Car won't hold boost for crap!
 

If this has been asked before and you know which thread it is feel free to direct me.
Ok so my turbo won't hold boost for shit! As soon as I go on boost it spikes to like 16psi then it goes down to 14psi where it should be and by 6k it's down at like 12psi. It really pisses me off cause I'm loosing 10-15 hp at top and my torque drops like a bitch. If you saw my dyno graph it also didn't help that I was going rich at 6k. Soooo what can I do to fix this?

stock greddy wastegate right? look to replace the actuator or run some helper springs.

Yes indeedy, my boost needle was all over the place until I replaced the greddy actuator. You'll probably end up with boost creep though. (positive)

Yep- most IWG actuators start to flake out around double the rating in a boost controlled environment. BTDT. Logging a run with the wg wire shut does wonders for trouble shooting. Just make sure you've got your boost cut where it needs to be for the run.

Which wastegate do you guys recomend?

Where are you getting your signal for your wastegate from?

I replaced my wastegate actuator with one from a new GT2871 and I got boost faster and held MUCH better than the Greddy unit.

Compressor

Then check out this thread my friend.

https://www.miataturbo.net/forum/t32479/

Should at least help the issue.. if not resolve it altogether.

If hes not getting boost creep now that means hes got plenty of flow bypassing the turbine so he wouldnt later.

What he has is boost spiking.


Here is where the WG is tied to.. (the line in the background is an oil line and doesnt connect to the wastegate in any way..)
Attachment 202429

Why is that not a sticky? That is awesome information, I'm going to try that and upgrade my wastegate. Tune my fuel towards redline a little and hit a dyno again should make a 10-15 hp difference

shoulda looked at how mine is plumbed when you had the chance...

http://www.boostedmiata.com/gallery2...serialNumber=3

The nipple just before the TB feeds the wastegate actuator. My boost is so steady you can rest your drink on it.

You shoulda looked at mine and helped a nigga out when I was complaining about my boost drop at the dyno

hahah. or that. I was just trying to find someone for you that knew anything about the DINK ecu.

Isnt your BOV open at idle/vacuum sir?

a little crack...why?

Just curious since its still an unfiltered gap

I don't care about things like that.

Does air even get sucked into it? I'm pretty sure the airflow is always out the BOV never in.

The BOV is open when your boost gauge reads Vacuum, in other words that puts "a hole" in your system between the turbo and the throttle body. So yes air gets sucked into it when the turbo hasnt spooled yet such as at idle. In that case the turbo is a bottle neck since its stopping the air from freely flowing into the intake. If you have a bottle neck with a hole, it will suck in air from the open hole to bypass the bottle neck.

If you have a air flow sensor and no recirculation system you will have a quite crappy idle since you have tons of unmeasured air entering the system due to the open bov. Thats besides the fact that you will be getting 9a/f when shifting gears when in boost..

It's partially open because the signal to the BOV is under vacuum, thus pulling the diaphragm slightly up.

Just because your vacuum/boost gauge says vacuum doesn't mean the entire intake track is in vacuum. The intake manifold and it's hoses are in vacuum because the throttle plate isn't open very much, causing a pressure difference since the engine is an air pump.

Your turbo is still spinning and still compressing air, so guess where that goes? Don't believe me? Go to you car and check.

Any body has a pressure gauge installed before the throttle body?

Ok si I just picked up a t28 wastegate of a Garrett for $10 on CL. I'm going to mod it, install it and re-do the hose to the Ic pipe. I'll update you guys when I'm done

Ok so I just Re-routed the wastegate hose to the coldside in the IC pipe and installed the t28 wastegate after a little mod. Split the rod into two pieces threaded both sides with a 1/4 20 dye. Added a treaded rod and bolted them up. Anyways just took it for a spin and holy shit what a difference! Holds boost like a champ and it spools up way faster. Best mod I've done for $10

Sweet. Im going to try this!

