some things to keep in mind... quoted from a dsm site i frequently visit....its a lot of reading...but its good stuff to know...
http://www.machv.com http://www.machvforums.com
"Spikes are a result of the boost controller not being able to react to the sudden increase in pressure spinning the exhaust turbine of the turbo. If the pressure increases rapidly beyond the desired setting, the boost controller should see this IMMEDIATELY and then open the wastegate. If it is too slow, then you will see a spike in boost pressure...when it finally reacts, the boost will drop to the correct setting. Get a better Boost controller to solve this issue.
Creeps are a result of the exhaust gases escaping through your turbine housing instead of going through the wastegate like it should when controlling boost. This happens when the wastegate opening is more restrictive than the turbine housing. Simple solutions are to port out the wastegate opening, get an external wastegate, or put in an more restrictive DP."
"Well boost spikes are a result of a slow responding boost controller. It really doesn't matter if you have a Manual or an Electronic one. If either one is **** poor, it won't adjust the wastegate opening fast enough to handle the surge.
It's like this. When your foot goes to the floor, you get a surge in exhaust. A boost controller monitors the boost pressure created by the compressor side of the turbo. The turbine side spins up faster as a result of a surge in exhaust pressure. (you on the gas). When the turbine spins up faster as a result of the exhaust pressure increase, so does the compressor. Your boost controller is set at a certain amount of pressure. When that pressure is reached, it is supposed to open the wastegate and bleed off the extra exhaust that is not needed to create/maintain the boost level it is set up for.
If your boost controller is slow to react to this sudden boost increase, (by slow I mean it doens't open the wastegate quick enough) you will get a boost spike. Not to be confused with a boost creep. The boost spike goes away when the boost controller finally reacts to the sudden surge and opens the wategate to bleed off the excess exhaust that is not needed to maintain the boost level set.
I have had both manual and electronic boost controllers. I had spikes with my manual and decided to get the Blitz DSBC because it has 2 solenoids to control the wategate actuator. It holds the boost very well and reacts to any surges in exhaust pressure. I have not had any spikes since the Blitz DSBC. Plus it is nice to adjust the stuff from the inside of the car."
"another cause of spiking can be due to excessive hosing to and from the BC. if you have a lot of slack, than get rid of some but still give it a little so that if the engine pulls, it won't pull the hose off. either that or the location where you tapped it isn't good. it's very normal as everyone said. i wouldn't worry too much about it
With a super long tube, your boost controller may have a delay getting the pressure all the way down your 12' tube to the wastegate actuator. Plus you will loose some of the strength of the pressure from the solenoid due to the extra long run of hose"
"Part I.
Boost creep is a result of having a very high exhaust flow capacity compared to the flow capacity of the wastegate. Since you didn't mention an external wastegate, we'll leave that part out......so you have an internal wastegate on your turbo.
Lets focus on how the wastegate/turbo/exhaust all work together to clear this up. The exhaust gases come shooting outta your exhaust manifold towards your turbo wastegate/turbine. The wastegate is typically shut when you first get going...that makes the hot gases flow towards your turbine on your turbo...thus creating boost. When you reach a certain level of boost, the wastegate opens....this opening is controlled by the boost controller and an actuator solenoid... With the wastegate opening, the gases start to bleed off through the wastegate toward your downpipe via the o2 housing. It meets up with the gases coming outta your turbine and continues towared the downpipe towards the catback system.
Lets say you set your boost controller to open up at 14 psi. Wastegate starts out closed, turbine gets all the gases, you reach 14psi....controller opens up the wastegate...mind that you are still WOT....the extra gases bypass the turbine and your boost level is maintained by the gases that are still flowing through the turbine....it essense, the flow of hot exhaust gases has been split up....but still continue to the o2 housing and downpipe.
If you put a huge a$$ downpipe-highflowcat-catback system on the turbo/wastegate/o2housing, the exhaust gases will want to find the path of least resistance. The stock exhaust system is configured in such a way that small appature of the downpipe,cat,catback, doesn't offset the flow capacity of the wastegate. In other words, the turbine opening is bigger than the wastegate opening. If you start to boost at WOT and your exhaust gases find it easier to slip around the wastegate through the turbine section to get to the o2 housing and the downpipe, you will get boost creep. That wastegate isn't letting out enough gases....even though the boost controller may be holding it wide open...the damn hole is too small. The flow capacity of the larger exhaust is fully capable of handling more gases....and it gets more of the hot gases if you are at WOT...but through the turbine and not the wastegate.
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Part II.
You can reduce the effect of boost creep by a couple of ways...the obvious is to reduce the flow capacity of the exhaust....if you were running a test pipe and had boost creep, you could simply reduce the flow capacity by adding a catalytic converter. The other way is to port out the wastegate and the o2 housing to give that wastegate a fighting chance against the turbine side of the equation. That turbine is getting all the excess gas during boost creep instead of the wastegate. Get a carbide grinder and chew up some metal to get that hole bigger...this is called porting. Don't go too big, or the wastegate flapper can't cover the hole and build boost fast by staying shut over the hole. Or get an external wastegate that vents to the atmosphere...that is the ultimate least resistance compared to the exhaust system.....if the gases had to choose between any type of exhaust vs. the open air...it will take the open air everytime...which is through the external wastegate....loud as hell....but no boost creep.
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Part III.
Your exhaust system is not at the level to create boost creep yet. If you had boost creep, the bad side is heat. Turbos and their turbines and compressors are made to operate at a certain boost level for peak efficiency....if you push that too far with boost creep, you will get cavitation in the spooling process....which heats up the air...and give you poor performance....but up to that poor performance, you are going to be ramming more air into your combustion chamber...if your fuel pump can't keep up...or your injectors are too small to handle that much air from boost creep...you will run lean....which is hot....which is bad. Boost creep kept unchecked will ruin your engine with time....Fuel cut might keep you in check for a while...but you are playing with danger.
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Part IV.
Backpressure is a poor term to use in the automotive industry. Follow Ryan's lead here and use scavenging instead of Backpressure. His example of the waterhose is pretty good. The only way you would get "BACK-pressure" is if someone put their lips on the back of your exhaust and blew real hard. All the exhaust flows in one direction...and not backwards toward the block. If there is a restriction in the system, the pressure will increase and possibly stop the turbine from spinning more freely due to increased pressure and slower exhaust velocity."
. muffler, that's up to you. muffler's mainly a sound preference so choose one you like. i'm gonna go with a 5zigen fireball (tentatively). supposed to be nice and deep and not too loud.
