I decided to sell my 96 blazer which is my daily driver and turn my 88 Iroc into my new DD. Right now its basically a stock 305tpi/700r4/3.27 with about 140,000 miles. The Iroc has been sitting for the last 6months and really wasn't drivin a whole lot before that. I plan on doing a full tune up and oil change, but I was wondering what mods would increase my gas milage? Right now I have K&N air filters, air foil, underdrive pulleys, a/c delete, and soon to have smog delete. I was wondering if an exhaust system would increase or decrease gas milage? also what other mods would help both performanc and gas milage? I'm not looking to make a race car out of it, I have my TA for that, just seeing what mods I can do that won't decrease my gas milage. any help would be great. Thanks

 

Use curse control, and light on the go peddle. A good tune up will do wonders.

 

I found this thread to be somewhat helpful. At least a place to start...

Eventually, once I getting mine running smooth, I'll be looking at fuel economy too, as I give it more HP anyway, lol

https://www.thirdgen.org/forums/tpi/...?highlight=MPG

 

What, exactly, is involved with the "Smog Delete" procedure?

Depending upon what you remove or alter, your fuel mileage may only reduce a little, or a lot. Don't expect it to increase.

If you remove or disable the air injection system, the engine can take longer to warm up the O˛ and achieve closed loop. That will mean that it runs unnecessarily rich for a longer time - Lower mileage. The only possible benefit would be to remove the air injection pump and install and wire a heated oxygen sensor to get an O˛ reading as soon as possible after engine start. In order for that to be successful, you MUST have a three-way cat converter designed for no external air supply. You'll have about ten pounds of metal and plastic off the vehicle, which might gain about 0.0001 MPG. The danger is that if your vehicle is required to pass an emission inspection, the visual inspection might not fly without an AIR system in place. A properly functioning A.I.R. pump will take 1-2HP at peak engine RPM. At cruise, it takes nearly nothing, which is why the air pump drive belts on the old "V" belt systems were so tiny.

If you remove or disable the EGR, chamber temperatures will tend to increase (even with a colder thermostat) so that timing advance can not be increased to a more efficient range during cruise - Lower mileage. As the load value decreases and vehicle speed increases, the ECM will attempt to increase ignition timing. If the chambers are too hot, and detonation is detected, the ESC will fold back the timing to prevent damage, but also cost you MPGs.

If you remove the EVAP system, more fuel will evaporate into the air instead of being burned in your engine - Lower mileage. I'm not sure where "Homer Glen" is situated, but I live in the extreme north end of Ill-Noise, and it was only 92ş here yesterday. Everywhere else in the state was likely warmer. At that temperature, a non-controlled fuel tank can lose 5-7% of its liquid volume to evaporation in a week. That's like lowering your mileage 7% because that fuel just isn't there to be used. What's worse is that the system is completely passive, requiring no engine power to function. If your system isn't working, repair it. You can measure the mileage increase in just a couple weeks.

A catalytic converter will cost no mileage or power if it is not failing, and properly sized and installed. Your car should have one (a remote possibility of two) converter. On a good day, you might get 23MPG and be able to make 260HP - If you're lucky. The LS7 engine makes over 500HP, can squeeze out 28MPG, and they have FOUR converters. Instead of torching off your converter "to increase power and mileage" you might want to consider installing a high-flow three-way converter.

The only other "smog device" on a ThirdGen is the PCV system. It is also completely passive, requiring no engine power, and unless you want to change your oil every five hundred miles to keep it clean and moisture-free, I'd stick with the PCV system.

Instead of arbitrarily removing hardware, consider that making it all fully functional might be a better idea.

Reducing the intake air restriction is a good idea. Just make sure you keep the K&N filter clean, and don't over-oil it.

Keep the IAC working, and minimum air position correct so that the engine does not idle at any higher RPM than is necessary. This will also require that there are no vacuum leaks, which includes having the correct PCV valve installed (they are all calibrated for different flows).

Keep the ignition system at peak performance. That doesn't mean that you need any special, fifteen electrode, unobtanium alloy, custom colored insulator spark plugs. You also don't need (or want) any super reverse-inductive, multi-layer, voltage increasing plug wires with a designer name printed on them. Special kevlar fiber, ten trillion volt resistive, see-through, neon-glowing distributor caps are not necessary. Platinum-plated, rare-earth, elf-mined copper and iron ore ignition coils are another waste of your time and money. When cruising, you're going to be operating well under 2,000 RPM and at very low throttle angles. You don't need enough spark volts and milliamps to blast through that "super-resistive, impenetrable" distributor cap, burn a hole in your firewall like a plasma cutter, and zap your audio unit.

