12psi in 2nd, 15psi in 3rd??

[jagwired]

like the thread says i just installed my boost gauge and took the car out for a few runs to see what boost levels i am actually running. WOT in 2nd i get a consistent 12 psi that holds til around 5500rpm(t-25 blah) in 3rd though, when i punch it i get a spike of 17psi then it drops to 15psi and holds til 5500 or so. This seems kind of strange, i havent had a chance to test 4th or 5th gear yet and 1st gear is worthless to test because its just spinning tires.

anyone else have this happen to them? mods in profile

 

[PGTred95]

You get more boost in 3rd than 2nd because you're putting more load on the motor. I'm guessing you probly get about 9-10 lbs in 1st gear too. W/a good boost controller you should be able to hold consistent boost from 2nd gear up, 'cept w/a T25 I run a B16G w/a Joe P mbc set at 20lbs. I get 20lbs from 2nd gear up. In 1st I get about 9-10.

 

[jagwired]

You get more boost in 3rd than 2nd because you're putting more load on the motor. I'm guessing you probly get about 9-10 lbs in 1st gear too. W/a good boost controller you should be able to hold consistent boost from 2nd gear up, 'cept w/a T25 I run a B16G w/a Joe P mbc set at 20lbs. I get 20lbs from 2nd gear up. In 1st I get about 9-10.

alright that makes sense,thx, but does that mean my boost will vary in 4th and 5th also?

i have my mbc and plan to put it in tommorow so i guess it wont be a problem, i'm more curious than anything

 

[psychlow]

4th and 5th gears can be higher as wind resistance, drag and the effects of gravity put a higher load on the engine, but they tend to stay pretty close to 3rd gear numbers on DSMs most of the time.

It's very unlikely that you'll get higher boost numbers than what you're seeing already on that hairdryer, though.

 

[jagwired]

4th and 5th gears can be higher as wind resistance, drag and the effects of gravity put a higher load on the engine, but they tend to stay pretty close to 3rd gear numbers on DSMs most of the time.

It's very unlikely that you'll get higher boost numbers than what you're seeing already on that hairdryer, though.

alright but when i put in my boost controller and i set it so 15 psi in second gear do i have to worry about too much psi in 3rd or 4th?

 

[psychlow]

alright but when i put in my boost controller and i set it so 15 psi in second gear do i have to worry about too much psi in 3rd or 4th?

Yes. You want to set your max boost in 3rd gear. Otherwise, you could be overboosting in 3rd+.

 

[Generation1JeY]

i dont know whats different about ur guys cars compared to mine, but any boost i set on my boost controller it holds the exact same in every gear. i have it set to 10 psi it holds at 10 in every gear, 16 psi, i get 16 psi in every gear, does this mean something or is it supposed to be like this? i have a standard turboxs boost controller

 

[Pearl90TSI]

Thats how mine is. I like it staying the same in every gear.

 

[jagwired]

alright i have had time to make a few more pulls in 2nd and 3rd gear.

results are:

2nd gear still a consistant 12psi til the t-25 runs outta air

3rd gear spikes to 17psi then down to 14psi...but then slowly creeps back to about 16psi.

is there really any point in putting on a mbc with this turbo if i'm already at about the max psi i should run with stock fuel/internals? would i still reap any benefits?

 

[Generation1JeY]

do u mean no boost controller as in u want to just free boost? u just disconnect the wastegate to do that, but if u do that u'll get above 17 psi cause the turbo will just spike really high and then come down gradually, but when its at its max pressure it could damage something. I dunno the t25 is such a weird turbo to deal with it seems, my 14b gives me no problems with boost spiking or anything like that.

 

[jagwired]

do u mean no boost controller as in u want to just free boost? u just disconnect the wastegate to do that, but if u do that u'll get above 17 psi cause the turbo will just spike really high and then come down gradually, but when its at its max pressure it could damage something. I dunno the t25 is such a weird turbo to deal with it seems, my 14b gives me no problems with boost spiking or anything like that.

no no, i mean that since with my current setup i'm already seeing boost levels of around 15psi in 3rd without a mbc, is there any reason to throw a boost controller into the mix or just leave it alone until i upgrade my turbo?

 

[psychlow]

If you put in an MBC and get rid of the stock BCS, you may just get rid of the spike problems.

Have you been able to look at a logger to make sure you're not knocking (checking for any dips in timing?) The spike/creep spike/creep thing would kind of have me concerned if I were you.

 

[jagwired]

i have already done the bcs removal along with the other free mods.

no i havent had a chance to see a logger, i dont have one and i dont think i know of anyone around here that has one...but maybe i should put the mbc on and turn down the psi a little until i can find out for sure about the knock

 

[Cheks_Talon_TSi]

i dont know whats different about ur guys cars compared to mine, but any boost i set on my boost controller it holds the exact same in every gear. i have it set to 10 psi it holds at 10 in every gear, 16 psi, i get 16 psi in every gear, does this mean something or is it supposed to be like this? i have a standard turboxs boost controller

My car does the same with the MBC on it. Excpet when tires are spinning (on low gears), the boost drops 2-3psi but after spinning it holds again the same pressure.

 

[Cheks_Talon_TSi]

i have already done the bcs removal along with the other free mods.

no i havent had a chance to see a logger, i dont have one and i dont think i know of anyone around here that has one...but maybe i should put the mbc on and turn down the psi a little until i can find out for sure about the knock

Maybe you can check with an EGT or a A/F Ratio Gauge.... before you install the MBC...

