Has anyone ever made power with the lean burn system?

Gearhed · Jul 4, 2020

Hi everyone, I bought an 85 fifth avenue the other day for $300. It's got 97k on it and runs like a top.
Everything I read about the lean burn ignition just talks about deleting it in favor of a different system, never about applying the system to a performance build. Has anyone ever done it? Is it really as bad of a ignition system as people say?

Aspen500 · Jul 4, 2020

Not much you can do with the Lean Burn (or Electronic Spark Control) systems to make power. The ECU will only do what it's programmed to do and I don't think there's any way to reprogram one with a performance advance curve, or anything else for that matter. They pretty much are what they are.

Mikes5thAve · Jul 4, 2020

You can't do anything with it. It's all based around stock timing, stock cam, stock vacuum readings and o2 sensor. It won't take advantage of anything you try to change performance wise and might actually be worse on power.
Its like doing stuff to a new without doing a tune.

Gearhed · Jul 4, 2020

It's a shame no one has ever figured out how to re-flash or chip the ignition computer. If you look at the inputs that it's getting, it should be able to be a fairly capable system, if only it wasn't all vacuum controls, and someone could figure out how to change the advance curves

Duke5A · Jul 4, 2020

Gearhed said:
It's a shame no one has ever figured out how to re-flash or chip the ignition computer. If you look at the inputs that it's getting, it should be able to be a fairly capable system, if only it wasn't all vacuum controls, and someone could figure out how to change the advance curves

It's not a question of figuring it out - it ain't worth it. Strip out the lean burn and put in a 4bbl and a performance distributor and what do you get? A turd. Same as before. There isn't anything the computer can do to wake up the motor. You're cut off at the knees with the cam and gears. Besides, all it controls is spark. If it did both fuel and spark you might be able to do something with it, but even then there are better options.

Gearhed · Jul 4, 2020

That's a solid point, but I'm talking less about waking up a stock motor, and more about applying the concept and hardware to create a system that in theory could be superior to a standard mechanical advance distributor on a non-stock engine. I'm sure it's not cost effective, just an idea that I was wondering if anyone had attempted

XfbodyX · Jul 4, 2020

Just like people do things for there own enjoyment to see how many mpg they can squeeze out of a certain motor/car combo a person could make adjustments to the external things that they could adjust and if they were tech smart on the way things were done in the 70-s a person could make themselves 100-s if not 1000-s of hours of frustration and or enjoyment.

From 76 the whole lean burn deal evolved a good bit, especially in the first few years.

Here is some text of what they thought they would achieve in 76, then updated in 77 most notably the cats on the US cars.

And to make things ever odder, the US had a set. std on emissions as well as goofy California and even Canada had std. of its own.

But the main hurdle for the common guy would be you would need the test equipment that the dealers had, and for example this very first version made fuss just at the price alone to the end user, $750 in 1976 money, like $3500 today.

It might be fun if one just wanted to do it, but if you were trying to sway from the core mission youd do better just to gut things and use modern tech.

XfbodyX · Jul 4, 2020

vid.

XfbodyX · Jul 4, 2020

Look at the red doba in this vid, red red red.

XfbodyX · Jul 4, 2020

vid using the tester

Aspen500 · Jul 5, 2020

The main hurdle is the 1970's computer technology, it was pretty basic, unmodifiable and reliability was questionable at best. I'm not sure but it might be possible to use a modern aftermarket ignition controller with the stock distributor(?) If you wanted to get sneaky, you could gut the original lean burn housing and put the controller inside and nobody would know it isn't stock. Just thinking out loud.

As always XfbodyX, excellent information

Gearhed · Jul 5, 2020

Aspen500 It's funny you say that. one of my co-workers also works in a shop that builds classic euro cars, and spends a lot of his time putting stealth efi systems into MGs and similar. He's been telling me that I should get a GM tbi unit, gut the lean burn computer, and stick a microsquirt inside it to control tbi and ignition. It's a cool concept,but one I doubt I'll ever do

Aspen500 · Jul 5, 2020

I have ideas like that all the time but there's a couple things that keep me from doing them and they are, in no particular order, time, money and the right knowledge to make it all work. I fix modern cars and trucks everyday at work, but designing an electronic system of my own,,,,,,,,,,,,,,,,,,,,,not so much.

