NefMoto

Why do people run tighter wastegates?
Whats the benefit of running a 20psi wastegate have been seeing more and more lately.

are you talking about tightening a wastegate, or running a different wastegate with a higher cracking pressure?

There is this idea that turbos will spool faster or won't be able to hold 25 psi w/o it.

I'm not convinced this is the case yet (with K04s)

SRM K24's now come with 20psi gates. Shame, because the ones they had were excellent.

(http://i44.tinypic.com/2rc97b9.png)

Higher wastegate pressures allow for more boost to be run, if the turbo can handle it. Exhaust pressure will open the gate at ~double the spring pressure of the gate. So if you have a 13lb spring in the gate, you can run up to ~26psi of boost. This only happens if the turbo can flow that much, eg not k03/k04 size turbos.

All of that is with respect to ME7 boost control. If you utilize the top port on some wastegates you can run more as boost pressure adds to spring pressure in that case.

IMO, stick with stock wastegate preload for k03/k04s as you can just use the factory PID maps from s4/rs4.

http://nefariousmotorsports.com/forum/index.php?topic=1239.msg27166#msg27166

Look at the text in red.

Kinda, that's for external wastegates. Internal have it at 3-4x the pressure due to flap being smaller.

Yea, makes sense. I would assume the lever arm on the flap has some effect on cracking pressure as well.

This all jives with my understanding as well. With that said, WHY would anyone want 20psi internal gates? Apparently the SRM K24s are getting outfitted with 20psi actuators (despite the old ones being some of the best I've seen). I don't get the logic. How do you have a working PID (without the 5120) with 20lb springs? Seems awfully shortsighted. Especially considering some people MIGHT want to run stage3- for a while, or be able to modulate boost under the cracking pressure.

Because pro tuner racecar

I think the use of higher WG opening presure is because people used to do that back when boost wasn't being controlled electronically and only via vacuum. Now with the ECU, we can adjust it how we see fit and don't have to try to have high WG open pressure to get high boost because the computer can just have a solenoid do it for us. Something that only cranking down on a WG spring could do back in the day.

Must be something they think is going to catch peoples attention in buying for people who dont know who knows Maybe they think its cool or something lol.

What did the SRM turbo have before for cracking pressure?

and just so we're all on the same page here.. the OP was asking about tighter WG's... that isn't the same as having a different spring in the WG itself.

I'd like to know this too


Very true, but with the limited amount of space in the stock internal wastegate location, they practically amount to the same thing, because no amount of preload games are going to fix things w/o a completely different WG setup in a different location.

They're advertised (or not, but spec'd) at 10psi. The first set I experienced were shipped and verified at 6psi, then adjusted to 10. The logs above had the gates verified at 10-11.

interesting post, i recently upgraded my wastegate to just an 8 PSI preload because my exhaust pressure kept pushing the old 3 psi spring open

regardless of having a 20 psi wastegate spring, if your outflowing the turbo whats the point?

Notorious, what was the wastegate spring rating of your old 605's? According to MRC they are 1 bar actuators adjusted to 20 PSI by TiAL themselves.

EPL Sets the 605 gates to 16-17 psi on an application that runs 24-30 lbs.

It's not an issue of exhuast pressure prematurely openning valve. It's a precision issue.

It's like taking a long range gun shot verse a short range shot. The larger the difference from spring rating to target pressure the less precise control will be. At some point, the slightest gate adjustment by controller will great affect pressure so much that it's to hard to hold target.

very true, boost control was very much a pain with that 3 psi spring trying to get a steady 19 psi it was all over the place which put me on the path of fabricating up a bracket and rod to fit a universal wastegate.

but elray, i was hearing the wastegate open at higher RPM's which i do not hear now? no clue but i'm satisfied with how everythings been working with my vehicle.... just need a better turbo some day :(

Excellent point. And that is precisely the problem with messing with the preload; you progressively lose more and more useful wastegate range.

I can only speak from experience and testing in the k03 and k04 turbos but fitting an up rated actuator to these turbos does make a huge difference. Firstly the majority of original stock actuators are old and worn, this leads to waste gates being blown open and n75 dc running at max. Secondly you can get a more linear boost control with a better stronger actuator than some OEM ones, that do a lot at the beggining, then not much then stop.

The ideal rating for a k03 and k04 is 12-14 psi, as previously stated double this and you get a max pressure of boost which is well within k03 and k04 hybrid territory.

Also the correct way of knowing what an actuator rating is is by running actuator pressure only, this will give you the running pressure of the actuator, not by preloading it and pumping it, that only gives the cracking pressure which is very different to running.

You also need to make sure you actuator has enough travel to fully open.

A word on tuning, which is also covered in a thread on this very forum:

http://nefariousmotorsports.com/forum/index.php?topic=4381.0title=


With high wastegate cracking pressure, it is very important to properly tune the car so that it knows when the turbos' wastegates open. It is covered in KFVPDKSD / KFVPDKSE maps which tells the ECU how to operate throttle for a given desired boost level. Stock set up is tuned to about 1.4 pressure ratio which is roughly 6psi - k03/k04 actuator spring pressure. Put a different spring on wastegate and car gets all confused and drives like crap in part throttle.

