# EFI engines more powerful than carbureted equivalents?



## RedOctobyr (Mar 2, 2014)

I've seen some posts about the new EFI engines, which sound really nice. 

People often appear to mention that these engines kind of grunt and power through heavy loads better than they might have been expecting. 

This makes me curious, are EFI engines actually more powerful than the carbureted versions of those same-displacement engines? Is this a bit like OHV engines being more powerful than the L-head versions of the same displacement? 

Is it possible that some of the reaction is because there's an electronic governor that should be able to hold the RPM more accurately than a mechanical governor? That could at least help perception, such as if the machine's RPM never varied at all, until it was finally overwhelmed by the load. 

I've observed my Tecumseh engine bogging down noticeably, and it still didn't open the throttle plate fully, so I know that mechanical governors are not perfect. And until I removed the heater box while putting a load on it, I thought the engine was running out of power, until I saw the throttle plate still wasn't being opened all the way. It helped give a poorer impression of the engine's abilities. 

I guess I'm wondering what's a realistic expectation for EFI. Presumably easier starting, fewer adjustments, hopefully more tolerance for old gas, and maybe better fuel economy. But also more power? 

I'm not taking anything away from people's experiences, or doubting the reports, or anything like that. Just curious. 

I'd love to see side-by-side testing of an EFI blower vs a carbureted version of the same machine, in heavy snow.


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## 524SWE (Jan 20, 2017)

doubt if there is any tolerance for old, stale gas you dump into the tank. if you mean gas that's been in the tank awhile I imagine since everything is virtually airtight gas will last a lot longer. as to the question of more power it's probably not a significant amount, just a more precise metering of fuel to air for all atmospheric conditions would seem to indicate a consistent maximum torque and power output for the engine design.


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## kaos (Feb 18, 2017)

RedOctobyr said:


> I've seen some posts about the new EFI engines, which sound really nice.
> 
> People often appear to mention that these engines kind of grunt and power through heavy loads better than they might have been expecting.
> 
> ...


Same power one just delivers it faster and smoother. Also EFI has many advantages elevation , smoother idle , better fuel efficiency. Mine just adds power as needed quickly smoothly. My MTD carb machine would just take longer to respond which can mean a stall.


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## SnoThro (Feb 20, 2016)

Ideally they'd be the same but this assumes a cleaned and properly functioning carburetor which isn't often the case as the machine ages. What you gain in EFI is virtually no lag since the mechanical governor is gone and theoretically vastly reduced fuel consumption if the computer is programmed to idle down when its not under any demand.


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## Strato (Aug 6, 2016)

My old MTD had a power rating of 10 hp. My EFI Ariens Platinum 24 has about 11.7 hp (21 ft. lb. converted to HP presuming 3600 RPM) - only a 17% increase.

But, measured by how each machine functioned under load - the difference is a lot more than 17%.

My MTD would always bog down in the heavy stuff, and quit if pushed too hard. The EFI does the opposite - it becomes angry. It's never quit. Even with the power dial wide open, the RPM's stay steady, or even accelerate as the load becomes more difficult.

By that measure, the EFI feels like more than twice the power of my MTD. Of course, that's a subjective assessment.

The real test is to compare an EFI machine with it's carbureted counterpart. I'd be interested to read a post by someone who's made that comparison.


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## RedOctobyr (Mar 2, 2014)

That's an interesting point about RPMs. Does the engine speed really increase under a heavy load? The control system would presumably have the ability to do that, if it wanted. Up until the throttle plate is opened fully, of course. I confess I'd assumed the system would simply try to hold a given RPM, based on the power dial setting, but they could have designed the system differently/better than that, of course. 

Having a tachometer mounted to one of these engines could be interesting. To see the RPM range for the power dial, as well as to see what it does under a heavy load (holds at 3600? Increases to 3800?). 

On a single-stage 2-stroke fixed-RPM blower, I once mounted a string to the governor, allowing me to increase the RPM on-demand. I have been kind of curious to try that on my current 2-stage, to see if the engine still actually has more to give, as it starts to bog down. Just to see how well the mechanical governor is doing its job.


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## kaos (Feb 18, 2017)

The engine literally feels the torque load increase and then adapts. If you hit a heavy area of snow the thing definitely cranks up the engine rpm. Then it idles back down......

It feels like a downshift in a car.....kinda, sorta. 

The disadvantage is the cost of a new EFI battery every few yrs. 28.95 or so.......


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## Strato (Aug 6, 2016)

kaos said:


> The engine literally feels the torque load increase and then adapts. If you hit a heavy area of snow the thing definitely cranks up the engine rpm. Then it idles back down......
> 
> It feels like a downshift in a car.....kinda, sorta.
> 
> The disadvantage is the cost of a new EFI battery every few yrs. 28.95 or so.......


My experience is exactly the same. Once the CPU senses a heavier load, the engine surges. It's not subtle.

Regarding the EFI battery, the folks at Ariens told me they should last about 5 years.


