Low Boost, Catback questions
 

Ok, I have been in the rotary game for a long time, but I have 2 questions I have never really seen asked before.

This is the one that you all are allowed to flame me on. I have an S4 TII that is getting ready to be road worthy again. Something was bothering me though about the turbo. I see absolutely no boost until 4k RPMs. This was in dead stock trim with a ghetto cat back install. I haven't verified this yet, but I assume the twin scroll is still completely functioning. At what RPM do you guys start to see boost in your S4 TII's? (I am swapping the turbo out for an S5 turbo and manifold in very good condition to see if this fixes any of my issues.)

Second, I have an 80mm Corksport DP and MP I just installed (to see if cat clogging was the culprit to my boost woes.) and I was wondering if the RB Rev TII Y pipe and Rev TII dual exhausts would bolt up to my configuration. I love the sound of the RB units and was curious if I could save money by just having them bolt up to my current configuration instead of also having to buy the RB DP and MP also.

Any info would be awesome guys and gals. Thanks again.

-Maniac

I think you might be OK with the CS->RB set up. I am using an RB DP and silencer to Apexi N1 EVO catback and it all fits perfect.

And a clogged cat might be your culprit for the spool, but I can't help too much as mine is an S5.

That's what I am hoping also. If it doesn't fit then I am gonna have a Corksport 80mm DP and MP for sale then lol.

At what RPM do you start to see boost on your S5? (this is the unit I am switching to.)

And where would the cheapest place to pick up some RB stuff be? Or is it only available off of their website?

I can't remember. I will let you know when I take her for a spin tomorrow.

And just so you know, I have a stock ported engine, an insanely ported wastegate and no emissions with a cone filter. All that CAN make a difference in spool.

I have stock ports, stock wastegate, massive DP and free flowing intake. I expect similar results.

I think I started to see boost around 2500-2700 RPM when I was still stock can't remember for sure though. I think you might have a clogged cat that might be why you aren't seeing any boost till 4k.

I have no cat in my s4 and I see positive pressure starting at about 2500 and full boost before 4000. Stock ports, stock wastegate.

I bet that "ghette cat back" was too restrictive.
Boost is also relative to engine load.
1st gear pull is not going to have as much boost as a 5th gear pull.
In general, the turbo starts to make positive pressure in the 2,500RPM range.
The twin scroll acutator kicks in at around 2,800RPM.
It should be making full boost by 4kRPM.
S5 turbo can make positive boost as low as 2,000RPM.

I'd be surprised if it does.
The "Rev" spec exhaust is supposed to be proprietary, so it doesn't match with any of the stock "breaks".


-Ted

Yeah, the ghetto catback was some knockoff N1's.

All of my boost woes happened in any gear at full load. I didn't even start seeing positive pressure until 3800 or above (using a mechanical boost gauge). I do have a dyno from a baseline pull I did and it is a little obvious when you are looking at it. Hopefully this S5 turbo takes care of the issue. Positive pressure in the 2k range would make my year!!!

On the exhaust.... damn. Guess I am gonna have to get the whole thing then :(

Be sure there's no leaks...
Intake leaks can cause loss of boost too. :(
Does the car make loud PSSSSSSSSHHHHHHHH noises when it's boosting?


-Ted

hows your timing? i know retarted timing will spool the turbo super fast, so im guessing the opposite is true?

You mean advanced timing?

Yeah, it'll produce boost, but it won't go anywhere...i.e. no power.


-Ted

To the best of my knowledge, I have 0 intake leaks. There is no boost leak I can hear while in boost, and I have thoroughly checked for intake leaks since replacing my TID. I should get my new calipers in today and be able to swap out the turbo while I am under there. I just want to have some more low end power than the nothing I have right now. I just picked up an FCD for testing purposes so I guess I'll check it all out if I am lucky enough to get it all in.

Also, I have checked timing and stabbed the CAS appropriately. My timing is literally spot on.

How ghetto was the ghetto catback?

2.5"? 3"? were you using silencers?

Low-end power and RX-7 don't really go together. You can expect it to be quick but you can't really make too much low end power (I assumer you mean full boost >3000RPMs?)


Also, please make ACCURATE, REAL THREAD TITLES. Everyone has questions. You need to be more detailed so future searches yield GOOD results RIGHT AWAY.