Age old spoolup question

[tazgn]

I did a search to see what timing and A/F combinations help spoolup, but of course it seems to be a 50/50 split as to what people are saying helps spoolup. So is there any definitive answer on this? More timing or less timing? richer or leaner??? I have a problem of my boost coming up QUICK to 5 psi, then stop. Then it builds up from there. My timing goes pretty much linearly from 32 degrees at idle up to 18 degrees in the upper right block (interpolated between the two areas). A/f goes from 13.9 at idle to 11.7 in the upper right block (interpolated again). Can someone please clear this up for me? More or less timing? More or less fuel? and what are the disadvantages to these fuel/timing settings?

Also, as a side note. It's been a while since I last played with the car (deployed for past 6 months). What is the conversion between Kpa and PSI??? What would be 0 psi in Kpa??

Thank You,
Derrick

 

[bruce]

trying only to explain things.
It takes energy to spool the turbo.
Exhaust energy, means EGT.

Basically you want fuel burning later so as to carry as much heat into the exhaust as you can.

Some try a lean miss, to drive the EGT high.

The rich and retarded, IMO is the best strategy since it's easier on the motor.

Major differences also exist in basic engine configurations, also. Those that have better N/A mode operation don't need to spool as hard to launch well. But sacrifice HP in boost mode, and visa versa.

 

[Reggie West]

Using the FAST unit you dont need to worry about KPA conversions.

You can select the PSI setting in your dash bar and it will display along with KPA. Remember though you have to keep the KPA reading on the dashboard in order for the Wide band O2 to work. That is what it references.

As for spool up. I have noticed that there is a stumble of sorts using the FAST right at the point where the turbo goes from vacuum to boost. This is usually where the stall speed of your converter is too. This stumble is not because of the FAST, rather it is a tuning issue with the fuel map.

What I have done, did this on a dyno too, data log the run. You can follow right where the motor sees boost. I would change the A/F tables around that area and see what it does for spooling the turbo. Small steps but you should see a difference.

I would not mess with the timing map. That is just me though.

If you have an EGT gauge that will help you too. With race gas, C16 or Unocal 118, you can run the EGTs to 1550 to 1600 degrees and be safe. You have plenty of injector to compensate for changes in the A/F values.

Of course, this is just my 2 cents.

 

[10SV6]

Bruce, I'm not seeing how the thermal energy ( high EGT's ) is getting converted into kinetic energy (energy exerted on the fins of the turbine, am I using the right term).

How much more thermally efficent does adding a turbocharger to an engine make it ? Are you sure we shouldn't be talking about the energy of the exhaust velocity? And doing as much as possible to increase the exhaust velocity at a given point in the RPM/boost curve (tuning for max performance at a given point?).

Reggie, I'm bringing this up because I'm seeing the same thing you're talking about. I'm thinking that the fuel map is too rich at that transition on the fuel map. The motor acts like a N/A car that is running way too rich. That stumble is taking pretty close too a second on my car to drive through. Timing rich and retarded compared to what I'd have in a N/A car at the same Map and RPM values.

 

[troyk]

Something I remembered from a friend of mine that had a 440 N/A w/vacuum advance. I tried this technique on my car I think it helped, but not sure.

They use to disconnect the vacuum advance, rev the car in park to 3000rpm. Then don't move the gas pedal & move the distributor & watch the tach. The RPM will change as you turn the distributor, because your making more or less HP. Turn the distributor till the RPM is at it's peak.

I don't know if the above method is the correct way to tune a N/A car or not, Just what I saw a friend do.

Anyway I applied this to my car. Since I was having problems at stalling at 2200rpm I reved to that instead.

I suspect this probably won't work for us at a higher rpm, because we are in boost by then & not using the same part of the map.

I came up with 50deg on my car. If I remember right, I had some pops at that timing, when brake torqueing it. So I backed it off 5 - 10deg. I'm guessing it acts a little different under load than in park.

Another idea I had, but never tried is. My trouble point is 2psi. Set up your datalogger to read as fast as it can. Record a WOT brake torque to 5psi then stop recording. Measure the amount of time between 1psi to 5psi(tring to get the amount of spool lag). Make an adjustment to your timing OR fuel, not both at same time. Then do another log to see if you time improved.

I used 1psi as the starting point, because I want to be in boost for this measurement & I want to get a rid of part throttle stumbles & other issues like that. This also should make a more consistant timimg. Now for the down side of this method.

Now since I've never tried this method I can't say for sure, but these are the problems I suspect will happen. Just like a dyno you want consistentsy. I suspect you'll have intercooler heat soak. Also, heat in the trans fluid I think will change your stall. If the fluid is hotter it will be thinner, right? This should cause your stall to be higher. So I'm guessing your 1st pull is not used for timing, just to get everything up to a nice warm temp. Oh yeh, don't forget to have your spare trans ready if you do this to much.

 

[Reggie West]

Bruce, I'm not seeing how the thermal energy ( high EGT's ) is getting converted into kinetic energy (energy exerted on the fins of the turbine, am I using the right term).

As far as EGTs go and what their value is let me put it like this. The higher temps create more pressure and velocity so they are interrelated. The higher the temps get the more the gases are " looking" for the quickest way out too.

As far as the lag time you are seeing in spool up you are right. It is right at the point where the stall speed on the converter is loading the motor and you are trying to spool a turbo at the same time.

I would be increasing the EGTs to compensate, so you lean it out.If you have a lot of lag there, once you find the lag is decreased ( right at where you see boost) you may want to smooth that whole area around the map to help out with that. Once you have that done the lag will be non existent.

It does not matter what ECM you use, the motor likes a smooth fuel curve and that takes some time to get it just right.

 

[Craig Smith]

Heat definitely is a factor in making a turbo work. Looking at this from a basic physics standpoint, heat and pressure are the two "forms" of energy present in great quantities in front of the turbo but not behind it. this tells me that heat and backpressure are converted to kinetic energy (and boost after that) by a turbocharger.

I guess I would have to ask what other properties of the exhaust stream are there that could be converted to kinetic energy? Yes, there is velocity, but I think heat and the right amount of backpressure are what it takes to create a high exhaust velocity.

Just more of my theorizing. I'll get back to work now.

 

[bobc455]

Also, don't forget basic chemistry- hotter gasses take up more volume (for the same amount of mass). More volume going through the turbo will help push it faster.

-Bob Cunningham

(p.s. for the Fluid Mechanics PhD's, I realize the concept is never quite so simple, but perhaps this will help make the point about EGT's)

 

[tazgn]

OK, OK... I understand heat will help the turbo spool, etc. But HOW do I fix the problem???????? More or less timing? I understand leaning it out a bit will help as far as A/F goes (while watching for knock of course)...

Derrick

 

[Reggie West]

Can you send a GCT file to me?

 

[Craig Smith]

We have worked directly with one prominent racer and were able to go from 0 psi to 20 psi of boost in about 0.5 second. The timing was retarded to nearly zero, and we threw a lot of fuel at it. It pops and bangs like you wouldn't believe if you've never witnessed it before, but the boost gauge sure showed a big difference.

 

[tazgn]

So it sounds like I want medium timing (say 25-30 degrees) at the driving around boost (or should I say vacuum), then drop that off rapidly to 10-15 degrees in the mid range (0-10 psi boost range) and then bring timing back up to my 18-20 degrees at max boost. Does this sound about right? This goes against everything I always thought, but it seems like it would work. It would build the boost Quick AND keep the knock to a minimum while building boost.

Derrick

 

[10SV6]

Craig, was that car a convertor equipped car or did it have a clutch ?