geoff17

Ok so I switched from a tc76 and a full exhuast over to a PT7675 CEA billet turbo and open downpipe and I now have boost creep. I know that this is due to relieving the back pressure both pre-turbine and post turbine. The wastegate (44mm Tial) is sprung to 9psi I believe which I think it maintained with the tc76 but we added a bleed with a vacuum t between the wastegate and boost ref port on the compressor and this netted 15psi steady through the entire rpm curve. Problem I am having now is with the PT7675 and no exhaust, just the downpipe and took the bleed out it sees 11-12 psi and creeps to around 16 by 6800rpm. I have no problem with it seeing 16 psi as once you get used to that power you never want to turn it back down but the power is progressing in like a centrifical blower. Essentially the wastegate will maintain 16psi and hold. So my thinking is that with the gate 100% open it can maintain 16psi but the power comes in slow getting to the 16psi. So can I spring the gate to 15psi to have boost come in quicker and go striaght to 15psi then the gate opens and is 100%open at 16psi and hold. On paper it makes sense that this should work I just want to know if anyone has any real world results of this?

Forcefed86

iTrader: (4)

Test your theory by holding the WG open and seeing what boost does at RPM under load.

Do you have any sort of piping after your WG? Does it vent to air or recirculate?

A spring loaded valve set to 15psi or so may cure your issue. Looks up "Grainger Valve". Worked well for me... Bleed type boost control is pretty finicky.

geoff17

1. How do I hold the WG open? As in take the spring out or take the gate off completely?

2. Wastegate vents to air, on the old setup it went back into the downpipe.

3. Not sure what you mean by the spring loaded valve. I currently don't have a bleed for boost control. Just the wastegate sprung to 9psi.

Edit: Looked up the grainger valve and it just looks like a homemade boost controller.

Forcefed86

iTrader: (4)

1.) Removing the spring is the best way. Removing the gate assy. will have less restriction.

2.)Sometimes having any tubing at all after the WG opening makes a big difference in restriction/creep. Like a dump pipe directing the exh flow.

3.)Did you google grainger valve?

http://lmgtfy.com/?q=Grainger+valve

Basically it holds all the boost back until a set point (say 15-16psi) then opens and lets the air through to the gate.

geoff17

1. Ok so if I remove the spring and for hypothetical sake lets say the car makes 16psi but not until 6000rpm then holds 16 psi all the way until 6800. Now say I spring the gate to 10 psi and the cars makes 10psi right away but from 5000-6000rpm it boost creeps up to 16 psi and holds to 6800 would this mean my gate placement is good to go for holding 16psi? Because then if thats the case what I would want to do is put a 16psi spring in the gate so it makes 16psi as fast as it can and then holds 16psi right to 6800rpm. Does this make sense? In theory it sounds like this would work. Any opinions?

2. Having tubing after the WG will help or hurt boost creep? What affect will the tube have?

3. I did google the grainger valve, it looks just like a homemade boost controller or like the "home depot boost controller". Again same question here as before could I set my boost up to 16psi and have it boost quickly to 16 and hold to redline?


Essentially what I am wanting to know is if the wastegate can hold 16psi and stop creeping there with a 9 psi spring in it now can I switch to a 15 or 16psi spring and get it build boost faster and still maintain 16psi to redline? Or would putting a 15psi spring in it cause it to boost creep to say 22psi somehow?

BMF_Racing

iTrader: (6)

It really depends. Guessing it might work in first or maybe second gear, but when you hit 3rd gear on the current setup does the boost jump as a result from the extra load? If no, it might work and not cause a spike that it can't recover from.

Raise boost to 25psi and that 44mm gate will be plenty big enough. lol

geoff17

I like your thinking on that last sentance, lol. Sadly I'm still a stock bottom end and just pump 93 and no methanol yet, did make 735 though.

We did make sure to dyno in 3rd gear with load by hitting the dyno brake and making a pull and it will maintain 16psi. I tested on the street and had a buddy watch the boost gauge and it maintains 16psi all the way through 3rd gear to about 140mph probably 64-6500ish rpm. Also while on the dyno the tuner did a 2-3 wot shift and the top of second gear hit the max boost and maintained that same boost all the way through 3rd gear, did the same thing on the street.

BMF_Racing

iTrader: (6)

then I'd say its def worth trying then. Watch it closely and get out of it if it jumps over 18psi. Maybe get a couple gals of race fuel as a cushion for that first testing, just in case it over shoots the 16psi you will be much safer than just 93. Good luck.

geoff17

Well I'll def give this a try this weekend. I'll have my buddy data log for me and watch everything real closely.

Forcefed86

iTrader: (4)

I don't think the car will make squat for boost with no spring, but It's a good test to see if you've maxed out your gate. It's usually how I run my base tune.

