Efi air fuel ratios??

[Gulf -LS7]

I was just wondering what air fuel ratios any of you SBC efi boys are running while cruising?? Im talking about 2500-3000rpm in top gear, ive been told not to run any leaner than 14.1 to 1 as the old SBC does like to run rich?? With 14.7 to 1 being the recognized perfect ecomomy cruising ratio i was just wondering what others are running in these circumstances and have you had any problems ie detonation etc.

[eliot]

I tend to hover around ~15afr in light throttle cruise - but my engine is largely stock (apart from the turbo's!) - cant say i noticed any great MPG improvment though. If you are going to run around that I would suggest a wideband to keep an eye on it.

[Pb3]

I am around 16 to 17 to 1 on cruise, again not a massive difference on fuel consumption but every little helps.

[Gulf -LS7]

16 to 1..... cripes!!!!

thats lean!! at 3000rpm im seeing around 14mpg on a run at 14.1 to 1, im running wideband but with no knock sensor the ecu can do very little if its pinking???

Phil, have you had any problems at those figures?

thanks

[Pb3]

Hi Kyle,

I've been running lean cruise for over a year, 3000+ miles with no issues. From what I have read (from the MegaSquirt documentation) that should be quite acceptable, if you experience lean surges then you know you need to back off a little! I am pretty sure I see better mpg as a result, although most of that comes from just running EFI and sensible AFR everywhere else.

[eliot]

Gulf -LS7 said:

16 to 1..... cripes!!!!

thats lean!! at 3000rpm im seeing around 14mpg on a run at 14.1 to 1, im running wideband but with no knock sensor the ecu can do very little if its pinking???

Phil, have you had any problems at those figures?

thanks

You shouldn't get any knock in lean cruise, because you are not labouring the engine. Thats why you can get away with it.

[Gulf -LS7]

Pb3 said:

Hi Kyle,

I've been running lean cruise for over a year, 3000+ miles with no issues. From what I have read (from the MegaSquirt documentation) that should be quite acceptable, if you experience lean surges then you know you need to back off a little! I am pretty sure I see better mpg as a result, although most of that comes from just running EFI and sensible AFR everywhere else.

Hi Phil

What do you mean by lean surges??

[Pb3]

Gulf -LS7 said:

Pb3 said:

Hi Kyle,

I've been running lean cruise for over a year, 3000+ miles with no issues. From what I have read (from the MegaSquirt documentation) that should be quite acceptable, if you experience lean surges then you know you need to back off a little! I am pretty sure I see better mpg as a result, although most of that comes from just running EFI and sensible AFR everywhere else.

Hi Phil

What do you mean by lean surges??

Uhm, easy to feel, difficult to put into words. But basically the car, with contanst throttle position, picks up speed a little, but feels odd. Then drops off like you touched the brakes. I believe it is to do with higher than normal cylinder pressures (due to being too lean), creates more power hence the accel, but that is about as far as my knowledge extends.

I just went back to the MegaSquirt docs and this is an extract:
"Tuning the engine for maximum economy with a wide band oxygen sensor is relatively easy. Set your cruise areas of the AFR table to a lean value, say 16.5:1. If you get surging (which indicates a lean misfire) decrease the AFR entries (say to 16.2:1) and try again. A lean 'surge' that feels like someone is pushing the car forwards, then pulling it backwards while you have a constant accelerator pedal position. Generally, this is a sign that you are too lean.". You may like to read the "Tuning for Economy" section at http://www.megamanual.com/ms2/tune.htm#economy for some back ground.

Edited by Pb3 on Thursday 5th February 13:41

[Steve_D]

I certainly intend to run mine up around 16-17 as that is where economy can be found.
However, it is essential that you have the right acceleration enrichment programmed in so that as soon as you start to accelerate you go rich. If it stays lean as you try to apply power things could go pop pretty quickly.

Steve

[Pb3]

Steve_D said:

I certainly intend to run mine up around 16-17 as that is where economy can be found.
However, it is essential that you have the right acceleration enrichment programmed in so that as soon as you start to accelerate you go rich. If it stays lean as you try to apply power things could go pop pretty quickly.

Steve

Hi Steve, I have run with no accel enrichments and you can providing your VE table is reasonably good. That is because as soon as you put your foot down, the throttle plates open and the MAP increases towards atmosphic pressure, that instantly puts you in a non-lean part of your VE table (hopefully, if calibrated right) and you have the required fueling for that MAP/RPM operating point, at whatever AFR that gives (which is why you richen up the VE table bins with increasing MAP or load). That means as the load increases (indicated by you MAP sensor) you inject more fuel to give a lower AFR, if not then that is when bad things can start to happen, fast. You will be able to determine your normal cruise operating area once you are up and running, driving around under various conditions will show you the rpm range and MAP range that you cruise at and you can start to lean that whole area off.

What accel enrichment will help with is getting over any 'stumble' due to the step change, and help accell the engine a little faster. If you use advanced accel, such as the XTau mechanism that does a good job and you can turn basic accel enrichment off and forget about it.

