[mullenc525]

...well its just an idea, but I had to catch your attention:dunno:

The techedge wideband (I supposedly have one in the mail) has a re-programmable NB output curve. I plan on datalogging the stock o2 curve on my techedge, then programming that curve into the wideband and replacing the stock o2.

However, why cruise at 14.7 when you can get better economy up to 17:1 afr? I will be running 94 octane once Im tuned since Im still on stock IC and HG, and wouldnt want to detonate at high boost. The high octane should resist detonation to a fairly lean ratio during closed loop (low throttle) operation, so why not lean it out?

With a typical tuning device, its impossible to do once and for all, since the ecu is always fighting to bring it back to 14.7 afr. I plan on shifting the 'asymptote' (near vertical part) of the NB output curve of my wideband to a higher afr, from 14.7 to 15.7, 16.7 or 17 for example.

This way, I wont be fighting the stock ecu to get a nice lean mix while in closed loop, itll do it itself all the while thinking its at 14.7 afr as it switchs its 'narrowband' from lean to rich.

Of course, im sure its going to fuck with the open loop maps. Therefore, I am going to modify an HKS SAFR to only apply fuel (air) corrections while the ecu is in open loop (vf = 0v).

So, what do you think? Ill try 15.5 afr or something first, and push it as high as 17:1. I think I will get a thermocouple to watch EGTs via the techedge wideband as well, just to be safe.


check out the techedge wideband

 

[90Legend]

Sounds interesting!

Dr. Jonez told me he did that as well and got around 28MPG on the highway.

I just took a 360 mile highway trip and got 24.7MPG.

I'll be interested to see how this turns out.

Dan

 

[Nocheez]

so to get an extra 10% in fuel economy, you're going to spend an extra 10% in higher octane fuel?

 

[mullenc525]

No. Im going to spend 3% extra on fuel so I can run 15 psi on the stock HG and IC relatively safely. Im going to fool with my wideband to gain ~ %15 fuel economy. Nice try though!

 

[Larry_A]

Although your closed loop efforts might actually work if the electronics work as you expect, pushing 15psi thru the stock IC for any length of time will likely mean more fuel needed for cyl cooling, which can measurably negate the benefits of higher boost from the resultant rich AFs. It's a vicious cycle that must be dialed in to find the right balance. An upgraded IC certainly would reduce your stress & your engine's if visiting 15psi on a regular basis is your goal.

At any rate, good luck in your efforts, & be careful if this is your only car.

 

[Suprawill1]

Although your closed loop efforts might actually work if the electronics work as you expect, pushing 15psi thru the stock IC for any length of time will likely mean more fuel needed for cyl cooling, which can measurably negate the benefits of higher boost from the resultant rich AFs. It's a vicious cycle that must be dialed in to find the right balance. An upgraded IC certainly would reduce your stress & your engine's if visiting 15psi on a regular basis is your goal.

At any rate, good luck in your efforts, & be careful if this is your only car.

Agreed! But the closed loop option is the higher mileage attempt.
Outside of emissions, if you have to deal with that, I'd be interested in your results.

 

[Larry_A]

Agreed! But the closed loop option is the higher mileage attempt.
Outside of emissions, if you have to deal with that, I'd be interested in your results.

As long as he can dial it in so TCCS won't attempt to correct beyond its +/- 20% range under closed loop, it should run emissions testing fine, all else operational.

But yeah, if the thing works as billed, I know noticeable mileage improvements will occur. A long while back I helped Brendan J tune his AEM to improve mileage from 13 to 15 mpg, IIRC. Of course, his was in strict open loop since the EMS just runs better that way. Closed loop on his EMS just didn't work as well as TCCS under his revision firmware/software, that is.

Anyway, I'm anxious to hear Mullen's results, & I hope his experiment doesn't do weird shi+ on him.

 

[Twigger]

I would definantly like to see how this turns out, the best gas mileage I got was 22mpg for 120 miles on the highway at 65mph.

