Tuning Question

[jss06c6]

Dominic,

Need to talk to another tuner sir.. While working with my '91 on the Dyno today, we discovered that cylinder 7&8 showed temps on the header primaries at about 1200 degrees about 6-8 inches from the head. The other cylinders showed the same issue, but not as far down the header primary. Temp at the head (about one inch from the exhaust port) was about 400-500 F. This indicates that the fuel is still burning while being pushed out of the cylinder. Can we change the injector pulse timing on the LT-5? I need to bring it in sooner so that the fuel is in the combustion chamber long enough to burn completely. I can do this with OBDII.. Can we do this with our ECM? I took fuel out of the top end of the tune and brought the AFR into the sweet spot, 12.8-13.1 across the 2000 to 7000 rpm band. Gained about 15 hp at the wheels from the past last week. We're at 373 rwhp (inertia) and 369 rwhp (loaded 10%) now.

Car is strong and the HP is carrying 367 at 5200 to 369 at 6900 rpm, flat. Very powerful at the higher RPM band! Still climbing at 6900 rpm!

Would be grateful for your thoughts and if we have the ability to start the injectors a bit earlier in the combustion cycle. I'm wasting BTU's in the headers!

Steve

[XfireZ51]

Steve,

Can u describe further what u mean by changing the injector timing? Is this an issue at lower or higher rpms? Or both? How does it work for LS motors?

BTW, what injectors are u using?

[jss06c6]

On an LS, we can initiate the injector pulse timing compared to the cam and spark timing, thus we can bring the fuel into the cylinder earlier, to make sure we burn 100% of the fuel.. We can change pulse width as well, which would shorten the fuel spray (fuel volume).

[jss06c6]

To clarify, pulse width can be lengthened or shortened to deliver the optimal amount of fuel to the cylinder, but we can also initiate the fuel delivery earlier or later in the combustion cycle to maximize the amount of fuel we burn on a combustion cycle...

[XfireZ51]

Maybe Todd wants to chime in, but the only thing I can think of is the Injector Bias and making sure its correct.
How does the LS cal do this? BTDC.? Cam timing?

[tpepmeie]

Injection end angle is not adjustable on the LT5 calibration. At least not by ordinary means. It’s hardcoded in the operating system.


Sent from my iPhone using ZR-1 Net Registry (http://r.tapatalk.com/byo?rid=90383)

[jss06c6]

Thanks Todd.. that's what I needed..:handshak:

[Top Toy]

Did you optimize ignition timing while on the dyno? Advancing the spark, within limits, should also reduce the unburned fuel.

Sent from my HTC U11 using ZR-1 Net Registry mobile app (http://r.tapatalk.com/byo?rid=90383)

[XfireZ51]

To clarify, pulse width can be lengthened or shortened to deliver the optimal amount of fuel to the cylinder, but we can also initiate the fuel delivery earlier or later in the combustion cycle to maximize the amount of fuel we burn on a combustion cycle...

Steve,

What injectors are u using? And is this strictly at top end or throughout the rpm range?

[jss06c6]

Dom,

I'll need to confirm from John Boyd's notes. I believe they are FIC.. the issue shows up under a 10% load on the Dyno sustained at 4500-5000 rpm.

Sent from my XT1585 using ZR-1 Net Registry mobile app (http://r.tapatalk.com/byo?rid=90383)

[jss06c6]

Did you optimize ignition timing while on the dyno? Advancing the spark, within limits, should also reduce the unburned fuel.

Sent from my HTC U11 using ZR-1 Net Registry mobile app (http://r.tapatalk.com/byo?rid=90383)Took it to the knock limit..

Sent from my XT1585 using ZR-1 Net Registry mobile app (http://r.tapatalk.com/byo?rid=90383)

[XfireZ51]

Dom,

I'll need to confirm from John Boyd's notes. I believe they are FIC.. the issue shows up under a 10% load on the Dyno sustained at 4500-5000 rpm.

Sent from my XT1585 using ZR-1 Net Registry mobile app (http://r.tapatalk.com/byo?rid=90383)

Yeah so right around torque peak. This is where u will see knock occurring. It may have little affect at that rpm, but is the proper Injector Bias set in the table?
Not sure FIC provides that altho they should..