Mounting 618 and 670 to KF-IV

[rdooley79]

I've been working on mounting the 618 to the Kitfox.

If you have a 582 you might consider swapping out to one of the larger Rotax 2 cycle engines. Here are the things that I've found doing the swap on my plane.

First the mag end bell housing is slightly longer than the 582. Also the total height is a little taller. This introduces the problem of needing to shim the engine up to clear the bell housing but not hitting the spark plugs on the cowling.

Step 1, shim the engine mount further from the firewall.
-I used four AN washers between the mount and the firewall this was perfect and allowed the engine to slip in snug but not tight!
http://www.teamkitfox.com/Forums/picture.php?albumid=379&pictureid=4632

Step 2, shim the engine up with found 1/4 inch thick pieces of aluminum or steel. If using aluminum you'll need to use a washer so as to not have the aluminum only bearing the engine weight against the steel engine mount. Over time the aluminum being soft will deform without a washer to provide a harder metal contact point. I used a large washer to spread the load over the aluminum shim evenly. I also added a second washer just to make the bell housing fit with a little more room. You'll need to get longer bolts to make this all work as a result. You can use the short bolts to get everything lined up and then swap them out so you don't mess up the threads in the process.
http://www.teamkitfox.com/Forums/picture.php?albumid=379&pictureid=4637

Step 3, mount the exhaust, (I'm on this step now and will provide pics with the exhaust hung.


Step 4, hook up to gauges, throttle, choke, electrical and radiator. Everything is the same as your 582. Mount the prop on the gearbox.

Step 5, Run her up and set the prop pitch for max static RPM of 6200. This should be a good climb and cruise as well as give you buffer if full power and not be right at red line. Red line on the 618 is 6800. I don't like to go over 6500.

[JimS]

I wish you great amounts of good fortune with your 618. Your IV should perform really well with it. That being said.... we have in our flying group one of Bombardiers top R&D guys. He had a 503 in his Chinook that he replaced with a 618 as it was on floats. He couldn't keep the RAVE valves from breaking. Fought with it about 3 years and finally went back to a 582 for reliability. Not trying to scare you off ...just keep a close eye on them.

JimS

[deejayel]

My 618 is a monster compared to my friends 582. I love it.

Be sure your rave valves are the new steel option rather than the problem ridden aluminum ones.

[rdooley79]

yep rave valves are the new steel ones.

Rotax Rick built this 618. His running guidelines are very critical to getting the temps up quickly to heat the engine evenly.

In the 8 hours I've ran this engine on my trike, it's AMAZING!

The issues with power valves seem to be related to carbon, temps and therefore what mixture and oil is being run. Rotax Rick only wants Amsoil Interceptor specifically made for "power valve" in these engines. There is no carb build up at all in my recent inspection. pre-mix 40:1, no injection systems. Also the needle, main jet are set a little differently than "stock". So far it's running perfect temps.

From the feedback on the 670 if it's fed this way, you don't have RAVE valve issues.

I'll let you all know how it goes. Incidently there is a 670 getting built in the next couple weeks that will quickly go in to the KF. The 618 is going back on the trike. I hate having BOTH planes down. been over a month since I flew!

Thanks for the best wishes guys! I'll keep this info coming.

[rdooley79]

I wish you great amounts of good fortune with your 618. Your IV should perform really well with it.

What would happen when the RAVE valves broke?

[deejayel]

Perfect. RR built mine as well.

[JimS]

What would happen when the RAVE valves broke?

From what I understand, significant power loss, not complete but a lot.
Jims

[deejayel]

I had one of the old aluminum ones break and fall into the cylinder. My piston was quite beaten up, but i never noticed any change in performance. It wasnt until I pulled off the head at Rotax Rick's shop that we noticed the problem.

I know my experience may not be the norm, but it sure gave me confidence in these little motors.

[rdooley79]

Now that is good info. I know Rick has made a point to use the steel ones since I got the 618.

On a side note. I shipped off the old 582 to Rotax Rick this morning. He's going to use all the parts from it to build a 670 and keep the remaining parts as partial payment towards the 670.
He offers a head machined from the stock 670 head. It has the recirculator port on the top and dual plugs just like the Blue Head. But for half the price.
This baby will put out about 90hp with only about 10lbs extra weight over the 582.

