Car pulls more at 10psi than 14psi

[carcrazy144]

Hey guys, got a funny question; i bought a mbc for my talon and was running 14psi on it. I currently backed it off because i got an odd sound when the turbo spools up, but the car runs about 10-12psi with the mbc backed off all the way. The car seems to pull much harder with the 10-12psi though which is odd to me, it should pull harder running 14psi obviously. Any ideas on why this may be?

 

[gixrman]

Its called compressor efficiency. Your turbo is pushing more air but its hot air which has less oxygen.

 

[sketzshane]

Is it the stock T25 turbo you are running? Between up to14 psi the turbo should be pulling harder. Are you sure that the boost is not leaking off? Have you ever done a leak done test to make sure?.

 

[Demon33]

Its called compressor efficiency. Your turbo is pushing more air but its hot air which has less oxygen.

+1 on possibly blowing hot air if using a small turbo, but not so much if using a 14b or larger turbo. It could also be due to knock (which leads to timing retard), boost leaks, inefficient intercooler and running lean at the higher boost pressure.

 

[skatershawn]

not a thread jacker but.. how is this fixed.. bigger smic or make sure there is a good flow of air hitting the smic??

i was thinking of ghetto riggin some co2 to shot out on my smic (during hard pulls) i know that would help!

 

[Demon33]

not a thread jacker but.. how is this fixed.. bigger smic or make sure there is a good flow of air hitting the smic??

i was thinking of ghetto riggin some co2 to shot out on my smic (during hard pulls) i know that would help!

Inefficiency of an intercooler can be cause by inadequate air flow across the intercooler, damaged fins (reducing airflow) or internal heat transfer interference such as an oily coating or corrosion inside the intercooler. Inefficiency can also be caused by an intercooler that is too small- not enough heat transfer time. But at only 14 psi even a stock SMIC should be adequate, but not necessarily ideal.

 

[fran_drivertsi]

If you are running 14psi, you might be detonating and computer pulls ignition timing, resulting in less power. 15 psi is an absolute max you can run on pump gas with no FMIC or meth/water/alky.

 

[carcrazy144]

sketzshane-I am running the stock turbo; i think i do have a boost leak cause my boost goes up to max, then back down, roughly changes 4psi when i accelerate hard. I haven't gotten around to making a boost leak tester and testing it yet.

fran drivertsi- My engine shouldn't be detecting knock and retarding the timing because i disconnected the knock sensor. It was throwing a cel code and i couldn't get the car inspected. Also, i didn't think that the smic wouldn't help enough running 15psi. If i clean out my stock smic or get a larger smic would that help?

 

[sketzshane]

sketzshane-I am running the stock turbo; i think i do have a boost leak cause my boost goes up to max, then back down, roughly changes 4psi when i accelerate hard. I haven't gotten around to making a boost leak tester and testing it yet.

fran drivertsi- My engine shouldn't be detecting knock and retarding the timing because i disconnected the knock sensor. It was throwing a cel code and i couldn't get the car inspected. Also, i didn't think that the smic wouldn't help enough running 15psi. If i clean out my stock smic or get a larger smic would that help?

I used to run 15psi on my stock T25 98 GST (pump gas) here in Jamaica(which is 90 Octane no meth kit etc..) I am sure that your gas is better than our piss gas (since the US has 93 Octane upwards) and I didnt get any excessive knock, car pulling timing etc... yet from what carcrazy144 has explained it seems that some how the car is pulling timing. carcrazy144 what gas do you use? I hope it is not 87 Octane!!!!

 

[carcrazy144]

Oh no. I only use sunoco 93. its the highest octane pump gas around here.

 

[97gstnick]

If you are running 14psi, you might be detonating and computer pulls ignition timing, resulting in less power.

I highly agree with the timing being pulled. "Hot air" factor alone is not going to make the car slower, its the timing that gets pulled that results in lost power. Running higher boost with "hotter air" and no detonation will make a car faster. It's when the hot air causes detonation that makes the car slower at a higher psi.

