Aftermarket Exhausts?

[trackmagic]

Straight/minimum bends does not affect the performance as much as you might think.

Do a search for "Formula 1 exhaust"

They snake the exhaust in there because the most important thing is the length and mostly on the header. After the header there is very little performance gains in the rest of the exhaust system. I'm sure it helps a little, but don't expect huge gains from the tailpipe.

I think I heard the FRS exhaust does have equal length headers? That's a pretty nice standard feature.

[Draco-REX]

Originally Posted by trackmagic

Straight/minimum bends does not affect the performance as much as you might think.

Do a search for "Formula 1 exhaust"

They snake the exhaust in there because the most important thing is the length and mostly on the header. After the header there is very little performance gains in the rest of the exhaust system. I'm sure it helps a little, but don't expect huge gains from the tailpipe.

I think I heard the FRS exhaust does have equal length headers? That's a pretty nice standard feature.

Yup, it's a 4-2-1 header. But right after the 1 it hits the primary cat. Moving that downstream will help quite a bit, I think.

[Dimman]

Originally Posted by Gardus

That doesn't look very good, why so many welds, you can make that with just one bent pipe and it'll be lighter and stronger. The problem with NA engines, especialy 4 pots in small cars, it's they tend to drone. A transversally mounted mufflers helps, and doesn't really affect the power much. I've seen that HKS went for a helmotz resonator on its louder system. We use it sometimes but it's heavy. As the market will be floaded with catback exhausts coming from the same factories in taiwan and china, we'll concentrate in making the best header+cat kit we can.

What's funny is the site says 'minimum welds'. Heh. Pie-cuts are not 'minimum welds'...

But it also says it is a full titanium system and depending on the capabilities of the company that is probably why they used pie-cuts. No access to a CNC mandrel bender and you can't buy pre-bent sections like you can with 304 and 321, so to make the bends they had to pie-cut.

This leads to a couple things. First it shows me that the manufacturer is not taking the best way to make it. Since they are not doing the basics as best they can, I would have less faith in the titanium weld quality of all those pie cuts. And there are lots of them. Plus they've been polished after the welding, so it is tougher to judge the quality there, too. Lastly they just call it 'full aerospace grade titanium alloy' with no reference to its alloy or spec (MIL, ASM, ASTM, etc...).

I would pass on these.

[mattles]

while equal length headers are great for performance, it more or less eliminates that wonderful rumbly exhaust notes other boxer applications are known for. Yes I am a ricer. I bet a competent exhaust system could be built to introduce a little rumble-rumble without losing any power.

[serialk11r]

Originally Posted by Draco-REX

Yup, it's a 4-2-1 header. But right after the 1 it hits the primary cat. Moving that downstream will help quite a bit, I think.

Naw from the pictures it looks like the "2" are cut short, and immediately hit the precat. The primary cat is a long way off.

I don't know how the pulse interference and scavenging usually go, but I imagine this cuts off some of the...tuning options.

[Draco-REX]

Originally Posted by serialk11r

Naw from the pictures it looks like the "2" are cut short, and immediately hit the precat. The primary cat is a long way off.

I don't know how the pulse interference and scavenging usually go, but I imagine this cuts off some of the...tuning options.

Hmm, been a while since I looked at it...



Yup, you're right. Either way, I'm sure there's some power gains by moving that cat downstream or removing it all together.

[serialk11r]

I dunno exactly how important the precat is for startup emissions, but seeing the O2 sensors before and after it gives me the suspicion that removing it will make the ECU go nuts.

[MarkRacerX]

Originally Posted by serialk11r

I dunno exactly how important the precat is for startup emissions, but seeing the O2 sensors before and after it gives me the suspicion that removing it will make the ECU go nuts.

Yeah good call, simple trick is use an o2 spacer so o2 after a pre-cat reads cleaner air as if it were going through a cat. Basically people drill out those Spark plug Anti foulers and thread into o2 bung, thread o2 sensor in and set. Nice simple trick when eliminating a Pre-cat with sensors on ea side

[Subaruwrxfan]

Originally Posted by MarkRacerX

Yeah good call, simple trick is use an o2 spacer so o2 after a pre-cat reads cleaner air as if it were going through a cat. Basically people drill out those Spark plug Anti foulers and thread into o2 bung, thread o2 sensor in and set. Nice simple trick when eliminating a Pre-cat with sensors on ea side

Yep, this is what I did with my Legacy GT when I went with a catless up-pipe.

[Godzpeed]

waiting to see what Amuse have to offer!

[OrbitalEllipses]

Originally Posted by MarkRacerX

Yeah good call, simple trick is use an o2 spacer so o2 after a pre-cat reads cleaner air as if it were going through a cat. Basically people drill out those Spark plug Anti foulers and thread into o2 bung, thread o2 sensor in and set. Nice simple trick when eliminating a Pre-cat with sensors on ea side

Yep. $5 fix.

[Gardus@Supersprint]

On recent engine the spacer thing doesn't really work well. You can use a mini-cat like the Bonalume HKS but that doesn't always work as well.

A good solution will be to make a manifold with longer stepped primary pipes.

A 4 into 1 collectors could be placed where the 1st stock cat is, this will make the manifold interchangable with the OEM one. The volume of the primary pipes will be much increased and backpressure will drop a lot, but you won't have a step on the exhaust ports.

You'll need to extend the lambda wire and put the bung after the 2nd cat, so you won't need to spend more money on a sports cats.

We did this on the Opel Corsa OPC/VXR, we removed the 1st cat with a pipe only downpipe, kept the secondary cats and moved the O2 sensor after it insted of betweend the two cats. With the catback this brought the power up to 201 hp from 189.

Obviously we need to experiment to see how this engine works with a manifold of this design, maybe it will gets power in the high rpm range but lose torque.

We could also make the primary pipes and a 200 cpsi sport cat as a single kit that replaces the full OEM header/1st cat/2nd cat section, with a 4-2-1 design that uses all the space available.

Obviously there will be also a fully catless option.

A mobile joint will be present to replaces the flex pipes on the stock manifold.

I'm thinking something between this:

It's an exige stepped 4-1 manifold, you can see the stepped design, the minimum number of welds and the 4-1 collectors, plus the flange thas is part of the flex joint, you can see in the full system pictures:


And this:

It's a 2L impreza headers. You can see the joints that allows the espansion of the primary pipe sand also the flex connection for free engine movement.

It'll be a complex design so it won't be cheap but I expect to see a very good power increase. Usually with this kind of design we can get from 15 to 25 hp from a 200/250 hp car.

[Draco-REX]

The O2 sensor in the picture is pre-cat, so removing the cat in the manifold won't effect it. The downstream sensor should be after the last cat, which would put it near the transmission. So that shouldn't be thrown off by removing the manifold cat either.

Likely a high flow cat in the mid pipe and the mods listed above should be enough to fool the downstream O2. Though once the ECU gets picked apart, it'll be a simple matter of just turning off the cat efficiency codes.

[Gardus@Supersprint]

You always have a precat and a postcat O2 sensor, you need to keep the precat one when the primary pipes merge, but sometimes if you go too long with the p.p. you got errors as the delay of the sensor doesn't match the time the gas needs to reach it.

The post cat sensor needs to be placed where the gas has the correct value, if you fit a single sports cat after that, if you remove the 1st cat and leave the 2nd after that. Usually the sensor wire needs an extention.
The distance of the sensor from the gas flow, the position on the pipe and the inside diameter of the bung can be tweaked to get the correct reading and avoid CEL.

Obviously if you have the possibility to modify the ECU in a way you don't get CEL anyway it's much easier.