 

[jagwired]

Maybe you can check with an EGT or a A/F Ratio Gauge.... before you install the MBC...

i dont have an EGT gauge and the air/fuel ratio gauge isnt accurate worth anything without a wideband

 

[Cheks_Talon_TSi]

i dont have an EGT gauge and the air/fuel ratio gauge isnt accurate worth anything without a wideband

It isn't so accurate but it will give you an idea... is better than anything...

 

[Generation1JeY]

ok wait so are u saying that if u have no bost controller hooked up (just straight pressure vac line to the wastegate actuator) u get 15 psi in 3rd gear, but in no other gear? If u have a straight vac line to the actuator it will not go up to 15 psi, i'm not sure how tight the spring is on the t25 turbo, but 14b actuator is a 9lb spring. if ur getting 15 psi with just straight pressure to actuator lines, then u probably just have boost creep, since its only happening it certain gears its most likely boost creep, but it could be that ur wastegate is messed up or something like that. Check all ur vac lines and make sure theyre all in good condition and not cracking or anything, and then get a simple pressure hand pump and plug it in to the actuator to test the arm movement. Correct me if i'm wrong the t25 actuator would be a littl above 10 psi? i think its not much different than the 14b its just the boost solenoid that gives 2gs more stock boost than 1gs

 

[psychlow]

My car does the same with the MBC on it. Excpet when tires are spinning (on low gears), the boost drops 2-3psi but after spinning it holds again the same pressure.

You guys that get constant boost in any gear - that's beacuse you probably don't have a T-25, or you don't have exhaust mods to let the engine breathe more freely.

Think about it, guys - 1st gear has less load than 2nd, 2nd has less load than 3rd. The engine runs through the gear fast enough to consume the air the T-25, meaning that the compressor doesn't have a chance to create more pressure before the air's getting used up by the engine. The T-25 is too small to keep up. Same when the guy above spins the tires - the compressor can't keep up when the engine revs that quick with no load.

In 3rd gear, where the engine moves through the gear more slowly due to increased drag and rolling resistance, not to mention a longer gear, the compressor has a chance to catch up with the engine's use or the available air and create more intake pressure.

To the original poster, please make sure that your wastegate isn't sticking shut for some reason. It sounds like that may be the case - otherwise, you may have a hole in the stock wastegate boost source lines.

 

[Cheks_Talon_TSi]

ok wait so are u saying that if u have no bost controller hooked up (just straight pressure vac line to the wastegate actuator) u get 15 psi in 3rd gear, but in no other gear? If u have a straight vac line to the actuator it will not go up to 15 psi, i'm not sure how tight the spring is on the t25 turbo, but 14b actuator is a 9lb spring. if ur getting 15 psi with just straight pressure to actuator lines, then u probably just have boost creep, since its only happening it certain gears its most likely boost creep, but it could be that ur wastegate is messed up or something like that. Check all ur vac lines and make sure theyre all in good condition and not cracking or anything, and then get a simple pressure hand pump and plug it in to the actuator to test the arm movement. Correct me if i'm wrong the t25 actuator would be a littl above 10 psi? i think its not much different than the 14b its just the boost solenoid that gives 2gs more stock boost than 1gs

I agree with him... I also think you have a boost creep somewhere in your vac lines!...
15Psi without MBC I believe is not normal...

Good Luck

Sergio G.

 

[jagwired]

hmm..well the wastegate and everything with the turbo itself are fine. It was rebuilt by majestic turbos in waco about 200 miles ago along with a brand new wastegate and actuator.(i didnt want to rebuild the t-25 rather than upgrading but i wasnt paying for it, so i had no say)

so i guess i may have a boost creep in the vac lines like a few of you have suggested, but how would i check/fix that?

 

[Cheks_Talon_TSi]

You guys that get constant boost in any gear - that's beacuse you probably don't have a T-25, or you don't have exhaust mods to let the engine breathe more freely.
Same when the guy above spins the tires - the compressor can't keep up when the engine revs that quick with no load.
To the original poster, please make sure that your wastegate isn't sticking shut for some reason. It sounds like that may be the case - otherwise, you may have a hole in the stock wastegate boost source lines.

Is true

 

[psychlow]

so i guess i may have a boost creep in the vac lines like a few of you have suggested, but how would i check/fix that?

"Boost creep" is usually caused by air not being able to get past the wastegate due to the wastegate being too small or restrictive. Your problem is similar, but not quite boost creep.

It's likely that the boost signal to the wastegate is being bled off or otherwise altered. The best way to check this would be to take the lines off and inspect them for cracks and leaks.

If there are no leaks, hook a pressure source (hand pump, or compressor regulated to ~12PSI) directly to the wastegate actuator to make sure that the wastegate opens at the right pressure. You may have gotten an actuator with a spring that's too stiff for stock boost levels, for some reason, when the turbo was rebuilt.

 

[jagwired]

ok well i checked the vacuum lines and it appears that majestic turbo's went ahead and replaced all of my water lines, oil linesc and vacuum lines connected to the turbo..they even powder coated the turbo

so i'm thinking that eliminates the idea of boost creep from the vacuum lines..unless there are some lines that i am missing

 

[psychlow]

Is your BCS still there and plugged in? Has it been modified in any way from what you can tell?