I'd like a 912 motor but would constitute an entire FWF swap along with all the accessories. That's a ton of money and time for a heavier motor and more cost. But 4 cycle is very nice.

TBO on a 670 is 450hours and is supposed to burn about 3.5-4gph.

I'll definately keep the info coming for anyone who might be interested in going to a larger Rotax 2 cycle motor.

[JimS]

How's your 618/670 running?

JimS

[rdooley79]

Hey Guys,

Haven't made as much progress as I would have liked. Went to Costa Rica for 10 days. Wife graduated College just prior to that and yard work for the party was necessary. Needless to say I got side tracked for about 2 weeks.
Today I pick up the engine hoist to help me plant the new engine. I almost dropped the 618, twice, when I was trying to lift it myself. Needless to say I don't want that to happen at all! I'll start mounting the 670 on the KF this week.



I was able to 'fit' the exhaust with the 618 and get everything shimmed to have it fit, snug, but very nicely.
http://www.teamkitfox.com/Forums/picture.php?albumid=379&pictureid=4702

I've attached pics of the 618 mounted and the cowl modification I needed to do to have it fit in the cowling. I think it turned out very well.
http://www.teamkitfox.com/Forums/picture.php?albumid=379&pictureid=4703
http://www.teamkitfox.com/Forums/picture.php?albumid=379&pictureid=4704



Also you can see the head that Rotax Rick modified for dual plugs. This is the stock 670 head that has the recirculator just like the Blue Head but provides a bit more compression. Rick estimates it bumps the 670 up to 95hp!
http://www.teamkitfox.com/Forums/picture.php?albumid=379&pictureid=4708

[rdooley79]

ok guys, Tonight was the first true flight of the 670!

The summary of below is; WOW, it's an awesome upgrade! Rotax Rick's 670 is a real performer.

So you all may know that I fly out of Boulder CO, where field elevation is a mile high. Density altitude was at 6800 this afternoon.

Take off distance was about 30% shorter and climb rate was about 30% better as well. Now I'm still getting used to the plane so results may vary but it was very apparent that the 670 gives a lot more power than the 582. It's truly a new airplane and performs much better than before. Since I have the prop set up for climb especially with summer here and density altitude getting worse every day. Cruise was right about 74 indicated. I'll have a gps next flight to get some better numbers. Fuel burn seemed noticeably less but I need more time to see what the fuel burn will be like. I was just so happy to be flying again with a much better performing plane. I'd recommend the 670 if you have a 582 on your KF and want more power.

I have her set up with;
Rotax 670
Dual Ignition
Custom 670 purple head, giving an estimated 95hp (at sea level)
C box 3:1 w/ Clutch
Warp Drive 3 blade 72" straight blade, pitched for 64000-6500rpm on climb out max throttle.
Rotax Rick 670 exhaust made for this type of installation.
Electric Start
Amsoil Interceptor pre-mix 40:1

I'm comparing it to previously;
Rotax 582
Dual Ignition
Grey Head
C box 3:1 w/ Clutch
Ivo Ultralight 3 blade, pitched for 64000-6500rpm on climbout max throttle.
Stock 582 exhaust.
Electric Start
AV-2 oil pre-mix 50:1


Doing the runup's the last week I have noticed that the 670 likes to be warmed up correctly. It just sounds right when it's nice and hot. The main thing with these larger motors is keeping the head as hot and therefore expanded as possible. Rick has a runup procedure that works great. I use Amsoil Interceptor pre-mix at 40:1. Using good automotive fuel.

What I liked about this is that it's a "bolt on" upgrade. You can re-use everything from your 582, keep it, mostly in place and just swap it out. You don't need to shim the motor mount or add the spacers to raise the engine up like the 618. It fits better than the 618. The rear bell housing is smaller on the 670 and that makes it fit without needing to add washers to move the motor mount slightly forward. You also don't need to add the shims to raise the motor up, it just fits on the 582 motor mount. The cooling system if working well before will be good for the 670. I have the larger belly radiator and it kept the 670 right at 164 degrees at cruise. Climb out it was 168 degrees, perfect. EGT's were at 1180 in mid range cruise flight and max power was about 960. That's with the carbs set up from Rick.