So did I miss all the threads saying waste gate signal should come from a post intercooler source? I thought I read through those and it was determined that there were more drawbacks than benefits. But if you're getting dead steady boost, I'm switching to the throttle body, I just freed up a barb there after removing my o2 clamp.

at idle my car is forceing air out of my blowoff valve, its slightly open and even if i take it totaly off, you can still feel it forcign air out of the intake tract

this is with a begi-s with the 2560

don't do it in the manifold! Do it on the cold side IC pipe right before the TB

Right right, I was referring to the two hose barbs on the throttle body, directly pre butterfly valve. I'll switch to one of those asap. What kind of space age rubber seals the compressor barb without melting though?

I thought those two nipples were after TB could be wrong tho. I used a regular rubber cap that you buy at any auto part store, it's fine for me buy since you track your car I don't know if it will melt

You're talking about how to plug that fitting up after you switch the source on the intake side? You can buy a cap and stick it in there, i dont know if you can take out the barb and put a screw in there to block it off.
Attachment 202322

Yes they are both after the throttle body. Braineack seems to have perfect boost, yet Miataspeed2005 says to put it before the throttle body. Who to trust, who to trust....

I did go for drive today with the wastegate signal coming from one of those two hose barbs. Didn't really find out if it worked, as my overboost was set to 1.5psi, and my laptop was at home. Oops.

Both Braineack and Miataspeed2005 are saying to put it post intercooler pre throttle body.

Correct

I'm sourcing it PRE-throttle. It's said the wastegate doesn't like vacuum. Plus the spots on the TB are very turbulent.

on the BOV ingesting air...It's a tiny, tiny, tiny little crack. The biggest source of air on the intake is the idle valve. The second you crack the throttle the BOV closes shut.

how much vac does the bov require to be open? 20-25?

I figure this should help anyone wanting to make their actuator adjustable:

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

Oh gotcha, I didn't see where those TB lines were routed, figured once went to the waste gate since I hadn't noticed the extra one before that last coupler. Guess I'll be drilling/tapping my intake for a 3/8" hose barb. Thanks!

^^

why dont you just buy a right waste gate and enjoy boost with a gate thats suppose to open at whatever psi you want it to open?

What the above would do a lot of time is boost creep since it doesnt open all the way or if youre using one for too much psi it will always be loose and have a lot of lag since the waste gate will not be shut completely.

your wrong, read this by Joe Perez


Here, we see the entire pressurized intake system. I have marked three points of interest. "A" is a point after the compressor but before the intercooler, typically the little hose nipple that comes stock on most compressor housings and is the classical boost reference. "B" is a point after the intercooler but before the throttle body, which is where my boost controller is referenced to. "C" is a point after the throttle body, within the intake manifold itself.

Now, putting aside arguments of boost threshold and such, can we all agree that, all else being equal, a boost controller is going to try to achieve the pressure to which it is set, at the point in the system being measured? And we'll also agree that the boost gauge on the dash is always fed from a point after the throttle body, such as the brake booster hose, the cruise control hose, etc.

Good. Let us assume that we have a hypothetical perfect boost controller (and a perfect wastegate) and that the boost controller is set to 12 PSI.

We'll start with point A, since that's where most people are referencing their wastegate to. In this scenario, the boost controller is always going to try to achieve 12 PSI at the compressor outlet. At relatively low speeds, the flow through the intercooler is relatively little, and thus the pressure drop across the intercooler is relatively small. Assuming WOT then, the pressure in the system at points B and C will be fairly close to 12 PSI. As RPM increases, the magnitude of the pressure loss across the restrictive intercooler also increases. So while the boost controller is ensuring that 12 PSI exists at point A (before the restriction), the pressure at B and C will decrease by the amount of pressure drop across the intercooler. By redline, we may be down to 9 or 10 PSI at points B and C, despite the fact that there is still 12 PSI at point A.



