Stainless exhaust pipe diameter on JTD, what size should I pick?! - Alfa Romeo Forum
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Stainless exhaust pipe diameter on JTD, what size should I pick?!

I'm looking to get a custom stainless exhaust for my car made up(Turbo back), but I don't know exactly what to go for. I am going to have the pre-cat removed and have a removal de-cat pipe too.

I've looked at supersprint and they seem to be 60mm diameter pipe all the way from the turbo back(apart from the turbo outlet which I think is a bit smaller)? I'd guess it'll be a slightly narrower pipe from the turbo to where the pre-cat originally finished.

I don't want it sounding like a boy racer, but I am happy for it to be acceptably louder(if you know what I mean). Should I get an unsilenced centre pipe or silenced?

I've been quoted a price not to miss out on of less than 300 for the turbo back system, just a Supersprint rear box is more expensive than that on it's own!!!!

Anyone got any thoughts?! what sort of performance gains do you think will be seen from doing this?

Cheers,

Mark
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Re: Stainless exhaust pipe diameter on JTD, what size should I pick?!

performance gains: the turbo wil spin up faster, and might keep spinning longer (higher in the rev range). no performance gains without a remap, but likely will throw out less soot..
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Re: Stainless exhaust pipe diameter on JTD, what size should I pick?!

Thanks for the response. I'm hoping that's what it'll do without having an adverse affect on the turbo's life or being too loud. I'm also hoping to get a remap done with red dot if there is another rolling road day to take full advantage of the exhaust, something was mentioned about a date in January for another RR day.

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Re: Stainless exhaust pipe diameter on JTD, what size should I pick?!

Quote:
Originally Posted by Cuore_Sportivo_155 View Post
performance gains: the turbo wil spin up faster, and might keep spinning longer (higher in the rev range). no performance gains without a remap, but likely will throw out less soot..
There WILL be performance gains without a re-map, just not as much as if it was re-mapped as well. Less back-pressure = performance gains.

I ve replaced just the back box on a mechanically injected (ie no ECU) diesel before, it wasnt manually "re-mapped" and there was a noticable performance gain and smoke levels dropped. A whole new system on its own would certainly see gains, that could be enhanced even more with a re-map
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Re: Stainless exhaust pipe diameter on JTD, what size should I pick?!

FYI the standard 2.5 V6 exhaust pipe is about 56mm and as example my Novitec exhaust is 64mm.

If you have a decat I think you may find a single back box quite loud but I guess it depends on the back box itself.
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Re: Stainless exhaust pipe diameter on JTD, what size should I pick?!

iirc JTD's pipe are 58mm so a 60mm pipe should just 'slip-over' it
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Re: Stainless exhaust pipe diameter on JTD, what size should I pick?!

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Originally Posted by Pascs View Post
If you have a decat I think you may find a single back box quite loud but I guess it depends on the back box itself.
I don't think it will be, the turbo "smooths out" the air flow and as such you get more of a medium drone than the 'reverberation' sound you get from the exhaust of a loud N/A petrol. My car has just a Supersprint backbox. No cats in the manifolds or under the car, no centre silencer, just the rear box, and its loud but not unacceptably so. I regularly hear louder Corsas. With a turbodiesel, the same exhaust would be a lot quieter. So I reckon nothing but a rear box would be required.

As a side note, a mate of mine has put a side-exit exhaust on his 2.5 diesel tranny van. No silencers full-stop, not even a backbox, and its not really loud but sounds rather cool


For 20v JTD exhaust sizes, I'd probably go with 65mm or so.

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Re: Stainless exhaust pipe diameter on JTD, what size should I pick?!

I'm suprised the standard pipe is only 58mm and the supersprint is a 60mm pipe. The only reason I said 60mm is because that's the spec of the supersprint exhaust for my car. If it's only a 2mm increase in diameter, will a 60mm pipe be much of an increase or worthwhile doing?! I guess the cat removals and removal of the silencer should hopefully free up some bhp & torque, especially after the re-map.

What is the general increase in diameter from the standard exhaust to a performance one, I know it probably varies but just a rough increase?

