I noticed something rather interesting today and can't explain it so maby someone on the board can help me . I installed larger M7 fuel injectors today to further fine tune the M7/venom nitrous kit allowing me to utilize a larger nitrous jet with an even greater margin of safety and was fully expecting to suffer a bit in the fuel economy area. Surprisingly enough on the 45 mile ride home at a average speed of about 60 mph I was astonished to get 46.1`MPG where I usually get the low 30's at best. I admit i was using my best manners driving as I was continually monitoring the mpg average waiting for it to take a dive. I have no idea why bigger 420 cc M7 fuel njectors verses stock 340cc injectors would yield better cruising mileage.If this trend holds then the amount of the four new injectors at $640 minus $320 after the core charge for the stock injectors are returned will pay for itself rather quickly. The amazing thing is this all came about while trying to maximize a performance increase not as a economy measure. Any body have some thoughts on this ?

 

Sure. The answer is simple. Your computer is lying to you :smile: Well, its more like your injectors are lying to it?? The computer calculates MPG based on the injector pulse width of the stock injector. When you install larger injectors, the computer shortens the pulse width at partial throttle to mantain stoich but the MPG computer doesnt know that and never will. The MPG computers use incredibly complicated algorithms to calculate the MPG and you'll never be able to get that going again. Kiss that function bye bye


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Cheese

 

>>When you install larger injectors, the computer shortens the pulse width at partial throttle to mantain stoich
>>
>>--
>>Cheese
>>
>>

Would this be true with the Speed Density system that the Mini Has? I would have thought it wouldn't have known new injectors were installed and maintained the same pulse width and with a larger injector, injecting more fuel.

I also wouldn't use the computer to determine true MPG. Would be better to fill up, drive and fill up again and calculate MPG.

 

>>Sure. The answer is simple. Your computer is lying to you :smile: Well, its more like your injectors are lying to it?? The computer calculates MPG based on the injector pulse width of the stock injector. When you install larger injectors, the computer shortens the pulse width at partial throttle to mantain stoich but the MPG computer doesnt know that and never will. The MPG computers use incredibly complicated algorithms to calculate the MPG and you'll never be able to get that going again. Kiss that function bye bye
>>
>>
>>--
>>Cheese
>>
>>

I believe macncheese say it all.

Bigger injectors doesn't mean better MPG it just more HP..but is nice to have one because I myself can't affored

 

>>Would this be true with the Speed Density system that the Mini Has? I would have thought it wouldn't have known new injectors were installed and maintained the same pulse width and with a larger injector, injecting more fuel.

Only @ WOT (open loop). If maxmini has a OBD logger he'll see the difference in his fuel trims.

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Cheese

 

the problem I see with bigger injectors is at WOT using the standard map. An already rich condition will be richer. fine when you need it (hitting the nitrous button), but what about WOT when the nitrous is shut off?

I thought the M7 Venom was included with a piggy-back. pulse width modifier, based on nitrous demand, and supplied with larger injectors with the needed supply ability, so does it also include a new fuel map for the before-piggy WOT condition using the larger injectors?

 

>>the problem I see with bigger injectors is at WOT using the standard map. An already rich condition will be richer. fine when you need it (hitting the nitrous button), but what about WOT when the nitrous is shut off?
>>
>>I thought the M7 Venom was included with a piggy-back. pulse width modifier, based on nitrous demand, and supplied with larger injectors with the needed supply ability, so does it also include a new fuel map for the before-piggy WOT condition using the larger injectors?

Good Morning everyone.......

Maxmini's finding did come as a surprise to me to as my own car has been running with the bigger injectors for at
least a 3 months, I have personaly not found any fuel savings above and beyond I originaly found with the M7 PB.
I will ask maxmini (randy) to calculate the fuel consuption the old fashioned way I'm sure he will not mind.