 

[limequat]

Lean cruise mode is something GM experimented with in the 80s, before the EPA put the smack down.

This would be a safer way to achieve better mileage, with the only expense being higher NOx. To do it properly, you'd probably need standalone.

Here's what you do:
If MPH > x
If TPS < y
Then Lookup AFR as a function of LOAD

People have achieved 10% greater economy this way.

 

[mullenc525]

some late 90s hondas did lean cruise as well, thats why they had a wideband o2 sensor (the one that was used in many early widebands).

Ideally, I would like closed loop to be at a lower throttle setting, because the way I am planning, it will run lean until ~70% throttle, where open loop begins. It could be that I may only run up to 15.5 or 16 afr.

As far as the stock IC at 15 psi - stock IC has been used to much higher levels, and I will be using 94 daily, which is pretty high octane.

 

[Clifton]

You have a modded turbo car and you are trying to get better mileage?

 

[Twigger]

You have a modded turbo car and you are trying to get better mileage?

I believe thats what this thread is about unless I'm mistaken.

 

[mullenc525]

You can suck 94 octane gas while you cruise on the highway, SUIT YOURSELF, but keep it outta my thread.

This wont cost me a penny more, so why not do it? I stand to save $30 a month in gas, learn a thing or two, and teach those that care (not you) in the community something neat as well.

 

[Suprawill1]

This would be a safer way to achieve better mileage, with the only expense being higher NOx.

That's exactly what I was concerned about in reference to passing emissions.

 

[sammydafish]

Properly functioning EGR should take care of the NOx emissions. You might even want to look at fitting a larger EGR valve for this purpose. It will also help keep things cooler during a lean burn. If you're concerned about passing an emissions inspection, you might not have enough HC to light up the cats. If you run to lean, the cats will cool to much and not longer operate. Notice than most late model compact cars have the cat integrated with the manifold or mounted very close. This is to ensure quick light up during cold start and maintenance of operating temperature during lean conditions (highway). One HUGE thing you've got going against you is that the chamber shape and valve angle of the 7M head is not favorable to a lean burn condition and you will most likely end up with terrible hot spots and detonation even at low load. This is the one place where the 7M was terribly lacking in technological development during production. The low compression of a turbo engine will also make your goal harder to achieve. In order to get a good burn on a lean mixture you need to compress it more. Lean misfires will be plenty without this. Your idea has merit and you will most likely succeed in some way by improving fuel economy to a point. A 15% gain might be a little overoptimistic but the experiment is worth trying. Keep an eye on plugs and listen closely for a lean misfire at cruise, this will surly kill emissions. One other concern you should be aware of is that the TCCS will learn long term fuel curves based on this modified o2 data. This will cause it to keep things lean even under full load conditions. This might be corrected with an AFC or other fuel computer that takes over at WOT.

Good luck, I'm interested to see how this whole thing works out.

 

[Racefiend]

What you have to remember is that at lower airflows (low rpm part throttle and full throttle boosting) the ecu still stays in closed loop and tries to maintain a 14.7 afr. This means that if you mess with your o2 output, you would be seeing 17 afr's while boosting at low airflows. Denotation may be a problem under these conditions.

 

[mullenc525]

when did I say anything about emmisions :dunno:

 

[chevyeater-on-sf]

You definitely need a standalone to do this correctly. Your car isn't going to idle too well at 17:1. You'll also be prone to detonation @ WOT (in open loop) after heating up the cylinder head with a lean cruise.

 

[limequat]

Lean cruise should be set at > 50 MPH so that it doesn't show up in emissions testing and it doesn't affect non-cruising driving.

 

[Suprawill1]

when did I say anything about emmisions :dunno:

You didn't. I did. I'm curious about your outcome but also concerned about emissions under this philosophy. I don't mean to hijack but I thought it a pertinent observation.