Tuning my turbo L28 and need some help

[S130Z]

Hey guys. So after getting my car back from paint jail and the installation of an Isky Racing turbo cam, I have started tuning. Since I do not have a dyno available in my budget, street tuning is all I have. I know where to tune my fuel maps into, but I am a little unsure about where to go with my Spark map.

 

Here is my setup:

Rebuilt L28ET with stock internals 7.4:1 compression.

Garret T3/T4 GT30 .70a/r compressor .63a/r turbine w/ intercooler

MSII 3.57 controlling fuel and spark off stock dizzy

440cc injectors

Isky Racing cam 490/276 intake 480/268 exhaust w/ 112* lobe center

 

Total Ign. advance @ 15psi is 21.4* @ 11.5 AFR and intake temps around 77-80*

 

My ZX pulls really hard up to about 5k and then the power starts falling off pretty fast. My questions are, can I use more timing to get more top end power? or is my stock intake really holding me back above 5k?

 

P.S. - I do not have a knock sensor, and I should probably get one...I know!

[jc052685]

Total Ign. advance @ 15psi is 21.4* @ 11.5 AFR and intake temps around 77-80*

 

 

At what RPM?

 

You can get much leaner as you get closer to redline also. You should be seeing your most rich AFRs at TQ peak and get leaner from there.

[S130Z]

That is from about 3500 RPM all the way mapped to 7000. I'm wondering how much safe yet effective timing the L28ET can take? And would 12.0 AFR a good spot to tune to gradually after peak torque? I am running 93 oct BTW.

 

Now in my mind, timing advance should gradually increase all the way to redline. I think this because the engine is spinning faster and faster, there for combustion should happen sooner so the flame front would hit the piston at the right time. Am I wrong for thinking this way?

[skirkland1980]

my timing is locked at 35. any less and it has no balls. I locked it at 20 and I though there was a banana in my tailpipe.

[Brad-ManQ45]

Timing advance is usually all in by ~3500 rpm. Then you start retarding based on boost.

 

Some will say 1 degree less advance per lb. of boost and some say a bit more.

 

You don't mention having a wideband O2 sensor.

 

If you have one, what's the A/F ratio when it starts to fall on it's face?

 

Why aren't you posting this in the Megasqurt forum?

Edited November 24, 2010 by Brad-ManQ45

[S130Z]

I'm not posting in the MegaSquirt section because it does not matter what stand alone system I am using to get a proper tune.

 

And funny you should ask about the wideband. Yes, I have one. And above 5800 rpms has been extremely rich....as in 9.2:1 rich. I have been tuning this out and she is pulling really nice up to 7000rpms now.

 

Thanks

[TimZ]

That is from about 3500 RPM all the way mapped to 7000. I'm wondering how much safe yet effective timing the L28ET can take? And would 12.0 AFR a good spot to tune to gradually after peak torque? I am running 93 oct BTW.

 

Now in my mind, timing advance should gradually increase all the way to redline. I think this because the engine is spinning faster and faster, there for combustion should happen sooner so the flame front would hit the piston at the right time. Am I wrong for thinking this way?

 

I've found this practice to work well - as others have said retard the timing as boost comes up, but then you can add a degree or two per 1k rpm from the torque peak to redline. Start with something conservative ans see how it works for you.

 

Here's pretty much what mine looks like - ignore the hp and torque numbers, this was taken from a third gear on-road pull, and is not an "official" dyno number...

Edited November 25, 2010 by TimZ