One of my "estimed colleuges" [sic] has pointed out I didn't really add much info to thread as far as the original subject... ??!!? (bastid /ubbthreads/images/graemlins/wink.gif )
He has a point ... I do tend to ramble ... /ubbthreads/images/graemlins/blush.gif
Thing is, I want to know the answer to these kinds of questions as well.
Only way to get there is to have a discussion, and bounce ideas off each other.
I'm not scared to show my ignorance on the subject if it brings the smart guys out to post. (even if all they do is correct my ramblings for technical accuracy /ubbthreads/images/graemlins/rofl.gif )
On topic,
I think every motor and/or parts combo is going to have a different volumetric efficiency from cylinder to cylinder, and it's going to be really hard to identify/quantify what each specific engine is going to need.
Something as simple as just a couple thou wider valve margin, or a slightly thinner valve seat can really skew things from cylinder to cylinder in the head.
Something as simple as a different style throttle body bolted to a "tested" intake manifold could make mockery of it's "as tested" variance numbers. Hell, even a teeny difference in the throttle opening angle/butterfly angle at wot from t-body to t-body can bias the flow and could skew the intake manifold flow numbers enough to measure.
It will be hard to predict or quantify the requirements of each cylinder when every build will have a different cylinder to cylinder variance, even if they use the same parts. It comes down to that particular parts combination, on that particular head casting, with that set of machined surfaces, breathing thru that specific mani.
Sure, you get some numbers on the mani...
... but they are most likely going to be from the manifold manufacturer (or someone with an axe to grind)
Sure you can get some numbers on the head...
... but that's also likely to be a little problematical, as those numbers will (most likely) come from your porter...
... and ...
I don't want to sound like an ass, but it's been my experience that it's unlikely that you'll get the straight scoop on some things from most porters a lot of the time. (been in the business awhile, I've measured a few myself, and I take their numbers with a grain of salt /ubbthreads/images/graemlins/wink.gif )
Nobody wants to admit there is a variance in their work, and at the very least, they will understate the actual "variance" number.
That actual number is probably going to be a bit misleading, as well.
A port's ultimate flow number is just one number of many that matter when it comes to discussing this issue.
At various heights in the valve opening, all the different variables in port entry angle, valve margin and seat width/angles will come into play, and the possibilities are just endless.
Add in the harmonics occuring in the intake manifold like Curtis's heimhertzialerical1l .. er ... alzheizehemineres...errr ... pressure wave/resonances (or some such, dunno, skipped school that year /ubbthreads/images/graemlins/blush.gif ) and all bets are off as to which specific cylinder is going to get a bigger gulp of air on that particualr intake cycle.
I believe there will be a pattern, and it may very well be similiar to what another engine with the same parts package will manifest, but it would be a little rambunctious to assume that all motors of a particular make will have the same flow imbalances.
... just too many variables ...
In addition, injectors are rated by quantity discharged over time, and the measurement printed on the paper that accompanies the injector set can be a little misleading.
Hopefully, keydiver will join this discussion, because he knows more about the subject than anybody on the web.
My experience has been that the manufacturers match their injectors to a tolerance at a given duty cycle. The plus/minus variance at other duty cycles is their dirty little secret. Most of the time they do a pretty decent job of manufacturing to a price point/flow accuracy. The numbers from them can generally be trusted to be reasonablly accurate at their given duty cycle.
The flow charts you get back from (some) of the cleaners is another story, altogether.
At the risk of stereotyping them all, (some do a really nice job) the companies doing this task just pop it open, hold it open for a time period and then measure the volume discharged during that time frame.
This doesn't really take into account the dynamics that an injector will "see" in a running engine.
The injection times are short
(milliseconds),
and the injector will spend quite a bit of that time just opening and closing at lower duty cycles. The fuel discharged on each injection cycle will be contingent on the same things that will affect flow past a valve/seat. Mechanical variances in the machining of the matching ball/seat or pintle end will affect the flow at low openings a whole sh*t ton.
An injector will spend quite a bit of time on an engine in the opening/closing part of the cycle at low duty cycles. There can also be variances in how quickly an injector "snaps" open. Any corrosion on electrical connections in the car (especially at the injector plug) will affect the juice available to make the injector function. An injector running at a lower juice level just has to react slower, and open later. This will decrease it's delivered fuel quantity.
