perscription7

hi all,
just got an 89 tII (my first rotary AND turbocharged car!!!). when i give it some gas in neutral, the boost level doesn't go above 1/3 of the way... when i'm in gear, it usually doesn't go above 1/2 way... most of the time, it stays between -20 and 0 - does this sound normal? (i haven't really pushed the car hard yet - as i need to replace the clutch asap.) im lost: does boost depend upon rpm, pedal position, gear, or all of the above? i notice the gas pedal has light play 1/3 of the way or so, and then is much more firm- when pushed beyond this point, i notice boost dramatically increases- does it have anything directly to do w/boost? could there be something wrong w/my gauge or sensor or turbo? how would i go about testing these?

any input would be greatly appreciated!

thanks for your patience w/my retarded ***!

Erik

hey, congrats on the purchase! any pics? well, the concensus is that the stock boost gauges aren't really too reliable/accurate. if its proper working order you'll probably notice it going higher as you gain speed or in a higher gear...(under load)...so you'd probably be at a higher boost level at full throttle in 4th gear as opposed to full throttle in 1st.

is the car all stock? i'm not sure how far up it should go when in working order. some people say their's goes all the way to the top (which i think is about 7.5psi) while mine and others only goes maybe half way up. how is the performance of the car? mine usually doesn't go above halfway but the car still hauls *** so i never really questioned it. i've been in 2 other 91 TurboII's and i definately remember that in one of them that was stock the gauge didn't go up more than half way either. Wankel7 on here has one and a video on his site...you can notice that the gauge isn't going above 1/2 there.

but i guess if you bought the car new from he factory the gauge would go up almost all of the way. the only real way of knowing what boost you're running is to get an aftermarket gauge...good luck and have fun with the car!

Wankel7

If I was to say what is boost is dependant on. I would say the throttle posistion is what is primary. Of course rpm is going to have an effect.

IE you floor it at 1000 rpm the turbo will not boost much because of the low rpm. Since the turbo is powered by exhaust gas flow. There is not much flow at 1000 rpm. But as you go through the rpms at full throttle you will get more and more boost. That should stabilze by about 3000 rpm. Then if anything the boost will fall off near redline. That is a limitation of your turbo. Even though there is more exhaust gas. The stock compressor can not flow the needed air at redline.

If you want to get any help from the experience on this forum. You really need an aftermarket boost gauge.

James

akageals

Hmmm....i'm glad somone finally said that. I have an '87 TII and the gauge will not go much above half but it really moves. I always thought I had a boost problem.....maybe I don't.

Todd

SaabGuy

When I got my car the boost guage would not go above half way. I think thats like 200hg or there abouts. (Thats 3.8psi)

I found a bunch of intake leaks and bad hose clamps which were spewing out when under boost but making a nice seal when idling. Fixed that, guage rose the 2/3 into the boost zone (250 hg, about 4.5 psi).

Then I found a major thing. Not really major, just enough to say to myself, holly **** that was a no brainer!

My turbo had gook and carbon crap (dirty) oily stuff in the compressor side. Also it did not seem to spin freely when I touched it. I sprayed a TON of Sea Foam (NAPA) in there and black **** kept comming out for about 10 minutes. Then I carefully wiped it clean with tishues and sprayed a little silicon lube (not wd40) in there to give the bearing a little slickness.
I guess this black stuff is what you would call coak or coke whatever I cant spell. Clean your turbos out! they get nasty from the crank case vent (i think) and oil naturally pushing out of the bearing!

Bam! Boost to 320hg (6psi)

akageals

Hey Saabguy,

I have replaced all the gaskets and vac. lines....don't think I have any intake leaks. My turbo does not really seem to spin freely either. When I take the TID off and spin the turbine around it stops pretty quickly...like just a few revs. Sound like it has some drag in it to you? Did you clean it on the car or off.

Rotorque

Hey Saabguy, I am also interested in hearing your answer to akageals' question. On car or off? Also, why not WD40? Any reason or can't you remember the name of what you did use and just wanted to provide what info you could? Ta.

ZachSpazz

The boost gauge on my TII nearly went to the top and all it had on it was an APEXi intake. She's now in the garage awaiting a heart transplant.

This thread makes me miss my car so much...I think I'm going to go to bed in her soft leather seats.

RETed

This is normal - boost is dependent on engine *load*.&nbsp You can't load the engine revving in neutral.



-Ted

NZConvertible

Boost being dependent upon load isn't strictly true. It just makes it generating boost possible. I'll explain.
Boost is entirely dependent airflow through the engine, which means throttle opening and rpm. If you floor the gas in neutral and hold it you can reach full boost. But here's the problem. Long before you actually reach full boost you will tear past the redline, and unless you have a rev limiter, the engine will probably die soon after. The reason you weren't generating much boost revving it in neutral is you lifted off the gas before it over-revved and before the turbo had time to spin up much. Same reason why you seldom reach full boost in first gear (even at full throttle); you run out of revs and shift before the turbo has time to reach full boost.
This is where load comes in. With some load on the engine, either provided by a dyno or simply accelerating the car or driving up a hill, you dramatically slow the rate at which the engine revs up, giving the turbo time to spool up.
Turbocharged drag cars often use transbrakes (which engage 1st and reverse at the same time, locking the drive) to put a load on the engine, allowing them to hold the throttle open on the start line and leave at full boost.
So the boost levels you were seeing were quite normal. Hope this helps.

