VE table numbers what do they mean, question about 83 pound injectors too

D

Dave King

Guest
Does a specific number represent a specific amount of fuel? Does
anyone have any experience with 83 pound injectors in a low 9 second
car at 3000 pounds?

I believe I"m throwing too much fuel at it that
the spark can't burn the amount of fuel I"m throwing at it. My EGT's
and spark plug readings aren't indicating that I"m throwing too much
fuel at it, but the speed Pro is reading 95%-98% duty cycle at 290kpa.
Thus I"m getting a lean spike thru the datalogger on the a/f. I believe that
the misfire reads lean on O2 due to the fuel NOT consuming the oxygen.
Does anyone know what typical VE table numbers are for 83 pound injectors
at a 800 hp level?


Dave King
97 Mustang Cobra
EDIS Ignition
9.4 at 147 mph
 
VE = volumetric efficiency.

Consider what would happen if you could keep the intake valve open for a long time. Say a minute :)

The pressure in the cylinder would equal the pressure in the intake manifold, right? If you measured the amount of air in the cylinder, it would be the highest possible amount of air you could get in it, the theoretical maximum.

Now get the engine moving, the valves are opening and closing fairly fast, and the cylinder does not get filled completely. Measure the amount of air that does get into the cylinder and you get the real life air flow.

Now divide one by the other, real life/theoretical maximum, and you get the volumetric efficiency. The close that number is to 1 (or 100%), the more air you are flowing for a given set of conditions.

This is important, because the computer can calculate what the theoretical maximum air flow is, but without a mass air sensor it doesn't know what the actual air flow is.

So it figures up the theoretical max air flow, and looks up the VE value that you gave it. It multiplies the 2 together to get the actual, real life air flow. Once it knows that, it knows how much fuel to squirt to match that air flow.

The VE should hit a maximum at your torque peak.

The VE is not a function of fuel injectors, it is a function of your engine mechanicals (heads, cam, intake, turbo, etc...) and rpm and boost.

Hope that helps

John Estill
 
My car weighs around 3250 and judging by 1/8 mph it should run 142-143 in the 1/4. I have 83's. If I remember correct, my duty cycle has never been over 60%. I know of a 1200 hp twin turbo Mustang that ran 83's & DFI. But I read about a car that was maxing out 96 lb injectors at less than a 1000 hp. I'm not an expert here, so I guess I can't help much. But I've always wondered how the above example could happen. What are your VE #'s? Are they close to or at 100%?
On a side note, it seems like someone told me they've seen VE#'s over 100. Maybe I misunderstood him becuase that's not possable right?
 
I'm with Bobo on the duty cycle.

800 hp x 0.5 BSFC = 400 lb/hr

400 lb/hr / 8 injectors = 50 lb/hr per injector

50/83 = ~60% duty cycle (assuming the injector is linear)

Unless your engine is really inefficient, but even a BSFC = 0.7 still gives a ~85% duty cycle.

As for a VE > 100%, a tunnel ram can do it (or so I've heard), but only in a fairly narrow rpm range. Without a tuned intake like that I don't think it's very likely, and with a turbo car I'd think it's damn near impossible due to backpressure. But then I don't really know that for a fact...

Some people like to reference VE to atm pressure rather than manifold pressure, that would mean you'd have a VE of something like 270% at 3 bar MAP.

John
 
I also agree that you should not be maxing out your injectors. 8 83 lb injectors should max out at about 1300 hp.

I think you need to make sure that your fuel system is flowing enough fuel to the rails. If you aren't, it could explain your high duty cycle. How much O2 correction are you seeing? Is it maxed out?

Craig
 
what are you running for a fuel pressure regulator? you're saying 270kpa, so that's about 25psi of boost... so you're fuel pressure needs to be going up 25psi when the boost comes in... otherwise you could be seriously limiting your injector capacity... for example, if you didn't have a boost referenced regulator, 83 lb/hr injectors would be more like 53 lb/hr injectors at 25psi of boost (assuming a base fuel pressure of 43psi) because you need 25psi of fuel pressure just to "break even".. the extra pressure beyond that can actually squirt gas into the cylinder...

maybe this isn't your problem, but this effect could definitely explain what others were talking about with larger injectors maxing out at lower power on one car vs. smaller injectors with more power on another...
 
My VE tables are over 100, my numbers go as high as 108-110. I didnt know VE
numbers = percentage. is the numeric number 100=100% maybe thats my problem.
Right now I'm running a fuel cell to a Weldon 2035 thru a dash 12 line. Then I come out of the pump into a dash 10 line up to the rails. I'm using a Weldon Regulator that is boost referenced. All supply line is dash 10.