I wish I didn't need to cut the cowling so much to fit the exhaust. But I wrapped it with exhaust wrap and that worked well. A ton of trimming little slivers off until it fit just right. In the future I'd like to get the cowling re-glassed to fit the exhaust and have it look right. For now though it's not that bad actually and works.
http://www.teamkitfox.com/Forums/picture.php?albumid=385&pictureid=4728
http://www.teamkitfox.com/Forums/picture.php?albumid=385&pictureid=4730
http://www.teamkitfox.com/Forums/picture.php?albumid=385&pictureid=4735

[SkyPirate]

Just changing drom an ivo light to a warp will make a big difference, the warp will out pull the ivo easily

[rdooley79]

True, that's why I changed to the Warp Drive. It's a much better rough field and climb prop.

However the change would not be accountable for anywhere near the performance difference, in my humble opinion. I've swapped props on my trike and saw a slight performance increase but nothing close to what the 670 performed increase experienced.
I just want to be clear as this engine is a new contender for people needing more power than a 582 but don't want to swap everything out.
Keep in mind that this was the first real flight and results may vary.

One additional detail that I failed to mention is that there was about a 3 knot tailwind for the first takeoff and I still experienced a conservative 30% shorter roll. I chose the tailwind takeoff as the terrain was more of a concern than a slight tailwind in this case. Once I get a better feel for this engine and how it performs these estimates will harden in to actual performance numbers but right now it's annecdotial and "seat of the pants" statistics. I do know that when she lept off the ground I was all grins!

[Aker]

Good info video footage would be great if you can.

Thanks.

[Aker]

Any more updates?

[rdooley79]

It's been a while. Life happened but I've been working on the bird in general. There were other things that needed attention. Since I've bought this bird it's been a much bigger project than I anticipated. The plane had more issues than I thought. I had a failure that really made me pause and very closely look at the plane. Flew for a couple hours and the plane was working great. I was taxiing out after filling up at a close airport. As I was lining up on the center line the throttle cable snapped. Right where it attached to the bell crank it had abrated and the cable had failed right at the barrel end. Very good timing I wasn't even moving but could have been a very bad day if it failed a couple throttle adjustments later. PHEW!
This made me take a long harder look at the plane and decided to do a few things I knew needed some love.

I've ended up;
Rebuilt throttle assembly from carbs to dash.
Re-wired the rats nest behind the dash and labeled everything.
New Odyssey 625 battery and relocated to behind the passengers seat.
Ran 4ga wire and replaced the solenoid.
Zip-Tied and organized all connections.
Replaced the starter motor with a new one.
Removed the halogen landing/driving lights.
Flushed and cleaned the radiator.
New coolant lines with less connections and better routing.
Ran all new fuel line and fuel filter, cleaned the gascolator.
Rebuilt Mikuni fuel pump
Reinforced the seat pan with cables/turnbuckles, keep from rubbing control rods.
Added foam to the seat bottom and back.
New bolts for seat belts.
Rebuilt the flaperon handle friction plate with new leather
Fabricated new exhaust mount.

http://www.teamkitfox.com/Forums/picture.php?albumid=385&pictureid=5003

http://www.teamkitfox.com/Forums/picture.php?albumid=385&pictureid=5004

The day after Thanksgiving I'm planning on running it up and checking everything out.

[rdooley79]

Alright Guys,

I wanted to give you all some close up pics of a 670 installed on a Kitfox 4.

Just had the annual inspection done and she passed. I had no doubt especially after the work just done.

