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Once the turbo compressor aheives the desired boost, the wastegate diaphram pushes open the wastegate. This lets gas bypass the exhaust turbine, so that the compressor can't generate more boost. If you don't have this, (Unless the turbo is quite small, and very accurately sized to the engine) the turbo will continue to generate higher boost levels. This will cause the motor to sh1t itself.
Motors with BIG turbo's need to run an external wastegate, to allow enough gas to bypass the exhaust turbine that the boost wont creep up.

well at least this discussion has some brains to it...

on the thread hijacking thing. Nispro are famous for not running wastegates and controlling boost through twin BOV's. they are also famous for being overpriced and #### tho.

some people still believe BOV's are a wank anyway.

loud bov's are a wank.

bov's that vent to the atmosphere instead of back into the intake are kind of silly, to waste boost like that.

there have been many OEM mpfi non intercooled non-BOV turbo cars and they work just fine. not quite the same as a carb'd car with a turbo but still.

make the kit modular, that way everyone can add their own things they like. Of course the kit isn't engineered to work with the add ons and you experts will be responsible for doing it right.

i'd just be happy to buy the components and do the engineering myself.

While I don't think our old mate Casper really understands what he is talking about, boost control through blow off valves is not quite as simple as how it was explained below.

It is true that you overwork your turbo to a degree through not allowing it to regulate it's speed by bypassing exhaust gas. However the turbo is regulated by the bov. This happens because the bov lets a proportion of the air that the turbo has just pumped, out to the athmosphere.This then means that not all the air the turbo as worked for will pass through the motor which equals less exhaust gas and hence less energy for the turbine(so it won't spin as fast).
So if you can get your head around that you'll see that the turbine speed is actually regulated. It's still not ideal but it's not as bad as it seems.

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Yep i see what your saying, If your using a decent size and quality turbo this wouldnt be a problem.

Also you could control boost with a restrictive exhuast i guess.

I would ask.... WHY??

you would def not remove the wastegate to make life harder.

a bonus which could be acheived cheaply would be keeping the wastegate gases seperate from the turbo gases for a couple of feet straight out of the flange.

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If by decent size, you mean sensibley sized and carefully chosen than yes.

I don't know if a restrictive exhast could be enough to gaurantee that overboost wouldn't occour.

What would the objective be of plumbing the
wastegate discharge into the exhaust further down stream? This would certainly be easeir with an external wastegate.

apparently the most important part of a turbo exhaust is as soon as it leaves the rear housing. If the wastegate joins at the same place, once you are on full boost with the gate open. Then lots of gas is going through the wastegate causing restriction to the gas coming out of the turbo, exactly what u dont want.

I guess once again it depends on which turbo you have, dump flange sizes etc. I've seen numberous WRX guys (yer i hate em too :)) do it with great success.

I'm yet to be convinced on the 'dump pipe' fashion that some manufacturers go on about.

Its a flange and a bit of pipe. not worth the prices some of these 'automotive fashion' labels sell.

Spend the money on better tyres and more frequent oil changes.

ok, you guiys are blowing this way out of proportion. i just finished building a turbo kit for a non turbo 7Mge toyota engine in my frinds supra. however i dont plan on doing the dattos this way, we DID bypass the internalwastgate, and used an electonicly controlled extrenal BOV on the turbo side, and a throttle controlled bov on the intake side, we set the turbo timers to NOT give full boost until 2600rpm, due to the fact that the 7MGE is a 300 cubic inch dual overhead cam straight six. it is also set to relieve extra, and only extra boost keeping it at a perfect 12-16 psi. i dont know what you guys are talking about saying i dont know what im talking about. if i dont than i wouldn't have made a 12 secong toyota supra now would i? or maybee an 11.003 sec 73 dart with a 340 and a weiland 871 blow now would i? if you dont trust my engineering skills then maybee you need to re-evaluate your opinion on what an 18 year ol KID from the us knows about building engines. i build my first v8 when i was 13 years old. ive been in this long enough to know what will destaroy what. the kit im making will utilize the internal watsgate, and not and extrenal blowoff valve. just wait and see. i am getting tired of the contraversy of one little modification. just stop critisizing what you dont understand. WERE ALL DATTO LOVERS HERE!!!!!!!

Hahaaa, When I was 13 Micheal Jackson touched me