I am looking for your views and experience of affects of fitting a decate zaust system on reliability.

1. Does a BB by itself warrant a remap
2. Does a BB & centre de-cat warrant a remap
3. Does a full de-cat warrant a remap

I have been "informed" that with option 2 Subaru are experiencing problems on Stis specifically and others with excessive heat build up leading to piston melt.

Views please
Nigeyboy

I think the main thing here is for what car?

BB on any model shouldn't cause any problems, as I should imagine with the centre as well, perhaps a re-map to be safe on sti's with centre too.

I think it's fairly common knowledge that the wise would re-map an sti with a full de-cat though, although I'm sure there are some instances where people have seen things like knock correction to be ok on sti's even with de-cat.

But for something like my car (94wrx) a full decat isn't going to cause major problems IMO, it does benefit (from my experience) on a car like mine to re-map the ecu to provide better boost control characteristics (no overboost@WOT)

But as a final say, I would reccomend a re-map with full de-cat on any model as like I said earlier boost characteristics change with a decat (namely overboost) and a good map will control the rate it comes in and it's allways going to be the best way to get the most from your modifications and safely for the life of your engine.

James (all IMO, coz I'm no expert)

My boost didn't move too much with a full decat, just under 1 bar (uk turbo) so personally, I dont think a remap is needed. I was advised this from here a while back, and when you look at the techincal side of it, the stock ECU is capable of handling a decat. But an ECU with those mods is good power! :D

MB

3. Yes, if an Sti

The boost doesn't need to move, only the airflow. Seeming that the way the decat (or other opening up of the exhaust) helps is by reducing the backpressure, the same pressure differential across the engine means that there is a greater airflow (hence more fuel required hence more power).

Anyhoo, yup, the ECU - if it uses a MAF, which presumably it does - will be able to compensate up to a point. That point is effectively a lot closer with the JDM cars as the fuel's all wrong here in the first place, and for all, the map gets pushed further the greater the change in backpressure, so the DP pushes the map the furthest. Your'e more likely to run lean, in other words!

i have an sti and havin really big problems with boost in 4th and 5th gear and i have a straight through exhaust, anybody got any ideas how to sort it. its like hitting a brick wall at about 4 tho revs then lets u go again.

cheers

db

Hi Liam, welcome to SN!

The brick wall you're hitting is the fuel cut.

you're overboosting cos the ecu isn't prroperly control ing bost . Then the ecu cuts off the fuel to protect the engine.

It could be caused by lots of things - do a search for overboost.
With a full decat a remap would be a good idea but probably best to get it checked out for physical probs first

As Nom states a MAF based system will cope to a point, your engine's ignition requirements will also change with a decat.

Liam if it's a classic STi then a simple manual boost controller will provide stable boost control if you're having issues, if it's a newage I'd suggest having it remapped so the ECU has complete control over it.

Basically, if it's a classic shape i.e 1992-2000, then you can fit what you like and not NEED a remap. Good idea to have one though if you want to make the most out of the exhaust, but your engine shouldn't implod without one.

If it's 2001+ (bugeye,blobeye, hawkeye) then you will need a remap if you fit a decat downpipe. If it's just a cat back, then you should be fine.

There you go, nice and simple! :rolleyes: