mmcd87

iTrader: (1)

Here's a question for you all - why can our cars take so little modifying (with regards to the engine) before an engine remap or similar is required?

The only reason I ask is that Volkswagen Group turbo cars for example seem to be much less fussy in this respect, with changes to exhaust systems such as decat, etc requiring no apparent modifications to the ECU for the car to run OK.

Are the Subaru ECU's not as apparently adaptable for any particular reason? For example, it sounds like people here would not change the exhaust without a remap - not for performance but also to correct resultant boost and fuelling.

Thanks in advance.

Splitpin

Because when you have a very accurately set up intake/engine/turbo/exhaust/ECU combination, and change significant parts of it, you will reach a point where it is at least preferable, and often unavoidable to change its control parameters.

I'd suggest that the operative word in that paragraph is the one I put in bold. They may seem to you to be less fussy, but would probably benefit just as much from the same attention as an Impreza when changes of the same scale are made. Without wanting to sound disparaging, it is also possible that "social" reasons may figure here - for example the VW user base being maybe a little less well educated in this area and thus just doing stuff without caring whether a remap is necessary or not. This isn't a VW thing - part of the reason the Subaru community does the things it does now is because people made mistakes (and learned from the experience) a few years ago.

In terms of processing power and adaptability, the computers used by FHI are as good if not better than anything you are likely to find.

You can change parts of the exhaust - primarily the back box - without affecting anything of note. The reason why it is often necessary to correct the boost dynamics and sometimes fuelling when going further is because the standard ECU is very accurately calibrated for the standard systems - and so, when you change the nature of the physical setup, you need to alter the control strategy to match.

If it is less necessary with other marques of car, it will be because the initial setup is less optimal and thus more tolerant of changes. However as above I'd also suggest that part of the reason issues like this are so well understood in the Subaru realm is that the Impreza has been in production, with more or less the same engine setup, for 17 years now. During that time it has amassed a significant knowledge base - and a group of very experienced professional and owner-tuners.

To pick up your own example, VW went to turbocharging on the Golf far more recently and thus they may be on a slightly steeper part of the learning curve.

bobby260480

iTrader: (3)

Well said splitpin +1

mmcd87

iTrader: (1)

Thanks for the informative post, nice to get up to speed on these cars! I guess it makes sense (particularly on PPP cars) that tolerances are tighter i.e. PPP is mapped for that specific setup.

I was aware of this on custom mapped cars, but some companies in the VAG scene with generic remaps do not always specify a set exhaust for example. I.e. 2 guys have equal stage one plug and play remaps - one runs the the car otherwise oem, the other an aftermarket exhaust with sport cat and uprated air filter. The ECU's in these cars seem far more able to adjust fuelling and boost accordingly - perhaps you are correct and in our case the tolerances are simply made much less and more specific.

I ask about exhausts specifically as I was considering removing the first cat in the standard exhaust as I have heard they can break down with age, etc and damage the turbo. But then I would have to remap and thus loose PPP - might as well just stick a new cat on?!

Splitpin

As above the key thing here is that generic map packages cannot be done to tolerances anywhere near as exacting as a full custom one (or, if they are, there will be a risk of some cars running outside a predictable/safe performance envelope).

The PPP is technically a generic map, but it is, as you say, intended for a fixed engine configuration. There's also enough safety margin in it to satisfy International Motors' warranty requirements. That latter issue, btw, is a key difference between the PPP and most of the third party remappers. I doubt those VW companies you're talking about give a flying fig about adherence to warranties in the way the PPP developers have to.

Without detailed knowledge of the way the VW engine and engine management systems are designed, it is impossible to comment specifically. However, the obvious point to make is that all cars are not the same, and, as I said earlier, the tighter the tolerances used to map and control an engine, the less leeway you have to change the physical setup before the control strategy needs changing.

It may be that the VAG ECUs have a more adaptable boost control strategy, or it may just be that they're no better than the way Subaru does it, but you don't know about it because the VW user base isn't quite so enlightened and advanced in its expectations as the Subaru one.

It may also be that the bloke you are talking about with the sport cat and the air filter is driving round with an engine that is running outside a safe performance envelope without (yet) being aware of it.

You can change to an aftermarket panel filter on an Impreza without any problem. What you can't do is fit something that fundamentally changes the scaling of the mass airflow meter. And, there's no reason at all why you would want to as long as you are on the OEM turbo anyway. The standard induction tract is not a restriction at all.

How do you know? It may be that they're less adaptable than Subaru's stuff, but that there isn't quite the same knowledge within the user base (and long-established, widely read internet community) to identify and discuss what's going on.

For the cost of a new cat-equipped up-pipe from Subaru, you could probably afford a custom remap. If I were you in that position, I would investigate the cost of one of Harvey's custom small diameter up-pipes, alongside the costs involved in buying a standard ECU for your car, having it custom mapped, and then selling the PPP unit. There will be some back-end costs with immobiliser synchronisation and so-on, but you might be surprised.

madscoob

iTrader: (3)

i have 3 oem up pipes (from headers to turbo) all broken and cut apart from a 93wrx 96wrx and a w reg p1 and not one of them had a cat inside . at what year did subaru fit a cat to the up pipe before the turbo as the whole idea seems nuts to me any breakdown of cat would destroy the turbo

daz1968

iTrader: (13)

newage 2.0 wrx has uppipe cat in place, ppp map would probably still control car ok with just this removed, but you may get a cel, and a remap could take advantage of the quicker spool of the turbo. I ran a ppp ecu with sportcat down pipe and decat uppipe with no known issues, but it would have been better had I had the car mapped for it. I just disabled the cel in the map. I did some runs with romraider logging and it still boosted fine and did not overboost at all. But in hindsight it wasn't worth the expense and hassle of fitting them without finishing the job with a proper map, so I put it back to ppp spec and sold the parts on as I had decided to change the car

mmcd87

iTrader: (1)

Thanks for the info