275 Downpipe or No downpipe?

Sports cat will be much friendlier to your engine as the stock one is very restrictive.

It's not only about max gain, but also on engine heat management, which brings longevity and power availability into equation.

 

You sure about that?

 

Having seen the stock pipe out of a car: yes, definitely. The routing and sizing is on the small side. Surely not an issue when used at normal pace on roads, but for prolonged track work with longer stints, I would most definitely change it.

 

Australian temperature? Plus track work? Sports cat and nice intercooler would be my first modifications of choice.

 

I'm in Oz & spend a lot of time on track (usually 20+ events/year) so have replaced the very restrictive & heat generating downpipe/cat with a 70mm decat downpipe.
Ive also fitted a Wagner intercooler & have an intercooler water spray system too.
With the increased boost I'm running & the shocking summer we've just had its a no brainer really imo.
Also my 275-R is one of only 2 'nurburgring spec' cars that came to Oz without air con or radio or sat nav etc, so have the added bonus of not having an air con core which can only help air flow through the rad.

 

Not so brave, I have another car for daily use if its too hot .
Removed the air con from my 200 also so it was a bonus for me not to have air con in the 275.
The I/c spray kit is custom (simple job), just get a couple of I/c nozzles from an Evo or STI etc & hook up an aux spray bottle/pump or simply tee into the oem windscreen bottle (just use plain water of course). I have a vacuum adjustable hob switch too so I can use the sprayer manually or have it come on automatically at a pre-set boost level (trick I learnt many years ago from my 99 Sti).

 

Here's a tip, if you go for the 70mm downpipe you don't need to replace the flexpipe section as it's already 70mm (it steps down to the 65mm Akra after the flange section). Also you wont get the real benefit from a 3" unless you replace the entire system with a 3". I'll get a sound clip up of mine soon (it sounds like a bloody WRC car running anti lag).

 

Not sure about standard cars but mine definitely has the 70mm opening, the standard downpipe is 70mm too but its choked down internally to about 60mm at the exit. You'll see what I mean when you remove the oem down pipe. I was also under the impression I would need to have a new flex pipe made with enlarged opening but that's not the case. I do have the standard downpipe with the witness mark showing the 70mm outlet mating surface, i'll send you a pic tomorrow when it's daylight.

 

Do you have a backbox?

 

Here's the pic of oem downpipe to flexpipe.
You can clearly see the soot build up witness mark that shows the large flexpipe opening as apposed to the choked downpipe opening.
For the record the flexpipe on my car has the 70mm opening & reduces to a minimum 2.5" all the way through to the Akra. Hope this helps clear things up.

 

Does anyone know if this the same opening for the stock systems or only the akra ?

 

I thought your car may be straight piped completely with no boxes, was going to ask what it sounded like.

But my exhaust setup is like yours. No mid box and a decat.

 

Hi Guys,

Just thought I'd add a bit of info in here to help clear a couple of things up.

The witness marks you see on the downpipe exit are from the factory gasket, which has a much bigger hole (Normally 3") than both the opening to the flexi and the exit of the downpipe, leaving the area to get sooted up in the gaps between both flanges.

Although the external tubing diameter is around 2.5" the internal diameter of the flexi-pipe is around 2" at it's smallest point which on a standard system isn't really as issue as you have a CAT in there which poses more of a restriction than the flexi-pipe itself, a system is generally only as limited as it's most restrictive part, although that's not strictly true it's a good rule of thumb to work out how to get more power - i.e a 3" cat-back system bolted onto a standard cat isn't going to get massive gains, and a 3" decat pipe onto a standard system isn't going to get massive gains, but combine them both and suddenly the car breathes a new lease of life.

You can flow big numbers through small pipes (a GTR system is a factory 70mm pipe and people run 800bhp + through those) but you're restricting your volumetric efficiency so switch it out for a larger (not too large) pipe and suddenly you can get more power per boost/fuel and keep temps down and have less reliability issues on top of that.

We've done quite a lot of development and problem solving with Megane's for various reasons, noise, power, temperature, weight e.t.c so we're happy to advise as much as we can if anybody has any other questions

Cheers

info@cgrautomotive.co.uk
01709 530871
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Oh right, would be interested to see what a straight piped one sounds like compared to my car.

 

Sound clip of akra & downpipe as promised, it's only stationary idle & throttle blips taken on my phone so not great but you can get an idea, so may help, there is flame too.

 

Yes it's a much deeper/better noise under load, i've also removed the midpipe silencer which combined with the downpipe is probably a bit too much for regular road use too be honest.

 

Megane RS 250 stock flex pipe - 47mm

 

Bit of a thread bump but has anyone changed the standard restrictive exhaust flexi to a larger one?

Just wondering if there would be any benefit to it when running at non hybrid turbo levels?