Whats the difference between a boost spike and a boost creep?

I have boost set at 12psi but over 6000RPM I see about 14-15

Im using a Power FCw/commander

 

I think I have it...

BOOST CREEP - Slow rise of max boost at high rpm - caused by inadequate size of the wastegate

BOOST SPIKE - Sudden rise in turbo boost pressure, caused by second turbo coming online around 4500 rpm in modified 3rd gen RX-7's, see the Manual Boost Controller how-to for a way to reduce spiking

I think Its a boost creep, Do I have to port the wastegate?

 

From what I've heard and read on the forum...porting the wastegate is the best solution. Possibly use a pop-off valve somehow as well (?)

 

Hey Rotary,
You've got a well known case of boost creep. That is exactly what caused me to blow up my engine. I had it set to 15psi and then in 3rd in crept past 20psi and .....! The thing is that I have a ported wastegate which should have prevented it, but it didn't. The only way to prevent it(in my cse) is to add some backpressure to the exhaust. Other than that you really can't do anything else with a DP, MP, CB combo. Be "very" careful!!

 

maybe Ill try a High flow cat...This should help out...

 

I guess you are having the same problem that I'm having right now. Sometimes I only get 10 psi and other times I get 14 psi.

 

You won't get any boost creep or spikes with a hi-flo cat. You'll lose some high end hp but gain it back down in the low-mid range. Usually a midpipe is the cause of it. If you like the MP you can have your PFC tuned to tune out boost creep or have a pop-off valve installed

 

Too much back-pressure causes boost creep, as I understand it. This is why it's always recommended to port the living poo out of the wastegate (and in piston cars, exhaust manifold) as much as possible, and have as large of an exhaust as you can get. This is the reason a lot of people with big turbos go with large external wastegates - to regulate boost better and control boost creep.

A boost spike is just that - a quick spike to "x" psi and it quickly settles down to a certain psi soon after. Boost creep is a much bigger problem than boost spikes, and is caused my a number of things. This is another reason electronic boost controllers have become so popular - they have the ability to "learn" a car's boost curve and help control boost spikes.

Someone please let me know if I'm way off base here. Thanks!!

 

Not way off, but definitely a little left of center . Too little back pressure causes the boost creep. Porting the wastegate is done because the stock size doesn't allow it to dumb enough boost. Adding a high flow cat instead of a mid-pipe rasies the back pressure and minimizes the amount of boost creep.

 

Mudd,
Actually you're 100% right! What happens is when you put the DP, MP, ad CB on you reduce the backpressure after the turbine to about 0 which in turn allows the turbine to spin much faster causing the compressor to spin faster which creates more boost. The reason why you port the WG is to allow the extra boost that is being made to be vented off. The problem is that the stock WG can only be ported up to 1.23" which is not enough to vent the extra boost that is created when puting a MP on, and backprssure forms at the wastegate causing the flow to slow down and boost to rise(creep). The reason why the Highflow cat "seems" to fix the problem is because it doesn't allow the spent exhaust gasses to flow as fast after the trbine, therefore, there is backpressure created on the turbine itself which prevents it from reaching higher speeds, which creates less boost, which requires a smaller WG opening to be vented off properly.

 

I have same problem with boost creep. I too have PFC and Mp. If porting WG doesn not help then what else can I do if I don't want to rob power by installing a high flow cat. I lvoe my mp, I think I woudl pop my engine before I gave it up, howeverm, I find myself having to utnr the duty down, so it doesn't hit the cut off.

Guys with PFC shoudln't worry too much, there is a fuel cut, it won't let it go beyound the preset value. akthough,Mine will sometimes, only if cold, and it is a bief spike, no big deal.

BTW, do you guys see smoke with yoru flames with mp?

 

Spiking does happen more often when the weather is cold. With a mp it is tough to tune boost creep out. It is a great but somewhat risky mod. For some reason I gained hp with a hi-flo cat over a midpipe but I think that adding some backpressure with my non-sequentials was the reason for the increase in power. I heard of someone installing a pop-off valve to take care of boost creep.

 

lets say you have FULL exhaust all the way, and are running a Dawes Devices boost controller regulated at 10 psi. will you get boost creep???

 

?

 

There is no way of knowing for certain, but there is a 95+% chance that you will without porting the WG. With a ported WG then your chances drop to about 40-50%. I think that a MP is a great addition to any car and with a "slightly" more restrictive catback and a ported WG you will never have problems controlling boost.