My boost climbs with RPM all the way to the highest point I can take it (8000 rpms) boost is approx 290-295 kpa at that point (I'm running a NOVI 2000 and its drawing about 1500 cfm into the engine).

The engine is a built up 4.6 32 valve Ford Mod motor. Lots of work to the intake,
heads, and big headers (1 7/8 to 2" into a 4" collector)


My VE table numbers are 107-108 at that point thru the overlay with the datalogger of the run. Timing is only at 17 degrees. EGT meters max peak temp reads 1150-1175 by the 1000 foot mark, and 1190-1225 thru the lights. My plugs are just right. They
aren't black, pitted, lean, or pepper on the ceramic. I am wondering though if they
are cleaning themselves up with the time it takes you to exit to the return row and
make way back to the pits.

To me it seems like a too rich condition at 8000, it almost sounds like I'm hitting
the rev limiter but I'm not (set at 9000 thru both fel pro and msd) I believe
the spark can't burn all the fuel I'm throwing at it.

I just didnt want to start to lower the VE tables without knowing and educating
myself a bit more about what the VE table numbers mean.
 
Originally posted by Craig Smith

I think you need to make sure that your fuel system is flowing enough fuel to the rails. If you aren't, it could explain your high duty cycle. How much O2 correction are you seeing? Is it maxed out?

Craig

Fuel system is plenty. WELDON 2035, dash 10 supply, and Weldon regulator
with boost reference. I don't use the car in closed loop. I set to run it in open loop
because of the 4" collectors and I run open headers.
 
Originally posted by JeffB
what are you running for a fuel pressure regulator? you're saying 270kpa, so that's about 25psi of boost... so you're fuel pressure needs to be going up 25psi when the boost comes in..

I'm running a WELDON regulator that has a vacuum line from the map sensor for reference. FP at 27 psi is 77 psi.
 
Originally posted by Dave King


Fuel system is plenty. WELDON 2035, dash 10 supply, and Weldon regulator
with boost reference. I don't use the car in closed loop. I set to run it in open loop
because of the 4" collectors and I run open headers.

If you are interested in running in closed loop, you can do it even with the big open collector. You just can't do it at low RPM or exhaust reversion will kill you.

On my car, I set closed loop to turn on at about 5200 RPM and it worked great. Once the motor is wound up and you get a good steady airflow across the sensor it's OK.

If your tuneup is good, the car won't necessarily run any different in closed loop. I just feel that monitoring O2 correction makes tuning the car as easy as possible, since you can apply the O2 correction values to the values in your VE table. It takes the guesswork out of the equation. Just some food for thought... :cool:

Anyhow, as far as your duty cycle goes, I don't get it. From all the info posted here so far, I have no clue right now why you are using so much injector. Sounds like everything is set up correctly.

Craig
 
OK, I take back the comment about not having a clue. The fact that you have a blower never really set in until now. A couple other things...

First off, your supercharger requires quite a bit of power to run. We've seen blowers like yours take 200 or more horsepower just to turn them! With the pipes disconnected from the blower, we have seen dyno tests with the belt on and off just to see what kind of effect merely spinning the blower had on the engine. As stated above, the blower takes plenty to run.

So, for however much power you are making, you also have to figure in the power it requires to turn the blower as well. If you have a 900 hp motor with a blower that takes 300 hp to turn it, you have to provide 1200 hp worth of fuel to the engine. That's why blower engines usually have higher BSFC.

Also, are you intercooled? If not, big inlet air temps often require you to throw a lot of extra fuel in to keep things working OK.

Given this, I suppose that maxing out 1300 hp worth of injector in a 900 hp motor isn't so ridiculous.

Craig
 
Craig, small question for ya. I'm running closed loop all the time now. But the car gets really rich on the 2 step/trans brake. I need the 2 step for somewhat control over the boost. Say if I was launching at 4000, what #'s do I need to type into my ecu? I'm not around my car now so I can't remember exactly how that screen goes. I remember there was a min rpm and max rpm right? Sorry to get off the subject lol!
Dave, I can't wait to see that 4.6 at some Mustang races. Why didn't ya go turbo? Granatelli has been on the warpath with his turbo/4.6. But I know ya got more left. I think I read about a guy that went high 8's with a simliar combo to yours right? But he weighed like 3300? I'm still haveing a hard time understanding 108% VE :D Good luck Dave.
 
So is the number 108 in the table mean 108%?

Anyone have any thoughts on the over rich condition?
 
You definitely don't want to be in closed loop when you are on a rev limiter. The misfire causes the O2 sensor to go NUTS and it may lean you out or fatten you up.

Your best bet is to set closed loop to turn on just above the 2 step RPM. Let's say your 2 step is at 4000. Set closed loop HI RPM to 4200 and set the low RPM to 4000. This means that it will go into closed loop when you exceed 4200 and go back into open loop when you drop back below 4000.