First pic is my favorite!
http://www.teamkitfox.com/Forums/picture.php?albumid=385&pictureid=5032

Second one is a good one too. This is the High compression head. No it's not a bluehead from a 582. It's the 670 head that's made for the 670! Then Rotax Rick has a shop put in the dual spark plugs. Notice that it has the recirculator hose just like a blue head. It's just as good as the blue head but it's made for the 670 AND has dual ignition. BONUS!
http://www.teamkitfox.com/Forums/picture.php?albumid=385&pictureid=5031
If you're wondering what's on the sparkplug, It's some rubber to make a solid positive contact with the cowl lip. Without the rubber it vibrates just barely touching. In this case it's better to contact it solidly. Works nicely actually. Simple solution.

http://www.teamkitfox.com/Forums/picture.php?albumid=385&pictureid=5036

In hindsight, I wish I would have put the exhaust probes coming in from the top. If you have any exhaust splatter, cut up some exhaust gasket for washers around the probe between the clamp and the y pipe. Or weld on some bungs, that would be the best.
http://www.teamkitfox.com/Forums/picture.php?albumid=385&pictureid=5034

The exhaust is wrapped with Titanium Exhaust Wrap (http://http://www.designengineering.com/category/catalog/dei-cycle/motorcycle-exhaust-pipe-wrap-kits/titanium-exhaust-wrap-lr-technology)! Yes I said TITANIUM EXHAUST WRAP!!!!! It's super light and helps your exhaust retain a uniform heat profile. It doesn't add any power but it does look nice and keep heat off of the components.

Also notice the simple yet strong bracket. That was a good buddies design and it turned out very nice!
http://www.teamkitfox.com/Forums/picture.php?albumid=385&pictureid=5030
This exhaust was made specifically for the 670. It's what makes the engine have a nice flat power curve and perform at 90h+hp. A key to this engine is the Exhaust.
http://www.teamkitfox.com/Forums/picture.php?albumid=385&pictureid=5035
http://www.teamkitfox.com/Forums/picture.php?albumid=385&pictureid=5037

The cowl did need to get trimmed quite a bit.
http://www.teamkitfox.com/Forums/picture.php?albumid=385&pictureid=5029

One of the modifications done when the battery was located behind the passengers seat was to install a charging connector. The connector has 8ga wire that goes directly to the Odyssey 625 battery. That battery then connects to the solenoid with 4ga wire. The connector sits just under the passengers seat frame crossmember. I've wired up a battery charger/maintainer to connect to this SB15 connector. I used all together 3 SB15 connectors to make a splice with the clamp cables that come with the charger and one for the plane. I can also use this for a booster battery connection as well. BTW, you can get all of these that you want at batteries plus. Their used in APC UPS units.
http://www.teamkitfox.com/Forums/picture.php?albumid=385&pictureid=5038

Stubby nose, needs a spinner. That'll come soon enough.
http://www.teamkitfox.com/Forums/picture.php?albumid=385&pictureid=4729

[t j]

Thanks for the update. I've got a 96 Ski Doo Summit with the 670. That thing pulls like a freight train

[LSaupe]

If I can ask what is your max power RPM and cruise RPM. Did you need to change the port timing at all? I had a 670 on an MXZ and was thinking max HP was up around 7800 RPM.

What gear box ratio are you running?

[rdooley79]

I cruise at 6000, redline is set at 6350. Cruise at 6000 is about 83mph indicated but that's at 7500msl so at sea level you'll get better performance.
You could get more power out of this engine but it's tuned for reliability and longevity.
Spinning the engine faster means the prop spins faster so that introduces gearing considerations. The RPM that the 670 likes to run is right at 5900-6000.
It just humms right along at that power setting. Fuel burn is averaging right around 4.5-5gph. That's about the same as a 582.

I didn't do any port timing changes but it did come freshly built with an hour on Rotax Rick's test stand, ready to go. The exhaust timing is done with the exhaust which is critical for these engines to make power with a nice flat power curve, consistent power throughout the rpm band. The exhaust Rick has available is the "breakthrough" for the 670 to be used on aircraft. Dual Ducati electronic ignition is a must to be even considered as a serious aircraft engine to me.

Mounting the exhaust is the trick with the 670. It's a larger exhaust and takes up more space.

The prop pitch tends to work best if you pitch it a little course. I'm running a 3 blade Warp Drive, 72" 3:1 gearbox. The 670 has more torque and can swing a loaded prop better than a 582 and provides good thrust as well.

