De-cat without re-map on sti 7?
 

I've been offered a well priced de-cat exhaust sytem for my v7 JDM STI. I can afford the system but there's no way I can afford the ecu-tek re-map to go with. The garage has told me they're running systems with out a re-map and have never had any problems.

Has anyone any experiance of doing this and is it reasonably safe? I've heard boost spikes are a problem. But are they a blown engine type problem?

If I could get away with it would downpipes be a bridge too far?

Cheers all. :thumb:

dont know if there engineblowers or not. I can tell you on mine before it was mapped the was definatly some serious spike. It wasnt at all nice to drive had loads of power while it spiked and then as the ecu bought it under control made it feel quite flat

Thanks mate. They told me it made it alot more responsive and driveable.

The most likely result will be a check engine light on the dash.... I ignored mine for two years till I finally got the re-map.... no other problems EXCEPT you are wasting the fuel you are putting in ! ! !
Mine made 340 bhp with the re-map and felt massively quicker than before.

The (cat in my case) system will help the car breathe better, so do it !

HTH

DunxC

only issue is often overboost

Thanks for your advise. de-cat it is. cheers

does the overboost have to be mapped out or will lengthening the wastegate arm prevent it.

Mine didn't show any symptoms...

Maybe I was lucky...

DunxC

I hope I'll be lucky too then!

Mine didn't show any signs of boost creep and it didn't bring the CEL on until it was mapped :( but thats another story ;)

Go for it, makes a noticable differance, my V7 UK ran 298hp with full 3" Turbo back decat before remap :norty:

Some cars run fine without a remap, others don't. A mate of mine has just been through Hell after his decat caused all sorts of problems. Even after the remap it wasn't right until some shoddy workmanship was sorted out. If you're gonna do it, do it right once rather than half doing it a few times and paying each time. My advice would be to get the parts whilst they're cheap and store them until you can splash on the map, then get it all done in one hit.

Seem to re-call mine was much more responsive as it came on boost. Obviously cos there was to much. cos of that when the ecu had pulled it back it felt a little flat. Although it did make 328bhp on P.E,s rollers before it was mapped. Thing is once its mapped that extra boost can be held for a while up the rev range which makes for a much better drive.

My advise would also be to wait and get it all done at once. I didnt have any eml problems as i fitted a cel-fix at the same time.

Whats a cel-fix?

A cel-fix is basically a resistor put in the circuit of the lambda/o2 sensor to fool the ecu into thinking the cats are still in place.

Would resetting the ECU after de-cat help any problems?

What would a cel-fix do if i de-cat my car? Would it help with boost spikes until i can afford a re-map?:wonder:

It WILL det after 5500rpm on the stock fuelpump with a decat.

Must be a JDM thing as mine still over fueled showing no signs of det right to the redline

NO all it does is stops the engine managment light coming on. Has no effect on boost spikes or the cars fueling

I think its more just different cars different things even two of the same age and model wont be the same.

I dont think anyone can say 100% it will or wont.

So i guess the safe answer is to have it checked.

Exactly ;)

The CEL fix I believe is for a WRX, not an STI. My v7 JDM STI does not have this problem and has a full decat.

Decatting the exhaust on these cars improves the flow of gas, with greater volume and faster flowing gas through the turbo it spins quicker than it did with the standard exhaust. This may help it spool a little earlier and may also mean it produces more boost than it is mapped for. The standard map targets around 1.3 bar but with decat my car was spiking to 1.5 bar. The ecu attempts to control this boost error by lowering the wastegate duty cycles but will most likely reduce them too much resulting in the boost dropping below the target. It will then increase them again, it will boost above target again and the cycle is repeated until it gets the correct duty cycle and your boost stabilises on target.

I found this was pronounced in higher gears, 5th and 6th mainly, and was a pita when you were on the motorway and put your foot down to overtake. The car would surge forward, hold back, surge forward again and I could see the needle on the boost gauge going up and down as it happened.

The other problem that can be caused or made worse on a JDM car is detonation. The standard map on these cars is designed for the standard exhaust and japanese fuel. Altering the breathing resulting in running higher boost can make the engine detonate or if it is already prone to it make it worse. The ecu can make timing compensations for this to an extent but not right across the rev range, so at the top end there's a good chance of det. A JDM car runs a lot of timing as standard compared to a uk car so is much more likely to be detting, my car was detting above 5000rpm and this had to be sorted out.

Solutions to these problems are:

1. Change the restrictor in the boost pipework to reduce overall boost and bring it back on target. This will only fix overboosting;
2. Fit a boost controller, this will only fix overboosting;
3. Adjust the mapping of the ecu, aka remap.

Option 1 is the cheapest.
Option 2 is probably not the best solution because it means the ecu no longer has control of the boost so can't cut it to save the engine.
Option 3 would be the best solution because it would allow everything to be set at once to sort out any boost issues, detonation, fuelling etc. and allow you to realise the car's full potential. Probably worth fitting a walbro fuel pump beforehand.

I'm sure there are many people running decats on their cars without any noticeable problems. The guy I bought mine off had been running it on the standard map with a decat and with it overboosting and detting and I have since done 50000 miles in it and had no engine problems (boost and detting have been sorted for nearly all these though). He didn't know because he only drove it around town or on country lanes so was never in high gears, and didn't have any knock monitoring to see the det.

If you don't already have a knocklink then I'd suggest getting one fitted before you fit the exhaust.

I'm starting to think I should knock the de-cat idea on the head until I can afford a Bob Rawl re-map to go with it. Thanks for all your advise and opinions.

That's why women invented credit cards....

shopping whilst skint !

LOL

DunxC

This is a fantastic reply and I thank you for it. I am now 100% in for a remap next month when I return from Japan, as I have the "surge forward, hold back, surge forward again" problem in 5th and 6th gears and I have a decat system.

Will this also explain my very poor 16-19 mpg (i.e. 160-240 miles per tank), and will a remap go towards sorting this out much? I also hear from someone that fitting a decat downpipe not only improves torque but mpg too? I apologise for the slight thread hijack.