PeteP

PeteP

Well Known Member
Planning on the rebuild of the O320E3D for the 9A. Should I stay with the 7:00 to 1 pistons or go to the 8.5:1 pistons. I know there are pros and cons for each just wondering what the consensus is.

Pete
 
I haven't done my E2D yet, but when I do I expect I will go with 8.5:1 pistons, dual P-Mags, and a Rotec TBI.
 
You'd still be able to use autogas (or 94 UL if that happens) with 8.5:1, so why not go with that choice? You'll get more HP and have a more efficient engine.
 
Just for background, here's what I've gathered:

This is based on a IO-360.

With 8.5 (180 HP), I can run premium auto gas (91 octane).
With 7.2 (165HP), I can run auto gas (87 octane),
With 9.5, I have to use 100LL.

Personally, I'm going to go with the 8.5:1, mostly for a good balance between power and future fuel alternatives.
 
N999ZA said:
Just for background, here's what I've gathered:

This is based on a IO-360.

With 8.5 (180 HP), I can run premium auto gas (91 octane).
With 7.2 (165HP), I can run auto gas (87 octane),
With 9.5, I have to use 100LL.

Personally, I'm going to go with the 8.5:1, mostly for a good balance between power and future fuel alternatives.
Click to expand...

With 9.0 (187 hp) = 91 octane
 
Where are you guys getting the data from that shows what compression ratio works with different octane levels?

I ran my -6 for over 1000 hours with 87 pump gas on 8.5:1 with absolutely no problem.

As I recall in CF Taylor's book there is no clear relationship between compression ratio and octane. I know plenty of motorcycles that have a 12:1 compression ratio that run fine on 87.
 
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rocketbob said:
Where are you guys getting the data from that shows what compression ratio works with different octane levels?

I ran my -6 for over 1000 hours with 87 pump gas on 8.5:1 with absolutely no problem.

As I recall in CF Taylor's book there is no clear relationship between compression ratio and octane. I know plenty of motorcycles that have a 12:1 compression ratio that run fine on 87.
Click to expand...


I used to run an LS2 in my GTO on 87 when Hurricanes would blow through and that's all you could get.

The difference is auto/motorcycle engines have electronic ignition and knock detection to adjust the timing if detonation starts to occur.
 
rocketbob said:
Where are you guys getting the data from that shows what compression ratio works with different octane levels?

I ran my -6 for over 1000 hours with 87 pump gas on 8.5:1 with absolutely no problem.

As I recall in CF Taylor's book there is no clear relationship between compression ratio and octane. I know plenty of motorcycles that have a 12:1 compression ratio that run fine on 87.
Click to expand...

Those motorcycles are running at 10k rpm with small cylinders. That's a very different proposition than our engines. Relatively speaking, we have slow turning engines and large cylinder volumes, which are both contributing factors for ping/detonation/preignition - whichever verson you worry about.

That's why cars manufactured back in the pre- automated engine management system days would ping at high loads and low RPM (like our airplane engines), but wouldn't ping at higher RPM and high loads...
 
Lots of conjecture here about knock detection, EI, fuel injection, etc.

My point is that nobody's ever done any real testing of different octane levels on Lycs that I've ever seen published.

87 octane worked fine in my engine, but according to the conventional wisdom aka "old wives tales" should have blown up a long time ago.
 
Ethanol

How do these 0320's (experimentals of course) do with the ethanol that the certified STC's don't allow?
 
rocketbob said:
Lots of conjecture here about knock detection, EI, fuel injection, etc.

My point is that nobody's ever done any real testing of different octane levels on Lycs that I've ever seen published.

87 octane worked fine in my engine, but according to the conventional wisdom aka "old wives tales" should have blown up a long time ago.
Click to expand...

I, too, know people with 8.5:1 engines who have happily run 87 octane. I just wonder what happens when you hit the "worst case" conditions. Hot, dry day, high atmospheric pressure, low altitude, gas that is slightly "off" for some reason, and an aggressive fixed pitch prop.

And I bet someone has done the testing. We just haven't seen it. ;-)
 
Low on compression and high on attention to detail

The low compression E2D is one of the most durable and dependable engines available for GA aircraft. How about building it to its original low compression ratio and focusing instead on efficient propeller, cooling, induction, and exhaust?

That's the route I took in my -4 and I'm delighted with the performance. The ability to run cheap gas worry-free just adds to the RV grin. To each his/her own, though. I'm sure I'd be just as happy with more power.

M
 
Back in the day...

airports used to have 80 octane avgas. Our O-320, 150 HP preferred that to 100LL - too much lead.

I've also not seen any published data on the effects of EtOH in airplane engines. If someone could point me to those data I'd appreciate it. Always been a mystery to me why automobile engines seem to run fine on it.
 
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Last night I thumbed thru my CF Taylor vol 2 book. In chapter 2 he has a chart that shows octane requirements on the Y axis, with bore diameter on the X axis. With a 5" bore (Lycomings are 5.125") the octane requirement is about 70, and it will go up or down from there based on spark plug arrangement, valve design, inlet temperature, etc.
 
rocketbob said:
Lots of conjecture here about knock detection, EI, fuel injection, etc.

My point is that nobody's ever done any real testing of different octane levels on Lycs that I've ever seen published.

87 octane worked fine in my engine, but according to the conventional wisdom aka "old wives tales" should have blown up a long time ago.
Click to expand...


I don't think it's that it should have blown up, or that it doesn't work (obviously it does), but that you're more succeptable to detonation.
 
Detonation isn't a worry

It's been referenced before in these forums. Look for Jim Deakin's articles on AvWeb's archives. You can't cause detonation in a atmospheric engine. That's my take-away from many years ago. The sole exception was one application, I think it was in a Navajo with ridiculously boosted engines.

John Siebold
 
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