So I bought a 88 GTA with 383 10.25:1, mini ram, accel 1000 cfm TB, 30# injectors, etc. The car had absolutely no rust which is the reason I bought it, did not but it for the performance. I plan to get an EBL Flash II to replace the accel gen 6 DFI. The car is getting only 15 highway mpg with 3.73 in a 12 bolt rear with a 700r4 (non-lockup). It is running rich, but I wanted to know if I could tune the EBL to get like 25 highway mpg. I know performance will be sacrificed but I do not care. Would reducing injector size also help with MPG?

 

The lean cruise highway mode will increase the mileage. And without giving up performance as it is only invoked during light cruise conditions.

RBob.

 

So I bought a 88 GTA with 383 10.25:1, mini ram, accel 1000 cfm TB, 30# injectors, etc.

Would reducing injector size also help with MPG?

Your 30# injectors are barely enough for that engine as it is. Keep them. What I would recommend is reducing the size of your throttle body if you're looking for miles per gallon. See... we tune fuel to the incoming air, with the air being fixed as a given. Open throttle body, engine sucks in whatever amount of air that it sucks in, and we tune the fuel to that incoming air. If you limit that air with a smaller throttle body, you will reduce the amount of fuel you need to maintain your proper air/fuel ratio, especially up top. A 1000-cfm is way overkill in your case, if you want miles per gallon, trying to achieve that with that big of a throttle body is a waste of time. Can it be done through the tune, absolutely, will the engine run good down low, doubtful. Get a smaller throttle body. Back in the day they used to call them "torque motors", where although they had plenty of cubic inch displacement on tap, the factory simply restricted their incoming air, so they ran out of it up top, but plenty of torque down low. They used gas sure, but being limited to a certain RPM kept them from using too much. What part of Central Jersey are you in...?

- Rob

Edit: Then again, just get yourself a lockup converter w/2.73 gears out back and be done with it,.

 

One thing to consider - you are messing up the environment with lean cruise. The EPA banned lean cruise.... well not in so many words, but it drives Nitrogen Oxides (NOx) through the roof by running very high combustion temps. In other words - it's extremely bad for emissions. Yes you might gain 1 or 2 MPG but it's hard on the cooling system and it's bad for the environment.

GD

 

I think the 3rd gens run 3 way catalytic converters no? Which convert the NOx to N2?

I run the highway mode on my 2nd gen.

I'm running cats (albeit only two way) and have more than doubled the fuel economy on it from the factory config. My dad saidb the best he ever got on the highway was 14 mpg with a smog carburetor, even with stock heads and cam.

Couple of years after buying the car from him I converted to EFI and have since then with 700R4, gear vendor OD, and tuning, (and my recent change over to Accel coil and module) I'm now getting 30-31 in "8th" gear on the highway.

What's hilarious is my 50 year old car with 30 year old engine technology is getting pretty much the same highway mileage as my wife's 2017 RX350.

But I figure the overall emissions reduction I've already achieved over the factory 1971 config, I'll accept a little higher NOx to get better mileage. It's still overwhelmingly a net positive from what I started with.

I dont know... I know what you're saying...

But I guess for as few people who are able to activate this function on 80s era cars that are already so scarce to begin with these days... we're talking an infinitesimal increase in aggregate emissions.

 

Fuel not burned creates no emissions.

 

You clearly have no idea what you are talking about. You should do more reading and listening and less posting.

GD

 

From Wikipedia:

Three-way[edit]

Three-way catalytic converters have the additional advantage of controlling the emission of nitric oxide (NO) and nitrogen dioxide (NO2) (both together abbreviated with NO
x and not to be confused with nitrous oxide (N2O)), which are precursors to acid rain and smog.[19]

Since 1981, "three-way" (oxidation-reduction) catalytic converters have been used in vehicle emission control systems in the United States and Canada; many other countries have also adopted stringent vehicle emission regulations that in effect require three-way converters on gasoline-powered vehicles. The reduction and oxidation catalysts are typically contained in a common housing; however, in some instances, they may be housed separately. A three-way catalytic converter has three simultaneous tasks:[19]

Reduction of nitrogen oxides to nitrogen (N2)

• 
• 
• 
• 

Oxidation of carbon, hydrocarbons, and carbon monoxide to carbon dioxide

• 
• 
• 

These three reactions occur most efficiently when the catalytic converter receives exhaust from an engine running slightly above the stoichiometric point. For gasoline combustion, this ratio is between 14.6 and 14.8 parts air to one part fuel, by weight. The ratio for autogas (or liquefied petroleum gas LPG), natural gas, and ethanol fuels can be significantly different for each, notably so with oxygenated or alcohol based fuels, with e85 requiring approximately 34% more fuel, requiring modified fuel system tuning and components when using those fuels. In general, engines fitted with 3-way catalytic converters are equipped with a computerized closed-loop feedback fuel injection system using one or more oxygen sensors,[citation needed] though early in the deployment of three-way converters, carburetors equipped with feedback mixture control were used.

