Efficiency potential of the L28 (MegaSquirt)

[FastWoman 52]

Hi all,

As fuel prices continue to rise, I'm wondering what the potential is of our L28 (or L24/26) engines is. I currently get about 19 mpg combined. I didn't worry about that sort of mileage as a kid, when gas was cheap, but these days that's what you would expect from a pickup truck, and 19 mpg will run you broke in a daily driver.

I have to believe that an engine is an engine is an engine when it comes to basic operating efficiency. So long as they're able to pull approximately the same vacuum, they should be operating with roughly the same efficiency, right -- at least for cruising? Maybe the hp:weight ratio is lower on our engines than on a modern 24 valve engine, but weight doesn't impact highway miles.

And of course the Z has sexy but inefficient lines. A more aerodynamic shape would be that of the egg-shaped Prius. That's obvious in hindsight, I suppose. But is that enough to limit us to only 20'ish mpg -- maybe the mid 20's on the highway?

I'm wondering how inefficient our EFI systems are. Could we squeeze several more mpg out of a MegaSquirt system, not to mention better performance? Is there an efficiency/performance incentive out there for making the switch?

[John Coffey 56]

Engine vacuum is not a good indicator of engine efficiency. Air fuel ratio is a much better indicator - to a point. Generally the biggest factor is the driver.

From BMW's eta engine studies in the late 1970s/early 1980s large throttle openings at low rpm are the most efficient way to accelerate. Shift early and get into top gear as quickly as possible. I experimented with this technique, never running the engine past 2,750 rpm in any of the lower gears, and saw a 8% increase in fuel mileage for around town driving in my street 2.4L 240Z. Then I stopped because I couldn't stand to drive the car that way.

Assuming you ahve more patience then me... tuning your car for that kind of use requires an emphasis on low rpm torque. As much compression ratio as possible and as much timing advance early in the curve as possible without low rpm detonation. Stock cams and smaller intake valves. Gearing also need to be high (the OEM 3.36 gears are good).

[LeonV 77]

I have heard multiple people getting 30mpg using MS. In fact, I know a guy who did a turbo swap using MS and did just that. Just takes some tuning and a precise fuel delivery system (not carbs).

[Oiluj 30]

Given the weight and drag of our cars is fixed, I agree with John that it's more a function of engine displacement and a good fuel mixture ratio, but mostly the driver.

My 2.7 L stroker w/ round-top carbs gets 26 MPG on the freeway if I drive in a sane, (but not boring), fashion. I havn't measured "in-town" milelage, but I'm guessing it's between 15 to 17 mpg. This is actually better than what I get from my 1997 ES300 (Lexus V6 Camry). But then the Z is a much lighter car...

Out of curiosity, I played with advancing the timing and leaning-out the idle mixture a bit and saw no measureable difference. Perhaps there is some small amount to be gained by minor ajdustments of valve timing, as done in modern engines.

Edited July 16, 2011 by Oiluj

[Zed Head 2,208]

Here is a recent post from zcar.com along those lines. Tony D has posted on this forum in the past. Most of the Megasquirt threads you see are for turbo or modified applications, so a straight AFM/ECU to MegaSquirt comparison is hard to find.

Reply #4 has the relevant comments -

http://www.zcar.com/70-83_tech_discussion_forum/micro_squirt_qestion_899882.0.html

[doradox 1]

Hi all,

As fuel prices continue to rise, I'm wondering what the potential is of our L28 (or L24/26) engines is. I currently get about 19 mpg combined. I didn't worry about that sort of mileage as a kid, when gas was cheap, but these days that's what you would expect from a pickup truck, and 19 mpg will run you broke in a daily driver.

I have to believe that an engine is an engine is an engine when it comes to basic operating efficiency. So long as they're able to pull approximately the same vacuum, they should be operating with roughly the same efficiency, right -- at least for cruising? Maybe the hp:weight ratio is lower on our engines than on a modern 24 valve engine, but weight doesn't impact highway miles.

And of course the Z has sexy but inefficient lines. A more aerodynamic shape would be that of the egg-shaped Prius. That's obvious in hindsight, I suppose. But is that enough to limit us to only 20'ish mpg -- maybe the mid 20's on the highway?

I'm wondering how inefficient our EFI systems are. Could we squeeze several more mpg out of a MegaSquirt system, not to mention better performance? Is there an efficiency/performance incentive out there for making the switch?

Modern engines have higher compression, lower internal friction, and ignition/fuel systems that are extremely precise. Add aerodynamics and low friction drive trains to that. I think your mid 20's highway goal is achievable though.

Steve

[aarc240 1]

If you are needing to rebuild an engine then you can very nearly equal the "modern" cars.

Fit late 280ZX narrow ring flat top pistons and assemble the engine like it really matters to you that it's actually built the way the factory meant it to be.

Use modern lubricants in the drive train, there's really no advantage to a "modern" drive train.

Our road 260z 2+2 is set up this way, 86mm bore, works 1972 rally cam advanced 4 degrees, 10.4:1 compression, precision assembly, 280z injection manifold with 250cc injectors, GM 65mm throttle body, headers with 6xEGT & EGO, Megasquirt3 with sequential injection & EDIS ignition, Chrysler Voyager coil pack, 5 speed C/R, 3.54 gears, 185/65R14 tyres (600mm or 23.6" diameter).

Gets 27mpg (converted to your gallons) on the highway, no idea around town, and will still turn the tyres happily (and doesn't get babied on the highway either).

Mistakes to avoid: fitting wider tyres, fitting a rear spoiler, not fitting a front spoiler / air dam, not fitting a factory engine bay undertray, fitting a sun roof, tuning MS thinking it's a race car, failing to keep tyre pressures at the upper end of the comfort range, failing to clean / polish the car, etc

[Tony D 1]

Really like John C said is torque and proper fuel management.

The Blue Turd will manage 27mpg if I never go over 65mph and accelerate rationally (not granny-like, but maybe upshifting at 3500 or 4000...) Take that speed up to 80 and the car gets 22mpg---plain and simple, drag increases. At average speeds of 100 I crack to 19mpg...

This is an L26, dome tops, late ZX tranny, and 3.7 out back.

Now what has shocked me was I thought that was really decent mileage. But three weeks ago, on the way to work (45 miles from my fillup point) the fifth gear shaft nut backed off and locked the tranny in 5th. So I trailered the car home, changed to an Early five speed I have, with the .85 O.D. Now I turn 36-3700 rpms on the 60 freeway going to work, instead of 31-3200 rpms.

My First Shock was that the car is a BLAST to drive with that early tranny and it's closer ratios.

SECOND was that my mileage went up from rock solid 22 to 23.6mpg on the first tank, and now monitoring it through four more tankfulls, it's been 24, 23.5, 23.7 average. Now really, IMO I'm really beating the hell out of the car since the ratios seem to BEG me to beat on it more now... It's a pleasant side effect which I COMPLETELY did not expect. Only thing I can figure is I'm in the sweet spot of the torque curve now.

The key for EFI conversion of this car will be to datalog the AFR's I currently have, and then set a TPS.MAP table which is equivalent. Then start to tweak it leaner---towards 17 or 18:1 in lightly loaded cruise conditions. Frankly I may re-enable EGR for this (using a diesel EGR Cooler) to allow more advance if it helps the mileage.

The key is to have MS in closed loop use a WBO2 that either has the provision to shoot for AFR target tables, or a configurable 'switching output' so that you set your desired AFR for something other than 14.7:1, more like 17.5, or 18:1 during closed-loop operation, and then stay in a driving situation that keeps you in closed loop.

An L26 or L28 should easily be able to get mid-high 20's with ANY fueling system calibrated for emissions compliance. If you run leaner, you can improve upon that.

I've seen L24's with 40mm Solex Mikuinis turn in 28mpgs on the run from LA to Phoenix with an Automatic and 4.11 differential (but the speed was strictly kept to 65 as the limit was only 55 then! Doesn't do that at 80, which is 4K+!

[Z train 0]

Really like John C said is torque and proper fuel management.

The Blue Turd will manage 27mpg if I never go over 65mph and accelerate rationally (not granny-like, but maybe upshifting at 3500 or 4000...) Take that speed up to 80 and the car gets 22mpg---plain and simple, drag increases. At average speeds of 100 I crack to 19mpg...

This is an L26, dome tops, late ZX tranny, and 3.7 out back.

Now what has shocked me was I thought that was really decent mileage. But three weeks ago, on the way to work (45 miles from my fillup point) the fifth gear shaft nut backed off and locked the tranny in 5th. So I trailered the car home, changed to an Early five speed I have, with the .85 O.D. Now I turn 36-3700 rpms on the 60 freeway going to work, instead of 31-3200 rpms.

My First Shock was that the car is a BLAST to drive with that early tranny and it's closer ratios.

SECOND was that my mileage went up from rock solid 22 to 23.6mpg on the first tank, and now monitoring it through four more tankfulls, it's been 24, 23.5, 23.7 average. Now really, IMO I'm really beating the hell out of the car since the ratios seem to BEG me to beat on it more now... It's a pleasant side effect which I COMPLETELY did not expect. Only thing I can figure is I'm in the sweet spot of the torque curve now.

The key for EFI conversion of this car will be to datalog the AFR's I currently have, and then set a TPS.MAP table which is equivalent. Then start to tweak it leaner---towards 17 or 18:1 in lightly loaded cruise conditions. Frankly I may re-enable EGR for this (using a diesel EGR Cooler) to allow more advance if it helps the mileage.

The key is to have MS in closed loop use a WBO2 that either has the provision to shoot for AFR target tables, or a configurable 'switching output' so that you set your desired AFR for something other than 14.7:1, more like 17.5, or 18:1 during closed-loop operation, and then stay in a driving situation that keeps you in closed loop.

An L26 or L28 should easily be able to get mid-high 20's with ANY fueling system calibrated for emissions compliance. If you run leaner, you can improve upon that.

I've seen L24's with 40mm Solex Mikuinis turn in 28mpgs on the run from LA to Phoenix with an Automatic and 4.11 differential (but the speed was strictly kept to 65 as the limit was only 55 then! Doesn't do that at 80, which is 4K+!

Tony,you do know that your EXERIENCE flies directly in the face of Dan B's theories-don't you?

[FastWoman 52]

Thanks, guys! It sounds like the conversion might be worth doing. I confess there's a side of me that wants to preserve the original Bosch L-Jetronic system, but there's also a side of me that wants a more affordable and better running daily driver.

What would you estimate my time commitment to be in making this conversion, considering that I'm competent with EFI engines, but a newbie with MegaSquirt?

[doradox 1]

Use modern lubricants in the drive train, there's really no advantage to a "modern" drive train.

It is generally accepted that CV joints are more efficient than Cardan joints. One might argue that CV joints aren't really all that modern though.

Steve

[Z train 0]

Fastchick-there are two Megasquirt conversions on my horizon-the wifes stroker and my L-24E.Just a matter of $$$$.And making a manifold for the stroker.

[Zed Head 2,208]

You can buy degrees of completion ranging from a bill of materials to be assembled yourself, up to essentially complete boards and wiring harnesses.

I'm sure you've seen this company's site but I'll post it for the record - http://www.diyautotune.com/ They seem to be the most established for Megasquirt, although there are others out there.

[Mikes Z car 34]

There is an HHO mileage improver that has been around for a while. It is nothing more than oxygen and hydrogen gas from electrolyzed water fed into the air intake. I know three people who claim to know someone who had one of these and two of them said they were getting 50% mileage improvement. I have read that it works better with carbureted cars rather than ones with O2 sensors. I ran across the owner of a local auto repair shop recently who says he saw an HHO device hooked up to a truck that was run on a dyno. I gather the usual dyno test is to run the RPMS up and back down to determine peak HP and torque. They observed a 20 HP increase with the HHO device though I don't know if that would translate to a mileage improvement. One of the reasons I bought my 240Z was to verify claims for the HHO device but I have been so busy rust proofing it and making it closer to stock I haven't done that yet. Anyone else tried the HHO device or have an opinion on it?

Mike

[Z train 0]

You can buy degrees of completion ranging from a bill of materials to be assembled yourself, up to essentially complete boards and wiring harnesses.

I'm sure you've seen this company's site but I'll post it for the record - http://www.diyautotune.com/ They seem to be the most established for Megasquirt, although there are others out there.

Good reference.ANother neat thing about MS,is that you can get the box with all the whisltes & bells and add features as you can afford or want to.Other (some)systems DO NOT have this feature.

[madkaw 542]

Sarah,

you might think about installing a wideband and see what's happening with you mixtures. My car got 30mpg going to Zcon at nashville with a 3.7 LSD and the T-5 trans. I didn't have the wideband then. NOW I have the wideband I realized that my car was running very lean, thus the great MPG. I have dialed the motor in much better with the wideband and still get great mileage. I have to measure again, but now with a 3.54 diff I think I am still around 30 running about 15.0afr at cruise.

The wideband will also hook up in conjunction with your MS unit, so you need to do that anyway

[FastWoman 52]

That sounds like a good idea, Steve! I might just do that.

I looked at the MS equipment on the DIYAutoTune website and have to say all the bells and whistles were dizzying. I see I can do everything from basic fuel control with banked injector firing to ignition control with advance and sequential injection. (How important IS sequential injection?) I can see I'll need to do quite a lot of studying just to determine what it is I might want to buy/do.

But the O2 sensor is certainly a good start. I think I'll ruminate on that a bit.

[Z train 0]

That sounds like a good idea, Steve! I might just do that.

I looked at the MS equipment on the DIYAutoTune website and have to say all the bells and whistles were dizzying. I see I can do everything from basic fuel control with banked injector firing to ignition control with advance and sequential injection. (How important IS sequential injection?) I can see I'll need to do quite a lot of studying just to determine what it is I might want to buy/do.

But the O2 sensor is certainly a good start. I think I'll ruminate on that a bit.

For sequential,you cam postion sensors.Really overkill requiring over engineering.But the other stuff is usefull.Example:

Start out with just the fuel.

Then the timing.

Then coil packs

Then elimiante the distributor altogether

[madkaw 542]

Z trains right-don't even bother thinking about sequential. You can do one step at a time. I suggested the O2 sensor because it gives you a lot of info right away and it looks cool to. It's essential for your MS to work also.

For me the next stage is timing-or a way to monitor timing for the eventual MS install. Your MS will need some input on engine rotation, then you will have rpm and AFR info to combine.

It's a little bit of a learning curve, but SARAH, you seem to have a handle of things from the posts I've read. I'd predict that you will be helping others with their install in no time.

[FastWoman 52]

Thanks Ztrain and Madkaw! So sequential isn't that big a deal... I can believe that.

So for the ignition, is the distributor gutted/modded to be a cam angle sensor? Are there kits for that?

Having the ignition under ECM control certainly sounds like the way to go.

[cygnusx1 18]

My L28ET will not run smoothly at anything much above a 14.5:1 AFR with megasquirt. If I try REALLY hard, I could manage about a 22mpg. That's about it. The L motors LOVE to run on the rich side. They really don't seem to run smoothly, or make any smooth power/torque unless you feast them with gas. It might have everything to do with combustion chamber design. I am using 440cc Ford Lightning injectors made by Bosch.

My megasquirt box happily runs a Ford EDIS-6 crank triggered ignition with no distributor of course. A nice healthy spark for sure.

Edited July 19, 2011 by cygnusx1

[FastWoman 52]

Dave, I think what you say is true. I've got my EFI tuned (via potentiometer) a bit on the rich side, and it seems to like it there. I'm sure I get at least 22 mpg on the highway. In fact I'm sure I'm fairly certain I'm in the mid 20's, but I'm perhaps tuned leaner than you are, and I probably drive a bit slower. The next time I'm on a good stretch of highway (which is very seldom these days), I'll have to determine exactly what I do get.

So I'm still on the fence about MS. Instead, I'm wondering whether I could preserve my antiquated analog AFM system and get the greater efficiency by rigging an accessory circuit to tweak the tuning of the EFI in real time, based on the output of a wide band O2 sensor. Or maybe I could have a mixture selection switch that would switch me from rich (performance) to lean (for cruising).

But I suppose it all starts with the sensor. How much should a muffler shop charge me to weld on a bung?

Any great ideas about where to mount the extra gauge? Pull the clock, perhaps? (I kinda hate to do that.)

And where should I mount the flux capacitor? Should it go in the rear of the center console area? (I have a high voltage relay that looks a lot like the doodad in the movie. I'm often tempted to mount it under the hood somewhere as a lark -- to see how many questions I get about it. )

[robftw 0]

I gotta say im pretty jealous.

I get about 10mpg but i have all of my emissions stuff removed, along with charcoal can etc... if i keep it under 3000 i can get MAYBE 15mpg..

[LeonV 77]

Sarah, go standalone, you will not regret it! You will have control over the whole fuel map (and spark, if so desired) with the flick of a finger. No need to mess around with different circuits and try to make an ancient EFI system more adjustable and efficient. With MS, set cruise leaner and higher load operation richer and voila, it's that easy!

[FastWoman 52]

I understand what you're saying, Leon, but I think some of the old stuff if kinda cool. The engine is the soul of the car, and I hate to go overboard with modernizations. If MS had a way to incorporate the AFM, I'd probably be all over that! I may still bite on the MS, though. I think I would want to keep the distributor and not go EDIS, but it would be cool to be able to disable the advance mechanism and make it a hybrid CAS/distributor sort of device, with the MS handling all the spark advance.

------------------

Rob, I suspect your mixture is way off!