This ^^^ is EXACTLY why i couldnt even achive my 10psi wg spring pressure on my setup,drove me nuts.
I havent tested my back pressure yet
( i assume rediculously high with a 65mm exd turbine,lol) at 21lb boost acting on a 66mm precision gate. When i figured out it was this and not a tuning issue, switching to a 4 port wg solenoid allowed me to achive any boost i wanted. This was an entry level turbo for me and i knew it would be an issue. I plan on a more efficient (exh side) turbo over the winter.

 

Would you say then, that the backpressure was not a consideration when ordering your wastegate? Would you have preferred that is was a consideration? Or was the use of the boost controller a good enough solution to not bother about factoring backpressure into your wastegate purchase

 

It actually was a consideration, i knew i would have alot of back pressure with the small exhaust side of the turbo. So i chose a large wg to help bleed off excessive exhaust. I just didn't realize at first a 3 port solenoid configuration wouldn't be able to clamp down on the top of the wg enough to get a desired boost pressure. Hence the 4 port which adds all control to the boost controller. This removes uncontrolled boost pressure from the bottom of the gate in a traditional 3 port setup.

 

Actually it may seem backwards, but the larger the turbine and the lower the drive pressure, the harder boost control becomes

Much more gate flow capacity needed for a a low back pressure setup vs high back pressure setup


Easy way to think of it, say you have a system than runs 1:1 at 10psi boost and one that runs at 2:1 at the same boost

With the 2:1 system you only need to vent off enough exhaust to hold 20psi in the exhaust.


With the 1:1 system you need to be able to vent and hold 10psi in the exhaust to hold 10psi of boost


Plus the lower the pressure the lower your pressure delta across the WG valve (atmosphere pressure VS pressure inside the hotpipe) so your gate orifice flow capacity drops


I have had a tc78,7675,pt88 and gt55 all on the same setup. All the small turbos I could hold 4psi absolutely no problems all through my rpm band

Swap on the gt55 and could not control boost until I added another WG

 

^^ Thanks. I was wondering about that.

 

lmfao

 

Would everyone kindly agree, that one correct way to choose a wastegate, is to determine the maximum boost you intend to run (off the boost controller) and then select a spring about half as strong as that?

http://www.turbosmartusa.com/technic...wastegate-faq/


"With a boost controller installed, a general rule of thumb is that the maximum boost level that can be achieved safely is double what the spring is rated to. If your target boost pressure is 20 PSI, a minimum spring rating of 10 PSI is recommended. This gives the wastegate more control over the exhaust gas. If the spring rating is too low, as boost levels climb and exhaust flow rates increase, the flow of exhaust can influence the valve more as the only force trying to close it is the spring force."


This is just one step. I have found many interesting references. I hope to find more details. I have finals this week so my free time is limited (when I was available this weekend I was using this as an excuse to procrastinate studying. But not anymore...) When I return finally I will have many details to provide. I'd like a strong foundation in the mean time from which to build facts, so I might come back with simple "do you agree y/n" statements like the one above to facilitate the rewards.

 

Stay in school

 

Excellent summation.

 

1. please clarify for exactness, you chose a larger wastegate or you chose a higher boost wastegate spring?


Reasoning:

he is saying that when you take into consideration (you care) about the exhaust gas pressure, you upgrade the wastegate spring to compensate, or else boost at the intake manifold will drop in a linear fashion with respect to EGP.





NExt issue,

If this


Is true, then one in every two turbo V8 owners posting on this website has had to purchase a 15psi wastegate to achieve 7psi intake manifold pressure, since

Reasoning:

And all I need is to find ONE of them to prove it (I don't own the engine to test with or I would). So where are you? Half of you guys should be able to help me out here.

 

This bullshit still ongoing ?

Where's the cleaner ?

 

And you would have to quote me. Just great. I do not want to have to defend that statement. Just to be clear it is because it is not true in all situations and circumstances. Just some of the time. Exhaust pressure is just a factor.

 

In my experience I have found that nearly every single OEM turbo car operates with a high EGP ratio of 2:1 or higher, and not a single one of them has a problem with their OEM wastegates limiting boost for the reason you propose. So of course it does not apply in all situations- I knew that from the start and that was my point from the beginning, that it simply should not apply to the majority of novice turbocharger situations, it is not something a novice is likely to encounter. Thus, a wastegate will work in the majority of situations provided it is application oriented, regardless of exhaust gas backpressure. Only those rare instances where EGP is climbing with an excessive ratio coupled to high intake manifold boost pressures will it become a consideration.

I found some good literature,
http://www.max-boost.co.uk/max-boost...st/exhaust.htm

This site is very detailed. They cover almost every nook and cranny about turbocharger setups, and even touch on the subject,

"Very roughly, for a stock(ish) turbo and a cat-less exhaust, the exh backpressure is about 2.5 times the boost pressure. So if we're running 1 bar boost, we've got 2.5bar pushing at the wastegate (against the actuator spring)
Then we calculate the area of the flap that the gases can see. Say it's 1 inch sq.
We've got (2.5)*14.7= 35.8psi (that's pounds per square inch!)
...so the gas force pushing the flap is 35.8 pounds. Simple.