[Gulf -LS7]

Pb3 said:

Gulf -LS7 said:

Pb3 said:

Hi Kyle,

I've been running lean cruise for over a year, 3000+ miles with no issues. From what I have read (from the MegaSquirt documentation) that should be quite acceptable, if you experience lean surges then you know you need to back off a little! I am pretty sure I see better mpg as a result, although most of that comes from just running EFI and sensible AFR everywhere else.

Hi Phil

What do you mean by lean surges??

Uhm, easy to feel, difficult to put into words. But basically the car, with contanst throttle position, picks up speed a little, but feels odd. Then drops off like you touched the brakes. I believe it is to do with higher than normal cylinder pressures (due to being too lean), creates more power hence the accel, but that is about as far as my knowledge extends.

I just went back to the MegaSquirt docs and this is an extract:
"Tuning the engine for maximum economy with a wide band oxygen sensor is relatively easy. Set your cruise areas of the AFR table to a lean value, say 16.5:1. If you get surging (which indicates a lean misfire) decrease the AFR entries (say to 16.2:1) and try again. A lean 'surge' that feels like someone is pushing the car forwards, then pulling it backwards while you have a constant accelerator pedal position. Generally, this is a sign that you are too lean.". You may like to read the "Tuning for Economy" section at http://www.megamanual.com/ms2/tune.htm#economy for some back ground.

Edited by Pb3 on Thursday 5th February 13:41

Thanks for that Phil

are you sure the manual is refering to our old technology?? I would love to try running a lot leaner but i dont want to cause any damage. When my engine was dynoed, Tim Adams showed me what happened to the power when the mixture was leaned off and surprisingly there was a big drop in bhp!! Im going to do a cam change on my 377 so when i remap i think i will lean off the cruising part of the map and monitor the situation.

Steve how you doing with building your efi system??

Edited by Gulf -LS7 on Thursday 5th February 22:05

[eliot]

Gulf -LS7 said:

Tim Adams showed me what happened to the power when the mixture was leaned off and surprisingly there was a big drop in bhp!!

Maybe so - but we are talking about light throttle cruise, where you dont need the power.
If you are new to tuning, then aim for around 14.7 until you are comfortable with it. I certainly didn't do lean cruise for a couple of years!

Edited by eliot on Thursday 5th February 21:00

[Steve_D]

Gulf -LS7 said:

.......Steve how you doing with building your efi system??

Slowly.
I am putting MS onto a 3.9 rover engine for the Dakar. Was intending to build that up slowly as well but some muppet forgot to put antifreeze in the Dakar which it did not like and spat out a core plug. Replaced it but it gushes out somewhere else under the inlet manifold so being as that engine has got to come out I will have to get my finger out and get the 3.9 done sharpish.

For the Ultima I have the MS kit on its way from the States, I have a Holly stealth ram inlet and throttle body, fuel regulator, fuel rails, all the connectors etc to wire it.
Still need pump, filters, three port valve, surge tank, injectors and many other odd bits.
Also missing inspiration on an air filter system as the throttle body points back from the manifold and has an oval body. I think the shape is common to some US GM cars but I have no idea which. If I can find that info I may at least be able to order an oval hose to make the first connection.

Steve

[jschwartz]

14.7 to 15.2 at cruise.
12.9 to 13.2 at wot on the normally aspirated LS engines

[GreenV8S]

Steve_D said:

I have the MS kit on its way from the States

Is that MS as in MegaSquirt? What was the reason for buying from the US rather than locally? (I assume you're based in the UK.)

[Steve_D]

GreenV8S said:

Steve_D said:

I have the MS kit on its way from the States

Is that MS as in MegaSquirt? What was the reason for buying from the US rather than locally? (I assume you're based in the UK.)

I needed a MSII kit and LC-1 wideband.
I could not find the wideband in the UK so ordered them both from the states.

Steve

[GreenV8S]

Steve_D said:

I needed a MSII kit and LC-1 wideband.
I could not find the wideband in the UK so ordered them both from the states.

Steve

There are loads of people selling the LC-1 kit in the UK. I don't know what the exchange rate is doing these days, maybe it works out cheaper buying from the US, but you could easily have got all that locally.

[eliot]

Steve_D said:

GreenV8S said:

Steve_D said:

I have the MS kit on its way from the States

Is that MS as in MegaSquirt? What was the reason for buying from the US rather than locally? (I assume you're based in the UK.)

I needed a MSII kit and LC-1 wideband.
I could not find the wideband in the UK so ordered them both from the states.

Steve

Do you ask Bill Shurvinton - he's the UK agent for both items and a very long time supporter of MS (like since the first group buy)
eta:
http://www.msextra.com/viewtopic.php?f=108&t=2...

Edited by eliot on Friday 6th February 21:22

[Steve_D]

eliot said:

Steve_D said:

GreenV8S said:

Steve_D said:

I have the MS kit on its way from the States

Is that MS as in MegaSquirt? What was the reason for buying from the US rather than locally? (I assume you're based in the UK.)

I needed a MSII kit and LC-1 wideband.
I could not find the wideband in the UK so ordered them both from the states.

Steve

Do you ask Bill Shurvinton - he's the UK agent for both items and a very long time supporter of MS (like since the first group buy)
eta:
http://www.msextra.com/viewtopic.php?f=108&t=2...

Edited by eliot on Friday 6th February 21:22

Yes, first port of call after getting great service from him before but nil stock.

Steve