downpipe installed, weird boost delivery

[MyBeatGSX]

I got multiple questions so I'll number them to make it easier to answer. FYI, I have no experience with internally gated turbos, so if this is all normal then I apologize.

1. After putting the downpipe on I'm now boosting a steady 15psi up to about 4-5k when it jumps to a steady 17psi until redline (previous was 15psi all the time). This doesn't seem like boost creep because its not a steady creep. It just goes from a steady 15psi and then suddenly pegs 17psi and stays there. I was expecting to get more boost with the downpipe, but I was expecting it all the time, not a late hit at high rpm. Everything else seems to be normal, the turbo spools fast and at the right rpm. Is this random spike normal or is it the infamous boost creep, or maybe something worse....?

2. All important mods are listed in my profile. Given the boost delivery just discribed, is it safe to leave it this way? Or should I adjust it so it doesn't spike over 15psi? I'm not hitting fuel cut (on a very humid 70-75* night), but I don't know if thats a good or accurate thing to judge by. I know what I really need is a WB or a dyno or both, I'm getting to it, I just need to know for the mean time.

3. This is unrelated to the other two but I might as well throw it in. The top right turbo bolt keeps backing itself out no matter how hard I tighten it down. WHY? I don't know what would cause it to back out. Is it as simple as just needing locktite or do I have a bigger problem? As far as I can see it doesn't seem to be effecting anything (i.e. no leaking exhaust) and it IS engaging with the threads (its not stripped).

 

[v2ner]

that's normal...especially w/ a bigger DP and a 16G. that is definitely a creep, not a spike. a spike only happens when the WG opens too slowly...usually at the beginning of the powerband. it's not much of a creep though just make sure your not runnin lean. man, u really need an AFC or another tuning device. your injectors should be good for 17 psi. hope this helps.

 

[v2ner]

oh yea, maybe your bolt cracked in half. one half in the turbo. just take it out and see.

 

[MyBeatGSX]

What would cause the bolt to snap in half and HOW am I supposed to get out the half stuck in the turbo (if that's the case). Or should I not worry about it as long as nothing is leaking?

As for the creep.... What are my options to fix it? Electronic boost control? I've heard the profec-b is good with creep problems. I'm guessing an external dump O2 housing would solve it right away, do you recommend any particular brand?

And just so I'm understanding this correctly. Boost creep is caused by the wastegate not being able to bypass enough exhaust to keep up with the turbine... or is that wrong? How would a large downpipe make that worse?

 

[oldman]

And just so I'm understanding this correctly. Boost creep is caused by the wastegate not being able to bypass enough exhaust to keep up with the turbine... or is that wrong? How would a large downpipe make that worse?

Picture coming to a fork on the road, to your left is a single residential road and to your right is a two high way, given both will take you to your eventual destination, which route are you most likely to take? This is what happens with boost creep, air flow is taking the path with the least resistance.

Now what do you think happens when you expand the two lane highway to a 4 lane highway? This is why the bigger the exhaust, the worse the creep. How do you fix this you ask?

1. Construct a new highway all together, aka external wastegate.

2. Install road signs for the road on the left to make it more visible at the same time expand it to a 2 lane highway, aka porting of the turbine/o2 housing. Remember the fork on the road is at the turbine inlet, installing an o2 dump is like expanding the residential road not from the fork but further down the road which will not help in making that decision of which way to go because no one knows about the road expansion when you're at the fork on the road. Hope that made sense.

 

[DSM90AWD]

Picture coming to a fork on the road, to your left is a single residential road and to your right is a two high way, given both will take you to your eventual destination, which route are you most likely to take? This is what happens with boost creep, air flow is taking the path with the least resistance

That was deep. Now go fix your car

 

[oldman]

That was deep. Now go fix your car

Bastard...

 

[MyBeatGSX]

I loved that analogy. So porting it will be. But in the mean time (and its gona be a long long while) can I get a second or third opinion on the 17psi (almost 18psi on a cool night) being safe given the mods I have. And would I safe in assuming that as long as I don't hit fuel cut I must have some headroom left with the stock injectors?

 

[siceclipse]

Its creep.
when i put in my test pipe, my FPbigT-28 jumped from the 15lbs it was set to, to 20lbs. i ported the shit out of a 1g o2 that i had laying around and it helped a lot. i will be porting the 2g one i found at the junkyard soon and that will go in with the Evo 16g.

 

[oldman]

can I get a second or third opinion on the 17psi (almost 18psi on a cool night) being safe given the mods I have. And would I safe in assuming that as long as I don't hit fuel cut I must have some headroom left with the stock injectors?

