boost spike?

[turbo2nr]

well first let me start off by saying HAPPY NEW YEAR NICO!

well im on my way home for a party thing morning , im in nyc and its cold like 29 degree cold..

so i stay off boost untill i get on the hi way.. i notice the car backfiring alot.. i think nothing of it.. well i get on the hi way and open it up a little, not much my safc said 66% throttle, the car felt FREAKING FAST. I looked at the boost gauge and i was holding 15psi! wtf! i let off i got scared my a/f was 11.8-12.1:1.. im tuned on a safc for 7-8psi...

i did a couple more test, the damm car kept going to around 15psi, i didn't dare take it past there.

yea the car felt fast like really good. but my question is could i have messed up anything by touching 15psi and letting off? i know the ka are known for the heads lifting under hi boost. (btw im using a turbonetics 62-1 t4) so its alot of air...

well the car feels ok no wired noises or rattles and shakes, i just hope i didnt hurt it.. maybe this is her way of telling me to turn her up...

[Zippy69]

I don't think you hurt anything. You do need to find out why you are holding 15psi, if you are set to 7-8. Cold weather will affect everything. Cold air is more dense, so you are able to pack more air in your cylinder than on a hot day.What kind of boost control are you using? Waste gate only? what type of waste gate? Internal or external? I would check your vacuum line on your waste gate for cracks or leaks.g/l

[480sx]

If you were only at 66 percent throttle and at 15 psi, it sounds like you burnt up your wastegates vacuum line. Lucky you didnt stomp on it man!

You would definitely know if you had done any damage.

[turbo2nr]

im using a turbonetics evo. 38mm wastegate and a turbo smart mbc.

well i just looked at the car and the lines are still on the wastegate and mbc. and they are secure. so its not loose... hmm makes me wonder now..

any one have any reasons why it would keep go as hi as 15psi and the wastegate would not open up? well their was times it would go to 7-8 ish and hold likes its suppose too, then as i give it more throttle it would jump up more.. also some times last night it would hit 12psi and hold steady there for a bit....

im thinking its more the mbc then the wastegate? im just concern with why it keeps going around 15psi region and if i had held it would it of went up higher?

i need to solve this problem , any idea or advice welcome
Modified by turbo2nr at 10:43 AM 1/1/2008

[Zippy69]

Take your manual boost control out of the equation, just disconnect the vac line and hook straight to the waste gate, then take it for a drive and see. Is your mbc a cheap one? If so, you may want to look into a better unit.

[kpc_0721]

hey my buddys dsm had the same problem, it was set at 12 psi and would go to 20psi and hold steady. Turned out he had a bad gasket between his turbo and manifold so check for any leaks around the exhaust area

[turbo2nr]

took off the mbc and the damm wastegate didnt sound like it was opening.. i have it dumped out by my fender... but it would hold 10psi i have the smallest spring in there the 4.8psi one.. so im thing the wastegate is faulty...

the car wouldnt make more then 10psi tho. im thinking maybe the diafram is torn or something... any suggestions? and i dont hear the wastegate opening fully, but it is regualting the boost around 10psi ish...

[Zippy69]

I'd def pull the waste gate apart. It may hold 10 now but 20 later.

[480sx]

Even though you have the small spring in there, that doesnt mean that your engine will hold 5 psi of boost. At 5 psi your wastegate opens, but its probably not letting enough gas escape to regulate boost at that low of a level. A 38 wg is pretty small actually, and has a hard time at low psi controlling boost.

Wastegates dont fail that often, it sounds like its doing its job. Also sounds like taking off the MBC fixed your first problem.

So now, without the MBC, your car holds 10 psi even if you stomp on it, ect?

You would be better off with a 10 psi wg spring, or something close to it. You will see full boost faster if you use one.

What turbo manifold are you using?

[turbo2nr]

well taking off the mbc allows me not to hi 15psi any more.

now on partial throttle it holds 10psi. and on hard acceleration's it also holds 9-10psi.

im using a turbonetics 62-1 and evo.38mm wastegate dumped to atm. 3" downpipes and exhaust and a rev hard manifold.

before the car would hold the 4.5psi with the small spring no problem. now it hits 10psi and i still dont hear the wastegate opening up fully, believe its very noticeable when my external opens its really really load.. i don't hear it know when i boost. im thinking its partially opening.

my analysis is that the spring has lose it tension, or the diafram has a small rip allowing it not to regulate boost at the desired.

also 480sx im curious right now with this turbo and this spring in my gate i dont hit boost full until 4500. so your saying by changing my wastegate spring to a bigger one (7--10psi) spring it will help in my spool up? im curious about this, any more info?


Modified by turbo2nr at 3:12 PM 1/1/2008

[coolbone28]

With the 4lb spring in there it hits 4 then starts to open up. So you are loosing all your exhaust gas energy from that point on. However it sounds like your are getting some boost creep for whatever reason so it eventually hits a higher psi. So from 4psi-10 its like you have a giant pre-turbo exhaust leak.

[turbo2nr]

when you say pre -turbo you ppl mean before turbo, so form turbo to manifold? wouldn't a leak there cause the turbo not to spool as fast and make less boost because my turbo is know to become loose form the manifold causing the turbo not to spool up as quick and not hit full boost..

as for the wastegate spring i think im gona try the psi spring.. i was doing more testing, the car holds 10psi and somtimes jumps to 12psi.. thats a big difference form 4psi.. something is deffinatly wrong with the wastegate.. for the mean time i just added more fuel on boost to compensate for added air. i rund 11.2:1 on boost on 12psi i should be ok right?

[480sx]

All depends on the rest of your fueling system. It sounds like the boost spike issue you were having was fixed when you removed the MBC tho.

That your wastegate was able to hold low boost before but now can not is concerning though. I would double check your vac source.

But yea, if you have a 4.5 WG spring and your target boost is 10, at 4 psi your wastegate is going to open. That is going to divert gas that should be going through the turbo around it, increasing lag, and peak boost capability.

[turbo2nr]

boost spike was not fixed when removing the mbc.. it just aided on not running as much boost, the mbc was doing its job. my wastegate is suppose to regulate boost pressure at 4.5psi no it doesnt regulate untill 10-12psi..

im concerned that later on it wont regulate at all and spike to 20+psi..

so im guessing rebuild this waste gate or get a new one right?