Home » Public Forums » GMCnet » NEW FUEL INJECTION (What is the "BEST" AFR)
| NEW FUEL INJECTION [message #254115] |
Wed, 02 July 2014 11:20  |
Neil
Messages: 271
Registered: July 2007
Location: Los Angeles and Magalia, ...
Karma: 1
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We are finishing up a MSD Atomic install.
A question for the FI gurus.
The MSD allows you, within a range, to program preferred/target AFR. What do you all use for running down the road?
I wasn't going to take a trip to the dyno on this, does anyone have any info/recommendations other than running straight stoichiometric of 14.7?
Thanks
Neil
Neil
76 Eleganza now sold
Los Angeles
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| Re: NEW FUEL INJECTION [message #254116 is a reply to message #254115] |
Wed, 02 July 2014 11:48  |
bwevers
Messages: 597
Registered: October 2010
Location: San Jose
Karma: 5
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I have a carburetor, and I get 7.5 to 8 MPG, with 3.07 gears.
With that said, I think my A/F ratio must be less than 12.
Power valve always open. Some people claim a lean mixture will
make your engine run hot.
Regards,
Bill
Bill Wevers GMC49ers, GMC Western States
1975 Glenbrook - Manny Powerdrive, OneTon
455 F Block, G heads
San Jose
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| Re: NEW FUEL INJECTION [message #254148 is a reply to message #254115] |
Wed, 02 July 2014 16:37 |
cbryan
Messages: 451
Registered: May 2012
Location: Ennis, Texas
Karma: 3
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Neil,
The lean cruise is fine, so long as you aren't asking much from the engine as far as I know. It is critical to richen up the mixture as you ask for more power from the engine. It caused a valve to seize in its guide and break a valve pedestal in Ken Henderson's coach running a Cadillac 500. He ran a long time trouble free at cruise, but when he got into steep grades, I think it overheated an exhaust valve and started the problem.
I bought a EFI tuning book and it says that under full power, run about 12.6 to 1. However, that was a drag racing book, so treat those numbers with some skepticism. Some differences with ethanol laced fuel, maybe automatically compensated for by the Oxygen sensor. The power valves in the carburetors that richen the mixture at full throttle are there for a reason. A richer mixture cools the engine, too. I don't know the way around the exhaust valve heating up if you want to run lean at low manifold pressure (low numbers of vacuum). Some fellows here can shed more light, but I would hate to see you lose a valve head. Maybe the Atomic MSD compensates for this automatically. I think at lean cruise, you can operate at 16 to 1, but you will have less power, and will open the throttle to compensate, which would reduce vacuum pumping losses in the engine, but it may get you into the regime where the mixture is richened. I don't think the solution is easy despite the conspiracy theories that the 100 mile per gallon carburetor was bought and mothballed because of the cozy relationship between automakers and oil companies. You are in the R&D process and if you can go up the Sierras making 12 miles per gallon, drive in Death Valley and in Canada for 100,000 miles with no ill effects and the reduced engine wear you are going to get with EFI, you are the one who needs to be answering questions in this forum.
I think something I have been looking for on the forum is absent for a reason. Folks who are running lean cruise are not posting their gasoline mileage figures. It may mean that they are still developing their system, or it may mean that the coaches run so well it is hard to keep their foot out of the gas tank! I believe if someone broke Gene Fisher's dictum that no matter what you do, you will get 8 - 10 mpg, that we would hear about it. We occasionally hear about 7 mpg. The GMC is a good mileage vehicle at 8 - 10 for what living space you get.
Best,
Carey
Carey from Ennis, Texas
78 Royale, 500 Cadillac, Rance Baxter EFI.
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| Re: NEW FUEL INJECTION [message #254185 is a reply to message #254148] |
Wed, 02 July 2014 20:01 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
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cbryan wrote on Wed, 02 July 2014 15:37Neil,
The lean cruise is fine, so long as you aren't asking much from the engine as far as I know. It is critical to richen up the mixture as you ask for more power from the engine. It caused a valve to seize in its guide and break a valve pedestal in Ken Henderson's coach running a Cadillac 500. He ran a long time trouble free at cruise, but when he got into steep grades, I think it overheated an exhaust valve and started the problem.
