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Craved

external wastegate sizes....

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just wondering: what actually governs the size of an external wastegate needed on turbo cars?

im currently gathering all the parts needed for my upgrade but looking into wastegates and what i would need to run on an rb25 with HKS GT3040 with

1.12 AR exhaust housing..???

i know what they do, BUT are they used in respect to the turbo size, engine size, boost level, or a combination of both?

think ive seen most people have used say a 38mm gate, but is a 35mm too small or a 45mm too big?

cheers

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its more boost level

for a lower boost u would use a larger diameter wastegate (let more air out)

whereas higher boost would require a smaller sized wastegate (let less air out)

this will allow ur wastegate to have a longer life

there was a thread on this not long ago - try searching for it

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i did do a search but nothing answering my question directly, or it somewhere inside a 30 page thread and i couldn't find it :)

ok if it's boost related then what would each of the sizes sought of equate to when install on an engine

e.g 35mm works 25 - 30 psi

38mm 20 -25

45mm 10 - 20 etc etc etc etc etc

an ideas?

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id think that a 35mm would be between 20-30

45mm between 10-20

38 mm would be something between the 2 id think but its close to a 35mm anyway

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if anyone can confirm these that would be great!

at least i've got an idea now!!

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Chris , I run HKS 3040, Trust Type R 45 mm wastegate and 21 PSI - 330 rwkw - Boost comes on at 3500, feel it all by 4100.

Hope that helps.

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thanks B-Man i'm only loking at running around 17-19 PSI since i havent decompressed the engine at all, can you adjust the boost level with much scope on the 45mm wg8???

also do you still use an EBC on your system or only use the gate to completely control BOOST

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Wastegate spring is good for 18 PSI (That's my minimum boost) Turbosmart e-boost controls the rest (18-21)

Now that I'm run in good and proper I'm gonna put it on the Dyno and give it a 25PSI hit and see what happens - he he he :D

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craved, I am running a 40mm with 3037, makes 321kw at around 1.5 bar (22lbs). I have run up to 1.7bar, or down to .8 bar. It uses a 10 lb spring.

the thread referred to for wastegate sizing is in the forced induction section - do a search for external wastegates and look for a thread started by SK.

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Save time doing a search, here is the abreviated version.....

I have pretty good success using this formula to determine external wastegate sizes;

Airflow in lbs per minute = diameter of wastegate in mm X boost correction factor

So let's apply it to your car;

300 rwkw = 480 bhp

480 bhp = 44 lbs of airflow = 44 mm wastegate

Now if you want to run 19 psi, then that's the right size wastegate.

But we need to apply the boost correction....

My experience indicates that to get 300 rwkw out of a GT3040 you would need to run around 1.5 bar (22psi). So using the formula...

44 / 22 X 19 = 38 mm.

For those who haven't read the thread..............

http://www.skylinesaustralia.com/forums/sh...ead.php?t=43638

Hope that helps

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Save time doing a search, here is the abreviated version.....

I have pretty good success using this formula to determine external wastegate sizes;

Airflow in lbs per minute = diameter of wastegate in mm X boost correction factor

So let's apply it to your car;

300 rwkw = 480 bhp

480 bhp = 44 lbs of airflow = 44 mm wastegate

Now if you want to run 19 psi, then that's the right size wastegate.

But we need to apply the boost correction....  

My experience indicates that to get 300 rwkw out of a GT3040 you would need to run around 1.5 bar (22psi). So using the formula...

44 / 22 X 19 = 38 mm.

For those who haven't read the thread..............

http://www.skylinesaustralia.com/fo...light=wastegate

Hope that helps

That url doesnt work, hehe

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LOL - your right R31nismoid!

thanks for the info people, im only really looking for 280Kw or so for now, not chasing big power yet!

so it looks like from everyones experiences that the sizes arent the main governing factor, mainly spring which makes sense .. so anything from 38mm to 45 will do!

thanks for all the info people, keep your experiences coming!!

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the theoretical stuff.......

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.

OK R31 Nismoid, let's use your car as a discussion starter.....

300 rwkw = 480 bhp

480 bhp = 44 lbs of airflow = 44 mm wastegate

Now if you want to run 20 psi, then that's statistically the right size wastegate.

My experience indicates that to get 300 rwkw out of a GT30 you would need to run around 1.5 bar (22psi). So using the draft formula...

44 / 22 X 19 = 38 mm.

So based on the 75% success rate of the formula in the samples so far, I would say a 38 mm wastegate would be the go.

Hi Steve and Dr Drift, I try Steve's question first............

What I am trying to do with the formula is give a baseline, something to think about. A 75% 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.

The other issue is exhaust flow rates through the wastegate, some manufacturers claim very different flow rates for the same size inlet / outlet / valve. Now I haven't tested every wastegate out there, but I have yet to see any difference in popoff valve type wastegates that I have tested. So for this discussion and the formula I have ignored the manufacturers claims. The Turbonetics flap style wastegate is an exception, they flow much better than the same size popoff valve on our flow bench.

