When we reported on the improved fuel injection nozzles made by General Aviation Modifications two years ago, we got a steady trickle of testimonial letters affirming that, yes indeed, these devices work as claimed.
But also some complaints: Why no nozzles for Lycomings? The simple answer is that GAMI is a small company and couldnt get around to the R&D work until about a year ago. (Besides, GAMI figured Lycoming engines wouldnt benefit as much from improved nozzles, a notion that turns out to be correct by degree.)
In any case, GAMI is now delivering improved nozzles for most Lycoming engines. These range in price from $699 for normally aspirated four-cylinder engines, $899 for turbocharged fours, $799 for the normally-aspirated O-540 series and $999 for turbocharged sixes. (Call GAMI for a list of approved engines or log onto their Web site.)
As STC mods go, these are relatively cheap. But are they worth even a modest investment? Thus far, we would say yes. Based on our own experience in the company Mooney and talks with several owners, operational smoothness and economy gains ranged from just noticeable to, as one owner said, amazing.
What They Do
As we reported in the October, 1996 issue, GAMIjectors address a fundamental shortcoming in most piston aircraft engines: Poor induction design.
GAMIs initial research on Continental engines confirmed what many owners and mechanics suspected but didnt clearly understand. Inconsistent fuel/air ratios to each cylinder cause wide variations in cylinder head and exhaust gas temperatures which translates to considerable loss of efficiency.
Worse, it aggravates the poorly designed cooling baffles in many airplanes by running some cylinders near peak EGTs, while others may be too rich or too lean.
In TCMs log-and-runner induction system, air flow to the cylinders turns out to be relatively efficient. However, because of unintended flow patterns, the forward-most cylinders rob fuel-air mixture from the second and third cylinders in the bank. This causes an over-rich condition in the forward cylinders and an over-lean condition in the rear-most cylinder.
GAMIs improved injectors are carefully resized to match the fuel flow to the available air for an ideal fuel/air ratio. Result: In TCM engines that had fuel flow differences of up to 3 gallons between the first cylinder to reach peak EGT and the last, GAMIjectors reduce the spread to a few tenths of a gallon. More important, CHTs are more consistent cylinder-to-cylinder, reducing hot spots and spikey temps.
For large-displacement TCM engines, owners report generally smoother operation and improved fuel economy of 1.5 to 3 gallons, depending on whether the engine is run lean-of-peak EGT.
At first glance, Lycoming engines would appear to have a more efficient induction design. Rather than the log-and-runner found on most TCM engines, Lycomings have a bottom-up induction design, with an individual pipe for each cylinder running from a plenum under the crankcase.
This introduces problems of its own and may be especially troublesome for the O-540 series. (See sidebar on page 14.) GAMIs George Braly says even the Lycoming system may be subject to fuel robbing, what he calls occult fuel transfer from one cylinder to another.
GAMI found that stock Lycoming fuel injection nozzles are sufficiently out of spec to aggravate the same kind of inconsistent fuel/air ratios found in TCM engines. The stock flow spec is 32 PPH at 12 PSI with a 4 percent service limits max.
Some injectors come close but GAMIs research found that many do not. And even if they do, in most Lycomings, induction airflow inefficiencies introduce significant variations in fuel/air charge to each cylinder.
Yet sometimes, by the luck of the draw, even the stock injectors may deliver a relatively well-balanced fuel/air mixture to each cylinder, which shows up as very little fuel flow difference between the first cylinder to reach peak EGT and the last.
In small displacement fours-IO-320s and IO-360s-the fuel flow spread may be as little as a few tenths of a gallon on a well-balanced engine.
Even in the O-540 series, the distribution of stock injectors may be such that theres less than a gallon fuel flow difference between the first to cylinder to reach peak EGT and the last. Absent any CHT problems, in those cases, it may not be worth installing GAMIjectors and the company has told some potential customers as much.
If you have an engine analyzer with digital EGT/CHT readouts, its a simple task to test the engines fuel/air distribution using a method devised by GAMI. Merely download the instructions from GAMIs Web site (www.gami.com) or contact them for a faxed copy at 1-888-359-4264.
Thats exactly what we did with the Lycoming IO-360 in the company Mooney. Tests at various altitudes revealed that with stock injectors installed, cylinder 1 reached peak EGT at 9.4 GPH, while the last cylinder (number 4) peaked at 9.2 gallons. Thats a near perfect spread, even for a four-cylinder engine. Although the engine would not run lean of peak EGT, it ran smoothly rich of peak. (In four-cylinder Lycs, smooth is relative.)
Upon reviewing our data, GAMI told us theyd normally advise against installing GAMIjectors, since any improvement would be modest. Nonetheless, since the airplane was at GAMIs Ada, Oklahoma hangar, we decided to try a set anyway.
