internal or external wastegate

[dot]

Hello there im unsure on what is best to use on a m20 turbo set up, a turbo with internal wastegate or the external type, does anyone run either of these could you give me some advice?on what power your getting with it? or problems you have/had? many thanks tunners

[ross2009]

personally external
but depends on what sort of power you wanna be running to get rid of the gasses quick enough as the internal wastegates penny valve is only small where as external wastegates you can have up to 50 mm plus

[dot]

well i was thinking around the 300-350 bhp,i thought the external but its easyer to source the manifold wiithout a waste gate provision,sweet bm you got there what set up do you have?

[ross2009]

A38mm external will work fine for that sort of power
Again really personal choice but you've gotta remember a 6cyl will flow more gases

Thanks dude 2.5 turbo welded head turbo cat cam t34 turbo megasquirt 2 v3
Did u look at the photo bucket album

[dot]

yes you have obviously spent a bomb!! on your motor looks really smart tho,have yo made your own waste gate port on that maniffold?it looks like a ebay manifold, i was thinking about one of those tcd manifolds

[ross2009]

thanks man yeah spent about 7 k on it in all yeah made the ports my self made the whole exhaust my self sounds lovely the tcd one ain't cheap I think there in the 300-400 mark

[dot]

yeah not cheap are they i might just modify a cheap manifold, have you vented your waste gate to atmosphere or back to the exhaust? im not sure if it would fail the mot with it vented to atmosphere

[ross2009]

mines vented to atmosphere I can't see why it would fail an mot as they only open on full boost don't think the mot
guy will be boosting it right up lol

[GeoffBob]

dot,

The only answer to your question is that it depends entirely upon the mass flow rate at which your turbine chokes, which is defined by the A/R of your turbine housing and the dimensions and blade pattern of your turbine wheel.

FYI, choking (as the name suggests) is when your turbine is flowing as much exhaust gas as it can physically handle. Any attempt upon the part of the engine to increase the flow of the exhaust gas through the turbine (say by raising engine rpm) simply results in an increase in turbine back pressure. No matter how hard you may try, there is no way you can flow more gas through the turbine when it is choked. The only solution (in order to flow more exhaust than is limited by the turbine) is to bypass the turbine with a wastegate. However, as with a turbine, a wastegate also has its flow limits, at which point it to will choke. A wastegate should always be sized to flow all the exhaust gas that the turbine cannot. For example, if you need to flow 30lbs/min air to support 300hp (rough estimate) and your turbine chokes at 15lbs/min (corrected) air flow, then you need a wastegate that can handle at least the additional 15lbs/min air flow or else your engine will experience boost creep. On the other hand, if your turbine is good for the full 30lbs/min then, except for the purposes of implementing boost control, you don’t need a wastegate. Believe it or not, years and years ago turbo engines actually worked this way (before the wastegate was invented).

The only way to know exactly what wastegate you require for your application is to know exactly what your turbine is capable of flowing. And if you don’t know what turbine you have then you’ll have to look to the experience of someone who has the same turbocharger on the same engine.

For more info on my experiences with internal vs external wastegates see here: http://www.e30zone.net/modules.php?name ... 34#2037734

HTH.
Geoff

[dot]

thanks for your advice geoff,im not really clued up on working out the flow rate of the turbo,from what i have read a turbine with a a/r of 50 would be ample for 300-350bhp and these are available with internal waste gate

[HairyScreech]

for 350hp on the m20 your looking at a fairly normal turbo and most will come with internal gates, its generally only highly boosted engines with aftermarket turbos that will be looking at external stuff.

theres lots of info on the specific turbos to go for on here, check out the build threads etc, alternatively give either ant@a-tec or gunni a shout.

[GeoffBob]

thanks for your advice geoff,im not really clued up on working out the flow rate of the turbo,from what i have read a turbine with a a/r of 50 would be ample for 300-350bhp and these are available with internal waste gate

You're welcome.

A/R refers to the AREA to RADIUS ratio of the turbine housing and is not an absolute indicator of the size of the turbine. Two turbines can both have an A/R of 0.8 say, and one will be twice as big as the other and be good for 500hp, while the smaller will be good for only 250hp. To compare apples with apples requires that we consider both the dimensions of the turbine blade and the A/R of the turbine housing.

FYI, so that you're aware, most of OEM fitted turbo's pulled from the abundant supply of hot hatches and similar will be good for 300hp and no higher since the turbine and wastegate combined will flow no more than 30lbs/min of exhaust gas, and even that will drastically shorten the lifespan of the turbine. If you want to use one of these you will need to bolt the internal wastegate closed and make arrangements to fit an external that is large enough to flow the extra exhaust gas to support the additional hp. Either that or find a turbocharger with a bigger turbine in the first place.

And remember, the mass flow rate of exhaust gas through (and around) the turbine is as much to do with the cubic capacity of your engine as it is the boost figure you choose to pursue. External wastegates are not for highly boosted engines, but apply to any engine where the mass flow rate of exhaust gas through the engine is in excess of what the chosen turbine and its wastegate can handle. You’ll achieve exactly this by fitting a turbo from a too small capacity donor engine if you are not careful. One of the things to look out for is whether the engine from which your donor turbo came was capable of achieving (regardless of required boost) the sort of hp figure that you are after. If someone threw it off their Subaru or Mitsubishi in favour of a bigger turbo then you are probably going to get the short end of the stick. There are, however, numerous examples in the M20 section of turbochargers that are ideally suited to your application.

For more information on how turbochargers work you can download a Garrett turbocharger catalogue here. The first few pages give a nice introduction to how they work and what all the bits do. Will help give you a heads-up when you eventually go shopping