since i just went though this, i thought i should write down what i learned before i forgot it. hopefully it will help some people ...

please accept my apologies beforehand for how long and rambling it is ... so here goes ...

the injector timing table is based on crank degrees, and specifies the degree at which the injector pulse should end. so it would be helpful if we came had a way to determine, for a given rpm and load, at what cam degree the injector pulse should end. note that crank degrees go from 0-720 instead of from 0-360 because the crank rotates 2 times for each revolution of the cam.

when there is little or no overlap between the closing of the exhaust valve and the opening of the intake valve, it may be desirable to actually start injecting the fuel before the intake valve opens. in this case, the fuel is squirted onto the back of the closed intake valve, because that may help atomize the fuel.

but if there is alot of valve overlap, then that approach is not as desirable, because when the intake valve opens, some of the fuel that was waiting to go into the cylinder will get mixed in with the exhaust (and ejected from the cylinder) and therefore not be burned, potentially resulting in a lean condition.

so a factor in deciding how early to start the injectors may be how much overlap there is in your cam.

here are my thoughts on a process to determine what values to put in the injector timing table ...

before we can pick an ending degree, we need a way to determine how many degrees the injector needs to provide the right amount of fuel. in order to do that, we need a way to figure out how much fuel is needed. once we know that, we can determine how many milliseconds the injector needs to be open to provide the fuel. then need to be able to figure out, for a given rpm, how many degrees the camshaft will turn during the time the injector is open. then, knowing the degrees at which the valves open and close, we can finally pick reasonable ending degrees for the injector timing.

for a certain rpm and load, we can estimate what the injector pulsewidth would be. for example, suppose we had a 410 with 42# injectors spinning at 3000 rpm under 50% load. what would the estimated pulsewidth be?

one cylinder has a maximum volume of 410/8, or 51.25 ci. since the volumetric efficiency of the engine is not 100%, for our example, let's use .85 as the VE factor, which means that a given cylinder will end up with a maximum of 51.25*.85 = 43.5625 ci of air. since our example is at 50% load, that would be 43.5625 *.50 = 21.78125 ci. this is the estimated amount of air (in cubic inches) each cylinder should receive per cycle.

there is a conversion factor that says one cubic foot of air contains .075 lbs of air. so in our example, we have 21.78125 / (12*12*12) = 0.01260489 cubic feet of of air. so we have 0.01260489 * .075 = 0.00094536675 lbs of air

now that we know we have 0.00094536675 lbs of air in the cylinder, we can determine how much fuel we need ... using the standard air/fuel ratio of 14.67, we would need 0.00094536675/14.64 = .0000645742316 lbs of fuel.

since injectors are given in lbs per hour, and pulsewidths are in milliseconds, we need to convert to lbs per ms. so for 42# injectors, we have 42/(60 minutes*60 seconds*1000 milliseconds) = 0.0000116666667 lbs of fuel per ms.

so to get .0000644421779 lbs of fuel, we would open the injectors for a pulswidth of .0000645742316/0.0000116666667 = 5.53493412 ms. but since there is a small delay (about .05 ms) before the injectors actually start squirting the fuel, lets add .05 to the pw, getting about 5.58 for the desired injector pulsewidth.

notice that if we figure out the pw for the case where load is 100% (WOT), then we can just multiply that by the load later to simplify things. let's do that here:

max air in lbs: (51.25*.85*.075)/(12*12*12) = 0.00189073351 lbs air
fuel needed for max air above: 0.00189073351 / 14.67 = 0.000128884357 lbs fuel
fuel in lbs per ms: (42/360000) = 0.0000116666667
ms needed to deliver the above fuel: (0.000128884357 / 0.0000116666667) = 11.05 ms
note that we will need to add the .05 ms delay to the pulsewidth after factoring in the load ...

so 11.10 ms is needed to deliver the most fuel the injecter should have to deliver. of course, this will be slightly higher if we want the afr to be lower. like when at WOT for example.

we will multiply this to the load later ...

ok, we are halfway there... now we get to figure out how many degrees the crank will turn during the 5.58 ms from our example above. that depends on how fast the crank is turning.

