Best size downpipe/exhaust for K24 7400

[gmac78]

Hello all,

Looking to start my upgrade to the Volvo 7400 turbo, i already have the turbo and injectors but thats about it.

I'm looking to convert to coil packs and ABY ecu, think i might have found a doner car for all the electrical side of things.

However, what size of exhaust and downpipe do i really need to get the best out of this turbo? Will 2.75" be suitable or should i go 3", no plans for further upgrades once this setup is complete as my requirements are basically strong low down boost with a decent top end difference over the homefry, from what i've read so far the Volvo 7400 fits the bill.

I am currently running with the standard 2.5" downpipe and 2.5" stainless exhaust with one small back box. It's a bit droney at low rpm so want to dial that out with the next setup.

I still have the standard 3B exhaust system so could utilise the back box if that was considered a good option.

Thanks
Gordon

[martinws]

A lot of people say a 3'' downpipe frees up the turbo a lot then drop the diameter down as you go back the way to dial noise down. I cant speak from experience as I run 2.5 all the way with one silencer then out the side infront of the OSR wheel. It sounds ok with windows closed on the motorway but like a group B car with windows down and exhaust glowing on the track. Mwahahahaha!

[gmac78]

I've just bought an RS2 exhaust manifold to compliment the turbo, i'm intrigued really, as wondering would i actually notice the difference between using the standard 2.5" down pipe and a 3"? Bearing in mind the Volvo turbo is not going to make big figures by todays standard but still 330-350 with good spool should be a lot of fun?.. I wonder what difference in spool and HP there is between using 2.5" and 3" down pipe?…

[SteveH]

I don't think you will notice any difference on the road with the setup you are planning. It's a fair bit of hassle and cost to make a new downpipe. The RS2 manifold will keep the turbo and wastegate in the standard S2 position, so it would be bolt on, job done. Not sure about the frame of the ovlov turbo and oil and coolant feeds for hassle free fitting. Don't forget you will need to shorten a couple of exhaust studs to fit the manifold.

[gmac78]

Yeh i know what you saying Steve, it's just i'm reading conflicting opinions from different websites which are making we wonder if 2.5" is suitable for downpipe/exhaust. Some say yeh no issues for that power level, whilst others say over 300bhp and 2.5" is substandard. Not wanting further expenditure if it's not really needed. Hmmm?….

[andy10v]

I would not stress about it, a 3" downpipe would be better, but its not a necessity.

[gmac78]

Hi Andy, yeh perhaps i should just see how it feels with the 2.5" setup and take it from there. Do you still have that cobra head intake hose available? Can't rem now if you said you were going to sell it or not? Cheers.

[andy10v]

I would, I still have the stock downpipe on the Rs2 turbo

[andy10v]

Sorry I forgot about the hose, £20?

[byd1380]

I think the restriction is in the Y piece under the car as it splits int the 2 cats, this might be diferent to yours and mine is URS6, I built a downpipe and ran this setup with my homfried standard K24 setup. I then switched over to the Volvo 7400 and at the same time went RS2 manifold and 3" downpipe. I can really recommend this turbo, it goes well for what it is, I would say making a good 350bhp.

http://www.s2forum.com/forum/showthread.php?t=52225

I still have the 2.5" downpipe section if it is any good for you. What intercooler are you running?

Ivan

[GazzaG60]

id go 3" and remove the cat if at all possible. get the gases out quickly.

from the middle you could fit a couple of boxrs to quiet things down. look at how the tailpipe exits regarding drone.

my 1 box 3" system i dont think would suit you. it is not quiet. the important part is getting the gases out as quickly as is possible without pressure buildup

[gmac78]

As much as i've been loving the ASBO levels of noise from my 2.5" stainless with no cats or centre box and one small back box, lately i've been thinking that for a change i would like to hear the 5 pot burble to see if i would prefer that. I am fast approaching the ripe old age of 37 and the drone from my current setup is starting to annoy me.

Which exhaust do you guys reckon flows better, my aftermarket 2.5" with just one small back box or refitting the full standard exhaust but gutting the cats, or perhaps just removing the cats all together and connecting the downpipe to the centre box with a small section of pipe? I'm guessing my current setup will flow more but the drone is annoying.

Would i loose much power by going back to standard and removing the cats all together? For those that have gutted just the cats on the standard system, is there much difference in noise?

Cheers

[Rikki Kitto]

I've run mine with gutted cars for a few years and it sounds fine, I've just fitted straight through pipes so have the empty cats if you don't want to kill yours your welcome to them pick up or cover postage costs

[orsum]

I am going the RS2 route for the mods but the ABY Exhaust DP is staying and the cats are staying put.

1) After the mods are done and I have driven it for a while the cats will go. I am told that will give a performance upgrade. But what inprovement in power will it give?


2) If that noise is ok then the DP will go to 3" to the stock system without the cats. But what inprovement in power will it give?

3) If thats ok the I will replace the conplete system from DP back. But what inprovement in power will it give?


If anybody can convert what I have said into power gains it may help everybody take the route they feel is best for them. Unless its just noise your after.

orsum

[macspring]

If it was me I start with;

1. RS2 airbox – Nice to have - if you can find one and can afford it, otherwise make one out of a spare S2 airbox.

2. oem style paper air filter – mandatory- inexpensive.
Wagner RS2 Evo Intercooler – optional – nice to have if budget allows.

3. Wagner front facing inlet manifold - optional - nice to have if budget allows.

4. Suitable sized new injectors –mandatory – to match turbo and chip

5. New plastic injectors ‘seats’, suitably sealed to avoid leaks – mandatory – inexpensive.

6. Silicone boost hoses in matt black - if you have the budget.

7. TFSI style individual coil packs – mandatory – not cheap, but definitely very worthwhile even with an ABY, no mind 3B ignition.

8. NGK spark plugs, avoid Bosch.

9. Wagner ES2 Evo Exhaust Manifold – KKK Flange, rather than a T3 Flange.

10. RS2 Downpipe (2.75” inch) - Bolts up easy.

11. Cat By Pass pipes from someone like ultimot.de, see their site for photos and costs, even if buying elsewhere.

12. Standard S2 Exhaust or a stainless steel exhaust 2.75” or 3” with as many boxes as possible to avoid drone annoyance and ricer noise image. Made by a specialist fabrication company, which will be dearer than the ‘franchised specialists” but worth it in the long run - measure twice and cut once.

13. Thin metal slash cut like oem tailpipes.

Most of the stuff is plug and play, with the exception of the front mounted inlet manifold, i.e. some rubber pipes has to be rerouted, and something else is affected ? . Look at someones ABY whose done it already. (Should have bought a UrS6).

The above information is based on experience, sometimes bitter tbh and reading the forums for the last ten years, I am not a mechanic, but do most of my own work, except the hard/complicated stuff.

HTH.

I can also pontificate on springs and shocks, ARBs, bushes, brakes – front and back, wheels, wheel spacers, tyres, steering wheel, instruments, seats, seatbelts, audio, headlights, indicators, wipers, alternator, engine mounts, gearbox mounts, earthing point, sump plug, fuel pump, chips, bumpers, bonnet grilles, flywheels, clutch, rear diff, centre diff, sump baffles, breather system, pistons, piston rods, engine gaskets, camshafts, cylinder heads, water pumps, main radiators, auxiliary radiators, remote oem key fobs, car jack, but you don’t need this thread hijacked.

Let us know what you end up doing, and how you get on.