boost falling off please help

[xsephish]

Fully built redtop hks 264 step 2 cams. Here is my issue I am running a gt2860rs on wastegate no boost controller at all it would spool up to 20psi at about 4200rpm then boost would start falling off and level out around 15psi.

My turbo elbow is one of those stupid isis screamer pipes not by choice but its what i had and was over budget. At the suggestion of my tuner we added a turbo smart e street series for the boost correction feature to prevent this drop in boost. It is a very reputable shop he has set these controllers up before but it isnt fixing the boost drop we can add boost but same thing happens. Also it is very consistent on the boost falling off. You can look at the boost log on the dyno sheet from wastegate and EBC set to 24 psi with correction and its the same full spool and the drop off lines all sit on top of each other if it werent for the 24psi spike vs the 20psi spike you wouldnt even know it was a different run.

My theory and where i need input is this. Is the screamer pipe my problem i know they dont seal all the way up to the back housing so am i creating such an exhaust leak by running that elbow that it is causing this issue? Someone please chime and and help me on this or atleast help me brainstorm issues of boost falling off. There is no boost creep it goes as high as we set it the dyno the EBC (peak boost recall feature) and me watching the gauge in the car all look good its this damn fall off from about 4.5k to redline.

Also at idle the screamer pipe is sucking in so much fresh air that my wideband cant read driving its fine and on the dyno AFR is good but just a side note.

added dyno graph

green= old ebay top mount t67 MBC 19psi
red= EBC with corection turned on and it looks like its fighting past 5.5k to hold 17psi
blue= internal WG only

blue and red both you can see 4.5k im fully spooled and about 4.7k it just starts dropping. I am happy with the numbers car is a blast to drive very responsive, just trying to get some more minds on this pressure drop and see if a screamer pipe could be culprit

Also it was really hot and humid out last night and that last pull was on a hot motor IC and hot water temps

[Kingtal0n]

If this is compressor map:
ATP TURBO - The Premiere Provider of Turbocharging Components (http://www.atpturbo.com/root/maps/gt28rs.htm)

Then your turbocharger's compressor is out of flow around 320RWHP. If you are trying to make more than that, it is likely that you are simply running out of compressor, and nothing will keep the boost up.

Since you have an open wastegate, this should be evident. As the boost begins to drop, doesnt the wastegate get softer? It should be closing to prevent the drop in boost, which would make it much quieter at that time.

A redtop with proper 264* cams should be capable of 400WHP @ 18psi by OEM redline with OEM components.
Knowing that, I would say set the boost below 15psi- peak power is dictated by the maximum flow of the compressor, in this case.
also, how is the wastegate set to 20psi by default? Do you actually have a 20psi wastegate spring in the actuator? Sounds like the turbo is meant for a 1.8L or 1.6L because 20psi from a 35lb/min compressor on a 2.0L engine is nonsense.

[xsephish]

https://www.turbobygarrett.com/turbobygarrett/turbocharger?productCd=GT2860RS

is what i have .86 back housing and we tried loosening the nut on the actuator lost about 1psi on the internal gate no ebc or mbc hooked up at the time and 18-20 psi is just where the gate opens and the drop and rate of drop is always there and always looks identical pull after pull ebc or not.

[codyace]

20 psi on a 2860 is pretty crazy to say the least, however on some cars they do make power...I'd hate to see air temps though from the flame thrower...I mean compressor.

A decent 2860 car will easily make 350-365 at 17-18 psi, and that's about all the more I'd really push it. As KingTalon suggests if it was a smaller cube engine (1.8t guys) then you could get away with spinning it higher.

With that said the reason for fall off could be many things, I think much of it surrounding the internal wastegate. Have you tried preloading the adjustment on it a little, and then using the controller for the boost? I'd try bringing the peak boost down and see how it works. Lastly, those screamer pipe outlets are known to cause odd fluctuations as well...i'm not engineer so I can't tell you precisly why, just stating that from others reporting it, and my own experience on other cars with too short of a pipe.

[xsephish]

anywhere between 320-350 is what im looking for the car is a DD i went the the discospud because i figured it would meet my needs and allow for a great usable fun to drive power band. Cody do you think the isis screamer pipe has an play on this? They arent really divorced they have that section that bolts in to "divide" WG from the turbine exit and dump the wastegate to atmosphere but it doesn't even sit flush against the back housing so you have an exhaust leak from the screamer section constantly. Do you think a different elbow would have any effect on this? I know you are a huge fan of the Greddy I was wondering if you had seen this one 排気パーツ Exhaust Parts - POWERED BY MAX (http://www.gtfactory.jp/cms/page.php?19) they are the same price point but it combines the elbow and downpipe all into one nice piece and is divorced in the same way the greddy is. I keep going back to the downpipe because we have tried to bring the boost down on the WG adjustment arm and are about out of adjustment room. This thing just wants to open at 18-20psi. It is the stock adjustable garrett actuator not HKS or anything.

[xsephish]

also just came to mind could i see boost fall off due to the greddy intake manifold in combination with the cams I have since i have so much flow in my head/intake

[carlameyer]

I would replace all vacuum lines first. Next suspicion would be injector seals or throttle body shaft seal. It could also be a leak on the wastegate. Ensure there are no cracks on the hotside of the turbo, particularly where the wastegate is separated from where the o2 housing connects. It could also just be the turbo if you have 100k on the car. Pretty sure stock turbos are not ball bearing. Trying to get the stock turbo to hold that much boost over 8,000 rpm is asking a lot. Even my 35R tapers by about 4psi or so above 8k rpms.

Aftermarket Car Parts (http://www.incarparts.com)

[xsephish]

I would replace all vacuum lines first. Next suspicion would be injector seals or throttle body shaft seal. It could also be a leak on the wastegate. Ensure there are no cracks on the hotside of the turbo, particularly where the wastegate is separated from where the o2 housing connects. It could also just be the turbo if you have 100k on the car. Pretty sure stock turbos are not ball bearing. Trying to get the stock turbo to hold that much boost over 8,000 rpm is asking a lot. Even my 35R tapers by about 4psi or so above 8k rpms.

Aftermarket Car Parts (http://www.incarparts.com)

all of those are excellent points for your first post troll but i will quote and reply for the bump thanks