in our example, the crank is turning 3000 rpm. since there are 360 degrees in a revolution, 60 seconds per minute and 1000 ms per second, then we have the crank turning at (360*3000) / (60*1000) = 18 degrees per ms. so in 5.58 ms, the crank turns 18 * 5.58 = 100.44 degrees.

notice that the only variable above is the rpm, so for a given rpm we can do this to get the degrees per ms:

360*(rpm)/(60*1000)
= 360*rpm/60000
= rpm*(360/60000)
= rpm*0.006

we'll use this later too ... on to the cam events ...

so let's say that our cam has an intake lobe center of 110, a lsa of 112, a duration of 230 at .050" and 290 total duration. so how does that translate into crank degrees? here's how:

by definition, crank degrees 0-360 refer to the first revolution of the crank, and degrees 360-720 refer to the second revolution of the crank.

intake events are offsets from top dead center (TDC) or bottom dead center (BDC)of the cylinder during the phase in question. for the intake valve events, TDC is at degree 360.

since the intake lobe has a center of 110, that means the valve is open its highest at 360+110=470 degrees. a duration of 290 means that the valve opens at 470-(290/2) = 325 and closes at 470+(290/2) = 615 degrees. similarly, the valve is at .050" or higher from degree (470)+/-(230/2), or 355 and 585 degrees.

a lsa of 112 means that the exhaust lobe center is 112*2 degrees before the intake lobe center.

so with a lsa of 112, our exhaust valve is fully open (the exhaust lobe center) at 470-(112*2) = 246 degrees. doing the same calcs as above, we have open/close at 101 and 391, and at .050" the open/close events are 131 and 361 degrees.

now notice that the exhaust closes at 391, and the intake opens at 325. so both valves are open for 391-325 = 66 degrees. this is the total overlap. similarly, at .050" there is an overlap of 6 degrees. in this case, i would probably want the fuel to start injecting when the exhaust valve closes, or at about degree 390.

now we are almost there ... for a given load and rpm, we can figure out how much ms of injector we need, and how many degrees that ms needs. now all we have to do is tie that to the cam events for our cam and we can fill in the table with values that should be fairly reasonable.

to finish off our example, with the 410ci engine and 42# injectors, 50% load at 3000 rpm with our cam as above, the calculation for that cell would be ...

the needed injector pw would be: 11.05 * .50 + .05 = 5.595 ms
the crank rotation for 5.595 ms at 3000 rpm would be: 3000 *.006 * 5.595 = 101 degrees (rounded)
if the pw starts when the exhaust valve closes ...
the injector fires from degree 390 thru 491 (390+101)

so 491 should be a fairly reasonable value for that cell.

_________________
95 GT Vert, TwEECer R/T v1.30A9
1970 block, 410ci, 10.27:1 CR, 42#, LMAF, CBAZA/T4M0, AOD, 2500 Stall, Custom Cam

1967 Fairlane Vert, 390FE, C6, 100% stock

i created an excel spreadsheet that implements all this stuff.

anyone know how to make it public?

_________________
95 GT Vert, TwEECer R/T v1.30A9
1970 block, 410ci, 10.27:1 CR, 42#, LMAF, CBAZA/T4M0, AOD, 2500 Stall, Custom Cam

1967 Fairlane Vert, 390FE, C6, 100% stock

Put it in the Documentation section, on the main page. I'd like to take a look at it.

_________________
94 GT, New PTK turbo, TW heads, TFS stage 1 cam, 75mm TB, 60#inj., full aeromotive fuel system, Snow stage 2 meth injection, forged 306, PLX wideband, PMAS pro tube Blowthru

Vortech Times 10.80 @ 126.44 mph, with a 1.57 60ft. 3600#s

fyi, i just edited the original post ... sailorbob pointed out a couple of spots that were inaccurate ... thanks sailorbob

stangfreek94, i posted it ... after i update it to account for the inaccuracies pointed out by sailorbob

