Turbo question, drop in psi

[JTS VENOM PERFORMANCE]

Ok here's th supposed problem plain and simple with my twins .

In the first three gears, you see about 7 psi,but where you can really se it is in fourth,.

cruise in fourth and hit it, the rpms climb, goes to 10 psi then slowly bleeds off to 7psi.

other than that smooth running. easily braking traction. Boost comes on hard and quick.In the first three, it rev's so quick you dont notice the drop, plus you are focused on shifting. but in fourth you have time to watch the problem.

intercooler was pressurized and ok now. going out now to do some checkkingon vacuum lines.

any suggestions good or bad while gone will be appreciated.
oh and do ahve a boost controller set for 10psi with 7 psi springs installed.

 

[Blaine@PSI]

stink my observation from here in texas, is that everything is working properly. your boost controller is limiting you to 10lbs which it is set at, and 7 lbs spring is there to "maintain" the boost. So how this works is as the turbo spools hard and fast the spring cannot control teh boost but the boost controller can so it does. It limits the over boost problem seen with many turbos. hope this helps.

 

[K-80-123]

Stink, On mine when driving around town the boost guage shows no boost till you push it and then the boost comes on hard....the waste gates open and close and you can hear the excess boost being pushed out.....even at zero boost on the gauge you can hear the waste gates open and close......Do you have the gates set correctly?.....Mine also pulls hard through all the gears....you have to let up some from 1st to 2nd or you get into the rev limiter.....that is something that will be changed when the AEM is installed......Did they flash your PCM?.....this whole mess sounds like the PCM to me and not the kit????.....of course I don't know that for sure but if your flash is not correct it seems to me that might cause it to fall on it face..........I wish I could help more.....but it sounds like engine management.

Walt

 

[Nowwhat]

I don't know if this helps Stink....But in my twin turbo GT2..I can't get into max boost until 3rd gear....the cars runs out of gear in 1st and 2nd before the boost can get to 18psi.....

 

[mopower1958]

Stinker I work on Strokes and Cummins every day, they won't make maximum boost till you load the engine with the rpm above 2500 rpm.Its like nowwhat said, in the first three gears you really don't have a load on the engine like you do in 4-6th. The turbo's boost from exhaust flow,and in I am thinking in 1st through 3rd the engine isn't loaded enough to boost.Try rolling along in third,floor it while holding it back with the brakes to simulate more load and see if the boost comes up. Just an idea from a shade tree mechanic!

 

[JTS VENOM PERFORMANCE]

ok , maybe phrased it wrong, everything seems to be working ok, but the psi is set at 10psi it the first few gears I understand it spools quickly, but you still see a spike of 10psi then down to 7,

but, in fourth roll ons it jumps to 10psi and the higher the revs go the more it drops to 7 psi, i thought it should stay at 10 psi ?

this is what David said he was having trouble with tuning , it would hit 10 psi but would drop to 7 on the dyno run.

everything else seems ok, and yeah walt it spools "real" quick in the first few.

should i change the springs to 10's to maintain 10psi?

the boost controller is set at 10 psi, its a blitz controller by the way.


Thanks guys for the info, I'm stummped. Looking at ya'lls posts I get the fact that there is no boost untill load. then they kick in.
and that boost is more evident at a higher load.
and that loss of adhesion to the asphalt occurs under boost
whith that
No the pcm was never flashed, using a vec II
figured at full load it should hold psi set from controller, from what I understood you double what the spring is capable of (7lb spirng capable of 14lbs)

am I making sense on this?

 

[FerrariTruck]

hey stink, when we were dynoing my friends turbo 350z we noticed that his car couldn't get past 6psi, however on the street he would hit 8psi only thing we could think of was that the dyno was enough of load for the engine rto really build up alot of boost. everyone here so far is right boost is directly related to load.

 

[Silverback]

I will elaborate when I get home this afternoon, but if the wastegates have 7PSI springs they will start to bleed off the exhaust flow (wastegates do not bleed off boost) to the tubro at that PSI. You need to explain to me, or send me a link to your Boost Controller. Are you referring to a Pop Off Valve?

 

[Ram From Hell]

I will elaborate when I get home this afternoon, but if the wastegates have 7PSI springs they will start to bleed off the exhaust flow (wastegates do not bleed off boost) to the tubro at that PSI. You need to explain to me, or send me a link to your Boost Controller. Are you referring to a Pop Off Valve?

Actually, won't the wastegates start bleeding off boost before they hit their target pressure? A wastegate isn't a "digital" device. As I understand it, it's going to start opening well before the target max PSI, and gradually open on its way to that pressure. This is the issue of "wastegate creep", yes?

 

[AWDisuzu]

the turbos probably can't flow enough to hold 10 psi to redline. especially if they hit 7-10 psi of boost right away. 8 liters of motor is a lot to boost for even a huge slow spooling turbo!

ok , maybe phrased it wrong, everything seems to be working ok, but the psi is set at 10psi it the first few gears I understand it spools quickly, but you still see a spike of 10psi then down to 7,

but, in fourth roll ons it jumps to 10psi and the higher the revs go the more it drops to 7 psi, i thought it should stay at 10 psi ?

this is what David said he was having trouble with tuning , it would hit 10 psi but would drop to 7 on the dyno run.

everything else seems ok, and yeah walt it spools "real" quick in the first few.

should i change the springs to 10's to maintain 10psi?

the boost controller is set at 10 psi, its a blitz controller by the way.


