Timberwolf wrote:

whee wrote:On fuel primer: a primer pump in the panel is a must in my opinion. Hand proping even a carb engine without a manual primer would be tough if possible at all.

I beg to differ. I prop planes multiply times a week. All of which are carb'd and lack the need of a primer. Now it may be a good idea for the bigger 6 cyl's for easier starting, but that would be the same regardless of hand prop or using an electric starter. Just saying, I disagree of your assessment of a primer being required.

I only have experience with the C85 in the Luscombe I owned. It absolutely would not start by hand without primer.

whee wrote:

Zzz wrote:Is it proven that 8.5:1 causes detonation with 91 or 92 auto gas? What is the threshold? I read different things.

No. Todd Peterson proved that 87 was enough for 8.6:1 TCM engines but the FAA wanted a larger detonation margin so required the STC to only allow 91 or higher. If I remember correctly it was the same deal on the 8.5:1 Lycomings.

There is no real threshold because the are so many variables. You hear guys claiming 10.5:1 pistons in there engines and running 91 but what have they done with timing and are they instrumented so the know they aren't experiencing some detonation? After all the digging I've done I've determined that running 91 in my 8.5:1 engine will be fine but I want the ability to run 85 in a pinch. To make that possible I feel like I need to drop down to 7.5:1. I think it was Light Speed Engineering that offers electronic ignition that can be retarded on the fly in case a low grade fuel in required...that might be a cool option.

When traveling in the boonies where I might have to use regular mogas, I carry a quart of TEL (tetraethyl lead) in my baggage so I can add it to the fuel and up the effective octane rating if needed. Kemco oil out of Utah makes the stuff I use but there are probably other suppliers. Probably too expensive to use on a regular basis, but worthwhile having in a pinch.

Greg

Looks like Precision no longer makes MS carbs. Marvel-Schebler has been resurrected. Not sure who actually owns them now.

Zzz wrote:

whee wrote:can be retarded on the fly

This might be my new tagline.

"If the shoe fits..."

Zzz wrote:Looks like Precision no longer makes MS carbs. Marvel-Schebler has been resurrected. Not sure who actually owns them now.

I think it's Tempest. Spark plugs, oil filters, and now carbs.

BRD wrote:I would third the lower compression. Then even 85/87 becomes no big deal - less $$ and is widely available. 235hp is plenty adequate for a Bearhawk.

Re flexibility-- besides availability, consider cost. Currently I'm paying about $3.30 for 87 octane E0. 92 E0 is available at a couple nearby airports, but costs $4.69. At my current 11gph, that's $15 an hour more.

A few years ago, my E0 87 source (Cenex) quit selling it, and I had to switch to a new place (Petit Oil) which sold 92 octane only at close to a buck a gallon more. Even at only 8gph then-- ouch!

hotrod180 wrote:

Zzz wrote:Looks like Precision no longer makes MS carbs. Marvel-Schebler has been resurrected. Not sure who actually owns them now.

I think it's Tempest. Spark plugs, oil filters, and now carbs.

http://generalaviationnews.com/2010/09/ ... rburetors/

Nope, here they are: http://msacarbs.com

I have a bearhawk with an 0-540 and here is what I used. For a starter a Hartzell x drive srz-9021 so far no issues, for the oil cooler I used a Positech 4222 which is mounted on the right rear baffle, the hottest oil temp I've seen is 176 degrees and usually it's around 165 degrees. My engine has 8.5 to 1 compression ratio with no fuel pump just gravity feed to the carburetor. For the last 20 hours I have been using 91 octane from the gas station which is $2.00 per gallon cheaper than the cheapest 100LL and the engine runs the same as it did on 100LL. The oil filter adapter on my engine is the stock one and it's not a problem changing the filter. I did use a primer and my engine will not start unless it is primed, it has taken me a while to figure out how much to prime to give it depending on the temp but now that I have it figured out it starts with in one revolution. My engine is carburated with regular mags, mostly because that's what the engine came with when I bought it and I didn't want to spend more money on fuel injection and electronic ignition.

A comment from one who will never, ever build an engine or do any mechanical work on one, but who has flown many carb'd and many FI'd engines:

You know, most "modern" aircraft engines are 1930's technology, and they've worked well for the last 80 years with carburetors. Granted that carbs have their problems, mostly with carb ice and fuel/air distribution, both of which fuel injection theoretically solves. But FI comes with its own set of problems, most notably hard hot starts, and it doesn't totally solve the ice problem, just moves it--which is why an alternate air door is necessary. But there's not a huge difference in the "mileage" from one to the other--it still takes about the same amount of gas to run a 540 cu.in. engine at 65% power whether carb'd or FI'd.

If you're a mogas aficionado, then carb seems the way to go. If you routinely go to high altitudes, though, mogas tends to cause problems, so once again it's a Hobson's choice, you pretty much must burn 100LL at high altitudes regardless of whether you have a carb or FI.

I doubt that there's a huge weight difference, but even a few pounds won't make or break a decision.

If mechanical complexity means anything, a carb is generally much simpler than FI. I would think that might be an issue, if something needs fixing in the field away from a shop. But both are pretty reliable, so that might not be too likely.

So it seems to me that it really boils down to cost--which intake system costs more to buy and maintain? Since I haven't looked into that at all, my suggestion is that it should be a consideration. In the grand scheme of things, a 1 AMU difference wouldn't favor one over the other, but a 5 AMU or more difference would.

Just my 2c.

Cary

Good thoughts, boys. Thank you.

A few sporadic thoughts:

Governor - look at PCU-X (for eXperimental without the cost of needless paperwork).

Case - suggest you look at the WD cases, I am picking the ND cases are going to be increasingly less supported in future.

Air induction / Fuel metering - whatever fuel delivery method you choose, I suggest Airflow performance for cost effective experimental parts at the top level of quality you expect.

Hoses - easy and cheaper to make your own at home in smaller gauges, larger gauges can be a bit of muscle-work and sweat without the expensive tools you probably don't want to buy.

Vans parts are your friend for any of their aircraft using a -540.

Oil filtration - think about changing the filter and where the spilled oil will go. I recommend a remote filter, mounted so it can be changed without de-cowling the engine or creating a huge oily mess.
Leave room for a filter-removal tool, they can get pretty tight even with grease.

Avoid spring clips on induction hoses, oil return lines, etc. Hex head hose clamps are an easier solution to work with and look sharper.

Plan your cable & hose runs ahead of time, when you are planning the firewall. No fun doing maintenance in spaghetti-junction. Cable ties are your friend.

Don't cheap out on the ignition harnesses, problems with them can be hard to track down and often result in changing the harness for a decent one anyway... and don't skimp on the noise isolation / filters associated with ignitions - especially the P-leads.

Horsepower - more really is more

Holy cow. P leads make noise? I never thought of that before but of course. It's just a ground wire right? Nope it's a spark antenna until grounded. Good call.