same sized engine, his cam specs are a little different than mine, but he has 5" exhaust.

Another friend professionally builds turbo kits for various cars/trucks and his philosophy with exhaust size behind a turbo is to use as large of an exhaust as you can. Limit the restriction so the turbo can breathe. Faster spool means you're into boost faster which nullifies the age old "too large of an exhaust and you lose low end power/torque".

 

[NEVL666]

again.. on a turbo, there is no 'too big' you want the least restriction possible after the turbo, period...

Yeah, you can waste money going too big because you aren't flowing enough to get gains from a big 4" exhaust but it isn't going to be bad.

Also, pipe sizing matters just as much as the design.. If you made a 5" system of loops, bends and mufflers then it can flow like crap

http://www.turbosocks.com/Turbo_Exhaust_theory.pdf

I read something similar to this before, but one thing makes me question Solo's design .. those two 180deg bends after the muffler. Do they add unwanted backpressure to the system, or is the oversized 3" tubing compensating for that? I know these bends are what give the Solo it's deep growl .. but is it at the expense of a few HP?

Quoted from your article:
"Other things you can do (in addition to choosing an appropriate diameter) to minimize exhaust backpressure in a
turboback exhaust are: avoid crush-bent tubes (use mandrel bends); avoid tight-radius turns (keep it as straight as
possible); avoid step changes in diameter; avoid "cheated" radii (cuts that are non-perpendicular); use a high flow
cat; use a straight-thru perforated core muffler... etc.”

 

[Cinderblock7881]

The dyno chart for solo pretty much disproves any thoughts that it robs power I would think. And I would gladly sacrifice maybe 1-2hp for the sound (but this is about performance not sound) So in all technicality, yes the bends could be robbing power, but they are very large, medium radius bends, with very little restriction to them at all.

 

[NEVL666]

.. I would gladly sacrifice maybe 1-2hp for the sound ..

Don't get me wrong .. so would I :wink:

 

[Turbosocks]

What I still believe to this day and even shown on their site of what they did is do the U bends for their amazing sound. I believe the choice to bump it up to 3" was to compensate for U bends.

Is it robbing any power in stock form, of course not. All of the catbacks that are out right now are all relatively great systems performance wise and will be for the typical bolt ons. Besides the Jun BL system of course with their less than impressive 5.5hp and 5.0ft.lb gain.

With a turbo upgrade, would a Magnaflow-bent style system in 3" probably perform better? I would bet money on it.

I have the Magnaflow and I love it. I felt a noticeable difference with it over the stock system with a muffler delete. Jeremy has the Solo and it sounds absolutely amazing and the car gets up and goes.

I do think that the Solo will have a slight edge, despite the U-bend setup when people start going up in bigger modifications (wheels, ported manifold/turbine/compressors) but hardly enough to show up on a dyno with any accuracy.

If there was a 3.5" system that would have cost me the same as my used MF catback and didn't sound like a broken helicopter, I would have slapped that on the car since it is boosted.

 

[Cinderblock7881]

lol, well said Socks. well said.