Ok moving on to the good Dr's question, "So if he's chasing more in the future and had to bear that in mind something like the turbosmart 45mm racegate or similar would be a good option?"

Sorry, but more what? Boost or horsepower? It is possible to make more horsepower with less boost ie; with a turbo capable of more airflow. In that case the formula says you would need a larger wastegate. If you wanted more boost (and therefore more horsepower) the same size wastegate may well be OK. You can get to the stage with "more boost" when a smaller wastegate is needed.

Interesting discussion???

Try this;

More power = more exhaust flow

More boost = more exhaust flow through the turbine

More boost = maybe the same exhaust though the wastegate, thus same size wastegate

Lots more boost = less exhaust flow through the wastegate, thus smaller wastegate

Moving onto Steve's question.........

More power = more exhaust flow

Less boost = less exhaust flow through the turbine

More power = more exhaust flow the wastegate, thus larger wastegate required

Steve, try the formula on your car "40mm, 1.7bar, 309rwkw"

309 rwkw = 520 bhp = 47 mm

47 mm / 1.7 bar X 1.4 bar = 39 mm

So the 40 mm wastegate looks OK.

I suggest you have play with the numbers you are thinking about for your car, post them up and we can discus.

KamikazeR33, it doesn't matter how many cylinders you have. The logic is that it takes X amount of air and fuel to get X amount of horsepower. So whether the engine has 4, 5, 6, 8, 10 or 12 cylinders to make 500 bhp is irrelevant. The only issue occurs if there is varying efficiency amongst the engines. Since I am limiting this formula to production, DOHC, 4 valve engines, I seen no real big problems in using the same calculations. BTW this is also why RPM is not considered.

I need a bit more information on your "hypothetical" to really give a decent fact based answer.

I would need to know usual stuff, the BHP, boost and wastegate sizes.

In the interim I'll try and answer this one....

Quote:

Also, about this "response" of a wastegate. Just say you are "coming on boost" very rapidly (as most larger, aftermarket turbos tend to), wouldn't you think that a wastegate that only needs to travel ~5mm to maintain the desired boost level (i.e. a large gate) as opposed to a smaller wastegate that would need to travel ~10mm to vent the same volume of gas would be able to do this faster, hence be more "responsive"? I concede the smaller one would be able to be more accurate in it's flow limiting, but then again wouldn't an "intelligent" boost controller be able to manipulate these regardless?

I am not sure that the travel "distance" of a wastegate is really an issue. Remembering that 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.

Hope that helps

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I’ll try and look at each one separately…

“What about turbo efficiency?”

Efficiency, is that heat, low boost, high shaft rpm, poor response low airflow etc there are so many ways that a turbo can be inefficient. I don’t know which one to pick for an answer.

“Exhaust manifold design/efficiency?”

If the exhaust manifold is so restrictive it limits the power output, you would need a smaller wastegate to match that power. This is logical as the manifold is doing some restricting, so a larger (than ideal) wastegate would achieve nothing.

“What if the engine is highly tuned to operate at a specific rpm (powerband)?”

Thus it would produce more power at that rpm and therefore need a correctly sized wastegate for that power. You have to size the wastegate for the maximum power (airflow) of the engine. Since you have gone to considerable trouble and expense to have a tuned engine, I would assume that you would want to use it in that rpm range all the time.

“I'm not sure if you are formulating a generic calculation to determine wastegate sizing or just providing a guide to wastegates based on current data”

Both actually. Currently there is no simple formula for determining what size wastegate you use. There seems to be 2 schools of thought, the first being to buy the “biggest” one you can afford. This presumes that bigger is always better, but we know that’s simply not the case with wastegates. Secondly the car owner has no idea, so he has to ask his wastegate supplier. If he is genuine, he will give an answer based on his experience. But what if he isn’t genuine? What if he wants to make the most money he can? Then he will sell the one that makes the most profit for his business.

In either case you can get the wrong answer (and the wrong wastegate), the first because his experiences may not match your requirements and in the second because he doesn’t care whether it is right or wrong for you.

So what I thought I would do is use my experience, then supplement it with real world data from 30 or so volunteers. This would then enable me to come up with a simple formula that anyone can use to check and see if the advice they are getting from their local supplier is good or bad. Stuff like…..

My local supplier tells me I need a 60 mm wastegate for my 200 rwkw Skyline. Why is he telling me something that is obviously wrong? Because it’s on special this month? He has 1 in stock that he hasn’t been able to sell? He only makes $100 profit on a 35 mm wastegate and $250 on a 60 mm one?

It’s all about empowerment, so you (the Skyline owner) can sift out the BS.

Hope that helps

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