Flyin’ Miata:
flyinmiata.com
(800) FLY-MX5S
Marren Fuel Injection
injector.com
(203) 267-FUEL
RC Engineering, Inc.:
rceng.com
(310) 320-2277
Superchips, Inc.:
superchips.com
(888) 227-2447
Photography by Alan Cesar
[Editor's note: This article originally appeared in the February 2013 issue.]
All car enthusiasts worth their salt can recognize the difference between a fuel-injected and a carbureted engine. Slightly wiser ones can identify throttle body injection, port injection and direct injection—as well as the merits of each piece of technology.
Even more esoteric knowledge concerns those round electronic devices themselves. Fuel injectors have been around for decades, so it stands to reason that they, like everything else, have improved over time. Occasionally you’ll find a guy on a forum somewhere talking about putting newer Ford Mustang injectors in an E30-chassis BMW, for example.
He’s not doing it for pony-car cachet; he’s doing it because the later injectors are better. It’s not even about flow rate. It’s about smaller nozzles, better atomization, and improved volumetric efficiency.
Fuel works best when it’s evenly dispersed within the air it consumes when it burns. That means a finer spray and smaller droplets are the ultimate goal when getting fuel into an engine. Fuel injectors were a big leap forward in that process, but the first port-injected cars are now very out of date. Their injectors force fuel through a single nozzle, one that isn’t as precisely cut as later offerings.
Injectors in today’s engines—we’ll leave direct injection out of this equation—can have as many as a dozen of these miniscule nozzles, and some are even vectored to aim the fuel directly at intake valves.
Is this just theory, or can measurable gains be found with more recent equipment? A little while back, we tried this swap on a 1999 Ford Escort ZX2. Upgrading to more modern injectors from a Ford Windstar minivan boosted fuel economy by more than 5 percent.
Really? We figured we’d try the test once more—this time using a 1991 Mazda Miata—and monitor the differences on a chassis dyno.
We started this test by installing fresh, original equipment injectors in our Miata. Our originals had seen better days, so we ordered a fresh set of used blue-top injectors from Flyin’ Miata and sent them to RC Engineering for cleaning and flow-testing. They weren’t terrible before cleaning, but afterward they posted a solid flow rate of 210cc per minute, plus or minus 1cc, across all four.
We had also been driving on a Mazda RX-7 airflow meter—a popular early Miata upgrade—for some months. Our good buddy Duncan Millar gave it to us after he scrapped his Miata, but admitted to having adjusted the clockspring inside it using just the old butt dyno.
First order of business when we arrived at the Superchips facility in Sanford, Florida: Make sure everything was topnotch. After
a few adjustments to the airflow meter, we went from 106 horsepower at the rear wheels to a stout 110.
The air/fuel ratio was too lean, though, barely getting richer than 15:1 at its richest point. We tried, but couldn’t adjust the airflow meter any further without causing an unstable idle.
Keith Tanner at Flyin’ Miata said our stock blue-top injectors were designed for an engine that makes around 93 horsepower at the wheels. They were simply maxed out.
To solve this problem as well as test the upgraded nozzles, we installed a set of red-body injectors from a 1999 Miata. Both of these sets were tested on the dyno the same day. We sourced a used set of these from Flyin’ Miata and had them cleaned and tested at RC Injection.
Cleaning proved a good move; one of them, before cleaning, flowed a mere 50cc per minute. That’s a far cry from the 250cc per minute they sprayed after RC serviced the set. That cleaning was money well spent.
These second-generation injectors have four nozzles in the tip rather than the single nozzle found on the blue-tops. The injector body is also much smaller, and they operate more quietly. To see a comparison of these two generations of injectors in action, here’s a handy video: youtu.be/VfynoxL2RZI. The new injectors simply replace the old ones; no fabrication or modification needed.
The change was immediately noticeable: Idle was smoother and quieter. And sure enough, these higher-flow injectors richened up our fuel curve into a zone that made Chris Wade, a research and development guru at Superchips, much happier.
We ran a few more pulls so we could tweak the air/fuel ratio and optimize it with these bigger injectors. When we were done, we had a half-click drop in maximum horsepower and torque, but the torque plateau was considerably fatter. We also eliminated the dip previously found between 3500 and 4500 rpm.