Jetting needs to be watched, especially at a mile high field elevation. Rick likes to run these engines rich, 40:1 and big main jets. I've had to go down in jet sizes because of my altitude. I'm running 162's with both needles dropped to the top notch. This makes the plugs look nice rich brown without being too rich. Rick sets them up at sea level with 180's, needles set to the middle notch. This made my engine cough and stutter but once I jetted it like a rich 582, it ran GREAT! I might go down to 160's but I'm watching the plugs as the true indicator, NOT egt's. They're showing 900 at WOT, 1150 at 5700. It's weird but talking with Rick about it he says that's about right and is typical. Also he confirmed the prop pitch being a bit on the course side working better also. I can say that it's running great now.

Swapping out the 582 for the 670 is a fantastic upgrade. Made my plane fly so much better. If only I could fly as well as the plane! Working on that.:rolleyes:

[Aker]

Any videos yet?

How much weight was gained with the 670? Is it approaching the weight of 912?

[Aker]

What is the weight of the plane with the 670 installed?

[rdooley79]

Weight with the 670 is 640lbs, in my bird. NOT every Kitfox is the same.

The 670 with tuned exhaust is 20lbs more than a 582 with exhaust.
20lbs for 25+hp gain AND way more torque. 670 puts out 90+hp. Rick says it's 92hp with the purple 670 head and tuned exhaust. It'd be cool to dyno it but that's not going to happen. I want to fly and enjoy the fruits of my labor.

Please don't turn this in to a 912 vs. thread. That's been beat to death.
This is for those of you who have a 503/582 bird and want more power WITHOUT changing everything firewall forward. Yes engine mount and most of your instruments would change with a 912. It's going to cost 3x more to get in to a 912, that's 80hp. Too many points to argue but not appropriate to this thread.

Thing's to keep in mind with my plane vs. yours;

Grove gear, master cylinders for dual controls and brakes are much heavier than stock.
Larger radiator + Coolant = more weight
Warp Drive Prop = Tank, heavier than IVO or Powerfin, more resilient to dings.
Paint is thick and heavy fabric used all over my KF.
Desser 22" Tundra tires vs 650x6's that were on it before.
Heavy transponder and ELT.

BEFORE the Grove Gear and 670, tires and prop, the previous owners W&B said 590lbs. So 50lbs gain with the upgrades but offset with 25+hp.

My W&B now is perfect. 2x 225lb guys, Full tanks(17g) and 40lbs of baggage. It puts me .1 in front of the max aft CG of 16".

The 670 it's self is only about 10lbs heavier than a 582. The exhaust is where the extra weight over the 582 comes in to play. The exhaust is about 10lbs heavier than the 582 exhaust. 20lbs total.

You "can" use the 582 exhaust on the 670 but it de-tunes it to about 70hp. The 20+hp gain with the 670 tuned exhaust is where all the torque and fuel savings come in to play.

Seriously, for anyone with a 503/582 powered Kitfox/Avid/RidgeRunner get the 670. It's AWESOME!

Contact Rotax Rick (239) 572-0021 -or- faircopters@aol.com

By the way, don't believe the BS about Rick. I've seen it and read everything. What a load of manure.
Most everything is related to proper engine set-up and tuning. Most of it is common sense, not everyone has that unfortunately.:D
-but they sure can complain about it on the internet-

Video will be done when it gets warmer. I just want more time with the engine and give you all a really good report and enjoyable video to watch.
20 flight hours on the 670 and adding more as weather and work allows. More updates coming. PM me with any questions. I'm happy to talk to anyone about the 670 or Rotax Rick.

[Grogen]

I've got a model II with a 670 with over 300 hrs. I love it and it made a good mountain plane out of the fox. Here are the specifics: pre 1991 670, newer models have different crank case casting, the older version is a direct bolt on to the 582 mount. C box 3:1, 38mm mikuni carbs with green sky altitude comp system, 72" power fin prop, tuned exhaust by CPI racing in Morgan, UT.