_________________
95 GT Vert, TwEECer R/T v1.30A9
1970 block, 410ci, 10.27:1 CR, 42#, LMAF, CBAZA/T4M0, AOD, 2500 Stall, Custom Cam

1967 Fairlane Vert, 390FE, C6, 100% stock

one thing i notice about this for my cam and injectors ...

at WOT, if my desired air/fuel ratio is 13:1, then at 5000 rpm my 42# injectors need 303 degrees to deliver the fuel, but the intake valve is only open for 290, so i will have to start the injector during the overlap. either that, or i need bigger injectors or higher fuel pressure

_________________
95 GT Vert, TwEECer R/T v1.30A9
1970 block, 410ci, 10.27:1 CR, 42#, LMAF, CBAZA/T4M0, AOD, 2500 Stall, Custom Cam

1967 Fairlane Vert, 390FE, C6, 100% stock

i believe the statement "cam rotation" should be replace with "crank rotation". i don't think you want to add cam degrees to crank degrees. since the cam card has numbers based on crank degrees, this topic only becomes more confusing if you start talking about cam degrees. the two revolutions of the crank for one cycle of the four stroke engine and the 0 - 720 degree statement should cover things.

i was just drag racing this past weekend and had pulse widths > 17 msec. i saw rpms of around 6200 at my shift points. I was kinda surprised the PW's slowly reduced to around 15.5 msec after i shifted into 3rd gear and approached the finish line.

i am still using the stock a9p timing table and my AFR's, recorded using a PLX SM-AFR (i have no idea how accurate this thing is or is not!) during the run were between 12.3 and 12.7.

i know my application is unique, i do not drive my fairmont on the road, so i do not care about fuel economy or emissions.

i am using 30# injectors, based on the AFR's i apparently still have some room left. based on PW's i am probably near 90% duty cycle, but this is only a guess, since i do not know how duty cycle was really defined by Ford engineering?

i ran the data log through EA and got some really crazy numbers for this table...which did not surprise me because as i said, my data log is outside the norm.

cheers, claude

_________________
81 fairmont, 347, c4, A9P, 75mm ProM C-42, 75mmTB, Mass-Flo EFI intake, 42# inj, CI cam, canfield 195 heads.

68 f100, 460, c6, A9L, 85mm PMAS, 1000cfm 4bbl TB, victor 460, 30# inj, lunati cam, d0ve-a heads.

Injector Duty cycle percentage is the amount of time the injector is ON vs OFF for all four strokes of a cylinder. The amount of time to complete a cycle (i.e. 4 strokes) is directly related to the RPMs. To get the complete cycle time follow this formula:

Complete Cycle Time in milliseconds = 60 * 1000 * 2 / RPMs
60 converts minutes to seconds
1000 converts seconds to milliseconds
2 is in there because there are 2 revolutions in 1 complete cycle

So at 6000RPMs, a cycle takes 20ms.

So you take the time an injector is open (in ms) and divide it by the time it takes to complete a cycle (in ms). This gives you your Injector Duty Cycle in Percents.

So if you are seeing 17ms@6000RPMs, that would be 85% Duty cycle.

_________________
...Always Somethin'

89 Ranger Supercab, 331 w/GT40p heads, ported Explorer lower, Crane Powermax 2020 cam, 1.6RRs, FMS Explorer (GT40p) headers, Slot Style MAF, aftermarket T5 'Z-Spec', 8.8" rear w/3.27s, Powertrax Locker, Innovate LC-1, GUFB, Moates QuarterHorse tuned using BE&EA

Member V8-Ranger.com

that was actually something sailorbob pointed out as well, and i updated my original post, but i missed that spot ... thanks for catching it, i edited it again.

