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Nomex Maximus

Well Known Member
Hello,

I am trying to decide which engine to select for my 7A.

I am pretty well decided on a superior XP engine. I can't decide on the horsepower. I expect that I will mostly do cross country flying with little aerobatics. I had been thinking that a simple 180 HP engine with a fixed pitch prop was the way to go or even the 320, but then I have sort of gotten the itch for the novelty of the XP-400 engine (with CS of course). My question: How much difference will the extra 40 HP make in the flying characteristics of the plane? Easier or harder to fly? What kind of fuel consumption will it draw? What kind of performance difference might I see?

Or, to quantify it differently, the XP-360 will set me back $21000 whereas the XP-400 will cost $32000, so if I didn't buy the big engine I could buy a high end Garmin unit along with the normal sized engine... decisions, decisions... could you all give me your thoughts?

-- John,
Wayland Twp, MI
empennage nearing completion
 
What will 40 hp give you? Probably 15 mph and 500+ fpm in climb over a 180 hp installation.

It will also burn roughly 20% more fuel if you push the throttle to the firewall.

One concern I have developed with low volume products (i.e. the XP-400 at this point) is that if the manufacturer goes out of business or drops the product, the spare/replacement part situation could get ugly.
 
Check with Doug

Better yet, do a search.

Doug changed the O-320 to an O-360 in Flash some time back and had some good insight into how the same plane handled differently with a bigger engine.
 
Mo power is better

I would be concerned about the XP400 (mainly weight) but a strong O-360 and CS prop would be a great performer.

One more time: O-360 (or IO360) and CS prop
 
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w&B

I am unfamiliar with the XP400 and do not know its weight. If the weight is substantially more than the 360 it may have a dramatic effect on the weight and balance.

Personally, I don't know why you would need more HP unless your mission requires it. The 360 seems to be plenty enough and much cheaper. You can buy a lot of avionics for the price delta between the 360 and 400.
 
From a performance perspective, your climb rate is proportional to excess power divided by weight, so an extra 40hp will make a fairly big increase in climb rate. Your top speed won't go up all that much though. Drag increases proportional to your airspeed squared...Team Rocket claims the top speed of their 250+hp F1 to be 250mph. My RV-6 will go about 218mph in level flight with a 180hp & constant speed prop. So, with a straight, light airplane yours should go between 218 & 250 if you have more than 180hp.

If you do the math (with lots of assumptions)...if my plane with 180hp does 218, it'll do 250 with 237hp, so that works out about right.

Now, I can't imagine saying I couldn't use more power...BUT, the 2-seat RVs fly extremely well on a 360 (and 320 for that matter). As far as acro is concerned, with my C/S 360 I can pretty much pull up into any acro maneuver from cruise flight. It doesn't have enough power to do a double Immelman though. ;)

I do know that if my Rocket friends pull their 300hp monsters back to cruise with me, their fuel burn is pretty close to what I get. Not that I could pull the power back if I had it.

Hope this helps!

p.s. Don't do 218mph in your RV-6. That's above the Vne.
 
groucho said:
If you do the math (with lots of assumptions)...if my plane with 180hp does 218, it'll do 250 with 237hp, so that works out about right.
Click to expand...

Drag increases with the square of the speed, but drag power (drag force x speed) increases with the cube of the speed, so you'll be needing more than 270hp to get to 250mph

An extra 40hp would, in theory, take you to 233mph

A
 
40 HP used to get my old VW to 65-70 MPH, sometimes a bit more.

Too bad it wont add that much to an airplane.

Mike
 
And the obvious answer-----------

40 HP used to get my old VW to 65-70 MPH, sometimes a bit more.

Too bad it wont add that much to an airplane.

Mike
 
why

I will probley be jumped on by the go fast boys but I really want too know why you think you may need 40 more horses. I have a RV-6 032-160 thats old and tried. Runs just great with a fixed pitch wood prop. I fly locally at 2250 and I'm showing on GPS any were from 140Kn to 150Kn. This is below 4000 ft. If I go CC
I'll climb to 7500 or 8500 and higher, pull 75%, lean and will show 7.2 GAl/hr. I true out at about 170 to 175Kn. And frankly, the airplane get from point A to piont B about 32 seconds before I do. Wife and I went to Savanna, Ga. from Chicago in 6hr 39 min plus 1 fuel stop/potty break.
As for paying 31K for an experimental engine, I think Van still may have a special on Lycomings and maybe cheaper than the EXP.
What ever you deside, enjoy and have fun.
Rich
 
The difference in cost of the two engines is nearly $30 per HORSEPOWER! :eek: Is it worth $11,000 to travel 30 miles/hour faster? (Not to mention increased fuel burn!) What's your mission profile? Racing? Then, "yes"! Leisurely flying? Then, "no".
 
The 400 is overkill unless you need it (high altitude, or high speed being your goals). I do like the IO-360 angle valves though, the extra fin area really helps out CHT's...
 