Next, we move the boost controller's feed to point B, and re-run the test, still at WOT. As airflow increases and pressure drops across the intercooler, the boost controller works to maintain 12 PSI at point B, and so we see 12 PSI being reported on the boost gauge, assuming zero pressure drop across the throttle body. (Give me this one for the moment on faith, and I'll come back to it.) Now, since we're still seeing 12 PSI at points B and C, and yet pressure drop exists across the intercooler, this means that the pressure at point A is steadily increasing. Under the same assumptions as in the first test (that 2-3 PSI of drop occurs across the intercooler at WOT at redline,) the pressure at the compressor outlet will have risen to 14 or 15 PSI by this point. This, of course, is because the boost controller is ignoring point A, and looking only at point B. Some extra heat is going to be generated owing to the fact that the compressor is now working harder than before, but as a percentage of the total heat being generated, this is relatively inconsequential.



Ok, now we'll move the boost controller to point C, and we'll also change one other assumption- we're no longer going to be at WOT. We'll be going up a fictitious hill (or accelerating past a fictitious truck on the highway) and so you are modulating the throttle with your foot to achieve, say, 8 PSI. What's important here is that we're added a second restriction in the system- the throttle plate. And there's going to be pressure drop across this. If boost starts to creep up, you're going to close the throttle a little, increasing the pressure drop across the throttle, and holding MAP at 8 PSI. Because you are actively holding MAP below 12 PSI, the boost controller is never going to reach its activation point, and the wastegate is going to remain completely closed.

Now the problem is that at this load condition, you're generating more than enough exhaust gas to spin the turbo well beyond 8 PSI. If you were to measure the pressure in the system at points A or B, you might find that you've got 20 PSI. Or 30 PSI. Or 40? Who knows, really. A lot is going to depend on the size of the turbo, the exhaust system, etc. But it's going to be a hell of a lot more than 8 PSI, or 12 PSI, or even the 15 PSI we saw at the compressor outlet in scenario B. And this is going to generate a shitload of heat. And heat is the enemy. Granted, reducing the throttle opening is going to reduce the volume of gas available to spin the turbine, and there will be an equilibrium point somewhere, but remember that the whole reason turbuchargers work in the first place is that there is presumed to be a significant excess of exhaust gas available at all but the lowest load conditions- otherwise, we wouldn't need wastegates, and for that matter, the damn thing would never spool up.


"But" you ask, "won't this also be the case at part-throttle conditions in scenarios A and B?" And the answer, of course, is no it will not.

We'll step all the way back to scenario A. You're climbing the same hill, at the same part-throttle condition. You're making enough exhaust gas to spin the turbo up into orbit, however the boost controller is going to make sure that there is never more than 12 PSI in the pipes at point A. Doesn't matter if you are working the throttle to regulate MAP to 8 PSI, or 10, or 4. The pressure in the intake pipes will never exceed the boost controller's setpoint, because the boost controller is watching the intake pipes, not the manifold. Once the pressure in the pipes reaches 12 PSI, the wastegate will open to ensure that it does not exceed this. Thus, the compressor will never generate more heat than it would in a non-throttled run.

Same goes for scenario B. The pressure after the intercooler will never exceed 12 PSI, and the pressure before it will never exceed 12 PSI plus drop across the intercooler. And since the mass of air flowing through the intercooler at this part-throttle condition will be less than it was in WOT scenario B above, the pressure drop across it will be less and the pressure at the compressor outlet will be less.

this is how i did the rod on the WG
Attachment 202224
how i mounted it
Attachment 202225
stock greddy WG vs. t28 WG
Attachment 202226

what does this have to do with what i said? we're talking about extending the wastegate. I responded to that, not what you are saying. I know that you want the wastegate to be connected between the throttle body and the intercooler otherwise its just dumb to connect it to the intake manifold.

for a stand alone boost controller, you want to connect it between the tb and the intercooler again.