Mikes5thAve · Jul 5, 2020

Not to mention you wouldn't want to go thru the work only to find out the computer is bad.
When the stock setup is working right its hard to touch it both for power and gas mileage. But the second you start modifying it's so much more easier to go with the 4 pin ecu and vacuum distributor. Unless you want to spend the money on a fuel injection setup of some sort and even the most basic ones these days are far more advanced then the old gm tbi systems were.

AJ/FormS · Jul 6, 2020

Gearhed said:
I bought an 85 fifth avenue

You wanna wake it up; get rid of the 2.20 final drive and the very low stall TC. You can easily spool up to another 40 hp with a 2800TC with the stall alone, and another bunch of Torque Multiplication with say 3.23 gears. 3.23s over 2.20s is plus 47%.
So in the big picture plus 40 hp and plus 47% TM means from turd to race-car,lol. And you haven't even laid a tune on it yet. Nor a 4bbl, nor a free-flowing exhaust. Just think what those will bring to the table.
Below is a 5.2M curve. This is not what's in your FA. But it's all I got. If you multiply any/all the numbers below about 3600rpm, by .60, you'll be close enough.
So compare the POWER difference from 1200 to 2800. I read 100 versus 155, and times .60 =60/93hp, which is Plus 55%
In torque that is 260 vs 292;
times .60 = 156/175 or plus 12%..
So out the back door, in torque, that is 1.12x1.47= plus 65% ftlbs into the rear axles.
There is nothing you can do to your engine short of supercharging, that can make this much difference off the line.
Happy HotRodding

toolmanmike · Jul 6, 2020

AJ/FormS said:
You wanna wake it up; get rid of the 2.20 final drive and the very low stall TC. You can easily spool up to another 40 hp with a 2800TC with the stall alone, and another bunch of Torque Multiplication with say 3.23 gears. 3.23s over 2.20s is plus 47%.
So in the big picture plus 40 hp and plus 47% TM means from turd to race-car,lol. And you haven't even laid a tune on it yet. Nor a 4bbl, nor a free-flowing exhaust. Just think what those will bring to the table.
Below is a 5.2M curve. This is not what's in your FA. But it's all I got. If you multiply any/all the numbers below about 3600rpm, by .60, you'll be close enough.
So compare the POWER difference from 1200 to 2800. I read 100 versus 155, and times .60 =60/93hp, which is Plus 55%
In torque that is 260 vs 292;
times .60 = 156/175 or plus 12%..
So out the back door, in torque, that is 1.12x1.47= plus 65% ftlbs into the rear axles.
There is nothing you can do to your engine short of supercharging, that can make this much difference off the line.
Happy HotRodding

View attachment 40605

Does 85 have a lock up 904? You can get a performance converter and still have the lock up feature for some economy.

AJ/FormS · Jul 7, 2020

I had an 84, that I inherited from mu Dad when he died. I'm trying to remember if it did but cannot; I didn't drive it much, and then sold it just to get it off the yard.
yaknow, I think it must have, cuz Dad swore he got 25mpgs with it on a regular bases. 25 Canadian is only 20 per USg but I think she was on her third timing chain, so heck, that's alotta miles to be still doing that well .
And I remember it being a bit of a turd on take-off, so it likely had the 2.45s with a 2.74 low gear and a very modest TC. That would put the Rs at about 2600 at 55mph in passing gear, and he did brag on it's passing power,lol. I never tried it. To me it was just something to get me to work until it sold. At the time, I had a low opinion of those cars; to me they were underpowered tanks. But as I think back about it, it was actually a pretty comfy car. Certainly more comfy and a lot quieter than my 68 Barracuda! I shouldda put a 400 in it...............

Mikes5thAve · Jul 7, 2020

By 85 they're all lockup. Not sure if one of the versions of AHB might have been non lockup but but probably not.

Has anyone ever made power with the lean burn system?

Gearhed

Well-Known Member

Aspen500

Well-Known Member

Mikes5thAve

Well-Known Member

Gearhed

Well-Known Member

Duke5A

Well-Known Member

Gearhed

Well-Known Member

XfbodyX

Well-Known Member

XfbodyX

Well-Known Member

XfbodyX

Well-Known Member

XfbodyX

Well-Known Member

Aspen500

Well-Known Member

Gearhed

Well-Known Member

Aspen500

Well-Known Member

Mikes5thAve

Well-Known Member

AJ/FormS

Well-Known Member

toolmanmike

Super Moderator

AJ/FormS

Well-Known Member

Mikes5thAve

Well-Known Member