 

[skatershawn]

ok my car does some what the same... it looses power up top on hard pulls, i think its knock for me, reason i beleive is i have NGK uridium plugs which are hot... and i think its pre ignition or knock.. i need to change them bad! :/

maybe that could be one problem you might be having... what plugs are you using?

 

[92dsm1]

sketzshane-I am running the stock turbo; i think i do have a boost leak cause my boost goes up to max, then back down, roughly changes 4psi when i accelerate hard. I haven't gotten around to making a boost leak tester and testing it yet.

fran drivertsi- My engine shouldn't be detecting knock and retarding the timing because i disconnected the knock sensor. It was throwing a cel code and i couldn't get the car inspected. Also, i didn't think that the smic wouldn't help enough running 15psi. If i clean out my stock smic or get a larger smic would that help?

Boosting without a knock sensor? You must not need your car to bad, 1 good detonation and you could scatter your motor. I think I would get a knock sensor. I bought one today for my 1g (not a 2g I know) for 42.00 from Autozone and the sensor had a Mitsubishi sticker on it.

 

[carcrazy144]

Boosting without a knock sensor? You must not need your car to bad, 1 good detonation and you could scatter your motor. I think I would get a knock sensor. I bought one today for my 1g (not a 2g I know) for 42.00 from Autozone and the sensor had a Mitsubishi sticker on it.

Like i said my sensor was throwing a code that wouldn't let me get it inspected. Is it really that bad to drive a dsm without a knock sensor hooked up?

ok my car does some what the same... it looses power up top on hard pulls, i think its knock for me, reason i beleive is i have NGK uridium plugs which are hot... and i think its pre ignition or knock.. i need to change them bad! :/

maybe that could be one problem you might be having... what plugs are you using?

I changed the plugs about 5000 miles ago, i bought bosch plugs. I can't remember whether they were iridium or not. They were good plugs just can't remember the material used.

 

[skatershawn]

Hope their not like platinum series.. those are hot plugs... Best plugs to use are the one and only NGK Coppers!!

 

[carcrazy144]

Hope their not like platinum series.. those are hot plugs... Best plugs to use are the one and only NGK Coppers!!

Are they really? cause that may be what i got. would that really cause my car to pull more off of 10psi over 15? Doesn't seem like plugs would make that much of a difference to me. they're only plugs.

 

[nytescion]

If you are running 14psi, you might be detonating and computer pulls ignition timing, resulting in less power. 15 psi is an absolute max you can run on pump gas with no FMIC or meth/water/alky.

negative

 

[rvaughn]

The knock sensor is there for a reason, your ecu needs to monitor it so it can detect problems and keep from blowing up... Even if you do run without it, its like playing Russian roulette, you can play with one bullet or five, one way just has better odds of killing you... your call...

 

[dsm-onster]

Please use a logger when you up the boost above stock. There's no need to blindly alter performance in this day and age.

 

[IHeartMyHonda]

factory replacement plugs (ngk) are a must in your situation. i have run 14 psi on a t25 before and it didnt seem to be outside its efficiency range. closer to 20 psi is when it doesnt make sense on a t25. anything above 15-16 psi is when they become more of an exhaust restriction than a power adder. as for the boost dropping ~2 psi after you go WOT, that could simply be boost spike, which isnt too surprising if youre running the stock squishy ic piping.

but to restate the best post in the thread, use a logger.

 

[juanpac0]

Make sure you're running NGK BPRxES (where x is the proper number for your turbo/boost level, in your case its 6), and check for boost leaks. On a turbo that small ANY boost leak is gonna severely limit how much boost is retained to redline. My guess is that you have a boost leak and the turbo can compensate at stock boost but when you ask it to hold 14psi it can't keep up since the air is escaping. I bet if you fixed any boost leaks you had it'd hold 14psi for a lot longer, and you wouldn't be stressing the turbo as much.

