Dumb question - What are the advantages of a carb engine?

[DCarlton]

Other than being able to use auto fuel in some cases, what are the advantages of a carbureted engine?  I've noticed that you can still buy planes with carb engines (Maule's for example).  I suppose there could be some possibility of lower maintenance costs but FI systems don't seem to require much maintenance either.  

[Hank]

My Mooney is carbureted. The O-360 engine is less expensive to build than an IO-360.

My engine is also very easy to hot start, unlike my fuel injected brethren. The O-series engines are stone simple to maintain and operate. 

But it's difficult to run LOP, and when I do, I can't go as far LOP.

[Mooneymite]

To get an idea of the starting issue, compare the number of posts on Mooneyspace dealing with starting an IO 360 as compared to the dearth of posts about starting an O 360.  Many the Mooney has been left at the fuel pump waiting for the IO360 to cool down enough to start.

The IO360 is an excellent engine and owners love them...once they learn a hot start technique that works.

No technique required for the O360.  Start and go fly.

[ArtVandelay]

I think you could use auto fuel with FI engine with some changes, like maybe reduce compression ratio and/or changing the timing.

[jaylw314]

I'd disagree that hot-starting the IO-360 is difficult, BUT... starting the carb'd Piper Cherokee was ridiculously easy in comparison

Also, carbureted motors are easier to manufacture--simpler overall

Edited June 30, 2021 by jaylw314

[DCarlton]

Interesting.  It's been a long time since I've flown a carb engine and yes hot starts can be an issue with the IO-360.  I used to dread hot starts until I overhauled my engine.  Not a problem now.  The procedure I use seems to work OK.  

[Jim Peace]

The two hundred and fifty dollar hamburger. After lunch I start my carb c and fly out. My friends with injectors not so much. 

[Hank]

28 minutes ago, DCarlton said:

Interesting.  It's been a long time since I've flown a carb engine and yes hot starts can be an issue with the IO-360.  I used to dread hot starts until I overhauled my engine.  Not a problem now.  The procedure I use seems to work OK.  

There are many "magic procedures" to hot start IO-360s. Everyone who has one suffers until they figure out what works for them. But there are so many versions!

For me, I advance the throttle ~½ inch, turn the key and push . . . .

[jaylw314]

Also, to be pedantic, the allowance for automotive fuel has more to do with low compression ratio motors than whether it's carbureted/fuel-injected. 

[Shadrach]

2 hours ago, ArtVandelay said:

I think you could use auto fuel with FI engine with some changes, like maybe reduce compression ratio and/or changing the timing.

Plenty of scofflaws running auto gas in 8.7 CR lycomings.  It can be done but in addition to the legal issues it's not a good idea from an operational standpoint.  CHTs will run somewhat hotter on Mogas.  The risk of vapor lock is the bigger issue.  Mogas does not meet the vapor pressure performance of Avgas.  I knew a guy with a C210 that would fill one side with Mogas and the other with Avgas.  He would take off, climb and descend on Avgas and relegate Mogas to cruise ops.  That's smarter than filling up with mogas, but if you can afford to run a C210, you should be able to afford to fuel it properly.  I see no real benefit to carburation other than cost. I'll add that I think most carbureted mooneys are under fueled.  They can be sorted but better to buy one that already is.

Edited June 30, 2021 by Shadrach

[Shadrach]

1 hour ago, jaylw314 said:

Also, to be pedantic, the allowance for automotive fuel has more to do with low compression ratio motors than whether it's carbureted/fuel-injected. 

It has more to do with the higher fuel pressures of the injected fuel system.  8.7CR of the IO vs 8.5CR of the O not that significant.

Edited June 30, 2021 by Shadrach

[GeeBee]

I used to have a courier run with a Beech C24R Sierra. RHV-MRY-SJC. The engine had to start every time, no if's and's or but's or we would loose the contract. Simple way to hot start an IO-360. Flood it to start with. That way, you know exactly where the engine is in the start, flooded. Then start it throttle open and mixture cutoff and be ready to do the dance when she catches. Never lost a start.

