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Old 03-10-2014, 04:41 AM   #1
majunche66
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Default turbo intake question, could this be the cause of my problem?

i have a modded 04 sti, built block, (carrillo rods cp pistons, acl bearings, cosworth pump high flow high volume. built and ported heads, cossy avcs cams 278/274)
precision 6262 .82 A/R rotated, 1200 cc injectors dual in tank walbros. dual plate exedy clutch, short shifter, bushings, coil overs. etc etc

rotated cosworth intake mani, custom fabbed all my piping.
basically "the works"
and it is running 3 inch dp all the way out. no cats no muffler or silencer. it is a little loud but i can bare with it.
the car is in south america, so noise or speed is not big a deal here.
hydra ems for engine management.

what is curious and my question is that i fabricated a 3 inch intake for the turbo and used a 4 to 3 inch silicon adapter. i have a rotated setup, it goes from turbo to fender obviously 90 degree bend, to another 90 small straight pipe and a final 90 degree to a filter that i placed a behind the plastic cover that has the sti sticker under the headlight. on the street i run it cover on, on the track cover off, could this be the cause of my power drop after 6200-6400 rpms?

what makes it worse, is that @ 18 psi the power keeps climbing the way it should. i looks like a proper dyno graph.

i increase the boost and the car makes the same power in some places and fluctuates a lot and makes more power on the mid range but not much gain as expected 10 hps per 2 psi. and over 6200 rpms it drops hard. and if i give it timing it it drops even harder.
i revised the tune. different afrs different timing combined them. you name it, and it did not make a difference. tried cover on and off a little change on afrs but not on total power delivery. i am sure there is a choking point on the system, i know heads are not. and exhaust system could not be since it is basically a straight pipe.

running out of ideas, any help would be greatly appreciated.
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Old 03-22-2014, 11:12 PM   #2
KamekazeSTI
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Sounds more like a fueling problem. Fuel cut? Or fuel pressure problem maybe?
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Old 03-22-2014, 11:22 PM   #3
pet3r
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What silicone intake adapter are you using? A few years back I was using a weak turbo inlet, and above 21psi it would start to collapse because it was sucking in so much air. It didn't have any ribbed supports inside of it. This happened at a boost threshold and not an RPM like yours.

What is your IDC at 6000+rpm? How much timing as well?
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Old 03-22-2014, 11:41 PM   #4
02nismokiller
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Quote:
Originally Posted by pet3r View Post
What silicone intake adapter are you using? A few years back I was using a weak turbo inlet, and above 21psi it would start to collapse because it was sucking in so much air. It didn't have any ribbed supports inside of it. This happened at a boost threshold and not an RPM like yours.

What is your IDC at 6000+rpm? How much timing as well?
He's rotated and doesn't have the stock style inlet, he's not collapsing anything lol.... But it does sound like a fueling issue, maybe your fuel filter is clogged. Or another big possible cause is that your running a reducer right off your turbo going from 4"-3" and having so many 90* bends for your intake

Last edited by 02nismokiller; 03-23-2014 at 12:15 AM.
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Old 03-23-2014, 12:50 AM   #5
majunche66
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Quote:
Originally Posted by pet3r View Post
What silicone intake adapter are you using? A few years back I was using a weak turbo inlet, and above 21psi it would start to collapse because it was sucking in so much air. It didn't have any ribbed supports inside of it. This happened at a boost threshold and not an RPM like yours.

What is your IDC at 6000+rpm? How much timing as well?
idc is anywhere from 72 to 86 to redline @20 psi of boost, i noticed that the fuel pressure is dropping after driving the car from 50 to 40/42 psi. (idle) maybe this is the problem. afrs keep the same. i will change the pumps this week. i have 2 walbros in tank. i would buy 2 aeremotives 340 and swap them. to see if it helps. also boost keeps dropping like crazy i tried raising the boost to 22-23 psi and it drops to 20-19 by redline.
time to start hunting the problem.
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Old 03-23-2014, 02:30 AM   #6
2Fast4U1DAY
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Quote:
Originally Posted by majunche66 View Post

idc is anywhere from 72 to 86 to redline @20 psi of boost, i noticed that the fuel pressure is dropping after driving the car from 50 to 40/42 psi. (idle) maybe this is the problem. afrs keep the same. i will change the pumps this week. i have 2 walbros in tank. i would buy 2 aeremotives 340 and swap them. to see if it helps. also boost keeps dropping like crazy i tried raising the boost to 22-23 psi and it drops to 20-19 by redline.
time to start hunting the problem.
Stock fuel pressure at idle with vacuum applied is 43 psi. It increases at 1:1 ratio in reference to boost. For every 1 psi of boost it sees fuel pressure should increase 1 psi as well... that said unless you have an aftermarket fuel pressure regulator, your fuel pressure sounds normal (unless you arent seeing 66 psi at full boost)...
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Old 03-23-2014, 03:41 AM   #7
majunche66
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Originally Posted by 2Fast4U1DAY View Post
Stock fuel pressure at idle with vacuum applied is 43 psi. It increases at 1:1 ratio in reference to boost. For every 1 psi of boost it sees fuel pressure should increase 1 psi as well... that said unless you have an aftermarket fuel pressure regulator, your fuel pressure sounds normal (unless you arent seeing 66 psi at full boost)...
I got twin walbros custom lines 10 and 6 return, and aereomotive fpr.
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Old 03-23-2014, 09:22 AM   #8
2Fast4U1DAY
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Quote:
Originally Posted by majunche66 View Post

I got twin walbros custom lines 10 and 6 return, and aereomotive fpr.
So what is your base pressure set at?