I bought a EFI tuning book and it says that under full power, run about 12.6 to 1. However, that was a drag racing book, so treat those numbers with some skepticism. Some differences with ethanol laced fuel, maybe automatically compensated for by the Oxygen sensor. The power valves in the carburetors that richen the mixture at full throttle are there for a reason. A richer mixture cools the engine, too. I don't know the way around the exhaust valve heating up if you want to run lean at low manifold pressure (low numbers of vacuum). Some fellows here can shed more light, but I would hate to see you lose a valve head. Maybe the Atomic MSD compensates for this automatically. I think at lean cruise, you can operate at 16 to 1, but you will have less power, and will open the throttle to compensate, which would reduce vacuum pumping losses in the engine, but it may get you into the regime where the mixture is richened. I don't think the solution is easy despite the conspiracy theories that the 100 mile per gallon carburetor was bought and mothballed because of the cozy relationship between automakers and oil companies. You are in the R&D process and if you can go up the Sierras making 12 miles per gallon, drive in Death Valley and in Canada for 100,000 miles with no ill effects and the reduced engine wear you are going to get with EFI, you are the one who needs to be answering questions in this forum.
I think something I have been looking for on the forum is absent for a reason. Folks who are running lean cruise are not posting their gasoline mileage figures. It may mean that they are still developing their system, or it may mean that the coaches run so well it is hard to keep their foot out of the gas tank! I believe if someone broke Gene Fisher's dictum that no matter what you do, you will get 8 - 10 mpg, that we would hear about it. We occasionally hear about 7 mpg. The GMC is a good mileage vehicle at 8 - 10 for what living space you get.
Best,
Carey
I don't have injection on my GMC but I do recall that even 14.7 to one is lean when asking for any amount of power. Lean cruise should be limited to very light down the road travel with very slight throttle openings. For someone not trying to set EPA fuel ratings, I wouldn't even bother anything leaner than 14.7 at cruise.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: NEW FUEL INJECTION [message #254199 is a reply to message #254115] |
Wed, 02 July 2014 21:26 |
rvanwin
Messages: 325
Registered: April 2007
Location: Battlefield, MO
Karma: 6
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Neil wrote on Wed, 02 July 2014 11:20We are finishing up a MSD Atomic install.
A question for the FI gurus.
The MSD allows you, within a range, to program preferred/target AFR. What do you all use for running down the road?
I wasn't going to take a trip to the dyno on this, does anyone have any info/recommendations other than running straight stoichiometric of 14.7?
Thanks
Neil
I run a TBI system with EBL. George and I did a lot of testing to try and find optimum settings for fuel and spark. Before we did a lot of testing, we installed Exhaust Gas Temperature (EGT) sensors so we could monitor changes in temps as we tried different AFR under different load conditions. If you are going to be changing AFR settings and experimenting, I would suggest EGT gauges. We found that with the wrong setting temps can climb dramatically in a matter of seconds.
Ultimately, we settled on 16.6 AFR at steady cruise with 5 degrees of additional spark advance. I'm not sure if the MSD system allows you to change the spark for those cells that you are setting the AFR for. Load is measure by the MAPP sensor. At 40 and 50 MAPP, my AFR is 16.6. My normal cruise is around 50 - 55 MAPP. At 60 MAPP, I drop to 16.4 and at 70, 15.8. I have the parameter set to drop out of lean cruise at 75 MAPP so back to 14.7 at that point. If load continues to increase, then the EBL goes into Power Enrichment (PE) with the AFR set to 12.8. Once in PE, the EBL will continue to enrich the mixture based on time in PE. This is done because when on a long pull, the engine will continue to heat and additional cooling is needed. I'm not sure where the AFR ends up on a long pull but something like 10.8 comes to mind. Actually, in lean cruise, the temps run a little cooler. The air will cool the combustion chamber slightly. But, when any load is applied at all, temps can rise very quickly so having the right AFR as load increase is a must.