 

 

[thinwing]

the only advantage ive experienced is again related to easy starts...mounted on a float plane...kicked away from dock with a current..(tidal or river )or just wind....th e panic that ensues while floatplane is drifting into another plane or pile or other obstacle trying to hot start a fuel injected continental on a 185.....0360 on a Husky...instant light off

[DXB]

Advantages for an O-360 Mooney outweigh disadvantages relative to IO-360 Mooney in my view:

 (1) much easier hot starts

(2) considered more bulletproof because no risk of a clogged injector (potential disaster in a 4 cylinder, merely stressful in a 6)

(3) cylinder replacement cost ~50% cheaper

(4) much cheaper overhaul. 

In my experience, the limitations of my O-360 relative to the IO-360 can be mitigated in large part also:

(1) 20 HP less - For me, adding Powerflow exhaust to my C produced a dramatic increase in power down low - it is now a solid 150kt machine in cruise (though benefit seems lost above ~7k feet)

(2) fuel efficiency - adding Surefly electronic ignition allowed me to lean an extra 0.5gph in cruise - still not true lean of peak on all 4 cylinders simultaneously but clearly better

(3) Poor cooling - still working on this one - will announce it here triumphantly when I eventually figure it out 

- 

[jaylw314]

2 hours ago, Shadrach said:

It has more to do with the higher fuel pressures of the injected fuel system.  8.7CR of the IO vs 8.5CR of the O not that significant.

Explain, please?  

[Hank]

1 hour ago, jaylw314 said:

Explain, please?  

My C has fuel pressure green stripe of 0.5 to 6 psi.

My injected brethren often cruise around 30 psi, while I cruise around 2 (two) psi.

[Shadrach]

51 minutes ago, jaylw314 said:

Explain, please?  

I believe it is unique to the Bendix injection system.  I do not know the exact details but I recall that Peterson Aviation did some testing and found a recurring vapor lock issue.  Any situation in the fuel system where a pressure drop occurs can make fuel susceptible to boiling. The higher the temperature and the drop the bigger the risk.  This can happen when a boost pump is turned off, it can also happen in other areas of the system. As I recall Peterson had problems at the flow divider.  AvGas is (by design) less volatile than auto fuel and less prone to boiling.  Airplanes are unique.  It would be rare for a car to take heat soaked gasoline from sea level and launch it up to  DAs of 10,000ft in under 15 mins.

[Shadrach]

1 minute ago, Hank said:

My C has fuel pressure green stripe of 0.5 to 6 psi.

My injected brethren often cruise around 30 psi, while I cruise around 2 (two) psi.

Yup, so to put a fine point on it, not a lot of room for big pressure differentials and therefore less likely to vapor lock. 

I think my Aeromotors boost pump will push  system pressure to near 33psi. That would be a possible in flight vapor lock scenario.  Pushing 33psi to a mechanical pump pushing 30psi and then shutting the boost pump off. Instant 3psi drop, fuel boils, mechanical pump cavitates and the engine quits.

Edited June 30, 2021 by Shadrach

[Shadrach]

1 hour ago, DXB said:

Advantages for an O-360 Mooney outweigh disadvantages relative to IO-360 Mooney in my view:

 (1) much easier hot starts

(2) considered more bulletproof because no risk of a clogged injector (potential disaster in a 4 cylinder, merely stressful in a 6)

(3) cylinder replacement cost ~50% cheaper

(4) much cheaper overhaul. 

In my experience, the limitations of my O-360 relative to the IO-360 can be mitigated in large part also:

(1) 20 HP less - For me, adding Powerflow exhaust to my C produced a dramatic increase in power down low - it is now a solid 150kt machine in cruise (though benefit seems lost above ~7k feet)

(2) fuel efficiency - adding Surefly electronic ignition allowed me to lean an extra 0.5gph in cruise - still not true lean of peak on all 4 cylinders simultaneously but clearly better

(3) Poor cooling - still working on this one - will announce it here triumphantly when I eventually figure it out 

- 

I think number (3)in both advantages and disadvantages are the most relevant.  (1) is the most overstated.  You flew with me on a relatively warm day.  There were no problems with engine starts no matter how quick the turn. A quick pick up with a hot start, two hour lunch followed by a warm start. Quick taxi across the field for fuel followed by another hot start. A drop off followed by another hot start.  Do you recall there being any challenge in getting the IO360 turning? I don't.  I do recall the full cross controlled Stuka final approach. Still carrying a bit of remorse for that all these years later.

