Int. or Ext. Wastegate

[Freebaggin]

There is some debate as to when to cross over to an external wastegate. I have R33, RB25DET and want approx. 250rwkW using bigger turbo preferably as bolt with integral wastegate(currently have 200rwkW @ 1bar with standard turbo + extras).

Questions:

* At what engine power/turbo flow does an internally wastegated turbo become a problem?

* What is the problem? (Boost control at high RPM?)

* What advantages will the ext. gate give me?

There must be a point at which the int. one becomes a problem, and there must be a relationship between turbine/bypass gas flow vs the diameter of the int. gate.

Does anyone have some HARD DATA on this? Zoom/HPI seem quite keen on external wastegates.

Cheers,

Lachlan.

[Guest INASNT]

I am about to do the same power upgrade to mine!

stick with internal for only 250rwkw with a replacement low mount turbo.

[Steve]

My understanding is that the problem is wastegate creep - before you have reached the desired boost, the wastegate starts to open slowing down spoolup time.

It will, to best of my understanding depend to a large degree on what sort of wastegate acutator you use - eg HKS have heavy duty ones that tend to stay shut harder and for longer. Also how much boost you will be using to reach your desired power, as 250kw at 1 bar boost is going to be alot easier to control than 250KW at 1.5 bar boost - with an internal gate.

So if you can afford it, an external gate should be the prefered option if you want optimum performance from your turbo. More accurate boost control and quicker spoolup - as a rule anyways.

Whatsisname's car is putting down close to the figures (just above) that you are quoting, perhaps he would be worth dropping an pm - see what setup he is running and what he thinks of it.

Hmm, think I rambled on a bit there.

Steve

[Freebaggin]

Thanks lads.

Yeah I know Matt's setup very well and he uses int. gated turbo and get's 250-260rwkW no probs and controls boost without an issue.

I'm not sure spool up will be effected significantly, since if the spring is strong and the actual control system is good with either system, the boost will rise just as fast, but I think it is more to do with bypass flow at high RPM.

What is the typical T3 internal gate diameter vs an external gate. The latter is usually 45mm is that right?

[Steve]

I have seen external gates 35mm to 55mm, 45 seems pretty common though.

[SlowGTS-t]

Originally posted by Freebaggin

Thanks lads.

I'm not sure spool up will be effected significantly, since if the spring is strong and the actual control system is good with either system, the boost will rise just as fast, but I think it is more to do with bypass flow at high RPM.  

The wastegate opening too early is "WASTEGATE CREEP". Electronic boost controller or just a simple relief valve will fix it in most cases. Not really problem.

Insufficient bypass at high rpm is "BOOST CREEP" where the boost just keeps climbing above the preset level as the revs build. This is a BIG problem

[Sydneykid]

Hi Freebaggin, we have an RB25DET that makes 250 rwkw with a GCG hi flowed standard RB25DET turbo. One of things they do when they do a hi flow is to increase the size (diameter) of the wastegate and increase the spring rate of the actuator. This overcomes the problem of not having a big enough hole for the excess exhaust gas to bypass the turbine. As SlowGTS-t said this leads to "boost creep".

External wastegates can be a bit of a pain adding complexity and maintenance issues. For your power target an external wastegate is simply not necessary. We don't even consider them until we are looking for more than 300 rwkw.

Hope that helps.

[Freebaggin]

Thanks heaps INASNT, Steve, SlowGTS-t & Sydneykid, pretty much as I thought. So if you size the hole, within the restrictions of the T3 housing and get the spring rate right, you'll be fine up to 300rwkW...cool.

Might end it there however, too much discussion about holes and gas flow....

[SlowGTS-t]

enlarging wastegate fixes "boost creep"

changing actuator spring changes spring rate which changes boost level.

Bending actuator arm or shortening it (ie increasing preload on the spring without changing it) reduces wastegate creep. Try it but be careful not to break the arm.

[armbrusb]

I have a stock RB20 actuator. I would like it to be set to 14 psi, can I go to any turbo place to get that done? Is it something I can do at home? What sort of price would I be looking at?

[Steve]

dont know how much they cost, but hks do 1bar actuators, might be worth dropping an e-mail to greenline.