manual boost controller = overboost in cold
 

I haz a manual boost controller getting signal off the compressor housing. In the cold I hit overboost. I don't have a log unfortunately.

I should also note that my BEGi gauge reads 17psi, MS reads 202kpa, and the dyno read 16psi.

I know there's a restriction pressure drop from the intercooler, but can a change in air temp drop pressure further? (not an engineer) My juvenile brain thinks that pressure should not change based on unequal temperature.

Get the MBC signal off the coldside tubing. End of story.

EDIT: I'm an idiot, that might not solve the overboost issue. What is your boost cut set at?

I pulled the signal off the plenum on another car and never had problems. I don't really want to take the pipes out, weld them, then refinish them.


Thoughts? Is it possible that pressure can vary from one side of the intercooler, aside from intercooler restriction?

18psi, 15 is target. I wonder if the additional power from colder air could cause the turbo to overboost?

My theory is that it'd have more to do with the MBC itself. It's just a spring, so if the unit is mounted somewhere that it gets warm, then the spring is weaker when hot. If you set your desired boost level with the warm MBC, then when it's cool it would have that effect.

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

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It is pretty common to see more boost in colder climates when using a manual controller. As an example I usually set my boost at 12 psi when it's cold out. In 85 to 90degree weather it will drop off to 9-10 psi. The MBC works off spring pressure and can not make adjustments for the colder more dense incoming air. By the are being colder and more dense, basically you are getting more air into the intake manifold. If you want it to stay constant either get rid of the MBC.

The point of a manual boost controller is to prevent boost pressure difference with ambient temperatures.

Either you need to loosen yours up a bit or you have creep.

I can adjust and I get no creep though. Weird.

Where you get your boost controller signal, the turbo will spin the same. Think about it. If you have X gauge that's getting manifold pressure at XX psi...then you are setting the boost controller to hit that target in the intake manifold. o if you get signal from the compressor housing or the cold side of the intercooler, the turbo will still be spinning the same to make XX boost in the intake mani. Now matter what you do, the pressure from the compressor outlet will be higher to makeup for whatever pressure drop that happens between it and the throttlebody. Any boosted system will see an increase when it's cold outside....but I never took thermodynamics in school..so I couldn't give an exact reason as to why.

And remember that not all gauges are accurate. My FM gauge spikes to 15psi and back to 13 at times.. but according t othe Hydra datalogs, it's actually just going between 12.9 and 13.6 or so. The boost gauge is good for noticing 'out of the norm' readings.

Also, the type of MBC matters too. I had to use a XSEngineering one one time, it sucked..boost was all over the place. I have the top of the line Hallman..the one wit the cool ceramic ball.. and it's rock solid.. have the same one on my GF's MSM.

The varience in pressure for you is because the IHI turbo sucks... it's almost too small to compensate for the extra psi in hot weather. You would benefit fro ma well-designed cold-air box. Are you even running a larger intercooler?

So what are you bitching about again?

With absolutely no boost controller your boost pressure will vary with ambient temps too, as will how quickly it can build boost.

As far as pressure differential from hot side to cold side of IC, 1. it can be restrictive. 2. Think about pressure as it relates to heat. If you cool a gas, pressure goes down. Period.

in terms of force on the diaphram, isn't 15psi at 100* the same as 15psi at 200*?

How can one side of piping have a different pressure than the other (aside from intercooler interference)?

I used to make 15psi with no wastegate actuator on my turbo, flapper door held open. So it's not the pressure needed to push the actuator that is affecting it. It's a combination of the ability of the turbo itself to create boost with different densities of air due to air temps and the inability of the wastegate system to bypass all exhaust pressure. My car at wastegate will make 8-9 psi in warmer weather but 11-12 when colder.

Yes I am running larger cooler. I have experience the same variance with climate changes on multiple other cars with various turbos. I've had a few turbo cars.