Boost will come on more quickly with a grainger valve at higher boost levels because it holds the WG shut until the target boost level is reached. Usually without one the gate slowly opens before your target boost level is reached slowing "spool time".

I'd try fabbing up a quick grainger valve (or buying one) and setting it to open at 15-16psi with shop air. Then put it inline with your WG's bottom port.

None of that will help with creep though... Removing any restriction on the WG (dump tubes etc) can help with that.

When I removed this pipe I saw no creep, with it I see a 1-2psi creep around 6300 or so.

geoff17

Ok guess there is no need to make any pulls then without a spring then. I'm not having any trouble spooling quickly so I don't think I need the "grainger valve". This turbo spools really quickly, all thats happening is it currently has 9psi springs in it so the gate opens at 9psi but it sowly creeps to 16psi and levels off. I was just worried that if I changed the springs to be setup for 15psi that it wouldn't creep further than 16psi all of a sudden. But if it can hold at 16psi with the 15psi springs I'll be happy. Just a little worried that it may spike up past 16 and not be able to recover.

skinnies

iTrader: (33)

How is your WG placement? Tial 44mm gate should be more than plenty to control it down to 3lbs or less and no creep if the kit was built correctly. I can control down to 1.5lbs with a precision 46mm gate and 1.5lb spring using a precision 7675 on my ltd.

geoff17

Its probably not that good. It is right at the merge but 180* from the T4 flange, (The gate sits right under the turbo). I just don't have the money right now to re-position the gate correctly and I also don't mind if it won't control down to real low boost. This setup worked flawlessly with the tc76 and the full exhaust on the car, but not anymore. If it will control it to 16psi with the 15psi springs I'll be happy. I just want the gate to open at 15psi and hold at 16 rather than open at 9-10 and creep slowly to 16psi.

Sarg

iTrader: (6)

That is actually what the home depot gate or a manual boost controller like the Halman is designed to do. It prevents the gate from seeing boost until a certain psi then dumps in the pressure to the gate to cause it to open.

Forcefed86

iTrader: (4)

I think running without the spring will tell you if the gate is being over run or not. May be the case if you have poor gate placement. If thats the case you could add another cheapo gate or wait and redo the original placement.

Yes, adding a stiffer spring should help out if a solid 16 is the goal. I miss all the old school gates with spring pressure adjustments on top.

geoff17

Alright so to update anyone for future reference. On paper and in theory my idea made sense but in real world application it doesn't work. I first took the 10 psi springs out of the wastegate and replaced with a 5.8 psi spring, had my buddy hook up the data logger and watch my boost gauge for me and when I went WOT it immediately made 5-6psi and held for a little while feeling like a dog and then around 4-4500rpm it started to creep and creeped up to 16psi by 6800rpm, it may have made 16psi before 6800rpm and just held that until 6800. So it seemed to me like the gate was functioning well enough to maintain 16psi and no more. So we came back let the car cool down a bit and I put in the 14.5psi springs and went back out. Had my buddy make sure his eyes were glued to the boost gauge and when I went WOT it immediately made 15psi then started creeping up almost instantly and he yelled at me to stop and ended up seeing 19psi before I lifted. I tried one more time hoping it wouldn't spin and get a cleaner pull and the same results an immediate 15psi then creeped to 20psi before I got out of it.
Moral of the story, I gotta moved my wastegate.

Bimmerdude

iTrader: (1)

Forcefed86

The synapse has that adjustment screw and multiple ports that push on different size piston areas so you can adjust boost by moving a vacuum line - but they are $400 and up.

If your "wasted" exhaust has to do a 180 that definitely has to be it - some boost controllers (like the high end Apexi thats $500+) allow for boost targeting where they will try to force the wastegate to open more at higher RPM's, but I'm sure a rework of the wastegate would yield cheaper and more effective results.

geoff17

Ok so before I go cutting a hole in this hotside to move the wastegate I'll get your guys opinions. First this is the placement as of now that does not work. The wastegate sits under the turbo in the merge making "wasted" exhaust have to flow backwards, a really poor placement unless there is a lot of back pressure like when I had the tc76 on there.

geoff17

I made some room last night to move the gate to where I think will work better by removing one of my (3) braces for the turbo (the one I removed went to where there is no bolt for the turbo to flange in the pic) This now made room to put the gate in the merge at a 90* angle or slightly upwards if I can. I would essentially just move the gate up 90* from where it is and it would sit in my merge over top of the alternator (the alternator is much lower than it looks in this pic, it will not be near it and heating it up) I'd then run the dump tube down so its not dumping hot exhaust onto the belt. What are your thoughts?

geoff17

Here's another pic if it helps: