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IO-390 vs IO-360 (PV) -- offsetting heavy nose

bmellis11

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I didn't want to hijack the other thread that was talking about the performance difference between these two engines, so I created this one to focus on the handling difference.

I am trying to figure out what engine/prop to eventually put on my RV-8. I will mostly be flying by myself. I want a stable cross country IFR platform that is also fun to fly VFR. I want a constant speed prop. I want to do the occasional roll or loop, but I'm not planning to do a lot of aerobatics. I really want power--I want the best cruise speed I can get, but what I really want more than a really fast cruise speed is an aggressive climb rate. I love the feeling of being pushed back into my seat and watching things on the ground get smaller and smaller. Also, practically speaking, I fly in the densely populated NYC area and was always taught to get as much altitude as quickly as possible just in case I have to find a place to put the plane down.

I have read a lot of threads that talk about how the RV-8 is nose heavy and less pleasant to fly solo with an angle valve engine upfront as compared to a parallel valve such as the IO-360-M1B. I'm wondering if that difference can be largely offset. It looks like the IO-390 is about 25lbs heavier than the IO-360-M1B. But if I use a composite prop over the heavy metal prop that many use with the parallel valve engine then I can save about 20lbs. That looks like a 5lb net increase with less weight farther from the CG due to the lighter prop if I go with the IO-390 and composite prop.

So if it comes down to an IO-360-M1B with a metal prop vs a IO-390 with a composite prop, shouldn't the W&B, and therefore the handling, basically become equivalent?

In terms of W&B I will also be installing aluminum landing gear, which will shave off 15lbs, though I'm sure that will have less of an effect on the pitch feel given that it's closer to the CG. My weight is 200lbs.
 
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I think you are trying to compare apples to oranges. I am however quite sure you would be very happy with the 390 given your priorities. There is at least one RV8 poster on here with a 390 who might chime in.
 
I bet there is a Porsche forum where someone is asking if they should get a 911 or a 911S.
My 180 hp -8 at 1400#, 500’MSL does 0-60 in 4 seconds. It’s off the ground in another second and at 1000’ AGL in 40 seconds from throttle-up.
 
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I understand the attraction to HP, another option is the Titan (CMI) IO-370, 205 HP without the extra weight of the angle valve.
MT or WW would be the preferred prop.
 
FWIW,
I installed a Aero Sport Power IO-375 with 9:1 pistons.
+/- the same weight/size as a IO-360

Not dyno tested but it certainly feels stronger than the 200 horses on its placard.
EFII doesn't hurt in the power/efficiency factor.

The engine turns a lightweight MT constant speed composite prop.

1125 lbs empty weight.
I'm 200 lbs and either with empty or full tanks, it stays in the CG enveloppe.

Departing solo with half-full tanks is a blast and there's no issues in handling caracteristics.
At Gross Weight, 0 Celcius and close to sea level, it climbs to 4000' in under 3 minutes and cruises (economy power setting, 8000') at 160 KTAS with 7GPH LOP.

Would I do the same if I were to build another? I'm happy with the package.
I flew in a RV-8 with a O-360 with "normal" (8,3:1 ?) pistons and can say that the difference in performance is hard to notice.
Probably more noticeable at Gross Weight in extreme temperatures and altitudes.

Lower compression pistons have the advantage that the engine will accept lower octane gasoline than 100LL.

All in all, it's an awesome flying machine !!!
Grinning before, during and after every flight
 
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Just so you know, the published weight of the IO-390-A3B6 is actually quite a bit less than the angle valve 200 hp io-360. I believe if you go with the EXP 119 it may be less still, but don't quote me on that.

According to lycoming they fall out like this:

IO-360-M1A = 300 lbs
IO-360-A1B6 = 330 lbs

IO-390-A3B6 = 308 lbs
 
Just so you know, the published weight of the IO-390-A3B6 is actually quite a bit less than the angle valve 200 hp io-360. I believe if you go with the EXP 119 it may be less still, but don't quote me on that.

According to lycoming they fall out like this:

IO-360-M1A = 300 lbs
IO-360-A1B6 = 330 lbs

IO-390-A3B6 = 308 lbs

The Lycoming TCDS disagrees with your numbers by a large margin. There's a 23-28lb reason people use the M1A/M1B
I'm guessing you found something that includes starters and alternator weight for the M1A and A1B6???, and somehow have naked 390.

