Interesting WCA test & potential boost creep solution
 

First the introduction.

I have stock engine, 99 twins, efini y-pipe, full exhaust with 3" internal diameter and m2 intake. This is all that affects breathing of my engine I can think of. My turbo control setup is as follows: Restrictions in nipples on the primary turbo housing were drilled out. The precontrol line from turbo nipple to precontrol actuator has stock 93 design pill in it and the precontrol solenoid are still connected - I didn't want to mess with transition yet, so I left it stock. The wastegate control line is empty, and the other nipple on the wastegate actuator is capped, so the wastegate control solenoid (WCS) doesn't affect boost control. The stock wastegate tunnel on the 99 twins has been ported as much as possible, so that flapper still closes the tunnel 100%.

As you can see, I have no restrictions in the wastegate control line and ecu-controlling-vents (solenoid) connected to the actuator, so the actuator always see's full amount of boost without any delay. So this should give me the lowest boost possible on my system.

But this lowest boost wasn't low at all. I'm getting 9-10psi on the primary and 12-13psi after secondary kicks in and rising rapidly. So I decided to inspect and measure operation of my wastegate actuator, so I could tell for sure my wastegate is really being opened 100%. I also tested my old wastegate actuator on old 93 twins. And these are the results:

The actuator rod on the new 99 twins starts coming out at 7psi. The wastegate flapper door starts moving at 8.5psi. At 13.5psi, the the wastegate flapper door reached it's maximum position - wastegate being fully opened. The actuator itself still want's to push the rod out to about 14.5psi, then it stops.
The delay of 1.5psi between actuator rod starts moving and the wastegate flapper starts moving is simple to explain: the actuator rod is preloaded - you have to pull the rod out to set the hole on the pin, and then actuator tries to pull it back in - farther from wastegate being 100% closed. Therefore, at the 7psi the actuator first releases this preload tension of 1.5psi. And only after turbo system is boosting 8.5psi (this doesn't mean your intake pressure is that high, because of pressure drop in the ic and pipes, leaks and such...), the wastegate starts opening.

The old actuator acted the same as the new one. It started pushing out the rod at 7psi and finished it's movement at 14,5psi. But the funny thing was, that it required more preload at the beginning, you need to pull the rod out more, to set it on the pin. This results in wastegate starting moving at 10psi, and it still wasn't fully opened at 14,5psi, when the actuator rod reached it's maximum position.
This is really weird, because the actuator rod isn't adjustable as with the precontrol actuator, so I have no clue where's this difference coming from.

Anyways, after this test, I'd like to make the wastegate actuator with adjustable actuator rod, so I could eliminate the need of 1.5psi preload. Which would mean my wastegate would start opening at 7psi and reching it's maximum opening state at 12psi.

But before that, I will try and attach the gauge on the wastegate control line, too see what's the boost at the beginning of compressor side of turbo system (and what pressure drop I have). If this happens to be too big, then that preload wouldn't matter at all.

I also need to test exhaust restrictors of different sizes I had made... I hope at least they will be able to lower the boost. I'll keep you updated.

is it possible to make it boolean? on -> off? 0% -> 100%?

Interesting...



Not without a different actuator. Even the BOV and CRV aren't on/off valves, but the pressure range from first open to full open is close enough.

If you have a rod that's non-adjustable and you'd like it to be adjustable, there's an old-school turbo trick you can do. Cut the rod in half at the middle, find a tapping die that fits the rod and cut threads into it, then get a threaded shaft that can screw over both ends. This gives you a good deal of adjustability. If you dig around on Google, you can probably find pics of it - I think the GN and Dodge Turbo guys pioneered this kind of mod.

The '99 actuators might be running a different spring pressure or something since the later RX-7's did run more boost.

Do you have a boost controller?

Dale

With electronic or manual boost controller it is possible to make it act almost like it.

I was planning on doing something like that, but I didn't have exact idea. Your's is great and I will try it!

I found both actuator start moving the rod at 7psi.

Nope, I must first lower my lowest boost so it does any good to me.

The advantage to having a boost controller is using it to bypass the factory boost control setup, giving you the boost you want without the stock ECU meddling with things.

BTW, here's the writeup on modifying the wastegate rod -

http://www.gnttype.org/techarea/imag..._wastegate.JPG

Dale

Thanks, that's a really helpful picture! I'll try that!

OK, almost two weeks have passed and I made and tested my adjustable-rod wastegate actuator. I took the old one from the old turbos. I cut it in half, tapped the threads on both ends and put a screw with in between. Exactly as fellow member dcfc3s suggested it. After I thoroughly tested it on the old turbos, I have cleaned it up and sprayed it black (just for my own satisfaction, I know it won't look good anymore after some heat cycling...). Here is the final result:
http://www.parsek.si/documents/soru/...omparison3.jpg


I have also taken demo pictures on my old turbos, with mityvac hooked up showing pressure in the actuator chamber:


http://www.parsek.si/documents/soru/...ressure_00.jpg
http://www.parsek.si/documents/soru/...ressure_07.jpg
http://www.parsek.si/documents/soru/...ressure_08.jpg
http://www.parsek.si/documents/soru/...ressure_10.jpg
http://www.parsek.si/documents/soru/...ressure_11.jpg
http://www.parsek.si/documents/soru/...ressure_13.jpg



I suggest you download them and then go trough them sequentially. This way you can see the exact movement of the wastegate flapper handle regarding to the pressure in the actuator chamber. You can see that it starts moving a little before 7 psi (at 7psi, it is almost the same as on 0psi -> WG fully closed) and end moving on 11psi. For reference, there's a picture showing 13,5psi and the WG flapper handle is still in the same position -> WG is fully opened.

After I put the actuator on the new turbos, I had to readjust it, because obviously the mounting points or the flapper handle location isn't in exactly same position as the with the old turbos. I had to shorten it for appr.5mm to set it as demonstrated on the pictures above: WG starts opening little below 7psi and is fully opened at 11psi.


OK, this is theory. My initial problem was boost creep. I had boost creep to 12,5psi, after the second turbo come online. At 12,5psi the wg still wasn't fully opened. Now I can get stable 9psi all the way to the redline on 2-4 gears (I couldn't test the 5th yet). So this modification definately helped me get my boost in place. Now I only need to take some time to install and set the profec, to raise it a little :D
I think this solution can be useful to anyone whose boost creep isn't so bad - it's worth a chance. If it won't eliminate it, at least it can lower it.

Nice work. Email me and I'll send you copies of your pics adjusted for better clarity. (I changed the contrast and gamma and they're much easier to see). <removed>
Dave

Awesome! Glad it worked out for you!

Dale