MPG on 550's

[Jeff Lange]

Only if you don't dial back your injector pulse.

Any modification you do to the fuel system needs to be tuned. There's no reason that 550cc injectors and a fuel pump/FPR will make your fuel economy change if done correctly.

If you are always boosting more, or don't tune it, of course you'll get crappier mileage. I get better mileage now with my Lex AFM and 550's than I did with the stock AFM and 440's (although it is almost identical).

 

[jdub]

You nailed it Jeff...and you have to have an appropriate fuel computer to do that

 

[Josh Sulsberger]

wow you guys must be doing something wrong. my friends mr2 with 1000cc injectors and an aeromotive 1000lph (i think thats what it is) gets 15mpg with just WOT runs. i'm not sure if thats the actual size of the fuel pump but it flows a gallon of gas every 20-30 seconds if its running at full capacity.

There's just something to love about this one...
Pumps a gallon of gas every 20 secs and gets 15mpg.
So, in theory, he's going 2700 mph when he's flowing at full cap?
(3 gallons/minute, 15 miles per gallon)

Not hating, just amused...

 

[aljordan]

Why don't you run your fuel pressure up to, say 45-50 psi and watch what happens to your gas milage. And your AFR's It's gonna make you run rich (of course) and your gas milage is gonna go down.

Umm.. I run 43psi static fuel pressure now. Thus.. fuel pressure has ZERO to do with fuel mileage.

The oxygen sensor will see any (as long as it's within 20% of the basic fuel calculation) rich or lean condition and trim fuel accordingly. This will achieve a stiochometeric ratio and you'll get the same milage as the guy who's on stock injectors. Unless your oxygen sensor is needing replaced.. which I'm willing to bet that 30% of them on the road are.

How about the aem guys seeing near 30mpg with 850cc injectors.

 

[aljordan]

Forgive me if I'm mistaken but aren't you the guy who recently claimed A/F ratios have no effect on EGT? Did your BSAT teach you that too?

Yup I did.. and yes.. it did. I don't think I said "no effect", however.

EGT's are mostly influenced by timing. You start to see this phenomenon when you deal with a standalone.

You ask.. why do my EGT's skyrocket when I lean my car out?

EGT's skyrocket due to timing being pulled. When you lean out the car too much, you start setting off the knock sensors. When the knock sensors.. sense knock, they tell the ECU to pull timing in order to save the pistons.

When timing is pulled (spark plug ignited later combustion stroke) you start introducing heat (due to ignition of air and fuel) later in the combustion cycle. Thus... EGT's rise.

If you want to see this yourself. Set your car to 0 degrees BTDC. You'll see 100C higher temps on your EGT guage. I drove for 130 miles this way on a new motor. Same air fuel ratios, just some retard set the retarded timing.

 

[bigaaron]

My mileage seemed to improve with the turbo upgrade and 550cc injectors. Like aljordan mentioned, it is gonna cruise at 14.7 a/f reguardless of the injector size. The fuel consumption will not increase unless you are on boost all the time. With a free flowing exhaust and intake on a healthy engine you really don't even use boost for cruising around, and with a bigger turbo it does not spool as fast or early so it's easy to keep the boost down when you don't want it.

 

[jdub]

Alan - And you're running a VPC and AFC...of course you'll be able to compensate. You're assuming everyone runs a fuel computer. With an AEM, you've replaced the entire ECU Apples and oranges.

If you run 43 psi with 550 injectors, the ECU will add too much fuel, it will run like crap, and mpg will suffer. Happens all the time...how many threads do you see about running rich after guys do this with no piggyback to tune fuel? The stock ECU can't pull enough fuel (shorten the injector pulse) to compensate unless it's tuned (w/ a piggyback) like Jeff said above. Your trying to tell me the fuel pressure and injectors are not the cause when that was the only things changed?

BTW - I'm running a Lex, 550's, Walbro, and AFPR. Right now, no piggyback fuel computer. I had to drop fuel pressure to "tune" AFR on my wideband from running rich. Before dropping the pressure...mpg was 17-18 and studdered under boost. After dropping pressure...mpg went to 21 and car pulled nicely under boost. Fuel pressure was the only thing I changed...guess it was magic since fuel pressure has no effect huh?

Here's link to a Toyota tech article on injection duration & controls...note the paragraph on page 2...."The amount of fuel injected depends on fuel syspem pressure and the length of time the injector is turned on":
http://www.cygnusx1.net/supra/Library/ToyotaTech/h43.pdf

Here's another link to a Toyota tech article on the EFI system concerning fuel delivery and injectors. Not specifically applicable to our discussion, but outlines how the system works.
http://www.cygnusx1.net/supra/Library/ToyotaTech/h22.pdf

 

[jdub]

retarding igntion timing will greatly effect EGT. Really.. a/f isn't an influence in EGT. The reason why people will see higher EGTs when leaning a car is due to the car seeing knock, and retarding the timing. WHen it pulls timing, EGT's riase.