Regardless of that, I doubt its a fueling problem. If a stock engine and turbo can creep on up to 22-23 psi without the "proper" fueling, then theres no reason you shouldnt be able to see the same thing. Its a boost control issue.

Why is it that you have 23 psi wg spring pressure? Is your goal to run 44-46 psi of boost? You want your wg spring pressure to be roughly half of your desired boost pressure.....

Last edited by 2Fast4U1DAY; 03-23-2014 at 09:45 AM.
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Old 03-23-2014, 01:46 PM   #9
DisoDisp
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Exedy twin plates suck ass.

Maybe its slipping a little at higher boost/torque.

But you should notice it pretty easily.
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Old 03-23-2014, 04:31 PM   #10
majunche66
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Originally Posted by 2Fast4U1DAY View Post
So what is your base pressure set at?

Regardless of that, I doubt its a fueling problem. If a stock engine and turbo can creep on up to 22-23 psi without the "proper" fueling, then theres no reason you shouldnt be able to see the same thing. Its a boost control issue.

Why is it that you have 23 psi wg spring pressure? Is your goal to run 44-46 psi of boost? You want your wg spring pressure to be roughly half of your desired boost pressure.....
running 18 pounds of wg spring, not 23. i raised the boost with the boost controller. it still tappers off.
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Old 03-23-2014, 04:33 PM   #11
majunche66
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Originally Posted by DisoDisp View Post
Exedy twin plates suck ass.

Maybe its slipping a little at higher boost/torque.

But you should notice it pretty easily.
it does not slip at all, it keeps pulling hard, making over 460 to the wheels, but drops to 430 towards redline.
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Old 03-23-2014, 04:49 PM   #12
2Fast4U1DAY
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Quote:
Originally Posted by majunche66 View Post

running 18 pounds of wg spring, not 23. i raised the boost with the boost controller. it still tappers off.
Either the wg is bad or you have a tune problem. My guess is the latter considering you say the boost fluctuates a lot. TD is probably off along with other parts of the tune
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Old 03-23-2014, 05:02 PM   #13
Brother EddieJ.
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Quote:
Originally Posted by DisoDisp View Post
Exedy twin plates suck ass.

Maybe its slipping a little at higher boost/torque.

But you should notice it pretty easily.
They do not slip. They stop engaging when worn and potentially shatter. Educate yourself before you just talk randomly.
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Old 03-23-2014, 05:08 PM   #14
DisoDisp
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We just had one slip last month, swapped it out and it wasn't badly worn.

We've had more than one slip btw, once you start getting into +500ft/lbs they start going at around peak torque.

Sometimes they let go significantly earlier.

The TRIPLE plates, haven't had any issues thus far over here.

Last edited by DisoDisp; 03-23-2014 at 05:15 PM.
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Old 03-23-2014, 09:04 PM   #15
majunche66
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Originally Posted by 2Fast4U1DAY View Post
Either the wg is bad or you have a tune problem. My guess is the latter considering you say the boost fluctuates a lot. TD is probably off along with other parts of the tune
What do you mean TD? Timing is anywhere from 12 to 17 peak tq to redline and afr steady on 11/11.1 and my boost controller is manual, there is no way to mess with the boost electronically.

Today took it to the track, lot of traction issues ran 11.7 easy on the launch. 1.77 60 ft
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Old 03-24-2014, 12:04 AM   #16
2Fast4U1DAY
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Quote:
Originally Posted by majunche66 View Post

What do you mean TD? Timing is anywhere from 12 to 17 peak tq to redline and afr steady on 11/11.1 and my boost controller is manual, there is no way to mess with the boost electronically.

Today took it to the track, lot of traction issues ran 11.7 easy on the launch. 1.77 60 ft
Ahh I forgot you said you are MBC... DOH! My b...
Hmmm and you said you tried different MBC's to verify that the problem isnt in fact the MBC? Have you tried a different gate or tested the current one to verify that the gate is functioning properly?
Did you try running a different rotated intake to see if you can see your target boost? In theory it *shouldnt* be the problem but in reality the stepped down coupler may be just enough restriction that you are choking the flow to the compressor... I see more now why you could think its the intake, but I cant seem to make sense of why its not supplying the compressor inlet with MORE air and not less... now I am stumped too hmmm

Last edited by 2Fast4U1DAY; 03-24-2014 at 12:14 AM.
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Old 03-24-2014, 03:07 AM   #17
majunche66
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Quote:
Originally Posted by 2Fast4U1DAY View Post
Ahh I forgot you said you are MBC... DOH! My b...
Hmmm and you said you tried different MBC's to verify that the problem isnt in fact the MBC? Have you tried a different gate or tested the current one to verify that the gate is functioning properly?
Did you try running a different rotated intake to see if you can see your target boost? In theory it *shouldnt* be the problem but in reality the stepped down coupler may be just enough restriction that you are choking the flow to the compressor... I see more now why you could think its the intake, but I cant seem to make sense of why its not supplying the compressor inlet with MORE air and not less... now I am stumped too hmmm
i hooked the boost controller after the TB, now boost is steady no more spikes or drops apparently.

i read on some other forum that the pressure that the compressor housing sees is not the same as the intake mani. made enough sense to try, and apparently it worked..
i will keep testing a report back.

thanks everybody for the input
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