Though we had a very slight loss in peak numbers, swapping to the later injectors provided a clear increase in midrange horsepower and torque. The engine has a smoother idle, too.
These red-top injectors are relatively early second-generation Miata pieces, but the difference in nozzle design is still dramatic. Compare those four tiny orifices to the single hole in the older ones originally fitted to our 1991 Miata. Still-newer injectors can have as many as a dozen such holes.
Newer injectors have smaller bodies, too. Our Miata injectors interchanged with no fuss, but it’s not always like that. When installing Ford Windstar injectors in an Escort, for example, we had to break off some of the plastic tabs on the electrical connector to get it to slip on. The plastic tabs also work to keep the connector from popping off, so we then zip-tied the connector in place on the Escort.
Fuel injectors are easier to change on some cars than others, but that’s mostly because there may be other stuff in the way. Once you have access, it’s as simple as unclipping the electrical connectors, removing the bolts holding the fuel rail in place, and popping the injectors out of their spots. When reinstalling, add a thin film of grease or oil to the O-ring to prevent it from binding and tearing.
The new injectors cost roughly the same as the old-style ones: about $40 apiece if bought rebuilt. If you’re scouring junkyards, newer-design injectors start appearing in cars from the late ’90s. Our local salvage lots sell them for $10 apiece. RC Engineering charges $24 each to clean and flow-test them. For a little extra up-front money, buy two sets of used injectors, have all of them serviced, and make one precisely matched set using the flow data—then sell off the remaining pieces on eBay Motors.
While the improvement wasn’t measurable in peak numbers, we could see the results on the full graph—and could hear it and feel it. This old Miata now has solid, stable power delivery, and we can say that modern injectors are a good way to improve volumetric efficiency on an older car.
Remember, though: If considering this upgrade, match flow rate as closely to the stock numbers as possible. Unless absolutely necessary, higher-flow injectors alone won’t make more power; they’ll just use more gas.
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That's a good read, I might try finding some later model 210's for my Probe. I've been trying to get the idle right and sharpen things up
This sounds promising. But just how can you tell what will fit what?
So the actual answer is- yes it will help IF you have a fuel problem already- too little or too much.
Before just changing injectors, see if you have a problem.
The only part of running that is much better with better atomization is the first 30-100 seconds. Once the injectors get hot enough, they are just injecting vapor, and the pattern is largely irrelevant.
Once the injectors get hot enough, they are just injecting vapor, and the pattern is largely irrelevant.
Please back up this statement.
noddaz said:Once the injectors get hot enough, they are just injecting vapor, and the pattern is largely irrelevant.
Please back up this statement.
Hm. Can't post the video I saw from about 15-20 years ago, as that was taken internally. But what was seen was seen was the designed pattern cold, a pencil spray as it warmed up, and then just vapor when it was hot. When the engine gets to operating temp, it's well above the boiling point of the fuel- and when you do an immediate reduction of pressure, that also contributes to the phenomenon.
Seems some indications that DI injectors do something similar, but there are no videos that show it.
If you don't believe it, no problem. But don't expect some magical change for peak power just because of the pattern change- unless there's already something very wrong. The improved patterns help for the cold region in many aspects, but not much for peak power.
Interesting that the 4 hole red top improved midrange power, but the old blue was far better below 2,500 RPM and slightly at high RPM. Perhaps that's more to do with tuning than the red injector's natural performance? While racing, that mid-range bump could be helpful coming off of turns for example, but the stock blue might feel better on the street if further tuning can't help the reds down low.
Regarding the hot vs. cold comment, the dyno chart IS with the engine at operating temp and it still shows a difference.
Interesting too that with the improved AFR of the reds, it's down on power slightly on the top end. Weird that a too-lean mixture made more power.
noddaz said:Once the injectors get hot enough, they are just injecting vapor, and the pattern is largely irrelevant.
Please back up this statement.
Gasoline's phase change is fairly low. Going from 60ish PSI to atmospheric when the engine temp is at operating temp is going to cause vaporization of a significant portion of the mass of the gasoline.
Depends entirely upon the volatility of the gasoline, so its hard to say how much will actually vaporize, but I'd generally agree with his statement.
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