Modified Stock Injectors - Import Tuner Magazine

Testing by Scott Tsuneishi and RC Engineering

The Internet-how did we ever build cars without it? Fifteen years ago, building a fast car meant taking your chances with finding an acceptable one in the local classified ads, calling around to local junkyards for replacement parts, phoning performance parts manufacturers for their "unbiased" opinions on what should be added next, and polling your friends (and friends' friends) on who should handle installs and tuning, etc. Forget diagnosing a problem-doing so often required vastly expanding your friend/junkyard network.

The world-wide wrenching guide speeds up these processes immeasurably. Fifteen years ago we'd count ourselves lucky to have a friend who'd at least seen a swapped Civic in person. Today, post up a request on your Honda forum of choice for which axles you need with a J-series swap into an EG Civic, and if you don't get 10 replies in as many minutes, you're on the wrong forum. Of course there is a glaring downside: disinformation spreads like the plague. For all those who write from firsthand experience; immeasurably more-right or wrong-want to convince you that they're right. But that's why we're here.

The Claim: Modified stock injectors can perform as well as aftermarket high-flow replacements.

While perusing the Net in times past, Senior Editor Scott Tsuneishi discovered an interesting claim put forth by multiple Subaru DIY-ers on many popular forums: With a simple modification, certain stock Subaru fuel injectors can be made to flow nearly twice their original capacity, reliably, and with no performance drawbacks.

The first part of what he read is verifiably true: many stock Subaru injectors rated at different sizes are identical, aside from different spot-welded restrictors placed at the tips of each to govern flow. It's the second part he wasn't so sure about: Remove the restrictors of those injectors-by cutting them off with something like a Dremel, or sanding them down altogether-and you've got an injector capable of safely flowing 800+ cc.

We knew we had two tests in front of us, hinging on two key terms of the claim: "800+ cc" and "safely." To verify each, we headed over to RC Engineering in Torrance, CA, with a grip of stock Subie injectors, and enlisted the services of John Park.
We knew we had two tests in front of us, hinging on two key terms of the claim: "800+ cc"
As a baseline, John tested the flow of our yellow-topped stock 535cc injectors, verifying their flow rates.
As a baseline, John tested the flow of our yellow-topped stock 535cc injectors, verifying
Note the fine atomization of the stock 535cc injector seen here, which is a product of the fuel being injected at high pressure through a dispersal medium-necessary for optimal ignition inside an engine.
Note the fine atomization of the stock 535cc injector seen here, which is a product of the

For kicks, we also subjected an aftermarket 800cc injector to the same tests as our stocker.
For kicks, we also subjected an aftermarket 800cc injector to the same tests as our stocke
Note the distinct dual-stream spray that doesn't contact the walls of the testing tube until relatively far downstream-important for injecting fuel through manifold runners and into the combustion chamber.
Note the distinct dual-stream spray that doesn't contact the walls of the testing tube unt
Next, our stock 535cc injector was taken to the belt sander, and its restrictor tip sanded down as per the instructions we found online.
Next, our stock 535cc injector was taken to the belt sander, and its restrictor tip sanded

Once reinstalled in the testing tube, John verified the output of our modified stock injector at 810cc-satisfying the flow claim of the argument for the modification. But the "safely" portion was considerably lacking. Note the haphazard spray pattern seen here, which would likely flood intake runners and cylinder walls in a real-world situation, and thus be difficult to accurately deliver into combustion.
Once reinstalled in the testing tube, John verified the output of our modified stock injec
Viewed outside the testing apparatus, the detrimental spray pattern is more visible. Gone is the fine atomization of the stock arrangement, and here to stay is fuel that would literally be dumped into the combustion chamber.
Viewed outside the testing apparatus, the detrimental spray pattern is more visible. Gone

The Verdict:

Yes, the modified stock injector did flow as much as an aftermarket high-flow unit. But as John told us, "The stock Subaru injectors are fitted with restrictive tips that increase fuel pressure and regulate spray pattern for better atomization to improve combustion." Imagine a garden hose with a spray nozzle attached, compared to one with the nozzle removed. Ideal combustion needs fine, wide-spread atomization. "Modified injectors might work if you modify and measure multiple injectors and select the most consistent ones," states John, "but I would never trust them on my engine." Good enough for us.