cat efficiency codes, cats and spacers

[sambb]

Agonising over which way to go with a dump pipe/front section - To build it around the stock cat (and avoid a CEL altogether) or build it around a 100 cell or the like and rely on a second o2 sensor spacer/standoff to avoid the CEL. Whichever way I go it'll flow into the stock 2.25'' system half way along.

I'd really like to hear from people who did a high flow cat/dump and used only a second o2 sensor spacer to avoid the CEL. Sucess or not? eg do the spacers work reliably say on 2.5'' front pipes but not on 3''? Are spacers more effective if only a front sysytem is done versus a full system? Are 100 cell cats way more prone to CEL with spacers than 200 cell cats are?

And out of curiosity, the second o2 sensor seems to be looking at only the flow after the first cat in the cat assembly- the sum of the two cats isn't looked at. Anyone know if its possible to eliminate the second cat housing (with a bit of welding etc) and still be guaranteed to avoid the CEL?

thanks

[rgvlee]

If you doing the downpipe wouldn't you have your tune updated to deal with this? And at the same time deal with any potential cat CEL issues as a result? I wouldn't think you'd take out the stock restriction without updating the tune to allow for this.

I was told for street that a 100 cell cat wouldn't pass emissions. 200 cell is fine which is what I went with.

[sambb]

Phase 2 will follow later. simply cannot afford dump + cat + tune all at once - not without getting divorced that is! If I can get away with hardware only then that'll atleast get the ball rolling. I'll just run an MBC in parrallel with the N75 to cap max boost if there turns out to be any nasty spikes and see how it goes on phase 1 like that for a while- happy to be a guinea pig on that one.

what got me thinking that the standard cat with enlarged in's and out's might still be good bang for buck was talking to Plautos. His exhaust was initially 3in into the standard cat and 2.5'' out and he experienced a boost rise from 1.3 bar up to 1.6bar so the standard cat has to be capable of good flow especially at phase 1 levels of tune - added bonus to doing it that way is no cat code.
But having said that a 100 or 200 cell with a spacer would likely be even better, but on a dollar per HP gain compared to the standard cat, who knows?

[noone]

From previous results with the Polo on stock turbos, the dump is where a lot of the power comes from in an exhaust upgrade. The rear muffler and rear section flow pretty well for the volume of output from a chipped Polo.

Bought a magnaflow Cat and exhaust spacer, never got around to getting it installed. yours cheap if you want it.

[brad]

Stock Cat is 800 cell IIRC. You should be able to be error free with a 200 cell cat. 100 will cause lights.

[Paazuzu]

Stock Cat is 800 cell IIRC. You should be able to be error free with a 200 cell cat. 100 will cause lights.

The dump pipe combined with the 200 cell cat will cause a CEL. Happened to me after laps at Lakeside about 4 days after installation.

[sambb]

Paazuzu,

Were you running a spacer on the second o2 sensor when the CEL happened? Is your XForce a 100 cell or 200 cell?

[Paazuzu]

Paazuzu,

Were you running a spacer on the second o2 sensor when the CEL happened? Is your XForce a 100 cell or 200 cell?

I was running no spacer with the Xforce 200 cell (euro 4 compliant for emissions). I was expecting a code eventually but knew I'd be getting the stage 2 tune which would eliminate it. If I was you I wouldn't bother with the spacer as your tune is going to remove the code. The exhaust by itself delivers a slight performance improvement, but you won't really benefit from it until you have the tune too. My two cents anyhow

[rgvlee]

The only improvement I noticed with the exhaust on stock tune was less lag. Performance same same.

[sambb]

sorry maybe I didn't make it clear. I already have a phase 1 tune and will be staying on that tune for a while after the dump pipe is installed. I'll phase 2 it down the track when it suits. Thats why in the mean time on phase 1 I want to be damn sure that I will not throw a code if I run say a 200 cell with a sensor spacer.
So yeah I'm wondering what experience front piped stage1/phase1 people had as far as avoiding CEL's with the use of sensor spacers.

[h100vw]

sorry maybe I didn't make it clear. I already have a phase 1 tune and will be staying on that tune for a while after the dump pipe is installed. I'll phase 2 it down the track when it suits. Thats why in the mean time on phase 1 I want to be damn sure that I will not throw a code if I run say a 200 cell with a sensor spacer.
So yeah I'm wondering what experience front piped stage1/phase1 people had as far as avoiding CEL's with the use of sensor spacers.

I went from the C-C and AMD stage 1 to phase 2 as soon as I fitted the DP. I might have driven 100km before doing the Phase 2. possibly not enough time to trigger a fault light.

I did notice though that the boost was wild at onset with just the DP and Phase 1. So your MBC might be a critical factor there.

You could run the std cat but will no doubt be loosing out a touch from a 200 cell.

I say get a 200 cell cat and spacer. If it throws codes at you, have something handy to read a clear the light regularly. In case anything new comes up. Bluetooth ODB and torque app.

Save hard for that Phase 2 tune. Not forgetting as a repeat customer, you don't pay the full cost.