_________________
95 GT Vert, TwEECer R/T v1.30A9
1970 block, 410ci, 10.27:1 CR, 42#, LMAF, CBAZA/T4M0, AOD, 2500 Stall, Custom Cam

1967 Fairlane Vert, 390FE, C6, 100% stock

chris,

i agree with what you posted and that is how i would calculate duty cycle also, but i do not know how the ford engineers calculated these numbers in the eec-iv software. do you? is this how binary editor and tweecer's calcon calculate duty cycle or is duty cycle defined by some output from the J3 service port?

look at EA's help screens for cam timing and look at what the author of this post is advising.

both agree that i need larger injectors, based on intake valve open time. but based on duty cycle calcs and my wideband output, i do not.

as rpm's increase, the time the intake valve is open decreases. as rpm's and load increase the injector pulse width increases. who says that if the injector pulse width is greater than intake valve opening time i need larger injectors? i'm afraid i have to disagree with anyone who tries to tell me this.

my guess is the stock application even violates this "rule" at certain rpm's and loads, yet ford engineers had no problems with this happening.

cheers, claude

_________________
81 fairmont, 347, c4, A9P, 75mm ProM C-42, 75mmTB, Mass-Flo EFI intake, 42# inj, CI cam, canfield 195 heads.

68 f100, 460, c6, A9L, 85mm PMAS, 1000cfm 4bbl TB, victor 460, 30# inj, lunati cam, d0ve-a heads.

Inj Duty Cycle is something that's calculated on the fly by BE or Calcon when you datalog both InjPW and RPM...thus you have to be datalogging both of these before InjDuty is included in your logs.

I don't believe there's an actual checkbox to allow you to datalog Inj Duty Cycle from the module because I don't think it's actually calculated anywhere in the EEC to be datalogged. At least, I can't think of any reason the EEC would need to calculate it.

_________________
...Always Somethin'

89 Ranger Supercab, 331 w/GT40p heads, ported Explorer lower, Crane Powermax 2020 cam, 1.6RRs, FMS Explorer (GT40p) headers, Slot Style MAF, aftermarket T5 'Z-Spec', 8.8" rear w/3.27s, Powertrax Locker, Innovate LC-1, GUFB, Moates QuarterHorse tuned using BE&EA

Member V8-Ranger.com

claude, i do not remember telling you (or anyone else for that matter) that you need bigger injectors.

how much overlap does your cam have?

if not too much of the fuel is going out with the exhaust before it is ignited, and your car runs the way you want it to, then i guess you are golden

my cam has 66* of overlap, and my computer thinks that it is always lean, no matter how much fuel i throw at it. and it pings over 3000 rpm even though i use high octane fuel and have pulled timing. and my gas mileage is absolutely terrible.

therefore, i think i must have alot of unburned fuel going out with the exhaust. so i have to change it so the injectors don't open until later so that less fuel will go out with the exhaust. that obviously limits the amount of time my injectors have to provide the fuel, because if the intake valve closes before the injector is done, then i may have a problem

if that is not a problem for you, then more power to you.

_________________
95 GT Vert, TwEECer R/T v1.30A9
1970 block, 410ci, 10.27:1 CR, 42#, LMAF, CBAZA/T4M0, AOD, 2500 Stall, Custom Cam

1967 Fairlane Vert, 390FE, C6, 100% stock

Just curious if the above can be added to to support the strategies that actually go with degrees when the injectors start firing instead of when the injectors stop firing. The GURE is setup for the start firing scenario

I'm actually working on my tables as I think Ford rushed it since it only has 380's at idle to a bit higher and low load conditions, then everything else is at 280.

_________________
'90 TBird SC 3.8L Supercharged
Gen III Eaton's M90 Blower, Blower OD'd at 12%, 76mm C&L MAF, 75mm ProProd TB, 42# RC Eng Inj, AFPR set at 43.5psi, Comp CAM Custom Grind .484 Intake .520 Exh, Duration @ 0.050 204 Int 206 Exh.

my apologies, i must have misread your post. i do not disagree with what you have posted and i think many people can benefit from adjusting the values in this table. i am not trying to start any kind of argument.

i don't have my cam card handy. i burn 110 octane, the guy who designed my cam recommended 104 and my static compression is 12.5:1.

is that 66 degrees overlap at .05" or at advertised duration.

you are correct, i don't think i have the problems you have. i don't care about fuel economy in my race car and it appears to me i am not going lean. one thing to remember is that a carb does not care when the intake valve opens and closes, which is of course why they are no longer used on new vehicles, along with many other reasons.

i think that my point is, at higher rpms you are going to have trouble keeping the injector pulse less than the intake valve open time.

best of luck with your tuning, and i am impressed with what you posted. i will give your spread sheet a shot when i get home and have access to my cam data.

cheers, claude

_________________
81 fairmont, 347, c4, A9P, 75mm ProM C-42, 75mmTB, Mass-Flo EFI intake, 42# inj, CI cam, canfield 195 heads.