I have found these settings work great for me. I have been running this way for over 4 years and in excess of 60,000 miles.
The EBL works differently than the Atomic MSD system so I'm not sure how much fine tuning of the parameters you can do. I think the additional spark advance when in lean cruise is very important, otherwise, you will not gain nearly as much efficiency. It takes longer for the flame front to advance when the mixture is lean so without starting the fire sooner, you loose the optimum pressure point on the down stroke (about 14 to 16 degrees ATD. In lean cruise, I run nearly 50 degrees advanced (I have a 403 so it can tolerate a little more advance, IMO). I have had to pull spark back a tad in the last year because of changes in gas formulation.
We have made several presentations at GMCMI Rallys. This is a copy of one of those presentations and shows some of the results of the testing we conducted:
https://docs.google.com/viewer?a=v&pid=sites&srcid=ZGVmYXVsdGRvbWFpbnxnbWNtaGVmaWNyZWF0ZWRvY3VtZW50c3xneDo2MGJjZjMwYmViNDNkNTQ1
http://tinyurl.com/lopefey
There is also a forum for GMC Motorhome EFI discussion where much of this has been discussed at one time or another.
https://groups.google.com/forum/#!forum/gmcmh-efi
You can request to become a member if you are not already.
Randy & Margie
'77 Eleganza II '403'
Battlefield, MO
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| Re: NEW FUEL INJECTION [message #254201 is a reply to message #254115] |
Wed, 02 July 2014 21:36 |
Chris Tyler
Messages: 458
Registered: September 2013
Location: Odessa FL
Karma: 7
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The 14.7 ratio is often cited because it is the theoreticly balanced air:fuel ratio. However it is not nessesarily what you want in all conditions.
Too lean a mixture will be hotter: if you have EGT to go with a wide band you will see temps rise. Also too lean tends to detonate, even under cruise condtions a knock sensor will pick it up.And at a certain piont it might be so leen it missfires, which thew wideband may miss or misinterpret as rich.
Numbers are a starting point. To be honest there are no magic numbers, its a matter of trial and error to find what works best for your application
Alcohol and MTBE additives are oxygen bearing and cause the sensor to be a bit off.
My GMC is currently carbed but will be FI down the road with the Air Sensors MAF/TBI system I used to run on my Trans Am.
Realizing its not the same application, my corvette acheives best road milage at 14.7 cruise, but best idle is at 12.9
76 Glenbrook
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| Re: NEW FUEL INJECTION [message #254213 is a reply to message #254185] |
Wed, 02 July 2014 23:51 |
mrgmc3
Messages: 210
Registered: September 2013
Location: W Washington
Karma: 2
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Bob de Kruyff wrote on Wed, 02 July 2014 20:01
I don't have injection on my GMC but I do recall that even 14.7 to one is lean when asking for any amount of power. Lean cruise should be limited to very light down the road travel with very slight throttle openings. For someone not trying to set EPA fuel ratings, I wouldn't even bother anything leaner than 14.7 at cruise.
I concur. On a vehicle this heavy there are some, but darn few, opportunities to run lean of 14.7:1. I'd say 55 mph no headwind and downgrades are about it. There is a balancing act between A/F and spark advance. Leaner A/F will drive exhaust temps up as will retarding ignition timing will raise exhaust temps. If you want to run lean and 87 octane I would suggest monitoring EGTs and using 1550F as an absolute upper limit under any circumstance or you'll break stuff. You should target lower temps like 13-1400 for lighter loads.
