03 Trailblazer Build.

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.

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!

Try 92 octane for fun. Some engines don't care either way but some really react to it.

squaredeal91 said:

Try 92 octane for fun. Some engines don't care either way but some really react to it.

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Im thinking about it! If i ran 93, i could probably put a few more degrees of advance in at peak TQ and HP, and lower the fuel mixture a little leaner...

These things really like E85 as i understand, i just havent given E a chance yet, mostly due to the injector maximum.

I think this weekend im going out to a local junkyard and pulling a 06+ head, cams, and exhaust manifold.

Couple pics from the 4200 website .. 02-05 manifold next to a 06+

02-05 vs 06+ valve specs


The 02-05 stuff is inferior in terms of cfm they can move in comparison to the 06+ stuff stock, and evidently with some porting, you can get further performance with them. Im thinking stock its a decent hp bump if you just slapped them on and did nothing (no tune, no porting). Its even greater with a tune and some port work.
that coupled with the 06+ cams Will really, really liven it up. The major change on the 06 cams are slightly more exhaust duration, a good bit more intake lift, and slightly more exhaust lift.

Following along on this one.

You likely have run across it already, but what made me aware of, and interested in the 4200’s was Corey’s Checker cab he swapped one into:
It’s by no means a how to series, but some good data points on what can work with them.

Corey had sold it and the new owner took it too a sloppy mechanics dyno day. Made 388hp at the wheels on 10lbs of boost

Unfortunately it was wrecked a year or two ago, so no more turbo checker.

legopnuematic said:

Following along on this one.

You likely have run across it already, but what made me aware of, and interested in the 4200’s was Corey’s Checker cab he swapped one into:

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It’s by no means a how to series, but some good data points on what can work with them.

Corey had sold it and the new owner took it too a sloppy mechanics dyno day. Made 388hp at the wheels on 10lbs of boost

xc_hide_links_from_guests_guests_error_hide_media

Unfortunately it was wrecked a year or two ago, so no more turbo checker.

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I have not seen that! Sure does look cool. I wish the 55' was road ready, as i'd love to slap a 4200 in it with a spooli boy.

Right now im doing what i did with my turbo lumina. Running it thru stages,
First a stock tune, then bigger injectors, then some sort of factory upgrades, and lastly, a turbo

The biggest problem with a turbo on the stock TB is the front end shock tower is almost right next to the manifold, so i have the choice of putting a 1700$ artec performance manifold on (fits the tb stock), or welding up my own. I got some CAD concepts already sketched up on the computer for a home grown turbo manifold.. i guess i gotta decide what to do. I'd really like a 2nd motor or a bare block i could use for mock up

Something like this is what i have in mind. The shock tower is my first obstacle, the second is the AC lines coming out of the firewall. I'd like to be able to clear both of those...

DIY youre looking at <300$ in materials and alot of time

Vbb199 said:

You must be registered for see images attach

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Just my ignorance showing, but is 43.5 the proper fuel pressure? I thought GM did 58 for most stuff of this vintage? If it is 43, that might be a cheap fix for maxed out injectors to swap in a 58 psi regulator (unless it's one that is regulated in the tank... ugh)

Hunter79764 said:

Just my ignorance showing, but is 43.5 the proper fuel pressure? I thought GM did 58 for most stuff of this vintage? If it is 43, that might be a cheap fix for maxed out injectors to swap in a 58 psi regulator (unless it's one that is regulated in the tank... ugh)

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Yea, the pressure sure is 58 or so, but most all injectors have a "rating" at which they flow, which is typically 43.5 psi... most of them anyways..

The injector data in the PCM is based off 43.5
Theyre rated as "26 lb/hr @ 3 bar (43.5psi)" from delphi or whatever

If i plugged 58 psi into the handy dandy calculator, that'd be 360hp @ 100% duty cycle , and i'd really have a hard time believing an unopened 4200 is putting that much out haha

Edit:
I guess i need to add, so you dont think im disagreeing

If you take 26lb/hr injectors, and put 58psi to them, thats 115% more flow than 43.5psi

The formula is sq-root ( new pressure/old pressure), which is 1.15

26 lb × 1.15 = 29.9 (30lb/hr)

If you take that 30lb/hr @ 58psi and put it into thr calculator, then you'd end up somewhere around 80% DC @ 315+ hp

Thats probably in actuality where i am on those injectors, as i hit 115% injector duty cycle yesterday on a steep hill climb in 2nd playing around and still didnt see any knock lol. The PCM's outputted duty cycle is based on 43.5 though, if that makes sense to you, i just hate running things so close to their max.

It could also be the pump i have in the tank. I had to put a stock pump back in... i was having issues with that bigger pump.
Theres also something regarding once you exceed 80% of idc, the linearity of the injector deviates and all your calculations can get fudged, and it starts putting wear on the PCM from the amperage draw i guess. They need a cool down time between cycles and larger pulse widths at higher rpms dont allow for that

theres also the concern of elevation
I live around 700ft here. So close to acceptable tuning conditions, but if i went elsewhere where the air was more dense or what have you that affects barometric pressure, i might could max these things out for real, and theres still not enough room to play with E85

Vbb199 said:

Yea, the pressure sure is 58 or so, but most all injectors have a "rating" at which they flow, which is typically 43.5 psi... most of them anyways..

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Thats 58 psi regulated @ the rail with a manifold referenced regulator

Hunter79764 said:

Just my ignorance showing, but is 43.5 the proper fuel pressure? I thought GM did 58 for most stuff of this vintage? If it is 43, that might be a cheap fix for maxed out injectors to swap in a 58 psi regulator (unless it's one that is regulated in the tank... ugh)

Click to expand...