Thanks guys for the info, I'm stummped. Looking at ya'lls posts I get the fact that there is no boost untill load. then they kick in.
and that boost is more evident at a higher load.
and that loss of adhesion to the asphalt occurs under boost
whith that
No the pcm was never flashed, using a vec II
figured at full load it should hold psi set from controller, from what I understood you double what the spring is capable of (7lb spirng capable of 14lbs)

am I making sense on this?

 

[JTS VENOM PERFORMANCE]

Hey bo glad your here! So should I install the 10lb springs if I want 10lbs boost?

Also can I install the 14 lb springs to obtain high boost of 14lbs and use the electronic controller to limit it to 10 lbs for low setting?

 

[FlyingLow]

With my turbo I always see higher boost at higher RPM and higher gears. And I see more boost on the street then the dyno. Being load dependent you will see more psi on the street. I go less throttle at 60 MPH and get lots of boost. Going WOT from a stop and my boost has to build.

Smoke

 

[Scrambler1]

I like AWDisuzu's statement. If you're hitting 10# boost early they may not be capable of pushing enough air for our big motors at high revs. I'd get them to send you a slightly bigger set to try. Just seems strange to me that they are hitting max allowed boost so early. Every turbo vehicle I've ever driven doesn't hit max boost until a higher load. You're at max boost way before that.

You should be able to hear the wastegate dumping air if its just opening too early. Try to find enough road to roll into it in 5th and see what happens. Maybe have someone else actually driving so that you can really study what's happening.

 

[Silverback]

Okay, first off let me apologize if this upsets some people, but I'm going to take the time to explain a few things on how turbos and wastegates work.

This has been stated a couple times and is in total error. Wastegates do not bleed off boost, and you will not hear the boost being bleed off. Wastegates are actuated by the boost and bleed the exhaust around the turbo which limits the boost. Pop Of Valves (POV's) which are located on the pressurized side of the intake bleed off boost and can be heard. In a turbocharged application they should only be there as a safety valve.

Before I get into a few other things I have a couple more questions for you Stinker. I need the make and model of the turbos. If you have a link for their site so much the better. I can then figure out if the turbos are large enough for your engine. I'm willing to bet my left nut that that is not the problem, but we need to know for sure. Second is do you have POV's on this setup? I think I remember seeing them in your pictures, but I'm not sure. Once again, if you do I need the info on them also.

Okay, I look at your boost controller and now understand how it works. Here is a quick explaination on how it works. You have 7 PSI springs in your wastegate, which means they will start to open at 7 PSI and maintain that pressure. What the boost controller does is bleed off a certain amount of boost (in your case 3 PSI) so the wastegate still opens at 7 PSI even though the intake is seeing 10 PSI. Make sense so far?

With the information I have at this time I see one of two things happening. First is if you have POV's they could be bleeding off the boost. That's not what I'm betting on at the moment based on your observations so far.

What I'm thinking is happening is your boost controller is not functioning correctly or it's not connected correctly. A properly operating wastegate does not allow boost to go up to 10 PSI and then slowly bleed it off to 7 PSI.

Damn, just thought of a couple more questions. Are your wastegates controlled by the boost by means of a pressure hose that runs to the wastegates or are they electronically controlled by the servos from the boost controller?

Tell you what. Answer these questions if you can and we can proceed from there.

I really hope this is helping.

A quick note to Eric and Smoke. Once again, not trying to be an ass, and I realize you are trying to help out, but the STS does not function in the same method as an energy driven turbo system. The length of the intake, exhaust, and pressure sensing components dictate that it opperates differently.

 

[Nowwhat]

What kind of boost is Walts truck holding...?

 

[K-80-123]

Good question.....the boost controller shows 7 psi on the low setting and 15 psi on the high setting.

Walt

 

[JTS VENOM PERFORMANCE]

Ok lets see...
2 wastegates 48mm turbosmart pressure acuated.
1 BOV or POV 50mm tial brand.
turbos are T-60's will have to get the name.
yes you can hear the bov unlease pressure when on decell.

Understood a wastegate should not bleed(only word I know how to describe it) from 10lbs to 7 lbs, should be opposite.

In fourth or fifth from a crawl to WOT (yeah baby) it would shoot to 10lbs then drop slowly to 7 lbs.

 

[Nowwhat]

the wastegates are operating properly if you are getting to max boost....your problem is maintaing boost.....

 

[JTS VENOM PERFORMANCE]

Ok heres another twist guys, I have sneaked off today from momma and talked with a couple hometown boys about the ride today.
First off they found a few things they were not happy with, but to small to go into details.

But they "really" didnt like the position of the drivers side wastegate, I'll take pics later ,but the wastegate is mounted facing opposite direction of exhaust flow to turbo, resulting in the worst flow you can have to a wastegate. So that may be part of my problem.

But they want me to bring it by friday or saturday , install the 10 lb springs, and for now do a tune for 10lbs straight to be sure its safe to drive without the drop for now.

Then later on its going back to them after I recoupe my $'s a bit , and it will basically be completely redone, new wategates(tial) two BOV's,new plumbing, and a complete fuel system. And eventually AEM computer.

They say it should work fine for now.

Also talked with them about becoming a vendor, and they said they would snoop around and check us out!

 

[JTS VENOM PERFORMANCE]

EXACTLY!!! evidently not enough beans!!!! cant maintain altitude! my boost keeps dropping!!!!!!

Kinda would make a good commercial for viagra, not enough boost it keeps dropping , quikly Scotty , pop another pill!LOOL

Can ya tell I'm feelin good?