40 more HP...

houndsfour said:
I will probley be jumped on by the go fast boys but I really want too know why you think you may need 40 more horses. I have a RV-6 032-160 thats old and tried. Runs just great with a fixed pitch wood prop. I fly locally at 2250 and I'm showing on GPS any were from 140Kn to 150Kn. This is below 4000 ft. If I go CC
I'll climb to 7500 or 8500 and higher, pull 75%, lean and will show 7.2 GAl/hr. I true out at about 170 to 175Kn. And frankly, the airplane get from point A to piont B about 32 seconds before I do. Wife and I went to Savanna, Ga. from Chicago in 6hr 39 min plus 1 fuel stop/potty break.
As for paying 31K for an experimental engine, I think Van still may have a special on Lycomings and maybe cheaper than the EXP.
What ever you deside, enjoy and have fun.
Rich
Click to expand...

OK, I guess I am not seeing the big bang for the buck that I would have thought I might for getting the big engine. I guess I was just fearing that if I went with a smaller engine I would someday regret it.

In some sense, I am not in any hurry to get anywhere when I am flying - in fact the longer it takes per gallon the better. I guess the desire for the big engine is the "cool factor". But I am now thinking I can live without that and save a bunch of money. So I guess my question now would be, how much better in fuel economy is a 320 as compared to a 360? I am sort of thinking then I would go with a 7:1 compression ratio engine and be able to burn mogas if I ever needed to... comments???

--Nomex
 
Nomex Maximus said:
OK, I guess I am not seeing the big bang for the buck that I would have thought I might for getting the big engine. I guess I was just fearing that if I went with a smaller engine I would someday regret it.

In some sense, I am not in any hurry to get anywhere when I am flying - in fact the longer it takes per gallon the better. I guess the desire for the big engine is the "cool factor". But I am now thinking I can live without that and save a bunch of money. So I guess my question now would be, how much better in fuel economy is a 320 as compared to a 360? I am sort of thinking then I would go with a 7:1 compression ratio engine and be able to burn mogas if I ever needed to... comments???

--Nomex
Click to expand...

Now you are talking my language. I like to cruise locally at 5 gph and still pass all spam cans in the area. That's where these machines are most magnificent. My hulk burns about 14 gph on take off and does clear the trees around here better than any certified airplane, but as soon as that is done its haul back the prop to 1700 and enjoy the flight. I get indigestion seeing 14 gph, like the cash register is really ringing up the bucks.

The cost difference from an 0320 to 0360 parallel valve is minimal. I'd go with the 0360 and a Catto prop and you nearly have it all. For sure you can cruise locally at 5 gph and take off performance will only be bested by someone with a CS prop. In a previous life, I cruised the Cozy MKIV with the 0360 and a FP Performance prop at 5 gph regularly on Missouri River patrols looking for enemy subs. The 0320 is no slouch either. I flew up to Boone 3 weeks ago behind Rick Galati's RV-6A, his machine moves out right smartly with a fixed pitch prop. The 0320 and 0360 will develope the same HP at a given fuel flow.

Just my 2 cents worth and by the way, the Subby H6 ain't all that bad on this mission either - it does just fine on Wal-Mart gas. Flew this morning on a mission to get the transponder recertified and it was a delight even with an OAT above 90. Until someone does something about the incompatible seals in Lycoming fuel systems, mogas won't be much of an option because fuel without alchohol is getting scarce. I don't know where airports selling mogas are finding it. I know one guy locally with an STC'd 182 who has given up on mogas because he can not find it without ethanol.
 
Some people seem confused about what you get with more power, they only want to compare speed verses fuel burn and are under the impression that with the extra speed comes higher fuel bills, this can be true but not always, depends on how you use it and where you use it.

I have an angle valve IO-360 with an MTV-15B 183-33 CS prop on an RV-4 and my dad has a -4 with O-320 and wood fixed prop. We have flown a number of cross countries together and found the results interesting. On a flight from Person Field Vancouver WA to Creswell OR and back at 3 or 4k? and the same speed I took a half gallon more then he took. On long cross countries when cruising at high altitudes above 9k I will cruse 20 to 25 MPH faster and on a 400 mile leg take two gallons less fuel, I get to altitude much faster and then cruse at much faster speed once at altitude there for spend less time on the same leg and burn less total fuel. At well over published gross say 1700lbs it climbs at 2000fpm and 1400lbs sustained climb is 3000fpm give or take depending on the day. My engine probably makes in excess of 200hp. Money is the only reason I can see not to go for more power. As for C of G my -4 can handle full fuel and a 150lb pilot solo or 5 gallons and a 230lb pilot and a 250lb passenger and still be in the CG limit, my 250lb passenger was also 6?6? tall and the plane handled fine but was light on pitch as expected, the extra weight on the nose made heaver passengers possible so long as your not to concerned about the total gross weight, I have actually increased my gross to 1750lbs based on its 24 year history of operating at these weights with no problems.
 
David-aviator said:
... <snip> Until someone does something about the incompatible seals in Lycoming fuel systems, mogas won't be much of an option because fuel without alchohol is getting scarce. I don't know where airports selling mogas are finding it. I know one guy locally with an STC'd 182 who has given up on mogas because he can not find it without ethanol.
Click to expand...

