Wastegate Actuator pressure, and spring strength

[bradc]

http://www.atpturbo.com/Merchant2/merchant.mvc?Screen=CTGY&Store_Code=tp&Category_Code=WGT

This website lists quite a few wastegate actuators, some are rated at 6psi, 12psi, or even 18psi. I don't quite get how this works, considering that a boost tap lets you have control over the boost anyway.

Does this rating mean that without any external control over the wastegate pressure, (just feeding **psi into the wastegate straight out of the intake manifold) that the wastegate doesn't open until the pressure reaches the spring strength?

This leads to the next question, is it better to run an 8psi spring with a lot of air bled off in the normal boost controller style to acheive (say) 14psi, or is it better to throw in a 14psi spring and not have any boost control, and what sort of boost curve does this imply? Will it peak really quickly and come onto boost quickly, then die off at the end of the rev range due to a lack of fine boost control, or what?

[Wodjno]

Right i'll have ago at this ???

More thru i'm not sure how it works either ! Than i do know ! :inquisiti

With a standard car ! The Wastgate is what stops the Boost from getting to high.. Add a boost controller to bleed off some of the air and the wastegate will stay shut longer allowing more boost to build.. On the standard car, lets say the spring is rated at 8psi ? The car may spike to 10psi, but will not be able to hold anymore boost than 8psi... If you increase the spring pressure to 12 psi, then you should be able to maintain 12psi of boost... So increasing our spring pressure to 12 psi, should allow us to hold maybe 17-18psi with the help of a boost controller .. But our turbo's would prolly go bang pretty quick :speechles Thats if our engines didn't first through detonation from the excessive heat the turbo's would be producing /pan

Best way to hold more boost, more safely is to upgrade the Turbo's :pimp2:

Waits to be told i am talking complete tosh :speechles

[bradc]

I'm going to be running GT25R's, but I just wanted to know how it all worked thats all :)

[Wodjno]

I'm going to be running GT25R's, but I just wanted to know how it all worked thats all :)

And i'll be on TD04 HL's flowing 495 Cu Ft per min each :D

[bradc]

why not ball bearing turbos?

[ako]

Ball bearing turbos - there are gains, but the price difference makes you wonder if they're worth it.

TD04's - $2-300 each
BB GT series turbos - Upwards of $1500 each

Tough one :p



As for the question - yes, its better to have a WG setting approximately what you want your boost pressure to be. Thats why external wastegates have different spring rates you can choose from. 8lb spring = 8psi boost. 12psi spring = 12psi boost.

So if you're aiming to run 20psi, don't use a 6psi actuator spring - you'll get better boost control by using say, a 12 or 14psi one instead. You could go for exactly the pressure you want, but then thats your bottom limit - its nice to have a lower setting available for economy / tuning etc.

[bradc]

New journal bearing turbos are still quite expensive though, and the way I see it is that if you are going through all the hassle of forged rods + pistons (and maybe crank) as well as custom manifolds etc, then why not just go for the best turbos possible, for the entire project they don't add a huge amount to the cost (ie around $10-15k)

[ako]

I have no idea what he's building up - I just gave a quick answer to why go bush as opposed to BB turbos :)

Its just cost vs gains really. If it will do the job, may as well save a couple grand and take the cheaper part which will do the job still anyway. You may sacrifice 400rpm in spool time, or have to run 0.5psi more boost to overcome the slight power loss - but to me whenever a figure for a car part crosses 4 figures, i wonder if theres a cheaper option :P.

Don't mind me, I'm just a cheapskate haha

If you have the $$ to do so, by all means you go for the best option, the gains are well documented.

[bernmc]

You can 'control' your boost by changing the wategate actuator spring tension alone. So eg, if you wanted 10 psi, you could run a 10psi tension spring, and no boost controller. However, you will loose power compared to a boost controller set to 10psi. This is because although the wastegate spring has a 10psi tension, the wastegate actually starts opening before 10 psi is reached-it's called 'pre-opening', and allows boost pressure to leak - a spring doesn't suddenly 'snap' to the compressed state - it gradually compresses as pressure increases.
Also, you loose any control over boost to accomodate eg change in ambient temperature/pressure, lower octane/poor quality fuel etc.

Advice I've read is to use a spring that is close to the typical boost you will want to run - this will be your minimum boost as you obviously can't reduce boost below the spring tension. Then use a boost controller for fine control.

[Kenneth]

There is also an argument for a higher pressure wastegate actuator spring holding the wastegate closed against higher exhaust back-pressure, which is a good thing.
I wouldn't be surprised if the small standard turbos on our cars build enough pressure in the extractors to start pushing the wastegate open at high RPM.