I am getting 98 hp out of it with 4.5-5 gal/hr. Great performance. I only wish I bored it out to 740 to start with. You can get up to 150 hp doing that. I have over 300 hrs on mine and hasn't skipped a beat. You do need to know how to run a two stroke and to keep it in perameters. I have an EIS to track all of the engine perameters, a must in my book. It alerts you immediately if anything is out of limits.

Let me know if you need more info. I would never go back to a 582 and I can buy several replacement engines for the cost of one 912. Not to mention the 912 is much heavier. Kitfox and 670 is a great combo.

[Grogen]

Orignial Cowling

[Grogen]

This is the current configuration. Cooling is much better, gained 4 mph, and no radiator (speed break) handing under the fuselage.

[Grogen]

I used my original top cowl and made my own bottom cowl. The front cowl is a piper hose you can get for $120 from Aircraft Spruce. I built my own brackets for the radiators mounted up front in the cooling holes in the front cowl.

[Grogen]

This is the other side. A tuned exhaust is important to get the HP out of this engine.

[Grogen]

This shows the old top cowl glassed into the new top and the aft portion of the bottom old cowl glassed into the new. Turned out great.

[Grogen]

Here it is without the cowls, just the front cowl. There is more room under the new cowl compared with the old one. I ran the 670 under both. The 670 is a little taller than the 582 (longer stroke) but will fit nicely under the original cowl, especially if you centered your prop hub in the ring cowl.

[Dusty]

Good to see some positive feedback on the 670, I'm keen to get mine going but my engineer is going a little too slow:mad:
A 670 is the only option for my 1050pound kf3 as any more weight will put my gross close to max weight on a trip!
We are taking a slightly different approach how to set this engine up with a standard exhaust but longer primary collectors creating the equivalent to a high torque 582 . Power is calculated in the mid to high 70's but a huge improvement
on the 582's 60 -65hp ,if that doesn't work we will fit a 618 exhaust but this will be a tight fit!
I will post updates when it is finally installed
Thanks for your post:)

[rdooley79]

Good to see another Kitfox getting a 670. I've been very impressed with both the power and the fuel burn. It's a great powerplant upgrade for us 2 stroke guys.

As for the exhaust, I am re-working it's mount on my plane. The coolant and fuel lines are just too close for comfort. I've seen the exhaust over time with vibration work it's way closer and closer to the coolant line on the pilot's side. If you look at my pic's above you'll see that it is close. Sure I could add some more brackets to stiffen it up more and probably stop the movement BUT it just makes me worry.

Decided to completely change how it's hung.

Here's what I want to do. May take a little cutting and welding but I think it'll be the safest way to mount. It solves all the problems and all the potential problems. No more worries!

http://www.teamkitfox.com/Forums/picture.php?albumid=438&pictureid=5347

http://www.teamkitfox.com/Forums/picture.php?albumid=438&pictureid=5346

http://www.teamkitfox.com/Forums/picture.php?albumid=438&pictureid=5348

http://www.teamkitfox.com/Forums/picture.php?albumid=438&pictureid=5349

[Grogen]

Wow... I like how the exhaust is hung on your plane. I think it is important to mount the exhaust to the engine itself and allow the whole unit to vibrate together. Attaching to the engine mount sets the exhaust up for structural failure. My biggest issue is noise. My plane is loud, so much so that it is hard to hear the radios. I have a muffler on my exhaust system but it is still pretty loud. How is your 618 exhaust for noise? The guy who did my exhaust got a 618 exhaust and built one from scratch. He tested the 618 exhaust with the 670 and was getting 95 HP on a dyno and he said it was pretty quiet. I would be willing to make that change if I could keep the HP and reduce the noise.

To Dusty, If you are only getting 70 HP out of the 670 it isn't worth it. The 670 will run all day at 6,500 to 7,000 and give you great performance. Everyone running Rotax two strokes is scared to go to 7,000 because the 582 "red line" is 6,500. In a snowmobile they run these engines up to 8,000 and they last for years. I run mine at 7,000 when needed then back it to 6,500 to 6,800. As I mentioned, I have over 300 hours on the engine and it is showing very little signs of wear. If I were to do it again and were in the building stage I would put a 740 big bore kit on before I put it together. That is were I am going when I rebuild this engine. Without the proper exhaust, the engine is being restricted and won't deliver even a portion of its safe potential.

