Matched Fuel Injectors have flow rates that are closer in tolerance than a random set of injectors (which is pretty much the stock case).

Anyway, even matched injectors aren't really matched.

So assuming you have a manifold with runners that are of equal length attached to a log plenum and 1 throttle body.

Do you just install the matched injectors randomly or use some other scheme....

The best solution would be an A/F ratio meter for each cylinder, and move the injectors around for the most balanced A/F ratio.

Without an A/F meter, individual EGT probes could be used to get the same EGT (assuming the same temp means same A/F).

But without having individual A/F or EGT meters is there some scheme that you can use to match up the injectors to each cylinder?

I've thought of:

1. Compression ratio check; Cylinder with highest PSI gets highest flow injector on the assumption it has the highest CR and is closer to detonation, so it gets slightly richer mixture.

2. Leak down test; Lowest leakdown get's highest flow injector (same reasoning as 1)

3. Runner opening in the plenum distance from throttle body; Does farthest get the lowest flow injector or highest flow?

4. Other?


Then there's other cases of different runner lengths, and other factors..

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

FYI these people will sell you a set of injectors that are individually flow tested.

I wouldn't even attempt individual cylinder tuning without EGT probes. We've got a V8 project car with an EGT probe in each cylinder for testing out different intake setups. Right now it's running a multiport system, the fuel distribution isn't perfect, but there wouldn't have been any way we could have calculated which one gets the most fuel without actual testing. It just seemed kind of random.

Eventually we plan to throw a Sequencer or MS3X on there and see if we can do some individual cylinder trim adjustments to see if it really makes much difference on the dyno.

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"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

The premise is thought-provoking and your rationale is sensible (and I have considered it myself, also). I would throw in one caveat to ponder, though:

You’ll pay extra $$ to get matched injectors, then have to toy about to figure out which cylinder is strongest, then identify the best injector to install in that cylinder. End result is that you’ve maximized the power spread between strongest and weakest cylinders, and that might lead to an engine that runs less smoothly than one that was ‘randomized’.

Just my thoughts, my EFI system isn’t running yet and I’m no expert.

Most engine / manifold setups tend to have certain lean and rich cylinders, mostly because of the manifold design.

When I was setting up my Buick, it was well known that the front two run rich, the middle two were in the middle and the rear two ran lean. It was easy to see why when you looked at the manifold. The air blasted past the front two but was directed into the rear two runners by the rear of the plenum.

I just had my injectors cleaned, tested and flowed. Using the numbers, the front got the two leanest, the rear the two richest and the middle the two that were left. This assumes that all the injectors flow within an acceptable range to begin with.

Unless you are running at the ragged edge, I do not think there are huge gains to be had if all the injectors are working within reason.

I vote with the EGT in each cylinder and sequential injection where you can tune each cylinder individually, and match the EGT. I don't see how you could sample the exhaust for AF ratio individually without a set of long runner headers and 6 or 8 O2 sensors. And, O2 sensors vary as well. EGT I think is the most reliable and consistent way of balancing fueling.

Sam

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i know this is an old thread but you just have to change the duration of the injector opening to adjust fuel flow...

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1965 Plymouth A/FX 512ci (under construction)
1968 Dodge Dart SL6 14.25 @ 91.5 1.91 60'
1973 Dodge Dart SL6 Stock
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