Stavros

Just want something clarified for me here...

How, on single carbs, single point fuel injection and single jet nitrous setups, do each cyl get an equal (or near as damnit) amount of fuel?

Is it purely the vacumn of each cyl sucking it to the correct places then?

As it cant be manifold shape, considering how little care is put into shape of a lot of them, and also considering very long engines, ie straight 6s, work fine with nitrous etc injected through a single nozzle downstream.

Ive always just accepted it "just does" rather than looked in to why exactly as its not something thats hugely relevant on modern tuned engines.
But I am, now.

Stavros

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foreigneRS

basically, yes. although i wouldn't call it a vacuum sucking it in - i'd say it was atmospheric pressure pushing it into the depression in the cylinder with the open valves.

but the emphasis is more on the 'near as damnit' rather than the 'correct' amount. multipoint is better for emissions, economy and can in theory be trimmed to exactly match each cylinder's airflow requirement

groomers

manifolds are designed for this allbeit not very well in some cases, but also the cavuum created by each cylinder drags it in.
suggest you buy yourself a hilliers book cant rember the full title but explsins everyhing about cars in full detail!

tabetha

They DON'T get equal amounts, owing to position of valves/shape of inlet etc away from the SPI.
With this arrangement it is IMPOSSIBLE to be equal, unless air entry is equal, which it isn't.
Even when air entry is exact, on TB's for example it is not that simple, as the nearest cylinder to the water pump flow has more cooling, so it runs richer, the further away one runs leaner as it has hotter water already heated by passing around the other cylinder walls first.
Engines like rover V8 on carbs have very eneqaul length inlets, as each carb on each side feeds two on it's side and two on the opposite side.
Interestingly when injected the port lengths are equalised by different height mouths in the plenum for each cylinder, but again cannot compensate for differing temperatures on each cylinder.
Some aftermarket ecu's are individually adjustable for FUELLING and TIMING on each cylinder, but of course a lambda/egt is needed for each cylinder then.
tabetha

Stavros

I know they dont get equal, I said that, but they get equal enough to run fine.

And I was talking about fuel, not air, so the bits about TBs etc arnt relevant.

And I know about individual cyl and ign trim, as my ECU does it. But I wasnt talking about that either.

Chip

iTrader: (3)

NITROUS POINT OF VIEW:

Depends on the inlet manifold, on some inlet manifolds the distribution is very even, on others it isnt.

Also depends on the type of injector used, and where its mounted and at what angle, its a VERY easy thing to get horrifically wrong, ive seen some awesome fuckups other people have done just by not knowing the basics.

On a GTR inlet for example, if you put the injector just in front of the throttle body and point it parellel with the airflow you will overwork cylinder 6, a simple twist by about 30 degrees of the nozzle, and your distribution gets much better.

With a well designed injector though, it doesnt actually matter as much as you might think it would, as its putting the nitrous and the fuel in together, so each cylinder gets the right mixture still even if they dont all get the same amount, so providing your timing is safe for the worst one, its not an issue.

On setups where only one cylinder is breathing in at once, like on a 4 cylinder, that helps to draw the nitrous and fuel mixture to that cylinder, but obviously on a 6 pot you end up with 2 cylinders wanting the mixture at once, so again its more of an issue.


CARBS / INJECTION

With regads to carbs and injection, its again down to the placement of the carb/injector and the design of the manifold thereafter to a certain extent, its more critical for a fuel injector I suspect as its forcing the fuel in under pressure, where as carbs the fuel mixes with the air on the way past as it gets drawn out of the jets, so again a bit like the nitrous even if the distribution is slightly uneven the mixture shouldnt be as the different amount of air drawn through will typically be mixed with the right about of fuel.


MULTI INJECTOR SETUPS

The thing you havent asked about but is also very relevant is actually multi injector setups like the YB and the problems you can have with that, each cylinder will get the same amount of fuel regardless of airflow, so when you start getting to flow levels where the cylinders no longer flow evenly this can lead to a difference in not only the volume of charge swallowed but also the mixture, with the potentially very dangerous effect that the cylinder that flows the most not only gets more air it also gets a leaner mix, so its a double whammy in terms of detonation.


EXHAUST MANIFOLDS

The final major factor which will effect the breathing per cylinder, and hence potentially the mixture per cylinder on injection setups, is the exhaust manifold if its unequally designed (i mean in terms of a flow difference not a length difference which in my experience isnt as drastic as people make out) can result at high rpm in a cylinder failing to empty its contents properly, which in turn will mean it will ingest less charge on the next inlet stroke.

Stavros

Good points well put

Some stuff confirmed what I thought, some stuff taught me some relevant shit, job done, thread closed, lol.

dojj

iTrader: (3)

if you have the time chip, can you clarify why this is?
is it just by trial and error or is there a method to the madness that means someone "knows" where to put the injector through experience (which is the same as trail and error in some peoles eyes but perhaps not if there are such things as charts with the relevant data for each different manifold's air flow)

or maybe i'm just reading it wrong, again

thanks