I'll have a chat with the guys at the garage to see what they recommend too.

Also, how come bigger exhaust = less smoke?!

Cheers,

Mark
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Re: Stainless exhaust pipe diameter on JTD, what size should I pick?!

+10% diameter for a performance exhaust? Seems fair enough..
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Re: Stainless exhaust pipe diameter on JTD, what size should I pick?!

Thanks Pud.

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Re: Stainless exhaust pipe diameter on JTD, what size should I pick?!

given the rpm range on a diesel the preformance increase from an exhaust is minimal.

obviously a very poorly designed exhaust will be restrictive to some degree but only really when above 5k rpm (ie not a diesel)

biggest restriction on the jtd is likely to be the elbow off the turbo?

58mm is plenty big for the power output imo

theres a good book on turbos etc available from demontweeks - cant remember its name but gives ideas of what dia for what rpm and power output 3 inch is good for 300bhp at 6500 rpm as a good indicator!
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Re: Stainless exhaust pipe diameter on JTD, what size should I pick?!

On my car I have both cat.removed and only a custom made straigh-free flow back box is fitted...and that with the BMC-CDA...the soound she makes is very nice, if you push her around. If you drive her in the normal way you won't hear almost anything.

So as said already, go only for free-flow back box.
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Re: Stainless exhaust pipe diameter on JTD, what size should I pick?!

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On my car I have both cat.removed and only a custom made straigh-free flow back box is fitted...and that with the BMC-CDA...the soound she makes is very nice, if you push her around. If you drive her in the normal way you won't hear almost anything.

So as said already, go only for free-flow back box.
Thanks KGB. Did you notice any or much difference after removing the cats?! Also, did you have the cats removed, backbox and BMC CDA done at different times or all together? I just wondered if it was a noticeable improvement performance wise all together or if done one at a time, were they noticeable and which was the biggest improvement?

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Re: Stainless exhaust pipe diameter on JTD, what size should I pick?!

Hello Mark_JTD,
Several months ago, I removed the precat and main cat, and put one freeflow backbox instead of the factory backbox. Instead of main cat I put one freeflow box with similar size as removed main cat. Also I have BMC-CDA air intake.
Sound is very good, with low frequency rumble on low RPM (2000), with reasonable sport note on middle RPM (3500) and acceptable loud on high RPM (over 4000). On high RPM sound from my JTD exhaust resemble the sound of petrol N/A engine, but noise is acceptable for me.
Best regards from Dusan.
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Re: Stainless exhaust pipe diameter on JTD, what size should I pick?!

Hi Dusan,

Thanks for the response. Sounds good from your description. Did you notice any sort of performance improvement from removing the cats & fitting BMC CDA?!

Thanks,

Mark
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Re: Stainless exhaust pipe diameter on JTD, what size should I pick?!

Main cat removed....turbo is a bit more responsive.

Pre-cat removed...turbo is another bit more responsive...you get some sound effects. Nothing anying.

Back-box.....more sound effects, you get some sporty note...nothing anoying.

BMC-CDA with the above mentioned mods....WOW....turbo pick up is a lot ...lot better...so much better that if your solenoid valve (the one controling the turbo) is bit old....meaning not as quick as it should be...the you will start having overboost problems...

the BMC-CDA will give you real performance increase...the rest will help your turbo and your engine to stay healty!!!

You should also note that your engine sound is better then ours....5 cylinder....

Furthermore you have the 20v unit...meaning you can go a lot further with the custom tuning of your remap....so much futher that not many cars will be able to keep up with you.

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Re: Stainless exhaust pipe diameter on JTD, what size should I pick?!

So putting things in perspective, and knowing that the CDA intake can be bettered with other offerings...

Would I be right in thinking that £ for Lb, its not really worth the cost of tackling the exhaust system unless it needs work anyway?

Would one be better off spending a hundred or two on a truly well sorted intake system?

Thing is, if the intake is done, big FMIC fitted, mapped to the limit and the silly intake manifold restrictions removed, how much benifit is the exhaust then - and is the elbow from the turbo the most restrictive point?
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Re: Stainless exhaust pipe diameter on JTD, what size should I pick?!