I believe the alcohol thing was originally prescribed by the EPA and the 'class' of the city where the gas is sold. They still basically require all metro areas with large populations to use ethanol NOW, some states [mostly midwest] are now requiring some ehtanol in all the road gas in their states just to promote agricultural production.

I believe the refineries can provide 100% gas if allowed. I know rural areas in Mo and Il had 100% gas as recently as last winter.

John
 
More info

From Superior on using autogas

"NOTE: Use of auto fuel blended with ethanol or gasohol is forbidden."

Check local pumps to see how many have ethanol in the gas. It is everywhere here so I don't even consider using autofuel.

O-320 vs O-360. Ask all the RV pilots you know (or do a poll) and find out how many started with less than an O-360. Ask how many upgraded to O-360 or higher. Then ask how many replaced a O-360 or higher with an O-320.

My suggestion to folks around here (Colorado) is O-360 or better (you will get the conflicting position of course)

O-360 (or IO-360) with CS prop.
 
Ethanol forbidden

Well I have yet to find and argument that holds water (pun intended) for not using fuel with ethanol, i fact for most of what i really do...i.e puttering about the local pattern...I bet ethanol laced fuel would be just fine. My AFP FI system is compatible with 100% ethanol. Now I don't know for this for sure, and you might have to insulate the FI lines to overcome hot start issues, but so far I have not seen why it would not work.

i don't use it cus I don't have to...My local Chevron sells ethanol free fuel. I would probably limit myself to 12k or below with autofuel.

The standard 8.5:1 engine will run fine on premium (92 octane I believe) fuel. A 7:1 engine will run fine on 87 octane. I noticed while in Co their regular pump gas is 85oct while in Oregon its 87...Be careful.

As an Rv7 owner i think the IO360 is more than enough. Would I like more?..Sure but is it worth a few thousand more?...Absolutely not...to me at least.

in fact the Rv-6 that Mike Seager trains in has the 320 and its a sweet flying airplane...for sea level performance its enough.

When (if ever) you go to sell your RV you will take a hit on value if it has the 320 motor in it I think.

If you live (or intend to fly at) high altitude then the 360 is the motor of choice....with C/s of course....But even thats debatable.

Cheers

Frank 7a
 
frankh said:
Well I have yet to find and argument that holds water (pun intended) for not using fuel with ethanol, i fact for most of what i really do...i.e puttering about the local pattern...I bet ethanol laced fuel would be just fine. My AFP FI system is compatible with 100% ethanol. Now I don't know for this for sure, and you might have to insulate the FI lines to overcome hot start issues, but so far I have not seen why it would not work.

i don't use it cus I don't have to...My local Chevron sells ethanol free fuel. I would probably limit myself to 12k or below with autofuel.

Frank 7a
Click to expand...

I do not believe ethanol matters one way or the other - what's important is the vapor pressure of the fuel (with or without ethanol) before take off.

I added some 93 mogas with ethanol this morning and it checked out at 45 kPa's with the Hodges tester, that's good enough for flight to 15,000' at the test temperature - OAT 90F+ today. If it cools down, it will be ok even higher. I've tested 100LL a number of times and it always comes in at about 62 kPa's which is good to about 22,000' before it cools down. So if you're going to fly real high, use 100LL, otherwise mogas is usually ok. But do get in the habit of testing it, not all mogas is the same.
 
That was my assumption

David-aviator said:
I do not believe ethanol matters one way or the other - what's important is the vapor pressure of the fuel (with or without ethanol) before take off.

I added some 93 mogas with ethanol this morning and it checked out at 45 kPa's with the Hodges tester, that's good enough for flight to 15,000' at the test temperature - OAT 90F+ today. If it cools down, it will be ok even higher. I've tested 100LL a number of times and it always comes in at about 62 kPa's which is good to about 22,000' before it cools down. So if you're going to fly real high, use 100LL, otherwise mogas is usually ok. But do get in the habit of testing it, not all mogas is the same.
Click to expand...


Without absolte proof that was pretty much my conclusion David.

Of course if you are relying on an engine driven pump (especially an egine diven pump that is not cooled well) i.e sucking uphill hydraulically speaking then the safe altitude to which you could use mogas may well go down.

This is why I have an electric pump in each wingroot...that is no mechanical pump.

I am just off to add the adjustable timing feature to my Pmags...I.e 25deg BTDC for mogas, flip the switch for 34 BTDC for 100LL.

I will find a syringe and vacuum guage to test each batch of fuel in the near future.
Cheers

Frank 7a
 
Check Out Eagle Engines...

John,

The guy that is helping me with the build of my 7A found out about Eagle Engines in Redding, CA that have great prices on new 0-360 & IO-360s using Superior parts. They have many options available and one would be going with their 10.1 to 1 piston option that produces 195 horses at around $22-24K depending on your options. This will give you the extra HP your looking for without the extra weight and you still have the extra money you would have spent on the XP-400 for your GPS etc. If you want to check out their site and call them for info and pricing go to http://www.eagleengines.com

Good Luck,

Bryon
 
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