Dual Wastegates

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Captainw1990
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Dual Wastegates

Post by Captainw1990 » Thu Mar 27, 2008 2:50 pm

I thought I read about this on here somewhere but I couldn't find it again. My Merk is no longer a daily driver so I am going to intercool it and run higher boost. I just planning on changing the compressor housing and fan to a larger setup hoping to keep the spool time down a little. To solve the problem of the smaller exhaust housing choking the engine at higher rpms I wanted to run an external wastegate along with my internal. Has anyone tried this and have some tips they could share with me?

Thanks,
Justin

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Post by yottabit » Thu Mar 27, 2008 3:32 pm

I've never heard of that before... it seems like it might work in theory, but it would be very wasteful (in the sense that you're diverting gas that COULD be producing more boost for you)

You know if you took the money you would've spent on that idea you could put it towards getting a more modern ball bearing turbo (or whatever other new crazy bearings they have) that will spool faster AND produce more power

EDIT: You might also be surprised how much the stock turbo can support. Definitely make sure you have every basic mod done, and maybe some porting, before you even think about messing with the turbo.

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Post by Rotisserie » Thu Mar 27, 2008 4:36 pm

i agree. heres my thoughts...

1: the internal wastegate can handle alot of abuse. some ppl port the hole slightly to increase its capabilities. at the most, i streamline the port a bit from the inside of the housing, nothing more. if you make the hole too large, the flap may not seal the port well enough to be fully effective. that brings us to the option of the second wastegate.

2: an additional wastegate is a useful option since the larger size diameter port can handle more exhaust, which means more stable boost at higher flow rates. by using both at the same time, you can use a small secondary wastegate and still have sufficient flow since all youre doing is regulating the backpressure between the cylinder head and the turbo. as long as you're able to dump enough remainder exhaust, you can go faster without run-away boost pressure buildup. beyond that, they'll both stay closed until you hit your boost marks, then open as they need to. as to how you'd use it? i say connect both wastegates to the same line and meter them as normal.

in the end, its a good idea. after all, wastegates equal higher stable boosted HP potential. as to where you mount it, depends on whether you're gonna continue to use your EGR. if not, remove the regulating nut screwed into the exhaust manifold and add the wastegate there. if you do it properly, you can prolly keep both. :thumb

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Post by hEaT » Thu Mar 27, 2008 5:05 pm

I think it may be just as effective to weld the internal gate shut and go to a external with a dump tube. That should support well over stock boost levels. You shouldn't have any boost creep anywhere in the stock turbo's effective range with that provided you don't get a cheap, tiny external wastegate.
Joe
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Rotisserie
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Post by Rotisserie » Thu Mar 27, 2008 9:08 pm

i wasnt trying to imply 'tiny', just that the biggest wouldnt be needed since you'd have the flow of 2 wastegates available.

now as for welding the internal shut, if you're gonna be doing any exhaust work, get your downpipe converted to a larger diameter and use a non wastegate flange in replacement. from there, save the old upper downpipe just in case you wish to return to stock. you never know...

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Post by Stealth_xr » Thu Mar 27, 2008 9:49 pm

your thinking to much. its a good idea but i think for a street strip weapon its overkill. If there really was alot of power to be gained you'd see it on more single turbo wastegate systems. Chances are you can run just a 38mm wastegate and be fine. They do also make bigger wastegates. I agree with yattabit all the way save your money get a ballbearing turbo and one big wastegate.

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Post by xrattiracer » Fri Mar 28, 2008 9:56 am

wont do what you think it will.
it requires the same amount of exhaust pressure/flow to maintain a given boost level all other things being equal, so a larger wastegate will just not open as far to maintain the same pressure.
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Post by CV12Steve » Fri Mar 28, 2008 10:47 am

True, as long as the single WG isn't flow-limited by size, which shouldn't be the case in most situations.
Stephen

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