[90GSTBOOSTED]

Hey guys. I still can't figure out why I get this power cut at full throttle.
I checked for leaks and the first time my BOV was leaking. I bought another one and it's fine now so it's not leaks. I just get these sudden cuts in power everything the car is WOT and starts boosting past 8-10 psi. My JoeP MBC is set to 14 psi now but with these cuts I can't get that high sometimes.
I did custom IC piping for both pipes. My UICP is 2 3/8" in diameter but my LICP is very thin at the moment, it's about 1.5 or 1.75" at the most because I had that pipe sitting around and didn't have any more couplers to put a 2 3/8" pipe for the LICP as well. So my question is, could having such a small diameter LICP cause these cuts in power at higher RPM (past 3500) or it's something else that I just can't find?
I have a logger and I have checked the knock and timing. Once I start feeling the short sudden power cuts some knock appears after about 2-3 seconds. The timing gets retarded down to 10-13', IIRC.
I have a new Knock sensor already ordered and it arrived. I just don't see it being the problem, even though sometimes I do get some phantom knock. The knock sensor will be replaced either way. I am just positive there is something else with this whole thing. Could be the thinner pipe? I can put a bigger pipe as soon as my new couplers arrive. I just want to know if this is what causes everything because I am really all out of ideas..

 

[CanadianTSi]

New plugs gapped at 28 and new wires would be a good start.

 

[90GSTBOOSTED]

I have new plugs, the colder NGK ones.
The wires are older, true, but I didn't have these cutting problems before I started changing to hard metal IC pipes. That's why I think it might be the small diameter lower IC pipe I put on there.

 

[90_talon_matt]

What pressure are you at when you do your boost leak tests? Do you use soapy water or are you just going by sound. Are you checking the throttle body and all along the intake manifold or just the ic pipes?

I know you've said that you checked for leaks but this situation just screams fuel cut caused by boost leaks.

 

[CanadianTSi]

If my 2" IC pipe can flow enough to make over 400 at the wheels I think 1.5" will be ok for 200.

 

[16g-95GSX]

While I don't believe your cuts in power are attributed to the small IC pipe, I would still change it. CanadianTSI, have you done any pressure drop analysis on your piping? You should try hooking up your boost gauge, or sensor to your compressor outlet, and heavily watch or log it through the whole rpm band, and then switch the gauge/sensor to your manifold and watch it there. 2" is very small, and it seems to me that at your level it is hurting you, especially if you have any heavy bends in it. Try changing your wires and seeing if that doesnt help. If you know any local DSMers, ask them if you can borrow their wires. Wires often go bad, so you can never be too cautious. If you have already leak tested it fully, that is where I would start.

 

[thegreatms]

A small diameter pipe will not cause a power "cut". It might reduce the amount of power you make in a gradual maner as rpms go up. Definatly no sudden drops in power. Say 10 hp at 4000 rpm, 15 hp at 5000 rpm 25 hp at 6000 rpm. Depending on how small the restriction is and how much air you are trying to flow.

In your case I doubt that a 1.5 in diameter is hurting you that much even at medium rpms (3500-5000). I would change it out soon, but i don't think it is the cause of your power cut.

 

[92LaserRSturbo]

Guys...hes boosting at 14psi, and hes on stock fuel. Come on guys, im thinking fuel cut...Anybody agree?

 

[90_talon_matt]

Fuel cut has nothing to do with the fuel system.

 

[92LaserRSturbo]

Fuel cut has nothing to do with the fuel system.

Uh....ok.....
Anywho, hes overrunning the stock fuel system. Thats why he gets fuel cut (at least thats what i think it is.). So, you go and try and get 16psi out of a completly stock fuel setup. He is flowing way too much for that stuff to keep up. ....Only thing he is missing to describe fuel is the word violent. But sudden is enough to convince me.

 

[I4g63t]

Uh....ok.....
Anywho, hes overrunning the stock fuel system. Thats why he gets fuel cut (at least thats what i think it is.). So, you go and try and get 16psi out of a completly stock fuel setup. He is flowing way too much for that stuff to keep up. ....Only thing he is missing to describe fuel is the word violent. But sudden is enough to convince me.

Fuel cut happens when you over run the MAS not the fuel system.

 

[90_talon_matt]

Fuel cut happens when the MAS flows a cap value in airflow. It happens when you overrun the stock metering system not the fuel system. He's cutting, most likely, because the boost leaks are causing him to overrun his MAS prematurely.

 

[CanadianTSi]

Its deffinitly not fuel cut and a car in proper working condition should not fuel cut at 14psi.

To 16g, my 2" IC pipe is only about 1-2 feet long coming off the turbo where it expands to 2.5".

As with most fair sized turbo's, the outlet is only 2" anyways so your always going to be limited by that...

 

[90_talon_matt]

A car in proper working condition with boost leaks can cut at 10psi.

 

[CanadianTSi]

A car in proper working condition with boost leaks

Oxymoron I think so.

 

[90_talon_matt]

I meant mechanically..........

 

[16g-95GSX]

As with most fair sized turbo's, the outlet is only 2" anyways so your always going to be limited by that...

Not true. The outlet is short and does not contain any bends. Just because the outlet of a turbo is 2" does not mean that having 2" piping the rest of the way would be fine. Pressure drop will still occur, and occur at a more rapid rate with smaller piping even if the turbo's outlet was 2". As I said, try testing your own setup by hooking the boost gauge up to the compressor outlet and logging it, then hooking it to the manifold and logging it, comparing the difference between the two. See what you find out. Ideally you would want to be able to increase the size of the pipe that you have and log absolutely no difference in pressure at the compressor outlet. That would tell you that your 2" pipe was properly sized, and the ideal pipe for your setup.

 

[thegreatms]

Oxymoron I think so.

Not really, I would call it more of a contradiction, or logical fallacy.


A oxymoron is when the contradicting terms accually make sense together. like: Jumbo shrip.

see:
http://en.wikipedia.org/wiki/List_of_oxymorons

 

[gota0have0boost]

Im going to chip in my 2 cents and say boost leaks. The pipe diameter shouldnt play a factor in what you're dealing with.

 

[mrpeanut]

Not really, I would call it more of a contradiction, or logical fallacy.


A oxymoron is when the contradicting terms accually make sense together. like: Jumbo shrip.

see:
http://en.wikipedia.org/wiki/List_of_oxymorons

That reminds me of Alanis Morissette's "Isn't it Ironic." Nothing in the song was actually ironic, they were all just very unfortunate things.