68 f100, 460, c6, A9L, 85mm PMAS, 1000cfm 4bbl TB, victor 460, 30# inj, lunati cam, d0ve-a heads.

my cam has 24* overlap @ 0.05" and 77* @ 0.006".

intake duration: 238/292
exhaust duration 255/308 (0.05/0.006)

just out of curiousity, what type of fuel economy are you expecting from 410 cubic inches? did whoever design your cam give you any idea what you should expect?

my speed density 351W gets less than 13 mpg. i refuse to measure how much fuel my 460 sucks.

cheers, claude

_________________
81 fairmont, 347, c4, A9P, 75mm ProM C-42, 75mmTB, Mass-Flo EFI intake, 42# inj, CI cam, canfield 195 heads.

68 f100, 460, c6, A9L, 85mm PMAS, 1000cfm 4bbl TB, victor 460, 30# inj, lunati cam, d0ve-a heads.

my cam is 230/290 intake and 230/290 exhaust with a 112 lobe separation angle. it has 6* overlap at .006 and 66* at .050

you have even more overlap than i do. what does your injector timing table look like?

mine had the stock values of 280 for all the cells under 60% load, and 420 for 60% and 70%.

when i get my tune right, i hope to see about 20 on the highway and 15 or so city. i have an AOD tranny with 3.27 gears.

_________________
95 GT Vert, TwEECer R/T v1.30A9
1970 block, 410ci, 10.27:1 CR, 42#, LMAF, CBAZA/T4M0, AOD, 2500 Stall, Custom Cam

1967 Fairlane Vert, 390FE, C6, 100% stock

absolutely ... that is actually easier. i can send you a version of that if you want, but it is essentially just picking the crank degree at which you want it to start. but i think i see where you are going ... the calcs can help you determine what kind of pulse widths you will need so you can make sure the injector completes its squirting before the valve closes ...

_________________
95 GT Vert, TwEECer R/T v1.30A9
1970 block, 410ci, 10.27:1 CR, 42#, LMAF, CBAZA/T4M0, AOD, 2500 Stall, Custom Cam

1967 Fairlane Vert, 390FE, C6, 100% stock

stock a9p table: 280 across the board up to 30% load @ 4000 rpms.
40% row has 332's
50% row, 5-380's, 2-420's, 2-464's
60% and 75% row, 6-420's and 3-464's

your line of reasoning is correct, but how much air is flowing at 3000rpms at those low lift numbers?

does maryland have emission testing? have you thought of paying someone to measure your AFR? would give you an idea if you are headed in the right direction.

what are your vacuum readings?

best of luck, claude

_________________
81 fairmont, 347, c4, A9P, 75mm ProM C-42, 75mmTB, Mass-Flo EFI intake, 42# inj, CI cam, canfield 195 heads.

68 f100, 460, c6, A9L, 85mm PMAS, 1000cfm 4bbl TB, victor 460, 30# inj, lunati cam, d0ve-a heads.

ok ... i have updated the spreadsheet and uploaded it to the documentation section again.

let me know what you guys think

_________________
95 GT Vert, TwEECer R/T v1.30A9
1970 block, 410ci, 10.27:1 CR, 42#, LMAF, CBAZA/T4M0, AOD, 2500 Stall, Custom Cam

1967 Fairlane Vert, 390FE, C6, 100% stock

How do you figure injector start? The spreadsheet is defaulted to 380, EA had come up with 35X most of the time when I was using it.