If you have the ability to tune with a linear lambda meter I'd suggest 14-15:1 at light loads, 12.5:1 will be close to max power, and for long pulls on grades you should target 11-11.5:1 to keep temperatures under control. Richer than 10:1 will give an incomplete burn and the resulting unburned fuel will wash past the rings, potentially doing damage if run this way for long.
Also note that E10 runs about 4% leaner than 100% gasoline, for a given jetting or injector pulse width. A lambda meter will read the actual A/F with either fuel.
Chris Geils - Twin Cities / W Wa
1978 26' Kingsley w/ very few mods; PD9040, aux trans cooler, one repaint in stock colors, R134a, Al rad, Alcoas, 54k mi
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| Re: NEW FUEL INJECTION [message #254221 is a reply to message #254209] |
Thu, 03 July 2014 01:43 |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
Karma: 11
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[quote title=djeffers wrote on Wed, 02 July 2014 21:14][quote title=rvanwin wrote on Wed, 02 July 2014 22:26]Neil wrote on Wed, 02 July 2014 11:20
We have made several presentations at GMCMI Rallys. This is a copy of one of those presentations and shows some of the results of the testing we conducted:
https://docs.google.com/viewer?a=v&pid=sites&srcid=ZGVmYXVsdGRvbWFpbnxnbWNtaGVmaWNyZWF0ZWRvY3VtZW50c3xneDo2MGJjZjMwYmViNDNkNTQ1
http://tinyurl.com/lopefey
Neither of these urls work for me.
Anyone else getting these?
Thanks,
Don & Susan Jeffers
78 Eleganza II
Don,
The links worked for me. Not sure why some are having trouble.
Randy said it well but I want to emphasize the heat issue... We are talking about combustion chamber heat and too much will ruin engines.
16s are great for cruising... Hence Lean Cruise. Lean cruise actually seeme to run slightly cooler... If it is crusing. Advanced spark at this point really helps.
14.7 is the "good burn" that many cars use but in a hill (and it doesn't have to be that steep) 14.7 will cause a 150 degree temperature rise in 30 seconds. That makes me nervous and never waited to see how high it would go.
When you start to pull you need at least 12.8 to keep the heat down. Fuel injection actually increases the fuel over time on a long steady pull. I have seen it in the 11s. (gotta love it that car makers all over the world 105 years after the Model T still use gasoline to keep the heat down in combustion chambers... cause gas is so cheap, you know.)
So you absolutely do not want it lean on a pull... carb or fuel injection. The power valve on the carb is the same idea as Power Enrichment in fuel injection. I am sure Atomic is taking care of that or they would be out of business due to engine failures. I don't know about Atomic spark control.
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
[Updated on: Thu, 03 July 2014 01:47] Report message to a moderator |
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| Re: NEW FUEL INJECTION [message #254223 is a reply to message #254221] |
Thu, 03 July 2014 06:24 |
mrgmc3
Messages: 210
Registered: September 2013
Location: W Washington
Karma: 2
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I assume the proponents of "lean cruse " are looking for fuel economy. There would be no other reason to run there. Yes, you can get a few percent improvement, but it is tricky . You'll have to add some advance as others have mentioned, but be very cautious here. You get painted into a corner running lean and advanced. You need to monitor EGTs and knock. High EGTs will burn or break valves. Knock will break pistons.
The fuel economy issue is challenging on this vehicle. Most of our driving is "steady state", that is over the road cruising. The primary forces at work, and the opportunities for mileage gain are found in;
1) aero drag
2) rolling friction
3) mechanical friction (this includes pumping losses in the engine)
If you look at each one there are small opportunities, but no matter how you slice it this is a 10,000 pound vehicle with a large frontal area. Gains will be small and the max I suspect is possible without going diesel is 15% if improvement are made in all areas. That limits us to 11, maybe 11.5 mpg tops.