[Dusty]

Fair comment on the 670hp,I would like to think I am being realistic for the rpm I run, better would be good!
Th 670 pistons are a lot heavier than 582 pistons ,my engineer calculated the load on the rod ends at various rpm with both 582 and 670( his program didn't factor in the rod length on acceleration) some truly scary numbers.
These got scarier as the revs went up,probably ok for short duration but would generate a lot of heat in our situation.
Rotax rick? Suggested full power when needed then back off when possible,which makes sense.
If these motors are doing regular 300 plus hrs then I may have to have a rethink!
300 hrs at 50 mph average speed (estimated) =15,000 miles.We don't have many snowmobiles here , but do they do that sort of milage?

The photos of the 618 exhaust mounted lengthwise look like way to go!

[Av8r3400]

High output, carburated, snowmobile engines rarely make 10,000 miles without rebuild.

[Grogen]

Snowmobiles, at least riding here in the rock mountains aren't usually ridden at 50 mph. For short bursts they will do 100 mph, but trail riding is 20-30 mph and of course when climbing you put a huge load on the engines and machine.

In my plane I take off full throttle then back off when airspeed and altitude are reached. I cruise at 85 mph at 5,900 to 6,100 at 6,000-8,000 ft (my field elevation is 5,000). The throttle is a little more than a quarter open in cruise flight. I burn around 5 gallons an hour. Even at these altitudes I am getting great performance. I can get airborne in 150' and land in 3-500' depending on winds. At cruise the engine is not even breathing hard, it feels very comfortable. The biggest thing about two stokes is keeping them within operating perameters and making corrections quickly when they aren't where they need to be. For instance, if you pull the power back to say 5,000 and push the nose over your EGTs will start climbing quickly. You are effectively leaning out the engine by "driving" the engine with airspeed and reducing the load. You can't let it stay there or you will burn it up. Either go to idle or level off and add power so that the fuel going trough the engine can cool things down. Just two strokes, if you watch what is going on and know how to bring things in limits the engine will last a very long time.


If you are only getting 70hp out of your 670 you won't know what you are missing. 20hp is a lot to give up because you didn't put the right exhaust on. My dad has a 582 model IV and my model II 670 will blow the socks off his plane. After flying mine, especially with two people in the mountains and experiencing a slight down draft that he didn't have the performance to out climb, he is moving to the 670 and wants to bore his to 740. It is the difference between being able to get out of a situation or letting Mother Nature pilot your plane. I flying in the air force and the plane I fly was build back in the 50's. The original was very underpowered and there were many accidents due to the aircrafts inability to get out of a bad situation. The planes have been re-engined with significantly more thrust. The performance accidents disappeared and made the aircraft much safer. I consider the 670 on a Kitfox a much safer and capable aircraft than one with a 582 or less. That opinion comes from direct experience with both. If you load up a fox with two people and full fuel with a 582 it's a little gutless. The 670 changes the equation and gives the pilot more options.

[Grogen]

Dusty, my wife lived in NZ when she was a teen and is planning on running the iron man in the spring in NZ. If we get to your neck of the woods I'll have to look you up!

[Dusty]

90 is better thn 70- 75hp:D
I suppose just because the power is there I don't have to use it.
The 618 exhaust will fit lengthwise ,if it gives stable rpm at cruise then I agree it is a must have.
I fly at 5700 70 kts 15litres per hour,I probably won't try to fly faster but. Better rate of climb is the goal as is a shorter takeoff.
On a real nice day ,not in a hurry 60kts:eek: just love the flying!
Fellow flyers are always welcome here.

[LORENZ]

Snowmobiles, at least riding here in the rock mountains aren't usually ridden at 50 mph. For short bursts they will do 100 mph, but trail riding is 20-30 mph and of course when climbing you put a huge load on the engines and machine.






Thanks for sharing. Do you have experience with the 912 vs the 670 when it comes to mes to STOL characteristics. My siezed 582 is comming out and Im debating the 670 and 912.

[FoxDB]

May I ask what jets you 670 guys are running in your Bing 54's?