The below are my questions and thoughts after trying my friend's 05 Rex with a Trust catless DP (not bellmouth and not Stainless Steel) joined by a 3" Fujitsubo catback last week. The boost went up from the stock 0.9 bar to 1.1 bar and that was within our prediction. The usual reset after the install was done.

Result:
The torque (acceleration) felt weaker between 0 -3000rpm but it gave a stronger pull from 3000rpm to the redline. I personally didn’t fancy the loss below 3000rpm because I will mostly be driving around the city using that sort of rev range. But, the better pull from 3500rpm was gorgeous to have. We didn’t hear any misfires or we were both too novice to spot any.

The good news is that I have now bought a 03 Sti stock Catback to replace my twin pea shooter exhaust (too quiet). I will be buying either a 3” Syms DP or any other bellmouth designed DP available along with any catless designed UP.

I am suspecting that the rather noticeable loss of torque below 3000rpm with my friend’s Rex was caused by the Non bellmouth designed DP. Am I thinking in the right direction? Will the design of the DP relates to the torque variation below 3000rpm?

Should I still go ahead with the swap of the downpipe if I don’t want to to lose any torque below 3000rpm? Would it better if I only swap out the UP and the Catback to avoid the torque loss below 3000rpm and boost spikes?

 

Personally I would think you'ed gain more low down torque from the non bellmotuh down pipe as more back pressure usually equals more torque low down.

 

Please take no offence to my post Davey. Before I did some research on Cobb site about torque vs exhausts sizes, I was totally with you about back pressure produces torque. You are certainly right for all the NA cars, but not for cars with turbos.

Torque and power are related to the rate of gas flow on turbo cars. The faster the gas can flow out of the exhaust the more power it is capable to produce. Therefore, back pressure doesn’t equal to torque on turbo cars. It is when the optimum size of an exhaust couple with the optimum rate of exhaust gas flow that produce the best torque and power.

My concern is that if I should go ahead with the swap knowing that I cant get any reputable ECU management such as ECUtek here at where I live.

Would those of you who have de-catted UP, DP or Mid pipe running with Stock ECU please share your result here?

Thank you and I am looking forward in hearing from you. Your input will be much appreciated.

 

knock knock

please help me out with my questions.

cheers

 

The lack of back pressure does allow the turbo to spool faster but regardless of where the bottle neck in the system is it still relates to back pressure in the cylinders, thats my view anyway

We are running a flat flanged de-cat down pipe, turbo spool up is excellent and the low end torque is still spot on, even with 3 passengers the car still pulls like a train.

 

It is good to hear that you are getting excellent result from your mods.

Is there any way other than EM that can solve the boost spikes on my 05 REX?

I hope I will not get boost spikes with my mods.