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Lycoming YO-360-A1A vs YIO-360-M1B, differences?

Dan 57

Dan 57

Well Known Member
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Mmmh, looking at Van's engine order page in the store, the 180HP variants are of the TB Lycoming are either the YO-360-A1A, or the YIO-360-M1B.
I realize one has a vertical, the other one a horizontal induction... any other difference justifying the $2887 price difference?variants.png
 
The M1B has a different sump style for the plenum chamber your intake pipes will draw air from. It will take the Fiberglass snorkel that Van's produces with the filter housing right in front of your #1 Cylinder. IT will have an alternate air valve up there on the side of the snorkel that you have to have a cable to operate. You can only use a certain starter as the Snorkel conforms around that location, thus limiting access. Any starter issues, you will be removing the snorkel to work on it. You have to get some brackets and a arm that mount under the cylinders (2&4 side) to route your cable through that controls the mixture. That cable will need to highly insulated so it doesn't get cooked by the engine heat. Lots of other items in there to scrap your knuckles on in installation :)
The sump on the M1B has a sniffle valve that lets out fuel that accumulates in the bottom after engine shutdown. This prevents an explosion in case of a backfire on startup, as you have a lot of air volume and some fuel there.
The M1B has an o-ring on the bottom of the intake tubes that seal up the tube going into the plenum. Kinda tricky getting that in there. So you will want to have some extra just in case you push it in to far and have to pull it out and pinch or bite some rubber off the seal.
Throttle locations are different.
Exhaust systems are different as you can't have the crossover exhaust running right over your M1B servo that is mounted horizontally.
You will have a sexy, sleeker looking cowling and lines on your airplane. Marginal difference, if any in performance. You look faster so it must be faster with the scoopless cowling :)
Baffling has some slight differences because of the filter location in front of the cylinders.
Fuel line routing is different to main fuel inlet, again, adding extra insulation due to the proximity to the exhaust system.
Cabin heat shroud is routed differently

I've done both installations and I would say the updraft is a little easier to install as you don't have all these tight accesses to your fuel servo and less over-insulating cables and lines to stave off heat.
However, if I had to do it again, I would still install a M1B. To me, the looks off the updraft scoop ruins the lines on RV's. That is just my opinion. I am sure others would disagree.

 
Aden gave a great explanation.

To add, the biggest difference (including price) is that the M1B is fuel injected. Fuel injected engines have their own quarks but I would not even consider a carbureted one for a new build; just my opinion.
 
Dan - I looked at the screen capture in your original post again. At the top it says “…. With no ignition or fuel system*“. Hmm, yes, I think I understand your question now - if neither the “O“ or “IO” version do not include the injection system, why the cost difference? Interesting.
I see Aden gave us the answer.
 
tthrew said:
Dan - I looked at the screen capture in your original post again. At the top it says “…. With no ignition or fuel system*“. Hmm, yes, I think I understand your question now - if neither the “O“ or “IO” version do not include the injection system, why the cost difference? Interesting.
I see Aden gave us the answer.
Click to expand...
Well observed Tim (y)
And thanks very much for that (fat) extensive answer Aden, learned a few things. Again ;)
I should have stated that it is not a new build, and that I have ordered a YO-360-A1A, vertical induction, as it gives me the possibility of installing either a carb, or to "upgrade" to a FI, or a EFI.

Thanks guys :cool:
 
Somewhat related question: do both engines use roller lifters? Or are they optional with either choice? thanks.
 
Dan 57 said:
I should have stated that it is not a new build, and that I have ordered a YO-360-A1A, vertical induction, as it gives me the possibility of installing either a carb, or to "upgrade" to a FI, or a EFI.
Click to expand...
Keep in mind the O engine will have the low pressure engine fuel pump designed for a carb, the IO will have the high pressure engine fuel pump designed for fuel injection.

My first build I bought a new O-360 from Van’s as they were not selling an IO-360 back then (other than an angle head engine). I never took the carb that came with the engine out of the box, just sold it outright. Installing an AFP fuel injection system for this vertical draft engine was easy, and once I got some help changing out the mechanical fuel pump was not all that hard.

But just get the fuel injected engine to start with, it will be a lot less hassle and less money. I gave away my old fuel injection system to my RV-6A neighbor to back fit onto his O-360 engine. His gain in fuel economy on cross country was amazing - so much he stop accusing me of lying about what my RV-8 was achieving.

Carl
 
During the Winter 24/25 I spent some time analyzing all the options open as to properly feed my new engine.
Offers were taken from all injection system providers, including SDS and EFII, and all pros and cons of FI vs carb weighed out...
And guess what is adorning my now 200h old was new 6 month ago YO? Yes ladies and gentlemen, a carb.

I happen to have made direct fuel economy comparison during long flights with different friends, all 360 engines equipped RVs. The FI economy advantage is here, but is minimal.
OTOH the carb offers many advantages over FI, so long live the carb :)
 
Dan 57 said:
During the Winter 24/25 I spent some time analyzing all the options open as to properly feed my new engine.
Offers were taken from all injection system providers, including SDS and EFII, and all pros and cons of FI vs carb weighed out...
And guess what is adorning my now 200h old was new 6 month ago YO? Yes ladies and gentlemen, a carb.

I happen to have made direct fuel economy comparison during long flights with different friends, all 360 engines equipped RVs. The FI economy advantage is here, but is minimal.
OTOH the carb offers many advantages over FI, so long live the carb :)
Click to expand...
Biggest FI turnoff for me is the magic spells people here have to perform to get it hot start. I am way too anxious for this problem!
 
Dan 57 said:
I happen to have made direct fuel economy comparison during long flights with different friends, all 360 engines equipped RVs. The FI economy advantage is here, but is minimal.
OTOH the carb offers many advantages over FI, so long live the carb :)
Click to expand...
Yep - if you cruise ROP the carb is not grossly bad. I cruise LOP 90% of the time.

Carl
 
Carl Froehlich said:
Yep - if you cruise ROP the carb is not grossly bad. I cruise LOP 90% of the time.

Carl
Click to expand...
I cruise LOP 100% of the time with all of our engines - FI or Carb. To get the carbed engines LOP you just pull the throttle back a smidge to get it off WOT and the lean roughness smooths out - at least on the 360’s.
 
Carl Froehlich said:
I cruise LOP 90% of the time.
Click to expand...
Thanks, so do I. Always at cruise, and in descent. The target being Carson speed, which in return means I usually regulate my IAS by using the mixture, which at this point is well LOP.
A couple of screenshots taken a few days ago (consumption is in metric, 18.8 LPH equals 4.96 USG/h, which in this case is slightly lower than the 5 I usually hover around. Quite happy with the distribution for a such lowly carb.


ex.png

PS
I'm retired and love flying, so no point in burning gas and make noise to move "faster" and make the very act of being airborne shorter... I usually try to make pleasure last longer...

PPS
Different to when I was flying pro and not allowed to loiter 😉
 
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