Typical T-25 boosting?

[Aphix]

I just hooked up a MBC to my T-2slow and tuned it to about 14-15 psi. As I was watching it, what would happen is I would rev it at 3/4 throttle and it would spike at 17 psi and then drop to 15, and then as I went past 5k rpms or so it would drop to about 11 or 12 psi until I shifted to a higher gear and then go back to 15. Is this common t-25 boost? It never dropped boost when I was running stock BCS. My current mods are a David Brode UICP, 1g BOV, and Injen style intake, and mbc. Also it is hooked up to the pressure source on the compressor housing.

 

[dsm1212]

im pretty sure that is common and mine does that also

 

[the_mork]

The t-25 will often fall off at higher rpms because it just can't push enough air to feed the motor.

The boost spike isn't uncommon and I wouldn't worry about it, the t-25 will have a hard time damaging your motor, damaging itself is another matter.

The only thing to worry about here is that you are starting to reach the outside of your turbo's efficiency range which will quickly heatsoak your intercooler and potentially could actually hurt performance, I think you're fine at the pressure you're at but I wouldn't try to push it any farther.

Also do a boost leak test, if you're losing air from your pipes or bov it isn't getting to your motor and potentially that is part of what is causing a slightly higher pressure loss at higher rpms.

 

[Aphix]

Thanks for the replys. I guess if the T-25 goes it gives me a reason to finally spring for a 16g haha. Also after I had initially installed the uicp and 1g bov I began to run 17 in.hg from 20 in.hg, and when I parked it today I opened the hood and found my bov recirculation pipe wasnt seated quite right and now its running 20 in.hg again, but I havent had a chance to take it back out. Hopefully that helps. I have a few other questions that I didnt want to start a new thread for.

1. After installing the injen style intake, I began to get a whistling noise when I let off the gas, I found it is coming from the MAF, not the BOV. Is this a common issue? I couldnt find another post on it.

2. I'm in the process of buying a custom 3" O2 back exhaust. I have heard people mention boosting issues with the T-25 and big exhaust, and there doesnt seem to be a specific thread on a 2g awd install that I can study.

 

[dsm1212]

correct me if im wrong but i think that you are refering to the boost creep issues right? after people install exhaust but you have a mbc right? so just keep the boost turned down

 

[Aphix]

That may be it. It was mentioned in a post awhile back. I'm just trying to cover all the odd ends here before I go slap an exhaust on and get problems.

Anybody have any idea what the whistling could be? My car sounds like a flute right now because of it.

 

[daren_p]

Are you sure this isn't just a normal noise, just that you didn't hear it pre metal intake pipe? The intake makes noises such as spool up, bov releasing much louder, so maybe you just couldn't hear it before?

For the exhaust, yes the T25 is tiny but a 3" system will be fine, especially if you plan on upgrading turbos in the future.

As for the boost, yes thats normal for it to drop off in the upper rpms once you try & raise the boost. Like mentioned, its just to small to keep up.

 

[Aphix]

It could have been muffled before, but it isnt turbo spool up or anything. I'm talking like going from 20 vac to 15 or 10 vac revs in park. Just little touches on the gas.

 

[kenamond]

My car whistles sometimes when coming off revs - not a BOV noise - and I just figure it's an edge or something on the inside of my intake tract that's whistling as air runs by it at just the right speed. It sounds like a true, clean, high-pitched whistle...not very loud, but certainly audible. It's always the exact same pitch (doesn't go up or down at all in pitch). It won't do it in neutral just revving the motor, though, so I can't pinpoint it with a parked car, head under the hood. If yours is the same, your guess is as good as mine. If it is like a flute, physics-wise, you might double-check that all of your pipes are aligned at the couplers, including the intake pipe-to-compressor inlet. But as others have said, metal intake pipes ring, rubber ones don't, so you might just be hearing that ringing. After upgrading my intake, I can hear the air rushing through the intake when I blip the throttle.

As far as the exhaust install, the hard part will be getting the old one off. Since I can't see your car while replying (I hate that), I don't know if you're AWD or FWD. If you're AWD, you can drop the entire exhaust in one piece from the O2 outlet to the muffler. I think the FWDs go over the "rear axle" and I don't know much about that. But trying to take the stock sections apart might be too much of a pain; I live in desert climate and garage the car (very little rust), and I managed to get the stock sections apart after it was off the car...using a *big* sledge hammer on a wrench for *every* bolt. Maybe pneumatic tools could do it on the car if you have them (I don't). As far as installing the other exhaust, it all depends on the exhaust. There are a lot of different models out there. Mine went on easily, but I had to grab a couple nuts/bolts/washers from the hardware store (the kit didn't come with *everything*). I jacked up the front and rear of the driver's side so I could get at the whole exhaust without moving jackstands around.

One other thing to keep in mind when you install your exhaust is that you'll have to readjust your MBC. Your boost will go up when you free up the exhaust. The exhaust has an easier time going through the turbine, so you have to open the WG sooner to limit boost to the same level as a stock exhaust. Mine was set at 14psi, but I hit 20psi on my first (very short) pull with a 3" exhaust. I'd start from scratch when you go to take it out for the first time; turn the MBC all the way down. Do some pulls to see if you have any creep problems - you should boost to around 9psi (WG actuation pressure). If the MBC is as low as it goes and you go much higher than 9psi, you might have some creep to deal with. If all looks okay, bring the boost back up gradually to where you want it through a series of pulls. I personally think it's risky to increase boost past stock without some sort of logger, and you probably shouldn't start doing this if you haven't done a boost leak test, not to mention other, routine maintenance. I'm not saying you haven't, it's just an FYI.

Good luck!

 

[Aphix]

Kenamond thanks for the great writeup. I'll probably end up just taking the intake apart and putting it back together in hopes that it will fix the whistle. For the exhaust install am I going to need a turbo compressor to O2 housing gasket? Unfortunately I live in the salt belt of America so I might have some trouble, but luckily I have started hitting all the O2 housing bolts with pb blaster already so there's hope. I'm in the middle of making a leak down tester so I should be able to get that up and running soon. And I was actually lucky enough to have data logging software on hand so I will make sure to use it when the time comes.

 

[EclipseTical]

Kenamond thanks for the great writeup. I'll probably end up just taking the intake apart and putting it back together in hopes that it will fix the whistle. For the exhaust install am I going to need a turbo compressor to O2 housing gasket? Unfortunately I live in the salt belt of America so I might have some trouble, but luckily I have started hitting all the O2 housing bolts with pb blaster already so there's hope. I'm in the middle of making a leak down tester so I should be able to get that up and running soon. And I was actually lucky enough to have data logging software on hand so I will make sure to use it when the time comes.

if you are replacing the stock o2 housing then its a good idea to throw on a new gasket, they are fairly cheap and good insurance against causing an exhaust leak.

You'll need to decide if you are going to take off the turbo or not to get the o2 off. . The o2 housing can be removed with the turbo still mounted in the car, it just takes patience and a few swivel sockets since clearance in that area is a bi***. It took me quite a few beer and smoke breaks to get that sucker off.

Just soak the hell out of the bolts as you have been for a few days before you want to tackle the install and you should be good to go.

 

[Aphix]

I'm kindof shying away from removing the turbo but I have the swivel sockets so thats good news. Thanks.