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 Waste Gate Too Big?  

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MuchDa-Bogan
  • MuchDa-Bogan
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  • Joined: 10-January 03
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  • From: qld
Post #1 post 2nd April 2006 - 10:35 AM
resently baught a new turbo (garrett t04b, ar.6 front .84 rear) and a 42mm wastegate as well.. some 1 has said to me that it will be too big causing heaps of lag and i should sell and buy a 38mm. i think he is wrong.. i think it will flow fine just thought i was get a 2nd oppinion.. if it matters my motor is a rb30et.. so it will flow a fair deal of exhaust

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QUOTE (boostaddict_4207 @ Aug 13 2009, 07:02 PM) *
lol yes the turbo is of ebay but they are good for a safe 350 hp there pretty good turbo's mate..


QUOTE (adviliax)
My best childhood mate lost his virginity at 13 to a 14yo chick for a packet of ciggies.
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Mrs_LJ_GSRRVR
Post #2

well im running a smaller turbo than yours and i run a 48mm wategate with no troubles at all.

MuchDa-Bogan
Post #3

yea i have been told heaps of storys like that.. but the guy that told me this is 1 that is "ALWAYS wright.... well at least in his mind smile.gif" he reckons it put out too much needed exhaust between gear changes causing lag.. also same with taking off in 1st

Mrs_LJ_GSRRVR
Post #4

what pressure is the wastegate spring and what boost do you run?
MaDDoG
Post #5

you cant have a wastegate thats too big and the size of your wastegate has nothing to do with spooling up at all. The wastegate is exactly that, a WASTE gate, a gate for the excess to go through once you have reached your preset boost level. So the exhaust gas does not get forced through the turbo, making it spin faster and creating more boost than you want.

MIT20
Post #6

maddog is on the money...

IEATU
Post #7

The downside to running a wastegate that is to big, is when the gate opens the boost will suddenly decrease. Running one to small and your boost will keep climbing with the gate fully open.

Its a trail and error situation unless you have a exact setup that someone else has and you know that it works. Try the 42 as it most likely will be fine.

the red krawler
Post #8

Mate you could have a 1m diameter waste gate on a turbo the size of a walnut, and it would still work fine.

The only thing that would cause lag in your situation is exhaust housing size. If its too big, it will be more laggy but allow for more top end.

Tell your mate to STFU
the red krawler
Post #9

QUOTE(IEATU @ Apr 2 2006, 12:04 PM)
The downside to running a wastegate that is to big, is when the gate opens the boost will suddenly decrease. Running one to small and your boost will keep climbing with the gate fully open.
[right][snapback]6076146[/snapback][/right]


A big gate wont open all the way.... It's only gonna open as far as is needed to keep boost under control. Its an actuator controlled by boost, so the actuator is only going to move until the boost is equal to spring pressure again...

MuchDa-Bogan
Post #10

QUOTE(MaDDoG @ Apr 2 2006, 11:32 AM)
you cant have a wastegate thats too big and the size of your wastegate has nothing to do with spooling up at all. The wastegate is exactly that, a WASTE gate, a gate for the excess to go through once you have reached your preset boost level. So the exhaust gas does not get forced through the turbo, making it spin faster and creating more boost than you want.
[right][snapback]6076086[/snapback][/right]

tryed tellin the guy that lol gate is closed untill boost is reached.. 1nce reached it is opened...
bigger gate will be better for person running lower boost... smaller gate for some 1 running higher boost as less exhaust needs expelled

neil_se
Post #11

Have a read through this and it might help clarify a few things.

http://www.skylinesaustralia.com/forums/in...tegate++formula

OK lets start off with the theoretical stuff, posted some time ago.......

1. The wastegate size is relevant to how much horsepower you are targeting
2. If you want to run high boost, then a smaller wastegate is better than a larger wastegate. The idea being that in order to generate high boost you need most of the exhaust gas going through the turbine, not through the wastegate.
3. If you want to run low boost then a larger wastegate is better than a smaller wastegate. The idea being that in order to keep the boost low you need a lot of the exhaust gas going through the wastegate not through the turbine.