Snrub

iTrader: (1)

My boost gauge goes into the top bar region, but not quite to the top. I've heard people say they're not very accurate. Assuming the lines on the gauge actually mean something, 3/4ths of the way to the top would be more than 3/4ths of max boost. (scale seems to get smaller futher up) Looks almost like a logrithmic scale... Anyone know?

akageals

I've been chasing a low boost problem since I bought my car. I put on a down pipe, removed the main cat, replaced all intake and exhaust gaskets and it wouldn't go above 1/4 - 1/2+ range. While fooling around with the ingnition system I THOUGHT I had fixed it...the car started boosting all the way to the + sign on the gauge and it felt great! However...since then it has dropped back down to the 1/2 way position and I can't get it to go back up. I think I have a problem in the control system but i'm not sure how to fix it! Anybody got any ideas?

Todd

RETed

That's kind of a weird thing to say - it's sorta like saying you can hit 160mph (becuase your speedo says so) if it wasn't for air friction...

The turbo produces boost due to differential between the compressor housing airflow and the turbine housing airflow.&nbsp This can only be accomplished with engine load, period.&nbsp The engine will always outflow the turbo - the restriction will always be the turbo.&nbsp You can rev the engine all you want, and it won't make significant boost.

Those launching off a dead-start are producing boost due to rev limiters and ingition retards which spit fuel into the exhaust and thus the turbo.&nbsp The raw fuel igniting in the turbo causes the turbo to spin faster, creating boost...



-Ted

NZConvertible

Um, can't see the similarity, sorry...What is "load"? It's simply a resistance, and this resistance slows or stops the engine from simply revving to the moon when you floor it like it would with no load. If you hold an engine at 7000rpm out of gear, it won't make boost because the throttles are almost completely closed to maintain that engine speed. Airflow through the engine is minimal. But apply enough resistance to the engine and you can hold it at 7000rpm at WOT. Airflow through the engine (and hence the exhaust turbine) is massive because the throttles aren't holding it back, so boost is produced and (hopefully) held in check by the wastegate. But you can't free-rev the engine all you want, you have to throttle it to avoid over-revving, which stops boost being generated.Yeah, that's another way to generate boost when stationary, but it's not by applying a "load". I was refering to drag cars using autos with transbrakes, because these provide a load and that's what we we're talking about. (Aren't these tech discussions fun?! )

allstyle

um oh. Ha ha.

HAILERS

Here's an old post from IRV that you use to figure out what your factory gauge is reading in psi. Each hash mark should represent an increment of 5. Keith
Wannabe ******

Status: Offline!
Registered: Mar 2001
Location: Lawrenceville,Georgia,U.S.
Posts: 520


Hi HAILERS. Haven't talket to ya inna while. OK, here goes one of my
long-winded diatribes....

:o The boost guage reads out in units of millimeters of mercury. We like to
see our pressure readout in psi (pounds/square inch). The conversion
factor is .1934. Crunching thru the figures, we get:
5 = 1.0 psi
10 = 1.9 psi
15 = 2.9 psi
20 = 3.9 psi
25 = 4.8 psi
30 = 5.8 psi
35 = 6.8 psi
40 = 7.7 psi
On my boost guage (when the fool thing decides not to stick at -20!), I
get a reading (max) of 35 in first and second, with it creeping up to 40 in
third. I put a boost test guage on the car, and it read 7.0 psi in first and
second, and a little over 7.5 in third. So, you see, it corresponds very well EDIT: AND IF YOU GO TO THIS URL http://www.teamfc3s.org/info/articles/fcd/Graph1.gif YOU'LL SEE A GRAPH THAT YOU CAN CONVERT THE OUTPUT OF YOUR BOOST/PRESSURE SENOR TO PSI.

RETed

The engine is revving at 7kRPM with the throttle closed and airflow through the engine is minimal?&nbsp Ohhhhhhkaaayyyyyyyy...


Like you said above, "resistance" is "load."&nbsp Having resistance to the engine (via the flywheel or trans) is not the same as free-revving in neutral.



-Ted

NZConvertible

You're the last person I thought I'd have to explain this to...
Next time your engine is running, see how much throttle opening is required to hold the engine at any engine speed (even 7000rpm if you're keen) out of gear. Stuff all! Why? No load on the engine, no resistance! How much air do you think is getting past those throttles? Note there's vacuum in the plenum; no boost! It's because there isn't much air entering the engine. Perhaps "minimal" was the wrong word, but it's still a fraction of the air going in at 7000rpm and WOT! I was never talking about flywheels and the like, that's resistance due to moment of inertia. I was talking about an applied load, either on a dyno or actually driving the car on the road.
I still maintain my original line: without some form of load on the engine you cannot apply much throttle without over-revving, and with the engine choked by those nearly-closed throttles, there's not enough airflow through the turbine to spin the compressor fast enough to generate boost.