If you look at each item in turn there is maybe 5% gain possible in each;
Aero drag - someone posted a real good point-by-point analysis a couple weeks ago of the opportunities. All items were incremental, but can add up to measurable gains. The one item I did not see mentioned would be closing off the rear wheel openings with large panels. There is no real chance to reduce frontal area so you are left with trying to improve cd by removing clutter, closing gaps, etc.
Rolling friction - pick the least aggressive (highway) tread pattern tire, with a hard compound and keep them aired up to max recommended pressure. Keep wheel bearings well maintained and adjust brakes to ensure no drag.
Mechanical friction - set engine operating parameters for low losses (as lean a/f as possible and max advance - both are playing with fire no pun intended - as there is great potential for engine damage as discussed). Up the compression ratio a little. If I were to rebuild my engine I'd aim for 9.3 - 9.5:1 CR with iron heads, maybe 10.25:1 with aluminum heads. That is about all you can add with pump gas. Reduce friction by adding roller valve train components like lifters and rocker arms. Headers will help and fuel injection will be more precise (there is only the very small thermodynamic benefit of some charge cooling vs. carb ). The Trans has some big parasitic losses, and this is where automakers have made big gains in the last thirty years (more gears, lockup converter clutches, minimum pump pressures - but we are pretty much stuck with THM425).
The only other opportunity I see for improvement is weight loss. Swap in aluminum for steel wherever possible (wheels, radiator, intake, water pump, etc)
Leave extra crap at home.
Chris Geils - Twin Cities / W Wa
1978 26' Kingsley w/ very few mods; PD9040, aux trans cooler, one repaint in stock colors, R134a, Al rad, Alcoas, 54k mi
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| Re: [GMCnet] NEW FUEL INJECTION [message #254228 is a reply to message #254213] |
Thu, 03 July 2014 07:24 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Chris,
I'm curious about where your EGT recommendations originate. IIRC, George &
Randy try to keep below 1250*F. That really bothered me when I installed
thermocouples and saw as high as 1325*F -- not under much load. Since both
TC's failed pretty soon, I didn't gather much data. I've now got a better
TC on one bank and the other's due any day, thus my renewed concern about
what temperatures to expect from my Cad500.
Thanks,
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI & EBL,
Manny Brakes & 1-Ton, etc., etc.
www.gmcwipersetc.com
On Thu, Jul 3, 2014 at 12:51 AM, Chris Geils
wrote:
> Bob de Kruyff wrote on Wed, 02 July 2014 20:01
>> I don't have injection on my GMC but I do recall that even 14.7 to one
> is lean when asking for any amount of power. Lean cruise should be limited
>> to very light down the road travel with very slight throttle openings.
> For someone not trying to set EPA fuel ratings, I wouldn't even bother
>> anything leaner than 14.7 at cruise.
>
>
> I concur. On a vehicle this heavy there are some, but darn few,
> opportunities to run lean of 14.7:1. I'd say 55 mph no headwind and
> downgrades are
> about it. There is a balancing act between A/F and spark advance.
> Leaner A/F will drive exhaust temps up as will retarding ignition timing
> will
> raise exhaust temps. If you want to run lean and 87 octane I would
> suggest monitoring EGTs and using 1550F as an absolute upper limit under
> any
> circumstance or you'll break stuff. You should target lower temps like
> 13-1400 for lighter loads.
> If you have the ability to tune with a linear lambda meter I'd suggest
> 14-15:1 at light loads, 12.5:1 will be close to max power, and for long
> pulls
> on grades you should target 11-11.5:1 to keep temperatures under control.
> Richer than 10:1 will give an incomplete burn and the resulting unburned
> fuel will wash past the rings, potentially doing damage if run this way
> for long.
>
> Also note that E10 runs about 4% leaner than 100% gasoline, for a given
> jetting or injector pulse width. A lambda meter will read the actual A/F
> with
> either fuel.