 

[carcrazy144]

Please use a logger when you up the boost above stock. There's no need to blindly alter performance in this day and age.

You say to use a logger; like DSMlink? is that a logger or what exactly do you mean by a logger? I'm new to the computer side of cars. I'm used to working on muscle cars without computers.

The knock sensor is there for a reason, your ecu needs to monitor it so it can detect problems and keep from blowing up... Even if you do run without it, its like playing Russian roulette, you can play with one bullet or five, one way just has better odds of killing you... your call...

How do i fix my CEL problem then? That's why i disconnected it in the first place.

Make sure you're running NGK BPRxES (where x is the proper number for your turbo/boost level, in your case its 6), and check for boost leaks. On a turbo that small ANY boost leak is gonna severely limit how much boost is retained to redline. My guess is that you have a boost leak and the turbo can compensate at stock boost but when you ask it to hold 14psi it can't keep up since the air is escaping. I bet if you fixed any boost leaks you had it'd hold 14psi for a lot longer, and you wouldn't be stressing the turbo as much.

In order to fix a boost leak with the stock squishy ic piping i would have to upgrade to hard ic piping correct? And does having boost leak really stress the turbo that much? How sever can that be?

 

[MrBoxx]

You need to find out what the CEL was EXACTLY. Use a datalogger, DSMLink, or have the code scanned. If the knock sensor is bad, you NEED to replace it. Right now you could be having a ton of timing pulled due to knock. You also need to get your boost leaks fixed.

Anyone running Bosch plugs, platinum, iridium, or otherwise, needs to get them out of the car and replace them with BPR6ES or BPR7ES, whichever is more appropriate for your boost level. The question isn't how "hot" they are, but the fact that platinum is a shitty conductor of electricity and the Bosch center electrode is smaller than the hair on your head. Refer to my Spark Plug FAQ for visuals.

 

[darkiller_666]

In order to fix a boost leak with the stock squishy ic piping i would have to upgrade to hard ic piping correct? And does having boost leak really stress the turbo that much? How sever can that be?

There are several places it can leak. Hard pipes wont necessarily fix it, but it definately makes for less boost leak possible places. I seem to always find Throttle Bodies that have boost leak.

Common leaking points are: (starting from the turbo)

J-pipe
Connection from J-pipe to LICP
LICP to SMIC
SMIC
SMIC to UICP
BOV
BOV Flange/Gasket
UICP to Throttle body elbow
TBE gasket to TB
TB to Intake gasket
TB shaft seals
BISS
Any and all vacuum lines off the intake
Lower Injector Seals
Intake manifold gasket
Intake valves
Intake valve seals
Piston rings

You could also have a PRE-turbo exhaust leak. This would be either at the manifold to head gasket or from the manifold to turbo gasket. You can run some seafoam through the engine to find those leaks.

You say to use a logger; like DSMlink? is that a logger or what exactly do you mean by a logger? I'm new to the computer side of cars. I'm used to working on muscle cars without computers.

A logger will allow you to see your ignition timing, and check for knock. Both are vitally important if you want to up your bust. There are a bunch of options for our cars. DSMLink would work, but is expensive. Id say get something smaller and learn then basics.


You should definately fix your knock sensor.

 

[skatershawn]

Are they really? cause that may be what i got. would that really cause my car to pull more off of 10psi over 15? Doesn't seem like plugs would make that much of a difference to me. they're only plugs.

well im not saying this is your main problem and what may be completely causing this! But running hot plugs on turbo engines isn't that good! It can cause pre-ignition which can destroy your motor! and can cause loose of power due to the fuel being ignited before its prime point! And increasing boost will cause it to happen more!

Theres all kinds of info on it!
Im just letting you know to checking it out!

heres a link on pre-ignition and knock!
Engine knocking - Wikipedia, the free encyclopedia
its the wiki version but its right on!

good luck man!