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Wastegate Sizing

Old 06-07-2004, 07:21 AM
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Too small ...creep , too large....lag, what is the proper sizing for a T78? I Thought maybe running 14 lbs all day wouldn't need a large wastegate ($$$$$) ?
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Old 06-07-2004, 07:41 AM
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Originally Posted by l8t apex' date='Jun 7 2004, 04:21 AM
Too small ...creep , too large....lag, what is the proper sizing for a T78? I Thought maybe running 14 lbs all day wouldn't need a large wastegate ($$$$$) ?
No - a large wastegate doesn't necessarily have to increase lag. The problem is that a wastegate (any size) will typically start to open at a lower boost pressure than you would like. For a small wastegate it just doesn't hurt you very much (but still has a detrimental effect on boost response).

You can sharpen the response using an electronic boost controller, or something cheap like one of those Grainger valve things or similar. I was using a fuel pressure regulator at one point (return type, low pressure).
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Old 06-07-2004, 09:55 AM
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Originally Posted by 83turbo' date='Jun 7 2004, 07:41 AM
No - a large wastegate doesn't necessarily have to increase lag. The problem is that a wastegate (any size) will typically start to open at a lower boost pressure than you would like. For a small wastegate it just doesn't hurt you very much (but still has a detrimental effect on boost response).

You can sharpen the response using an electronic boost controller, or something cheap like one of those Grainger valve things or similar. I was using a fuel pressure regulator at one point (return type, low pressure).
I have the HKS fuzzy logic boost control. Its works awsome. My TO4 is being replaced, my Cartech waste gate dosn't match the DP (square)flange and I am going with a different Turbo. So while the boost is controled by the HKS are the sizings in wg port something that I must consider? 38MM seems to be the average 48 large.

Also ...a make that is good that doesnt cost a motor for the name.

Thanks as always 83TURBO.
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Old 06-07-2004, 10:56 AM
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Wastegate size may affect the adjustment paramters on your boost controller. I haven't played with the HKS, so I can't say much here.



As for the wastegate - 38 mm sounds okay (depends on your turbine size, AR, etc). I had good luck for a while with a Turbonetics Racegate, which I believe is that size. Well, I should clarify - it controlled boost nicely when it wasn't broken. I went through a few diaphragms ($25 each). I think they died from excessive heat. The shaft broke at one point, which didn't prevent the gate from limiting boost but did prevent it from closing (as the broken ends wore against each other). Supposedly they have improved the design, but I don't know if they finally got it right.

Yeah, good wastegates cost $500 and up. I have a pair of Richard Lee wastegates, which are very well made. The problem is the small actuator diaphgram. The smaller it is (in relation to the valve size), the more influence exhaust pressure has on opening the thing. I'll put it this way - I don't use boost air to open the wastegates at all. Exhaust pressure does it. My boost controller applies air to the other side, to keep the gates closed as needed.
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