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Boost Fluctuation @ WOT -- Bad DV?

L

lilfleck

Go Kart Champion
Hey guys,

I noticed that the boost needle fluctuates up and down at WOT sometimes. I have a Rev C DV. When I installed it during the K04 install, I checked it and it looked fine; no tears.

I tightened the crap out of the turbo outlet pipe clamps and ensured the (green) O ring gasket was on the intercooler piping.

Could a leak on the intake cause this?
 
Merkle

Merkle

Banned
I would start by taking a look at the DV and examining the piping while you're down there.
 
grambles423

grambles423

Automotive Engineer
Depends on what REV C you have. Newer REV Cs are actually piston type valves like the REV D but make less noise.

What sort of range is the fluctuation? Like a spike around 24 down to 20 and hold at 21-22?
 
L

lilfleck

Go Kart Champion
How do I know if its pistol vs a diaphragm style?

I spike at 23lbs and it usually holds at 19lbs. Sometimes the needle jumps up and down to what looks like 23-21-19-21-19-21-19. I think I have to adjust the needle on the boost gauge because when the car is off it doesn't rest in the exact center of 0. It rests a little bit to the left. That being said, if it is off, it could be slightly higher.

It's not easy running logs by myself. Trying to find a good stretch of road that I can run on is tough and it has to be really late at night for no cars to be around. I tried running one log on the highway after I replaced the elbow. I did hit some bumps in the road, but here are the timing vs boost requested vs actual:

0 300 1040
1.53 570 1030
3.31 1740 1100
3.31 2400 1330
4.08 2400 1720
6.38 2390 2340
6.38 2390 2280
6.63 2390 2330
6.88 2400 2310
6.88 2400 2300
6.63 2380 2290
6.38 2310 2200
6.12 2260 2110
5.61 2140 2040

Also worth noting that I recorded misfires on 3/4 cylinders during this log. I have new coil packs and plugs on standby...
 
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D

drepai

Go Kart Champion
It has nothing to do with your dv, if your gauge is jumping around like that on throttle then it's compressor surge. Your turbo is working out of its efficiency range at those engine speeds and making more boost than your engine can swallow. This results in a reversal of air flow through the compressor which will make it 'chop' air instead of push it; it's an issue with your tune.
 
S

Sspcivic31

Drag Race Newbie
Go log rpm, n75, requested, and actual. See what the n75 is doing if its pegging during the fluctuations you have a leak somewhere.
Also before you log check the ambient pressure so you can subtract it from the boost values to get actual gauge pressure.
 
greasyginzo

greasyginzo

Go Kart Champion
apa11393 said:
It has nothing to do with your dv, if your gauge is jumping around like that on throttle then it's compressor surge. Your turbo is working out of its efficiency range at those engine speeds and making more boost than your engine can swallow. This results in a reversal of air flow through the compressor which will make it 'chop' air instead of push it; it's an issue with your tune.
Click to expand...

This

That is a documented issue with APR ko4 isn't it?
 
J

jamlee

Ready to race!
since the weather got cooler here in texas, i started noticing slight rpm fluctuations as well when im going wot. i have a digital boost gauge too and boost seems to fluctuate also. inputs?
 
DriverMotorsport

DriverMotorsport

Ready to race!
According to that small amount of data, there is absolutely nothing wrong.

Granted it isn't perfect, but it's not a serious issue. Could be a small leak or could just be nothing. Because it is such a relatively small problem, finding it will be difficult and hard to quantify in data.
 
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