Gavin

[sambb]

Yeah I remember you writing a while back that boost spiked badly with phase 1 and a dump so I've got all the MBC bits together and ready to go.
What's the max requested boost on phase 1? My boost gauge shows 19psi on a third gear pull but that's manifold pressure and the gauge accuracy mightn't be perfect - I'm guessing I have a pressure drop across the intercooler compared to what the N75 is dealing with too. I suppose I'll just set my turbotech MBC to just shunt whatever it needs to around the N75 so that I still see a max of 19psi on my gauge and don't blow any requested boost ceilings.

I am leaning toward a 200 cell with the spacer now. I think I'd have to be pretty unlucky to get a CEL with that setup. I hadn't realised that the stock cat is an 800 cell which sounds pretty dense.

Yep phase 2 with an SAI delete is definitely in the plans.

[sambb]

An update on the exhaust job:

Had the exhaust manifold cyl 3 runner ported. Its the one that snakes around one of the turbo bolts at the flange and is really constricted. It looked about a 1/3rd samller than the others. Port matched the manifold to the turbo (was a 2.5mm difference in I.D's). Had the wastegate runner entry re-radiused and ported and the stock wastegate actuator (which was cracking at only 4psi) ditched in favour of a turbosmart IWG75 (XR6T model) using the 7psi spring to mimic a working stock actuator.
The exhaust dumps into 3in stainless and a 200 cell cat with a spacer from dubaddiction (has only a tiny hole for the sensor to sniff through) and it hasn't cat coded which is great.
As Gav predicted the peak boost spiked big time , so at the moment I've fitted a norgren 1 way needle/seat air bleed in parrallel with the N75. It works well and really finely adjusts boost down from whatever maximum it was going to reach. With it dialled in I hit bang on 20psi and hold near that peak for a lot longer although it does still taper down a fair bit. The flatter boost curve worried me that it might be a touch lean at high rpm's but we went for a few runs with the AFR meter up its bum and it was bang on 12:1 in 2nd and 3rd gear pulls which is nice and safe so pretty happy with the result.
Next things will be to get it logged to see if there is any timing pull, and looking into why the boost is still trailing off. It could be that we need a stiffer wastegate spring as running 20psi with a 7psi spring doesn't seem to make much sense, so we can fit the additional 5psi spring inside the 7psi one, as per the kit, to give a 12psi actuator and see if that alters things. If not then the stock rear section of the exhaust is probably increasing back pressure towards the end of a pull and if thats the case then I'm happy to stop there.
All up, I'm pretty happy!

Can anyone tell me which of the N75's - stock, 'J' or 'H'/ECS race, gives the least aggressive spool up? ie most control over initial boosting.

[h100vw]

An update on the exhaust job:

Had the exhaust manifold cyl 3 runner ported. Its the one that snakes around one of the turbo bolts at the flange and is really constricted. It looked about a 1/3rd samller than the others. Port matched the manifold to the turbo (was a 2.5mm difference in I.D's). Had the wastegate runner entry re-radiused and ported and the stock wastegate actuator (which was cracking at only 4psi) ditched in favour of a turbosmart IWG75 (XR6T model) using the 7psi spring to mimic a working stock actuator.
The exhaust dumps into 3in stainless and a 200 cell cat with a spacer from dubaddiction (has only a tiny hole for the sensor to sniff through) and it hasn't cat coded which is great.
As Gav predicted the peak boost spiked big time , so at the moment I've fitted a norgren 1 way needle/seat air bleed in parrallel with the N75. It works well and really finely adjusts boost down from whatever maximum it was going to reach. With it dialled in I hit bang on 20psi and hold near that peak for a lot longer although it does still taper down a fair bit. The flatter boost curve worried me that it might be a touch lean at high rpm's but we went for a few runs with the AFR meter up its bum and it was bang on 12:1 in 2nd and 3rd gear pulls which is nice and safe so pretty happy with the result.
Next things will be to get it logged to see if there is any timing pull, and looking into why the boost is still trailing off. It could be that we need a stiffer wastegate spring as running 20psi with a 7psi spring doesn't seem to make much sense, so we can fit the additional 5psi spring inside the 7psi one, as per the kit, to give a 12psi actuator and see if that alters things. If not then the stock rear section of the exhaust is probably increasing back pressure towards the end of a pull and if thats the case then I'm happy to stop there.
All up, I'm pretty happy!

Can anyone tell me which of the N75's - stock, 'J' or 'H'/ECS race, gives the least aggressive spool up? ie most control over initial boosting.

I haven't played with any but the stock N75 is what the tune is written around. Don't forget that the boost will naturally fall away as revs increase, unless you can make the cold section increase in size at the same time.

Consider boost and flow at the same time. Again I haven't looked at them together but if you graphed boost and MAF at the same time, it would be interesting... Boost might drop off but MAF doesn't

Gavin

PS got that $50, thanks.

[sambb]

From a bit of reading on vortex it seems that N75's can vary big time in the boost levels they allow and where in the rev range they have the biggest impact. Where I was coming from was Ideally I'd like to be bleeding as little air as possible around the N75, so If I could run one that tempers the initial overboost more effectively than the one I'm running now then I thought that might better. I had read that the 'J' was good at mellowing the initial boost ramp up better than some other N75's without adding any additional peak boost. Has anyone run it and can confirm this?