_________________
David Claflin
1990 LX, 9.6:1 compression, 306, 92MM Pro-M MAF, 90MM Wilson TB, TFS-R intake, Neil Erickson ported Edelbrock performers, Jay Allen cam, Accufab 1 3/4"longtubes, 3" exhaust, T5, 3.73's, Cobra disk brakes, QuarterHorse, 7.68@89.9, 21/28MPG on real gas

notice that that cell is blue, which identifies it as a user entered cell, meaning that the user of the spreadsheet decides what value to use for that cell.

that said, here is why i have 380 in that cell. the cam info on the sheet is from my cam. when you look at it, you will notice that i hav 66* of overlap, and that the exhaust valve closes at 391*

now the behavior i was seeing from my logs was that it was always reporting lean, even though the gas mileage was absolutely horrible and it smelled really rich.

also note that the stock values for this table in my strategy is something like 280 across the board and then 420 in the high load cells.

so my theory is that the injectors were dumping their load before the injectors opened and the overlap was causing alot of the unburned fuel to go out with the exhaust, so it really was lean.

so while the theory of squirting the fuel on the closed intake valve to better atomize the fuel is probably a good one, i believe it does not work for my cam because of all the overlap.

so for my cam, i selected 380 as the start because that is only 11* before the actual closing of the exhaust valve and it takes a moment for the injector to start after receiving the signal, so this is the earliest i want the injectors to start so that i don't lose alot of fuel in the exhaust.

this seems to have helped my tune ALOT. my idle is much smoother, it doesn't ping over 3000 rpm anymore, and the fuel gauge does not go down nearly as fast.

i hope that answers your question ...

_________________
95 GT Vert, TwEECer R/T v1.30A9
1970 block, 410ci, 10.27:1 CR, 42#, LMAF, CBAZA/T4M0, AOD, 2500 Stall, Custom Cam

1967 Fairlane Vert, 390FE, C6, 100% stock

What I still don't understand about heavy overlap cams is how you don't still indicate a lean burn. If overlap is indeed scavenging fuel and air out the exhaust, even if you delay the injector opening until after the exhaust has closed significantly, you still have unburned air going out the exhaust which I'd think the HEGO would pickup and register as a lean condition.

The only thing I can figure is the EEC is only watching the HEGOs during times it knows a HEGO would be monitoring a cylinder's exhaust air. So it may very well be registering the unburned oxygen, but those readings are being ignored in favor of readings when the EEC knows a cylinder's "fresh" exhaust gas is passing over the sensor. Any truth to this theory?

_________________
...Always Somethin'

89 Ranger Supercab, 331 w/GT40p heads, ported Explorer lower, Crane Powermax 2020 cam, 1.6RRs, FMS Explorer (GT40p) headers, Slot Style MAF, aftermarket T5 'Z-Spec', 8.8" rear w/3.27s, Powertrax Locker, Innovate LC-1, GUFB, Moates QuarterHorse tuned using BE&EA

Member V8-Ranger.com

That makes sense, I looked at what it shows for cam specs and have set mine down to 10 degrees before intake opens. I'll give that a try on MOnday and see how it works.
Do you by chance have longtubes on your car??

_________________
David Claflin
1990 LX, 9.6:1 compression, 306, 92MM Pro-M MAF, 90MM Wilson TB, TFS-R intake, Neil Erickson ported Edelbrock performers, Jay Allen cam, Accufab 1 3/4"longtubes, 3" exhaust, T5, 3.73's, Cobra disk brakes, QuarterHorse, 7.68@89.9, 21/28MPG on real gas

i believe you are right. i'm sure you know about the exhaust pulse delay table. that must be what it is for ...

david, i DID have long tubes (KOOKs), but i ditched them in favor of accufab mid-lengths. much happier now

_________________
95 GT Vert, TwEECer R/T v1.30A9
1970 block, 410ci, 10.27:1 CR, 42#, LMAF, CBAZA/T4M0, AOD, 2500 Stall, Custom Cam

1967 Fairlane Vert, 390FE, C6, 100% stock

That's what I was wondering about, the long tubes have a common collector where the pulses are kind of blended vs. the shorties where the O2 can actually sense which pulse came from a particular cylinder.

