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Thank you! Can't wait to get it out to you!

Who would like to hear a (mostly) straight piped 981 Cayman race car? :)


-Mike
It better sound good... I'll ship that fecker back, packed tightly with dog $h!t! 🤪
kidding of course, I'm still new and yer still get'n use to my smarta$$

I'm confident that this will be the spark that ignites mods, mods and more mods.

As for the sound clip... umm, this is a F4T forum. If they had it I would insert the ToeTapping emoji
Again I'm just being a smarta$$ and poking fun at the whole GTS 4.0 mess. I don't care what it is, as long as it's motorsports related and goes fast!
 
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Discussion Starter #67
It better sound good... I'll ship that fecker back, packed tightly with dog $h!t! 🤪kidding of course, I'm still new and yer still get'n use to my smarta$$

I'm confident that this will be the spark that ignites mods, mods and more mods.

As for the sound clip... umm, this is a F4T forum. If they had it I would insert the ToeTapping emoji Again I'm just being a smarta$$ and poking fun at the whole GTS 4.0 mess. I don't care what it is, as long as it's motorsports related and goes fast!
You had better think it sounds good, or I'll ship it right back in a bigger box with some of my golden retriever's choice nuggets! :poop: Sarcasm aside, we do encourage anyone on the fence to try our products and it's not an issue to return if you want to switch to something else or have regrets - you shouldn't have to live with something you're not happy with. Sometimes you just can't judge from videos, and we'll support your leap of faith regardless of the outcome.

I apologize ahead of time for dumping fuel on your mod bug!

I think we can all agree that Porsche's sound great! I wouldn't really know anymore though, all the race car revving this week has left me partially deaf. o_O

-Mike
 

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You had better think it sounds good, or I'll ship it right back in a bigger box with some of my golden retriever's choice nuggets! :poop: Sarcasm aside, we do encourage anyone on the fence to try our products and it's not an issue to return if you want to switch to something else or have regrets - you shouldn't have to live with something you're not happy with. Sometimes you just can't judge from videos, and we'll support your leap of faith regardless of the outcome.

I apologize ahead of time for dumping fuel on your mod bug!

I think we can all agree that Porsche's sound great! I wouldn't really know anymore though, all the race car revving this week has left me partially deaf. o_O

-Mike
My 12 year old mastiff & boxer rarely have a solid BM, so I'll be using a funnel! On the positive side I've got plenty! :sick:

No worries on the downpipe, I'm confident it will meet my expectations. But its cool to know you all are in the Customer Satisfaction business! It's a rarity these days!

Tis a slippery slope when it comes to mods... I've been down the road more than I like to admit. But It's fun and you can't take any of this crap with you when your gone and I don't plan on leaving anything for the kids!

Can't wait to get mine.
should be sometime next week :D

Will be installing myself.
Lots of pics to follow.
You're gonna have to wait, because I shouldn't have to wait for anything... Merica!

One of my friends had a very confused look on his face when I told him I was installing myself. Just couldn't believe that someone would want to work on a car and said he'd rather write a check. 🤪
 

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Sort of off topic.

One of my friends had a very confused look on his face when I told him I was installing myself. Just couldn't believe that someone would want to work on a car and said he'd rather write a check. 🤪
Yeah. It all depends on how you want to get your fun. I used to do much of my own maintenance and loved it; now at age 70+ I like driving more and am fine with writing cheques. I still cook and bake though, and I have friends who can't believe that I don't just go to the bakery or use pre-cooked dinners.🤷‍♂️
 

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Does the catted downpipe have larger diameter than stock? I feel like it should to take advantage of more flow/power, unless there were no room.
 

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Sort of off topic.


Yeah. It all depends on how you want to get your fun. I used to do much of my own maintenance and loved it; now at age 70+ I like driving more and am fine with writing cheques. I still cook and bake though, and I have friends who can't believe that I don't just go to the bakery or use pre-cooked dinners.🤷‍♂️
Actually, the more I think about it... I too have been paying for things to be done that normally I would have done myself.