Hitting fuel cut has nothing to do your fuel supply capacity, you hit fuel cut when ecu sees more air coming into the system which exceeds the maximum amount programed into the ecu to guard against run away boost or unintentionally, boost leaks as well.

What you need to worry about here is running out of fuel, aka fuel starvation which will lead to knock and pulled timing. Yes you can run higher boost to bandage the boost creep for now but you should only go this route if you have at least a logger so you can monitor knock count, running lean melting pistons is no fun.

 

[MyBeatGSX]

I was thinking about the fuel cut and figuring that it would tell me if I'm over running the stock injectors because the ECU would cut fuel before the airflow got too high for the stock parts. Am I looking at it the wrong way? I thought this wouldn't be the ideal thing to go by, but isn't it better than nothing?

As for the boost. I don't plan on changing the setting from the current 15psi, but obviously its not holding at 15psi. So is the creep to 17psi putting anything in danger? I just want to know if its still safe to hit full boost or if I should stay off it until I can get some kind of AFC or at least look at how its running with a WB?

 

[oldman]

I would not go over 16psi without logging with a 16g, your best option is to get off your ass and port away.

 

[MyBeatGSX]

Will do.

I'll be off to the dyno this weekend anyway. I'll post up the results.

 

[MyBeatGSX]

Well the results are in and they shocked even the guys at the shop. With the boost creeping to almost 18psi, the WORST a/f seen in 3 runs was 11.5:1. Typical on boost a/f started in the low 11's, dropping to off the chart rich (<10.5:1) at full boost, and coming back into the low 11's when the boost started creeping, it usually finished around 11.1-11.3 at redline with the boost fully creeped to 17.5psi. This is on 93 octane.

So now I don't know what the think. The boost creeps to dead on 18psi on a cool night and that's ALOT of boost for stock injectors... But maybe because the small 16G doesn't exactly flow a huge amount of air then its not a problem or maybe I have a magical fuel system? I know I need a pocketlogger so don't beat me over the head with it. If I can get away with 17-18psi then why not? An S-AFC and 550's are on the way (in a month or so), but in the mean time its still my daily driver. Any thoughts or opinions?


And if anyone is wondering.... 211.86hp @6,000rpm and 203.40 lb/ft @3,100rpm gotta love small turbos...

 

[92awddsm]

Well the results are in and they shocked even the guys at the shop. With the boost creeping to almost 18psi, the WORST a/f seen in 3 runs was 11.5:1. Typical on boost a/f started in the low 11's, dropping to off the chart rich (<10.5:1) at full boost, and coming back into the low 11's when the boost started creeping, it usually finished around 11.1-11.3 at redline with the boost fully creeped to 17.5psi. This is on 93 octane.

So now I don't know what the think. The boost creeps to dead on 18psi on a cool night and that's ALOT of boost for stock injectors... But maybe because the small 16G doesn't exactly flow a huge amount of air then its not a problem or maybe I have a magical fuel system? I know I need a pocketlogger so don't beat me over the head with it. If I can get away with 17-18psi then why not? An S-AFC and 550's are on the way (in a month or so), but in the mean time its still my daily driver. Any thoughts or opinions?


And if anyone is wondering.... 211.86hp @6,000rpm and 203.40 lb/ft @3,100rpm gotta love small turbos...

With power that low, you probably wont overrun the injectors. On a dynojet and with a fair tune, you should be able to put down at least 250awhp. I would go over everything(compression test, boost leak test, etc) and see where your problem is. Once you find the problem, it will probably cure the late creep and the lack of power also.

And for the afr, the 255 helps from going lean at higher boost levels.

 

[MyBeatGSX]

Would no tune explain the low power numbers? At the moment its a stock computer with a cut TPS wire to get rid of the random missfire crap. I'm also stilling running the stock side mount, which was so hot I burned my hand on it (crappy dyno fan didn't help, I could have blown on it harder, and the mist bottle just wasn't cutting it after the first run).

The boost leak test I'm gona have to try. But as far as a comp test, wouldn't I be blowing out the dipstick, smoking, or burning oil if I had bad enough blow by to lose 40hp? It doesn't say it in my info, but I also have a 4 layer metal head gasket, so I'm really hoping I'm not losing anything there. Could it also have to do with the fact that I'm actually only running 15psi for 80% of the powerband? By the time the boost hits over 17psi the engine is past peak power. Maybe if I turned it up to actually run 17psi it would help with the power? If I'm not overrunning the injectors on 18psi at 7,000rpm then why should I have to worry about overrunning them at 17psi at 4,000rpm? Or is that not a good idea? How about the ignition coils? I'm still on the originals.

One other note. If you look at the dyno chart (link back that way in the info<<<), the first run (blue) looks like some serious timing got pulled around 5,500rpm. Maybe a little knock? Maybe a big knock?