Straight Through Exhaust a good idea???

[S10EAT]

Hi guys,

Just wanted to get people's opinions on this one.

I currently have a completely straight through 2.5" exhaust from a milltek decat at present on my Seat Leon TDI 110 SE.

I also have a "swirl" kind of technology backbox that I had on there previously and had it removed as it was falling off.

My question is, all these tdi's are turbo feed engine's, do they still require a little bit of back pressure to the engine provided by a silencer or backbox.

Is it healthy for the engine to have a completely straight through pipe???

Please throw your opinions on the table!!

Cheers,

Dominic

 

[samussamus1]

I replied to your other post

 

[Pimped up vario]

I don't know about your other thread so I'll post here. I haven't seen any formula or googled it myself but the mate who done a 227 bhp tdi engine build said that the bigger the better for more air flow was the way to go.

 

[EB-80]

I have no cat or backbox. I'll be fitting a stainless system at some point though. It sounds ok but its a touch loud imo.

 

[Seatmann]

If you're not going crazy with tuning I'd probably go with the smaller 2.5 rather than bigger. I'm sure there's something about egt's (exhaust gas temps) with the wrong size and not the mods to back it up. Egt's can be bad for the turbo and kill it.

The thread was on the tdi club anyway and it was tuners mostly that were talking about it.

 

[BenG]

I'd have thought a free-flow exhaust system would reduce EGT if anything, as the exhaust gases will dissipate less of their thermal energy in overcoming the restrictions in the exhaust system?

I suppose reducing back pressure could risk overspeeding the turbo, but the variable vane control system would presumably stop this?

The straight-through systems seem a bit noisy on TDIs though - check the vids on Youtube. Quite a lot of boominess and a weird 'pigeon' noise when lifting off. I couldn't live with it and got a silencer in my stainless system...

 

[john_tdi]

you don't need to worry about having back pressure. straight through is fine. Don't go smaller than 2.5.

 

[Seatmann]

Personally I'd fit a straight through all the way to the back then one of those straight through type back boxes just to take the edge off and kill the boom.

 

[benj1989]

I would imagine that have the back box taken out will give the best gains/noise is that right?

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[Seatmann]

I would imagine that have the back box taken out will give the best gains/noise is that right?

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Yes, the back box is pretty heavy and a bit restrictive. I haven't ever noticed anything from removing the cat.

 

[benj1989]

Would really loke to do this but worried about the cost tbh.

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[BenG]

Should be cheap to get the cat and rear silencer removed and replaced with just a straight pipe? The cat and silencer are the expensive parts.

TBH when my system was built I picked up the old back box and it didn't seem that heavy - maybe 2-3kg - despite the size. I had a straight-through silencer put on the back and the engine is very quiet - no more noise than the original system, although I also kept the cat.

If you can live with the squawking sound on lift-off, and maybe some droning at constant speed, then a straight pipe would be most efficient and maybe reduced turbo lag a bit. Get any remapping done after the exhaust is put on, to take advantage of any reduction in back pressure.

 

[andypandypoos]

my Ibiza has no cat and no silencers, it's not quiet and whilst I don't actually find it bad sitting on the motorway it's loud on full throttle

 

[benj1989]

Did it cost a lot to have the decat and pipes put on?

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[andypandypoos]

well the downpipe was from darkside and the (de)cat-back is a piper from unit18 but just getting the cat and back box replaced with just pipes would be cheaper

 

[leero783]

So i have 2 boxes on my exhaust check this photo

So number 2 is obviously the cat but what is number 1 is it just a silencer and do you get any advantages removing it . I will be removing cat soon but wasnt to sure weather is worth taking the silencer out , will i gain anything from removing the silencer or the even the cat ?

 

[Pimped up vario]

I don't know about power gains but removing the cats makes the car smell more of burnt diesel. Whiffy.

 

[john_tdi]

I've never noticed a smell after removing a cat! If you smell diesel then chances are the car is overfueling.

Removing the cat and fitting a bigger downpipe may only give small amount of power, but thats not the point. It will help the turbo boost sooner and it will boost for longer, in turn making the car more responsive and faster.

 

[benj1989]

Anyone have a idea how much it would cost to get my back box taken off and a duel exit custom back box put on from the likes of powerflow ect...? The look id like is one pipe each side of the exhaust like the btcc one but without the suitcase bit. I would also need a bit cut off my standard bumper. Iv tried emailing abd calling powerflow but they never get back to me. Only looking for idea of price

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[john_tdi]

your best bet is to go to see some custom exhaust places. I would of thought it would be around the 100+mark.