cat efficiency codes, cats and 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?

[noone]

I've played with the N75, J's, a swapped out version, MBC's, etc. Unless its not working properly, the stock one is best.
The turbo is small, its not going to flow strongly above 4500rpm, my Polo is super torquey from 2500-4000rpm, thats where the fun-band is with the stock turbo.

[sambb]

My problem though is that my tune doesn't match my hardware anymore and so the stock N75 isn't coping. So if there's an N75 out there that can get more pressure into the wastegate for a given amount of closed time/duty cycle then it will probably help me control initial spool up better. For example on vortex threads people that had surging issues were swapping to different suffix N75's and their surging would stop ( I think it was the "J"), and the ECS N75 race (which apparently is just a rebranded "H" suffix VAG N75) has much bigger I.D's so controls bigger pressures differently. You had an N75 race at one stage didn't you noone?

[Dugle]

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.

I had no CEL problem with my dump and 200 cell cat before tune, maybe it's due to me not doing laps.

[sambb]

Do you have a 2nd cat sensor spacer?

[Paazuzu]

I had no CEL problem with my dump and 200 cell cat before tune, maybe it's due to me not doing laps.

Fair enough mate, I stand corrected. Mine was fine for about a week and then I went to laps and it threw the code.