> --
> Chris Geils - Twin Cities
> 1978 26' Kingsley w/ very few mods; Headers, Progressive Dynamics 9040
> battery charger, aux trans cooler, one repaint in stock colors, 44k mi
> _______________________________________________
>
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] NEW FUEL INJECTION [message #254237 is a reply to message #254228] |
Thu, 03 July 2014 08:30 |
rvanwin
Messages: 325
Registered: April 2007
Location: Battlefield, MO
Karma: 6
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Senior Member |
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Ken Henderson wrote on Thu, 03 July 2014 07:24Chris,
I'm curious about where your EGT recommendations originate. IIRC, George &
Randy try to keep below 1250*F. That really bothered me when I installed
thermocouples and saw as high as 1325*F -- not under much load. Since both
TC's failed pretty soon, I didn't gather much data. I've now got a better
TC on one bank and the other's due any day, thus my renewed concern about
what temperatures to expect from my Cad500.
Thanks,
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI & EBL,
Manny Brakes & 1-Ton, etc., etc.
www.gmcwipersetc.com
I think where EGT measurements are made make a big difference in what temps are "acceptable". Ideally, measuring in the combustion chamber would be the most accurate and you would see temps approaching 1600 degrees F or maybe even slightly more. The IC engine relies on the cooling system (water, air, oil), exhaust gas, and AFR to keep heat under control. Exhaust gas will cool as it leaves the combustion chamber. I'm measuring temps after the collector on headers which allows the EGT to cool somewhat. I measure there on both banks because that is the first place where gases from the four cylinders come together. I can't afford to put EGT sensors on each tube. I'm guessing measuring on an engine with exhaust manifolds would show higher temps. I use the temps as a relative measurement. In other words, I'm looking for changes in temps. I know where the temps run under normal circumstances and watch for temps that exceed normal. So when Ken says I try to keep temps below 1250 degrees that is correct for the way I am measuring. On hard pulls, I see temps approaching 1350 degrees. I try to never let temps exceed 1350 because I think the combustion chamber will be approaching temps that will cause failure.
I have found that lean cruise actually drops EGT slightly until some load is applied. My engine stays in lean cruise most of the time in steady cruise conditions. Even on slight up and down variance in terrain (we have lots of that here in MO), my engine is able to stay in lean cruise. I have 3.70 gears on a 403 engine which helps keep the load under control. When the engine goes into lean cruise, the instantaneous mpg gauge (an EBL feature) jumps 1 mpg. That, coupled with Deceleration Fuel Cut-Off (DFCO), plus the overall efficiency of fuel injection does help improve gas mileage. But as someone said, you are not going to be overwhelmed with the increases, however, I believe the 1% to 2% improvement at today's gas prices does add up. After all, if I can save 35 to 70 cents per gallon, I'm not going to complain. As a disclaimer, increases in mpg with fuel injection will vary considerably depending on a lot of factors. A very well tuned Q-jet will deliver excellent fuel economy and if you have one, then fuel injection may not buy as much. I have seen many fuel injected engines not tuned as well as they should be (usually in spark control more so than fuel control). And as someone said, a well setup fuel injected 455 or 403 will be more responsive so the tendency is to use that responsive feeling by pushing the go pedal more.
If I'm not clear, I like fuel injection for the 455 or 403 (lol).
Randy & Margie
'77 Eleganza II '403'
Battlefield, MO
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| Re: [GMCnet] NEW FUEL INJECTION [message #254243 is a reply to message #254228] |
Thu, 03 July 2014 09:01 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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What I want to know is, "When do you guys have time to watch the traffic or
see the Scenery?" (Grin)
Jim Hupy
Now in Ukiah, California. Headed for Jerry Work's
On Jul 3, 2014 5:25 AM, "Ken Henderson" wrote:
> Chris,
>
> I'm curious about where your EGT recommendations originate. IIRC, George &
> Randy try to keep below 1250*F. That really bothered me when I installed
> thermocouples and saw as high as 1325*F -- not under much load. Since both
> TC's failed pretty soon, I didn't gather much data. I've now got a better
> TC on one bank and the other's due any day, thus my renewed concern about
> what temperatures to expect from my Cad500.
