LA3 in 84 SVO

[brsvo]

I did the LA3 swap on my 84 when we redid the harness. My question is can I run a boost control off a 87/8 TC or does it require the knock sensor to work? I know the KS won't work right on the inline intake so will the BCS work without it? The reason I ask is my hearing sucks and I cant hear the ping and would like to control it by other (more reliable) means.

[MikeFleming]

The stock EEC systems contains an interactive boost/advance-retard electronic management system. it will increase boost, according to pre-programmed load values, while also listening for knock.

If/when knock is detected, it will immediately decrease spark lead (which can happen for the very next firing cycle) and then reduce boost pressure (which has significant lag time in relation to the number of firing cycles due to it's mechanical latency and manifold volume). When both spark and boost are reduced enough to where detonation is no longer detected, it will - first - advance timing (which will lower chamber and exhaust temps) then it will increase boost pressure again (up to the programed table values). It is an interactive, iterative process: Lather, rinse, repeat.

Two rather important issues happen from the above. (1) The engine has a tendency to appear to be surging and drivers don't like that. But rather than get better octane (sometimes not readily available) or reduce boost pressure, thus power levels, they (drivers) prefer to bypass something to stop the surging. Which creates the next problem (2): Chamber and exhaust gas temps skyrocket when load is high and ignition timing is retarded. And that leads to durability issues.

If the EEC-BCS function is bypassed, then the boost pressure will stay at whatever value the boost control system is set to maintain. And the EEC will issue whatever timing value the pre-programmed tables specify for that load/RPM value. If the KS system is working AND the EEC cannot adjust boost pressure, it is limited to only retard timing and keep it there. Which results in long periods of time where EGT values are very high (when detonation is detected).

If the EEC-BCS system is functioning but WITHOUT the KS system providing feedback, the EEC WILL NOT retard timing since detonation is never detected. It will maintain boost pressure according to the pre-programmed load/RPM tables as that is all it has to work with.

When severe detonation happens the EEC will not be able to compensate at all - it will not reduce timing or pressure. It then is totally up to the driver and the strength of assorted engine components. I, personally, do not recommend this path.

[brsvo]

As I figured there is no reason to run the boost controler with out the KS and no reason to run the KS with the inline intake. So I am a time bomb waiting to go off is what your saying. No I am not willing to go to the square intake. Maybe I'll just run without control (limiting me to 10 Lbs of boost) and with the octain switch in unleaded then I would presume I would be pretty safe from blowing this thing up due to my poor hearing.

[MikeFleming]

Providing there isn't much detonation, running in the Premium position will produce lower chamber/exhaust temps than running in Regular (at 10 PSIG). On the PE, the ignition timing difference between the two switch positions is a fixed six (6) crank degrees.

It varies with load, RPM, TP in the LA* series.

[brsvo]

Thats the problem I can't tell how much there is! I had a friend in the car and he told me it was pinging alot and I couldn't hear it till I listened real close with the radio off and the windows up.

[MikeFleming]

These engines were very octane sensitive when new and get more so as they age.

Unfortunately real octane these days is $$.

[gssterl]

i swappeded to a LA3 in my 84 as well. i have my KS disconnected as well and always make sure to put 93 oct in her. i havent had any signs of detonation in 2 yrs. use the good stuff or keep you foot out of it if it isnt available and you will be fine.

[brsvo]

I might as well add this in here. What advantages or dis advantages are there to running the ACT (air charge temp sensor) with the LA3 on an 84? I know some say its not needed but there must be a reason for it.

[SVOC]

I might as well add this in here. What advantages or dis advantages are there to running the ACT (air charge temp sensor) with the LA3 on an 84? I know some say its not needed but there must be a reason for it.


Hot air is less dense, which means volume wise there is less air in the combustion chamber, but on top of that it is also super heated, taking cylinder temps skyward.
This increase in cylinder temps leads to detonation.

If the ACT is before the turbo it is reading an ambient temp of incoming air, but as boost occurs (compressing air raises the temperature) this temp is the temp the PCM need to be seeing so as to pull the right fuel maps to to properly account for the change in temperature and density, this is also true for the timing maps.

To throw this in, talking about cylinder temps, I see more of you disabling the EGR, even though it's archaic in it's operation it still doesn't operate during full throttle/cold start/idle.
What it does do, is control peak cylinder temps, so during part throttle application more timing can be added to increase performance, in doing so overall cylinder temp can be kept cooler rather than get heat soak and expecting the cooling system to draw it away which can be slow pending on the thermal efficiency of the cooling system.

A few factors here when tuning wo/the KS and adding boost, the most important is knowing that as you increase boost the amount of timing advance is lessened, to complicate things the ambient temps of the day/weather, and under hood temps play a huge part.

Lets say 6pm one 70* evening you add boost up to 23lbs with 12* of timing and it ran like a scaldedass ape and you loved it, the next day you left work and go on MoPac (Brown knows what I'm talking about) and in stop and go traffic for and hour and a half, the ambient temp was 100*>
Another potential victim pulls up next to you and revs his engine, you get a break in traffic and you take the bait, because of the rise in temps, boost, and timing cylinder temps were up and caused detonation under heavy and WOT enough so to "pop" the head gasket.


http://image.gmhightechperformance.com/f/9058755/0609htp_12_z%2Bsaturn_sky_redline%2Bturbocharger_system.jpg

[brsvo]

ACT is in the intake manifold on 87/88 LA3 cars and my 84 for that matter as I added it when I swapped the computer and rebuilt the wiring harness. I also still have the EGR in my 84. Still at 10 lbs of boost it pings under load with 93 octane at 10' base timing. What happens if I didn't add it?

[MikeFleming]

The manifold "post turbo" ACT as used on the LA-series of EECs is used for very minor timing corrections based on air temperature in the manifold. It plays no part in any fuel calculations - that is all done using the BAP (baro pressure), VAT (vane air temp) and VAF (vane air flow volume).