The International Cessna 170 Association

We’ve tested at work. You get about 85% increase in efficiency out of the first variable timing unit and the other 15% with the second variable timing unit. So the point about the fuel and HP you get if you just use one. The biggest point and why everyone should really like them is the no maintenance feature when compared to regular magnetos as well as the ease of starting due to TDC retard at start. They’re also lighter than Slick/ Bendix mags.

I would like some comparison figures on their performance . All I have is stories from a couple of pilots that have had a few drinks and standing around a bar. Reliability is a big factor also. While I love new technology and fit it to my aircraft if possible ,I also love doing research and have found very little facts and figures to justify purchasing these mags. The concept is great but so is Darth Vader mind reading abilities .

you get about a 5-10 deg hotter CHT when operating at best power and you may get about .5-1 GPH better fuel burn at economy cruise running LOP. CHT's come down at economy because you're on the lean side of the power curve and the heat isn't in the cylinders. You may see about 1-2 HP gain when running advanced as well but i take that as noise between engines. This is Lycoming powered engines, but i'd expect the trends to be similar in the Continentals. Again, i stress the advantages of TBO and maintenance costs over the fuel burn/HP numbers.

I think Miles was on the money when he referred to AMU,s . Fuel is the cheapest cost of flying . By the time I pay for the mag it will cost me about $2300 Australian. That buys a lot of fuel. As I have a new engine and mags overhaul is a long way off . But it’s a good thought that progress is continuing on our engines.

The guy across the taxiway installed a Surefly SIM on his Grumman recently, with the variable timing option. Early reports talk about easier starts and more power. I'm pretty confident the "more power" claim is anecdotal, but it wouldn't surprise me if it was in fact true. The kicker was the requirement to install an engine analyzer and a manifold pressure conection in order to take advantage of the variable timing. Who's going to be first with a C170 electronic ignition PIREP?

To reduce the cost of flying a couple of simple things which can be done which doesn’t cost that much. Clean out all the junk in the aircraft , vacuum every little nook and Craig .give the carpet a wash. I do not Carry parts that could come in handy . Buy a good GPS unit or IPAD app. That saved me heaps of money . I fitted a CHT gauge that read all cylinders and a EGT gauge . My fuel costs dropped nearly a third. I use “Windy” a app on my IPAD and I use all the winds to my gain. Much more fun than hoping for a electronic mag to help reduce costs. That’s my 1.5 cents worth .

rschreiber wrote:The guy across the taxiway installed a Surefly SIM on his Grumman recently, with the variable timing option. Early reports talk about easier starts and more power. I'm pretty confident the "more power" claim is anecdotal, but it wouldn't surprise me if it was in fact true. The kicker was the requirement to install an engine analyzer and a manifold pressure conection in order to take advantage of the variable timing. Who's going to be first with a C170 electronic ignition PIREP?

According to the installation manual you do not need an engine analyzer just a CHT gauge. The manifold pressure line would be an easy install on the 170 as it has a fitting on the right intake manifold.

From the install manual:

"To operate the SIM in advance timing mode, the engine onto which the SIM is installed must comply with the following requirements:
1. Normally aspirated,
2. Have Cylinder Head Temperature (CHT) monitoring capability,
3. Use minimum of 100-octane low lead aviation fuel."

I roll my eyes a bit when I hear or read anecdotes from someone who has installed the latest gizmo on their airplane and claim “more horsepower”, etc.

If we are talking about a C145/O300 with a fixed pitch prop... it’s a simple matter to determine how much horsepower is being developed with an “accurate” tachometer. The ONLY time this engine develops 145 HP is when it turns 2700 RPM. And with the standard props, and in accordance with the TCDS, the static RPM should be 2230-2330 (or thereabout depending on minor factors) and that means we’re only seeing about 118 HP on takeoff. (And now it’s easy to see why this airplane isn’t a rocket-ship on takeoff.)

If a new trick-exhaust system is installed... or a new spark-maker is connected to the spark plugs... and you still see the same static RPM you used to see.... ?? ....then you’re still making the same HP as previously. Claims of “more percent efficiency” are feel-good words but pretty hard to determine using analog speedo-type tachometers and varying atmospheric conditions on different days following the installation.

It’s also a common human trait that, after installing more AMU’s on a gadget into our airplanes, it’s pretty hard to publicly say “Well... it cost a lot so I hope it does a lot because I don’t see anything change.” It’s a lot easier to feel good about the money and effort if I pronounce the expenditure as “more efficient”.

If you get a Surefly, be careful how you or others maintain your airplane. Early in my apprenticeship I came across a SR-22 with a Surefly and without thought I did what we do to all airplanes in for annual, I tested the plug leads with our lead tester. It wasn't till I went to check timing as we would normally do and the Surefly couldn't be timed we figured we had a problem.

Turns out we (my supervisor and I) learned with a phone call to Surefly, it was a no no to lead test the leads on a SIM. And you also can't time it with a mag timer. We asked how we were suppose to know that because at the time there was nothing in Surefly documents that would have clued us in to that. There is now after we got a new SIM curtesy of Surefly.

This same aircraft just came back in the shop for a new annual. My supervisor was quick to remind me not to try to time it or check the plug leads.

GAHorn wrote:I roll my eyes a bit when I hear or read anecdotes from someone who has installed the latest gizmo on their airplane and claim “more horsepower”, etc.

To be fair to Surefly, they make no claims of increased horsepower, their main marketing point is the low maintenance and longer service life than a mechanical magneto. Given that these units are pretty close in price to a new mechanical magneto it may turn out to be a good replacement option. Having said that, I think I would take a wait and see approach.

I have one on my bonanza, it makes hot starts very easy, and there is a slight performance increase, it runs much smoother above 10k feet and there is a noticeable difference when you go higher then that when watching the mag drops.

I don't think it would make a difference on the way I fly the 170 though, I don't take it high enough to matter and I don't have any starting issues.