>
> Thanks,
>
> Ken H.
> Americus, GA
> '76 X-Birchaven w/Cad500/Howell EFI & EBL,
> Manny Brakes & 1-Ton, etc., etc.
> www.gmcwipersetc.com
>
>
> On Thu, Jul 3, 2014 at 12:51 AM, Chris Geils
> wrote:
>
>> Bob de Kruyff wrote on Wed, 02 July 2014 20:01
>>> I don't have injection on my GMC but I do recall that even 14.7 to one
>> is lean when asking for any amount of power. Lean cruise should be
> limited
>>> to very light down the road travel with very slight throttle openings.
>> For someone not trying to set EPA fuel ratings, I wouldn't even bother
>>> anything leaner than 14.7 at cruise.
>>
>>
>> I concur. On a vehicle this heavy there are some, but darn few,
>> opportunities to run lean of 14.7:1. I'd say 55 mph no headwind and
>> downgrades are
>> about it. There is a balancing act between A/F and spark advance.
>> Leaner A/F will drive exhaust temps up as will retarding ignition timing
>> will
>> raise exhaust temps. If you want to run lean and 87 octane I would
>> suggest monitoring EGTs and using 1550F as an absolute upper limit under
>> any
>> circumstance or you'll break stuff. You should target lower temps like
>> 13-1400 for lighter loads.
>> If you have the ability to tune with a linear lambda meter I'd suggest
>> 14-15:1 at light loads, 12.5:1 will be close to max power, and for long
>> pulls
>> on grades you should target 11-11.5:1 to keep temperatures under control.
>> Richer than 10:1 will give an incomplete burn and the resulting unburned
>> fuel will wash past the rings, potentially doing damage if run this way
>> for long.
>>
>> Also note that E10 runs about 4% leaner than 100% gasoline, for a given
>> jetting or injector pulse width. A lambda meter will read the actual A/F
>> with
>> either fuel.
>> --
>> Chris Geils - Twin Cities
>> 1978 26' Kingsley w/ very few mods; Headers, Progressive Dynamics 9040
>> battery charger, aux trans cooler, one repaint in stock colors, 44k mi
>> _______________________________________________
>>
>>
> _______________________________________________
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| Re: [GMCnet] NEW FUEL INJECTION [message #254247 is a reply to message #254228] |
Thu, 03 July 2014 09:28 |
mrgmc3
Messages: 210
Registered: September 2013
Location: W Washington
Karma: 2
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Senior Member |
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Ken Henderson wrote on Thu, 03 July 2014 07:24Chris,
I'm curious about where your EGT recommendations originate. IIRC, George &
Randy try to keep below 1250*F. That really bothered me when I installed
thermocouples and saw as high as 1325*F -- not under much load. Since both
TC's failed pretty soon, I didn't gather much data. I've now got a better
TC on one bank and the other's due any day, thus my renewed concern about
what temperatures to expect from my Cad500.
Thanks,
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI & EBL,
Manny Brakes & 1-Ton, etc., etc.
www.gmcwipersetc.com
Ken,
The absolute upper limit of 1550F is GMs internal upper limit. If you can dial in 12-1300 numbers, good on you. Colder is better, but you'll be hard pressed to run a lot lower than 1500 on a grade with anything close to a peak power A/f like 12.5:1. This is why carbs typically go richer, the don't have timer functions like EFI. Ideally at WOT you would run 12.5:1 A/F for 10 to 15 secs then taper down to 11:1 for a long grade load to maintain temp control.
Chris Geils - Twin Cities / W Wa
1978 26' Kingsley w/ very few mods; PD9040, aux trans cooler, one repaint in stock colors, R134a, Al rad, Alcoas, 54k mi
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