Chevrolet Cruze Forums banner

to tune or not to tune

3742 Views 15 Replies 9 Participants Last post by  marty68
Hello Cruze owners. I am new to THIS forum. I am taking delivery of a gently used 30k mile Cruze lt with rs package sun roof etc. in victory red.
my question is, (yes I have used the search function) what tune to use and should I use a canned tune.
I like the idea of the trifecta tune's cruise on cruise off functions.
does the "cruise on= tune off" mean everything including shift points remain as the general assigned them?
I should state I drive 55 miles each way to work. the freeway is 1 mile 1 stop sign from my house. the parking lot at work is 1 mile 2 stop signs from the freeway.
My car I am retiring ( to nephew) is a great running best car I ever owned 2004 Saturn ion quad coupe with 240k and still has original rear brakes.
Thanks for you responses in advance


  • Like
Reactions: jsusanka
1 - 4 of 4 Posts

· Banned
9,198 Posts
Been tuning my vehicles for years, over 60 to be exact. Have a spark advance timing light, got rid of my distributor tester a long time ago. Have both a CO2 and an AF ratio meter, and the tools to make my own carburetor jets.

Al Gore would have a fit to see me tune a vehicle for maximum CO2, spark advance curves and initial timing are base on the kind of fuel you are using and all of these adjustments are manual. With my motorhome averaging 9 mpg, got that up to 15. 92 DeVille was only getting about 24 mpg, got that up to 31. List is long, want to hit that magic stoichiometric numbers with carb vehicles, O2 sensor does this for you in closed loop operation, and open loop operation learns from this.

Anti-knock sensors provide the maximum allowable spark advance depending upon what grade fuel you use. Did try 89 octane ethanol free gas in my Cruze, both my fuel economy and performance suffered. Boat was real easy, the old stuff, on a still lake with 91 octane fuel in it, spark advance topped off at 3,000 rpm. Had my kid drive it, sat on the rear seat, engine cover off with an accurate tach attached, simply rotated the distributor for peak rpm.

Friday, put new plugs in my Cruze gaped to 25 mils, 45K miles is more than enough, yesterday took a 300 mile trip keeping up with traffic, more like 77-78 mph and averaged 41.7 mpg, 2012 2LT with a manual transmission. If I drove it at 64 mph, would have average 46 mpg. Also switched to 30W-0 motor oil, claims full warranty, but already know from a long history, lighter grades of oil to lubricate far superior than that thick grease stuff does.

Tuning in these new cars translates to playing with the firmware, with over four years of these discussions, nobody could explain to me precisely what parameters are changed, promise to keep an open mind. Plus we have some very strict EPA laws. 3rd gear in the Cruze gets you up to 77 mph very quickly when you have to but forget looking at your instant mpg. And not exactly what you would call a muscle car.

So what exactly is a tune doing? One thing I did read, is you have to use at least 91 octane fuel, already doing this. In trying different brands of gasoline, some stations really lie, but doesn't help having an EPA with over 150 different blends of gas.

· Banned
9,198 Posts
ECU increments the spark advance until it gets signals from the anti-knock sensors, then backs it off just enough until these signals disappear to prevent preignition. Greater octane fuel provide more spark advance for a long combustion cycle.

Another cause of anti-knock signal is detonation, compression of the air/fuel mixture creates heat that can combust the fuel, before the piston even gets close to the top of its cycle. This can be caused by purchasing ethanol based fuels with a poor mix. In this event, you get no spark advance, period. Already got bad mixes of E10, instead of getting 37 mpg, more like 17. Whoever said alcohol and gas does not mix, knew what they were talking about in more ways than one.

Really can't fool around with injector dwell, too rich, more power, but will toast your catalytic converter, plug it up and even get poorer economy and performance. To lean, combustion chamber gets too hot, burns out exhaust valves, even holes in pistons, and pisses off the EPA with excessive NOx production, VW tried this. But fuel economy will increase.

Nothing can be done about the compression ratio by playing with code, strictly mechanical. Was common to use 10.5:1 iin the 60's, but only super high octane fuel could be used. Cruze at 8.5:1 is low, but compensated by the turbo that effectively increases it by pumping in more air/fuel. Also allows for using a lower octane fuel like 87, finding some stations around her now offering 87 ethanol free. But this will slow slow down your Cruze and burn a lot more of it.

Valve timing can be played with just a little, but leaving the exhaust valves open a tad too long limits EGR, again higher combustion temperatures that can and will burn up your exhaust valves.

The guys that work with this stuff have millions of bucks worth of equipment, try to do their best, but also have warranty and govenment regulations to contend with.

