I currently am running a Recirc Tial QR BOV and was having some turbo surge around low boost. Had a -11 spring and based on what other threads were saying, I went with a -6. Since i have a recirc BOV after the MAF, would this affect my A/F. Or a more broader question. Will changing the spring have a negative effect or require a retune?

Thanks in advance

 

FWIW, I too am about to change the spring in my QR. I am going from 11 psi down to 9 psi (decel code issues). I have been very careful to wait until my car is ready for a complete new set of installs and tune before doing this. If you have a problem with your BPV, it could turn into a BIG problem really quickly. My advice is to have it checked by a tuner after install. The TiAL is a particularly finicky BPV. I would hate for something to happen.

 

Short answer: In general and overall, it should not, because you're recirculating.

Longer answer: However, the volume of the intake system causes the MAF's value to sometimes be unequal to what's being ingested by the engine; you can think of the two values as being shifted in time. At constant WOT, the shift in time is almost irrelevant once you get going. But with transient throttle, the difference can cause grief. (DSMs, for example, which were pure MAF, would get tip-in rich knock when you first floor it, because the MAF is saying that a ton of air is being ingested when much less is actually going into the engine while the rest is piling up in the intake path.) The more that the CBV is open, the more error might be introduced between what the MAF is currently reading and what's actually going into the engine. Therefore, a softer spring in the CBV might cause a bit of grief with transient throttle. Of course, the estimate of air being ingested by a 4B11 is a bit more sophisticated than the old 4G63 pure-MAF system, so even transient throttle might not be a problem.

 

I've already got a Bunch of bolt-ons and IVEYTUNE and watching my fuel trims i haven't seen a change from the normal running rich (10-10.5) like it was before. but what i do see is a change in my top end. before it felt like it was actually loosing power around 5k but now it's straight through. So at the moment, i am seeing 2 positives from changing the spring, no turbo surge under low boost and more top end power. But i will keep an eye to make sure that i won't go lean due to the potential extra air

 

You are absolutely correct. BUT, if something goes wrong (spring decides to get stuck on the side of the diaphragm or something), you are going to want that added layer of safety having someone you trust datalog and make adjustments if necessary. When it comes to modifying cars (especially when modifying something with internal moving parts), two is one and one is none.

 

Yeah, everyone whom I talk to says the same thing about the lower pressure spring. It is totally counter-intuitive, but if it works it works. I will be doing the same.