Regarding the new injectors we originaly decided that a larger injectors would be necessary above and beyond 240 HP
which is very easy to accheive with the M7/Venom system. With bigger injectors low speed and idle charcteristics
usualy suffers but in this case none of that showed it's ugly head, the car has better cold start ability and the idle is
spot on with no rpm fluctuations. At WOT (no nitrous injected) car pulls strong with no sign of bogging or running
overly rich, and to prove that the car is running strong last time on the dyno with only M7PB and Supertrapp
exhaust and injectors we ran 6hp stronger then a car with everything but a pulley.

Regarding the nitrous computer yes it does change the pulse width as the O2 sensor senses a lean condition.
The kit will be supplied with larger injectors as we found that the ECU will start to pull back on the throttle,
basicaly it will dropp the supply volage to the throttle by half at 5k rpm making it pretty hard to get a clean run.
Up to this point I been testing different valves and currently running at about 275hp with no leaning out or
other annomalies.

And as always please call me any time for questions etc.

peter horvath
562-712-3270



_________________
Lightest and fastest in SoCal

 

Peter,
Can you comment on your fuel trim values? I'm curious what your LTFT value is.

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Cheese

 

Great, some info that agreed with mine on fuel injectors, just waiting for someone to post......

Stock injectors have a 185 crank HP limitation

 

>>Great, some info that agreed with mine on fuel injectors, just waiting for someone to post......
>>
>>Stock injectors have a 185 crank HP limitation

I don't get it. If the stock fuel injectors are only good for 185 crank HP then how are people pulling 185+ wheel HP without changing the injectors? Pully/ECU/Intake/ehaust is reported as giving 185 at the wheel and about 205 at the crank. I don't get how if the injectors won't give enough fuel.

 

It is due to the 80% duty cycle, which stops it at 185HP, but since the requirements are higher the duty cycle goes up at 100% duty cycle(which is not good) the injectors are capable of supporting 235hp, but the life of the injectors will be comprimised to overheating the injector.....it is recommended to stay below 80% duty cyle to give the injectors a chance to "cool".....

 

refraise the 100% can go to 100% it doesnt jump from 80 to 100 it can be anywher inbetween

 

>>
>>>>Would this be true with the Speed Density system that the Mini Has? I would have thought it wouldn't have known new injectors were installed and maintained the same pulse width and with a larger injector, injecting more fuel.
>>
>>Only @ WOT (open loop). If maxmini has a OBD logger he'll see the difference in his fuel trims.
>>
>>--
>>Cheese
>>

Just so I understand this, are you saying that the system will run closed loop anytime you are not at WOT? If that's true when you add a SC pulley, your engine will only run leaner at WOT and not at all power settings, correct?

 

>>Just so I understand this, are you saying that the system will run closed loop anytime you are not at WOT? If that's true when you add a SC pulley, your engine will only run leaner at WOT and not at all power settings, correct?
>>


You are correct, sir. That's how EFI keeps emmissions in check.


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Cheese

 

Any car using injector pulse width as a function in the fuel mileage calculation will have this readout in error if the injectors are changed for higher (and for that matter, smaller) flow, changes in fuel regulator pressure settings, or higher pressure fuel pumps. The fuel mileage function is a relatively simple implementation to add to an ECU, but it is soley dependent on the original fuel flow characteristics of the injection system.

You take an injector with x flow rate at a given pressure. Take the rate times the amount of time the injector is open (pulse width) to get a fuel 'packet'. Add together and average out the number of 'packets' over a given distance and you arrive at good approximation of fuel usage. Unfortunately, this calculation relies on a 'dead reckoning' assumption that the theoretical design values have not been changed. Changing injectors, regulators, etc, upset that assumption, and unlike the closed-loop fuel delivery system which compensates for increased fuel flow, the calculation is entirely 'open loop' in operation; it cannot correct itself.

This also explains the sometimes wide variance in people's gas mileage figures; fuel regulator values and such do vary from car to car, and directly affect the mileage reading.

 

Theres a lot more going on then just injector pulse width. Its actually setup for the specific injectory used, factoring in the opening and closing times of the injector, the MAP values, etc. This is why you'll never see an aftermarket MPG gauge.