Variances in their opening/closing times will affect the dynamic flow much more than you would imagine.
A few years back, I put a piezio electric mic on the each of the four individual injectors, and then passed that signal into a rta set-up (good to have friends in the car stereo biz!) It was really interesting to see the plots of their operating sound versus each other. At different duty cycles, they gave up their dirty little secrets, and the results really suprised us. Not all injectors are linear, and some are worse than others. As they near the end of their service life and/or need to be cleaned, the sound they make tells the tale, that much is for sure!
It doesn't seem like it'd be too hard to fab up a simple little timing rig to pulse the injectors at different duty cycles and measure the result. If they are pulsed to an accurate, repeatable timeframe, some points could be plotted on a graph and a nice flow chart/graph could be generated. Giving a +/- flow variance rating at various duty cycles/flow rates would enable a discerning tuner to dial in a combination to a much higher degree of accuracy. I'd love to see Curtis build us a pump/lines/injector rail test fixture. Then, we could get the geeks in on an injector driver package that would let us cycle the injectors at different duty cycles. I'd love to see if we can learn something about that aspect of injector matching (Curtis, wanna get on that? I think the 4am time slot is open in your schedule /ubbthreads/images/graemlins/tongue.gif )
Then there's the injectors actual physical position in the fuel rail to consider. The dynamics of what's going on there is waaay beyond my comprehension level.
Does #4 get more than #1 just because it's closer to the feed entry?
I dunno for sure, but on stockish cars, probably not. One good thing about the mitsu fuel rails is they have a pretty large internal volume compared to many other manufacturers designs. This will help minimise the affects of location on the injected fuel quantity from each injector station.
On a monster twin pump mack daddy system, all bets are off, and there may be a significant advantage to feeding both ends of the rail, and pulling the exccess fuel out past an fpr located in the center of the rail.
Don't see it much on mitsu's, but we used to upgade the factory end feed system on the inline datsun z six cylinder motors, (and it helped a sh*t ton). Those were a long rail/small diameter feed, and theese are short rails, with a large internal volume, so there may not be much gain there untill you get to silly fuel flows on mongo injectors...
But, in these motors, every little bit helps when you start getting close to the ragged edge.
I'm also a little curious about pulsation dampners.
See them all the time on the nicer engineered o.e. systems.
They are used to smooth out the pressure variations in a fuel rail when an ijector pops open and the pressure fluctuates. Their use stabilises the fuel pressure in the rail, and helps average/optimise the fuel injected on each pulse.
Never seen one on a mitsu...
I dunno, and I'm sure no expert on this (or any) subject, I just thought about it once or twice on long road trips.
.
.
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There is something I've been curious about for awhile, and I'm hoping one of the map tuning guys can chime in here with their experiences.
Back in the day, we didn't have all the toys that are available today.
We used the snap-on counselorII ocilliscope for day to day troubleshooting and tune ups, and it had an interesting feature I used to play with.
... vaccuum waveforms ...
You could synch a vaccuum waveform with the ignition firing order, and generate a realtime picture of vaccuum relative to crank position.
A saavy cat could extrapolate a ballpark cylinder specific realtime volumetric efficiency rating based on the vaccuum reading of each individual cylinder as it draws in a fresh mix, fires, and then rotates thru the other strokes... (caught a lot of intake valve/combustion chamber sealing issues that way, and could pin them down to a specific cylinder)
We would also measure the temp of the exhaust mani at the flange on the individual cylinders, and throw that info into the mix.
At any rate, you could definately see which cylinders were doing their share and which holes were not operating as efficiently at that throttle opening/load point, and then fondle the variables to optimise things.
Do any of the high zoot map based tuning platforms allow for logging vaccuum waveforms?
Can you set up the system to log a vaccuum waveform and then synch it to the injector firing for timing info? (can't use the ignition firing, as they double fire the plugs, one wasted/one true)
That would be a really cool diagnostic feature! (you'd have to mount the map sensor on the mani to minimise time lag)
Again, I'm not an expert, (by any means!) I just like technical discussions, and this is an excellent topic.
Guru's, what say you?
There's some fly sh*t in the pepper of every tune we do, and it would be nice to pick some out so we can make more power on all four holes.
Optimising an engine is much better than tuning to the weak cylinder. /ubbthreads/images/graemlins/wink.gif