EGT's are raised due to the point at which the heat is released in the combustion cycle. It is released later and later, and eventually, the exhuast will be open when heat is released (I'm being very simplictic here).
o
EGT's and air to fuel ratios.. really have no correlation.

This is what you actually said Alan

Yup I did.. and yes.. it did. I don't think I said "no effect", however.

EGT's are mostly influenced by timing. You start to see this phenomenon when you deal with a standalone.

You ask.. why do my EGT's skyrocket when I lean my car out?

EGT's skyrocket due to timing being pulled. When you lean out the car too much, you start setting off the knock sensors. When the knock sensors.. sense knock, they tell the ECU to pull timing in order to save the pistons.

When timing is pulled (spark plug ignited later combustion stroke) you start introducing heat (due to ignition of air and fuel) later in the combustion cycle. Thus... EGT's rise.

If you want to see this yourself. Set your car to 0 degrees BTDC. You'll see 100C higher temps on your EGT guage. I drove for 130 miles this way on a new motor. Same air fuel ratios, just some retard set the retarded timing.

I'm not sure where you get this from, but the knock sensors will not pull timing until they detect knock...leaning the mixture out will not necessarily cause knock as you alluded to in the FP/550 discussion. So explain what happens below WOT...say at 75% throttle. Is the ECU gonna pull timing due to knock? EGT's are not gonna go up due to leaning fuel out?

AFR greatly affect EGT...how do I know that? In piston powered airplane there is a red mixture knob...a control pilots are taught very early to respect. We set cruise mixture to get the best "MPG" by setting this knob using EGT as a reference. Mess this up and you'll be finding yourself a place to land pretty darn fast...there's more than one "smoking hole" out there due to leaning the motor, making EGT go through the roof.

There are no knock control systems in a piston aircraft...timing is fixed. EGT is the primary method to set power and economy (fuel flow). The engine is run typically above 75% for hours...100% for takeoff or go around. You manually adjust the mixture according to EGT...you can go to zero fuel (that's how you shut the engine down) to 100% fuel...complete control over the mixture. There is no ECU, no O2 sensor...the pilot is the ECU

Not too sure what school you went to, but pilots (and I am one) know a great deal about about this...AFR has a far greater impact on EGT than timing ever will.

 

[aljordan]

This is what you actually said Alan

Ya. That's it. Thanks for reinforcing my thoughts with an earlier post.

I'm not sure where you get this from, but the knock sensors will not pull timing until they detect knock...leaning the mixture out will not necessarily cause knock as you alluded to in the FP/550 discussion. So explain what happens below WOT...say at 75% throttle. Is the ECU gonna pull timing due to knock? EGT's are not gonna go up due to leaning fuel out?

Leaning the mixture will not always cause knock.. depends on where you start leaning it from. If you continue leaning, preignition (pinging) happens and the knock sensor pulls timing.

I get this from tuning an AEM on a talon for a three hours in addition to *weekends* spent with another AEM owner getting his car just right. I get this from a 4 year automotive degree from a NAIT (national association for industrial technology) accredited university. I get it from my own experiences.

I *CHALLENGE* you to do this. Set your timing to 0 degree BTDC. Drive the car at cruise on the highway at 80mph. Look at your EGT's. My greddy guage told me I was seeing 750C(ish) at the collector. Normally I'd see 600ish. I drove a round trip of 140 some miles that day. No damage to the car.

Do this.. and get back to me. Tell me that EGT's aren't influenced by timing.

AFR greatly affect EGT...how do I know that? In piston powered airplane there is a red mixture knob...a control pilots are taught very early to respect. We set cruise mixture to get the best "MPG" by setting this knob using EGT as a reference. Mess this up and you'll be finding yourself a place to land pretty darn fast...there's more than one "smoking hole" out there due to leaning the motor, making EGT go through the roof.

So.. leaning out by 5% across the board shows a difference on the egt guage? How much of a difference? 10%? How much hotter does 10% get you?

Didn't you bring up comapre apples to apples?? An aircraft that travels at 10k feet above ground compared to some a car that travels on the ground.

There are no knock control systems in a piston aircraft...timing is fixed. EGT is the primary method to set power and economy (fuel flow). The engine is run typically above 75% for hours...100% for takeoff or go around. You manually adjust the mixture according to EGT...you can go to zero fuel (that's how you shut the engine down) to 100% fuel...complete control over the mixture. There is no ECU, no O2 sensor...the pilot is the ECU

I don't know much if anything about aircraft motors.. so I can't comment on this. How much resolution does this EGT have?

Not too sure what school you went to, but pilots (and I am one) know a great deal about about this...AFR has a far greater impact on EGT than timing ever will.

I used to think that EGTs were influenced by air/fuel ratios. I was on a forum started by Corky Bell many years ago (even have an autographed copy of Maximum Boost by him :icon_bigg ). He was the one that explained it to me years ago. I didn't believe him and questioned it further. He was very technical in his explanation. It took me a while to see it, but eventualy I did. All of this was further reinforced by my personal experiences on a dyno and aem time.