_________________
David Claflin
1990 LX, 9.6:1 compression, 306, 92MM Pro-M MAF, 90MM Wilson TB, TFS-R intake, Neil Erickson ported Edelbrock performers, Jay Allen cam, Accufab 1 3/4"longtubes, 3" exhaust, T5, 3.73's, Cobra disk brakes, QuarterHorse, 7.68@89.9, 21/28MPG on real gas

I loaded it up and haven't really noticed a difference, the idle "seems" better but sometimes you can wash a car and have it seem to run better . In tunerpro the RPM scale only goes to 4K, does the ECU correlate where the injector firing will be after the 4K point??

_________________
David Claflin
1990 LX, 9.6:1 compression, 306, 92MM Pro-M MAF, 90MM Wilson TB, TFS-R intake, Neil Erickson ported Edelbrock performers, Jay Allen cam, Accufab 1 3/4"longtubes, 3" exhaust, T5, 3.73's, Cobra disk brakes, QuarterHorse, 7.68@89.9, 21/28MPG on real gas

With all that has been written here in the past about injector timing the discussions around overlap and "purging" have troubled me the most. I don't think you actually get a purge effect until high RPM, especially if you are running through a street legal exhaust system. Instead I would think you get a lot of reversion at low and mid RPM where we spend most of the time on the street. Of course at high RPM when the exhaust flow velocity can create a vaccum in the exhaust the EEC is in OL so its not looking at the O2 sensors anyway. Didn't someone here put a vacuum/boost guage on the exhaust to back up these points. I guess I better search...

_________________
94 GT, CBAZA/J4J1, 347 (on a R302 block), F303 cam, Performer II Intake, 1.7 Crane RR's, 1 5/8 Shorties, 70MM BBK TB, C&L 85mm Tuner MAF, Pro-Charger D1SC, 60#'s, TKO 600. Runs 11:80's

How does your approach compare to Clint's EA? I rely heavily on EA for injector timing calculations and doing all the math manually hurts my head... Do I give up EA and use this method, are they complimentary, or are they overlapping?

_________________
94 GT, CBAZA/J4J1, 347 (on a R302 block), F303 cam, Performer II Intake, 1.7 Crane RR's, 1 5/8 Shorties, 70MM BBK TB, C&L 85mm Tuner MAF, Pro-Charger D1SC, 60#'s, TKO 600. Runs 11:80's

Honestly, I can't answer that question because I have used EA very little and I don't know enough about how it makes the decisions it makes, but I can say this ...

My intention for the spreadsheet was to be a guide for determining reasonable values for the cells in the table.

My spreadsheet is based solely on the theory of the process. And it does all the math for you, so it can help there ...

My understanding is that EA needs a log and the LOAD and PWs recorded therein to make the decisions it makes.

_________________
95 GT Vert, TwEECer R/T v1.30A9
1970 block, 410ci, 10.27:1 CR, 42#, LMAF, CBAZA/T4M0, AOD, 2500 Stall, Custom Cam

1967 Fairlane Vert, 390FE, C6, 100% stock

i would be extremely impressed if the EEC-IV software was actually able to monitor a cylinders exhaust with a narrow band O2 sensor.

my uneducated wild assed guess would be the EEC is looking at the left bank and the right bank and would not be able to distinguish individual cylinders. especially at rpms above 4k.

cheers, claude

_________________
81 fairmont, 347, c4, A9P, 75mm ProM C-42, 75mmTB, Mass-Flo EFI intake, 42# inj, CI cam, canfield 195 heads.

68 f100, 460, c6, A9L, 85mm PMAS, 1000cfm 4bbl TB, victor 460, 30# inj, lunati cam, d0ve-a heads.

With a heavy overlap cam, you have lots of time with the exhaust and intake valve open at the same time. And you are right, at lower RPMs, you will get reversion. However you also get that same air that's being reverted back into the intake, pushed out the exhaust even at lower RPMs since the exhaust valve and intake valve are open at the same time. Since there's not a good name for the pulling of unburned intake air out the exhaust, I will refer to it as over-scavenging. The difference between over-scavenge and reversion is when they happen.