In 1972 when the HEI first came out, GM was recommending a spark gap of 65 mils, somebody was smoking crack, were toasting cats like crazy, shortly after reduced that to 45, still way too much. Had a 73 Fleetwood at the time gaped mine at 35 mils, put over 200K miles on that car with zero cat problems and a lot better performance and fuel economy.

A lot more sense was used with the Cruze at 28 mils, but those coils are in the toy class, so gaped mine at 25 mils, could even try lower, ha, a chain saw running well over 6000 rpm is gaped at 17 mils.

Daughter's Soul was at 45 mils, cut that down to 30, what a huge difference for her with performance and fuel economy, also using toy like coils.

In theory, not improvements can be made in an ignition system if you get a spark each and every time at the right time. But sure won't get that with a large gap.

· Banned
9,198 Posts
One of the most drastic changes ever was between model years 1971 and 1972, had a brand new EPA, leaded gas time was coming to an end with this new unleaded gas. Major problem with it, its combustion chamber temperature increased from 2,100 *F to over 2,600, so an EGR valve had to be added that actually pumped in exhaust gas into the combustion chamber to add more cooling to the combustion chamber.

If you would bypass it, would quickly burn up your exhaust valves and get holes in your pistons, can't take that heat. Other factor was adding a catalytic converter, more exhaust gas restriction. As only low octane unleaded gas was available, the compression ratio had to be decreased from 10.5:1 down to 8.5.

The decrease in performance was not too noticeable, Nixon by an executive order decreased the speed limits from 70 mph down to 55.

If the price of unleaded gas jumping from about to 30 cents per gallon up to 75 cents per gallon, could still buy unleaded, but that increased to $1.55 per gallon.

At that time, had my beloved 1970 Buick Riviera, required high octane leaded gas, 87 would cause severe detonation in that 455 CID engine. With EGR as high as 30%, that made that 455 engine more like a 318, but what the hail, still could do 55 mph.

Car became worthless, so I could keep and drive it, had to buy Canadian head gaskets, that did drop the CR down to 9:1, Canada never had high octane fuel, they were rather fat head gaskets. So I could burn unleaded, was lucky, went to my wrecking yard when I could walk back in there with my own tools, can't do this anymore. Found a 72 Buick with the EGR, removed the entire intake manifold with the carb and the EGR valve and got it for ten bucks. Won't let you do this today anymore, have to buy the entire engine.

While this car had factory dual exhaust, was not required by law to add the cats, back then would have been at least another 500 bucks. So was able to get my use out of that car poking along at 55 mph. Fuel economy did suffer, in good tune at 70 mph, averaged 20 mpg, at 55, and these required mods, below the peak torque value of that engine, best I could do was 16-17 mpg.

Screw you Nixon, hate your guts. But this was not the only problem besides paying $1.55 for high octane leaded. Practically overnight, all the full service gas stations disappeared and replaced with convenience stores! You could no longer stop to get a flat tire repaired or even air, but you sure could buy a case of beer. Bet not too many on this board even know what a full service gas station was like.

Getting back to the Cruze, the better way for EGR is to close the exhaust gas valves early to leave that mess from the previous cycle and does have variable valve timing.

What they could do is to change the firmware to keep those exhaust valves opened longer to get rid of that burnt up fuel, but just to get a short burst of power for a very short duration as not to put holes in your pistons nor burn up you exhaust valves. EPA's concern is excess NOx production by doing this, but they are not the least concerned if you toast your engine, so they never talk about this fact of life, just excess NOx production. We recently learned VW was doing this, in deep trouble now.

But there are other ways to pick up around 5 extra HP, turn off most of your electrical and in particular you AC if its on, this decreases the load on that little 1.4 L engine from both the AC compressor and the alternator.

But why did you buy a Cruze for anyway? Our key reason, fairly comfortable car, fun to drive, but most important, fuel economy. Since we purchased ours, had to pay as much as $4.55 per gallon due to some minor pipeline leak in Janesville, WI.

Without a vehicle, for earning a living, taking our kids to school, getting groceries, even a vacation, we are helpless. They got us where they want us.

· Banned
9,198 Posts
In Canada any model vehicle 1990.5 and older doesn't have to have cats :)
Yeah, but you can't use R-12 refrigerant anymore, if you run low, have to pay a small fortune to convert to R-134a. Your government brought all that BS presented by Al Gore. We can still use R-12 for our old stuff, but have to pay an arm and a leg for it.

For many vehicles, the only way to convert to R-134a is to completely replace the entire AC system, well except for the evaporator. And what makes this kind of inconvenient, is they don't even make replacement parts that fit these older vehicles.

Another minor problem is that older vehicles cannot use ethanol based fuels, its kind of like they want this older stuff off the roads. Mexico never banned R-12 with practically a 365 day cooling year, but Canada did with about a seven days cooling period. World has gone nuts.
1 - 4 of 4 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.