IO-360-M1A = 279 LBS
IO-360-M1B = 279 LBS

IO-360 A1B6 = 302 LBS

IO-390-A3B6 = 307 LBS.


360 TCDS Link https://drs.faa.gov/browse/excelExternalWindow/2ba01b40-f078-40f7-9cd4-5c502de78e3d?modalOpened=true
390 TCDS Link
https://drs.faa.gov/browse/excelExternalWindow/01a5a83b-5cfe-4c39-a34e-e2eedbaa55f7
 

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I think you are trying to compare apples to oranges. I am however quite sure you would be very happy with the 390 given your priorities. There is at least one RV8 poster on here with a 390 who might chime in.

I fly an RV8 with the somewhat traditional setup of 180 HP LYCOMING with Hartzell Blended Airfoil CS prop.

I did some test flying of my friend’s 200 HP angle valve Lycoming with Whirlwind 200RV prop. It was later CHANGED to the IO390 119EXP with Whirlwind HRT CS prop. I flew it to and from AirVenture.

With these three reference points, I believe you will LOVE a proper IO-390 119EXP setup.

Offline I am sure the builder/owner will be willing to discuss the installation and how the W&B was achieved.
 
The Lycoming TCDS disagrees with your numbers by a large margin. There's a 23-28lb reason people use the M1A/M1B
I'm guessing you found something that includes starters and alternator weight for the M1A and A1B6???, and somehow have naked 390.

IO-360-M1A = 279 LBS
IO-360-M1B = 279 LBS

IO-360 A1B6 = 302 LBS

IO-390-A3B6 = 307 LBS.


360 TCDS Link https://drs.faa.gov/browse/excelExternalWindow/2ba01b40-f078-40f7-9cd4-5c502de78e3d?modalOpened=true
390 TCDS Link

https://drs.faa.gov/browse/excelExternalWindow/01a5a83b-5cfe-4c39-a34e-e2eedbaa55f7

I agree that the numbers I posted don't make a lot of sense, but they come right out of specification section 2 of the Lycoming Operators manual for O-360 and associated models and are listed for "dry weight"

I understand that there's a discrepancy with the TCDS and have no explanation for it. The TCDS and Operators manual are both FAA approved documents.

https://www.lycoming.com/sites/default/files/O-HO-IO-HIO-AIO & TIO-360 Oper Manual 60297-12.pdf
 
Read page 2-7 of your link. That weight includes the starter and alternator.
The weights I posted do not include starter and alternator.

Doesn’t matter about starter and alternator much, as long as they all have it or they all don’t have it included in the quoted weight. (Edit: keep in mind they were probably using a monster 17lb starter in those numbers you had from the ops manual) key point is to start with the same baseline without starter and alternator. You can add and vary results depending on what combo is required. The baseline delta shows the M1A/M1B is the lightest and the IO-390-A3B6 as the heaviest. Not fair to compare a 390 without starter and alternator (your 308lbs) to a 360 WITH a starter and alternator and point to which one is lighter/heavier.


Where did you get the weight for the 390? Did that source describe what was included in the dry empty weight? the starter and alternator or without?

Lycoming Ops/Install manual 390 says 315Lbs. That includes a starter but NOT an alternator. That is an important detail.
See page 9 https://www.lycoming.com/sites/default/files/IO-390-A Op & Install Manual 60297-34.pdf
To be fair add 8-12 pounds for an alternator it’s brackets, hardware, and belt. Now that 315 is 325 +\- 2 lbs

If you account for a 390 with a weight that includes the starter at 315 and estimated an alternator weight then add,you can compare that to the weights you gave for the M1A and the A1B6
Now the comparison makes a lot more sense. Now the Angle valves are close in weight and the parallel valve is much lighter.

TCDS for M1A/M1B is 279, 390 was 307. That’s 28lbs difference From M1A to the 390 these are no starter and no alternator weights.

Makes a difference when you compare weights equally and the delta worked out almost exactly the same wether it had or didn’t have starter/alternator included in weight.
 
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