Waste gate adjustment?

[bobbo]

I had the car out for a run yesterday and I noticed on a pull when shifting and applying full throttle there is a very short delay before full boost comes on.
I'm using N1 turbos
HKS actuators
PFC and boost controller
Vielside equal length dp; and
Tomei Ti exhaust.

Thoughts?

[Cuami]

If you aren't releasing pressure fast enough between shifts via your blow off valve(s), that may cause a delay in boost.

[Skym]

Usually hear a flutter sound when that happens.

Also the delay can be the TPS settings on ECU (engine suddenly running too lean thus hesitating).

[Bruizer]

I had the car out for a run yesterday and I noticed on a pull when shifting and applying full throttle there is a very short delay before full boost comes on.
I'm using N1 turbos
HKS actuators
PFC and boost controller
Vielside equal length dp; and
Tomei Ti exhaust.

Thoughts?

Turbo lag. Pretty normal.

[bobbo]

This isn't lag a the revs wouldn't be falling below ~5500.
I'll look at my wide band more closely next time and see if its going lean.

[Dragon Humper]

If you aren't releasing pressure fast enough between shifts via your blow off valve(s), that may cause a delay in boost.

I can't see that...I got much more drop off between gears between 4500 & 5500 rpm with a BOV. With out it, coming back into boost is instant. The car came without one from Infini, like a dope I put one in because..."no BOV will hurt your turbo(s)". That was before I wised up.


Jon.

[Skym]

I had a modified stock BOV that when backed off throttle and got back onto throttle, caused hesitation because the BOV didn't go off at all at lower boost levels, but had a flutter sound (turbo hitting surge line on compressor map) when then the BOV did go off. At higher boost levels the modified stock BOV released properly and no flutter sound.

Changed to Synapse BOV and there was no hesitation (exactly like a factory car) and can get back onto throttle off boost and engine responds straight away. That's without changing any settings on ECU.

Stock BOV's can leak, well known problem (sometimes valve inside BOV doesn't close due to oil deposits).

[bobbo]

A sticky bov is quite possible as I've never cleaned them. They do release at high boost levels but haven't paid attention to whether or not they open at lower levels.
I assume cleaning them requires nothing more than removal and spraving the valve and seats with MAF cleaner or the like?

[Skym]

Between the valve, valve seat can get blowby deposits (dried up oil), probably more so with racetrack use. Or if turbo blew the oil seal on compressor side. It's also a good idea to clean the inside of the intercooler as well, as can be pitch black and cause heat soak. If blow on intake pipe side of BOV (valve) you shouldn't feel air out the outlet pipe side of BOV. If clean the BOV and it still leaks alot, replace the BOV.

Sometimes it's the gasket under the BOV that leaks. Some remove the stock BOV's but don't change the gaskets. If you look at the BOV gasket it has ridge on the inside of the gasket that crushes and once crushed, reuse the gasket it doesn't seal as well as the first time it was fitted. You have to replace the BOV gaskets (use once only type of gasket) once you remove the stock BOV's.

In some cases the BOV spring has failed. You put a vacuum gauge on the nipple to top of stock BOV and create vacuum to see if the BOV spring falls within spec (see engine manual for testing process, vacuum specs).

[Cuami]

I can't see that...I got much more drop off between gears between 4500 & 5500 rpm with a BOV. With out it, coming back into boost is instant. The car came without one from Infini, like a dope I put one in because..."no BOV will hurt your turbo(s)". That was before I wised up.


Jon.

That's not what I was getting at really... My comment wasn't geared towards having one vs. not having one.

Just that if one were installed and it were not releasing enough pressure due to the various possibilities outlined by skym above, it would cause a delay in boost.

@Bobbo Found a pretty detailed how to for BOV cleaning for ya... Turbosmart also has a demo vid on YouTube if you're interested

http://www.ozmpsclub.com/forum/how-s/3073-how-service-blow-off-valve.html

[Dragon Humper]

Having a BOV that "is not relieving enough pressure" is just like not having one. My BOV was working as intended and I adjusted it ALOT to try and get rid of the fall off. Removing it entirely fixed what wasn't broken. Never should have put one on in the first place.

So, yes, I knew what you were getting at and, no, I do not agree based on my setup...which is more extreem than most I admit. I have no MAFs.


Another thing that can happen with a MAF only system is reversion through the MAFs. If that happens, the fluttering you hear when excess pressure builds up will add to the normal amount of air and cause a big dump of fuel to happen. Add that to an abrupt throttle input and the motor will deffinately stumble or hesitate. Which would be perceived as lagg.



Jon.