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Cheese

 

I had no idea this would be such a interesting thread. I see what you all are saying and it makes total sence especially since today i saw 51 mpg for a bit LOL . I am in the process of doing it the old school way and will let you know as soon as the tank is down. Randy

 

Finally put a tank full thru with what I call a well rounded variety of miles. Some canyon, some hwy crusing a few nitorus pulls and the usual city driving. Got 280 miles with 11 gallons of fuel for a 25.45 MPG average. This is suprisingly close to normal for me which was a bit of a relief as I thought for sure I would suffer in that dept due to the larger fuel injectors. Its all good , Randy

 

>>Finally put a tank full thru with what I call a well rounded variety of miles. Some canyon, some hwy crusing a few nitorus pulls and the usual city driving. Got 280 miles with 11 gallons of fuel for a 25.45 MPG average. This is suprisingly close to normal for me which was a bit of a relief as I thought for sure I would suffer in that dept due to the larger fuel injectors. Its all good , Randy

Randy,
25 to 26 mpg are decent numbers for a highly modified MCS like yours. You have better power and still reasonable MPG in mixed driving. Normally we usually worry that a performance mod might hurt mpg a bit. Sometimes the reduction in mpg is merely due to our more enthusiastic driving habits after the upgrade. The MINI computer is often fooled but it is a fun gadget to watch and wonder.

 

I agree with you 100 %. Its not that the mods necessarily use more fuel its that the car is so much more fun to drive harder . You have to hear what this thing sounds like with the tuned header and borla race system with the center resonator removed. I had it without the cat at first but decided to put the sotck cat back for now but remove the resonator. It was even more interesting then :smile: Randy
>>
>>Randy,
>>25 to 26 mpg are decent numbers for a highly modified MCS like yours. You have better power and still reasonable MPG in mixed driving. Normally we usually worry that a performance mod might hurt mpg a bit. Sometimes the reduction in mpg is merely due to our more enthusiastic driving habits after the upgrade. The MINI computer is often fooled but it is a fun gadget to watch and wonder.

 

Bringing back up the topic of fuel injector sizing (I just love Grassroots Motorsports Magazine):

If the stock injectors are 340cc:

Either our BSFC is .60 and they are only sized for 163 bhp or our BSFC is .50 and they are sized for 200 bhp:

BSFC = Brake Specific Fuel Consumption (ranges between 0.4 and 0.7)

Flow rate = (max bhp x BSFC)/(# of cylinders x safe max duty cycle) x 10.515

 

Andy If it helps the calculations at all but the injectors are now 400 cc. Randy

 

You know what is even funnier than getting better MPG with larger injectors? The fact that MaxMini can come and talk like he is a customer with no link to M7.


BOO

 

>>You know what is even funnier than getting better MPG with larger injectors?
>> The fact that MaxMini can come and talk like he is a customer with no link to M7.


Ah Hahahahahah

I thought I was the only one who thought that!!!!!

 

y two favorite internet sleuths at work again. I admit it I am so ashamed for deceiving you all. While I am at it let me list in alphabetical order the companies I am presently sponsored by or have an association with so you can all sleep better at night :smile:

BMP/Pro Mini
Borla Exhaust
Bridgestone Tire
Car Sound and Performance Magazine
Denson USA
Diamond Audio
Diamond Racing/Pipercross USA
Falken Tire
K&N
Meguairs
Moss Mini
M7
Pilo
Rogue Engineering
Traffic Jammz
Valvolene
Wheel Power

Now with as much authority as you two seem to have in internet land I am sure that many companies have realized your worth to the mini community at large and have sought you out for opinions, evaluations and exposure for their products in far greater numbers than my simple project here. Perhaps you would care to share some of your supporters with the viewing audience . I mean looking at the vast amount of posts with such authority on such a wide selection of mini related items you guys must have companies beating down your door to have you work with them.