Craig
 
Dave it is 108%, but I don't think that actually tells you it is rich. I think it just means your motor is very efficient?
Craig, my car was running really rich on the 2 step/transbrake. It would go to like 9:1 a/f when I let go of the button. I just assumed the fuel wasn't getting burned in the cylinder. The thing that I realized is scary about that is my O2 is in the header (gonna be moved to the dp) and the fuel would have been burning in the header right in front of the O2? :O
 
Dave -

I'm curious, how did you get to your VE values? Where did the 100+ numbers come from? Do you have the wide band O2 sensor to use if you want it, or are you just reading plugs and such?

I don't know if a supercharged engine can really get over 100% or not. Your numbers could be real, might not be, I dunno.

Just FYI, just because that NOVI is *rated* at 1500 cfm doesn't mean it is actually pulling that. The cfm depends on engine speed, pulley speed, local atm pressure, intercooled or not, etc... Lotsa variables. If you aren't intercooled, at your 8000 rpm/28 psig/100% VE you are probably closer to 1300-1400 cfm, and the supercharger is sucking about 160-175 hp off your crank. If you don't have an intercooler, I would estimate you see 375-400 deg manifold air temperatures at that 8000 rpm point. True?

John
 
re:

Plus don't forget, the VE table numbers are affected by the inj size entered. For example, if you tell the box 100 lb inj but really only have 90 lb for whatever reason then the VE table numbers will have to be "artificially" inflated to make up the difference.

TurboTR
 
If 108=108% how is this possible? How can you tell the injector to stay on longer than 100% of the time?

By the way the NOVI 2000 is rated at 1700 CFM. I'm estimating that its moving
1500 CFM right now. My discharge temps are around 235 to 240 degrees.

Right now I'm running closed loop but I"m not giving the 02 sensor much control right now. I'm not letting it remove any fuel and I'm only allowing it to add 5% fuel
above 200 kpa. I"m idling in open loop because of the 4" open collector and the
02 sensor placement.

For tuning, I have the 02 sensor and correction data info datalogged on each run and
I"m looking at the spark plugs and EGT's and A/f from the sensor's data log to determine fuel trim. Like I said I'm only allowing the 02 sensor to have very little control because of my setup (02 placement, open exhaust, leaded gas, big $$$ to
repair if I run of fuel)

I another reason I run the program with very little 02 control is because I don't feel
the numbers (a/f) on the 02 sensor jive with the other tuning data (plug readings, EGT's) and plus I don't see any black smoke coming out of the exhaust going down the track.

It's not hitting any rev limiter at 8k it just feels like it. The Fuel rev limiter on the speed pro is set to 9000 rpms and the MSD box is set to 8750 rpms. It's like I'm hitting a stone wall at that point. In my opinion I feel
that either 1 of 2 things is happening.

1. I'm throwing too much fuel at it and the ignition can't burn the fuel fast enough.
2. The MSD EDIS ignition is not up to the task. With the EDIS type ignition there
is only one choice for a spark box. IF this is the case I"M SOL.

Right now I"m setting up my VE tables so that the numbers are going up in RPM and per KPA. They aren't maxing out at Peak torque (6800) and tapering off.

I just wanted to educate myself to this program, the values, and the meaning of the tables before I went any further. I have someone very knowlegeable to help me tune but he never used Fel PRo before. He's an electromotive expert. I definetely do not want to run out of fuel at 28 psi!~
 
One more question I would like to throw into the pot since everyone is being
helpful is a question about inputing injector size and VE table numbers.

Say if a car is perfectly tuned. A/F is perfect, plugs, and EGT's look great.
But the car is running a little high on the duty cycle. If this person had 83 pound
injectors and wanted to go to 96's or 160 pound injectors to reduce the duty
cycle, would that person only have to go into the global parameters and enter
the size of the new injectors he would buy or would further tweaking of the VE tables be necessary? Would the speed pro automatically calcuate the difference needed
(VE) because an injector size changed physically and was inputed in the global settings properly? OR would I need to reduce the VE table numbers and retune the car?
 
Originally posted by Dave King
If 108=108% how is this possible? How can you tell the injector to stay on longer than 100% of the time?

108% VE does not equal 108% injector duty. The VE is just used in calculating the actual air flow the engine is seeing, that is then used (with the a/f ratio and injector size) to calculate the inj pw required to match.


By the way the NOVI 2000 is rated at 1700 CFM. I'm estimating that its moving
1500 CFM right now. My discharge temps are around 235 to 240 degrees.

Really? Only 240 deg? Non intercooled at 28 psi?

And a good point from Mr. TurboTR, are you SURE you have 83 lb/hr injectors?

John
 
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