I have tials with ~20psi spring pressure (I adjusted them to lowest possible tension while still staying solid closed) and after I massaged these tables and made other changes for flow (RS4 modified mani with 80mm hemi throttle here), my car is now butter smooth and can reach any boost from 0 - 30psi+ accurately and without any hiccups. Boost levels between 0psi to about 22psi (where DC is still 0) are attained via throttling.

Lots of unawares in this thread but this guy knows what's up

Interesting stuff will look at those maps, but do they need massaging up or down? I assume down ..

prj does a great job breaking it down here:

http://nefariousmotorsports.com/forum/index.php?topic=4381.msg43866#msg43866

X axis for these two tables is vpssplg_w (which is a desired compression ratio) variable. Find a column (for a given RPMs, I chose to hone on it at 4k and 5k) where cell value starts exceeding value from PSPVDKUG table as you move towards right. If you look at the X-value (column header) for that cell, it will tell you the pressure ratio, this value (minus one unit, so about 0.4bar for stock) is your current wastegate cracking pressure.

Goal is to redefine vpssplg_w axis to something that would make sense for your wastegates. So in my case, I took 20psi (that's what mine are cracking open at), converted to bars (roughly 1.36) and added 1 to it which gave me the compresion ratio. Then I redefined X axis, which I defined as a table so that I can edit it, by multiplying all cells by result of new compression ratio 2.36 divided by old one 1.36 = 1.75x (rounded up).

Old stock and new Tial770 20spi gates attached.

Have you checked to make sure that axis data isn't shared by other maps?

As far as I can tell, by searching several OLS/XDFs for map address, it is only used for these two maps. Anyway, by now it would be super obvious to me if somehting important shared it since my own car would tell me that. I have no time/energy to dive into assembly so I can't tell if something else is fetching this address.

Both axis' are shared only between the two maps SE and SD

From what I understand by reading the installation instructions is the cracking pressure on the Tial gates is ~18.5 psi, and that is what you are suppose to verify and set it to using a dial indicator and a pressure tester (which is what I did before installing them).  With it setup like that I saw a base boost of approx 22 psi w/ 0% WGDC on the N75.

I think most people here are still getting confused about WG cracking pressure and preload.... changing the preload (shortening the stroke) doesn't actually change the cracking pressure on the WG as much as effectively shorten the WG arm travel and possibly causing higher EGTs due to a half open WG flap.

China actuators cranked all the way FTW

I wouldn't have it any other way :P

It has alot to do with VE also.

Same turbo, same 18psi actuator on 2 different 1.8t's:

I think if we choose the threshold column (of column where cell value starts exceeding value from PSPVDKUG) in that way, ECU will use it even when vpssplg_w is slightly less (but greater than axis value of previous column). Taking this into account, shouldn't we take axis value of previous column and make all scalings basing on it? Then ECU would go towards WOT & PID regulation only when vpssplg_w would really exceed the choosen threshold pressure ratio. There is almost no difference which column to take as basis, but IMO choosing and scaling previous column to the column where cell value starts exceeding value from PSPVDKUG makes the pressure threshold more sharp and exact.

I can't concentrate today so I don't get your point, sorry. Easiest way to redo the table to get it to work is just redo X-Axis with your wastegate cracking pressure to replace stock cracking pressure. This has to be done regardless of any other changes you want to make as the compression ratios in x-axis are only suitable for very low cracking pressure.

If you want to alter the table otherwise, go ahead but the X-Axis alterations have to be done anyway.

You are absolutely right. The question was raised about which point of X axis better suits as base point for rescaling of the whole X axis for new WG cracking pressure.
On my opinion (let's discuss it) it's better to choose previous point of X axis (from previous column), the point where cell values haven't started to exceed the PSPVDKUG threshold yet. In other words, this has to be right-most column where cell values still do not exceed PSPVDKUG. Because our goal is to define in X axis exact threshold (= WG opening pressure) below which ECU doesn't go WOT. This means in the cells under choosen point of X axis you still have to see cell values which do not exceed PSPVDKUG. Remember how ECU searches axis values, it finds the least greatest value. Therefore if in column with your new WG cracking pressure there will be cells with values greater than PSPVDKUG, ECU will go WOT earlier, when vpssplg_w is less the axis value.

I did exactly this on the bench with my spare K04-23 , the stock actuator cracked open at 4 psi ! And this was a new actuator from BW ! I verified the results with a second KKK actuator for this turbo and the same . Now this is 0.3 bar , so 1030/1300 = 0.792 , which is where the first point over VDKUG appears ... Correct ?

What to do if from stock in PDKSD , all values already exceed VDKUG ? CWPLGU is set to zero ?

Comments highly appreciated - thank you

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