That's why actuators that can hold high boost pressures need to have much stronger springs. "

In those cases they upgrade both the spring and diaphragm together, like here,

http://www.bankspower.com/techarticl...astegate-Works

" This happens because turbine inlet pressure also increases as boost pressure rises. The fix is to use a bigger spring in the wastegate actuator to hold it closed until the desired peak boost is achieved, however, that also requires a bigger actuator diaphragm to override the heavier spring when the desired boost level is reached. "


A high performance wastegate supplied by the manufacturer has this as part of it's design. The engineer knows the surface area of the valve, calculates resulting pressure vs the intended spring selection, that way the customer does not have to worry about the EGP except in extreme situations, rare to novices. I have found no evidence otherwise, and I stand behind my original statement and every post hence forth with the only disclaimer that I used the word "technically" specifically with respect to these rare instances of high EGP, and I appreciate you all for bringing it to my attention that the typical backyard V8 Turbo does have as high an EGP ratio as an OEM turbo car in many situations... thank you and I look forward to providing more information and hopefully some good responses from wastegate manufacturers.

One more thing. It would really change my mind if people start showing up with 15psi gates that only held 7psi or 10psi. I think that is an extremely rare situation across all engine platforms- at least I have never heard or seen one. But I would love to find some folks who have! Certainly it isn't 50% of all turbo V8 owners though. 50% may have high EGP ratios but not all of them have a problem achieving pressure in their intake manifolds because of it, at least as far as the wastegate is concerned. This is up for debate, I would love to find some examples of this problem! Rotary guy, your application is far from typical, and I am sure you are using more than 15psi of boost to see this issue crop up.

 

Serenity now! Serenity now!

 

And wonder why ls1tech is a failure

 

My friend, you are going 8.5's at 165. This is hardly novice territory in my opinion.

Next, somebody provided an interesting solution without realizing it. If I understand correctly, you can increase diaphragm size and spring size together- keeping the same boost setting. This would also serve to reduce response- more mass to move means slower to respond. Same thing with larger bypass valves happens for the same reason. So the real recommendation here is to use the smallest, lightest components that will achieve the desired boost setting in all applications- something that a novice should be aware of, but he isn't going to pre-calculate his EGP somehow and come up with plan of which gate to buy. Novices have no formulas, no experience, they can only go by what we tell them and copy what others do.

Ill give you a chance now then, How would you recommend a gate to a novice running 15psi with the hopes of achieving 25 at some point? Would you tell them to buy a 25psi spring with the hopes his/her EGP flops the gate open from the get go limiting boost? I dont think so, so why not give some experienced input here.

 

Forget that guy man some of us really appreciate your input. Let him be a keyboard jockey. Eventually he will get tired of talking in circles. He has made quite an *** of himself already let this thread die

 

This is essentially what I am saying. If the application calls for a large gate- for a low boost application, the gate will flop open easier and it flows more too, allowing boost to stay low.

The opposite, a tiny gate, we both understand this is for flowing less exhaust, the smaller surface area makes it more difficult to push open by exhaust, it holds a higher boost, it should also respond quicker because it is smaller.

agree, agree /agree

In both cases, you use the gate the application calls for- but you do NOT say to yourself, "well I am going to have a very high 2:1 drive pressure ratio, so I should probably buy a spring for twice the desired boost pressure", this is not a solution and it should not be considered a solution by a novice new to turbochargers. The same gate can be used on several different setups that have vastly different drive pressure ratios, and the majority of them will still net the same intake manifold boost pressure.

Is it bothering you that the manufacturer has taken the drive pressure into consideration, and I am failing to mention this in my first post? If I add somewhere that the spring resists opening for a wide range of drive pressure ratios due to the design implemented by the manufacturer will it fix the statement? I take things like this as a given (we HOPE the mft is doing R&D and we sometimes forget that they may not)

 

You are making this way too complicated. Purchase a wastegate sized to compliment the size of the turbine. Stop trying to reinvent the wheel. You could get your point across in 4-5 sentences. Try it.

 

Limit: 4-6 sentances, go! with respect to external gates:
The manufacturer of the gate assumes you are going to buy the right size gate for your application. If you have the right sized gate, then the supplied spring setting will be fairly close to your expected, desired boost setting as advertised for a wide range of exhaust gas pressure ratios, or "drive pressures". Typically you choose a spring that supplies half of the total amount of boost you wish to run, then use a boost controller to dial it up and down, with the spring moving a diaphragm against an atmospheric pressure reference for the lowest setting possible (I don't know of anybody providing a vacuum to their dome to pull the valve up early). Exhaust gas pressure is not a typical novice decision factor when choosing the first spring, it isn't until you already tried a spring and need a bigger spring for some reason (I wouldn't opt for a 30psi spring if you are trying to get 15psi) that you might step up, and even then you can still usually manage with a mediocre spring, because modern boost controllers like the profec B spec-II can hold a gate shut until a specified boost so they don't crack early.