[AL91GTR]

Hey, hope i'm not thread jacking, but:

Think having dirty, leaky bov's might cause boost to fall off while on throttle? I boost to 1.0 bar and then it slowly drops off to 0.8 and then back up after shifting and then drops again..

I was a lazy bastard the other day when I just put my car back together and didn't clean the stock bov's. I have started thinking that it may be the bov's or a small vac hose leak may be the issue.

[Cuami]

Having a BOV that "is not relieving enough pressure" is just like not having one. My BOV was working as intended and I adjusted it ALOT to try and get rid of the fall off. Removing it entirely fixed what wasn't broken. Never should have put one on in the first place.

If you don't have a blowoff valve, the pressure immediately rushes back toward the compressor to release itself from the system... The turbos we have nowadays can take that pressure without a problem, so, I do agree that you don't necessarily 'need' a BOV. Most people just have them for peace of mind or sound... Or whatever.

However, it isn't the same as running BOVless.The built up pressure from the turbo will exit following the path of least resistance... And when you have a BOV, it acts as that path so that the air doesn't flow back to the compressor. Now... If you have a malfunctioning BOV and the pressure isn't exiting at the rate it's supposed to then the BOV will remain open still trying to relieve pressure when you're in the next gear trying to build boost. The pressure won't flowback to the compressor to release itself because the open BOV is still the path of least resistance. And that's where the delay comes from...


Edit:

Another thing that can happen with a MAF only system is reversion through the MAFs. If that happens, the fluttering you hear when excess pressure builds up will add to the normal amount of air and cause a big dump of fuel to happen. Add that to an abrupt throttle input and the motor will deffinately stumble or hesitate. Which would be perceived as lagg.
Jon.

This is also something to consider... One of the reasons I dislike MAF sensors lol...

[Skym]

Hey, hope i'm not thread jacking, but:

Think having dirty, leaky bov's might cause boost to fall off while on throttle? I boost to 1.0 bar and then it slowly drops off to 0.8 and then back up after shifting and then drops again..

I was a lazy bastard the other day when I just put my car back together and didn't clean the stock bov's. I have started thinking that it may be the bov's or a small vac hose leak may be the issue.

Leaking BOV does cause boost to drop off at higher rpm while on throttle, gets worse above 10 psi. But the stock ECU can pull ignition timing (knock maps) that can cause boost to drop 2 or so psi on dyno chart in the mid range, which sounds like what you are describing. Stock ECU can switch in and out of knock maps automatically, so might vary the boost level. But I would eliminate intake airleaks first to rule that out as the cause of the ECU pulling the ignition timing, then fuel pump (fuel pressure check), etc.

[Skym]

If you don't have a blowoff valve, the pressure immediately rushes back toward the compressor to release itself from the system... The turbos we have nowadays can take that pressure without a problem, so, I do agree that you don't necessarily 'need' a BOV. Most people just have them for peace of mind or sound... Or whatever.

However, it isn't the same as running BOVless.The built up pressure from the turbo will exit following the path of least resistance... And when you have a BOV, it acts as that path so that the air doesn't flow back to the compressor. Now... If you have a malfunctioning BOV and the pressure isn't exiting at the rate it's supposed to then the BOV will remain open still trying to relieve pressure when you're in the next gear trying to build boost. The pressure won't flowback to the compressor to release itself because the open BOV is still the path of least resistance. And that's where the delay comes from...


Edit:


This is also something to consider... One of the reasons I dislike MAF sensors lol...

That mild compressor surge (flutter sound) still does some damage, as from what I understand the rotating assembly (CHRA) is violently slowing down and accelerating again.

The worst form of compressor surge is at higher rpm that can damage engine, turbo, for example on a Skyline -

http://www.youtube.com/watch?v=nCj6Spwl1CU

The purpose of the BOV is to recirculate the air so it goes back through the turbo, which allows the turbo to maintain the rpm during a shift, so when get back onto throttle the hesitation (turbo getting back up to speed as more rpm = more boost with a turbo) is eliminated or reduced. This can be measured / checked on a hub dyno with transient hp. That's what the Synapse BOV does really well and there's no lag when back onto throttle (just like it was at factory), the engine, car just accelerates (increases the transient hp).

The stock MAF setup is a draw through MAF setup which needs a reciculating BOV, so once air behind MAF is reduced or increased, the ECU has no idea that it has.

With MAP setup it takes it from the MAP sensor on intake manifold, so any change in amount of air in intake piping can be detected at intake manifold, compensated by the ECU which results in a steady idle, etc.

On some American made engines they run both map sensor at intake manifold, draw through MAF setup.

The other MAF setup is the blow through MAF setup with MAF inbetween intake manifold, intercooler (using a Ford Racing MAF that's rated at 700hp which stock ECU can run).