22.3 psi @ 3806 rpm

[Lextreme II]

I have been tuning with my car the past few days. My wastegate spring is set at 9 psi. I intercept the signal with a manual controller. I throught it was set at 13 psi, while i was testing it last week, it went up all the way to 16 psi. After few more tunings, I test the car out this morning, the car hit 22.3 psi at 3806 rpm. WOW......... What the? The car felt very smooth at 22.3 psi.

The reason the pressure went above 16 psi was because i was looking my laptop and forgot to monitor the boost. I got it all recorded and proofs below. Once again, the split second only max out at 16 psi for programming, but it will still work beyond 16 psi.

Note:
Table A = Fuel
Table B = Timing (retard)

The first graph is cruising at 1969 rpm at vacuum 19.1 psi.
The second graph is when all hell break loose at 3806 rpm. I draw a purple line to indicate the point of referrence. Notice the time and date of recording. This is no BS.

Obviously i am not going to run around with 22 psi. I need to adjust the controller down to 1 bar or so. The engine life would not last that long if I keep on boosting 22.3 psi. What does it tell you. A healthy 1uzfe with decompression and proper tuning can handle mucho boost.

Here are the LS400T Specs

 

[chrisman]

holy cow david,, be carefull..you should save the hi boost runs for the last race of the year..he, he.. not the first ..

i know the 1 uz is built very well--but be carefull anyway..

 

[dandan]

Are you sure your pressure readings are correct?

19psi of vacuum is not possible, a full vacuum is -1bar or -14.7psi.

 

[poid]

the vac readings could be in inches of mercury?

 

[Lextreme II]

Oh i can assure u this is 100% correct. I have an Autometer Boost gauge and the Split Second R4 soft share the same vacuum like and they always read the same.

 

[dandan]

So are you saying you were pulling more than 1 bar of vacuum?

 

[Lextreme II]

Yes, Depending on the tuning. Even my cobra idle at -18 psi. The vacuum is normal.

 

[poid]

Lex, what were you using for these readings? Because vacuum is usually a different unit to boost, boost is normally psi, vacuum is normally inch/Hg or Mbar...your reading of -19.x looks like a inch/Hg reading to me, which would make more sense than a psi reading.

 

[Lextreme II]

Please refer to the first graph upper right corner. Look for Pressure.

 

[poid]

yeh i see the readings on there, but there are no units associated with them.

 

[Lextreme II]

psi Pound per square inch

 

[BlownV8]

I would have to agree with poid, vacuum is in inch/mg. Have a look at your boost guage, it should have it written on it, similar to this one.

 

[Lextreme II]

ok,

I guess i am wrong then. Here is my gauge with engine off.

Here is another example of an autometer boost gauge:

Looks like the idle is about about 16 inch/Hg

 

[R-Jay]

on a turbo car (decompressed), 18-19 in/hg is normal at idle.... my 180sx idled at 19in/hg and that was normal across most nissan turbo models.

 

[chrisman]

r-jay is right.. turbo cars generaly speaking, have less or no valve overlap, very conservative cams-- this tends to give you a high vacuum at idle..
i know that in the past i have been confused by PSIA-- that starts at , i think 14.7 vacuum.. and then goes up from there.. you need to keep an eye open for when this is used.. it accounts for atmospheric pressure, so the scale is different..

 

[Lextreme II]

The vacuum pressure also changes according to your engine status. Lean or Rich will alter it. I dont remember lean or rich will increase vacuum.

 

[dandan]

Aha, things are making a little more sense now.My observation is that any more than 1 bar (14.7psi) of vacuum is actually impossible.

Seeing as you thought you were pulling more than that I thought you may have had a datalogging pressure transducer with your scales a little off ( affecting boost readings as well). As it seems it's a bit of simple confusion regarding the vacuum units and you are indeed actually making some serious boost and the motor is holding up so far. Nice one.

 

[Lextreme II]

Vacuum pressure was -19.1 inch/hg. However overboost was 22.3 psi. Lots of fuel (12.7 AFR) and timing retard (16 degrees @ 22.3 psi), so far 22.3 psi with stock internals are still doing pretty good.

 

[GSMnow]

I have seen bost spikes like this on a few turbo cars. At low boost pressures (8 psi for example) the wastegate does not have to open very far to vent enough exhaust to control the turbine speed and limit the boost. Now when you use a "T" fitting and bleed valve system to trick the boost higher the wastegae opens later after you are making more boost. This works fine to a point. The problem is that the engine is now making ALOT more exhaust flow so the wastegate must open much further to vent enough flow to get the turbine under control again. Integral wastegates are notorious for boost runaway like that. Even external gates can run into trouble if the boost control is bleeding off to much pressure that it can't open the gate far enough, or if the valve is just too small for the flow. This is why wastegates actually have horsepower ratings. My 1990 Eagle Talon topped out at 26 psi of boost on me in the mid rpm range before it went into fuel cut shutdown. I thought the engine blew up because it pulled so hard and then shut off. It is a very scarey feeling. My friends RX-7 did the same thing. It would hold 13 psi just fine, but when he tried to adjust a regulator type boost contoller to 15 psi, it shot straight to 22+ OUCH. He had to get the bigger Turbonetics dual outlet Delta Gate and use an electronic controller which could then apply full boost to the valve to open it after reaching desired boost.

Gary M.

 

[Lextreme II]

I need an electronic boost controller. Anyone have an extra one that they are not using?