Three-way converters are effective when the engine is operated within a narrow band of air-fuel ratios near the stoichiometric point, such that the exhaust gas composition oscillates between rich (excess fuel) and lean (excess oxygen). Conversion efficiency falls very rapidly when the engine is operated outside of this band. Under lean engine operation, the exhaust contains excess oxygen, and the reduction of NO
x is not favored. Under rich conditions, the excess fuel consumes all of the available oxygen prior to the catalyst, leaving only oxygen stored in the catalyst available for the oxidation function.

Closed-loop engine control systems are necessary for effective operation of three-way catalytic converters because of the continuous balancing required for effective NO
x reduction and HC oxidation. The control system must prevent the NO
x reduction catalyst from becoming fully oxidized, yet replenish the oxygen storage material so that its function as an oxidation catalyst is maintained.

Three-way catalytic converters can store oxygen from the exhaust gas stream, usually when the air–fuel ratio goes lean.[20] When sufficient oxygen is not available from the exhaust stream, the stored oxygen is released and consumed (see cerium(IV) oxide). A lack of sufficient oxygen occurs either when oxygen derived from NO
x reduction is unavailable or when certain maneuvers such as hard acceleration enrich the mixture beyond the ability of the converter to supply oxygen.

GD

 

So essentially - outside of 14.6 to 14.8 AFR, your three way catalytic converter ceases to function and you F the environment.

That said, I don't have cats on any of my vehicles and that's not likely to change. But for the sake of argument - those are the facts.

GD

 

He admits it!! We can F the environment together.... lol

 

All of this said... you are right about 1-2 mpg increase. That's about all I got out of it. I used the WB to dial in about ~16:1.

But I've had the heads off and the pistons and valves don't look any the worse for wear, so the engine seems relatively happy cruising along at light throttle with that AFR.

 

Sorry for the late reply, I'm in Hamilton, NJ. It's near Trenton. Besides the actual convertor, what else would I need for the lockup function. This is an art carr 700r4 with 3000 stall. I wouldn't mind getting 2.73 gears. That would be best since I do a lot of highway driving. Looking to make this a semi daily driver.

 

Yes, then the idea is to keep the RPM as low as possible when you're driving around town and on the highway, this will keep your fuel demand low in terms of the average fuel being used. So you see, it doesn't really matter what size your injectors are, your engine will take in a fixed amount of air the way it's been built, and your just metering your fuel to that air. You can run it a tad leaner to help reduce fuel consumption, but the biggest difference would come from your gearing. My old C4 was at a mere 1600-RPM at 70-mph on the highway thanks to its' 2.54 gearing out back. Not the greatest for performance by any means, but I saved a lot at the pump lemme tell ya....

Art Carr was always big on building non-lockup converters, that was his preference. I don't believe he did anything drastic with his 700R4's and 200R4's, they were just built take a beating with his choice of a non-lockup converter. The EBL can control converter lockup, as well as a pressure and /or toggle switch. But if you ask me, even with the non lockup converter, the 2.73 gears, in conjunction with a taller tire (height wise, not width) for that matter than what you're already running, will make the biggest difference. I'm not too far from you so if you get your hands on an EBL, I'll get you going right away with it...

- Rob

 

Combustion temperatures are cooler in lean cruise and my Express van runs cooler in lean cruise on both engine coolant temps and oil temps than it does running at stoich. There is more oxygen leftover in the chamber which actually keeps the cylinder temps lower. At a steady 80 mph the EGTs are noticeably cooler at 16.5:1 than they are at 14.7:1, like 150°F lower. 600°F vs 750°F at cruise.

I get 2 mpg better with a ~500 hp 383 and 5.13 gears than I did with the small cammed 350 and 3.73 gears. The 350 with the taller gear was always having to work hard to keep the van rolling at speed. The 383 does it effortlessly in lean cruise. I have run triple digit speeds and it stays in lean cruise. Running 3,000 rpm @ 75 mph I get 19 mpg. With the stock 350 and 3.73 gears, overdrive was useless as far as MPG went. Got the same mileage at 3,000 rpm in 3rd as I did at 2,200 rpm in 4th, big difference in response and power though on hills. Had to practically floor it in 4th to get it to drop to 3rd, where it would just hold speed without moving the pedal in 3rd. Chevy actually gave me a good laugh a while back. Running on a highway with traffic rolling ~105, the accelerate function of the cruise will accelerate to 98. You can accelerate past 98 with the pedal and set the cruise to maintain a higher speed than that. At 3,000 rpm, no load that 383 pulls 25 in/hg vacuum. At 3,000 rpm/75 mph on flat road it pulls 17 in/hg. At 4,000 rpm/100 it is pulling 17 in/hg. After about 1 hour running that speed and the rest of the trip at 75-80, that tank still got nearly 18 mpg.
​​​​

 

That's a good point.

Combustion temps (the temperature of the actual combustion gasses) are higher and lead to production of NOx. That doesn't necessarily translate to higher EGT's and higher coolant temps. You are burning a lot less fuel and air in general so the temps you are measuring are lower. But the gasses are higher - there's just less of them so the heat dissipates quickly. The NOx is still there, and still higher, regardless of the temp of the exhaust tubing, and the engine coolant. That's why they banned lean cruise. Properly managed - It's safe the engine, and good for MPG..... it's just bad if you want to make less smog and acid rain.

GD