4” exhaust system

[Francob]

Evening all,

Is anyone running a 4” down pipe and exhaust system ? If so any photos from underneath ?

Cheers

 

[Mpls24]

I have but don't think I have any pictures, what is it you want to see?

 

[Francob]

I have but don't think I have any pictures, what is it you want to see?

Thanks for the reply, I tracked the guy down on insta I was looking for, I just wanted to see the fitment and ask a few questions on clearance etc.

 

[JoeLanger]

I got a 4 in so going to 3.5 system.
Should be photos on my build thread.

It fits fine but I guess it depends on your mani

 

[Wolfie1]

There is not really any benefit to a 4” system on an fd unless your like at 800bhp

 

[Francob]

There is not really any benefit to a 4” system on an fd unless your like at 800bhp

I hear you but also think it’s good to future proof.

 

[Wolfie1]

I hear you but also think it’s good to future proof.

i used to work in a performance tuning place, and we had a 1060bhp track evo and it ran a 3” system with no issues, we did a lot of testing with it and the 1 thing that made the biggest difference to power was the intercooler core, ets gave the best out of 6 cores we tested, we did also try a 4” system on it and it didnt make any difference at all, take from that what you want

 

[Francob]

i used to work in a performance tuning place, and we had a 1060bhp track evo and it ran a 3” system with no issues, we did a lot of testing with it and the 1 thing that made the biggest difference to power was the intercooler core, ets gave the best out of 6 cores we tested, we did also try a 4” system on it and it didnt make any difference at all, take from that what you want

My main take from that is a still want a 4”, cheers though.

 

[Francob]

Here’s an interesting point of view.

https://www.facebook.com/STAVTECH/posts/1301413410035178

 

[Sturneyrx7]

I guess the real question is what are your goals? Yes the difference between 3” and 4” will be obvious, as it would be with 3” to 3.5”.

3.5” would be the relay to go unless you are planning on 600hp+

 

[Francob]

I guess the real question is what are your goals? Yes the difference between 3” and 4” will be obvious, as it would be with 3” to 3.5”.

3.5” would be the relay to go unless you are planning on 600hp+

My motto is why put a limit on it? Pointless me fitting a 3.5 to then rip it off 6 months later besides any help with spool is a bonus with the big ass turbo I’ll be running.

Regardless this post wasn’t to debate the performance benefit of different diameter exhaust, it’s was to see some pictures fitted, it irrelevant now as found what I was looking for.

cheers all

 

[Sturneyrx7]

My motto is why put a limit on it? Pointless me fitting a 3.5 to then rip it off 6 months later besides any help with spool is a bonus with the big ass turbo I’ll be running.

Regardless this post wasn’t to debate the performance benefit of different diameter exhaust, it’s was to see some pictures fitted, it irrelevant now as found what I was looking for.

cheers all

this is a fair point...if every applied to every element of your build and not just the exhaust...

but I get it was never the question you were asking

I would advise to consider the need for a full 4” exhaust system. The downpipe can be tight for space, underneath the car much worse and you could be making life difficult for yourself unnecessarily.

 

[JoeLanger]

The price of your downpipe is in labour, the extra material costs by going 4 inch is negligible.
If it fits,then go for it what have you got to lose?

 

[Francob]

The internet’s a weird and wonderful place.

 

[Mynameisjeff]

Evening all,

Is anyone running a 4” down pipe and exhaust system ? If so any photos from underneath ?

Cheers

Full 4” built and fabricated by Sam. Two boxes plus resonator thing and down turned pipe. Made plenty of noise and power. Plus all the flames blew the insides out and eventually sounded offensive

 

[Francob]

Full 4” built and fabricated by Sam. Two boxes plus resonator thing and down turned pipe. Made plenty of noise and power. Plus all the flames blew the insides out and eventually sounded offensive

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Nice mate, what was it like at motorway speeds ? Droning or ?

 

[Mynameisjeff]

It was decent on the motorway even with most of the interior stripped. Drove to Leicester and back in it with Jay mapping and didn’t get out at the end of the day with our ears ringing. Iirc it was 105db static at a rockingham no noise limit track day I went to.

 

[Francob]

It was decent on the motorway even with most of the interior stripped. Drove to Leicester and back in it with Jay mapping and didn’t get out at the end of the day with our ears ringing. Iirc it was 105db static at a rockingham no noise limit track day I went to.

That sounds ideal, thanks for the info.

 

[Marky]

That sounds ideal, thanks for the info.

Are you building the exhaust yourself? If so I have the old 4 inch system off my car from the middle box back,runs 2 Decent sized Magnaflow box’s and also a down turn adjustable angle tailpipe. Will need to be cut and tweaked to suit your car as I disn’t Have a stock fuel tank

 

[BenLewisMAV]

Interesting article from Stav as always, we've had quite a few interesting discussions about all kinds of tuning. He's one of those guys who is always trying and learning on his own stuff. When he ventured into the world of rotary he made some interesting experiments using aux. injection, sadly a simple mistake cost him the engine but we put it back together.
The example he posted on Stavtech was a high flowing piston engine, looking at the mods, 3inch could well have been a restriction. Turbo engines hate back pressure anyway but peripheral exhaust port rotaries hate back pressure even more!
4" will help spool for sure, so make sure you have plenty of wastegate.
If you have decent sized ports you might notice a big difference, but even with stock ports you'll see some improvement - flow, flow, flow!

Getting into it in a bit more detail, I think most people don't automatically go big exhaust because of what is historically available - most of the big brand japanese cat-back or high flow systems are maybe 3" and most motorsport/performance exhaust places stock up to 3", 4" is a bit more specialist. Most Japanese tuner exhausts are still designed to still fit around the stock packaging and some still consider the other factor - noise. Generally you need volume to remove noise, getting that silencer volume in place can be difficult if your base exhaust diameter is already ~100mm and you have any concerns with clearance, such as the ground.
You can do clever things with resonators and helmholtz but they typically only attentuate certain frequencies (say for example for a 4krpm static test ) but then they are noisy the rest of the time, so no good for a drive by test.

I live about 10min from castle combe so need to be able to get through the noise tests at 98db, which on a road legal track car makes it a balance of getting the car low to improve dynamics and aero, fitting the biggest silencer volume I can without hitting speed bumps on the way home, and accepting that I might lose a bit of spool (and torque that goes with it) and top end flow (and peak power that goes with it). With a medium Borg EFR turbo, spool and torque aren't actually an issue, it's keeping it under control and avoiding compressor surge and boost creep that's now the challenge. With my small ports, these issues would be made worse by a using a larger exhaust, but it's a pretty specific (and hp limiting) case.

With your larger ports and turbo (HX50 iirc?) they'll love the extra flow! And it's not impossible to get a quiet 4" just a bit of creative packaging and not as well trodden ground. Good luck and look forward to seeing the updates