But what is high boost? Well for the sake of this discussion I have settled on 1.2 to 1.4 bar (18 to 21 psi) as being the divider, thus 1. 2 bar and under is low and 1.4 bar and above is high. How did I arrive at this number? Well based on the results of the surveys, this seems to be the most common point where the wastegate sizes change from theory 2 to theory 3 (above).

The next bit of theory is that it takes 1 lb per minute of airflow to make 11 bhp in a current generation 4 valve engine. This is a pretty well established piece of turbo sizing philosophy. But how do we relate this to wastegate sizing? Well referring to the results of the surveys, it seems a straight 1 to 1 relationship is not too far from the average, so 1 lb of airflow = 1 mm of wastegate diameter.

What I am trying to do with the formula is give a baseline, something to think about. An 85% fit type of thing. At the moment there seems to be a majority of guys wanting external wastegates who don't even know where to start. They have been told for big horsepower you need a big wastegate, which is not necessarily true. They have been told you can't have too big a wastegate, which is definitely not true. They have been told for high boost you need a big wastegate, which again is not necessarily true.

In order to do this there is one main assumption, that the turbo is pretty much the optimium size for the target power and boost. If it is totally wrong then whether the wastegate is sized correctly or not is really irrelevant. The turbo / engine mismatch is gunna kill horsepower / response anyway.

A a 50mm wastegate valve is going to weigh twice as much as a 35 mm one. So there is an inertia issue to be considered. I think that is really the crux of the problem. The diaphram has to move twice as much weight, in and out very rapidly. This has 2 undersirable effects incomparison to a smaller (more correctly) sized wastegate.

Firstly the too large a wastegate has to open and close more often, as it has too little exhaust flow when closed and too much exhaust flow when open. This wears the diaphram, due to the requirement for more movements and more weight.

Secondly all this opening and closing of the wastegate affects the amount of exhaust flow though the turbine, this leads to fluctuations in the boost control. eg; I have seen a relatively low powered engine, with a very large wastegate, move up and down 0.3 bar in its boost as the boost control circuit struggles to keep up with this open, closed, open, closed requirement.

----------------------------------------------------------------------------
Enough theory down to the practifcal stuff;

As many will remember I got 40+ guys on this forum to fill out a few simple questions on their car. I then compared what the formula came up with for the wastegate size and what their car actually had. In 35 out of the 40 cars, the formula came up with the same wastegate sizes as they had. In 2 cases it was one size different, but when I checked these 2 further out I found that the guys had actually told the wastegate supplier that they wanted to run more boost than they actually were. So the formula was right, they just had the wrong size wastegate. In one case they guy had moved down a size in turbo after a failure.

Now these wastegates had been specified by a number of well known turbo experts from GCG, Peter Hall, CAPA etc locally or had come in kits from HKS or Trust. Better still the guys seemd pretty happy with the results.

This was all done over 18 months ago and since then I have used the formula to select 5 or 6 wastegates. I have been very happy with the results, as have the drivers. Good horsepower and good response, why wouldn't we be.

Enough for now beer.gif

MuchDa-Bogan
Post #12

thanks mate for the info.. couldnt have asked for any thing more smile.gif cheers

the red krawler
Post #13

I disagree with the part about a wastegate too big = bad.

Lets use extremes:
100mm wastegate
10mm wastegate

The actuator is controlled by boost pressure. So long as boost is higher than spring pressure, the wastegate will open. The bigger the difference between boost and spring pressure, the more open the gate will be.

A 100mm gate is going to be allowing far more air past the turbo than a 10mm gate at any particular percentage open.... So why would the 100mm gate have to be open as far as the 10mm gate at any particular boost level? The actuator will only open the gate as far as is needed to keep boost under control. Its not going to hit 6psi then snap the gate wide open.... Its not a on/off device, its a mechanical valve that opens all the way through 0% -> 100%.

