03 Trailblazer Build.

[Vbb199]

Nothing super duper exciting to tell, ive been doing transmission tuning as well as fuel/spark tuning, optimizing the truck.

These atlass 4200s were quite ahead of their time for GM. They utilized VVT, known as variable valve timing... which is controlled hydraulically. If youve ever rode in or drove a honda with VTEC, its very similar. The VVT essentially manipulates cam overlap.

Its only on the exhaust cam, but it really allows the truck to FLY at the higher rpms, as the base VVT angle is set at 12° in the 4500-6500 rpm range. That stock setting alone feels like a mini turbo kicking in. I played with it a bit today and got it ramping in 17-22° along that rpm range and man does that truck rip.

My wideband o2 sensor for whatever reason is buggy, so i may just buy a new one from AEM. Its the old turbo lumina sensor/gauge, so i havent fiddled TOO much with higher rpm fueling and spark, as i have no way to see where i am in relationship to the commanded fueling... so i'l order one soon.

Im quickly running out of overhead on those stock injectors, theyre 26 lb/hr injectors and im presently at 90% duty cycle around 6k rpm.

Ive sent it on to 6500 and the thing STILL seems to be pulling. Perhaps i'll get brave soon and send it to 7,000... im just afraid of beating up my transmissiom too much... we'll see.

Im dying to swap cams in this thing or play with E85 gas, with the 10.2:1 c/r, ya gotta keep timing low at peak Tq, for fear of spark knock, where as some E85 would really liven it up... but my injectors would max out.

Perhaps i'll look into throwing a set of 60 pounders in ive got laying around.

 

[Vbb199]

Well ive been further playing with it, and today i finally maxed the injectors out (104.6%). I can probably enlean the fuel mixture at 6300 rpm, as im targetting mid-11's afr... which would spare a little injector duty cycle, but im running 89 octane and trying to keep the pistons cool.

Im sortof scared to go for more like 12.x afr (leaner) because of the 89 octane, but maybe i'll try it.

Either way, theres no real way to prove this without a dyno, but maxing the injectors out over 100% is approx a 300+ hp crank output.
Thats probably damn near close to the most i'll be able to wringe out of the motor without a power adder or E85. 20°-22° of spark advance. It seems to knock if i get too close to 24-26°

On the monitor, im closely estimating Torque by calculating cylinder airmass, so at 4800-5600rpm , i was seeing a consistent peak torque, somewhere around 275-300 at the crank. Even at 6300 cylinder mass just drops a little. This things a torque monster!

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