[DCarlton]

Appreciate the discussion.  Interesting.  I can understand the attraction to being able to use MOGAS as well as minimize overhaul costs.  I've wondered what I would choose if I had an opportunity to spec out a new plane like a Maule.  Even when buying an older M20, we have choices. 

[carusoam]

The challenge with automotive fuels… the unknown alcohol that may get in the system….

All of our rubber bits… seals and sealant make this a NoGo….

 

As far as why I bought the carb’d M20C over the M20E when I had the chance…

The M20E cost 10 AMUs more than the M20C… in Y2K dollars…

 

The M20E… with a decent engine monitor….  Produces 10%more hp than the M20C, and is fun to run LOP…

 

I kept my CB status for a very long time… 

Best regards,

-a-

[Hank]

What many people misunderstand:  humidity levels given on weather reports are "relative humidity," or the amount of water in the air ad a percentage of the amount the air can hold. Ad temps rise, the amount of water the air can hold rises. I'd throw out some numbers, but my Gas Tables are at home. 

Water is H20; air can be considered as 78% N2 and 22% O2, ignoring the many trace items found therein for many purposes. Hydrogen is the lightest element in the universe, so H20 weighs less than O2 and N2. Thus increasing humidity makes air less dense, aka higher DA.

[DCarlton]

10 hours ago, Hyett6420 said:

Any Battle Of Britain pilot will tell you the advantages of an ijected engine over a carb’d engine.  The Uk planes ahd the latter, the Germans the former.  German planes were very superior in climb, descent and negative G manoeuvres than the UK planes.  The UK planes could just outturn the German ones however.  
 

Onto Mooneys….someone mentioned Hotstarting….to me its the most simple procedure out there on my J.  I get in, turn on master, check i have fuel pressure (normally do if its a hot start, if not hit the fuel pump for a the time needed to add pressure, NO MORE), then just turn her over, as she fires, put in mixture, pump throttle a little if required and bobs your uncle.  Works EVERYTIME.  Of course tomorrow it wont,

I never check my fuel pressure during hot starts (since I don't use the pump).  I'll start doing that now.  Curious thanks.  

[jaylw314]

23 hours ago, Shadrach said:

I believe it is unique to the Bendix injection system.  I do not know the exact details but I recall that Peterson Aviation did some testing and found a recurring vapor lock issue.  Any situation in the fuel system where a pressure drop occurs can make fuel susceptible to boiling. The higher the temperature and the drop the bigger the risk.  This can happen when a boost pump is turned off, it can also happen in other areas of the system. As I recall Peterson had problems at the flow divider.  AvGas is (by design) less volatile than auto fuel and less prone to boiling.  Airplanes are unique.  It would be rare for a car to take heat soaked gasoline from sea level and launch it up to  DAs of 10,000ft in under 15 mins.

Huh, TIL, never heard of that before!

[jaylw314]

17 hours ago, Hyett6420 said:

Any Battle Of Britain pilot will tell you the advantages of an ijected engine over a carb’d engine.  The Uk planes ahd the latter, the Germans the former.  German planes were very superior in climb, descent and negative G manoeuvres than the UK planes.  The UK planes could just outturn the German ones however.  
 

Onto Mooneys….someone mentioned Hotstarting….to me its the most simple procedure out there on my J.  I get in, turn on master, check i have fuel pressure (normally do if its a hot start, if not hit the fuel pump for a the time needed to add pressure, NO MORE), then just turn her over, as she fires, put in mixture, pump throttle a little if required and bobs your uncle.  Works EVERYTIME.  Of course tomorrow it wont,

Hah!  There's that fantastic scene from "The Battle of Britain" where the Me-109 and Spitfire do barrel rolls chasing each other, and you can actually hear the Spitfire misfire and trail black smoke over the top.