I did forget something you just reminded me of though

Decapped, the 26 lb'ers will flow at 75 lb/hr
Im just worried about doing that

Vbb199 said:

Yea, the pressure sure is 58 or so, but most all injectors have a "rating" at which they flow, which is typically 43.5 psi... most of them anyways..

The injector data in the PCM is based off 43.5
Theyre rated as "26 lb/hr @ 3 bar (43.5psi)" from delphi or whatever

If i plugged 58 psi into the handy dandy calculator, that'd be 360hp @ 100% duty cycle , and i'd really have a hard time believing an unopened 4200 is putting that much out haha

Edit:
I guess i need to add, so you dont think im disagreeing

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That makes sense, just wanted to make sure you were accounting for that and didn't just forget to increase the fuel pressure or something. I'm following along and enjoying what you're doing, keep up the good work!

Hunter79764 said:

That makes sense, just wanted to make sure you were accounting for that and didn't just forget to increase the fuel pressure or something. I'm following along and enjoying what you're doing, keep up the good work!

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GM has/had some strange things in this PCM. Starting is the hybrid Alpha-N / Speed Density management type...
THe LS stuff and v6 stuff of the same era was speed density (MAP sensor based) or MAF based (im sure you know what the maf is) ... these 02-05 4200's use Engine Load vs RPM for their part throttle and high rpm tables, then they use MAP for idle and spark control

Engine load is defined in seperate parameters based off of throttle position which GM again didnt configure it like 10% throttle = 10% engine load; but instead 10% throttle meant something else... and so forth up to 100% throttle

Strange... given my experiences tuning mostly V8 and V6... this is difficult to tune, but ive got a pattern down now and know how to.

If thats not weird enough, the way the injectors are setup from the factory is strange

Theyre setup as 26lb/hr @ 43.5 psi, but the fuel flow table in the pcm is arranged as if the regulator had no return... even though the truck DOES use a return.. beats me why gm is doing that. Ive checked pressure at the filter (underneath the damn car is where the valve is) and it shows 58 psi

Ive changed the table since then to behave like a return-equipped regulator but as to why GM did any of this beats me

Didnt get a chance to get to the junkyard yet for that 06+ hardware... but ive been messing with my trailblazer a little more in the PCM.
Mostly fiddling with VVT cam angles for optimum performance.. namely finding the sweet spot that cools the combustion chamber down , thus allowing me to use the best spark advance.

Like for example, in the lower rpms (1000-2000) i was previously using 4-8° of cam retard, but the consequences were, i had to lower spark advance way down to 10-13°, because the motor would knock at much higher degrees

By raising cam retard up to 15-16° in this range , it effectively cools the combustion chamber down enough with EGR gasses (the vvt doubles as an EGR valve), allowing me to run more like 15-20° of spark advance... yielding more power, and better bottom end.



Then theres the seperate issue ive heen having....

Torque converter clutch slippage....
So i guess it was always flaring in lockup, it just got worse the more i tuned the trans. I looked at a data log from first time i drove it on the road 4 weeks ago with stock everything and it was flaring then. ... bit minor amounts.

Within last week, it got so bad i was seeing like 3-500rpm slippage in the converter on the laptop (its supposed to be <20rpm).. it'd flare like hell when it commanded lockup too.. sheesh talk about making me cringe. I guess in stock form it wasnt noticable because the stock config has pressures set really low, and lockup is set to occur after like, 55-60mph.. which i guess was high enough rpm and low.enough engine load, it wouldnt flare up but like 100 or 200 rpm.

Over the course of tuning, i had lowered the parameters so lockup would occur closer to 45-50 mph and up, which really helps my mpg in town. I also raised pressures up which i guess all of this combined finally manifested the nasty converter flare i was having.

It was awful.. like i said 3-500rpm slippage when LOCKED.

I added a quart of fluid last week and it helped alot, but still slipped like 1-200 rpm and flared when it commanded lockup. Yuck.


I was thinking today i was gonna have to drop the pan and block off the pressure valve in the trans so it'd send max pressure to the TC...

But added a half qt first

That fixed it! It wont even slip 15rpm now. I even went uphill in 4th, bogging the motor down trying to make it slip and it wouldnt.

AND 4th gear now shifts super firm. It was tight before, but not THIS firm.

I have NEVER, EVER felt a 4L60e shift into 3rd or 4th so firmly. Its actually insane. THATS how i built it to run. Tight @ss clutch clearance, with a blocked off accumulator piston. I wanted 3rd and 4th to slap. Theyre the weak links in these guys.

And lockup hits firmly enough it feels like a 5th gear, and theres ZERO slip now.


I guess i lost more than i realized when it spat the corvette servo out lol

Doesnt help that dipstick SUCKS.

Vbb199 said:

Been a while since ive touched this one. I was making slow and steady progress, then i hit a roadblock and parked it for a while.

I believe i mightve said earlier i built a decent 60e for my TB. I think i didnt include i was having a binding in reverse smh

I thought it to be wheel related, and alas it wasnt, after laying on the gas, it spat the servo and snapring out the side of the case LOL

So i figured i fudged the trans build, and said F it, i'll deal with it later. I had been working on my house and all the projects had to sit.

Last weekend i put a stock servo back in it. I had previously put a used corvette servo in it, and i recall checking and setting band clearance when i had the trans apart... no idea why it was grabbing so hard in reverse, but putting a stock servo assembly back in solved that. Reverse is nice and free again lol

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This little sin finally came back for me.

When it spat the servo out, it took one of the tabs that hold the servo cover Clip with it.

I JB welded it back in place for the time, and let it go


well surprise surprise
Today the JB welded-mickey mouse BS blew off, and took more of the cast tab with it.

So now the trans has to come out, and ive got to switch housings entirely.


I had a strong feeling the JB weld wouldnt hold forever. Especially how hard it shifts into 2nd when you give it the beans.