issues at low boost

[TurboCajun]

at WOT i have no problems with boost, but just getting on the gas a little and when the boost gets to 8-10 psi it falls out completely and sputters. could this be the manual boost control that is causing this. If so is 22-24 psi to much for the adjustible waste gate to handle and do i need the restrictor y?

[Steve Wood]

sounds like compressor surge to me

[TurboCajun]

ok Steve I have been reading a lil, and not sure i quite understand why mine would be doing this only certain throttle, i didnt have this problem with the hot air setup, this cannot be normal for the intercooler setup ?. here is my thinking- the manual boost controller is staying closed until it gets to the desired boost setting so at part throttle it is giving too much boost for the amount of rpm for the engine. if true just using the waste gate actuator as it opens progressively would be the right thing to do

[Steve Wood]

Nothing to do with the boost controller....

it depends upon intercooler volume and the compressor map of the given turbo.

In essence, the additional volume of the intercooler reduces back pressure against the compressor wheel...the turbo then starts making boost with less effort and begins to spool up.  The throttle blade is mostly closed and the additional air being pumped cannot get into the plenum.  It then builds up pressure against the compressor wheel and tries to stall it out which causes a chatter affect when the wheel tries to accelerate but is braked.

If it is not too bad, it will stop when you mash down on the gas and the throttleblade gets out of the way.  If it is bad enuf, you will have to lift your foot for a split second and then come back down on the gas to get thru the spot.

The characteristic s and feel will vary from turbo to turbo because of the compressor map differences.  In my experience, it usually occurs somewhere between 0 boost and 10 psi-always at low throttle.

My GN used to shake like a wet dog with a front mount and a T63E, but it is barely noticeable with a T66bb.  I could not drive thru it with the the 63.  On my T, with stock ic and a TE 44, there was absolutely none.  With a larger slic, and a TE44, it does it pretty badly, but, I can drive thru it with more pedal.

I can hear the wheel stalling just like it does when I take my foot off the gas at wot.

If you can figure out how to have the waste gate partially open at part throttle, and closed at wide open throttle, that will alleviate it.

[TurboCajun]

the way that you have explained it is exactly what is happening, if i continue opening the throttle it doesnt happen, is there a real concern for this being an issue, or as long as i know how to control it, will it be ok?. on another note i add some boost today I am at 22psi, I went make a run on the road and made my first WOT in third gear everything looked good so i made a complete run from a dry stop. the car took of kinda slow like a stumble until the boost hit 22psi then pulled really hard, the O2s on scan master was at 812 at first WOT and at about 85mph in third gear it had creaped down to 715 but I had 0 knock, i think that i am getting too much fuel at the beginning (reason for stumble) and maybe not enough at the end of a run. note: i have the alky coming on at 10psi and set on 6.

[TURBOPOWERED68]

i also get boost surge and it feels like the car is stalling out-But it isn't.
basically the surge hits and the car pulls the surge is over the car goes back to normal-which feel like a stall. 
i pretty much know when the surge is coming and i automatically back of the gas with out even thinking about it.
 

[Scoobum]

Some turbos are worse than others for surge. My 6152 would almost rattle my fillings loose. Luckily it didn't occur at a comfortable cruise speed. Just punch the throttle harder...and it'll go away.

[Steve Wood]

the way that you have explained it is exactly what is happening, if i continue opening the throttle it doesnt happen, is there a real concern for this being an issue, or as long as i know how to control it, will it be ok?. on another note i add some boost today I am at 22psi, I went make a run on the road and made my first WOT in third gear everything looked good so i made a complete run from a dry stop. the car took of kinda slow like a stumble until the boost hit 22psi then pulled really hard, the O2s on scan master was at 812 at first WOT and at about 85mph in third gear it had creaped down to 715 but I had 0 knock, i think that i am getting too much fuel at the beginning (reason for stumble) and maybe not enough at the end of a run. note: i have the alky coming on at 10psi and set on 6.

It is a bit rich at the beginning and a little lean at the top end....the alky is saving you from detonation, but, it is a dangerous way to fly.  I would add some fuel up top.

You might try turning the alky on between 12-14 psi and see if that cleans up the bottom end.

I have seen two cases in the past few months where the guys were arguing with me that they needed larger injectors, and I was arguing that the car was too rich.  They were running widebands with the A/F at 10.8.  I said they were too rich based upon the factory O2 readings and the appearance of the timing retard patterns.

I was right in both cases.  The fuel pumps were dying and they were running basically on the alky.  One was running down in the tens with dual nozzles.  They both were running widebands and were caught up in the magic of the wideband.   One has to understand that a wideband can read a given A/F, but when one is spraying alky, one has to understand that one can get that A/F with a lot of gas and a little alky, or a lot of alky and a little gas, or many shades of gray in between the extremes.  Now, 10.8 , or whatever, is the number that the wideband came up with from a combination of two different types of fuel and the performance of the various combinations can vary significantly.

Alky can get really dangerous, and sometimes, erratic.  That is the reason I don't like dual nozzles on a street car, and consider it dangerous on a strip car.
I think one should use as little alky as possible to control detonation and not rely upon it as a fuel...just as a chemical intercooler.

This belief has evolved over the past couple of years as I have looked at a lot of PL logs.  It is also the reason I don't believe in the magic wideband when alky is being used.  I still look at the factory O2 numbers and when I see a lack of tracking between the two, I start wondering why.

In your case, I would be looking for factory numbers in the 740-750 range at the top of third gear before I was comfortable.  We all know the factory O2 is a switching sensor truly accurate at about 14.7-1, but, if one looks at enuf logs, one sees that it is quite consistent on a given car.

Back to the compressor surge, I would not try to keep it at the surge point...either back off and come down a bit harder, or give it some more gas and see if you can drive thru it.  It is hard on the bearing in the long term but  not a big problem in the short term.

[TurboCajun]

I completely understand on the issue of the compressor surge and have been driving with the actions of not letting it surge. thanks.
at 20 psi as i was running before i was still rich on the bottom and running 730-740 on the top but now that the boost is up I did not feel safe. i will make the adjustments as you suggested, starting the alky at 12-14 and more fuel on top. I am guessing the richness at the bottom is my reason for not getting a better 60ft than 1.8

[Steve Wood]

It does not help, that's for sure...rich bogs the spool.  If you can, you can try adding a little more timing in first gear as well.  That will build more heat and speed the spool after launch,.

[Scoobum]

I generally start the alky at 10...and then keep bumping it up until I see slight KR...and then bring it down just a tad. Eric has figured out how to add full timing instantly with his 5.7 alky chip...which really makes these cars jump when you come off the line.

[TurboCajun]

would that chip be good for normal driving also?

[Steve Wood]

I doubt you would see much difference...

[Scoobum]

I doubt you would see much difference...

X2

[TurboCajun]

I adjusted alky to come on at 12-14 psi, took fuel out in first gear(124) , added fuel @ WOT (134), add timing in first (132), i only seen knock @ a down shift, in third gear O2s at 80 mph was at 740, i may need more fuel, butttttttttt the compressor surge is worse, I have to go WOT not for it to surge