Just use original design plugs with correct gaps, good quality resistor/suppression plug wires, a good distributor cap and rotor, and verify all system connections and grounds are intact.

When you drive for mileage, stay out of the acceleration mode as much as possible, and use the deceleration fuel cutoff as much as possible. Some people have the impression that accelerating from a stop as slowly as possible will yield the greatest MPG. One study performed by BMW indicated that accelerating to the cruising speed more quickly, then entering cruise mode as soon as possible, will yield the best city driving MPG. That doesn't mean burning the tires all the way to 45 MPH then backing off, but accelerate so that the system spends as little time as possible in the acceleration mode.

On decel, anticipate traffic flow and back out of the throttle well before applying the brakes. Fuel is cut off in decel mode until the vehicle speed drops to around 12-15 MPH in most stock ThirdGen programs (IIRC), and any time spent in this mode is simply getting more miles traveled for almost no fuel used. If the brakes are not applied on deceleration, the TCC (in automatic trans cars) will unlatch in a "coast release" mode at a programmed vehicle speed, and the engine RPM will tend to "float up" to whatever rpm the convert drags it along at. As soon as a little throttle is applied, the TPS voltage increases, and the TCC will lock again, potentially raising the RPM and using a wee bit more fuel on coast at some speeds. Once you're below about 33 MPH, it won't matter, however. The important thing is that when transitioning from coast to acceleration or cruise, you apply the throttle very gradually to allow the TCC to engage before increasing vehicle speed.

Then there are all the common factors to consider, like tire inflation, wheel alignment, brake adjustment and clearance (you don't want any dragging, including the park brake), reducing vehicle weight (don't haul around that tool box, track jack, slicks, or spare heads in the cargo well unless you need to), and cleaning up the aerodynamics. If you have a Firebird with the headlights stuck open, fix them. They're costing you mileage and money. Don't put three "aero" wings on top of the rear deck, and hang two more on the underside.

 

Thanks for the help.

As far as smog delete, I was going to pull the pump off and put the delete pulley in that I alrady have. I figured that would help loose weight and free up some power not haveing to turn the pump. I was also going to get rid of the air line on top of the exhaust manifolds just to clean up the engine bay(personal preference) I plane on removing the cat because after 140,000 miles I'm not sure if its ever been replaced and if it clogged that will be effecting HP and MPG. That is basically all I plan on removing from the smog equipment. I dont have emissions anymore so its not a problem. I also plan on doing a rebuild on the front end and then getting it alligned. I saw spohn offered a front end rebuild kit. Tires are almost brand new and I will be checking tire pressure on all of them. I also plan on doing a lot of suspension work just to make it ride nicer. I was mainly just curious if headders and a 3inch cat back would hurt my hurt my MPG or help it since it would have better air flow? Same thing with going with a better intake and runners?

 

damn.... i gotta get an evap system....

question, how can i find out which PCV is best for my engines flow?

 

Acutally, they are dwarven mined... and damn, I spent a lotta cash on all that, the guy at ***** Auto told me it would help fuel economy

 

Vader, that is a great reply
with the number of people who are always asking about removing the emissions equipment, i vote this to be made a sticky, or at least linked in a sticky or moved to the FAQ Board.

 

I second that!
Very good explanation to all the folks who love to "tear out all their smog stuff"

 

headers & cat-back exhaust will improve your MPG. the engine doesn't have to work so hard to pump the exhaust gases out of the motor.

since you have the auto trans, you should put in a shift kit, that will reduce slippage, which also improves MPG.

it is constantly debated whether MSD-6 provides improved combustion. improved combustion ensures that you're burning all the fuel-air being provided, so that your car goes as far as possible for a given amount of fuel. So I've installed MSD-6AL's in all my vehicles.

make sure your tire air pressure is optimized, preferably on the high side to minimize rolling resistance. also that your fluid level in your diff is at the right level (same for the trans). ensure that your exhaust is firmly mounted so as to not introduce extraneous knock sensor signals.

and of course, check your spark plugs to ensure that they are running clean (and/or slightly lean). make sure your spark plug wires are good, and your distributor cap & rotor contacts are not eaten away.

The evaporative emissions canister might actually help MPG by storing and reintroducing gas fumes for combustion. the benefit is probably not measurable with current technology...

 

you can buy my 2.77 ring and pinion and 2 series carrier....that will help your highway mileage! lol

 

I know it's the second time for it being said...but...

Keep those tires pumped!!!!

I tell people to think about when you try to ride a bike with a flat tire or even really low tire - how much harder it is.

I think it's a good idea to check them every month, and visually check them all the time.