Anyone wanna clarify why this is/isnt the case?
MaDDoG
Post #14

i cant follow this logic of that running a larger wastegate is going to make your boost drop off, it is the preset boost level that is keeping it open. If it is say a 10psi spring, it takes 10psi to move it open, and as red krawler said it is a mechanical thing, its not a "on/off" device. Once boost was to lower from say the 10psi the gate will close and turbo is going to be spinning faster and faster as the gate is closing, but it all happens extremely quickly. They work in harmony with each other. Its not the gate shuts then a second later the turbo now starts to spin faster, as the gate is closing the turbo is spinning faster at the exact same time. I ran a 50mm wastegate on various applications and never had a problem with boost dropping when the gate opened unsure.gif

killswitch_13
Post #15

i think that there will always be a few different opinions when you have a bunch a people thinking they are experts. In amoungst here lies the right answer, but whose answer is right won't be known until an actual turbo expert lays it out straight... I myself am not an expert, as all my info i have ever recieved about turbos etc is all 2nd/3rd hand information told from a mate who heard from that guy who read it at....... but from how i understand it all, to me the red krawler and MaDDoG's answers sound right to me.

Mrs_LJ_GSRRVR
Post #16

the mate of mine that built my turbo, built one for a 200sx. The car was running 18psi but only had a 8 pound spring in the wastegate, and it didnt come onto full boost until 4500rmp. he changed the spring to a 15psi one but still running 18psi and now it comes on full boost at just over 3000rpm . this was using one of them 48mm, $200 wastegates off ebay.

chris davey
Post #17

I have a 50mm wastegate with a ta45s on a 2.5L engine with 15psi spring. No problems to speak of. A 42mm on a 3L will be fine with that turbo. I would rather go too big than too small.

SomeFReaK
Post #18

my argument is that too big a wastegate can rob you of power your trying to create.

Using an extreme example again, a 100mm wastegate will open when the boost pressure is reached however it will let too much exaust pressure out too quickly and the turbo will slow down and as a result force less air into the engine. This will most likely happen quickly, the driver probably wont notice the boost drop at all, but overall the car will be putting out less power.

TwinCam16
Post #19

Just tell Jappe that, yes, once again he is wrong.

2muchofthiss?itisnotenuf
Post #20

But surely as the revs rise you are making more exhaust gases to keep the waste gate open??

the red krawler
Post #21

QUOTE(SomeFReaK @ Apr 3 2006, 10:16 PM) [snapback]6081849[/snapback]

my argument is that too big a wastegate can rob you of power your trying to create.

Using an extreme example again, a 100mm wastegate will open when the boost pressure is reached however it will let too much exaust pressure out too quickly and the turbo will slow down and as a result force less air into the engine. This will most likely happen quickly, the driver probably wont notice the boost drop at all, but overall the car will be putting out less power.


How?

The gate will open, yes, but as I mentioned before its a mechanical device that only opens as far as is required to keep boost under controlled.

Its not gonna suddenly slam open 100% as soon as you hit the set boost level and dump all your exhaust straight past the turbo thus coming off boost again.... It'll creep open 1%....2%....3%....until it is bleeding enough to hold your set boost level.
SomeFReaK
Post #22

QUOTE(the red krawler @ Apr 4 2006, 07:14 AM) [snapback]6082245[/snapback]

How?

The gate will open, yes, but as I mentioned before its a mechanical device that only opens as far as is required to keep boost under controlled.

Its not gonna suddenly slam open 100% as soon as you hit the set boost level and dump all your exhaust straight past the turbo thus coming off boost again.... It'll creep open 1%....2%....3%....until it is bleeding enough to hold your set boost level.


What i am saying is that 1% or whatever lets out too much gas and the turbine looses momentum (and thus looses boost pressure).
dr460n
Post #23

I just did a search and found a wastegate thread, better than creating one.

So what I get from this(because I'm re-thinking my MBC and wastegate setup) , is that I should get a 42mm with a spring rated slightly lower than the boost I want to run and I should be fine? I only want to run low boost atm (10psi) but this is also thinking of the future, any help appreciated cheers.

dr460n
Post #24

Also, would I just use the aftermarket wastegate/actuator to control boost? Is there a better thread to read in the tech section?

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