Normal scavenging happens when you have a very efficient exhaust system. The exhaust air's intertia moving through the exhaust system creates a vaccum in its wake which literally pulls more exhaust out of the cylinder than would've come out on its own. That's a good thing and is why aftermarket exhaust systems work better than stock systems.

Over-scavenging happens when the intake and exhaust valve are open wide enough at the same time that the scavenging draws unburned intake air from the intake valve, out exhaust valve into the exhaust system. This is a good thing for performance because if flushes the combustion chamber of the exhaust. But at cruising loads, it's not necessarily a good thing since it causes the HEGOs to see oxygen and think there was a lean burn, when that may not have been the case at all. But as mentioned above, the EEC can guesstimate when to monitor the HEGOs and when to ignore them. But a WB has no way of knowing this and thus I'd think it possible to get false-lean conditions on a WB due to over-scavenging happening at lower RPMs. Perhaps there's enough smoothing going on in the WB logic that over-scavenging lean spikes are eliminated, I can't say for sure on that one.

Now for reversion. To my knowledge, there are 2 types of reversion. They probably have different names, but I don't know them. So here are "my" names for them...Exhaust Reversion and Intake Reversion.

Exhaust Reversion happens when the intake valve opens too far while the piston is still rising for the exhaust stroke. Some of the exhaust gets pushed into the intake. From what I understand, most cams, even stockers do this to a fair amount which is why intake manifolds often have quite a coverage of black soot lining them. The effect is that the exhaust lowers the vacuum level in the intake. The sooner the intake valve opens and the wider it opens before the piston heads back down increases this effect. The reason the intake valve opens so soon is because at high RPMs, the quicker you can get the valve open to it's widest, the more air that can get into the cylinder especially with stock heads. It's not nearly as big of a problem with aftermarket heads that have larger valves. When people talk about reversion, I don't believe it's exhaust reversion they are referring to.

Intake Reversion: At high RPMs with a good intake system, a similar behavior to exhaust scavenging happens. The intertia of the air being pulled into the cylinder creates a positive pressure at the intake port which pushes more air into the cylinder than what would've gone on its own. At higher RPMs, the intertia is still pretty strong while the piston is headed upward on the compression stroke. So holding the intake valve open a little longer allows for this intake scavenging effect to push just a little more air into the cylinder before the intertia looses strength. The downside to this is at lower RPMs, there's not nearly enough intertia to force more air into the cylinder AND the time it takes to fill the cylinder is much longer. So with the same high RPM cam that took advantage of this intake scavenging, you literally push some of your aspirated air/fuel mix back up into the intake before the intake valve closes. This pushing of air back into the intake is called reversion. This plays hell with SD EFI systems since the return of air into the intake lowers the vacuum in the intake for a brief moment until the intake valve closes and vaccum is restored. With a moderate to radical cam, a vaccum gauge won't show a stable vaccum at idle, like you would with a milder cam. You'd see the needle bouncing at idle as the reversion occurs. The effects are even worse with carbed motors because the carburetor needs vacuum to draw the gasoline into the air. Without vacuum, the carb doesn't do it's job. So with this kind of cam, you almost always have to run a higher idle to keep the RPMs at a point the carb can tolerate. To help with the effects of reversion on carbs, you can get dual-plane intakes which separate out the cylinders in such a way that the cylinder intaking (creating the vaccum) is physically separated from the cylinder creating reversion. This separation goes right up to the barrels on the carb so the reversion happening has no effect on the vaccum created by the cylinder trying to aspirate air through the carb.

Anyway, my point is that it is possible that you can get intake reversion and over-scavenging happening at the same time at certain RPM/Loads when both are strong enough to co-exist.

Does that make sense or am I spewing crap from my fingertips again?

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89 Ranger Supercab, 331 w/GT40p heads, ported Explorer lower, Crane Powermax 2020 cam, 1.6RRs, FMS Explorer (GT40p) headers, Slot Style MAF, aftermarket T5 'Z-Spec', 8.8" rear w/3.27s, Powertrax Locker, Innovate LC-1, GUFB, Moates QuarterHorse tuned using BE&EA

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