But... I'm very OCD about things and if I know it's not going to be to my standard I'll take it on to ensure it is.
 

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Does the catted downpipe have larger diameter than stock? I feel like it should to take advantage of more flow/power, unless there were no room.
I'm not sure if size changes, but bigger is not always better.
As you increase diameter you also decrease velocity.
With decreased velocity the gases have more time to cool further decreasing efficiency.
 

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I'm not sure if size changes, but bigger is not always better.
As you increase diameter you also decrease velocity.
With decreased velocity the gases have more time to cool further decreasing efficiency.
In terms of power it is better. The less back pressure the more efficient it is for the motor to breathe. Yes the velocity decreases but volumetric flow increases and along with that pressure drop.

Now in some cases you may lose low end torque if the diameter is too large l, but in most cases, there is more power to be gained. This is why most drag racers just install a piece of large diameter pipe only a couple of feet from the turbo exhaust side. They would also need to tune to ensure that the boost doesn't spike. But in our case with the 200CEL cat, it should be fine.
 

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In terms of power it is better. The less back pressure the more efficient it is for the motor to breathe. Yes the velocity decreases but volumetric flow increases and along with that pressure drop.
That was the universal truth for the NA engines.

Can anyone with engineering experience on turbos tell us whether a drop in back pressure helps or hurts the efficiency of the turbine (which moves with exhaust gases and by the modification proposed above they are slowed down).
 

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Here's an article that discusses this... is it the definitive answer? I don't know, but it is an interesting read.

I'm sure that Mike will chime in here with some better answers as well.

Peer Pressure
If you do your research on exhaust systems, you’ll notice that popular opinion is split between two schools of thought. Some will adhere to the notion that zero backpressure is best for exhaust systems. Others will say that backpressure is necessary to generate performance from the exhaust. So which one is correct? To get the right answer, you’ll want to consider what type of engine is in question. On turbocharged applications, an exhaust system that provides the least amount of backpressure is best. For naturally-aspirated engines, the answer is slightly more involved since exhausts on non-turbo vehicles need to accomplish two goals.

The first objective of exhaust systems is to create an easy path for exhaust to flow out of the engine while the piston is traveling from bottom dead center to top dead center during the exhaust stroke. If the exhaust system generates substantial backpressure during this event, the piston must use energy (horsepower) to move up the cylinder. The amount of energy used to counteract the backpressure is known as pumping loss. The best way to eliminate pumping loss is through the “bigger is better” philosophy of exhaust design.

Unfortunately, reducing pumping loss is not the only consideration for naturally-aspirated engines. The second goal is to establish the speed of the exhaust flow that will help draw in more air-fuel mixture during the valve overlap period – the period of time when the exhaust valves are closing and the intake valves are simultaneously opening. An exhaust system that sets an optimal velocity can assist in maximizing the filling of the cylinder with the combustible mixture of air and fuel. This is primarily the responsibility of the exhaust manifold (header) but a substantial amount of flow is determined by the exhaust system that is downstream of the exhaust manifold.

Team Members
As you can tell by now, the exhaust system consists of more than just the muffler. In reality, every component after the exhaust ports of the cylinder head(s) has an effect on the performance of the exhaust system as a whole. A bottleneck anywhere in the system could create a restriction that subsequently negatively affects engine output. The individual components of an exhaust system include the exhaust manifold (header) for naturally-aspirated engines, exhaust manifolds (turbo manifolds) and downpipes for turbocharged engines. Both turbo and non-turbo vehicles will have an intermediate pipe (B-pipe), catalytic converter, exhaust piping and muffler.

