Boost Fluctuation

[mtbraun]

I have been slowly turning up boost and now have it set at 20psi with no KR. I noticed that when I go wot and the turbo spools, boost immediately jumps to 20psi, then drops to 18 psi and stays there until the 1-2 shift. Then bounces back to 20psi and drops to 18 again.

What would cause this?

 

[mtbraun]

Any ideas?

 

[aminga]

Stock wastegate solenoid setup?

 

[mtbraun]

Stock waste gate actuator, RJC boost controller.

 

[aminga]

Dunno then. Is it going rich?

 

[mtbraun]

Actually a bit lean. recall O2s in the 750-780 range.

 

[Ttype6]

Actually a bit lean. recall O2s in the 750-780 range.

Is your actuator adjustable?

 

[87-WE2]

Newb guess here because mine is doing the same thing (when it runs right)!

Are the lines from turbo to RJC BC to actuator in top shape? Seems like if they were cracked they could pressure up a little high, then start to bleed down causing the move up to 20psi, then back down to 18 psi. My lines are a little ugly, so I figured that's what was causing it.

 

[notacarlo]

Not that this is your issue, but that little stock 25 year old turbo does not like 20 psi and is out of it's efficiency range. Yes it can do it, but that intercooler is struggling to cool that super heated air.
It's possible that this is the cause of a lean condition. 750-780 wot at the top of third is perfectly acceptable using narrow band.
The exhaust pressure is likely overcoming the waste gate spring and pushing the flapper open at 20 psi. I recommend an HD waste gate (which I believe starts at about 18 psi) shortly followed by a turbo that can reliably support 20+ psi. The turbo is the weak link in your combo.....that and a stock transmission. You have most everything else to support more power.

 

[notacarlo]

If I remember right, I don't think an HD actuator will bolt on the the stock turbo compressor housing. I could be wrong....after all I do currently drive a ford.

 

[mtbraun]

Is your actuator adjustable?

Nope - stock actuator.

 

[mtbraun]

Newb guess here because mine is doing the same thing (when it runs right)!

Are the lines from turbo to RJC BC to actuator in top shape? Seems like if they were cracked they could pressure up a little high, then start to bleed down causing the move up to 20psi, then back down to 18 psi. My lines are a little ugly, so I figured that's what was causing it.

Lines are new.

 

[mtbraun]

Not that this is your issue, but that little stock 25 year old turbo does not like 20 psi and is out of it's efficiency range. Yes it can do it, but that intercooler is struggling to cool that super heated air.
It's possible that this is the cause of a lean condition. 750-780 wot at the top of third is perfectly acceptable using narrow band.
The exhaust pressure is likely overcoming the waste gate spring and pushing the flapper open at 20 psi. I recommend an HD waste gate (which I believe starts at about 18 psi) shortly followed by a turbo that can reliably support 20+ psi. The turbo is the weak link in your combo.....that and a stock transmission. You have most everything else to support more power.

A turbo and converter are on this winter's project list!

 

[Ttype6]

Nope - stock actuator.

A manual boost controller is great for producing quick spool up. The way it does this is that it doesn't allow any of the boost signal to go to the actuator until the boost signal is strong enough to move a check ball that has a spring pushing against it to keep it from moving. This allows for faster spool up because all of the exhaust energy is allowed to spin the turbine. On the stock set up,the boost pressure is allowed to go to the actuator and push on it and open it before the desired boost is reached. This allows some of the exhaust energy to by pass the turbine which stops the turbine from spinning up as fast as it would if all the energy where allowed to act on the turbine.

What is going on in your case is that your boost controller is adjusted so that 20lbs of pressure is needed before the ball moves,letting pressure act on the actuator.
Your actuator is set to make about 13 lbs of boost by itself.
When the boost signal is finally allowed to act on the actuator,the actuator moves too much because it is set for 13 lbs of boost.

The solution is to get an adjustable actuator so you can adjust it to make it harder to open.

You don't and never will need a HD actuator.

 

[Ttype6]

Nope - stock actuator.

What kind of fuel are you using to run 20 lbs of boost?

 

[Ttype6]

You could remove the clip,that is currently retaining the actuator rod to the wastegate crank,and instal one end of a week spring in it's place. Drill a small hole ,in the actuator bracket,to accept the other end of the spring. This will make the wastegate harder to open,the same as an adjustable would do.

So,not only do you not need an HD actuator,you don't,technically,need an adjustable one.

 

[notacarlo]

Yeah....stick with the 25 year old worn out actuator and place bandaids on your issue.

 

[notacarlo]

It's likely a HD actuator will come as part of your new turbo package.....and/or be recommended by the vendor.

 

[Ttype6]

Yeah....stick with the 25 year old worn out actuator and place bandaids on your issue.

What does the age have to do with it.It either works or it doesn't.
Bandaids? The difference between a stock actuator and a HD is a stiffer spring.
Your Bandaid is a lot more expensive than the one I use and recommend and he can't get one tomorrow and try it on his car.

It's likely a HD actuator will come as part of your new turbo package.....and/or be recommended by the vendor.

The HD actuator is recommended when you want to produce boost pressures in excess of 22 lbs.
If you use an HD actuator you'll have a hard time running low boost when you run 93 octane.
With the set-up I use and recommend,you,simply remove the spring to run low boost and the spring is chrome plated.

 

[notacarlo]

It's his choice, his car. I put 20 years of experience into my suggestion and that's all it was. Sorry if I came off like a dik. Rereading it, it seems I might have.