 

[7MGTEsup]

I would like to back up Al on this one, I accidently drove my car with the base timing at 10 degrees after tdc I only drove it for about 5 miles and it got very hot indeed. Timing has a massive influance on egt's.

 

[TurboWarrior]

I have the lex and 550s thought the car hasn't run yet. should I bring out the screw as much as possible? I didn't know it ran THIS rich with 550s/lex

 

[jdub]

The Lex/550 combo doesn't run rich if tuned with a SAFC (or other piggyback w/ fuel control ability...or standalone EMS). Lacking the electronics, the only way (I know of) is to adjust the fuel pressure. You need a wideband O2 to see what's happening to AFR's in both cases. You can get a bit more bypass air with the screw to lean it some.

 

[TurboWarrior]

alright cool thanks jdub. Next thing on my list is an safc

 

[aljordan]

Alan - And you're running a VPC and AFC...of course you'll be able to compensate. You're assuming everyone runs a fuel computer. With an AEM, you've replaced the entire ECU Apples and oranges.

I could do corrections, but I don't. I run the dials straight up on my afc, and the vpc in order to have an unmodified timing map. Car runs well under WOT and at cruise. Seeing the FJO bounce between 14.5 and 15.5 once the car (oxygen sensor) is warmed up.

This is a basic principle on how modern automotive EFI systems work. There is a basic fuel calculation (BFC) that is done by reading afm hz. This sensor is the input for the basic fuel calculation (CTS, IAT, TPS, o2, are modifiers). This is an approximation on what the car needs in terms of fuel to match the incoming air. Once this BFC is done, the computer will look at the oxygen sensor to fine tune the mixture in order to acheive a stiochometric ratio of 14.7 to 1. Toyota has an ecu output called "vf" that shows you how far off the BFC (+modifires) is compared to 14.7 to 1. You can also look at this as how hard the oxygen sensor is working in order to reach a stoich condition. See information on this on the SONiC site.

If you run 43 psi with 550 injectors, the ECU will add too much fuel, it will run like crap, and mpg will suffer. Happens all the time...how many threads do you see about running rich after guys do this with no piggyback to tune fuel? The stock ECU can't pull enough fuel (shorten the injector pulse) to compensate unless it's tuned (w/ a piggyback) like Jeff said above. Your trying to tell me the fuel pressure and injectors are not the cause when that was the only things changed?

As stated above.. I have no correction on my setup and think I get get good mileage. Granted I've not checked mine since the rebuild, but I did do 185 miles in a tick over half a tank (fuel gauge reading). The lower half too. We all konw how quickly that lower half of the tank goes.

I would say the people who are suffering from bad mileage should look at their car. Specifically the osygen sensor. That sensor is the most important piece in the quest for fuel mileage.

BTW - I'm running a Lex, 550's, Walbro, and AFPR. Right now, no piggyback fuel computer. I had to drop fuel pressure to "tune" AFR on my wideband from running rich. Before dropping the pressure...mpg was 17-18 and studdered under boost. After dropping pressure...mpg went to 21 and car pulled nicely under boost. Fuel pressure was the only thing I changed...guess it was magic since fuel pressure has no effect huh?

Driving style would deffiantely make a difference of 3 mpg. This comparison can't really be made unless you drive on the same stretch of highway in similar ambient conditions with the only change being a drop in fuel pressure. Highway mileage is a stellar way to see mpg changes. Luckily, or unluckily, I used to drive an hour on the interstate to school. 63 miles one way. Excellent way to check highway mileage.

Here's link to a Toyota tech article on injection duration & controls...note the paragraph on page 2...."The amount of fuel injected depends on fuel syspem pressure and the length of time the injector is turned on":
http://www.cygnusx1.net/supra/Library/ToyotaTech/h43.pdf

The above is strictly concerning fuel injectors and EFI enrichment. These are the modifiers that I touched on above. Of course more pressure/ bigger oriface will increase output.

Here's another link to a Toyota tech article on the EFI system concerning fuel delivery and injectors. Not specifically applicable to our discussion, but outlines how the system works.
http://www.cygnusx1.net/supra/Library/ToyotaTech/h22.pdf

My Bachelor of Science in automotive technology lets me know this already.

Bottom line is this.. If you're seeing an air to fuel ratio of 14.7 to 1 you're using one part fuel, for every 14.7 parts of air. No matter what injectors you run or what your fuel pressure is. The oxygen sensor is there to ensure the car runs at 14.7 to 1 for a "good" blend of emissions, reliabilty, and driveability. It is that sensor's sole purpose and it does this very well. IF your wideband isn't showing a ratio around stiochometric, then it's time you looked into replacing it.

 

[Nick M]

You both are correct. The ECU will try to lean out the rich mixture that will happen.

I always thought stand alone will get much better fuel on cruise. Even the 5.0 got about 28 mph going 75+ on the highway. Sequential injection FTW. Wait, AEM can run sequential can't it?

 

[donnys90T]

My Bachelor of Science in automotive technology lets me know this already.

Forgive me if I'm mistaken but aren't you the guy who recently claimed A/F ratios have no effect on EGT? Did your BSAT teach you that too?