Commonly, OEM exhaust manifolds are constructed from cast-iron. These factory pieces are produced to channel gases from the exhaust ports of the cylinder head(s) to the remainder of the exhaust system. In most cases, OEM exhaust manifolds are very restrictive and extremely heavy. Replacing the factory exhaust manifold with an aftermarket offering can offer a less restrictive pathway for exhaust gases to exit the engine. In addition, most headers will provide a weight savings over the factory cast-iron pieces. In some cases, the OEM places the catalytic converter directly onto the exhaust manifold.All others will be downstream of the exhaust manifold. Much like the exhaust manifold for naturally-aspirated vehicles, turbo manifolds serve the same function to channel exhaust gas out of the engine. However, instead of sending it out to the remainder of the exhaust, turbo manifolds direct exhaust gas into the turbine housing of the turbocharger. From there, the downpipe sends the spent gases to the remainder of the exhaust system. For these turbocharged applications, eliminating any bottlenecks in the exhaust after the turbocharger’s turbine section is an easy way to make more power. Like previously mentioned, a “bigger is better” philosophy is most effective on turbocharged engines and free-flowing exhaust systems need to be in place from the turbo all the way to the exhaust tip.

Material Possessions
Exhaust systems can be constructed from a host of different materials. The most common metals used are mild and stainless steels. While the weights of mild and stainless steel are comparable, stainless steel is much more resistant to corrosion, whereas mild steel is very susceptible to rust. When deciding which exhaust to buy, take notice of which grade of stainless steel is used. Some exhaust manufacturers use T409. T409 has enough chromium and nickel to resist corrosion but it is not as strong as T304. T304 alloy has approximately 20-percent chromium and 10-percent nickel, which allows it to be even more corrosion resistant than T409. If reducing the weight of your car is a requirement when replacing your exhaust system, you might want to look into exhausts constructed from more exotic materials such as titanium. Titanium alloys can offer the same strength of steel at just half its weight. The mechanical properties of titanium can also make them very desirable in high-temperature applications. Although it may sound like all exhausts should be made in titanium, the processing and manufacturing of titanium alloy tubing adds considerable cost in comparison to stainless steel construction.

Don’t Get Bent
In addition to the materials used in the construction of exhaust systems, the design and manufacturing process largely determines the end performance as well. At the simplest level, the diameter of the exhaust piping needs to match the demands of the engine. Like previously mentioned, bigger is better on turbocharged applications. Non-turbo applications will need to be more finely tuned in order to determine the optimal exhaust piping diameter. It’s important to know that the diameter of the exhaust and the sound level emitted are directly related. The larger the exhaust, the louder it will be. Many manufacturers complete decibel testing on exhaust systems, use this data to get an idea of how loud your car will be.

To fit each vehicle’s specific chassis, exhaust systems will have numerous bends in the piping to route the exhaust to the rear of the vehicle. A high-quality exhaust should be mandrel-bent as opposed to pressure (crush) bent. Pressure bending creates a decrease in diameter whereas mandrel bending maintains the tubing’s original diameter after the bend is made. This is due to the material being allowed to stretch on the outside of the bend and compress on the inside during the bending process. The precise execution of the exhaust systems’ bends plays a major role in determining the fitment of the system. Maintaining clearance to other components is critical in the design of high-quality exhausts. Rubbing, rattling and vibrations create unpleasant noises, unnecessary wear and even failure of some components.

Exhausting Options
The most common exhaust offering is the cat-back system, which gets its name because it replaces everything downstream of the catalytic converter(s). Many enthusiasts will opt to replace their factory exhaust with a cat-back system. While this option gives the appearance and sound that is desired by many, it may not give the best performance gain. In many cases, eliminating the factory catalytic converter(s) proves to add the most power. On turbocharged applications, the downpipes are typically the biggest bottlenecks in the system and thus aftermarket downpipes deliver the most performance out of all other exhaust components. Each application can respond to modification differently, so consult the tuners of your specific application to know your best starting point.

Pipe Dreams
This can be a lot of information to consider so don’t get overwhelmed by the options. Narrow it down to what fits your application and the goals you have for your car. From there, rely on your local tuners for further recommendations and use this article to sort through the various features.
 

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That was the universal truth for the NA engines.

