SoCalLove

Just got back from searching this. I thought I knew what boost spike was but the discussion on spike and then boost creep got me confused.

So can someone tell me what are the two? The reason I'm asking is I've been reading a lot of boost problem threads concerning spiking w/ their mods.

Heres my situation, I have zero mods. EX: I was cruising at 85-90mph in 5th gear. I decided to floor it and my boost goes past 10 and I look down and its about to go past 12lbs thats when I let off the gas.

Soooo can someone enlighten me w/ a clear definition on spike/creep and why my FD is doing that (hopefully its normal).

Thanks.

911GT2

Well, i'm by no means an expert, but i can define the two for you.

Boost spikes are caused by the wastegate opening too late. The stock ECU doesn't take into account how much boost you have at any specific RPM, it "knows" what it should be, and opens the wastegate then. For example, if your intake and exhaust are opened up, the first turbo will spool a lot quicker. This will make boost climb faster, but the stock ECU will not read any specific boost pressure, and will still open the wastegate only when the first turbo "should" start making more than 10 lbs of boost. "Should" implies that it opens it at the time when the first turbo will be making 10psi in full stock trim. Ditto for the second turbo.

Boost creep is cause by the wastegate not having enough flow. If the exhaust and intake are opened up so that the turbos spin faster and faster, when the ECU opens the wastegate, even in fully open form, there is too much air going through it, so some gets stuck behind, and pressure climbs and climbs.

Both of these scenarios have to do with modified cars, so yours is a problem i have no idea how to fix. But you asked for definitions, so there ya go. Good luck with it.

911GT2

OK, i just read the rest of your post. The spike after you let off is more than likely normal. The blow off valve vents pressurized air, as in after it has gone into the turbos, so a small spike is more than likely normal. This is because it takes a second for the BOV to open, resulting in higher boost for a second.

nmo93

not sure if you saw this while you searched, but it's in the archives too. read the second post.

https://www.rx7club.com/forum/showth...pike+AND+creep

nick

SoCalLove

Thanks for clearing that up guys. I was also sure my dilemma was normal as well.

SoCalLove

Oh yeah, and also it would've been nice if I saw that, but I rarely look for threads as far back as a year ago

JONSKI

Here is a copy-and-paste from this thread about boost-creep:
When you open up your exhaust, you turbo system will be dealing with more exhaust. Part of your turbo system is something called the wastegate. The wastegate diverts exhaust away from your turbines so that they don't deliver as much pressure to your intake. However, if your wastegate is too small, then your turbines will be spinning faster and faster as your revs increase, even when the wastegate is completely open. This is referred to as "boost creep". If you boost creeps too high, then you will pop your engine. Porting (enlargening) your wastegate will prevent this, because it will be able to handle the extra exhaust that comes with exhaust upgrades. Another option you have is a "restrictor plate". A restrictor plate is a plate with a hole in it, that you put between either your downpipe and midpipe or your midpipe and catback. The hole in the plate is smaller than the diameter of your exhaust, so that it restricts the flow of exhaust so that the wastegate isn't overloaded. This should just be a temporary mod, while you are waiting to port your wastegate.