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## LouC (Dec 5, 2016)

Some manufacturers have used mechanical (centrifugal) governors (like Suzuki) vs the more common air vane governors that you see on Briggs and Tecumseh engines. Not sure if they are really better or not but I'm sure EFI will result in better fuel atomization and resultant improved cold starting and running. However, the era of cheap to repair OPE will start to come to a close once they become universal.


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## RedOctobyr (Mar 2, 2014)

I'm used to seeing internal, centrifugal governors on my Tecumseh engines, at least. I want to say my Briggs tractor engines have also been internal governors, but I can't say for sure. 

I can think of external, air-vane governors that used a pivoting plastic "flag" that responded to air blowing off the flywheel fins. But that was on 3.5hp Briggs mower engines that I was messing with quite a while ago, as a kid  Are those the style you're referring to? 

Interesting point about OPE repair costs. At first I'm sure the parts will be expensive. But as they go mainstream, hopefully costs will go down, especially if aftermarket options become available. And if the parts are reliable, that should help, at least. 

For those of us who buy our equipment used, I could unfortunately see it reducing the number of good deals on machines that just "won't start this season". That's good for the current owners, of course.


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## scrappy (Dec 7, 2014)

I've never seen or heard of a wind governor on any Tecumseh. 
If it's boggin something is out of adjustment. 

I like EFI. It sure has done wonders for cars. As for small engines... the proof will be here in 10 yrs.


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## SnoThro (Feb 20, 2016)

Strato said:


> My old MTD had a power rating of 10 hp. My EFI Ariens Platinum 24 has about 11.7 hp (21 ft. lb. converted to HP presuming 3600 RPM) - only a 17% increase.
> 
> But, measured by how each machine functioned under load - the difference is a lot more than 17%.
> 
> ...


Its actually normal for the RPM to drop a bit under load since torque is increasing. A carbureted engine will do the same as what you're describing your EFI does. If your 10HP was stalling out then there was an issue. There is no magic to EFI over carbureted, its just different methods to get to the same goal.


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## Strato (Aug 6, 2016)

SnoThro said:


> Its actually normal for the RPM to drop a bit under load since torque is increasing. A carbureted engine will do the same as what you're describing your EFI does. If your 10HP was stalling out then there was an issue. There is no magic to EFI over carbureted, its just different methods to get to the same goal.


Subjectively, the difference is huge.

My 10HP MTD was well-serviced, and had ample power. It just couldn't handle the heavy, dense stuff in one gulp like the EFI does. 

When blowing the EOD mound, I had to "shave" it, or the MTD engine bogged. I see my neighbors struggle with the same issue.

With EFI, there's no need for finesse. I just take aim, and charge. The EOD mound is annihilated in a few passes.

I own 10 carbureted engines. All of them grind to halt when the load is too much.

I've never had a carbureted engine that "muscles-up" like like my EFI blower.

I'm sure you're right - there's magic to EFI over carbureted. It just feels that way.


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## RedOctobyr (Mar 2, 2014)

scrappy said:


> I've never seen or heard of a wind governor on any Tecumseh.
> *If it's boggin something is out of adjustment. *


I don't think that RPM sagging under a heavy indicates user error, anyways, or that something is adjusted wrong. I think some of it is just normal. 

My Tecumseh OHSK would drop by about 300 RPM or so (per the tach) under a heavy load, and still wouldn't have the throttle plate opened fully. I adjusted the governor multiple times per the manual, and then replaced the governor spring, which seemed to help. But it still isn't perfect. 

As another reference, my Generac generator is meant to run at a single RPM, 3600, to provide 60Hz power. But the service manual still says to adjust it to (as I recall), 61-63 Hz (3660-3780 RPM), with no load. As you add electrical loads (only to about half of the rated load), the RPM sags closer to the intended 60Hz/3600RPM. This is a Generac-brand engine, also with an internal centrifugal governor. 

It seems to me that there is some understanding that mechanically-governed engines will not hold RPM perfectly, even when before the throttle has been opened fully.


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## DriverRider (Nov 20, 2016)

RedOctobyr said:


> I don't think that RPM sagging under a heavy indicates user error, anyways, or that something is adjusted wrong. I think some of it is just normal.
> My Tecumseh OHSK would drop by about 300 RPM or so (per the tach) under a heavy load, and still wouldn't have the throttle plate opened fully. I adjusted the governor multiple times per the manual, and then replaced the governor spring, which seemed to help. But it still isn't perfect.
> It seems to me that there is some understanding that mechanically-governed engines will not hold RPM perfectly, even when before the throttle has been opened fully.


It is operating as intended. Due to the governors mechanical design there will be a slight delay as springs, weights and linkages move to compensate. Not having the throttle open fully is a safety measure to protect the engine from over-speeding. 

If the governor were to open the throttle fully and the load was suddenly removed from the engine which has to be expected for mass markets an over-speed can occur damaging the engine before the mechanical governor has time to correct.


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