After an initial flight trial and some minor tweaking of one nozzle-very minor, were talking tenths of a pound per hour here-we werent able to improve the fuel flow. In fact, the spread increased a bit, due to an overichness in cylinder 3. Nonetheless, the engine will now run smoothly lean of peak, which we couldnt quite manage before the GAMIjectors were installed. GAMI has since sent us a newly calibrated nozzle for the number 3 cylinder but we havent tried it yet.
Most noticeable is that when leaning aggressively, the engine no longer runs rough as it approaches an over lean condition, but tends to give up all at once, much as GAMIjector-equipped TCM engines do.
For the book-recommended 100-degrees rich-of-peak, best-power setting, we noticed little if any difference between pre- and post-GAMIjector numbers, although two owners we talked to reported what appears to be slightly greater power output.
To us, the major potential benefit is smoother operation at lean settings, especially lean of peak. At the mid-altitudes we tend to fly, the IO-360 will run smoothly lean of peak, although with noticeable airspeed loss.
The tradeoff is about 6 knots for a fuel flow reduced by about a gallon. If range is a consideration, that adds about 45 minutes of endurance and just shy of 100 miles.
Low Altitude LOP
According to Braly-and confirmed by our trials-a better lean-of-peak profile for a normally aspirated aircraft is at lower altitude (below 4000 feet) with throttle wide open. The engines volumetric efficiency is better at that setting because the throttle plate introduces less friction into the induction system and theres less variability in combustion events within each cylinder and between cylinders.
This yields noticeably smoother operation at leaner mixture settings and with more power available, theres less airspeed loss at equivalent fuel flows. The higher available power down low also offsets any advantages of climbing higher to improve true airspeed.
As an aside on running lean of peak, GAMI provided us with emerging oil analysis data that suggests that lean operation reduces wear metals in the oil. Braly told us some TCM owners have been tracking oil analysis trends before and after lean-of-peak operation. One data set we were shown indicated significant reductions in iron, chrome, lead, copper and aluminum in a TCM IO-520. (The samples straddled 138 hours of total engine operation.)
Although far from conclusive, those findings make sense, since lean-of-peak operation is bound to produce fewer deposits, less lead fouling and no oil dilution. With no abrasive deposits on the cylinder walls, its logical that there will be less wear.
Were not jumping to any conclusions that lean-of-peak operation will absolutely, positively point the way to TBO, but the findings are intriguing.
What Other Owners Say
We spoke to three other owners of GAMIjector-equipped Lycomings, two IO-360 operators and one IO-540 owner. Their experiences largely mirrored our own and those of TCM owners we have interviewed previously. With only a couple of hundred Lycoming GAMIjectors sets in the field, these owners definitely represent early adopters.
Cheryl Fink of St. Petersburg, Florida, owns an IO-540 equipped Lance which she frequently races. The airplane is also fitted with a number of LoPresti Speed Merchant mods including a cowl, flap gap seals and spats so she has accurate before and after speed data. According to Finks trials, the engines leaning spread before GAMIjectors was 1.5 GPH and .6 after the nozzles were installed.
However, Fink told us she operates the engine rich of peak so fuel consumption isnt the main concern, speed is. On that count, data Fink provided us showed a 2 knot increase in speed after the GAMIjectors were installed, with no other variables in the mix.
A word of caution: Although its logical that ideal fuel/air ratios will increase power slightly, we wouldnt expect it to be noticeable in most cases. (It isnt in our Mooney.) Fink and two other owners report noticeable improvements in smoothness at cruise power settings and one Mooney 20F owner from Argentina reported turbine like smoothness. (Well go along with improved smoothness and although weve made a few mistakes in our time, confusing a Lycoming four-banger with a PT-6 is not one of them.)
What to do here? We have no reservations in recommending GAMIjectors for injected Lycoming engines. That said, it appears that results may be widely variable with type of engine and even among the same types, engine-to-engine. Some will see dramatic improvements, some quite a bit less so.
Initially, GAMI was supplying injectors only to customers capable of providing detailed leaning data but theyve now collected enough Lycoming experience to take a reliable shot at workable injector sets for any injected engine, whether equipped with a digital engine monitor or not. GAMI reports that in eight of 10 cases, the nozzles improve smoothness and/or operating economy.
Nonetheless, our view is that to get the most out of GAMIjectors, it helps to have a digital engine monitor and accurate fuel flow.
When youre leaning aggressively and tenths of a gallon of fuel flow matter, its nice to see instruments that reflect that level of care, not to mention informing your understanding of engine operating theory.
As with TCM nozzles, GAMI offers a 30 to 45-day money-back guarantee. If you try the nozzles and arent impressed, you can return them for a refund. Youll be out only the hour or so of labor required to install them.
In our experience, not many products can make that claim.
Contact- GAMI, 2800 Airport Road, Hangar A, Ada, OK 74820; Phone 888-359-4264; www.gami.com.
by Paul Bertorelli