Backpressure is something that can hurt your turbo/engine if you go over certain limits.

For sure the car will be better of without both cats. and a free flow back box.

Mapped to the limit....the 20v can produce around 260hp and 600NM...with good intake, exhaust and FMIC.

I was looking yestarday at Bosch motorsport diesel performance parts...with another 12 000Euro....you can really launch your self....if you find the right gearbox and clutch.
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Re: Stainless exhaust pipe diameter on JTD, what size should I pick?!

About Mark_JTD question of performance improvement...
Several Alfa 147 1.9 JTD 8v of my friends are remaped, and only my Alfa had mentioned modifications (de-cat, BMC-CDA, etc.). All agree that my Alfa run better than others, especially in low RPM (under 2500). Turbo lag is significantly smaller. I assume that this was due to additional modification. I am forgot to mention block of EGR valve and replacement the overboost valve (i.e. solenoid valve), according to recommendation from our friend kgb.
I hope that this help in your tuning activities and good luck. Dusan.

Last edited by dusanGT; 11-12-08 at 22:17.
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Re: Stainless exhaust pipe diameter on JTD, what size should I pick?!

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Originally Posted by dusan View Post
I am forgot to mention block of EGR valve and replacement the overboost valve (i.e. solenoid valve), according to recommendation from our friend kgb.
I hope that this help in your tuning activities and good luck. Dusan.
"Remove overboost valve" - does this disable overboost totally? So on full throttle the turbo boosts to the maximum, with no split second of overboost before dropping down to the normal maximum? That would be a really handy mod for those suffering MCSF errors due to MAP sensor reading too much boost.
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Re: Stainless exhaust pipe diameter on JTD, what size should I pick?!

Hello Pud_237,
When I say replacement I mean replacement of old (dirty and lazy) overboost valve with new overboost valve...
Best regards from Dusan.
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Re: Stainless exhaust pipe diameter on JTD, what size should I pick?!

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"Remove overboost valve" - does this disable overboost totally? So on full throttle the turbo boosts to the maximum, with no split second of overboost before dropping down to the normal maximum? That would be a really handy mod for those suffering MCSF errors due to MAP sensor reading too much boost.
I will be working on that next week if time permits....one way to cut the voltage, so the ecu doesn't see the overbost...the other way is to get a 3-4 bar map sensor....and rework all the turbo maps.

Good thing is that 16v and 20v units have the 3bar sensor.
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Re: Stainless exhaust pipe diameter on JTD, what size should I pick?!

I've replaced that valve, so it should be working correctly ready for mapping in January. I've got to decide now which airfilter route to go down before the map BMC CDA or GSR. I had a similar pipe to the GSR on my Fiat Coupe with an Apexi filter but made by Pro Alloy, same make as the FMIC that worked quite well. The only problem with that is you needed the FMIC as the straight induction pipe used more space and needed the standard wing mounted intercooler to be removed to accomodate the filter on the end of the SIP. I'll need better induction than I've got, but I don't know which route to go down, GSR or BMC CDA?!

So, with the cat's removed and the free flowing backbox, a re-map and either a GSR intake or BMC CDA, what would the estimates be on bhp and torque after the map?!

Cheers,

Mark

Last edited by Mark_JTD; 12-12-08 at 10:34.
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Re: Stainless exhaust pipe diameter on JTD, what size should I pick?!

Maybe 240bhp if you pushed it on the map. Should do 350lbft no problem, which is more than the gearbox is rated for but don't let that stop you

Whether you go down the route of GSR or BMC, you first need to decide if you are going to keep the standard wing intercooler or fit a front mounted one. Personally, seen as you are going to all this effort with the exhaust, I would have a FMIC fitted and use silicone piping, you could sit a CDA on the end of that as a filter too if you like, or use a K&N cone.
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Re: Stainless exhaust pipe diameter on JTD, what size should I pick?!

BTW, what is the stronger MAP sensor (pressure in bar) that can be connect on 1.9 JTD 8v engine?
Thanks for your answers. Dusan.

Last edited by dusanGT; 12-12-08 at 20:16.
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