Can anyone with engineering experience on turbos tell us whether a drop in back pressure helps or hurts the efficiency of the turbine (which moves with exhaust gases and by the modification proposed above they are slowed down).
It helps the efficiency but if you restrict it too much, you also increase EGT (exhaust gas temp,.) and put a load on the bearings. I've seen a turbo explode due to clogged cat for this reason. On the other hand if you open it up too much, the wastegate might not be able to control the inertia of the free flowing wheel as well.

I'm not a "turbo" engineer but have an undergrad in mechanical engineering and masters in Reliability Engineering, and been a backyard mechanic for 20+ years, mostly turbocharged cars.
 

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It helps the efficiency but if you restrict it too much, you also increase EGT (exhaust gas temp,.) and put a load on the bearings. I've seen a turbo explode due to clogged cat for this reason. On the other hand if you open it up too much, the wastegate might not be able to control the inertia of the free flowing wheel as well.

I'm not a "turbo" engineer but have an undergrad in mechanical engineering and masters in Reliability Engineering, and been a backyard mechanic for 20+ years, mostly turbocharged cars.
Well, we were talking about freer exhausts and their effect on the turbo. I've read that the lower backpressure and the lower exhaust gas velocity will affect the spool up time/turbo lag, which makes sense. I can also understand that the factory wastegate may not be able to deal with the volume of gas when you pull your foot off the gas.

My line of thinking is that Porsche engineers must have optimized the whole system. Aftermarket engineers, in search of more performance, will push certain attributes of the system, get the better performance, at a less optimized system. The question is, what are the repercussions of this less optimized system? That's what I am trying to find out.
 
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Discussion Starter #80 (Edited)
Does the catted downpipe have larger diameter than stock? I feel like it should to take advantage of more flow/power, unless there were no room.
The volume of area within the cat is increased. The piping itself is slightly larger but not too much as it is efficient enough for most vehicles. If you plan on shooting for massive power, like most components on the car you would want a bespoke race inspired setup which would include larger diameter piping through the exhaust to maximize flow - we're talking big turbo builds. Sometimes you have to work within packaging restrictions, like in the case of the the 718 once the downpipe splits the fitment is quite tight. If you only care about power and not sound you would likely do a large radius single exhaust straight out but this would drone considerably if you were to try and daily drive it. We're in the middle of designing race exhausts for 986-981 and the diameter of piping can impact volume and tone greatly - but we have the benefit of not needing to consider sound and civility so much as weight and power since they are for track use.

Naturally aspirated cars can have the exhaust setup engineered to optimize flow. The goal is to create a scavaging effect within the chamber to pull out the spent exhaust gasses by smoothing exhaust pulses and sizing the volume and length of runners, merge collectors, and piping length with that in mind. Engineers can pull more power out at certain parts in the power band through changing the runners - like a race exhaust would be tailored for higher RPM use where the motor is designed to maximize efficiency. On the intake side of things this can come into play with variable length intake manifolds like Porsche's VarioCam technology.

Turbo cars focus more on selecting the right efficiency range of the turbo for the intended driving style / desired performance, choosing an intercooler setup which maximizes cooling without causing a pressure drop by going too large, and optimizing power through engine tuning. As mentioned above you can get boost spiking by removing restrictions in an exhaust on a car that is designed to have it - you would need to tune this out - and we have experienced this on the 718 platform. We've seen McLarens have this issue as well.

It's common thought that you don't want to restrict the turbo, the more flow you get the more efficient the turbo can be. There is no tuning of the pulses coming from several cylinders as you're getting flow from one source. Some (older, Subaru) downpipes have plates in them to "divorce" the flow from the internal wastegate separately from the turbo. I had a Garrett GT2560R setup on a Miata which dumped the wastegate flow further down into the stream. We have an old F1 engineering book that claims the most efficient exhaust for a turbo is a cone coming off of the turbo that grows in radius as it protrudes - would anyone like a Competition Cone Exhaust? :)

-Mike
 
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