Sonex Trials

From time to time I have folks contact me about cooling issues on a Sonex. Tom Huebbe from Missouri has a Sonex and has experienced high chts for some time. This past winter he pulled his heads and added some fin extensions, his email with the results:  

Hi Wayne,   Tried to download the pictures I have from my wife's digital camera, but something is screwed up with her camera so I will try to take some more pictures and get them to you.   In the meantime here are my results:  To begin with I have been flying my Sonex since 2006 and have about 350 hours on it total time.   Have been having problems with high CHT's and oil temps. since day one.   I had been flying behind VW's since early 80s' but all in single place, small engine airplanes,  1600 cc and 1835 cc and never had any problems with high CHT's or oil temps.   Had about 1300 hours in those two planes---no issues.  I am sure because they were small engines and not hauling around much weight.  With the Sonex is it quite different especially with two people aboard.    My engine is a 2276,  94 mm cylinders, and 82 mm crankshaft using an Aerocarb.   I also tuned the engine using my son's wide band fuel/air meter and verified the timing on both ignition systems.   I also verified my CHT sensors using two other digital thermometers so my CHT temps I read are quite accurate.  My sons and I also measured the pressure in the cowl using a manometer.   We tried just about everything to try and bring the temps down to no avail.   I have always measured the CHT the same:  under the spark plug right up against the head so I am always comparing apples to apples.  Typical flying day is:  start up cold and taxi to take off which can be 1/4 to 1/2 mile depending on which runway to use.   CHT's will be up to 350F by the time I do runup and ready to fly.   Take off and climb at 90 MPH and by the time I am turning downwind the CHT's are already above 400F heading for 450F.   I cannot get to pattern altitude without the temps going above 450F.   I then have to level off and reduce power and wait until the temps get down below 400 F and then try to climb some more.   Have to do step climbing to reach cruise altitude.   Oh, also my airport is here in Missouri,  440 MSL.   I usually end up cruising at at 2500 to 3000 ft. altitude because it takes so long to climb.  After I reach cruise altitude I then pull the power back to cruise at about 22-23 inches M.P. and then my CHT will very sssssslllllllooooooooowwwwwwllllly  fall to 360-370 F.   I know this is too hot because my old planes never did this and the VW's I raced years ago never ran over 280F cruising and 310F racing very hard.  We always thought anything over 360F was getting hot and never wanted to run over 380F.

Now, new results with the fat fins we welded on:   Taxi forever and never get above 280F.    Takeoff and climb at 80 mph W.O.T. till reaching pattern altitude and do not get above 376 F tops.   Also, left and right heads are now ALWAYS within a couple of degrees of each other.   Never did that before either.   When I pull back to 22-23 inches of M.P., and go into cruise flight,   CHT's will pretty quickly fall to 290-300F and stay there.
This is with two people aboard and near gross weight.   As I said before this is measured under the spark plugs not way out on the fins someplace which will make you THINK you are running cool all the while you are toasting your heads.    The engine now runs just as cool as my little engines did.   Just need more fin area to dissipate the extra heat the bigger engine makes.   It is well worth the effort to not cook the heads with all the associated problems a person will run into running such high temps.---regardless of what some "experts" may tell you  is acceptable to run.

This may not be as good as your results, but each plane is very different.   And, I had to work within the confines of the cowl I already have.
I am now a happy camper.

Regards,
Tom

Congratulations Tom! When we get some pictures I'll post them for folks to see.
Wayne

Slow News Day

I wanted to let everyone know I was still alive. I apologize for not starting on the dual plug demonstration but I have been very busy at work to support my habit. A trip out of the country, the condition inspection on my plane and flying has also consumed many hours.
 Several people are working on their own fat fin heads and I want to share some pictures. Dane Smith, M.D. from down in South Carolina was kind enough to send some pictures and talk about his progress. It looks like he has a good start.

He took his heads to a professional welder and had them tigged, the price sounded good to me all things considered. I won't say how much here, it is not my place but I think those who are wanting this mod  could get it done for less than you think. Time to shop around. As soon as he knows how much it helped I'll let everone know. In the mean time enjoy some more pictures.    

I also want to let everyone know the condition inspection went very well. I inspected the cylinders, combustion chambers and valves with a borescope and run a compression test. The engine checked out fine.  I have not been able to fly as much as I would like due to work and weather conditions but the hobbs meter is ticking off the time.
 One last thing, it appears Kitplanes may do a follow up article, look for it in the near future.   

Kitplanes

Just wanted to let everyone know that Kitplanes did an article on my airplane and me and it will be in the April 2011 issue. Apparently they saw my pictures in Zenith's photo albums and asked to contact me. The interview was done the latter part of May 2010 right after the 1st generation fat fin heads developed a crack between the valves in the number two cylinder that let the seat move around. I mentoned this event in an earlier post. I was a little less than optimistic about the vw at this time and the article copy reflects my my mood at that time.
 I'm a " the glass is half full" kind of guy and I just call things like I see it. It's either back or white, I don't see things in shades of gray. I figured out that there are more people who stretch the truth in the homebuilt community than anywhere else on the planet. At first I believed all the hype people were spewing, the performance, weight, temperature, fuel consumption claims because I WANTED it to be true and in the end I found out the truth. Thats about the time when I decided to take matters into my own hands and fix it. I also came to the conclusion that I had to tell the truth, how many times have you heard about experimental planes not meeting published performance figures?
 I promised from this point on that I would always tell the truth, be honest and open with my experience and data, and for that I have caught the most hell. Like I said earlier, if you don't tell people what they WANT to hear then you are an idiot. I have had some tell me that the "expert" says you need to do this or that after thay didn't get the expected response from me in regards to performance. Guys, I just tell the truth. I've just about tried it all.
 The important thing to remember when you read the article is the time when the interview was done. I just told the truth. Since the interview a lot has happened, 9 months has elasped, hours have been flown. I have flown the plane a total of 35.5 hours since the installation of the Generation Two heads, this includes flying through the summer (and winter) as well as a total of 54 full power takeoffs and climbs........ with no issues what so ever.  What does this mean? Nothing really. Only extensive testing will prove the viability of the heads. When, or rather if I get a couple hundred trouble free hours on this thing then I'll have to say Bob and I are on to something, so I guess I'll just have to keep flying.
 I flew this evening for another hour and had a wonderful time, I just get in the plane after a preflight and go at full power with no special handling. That throttle is tight against the panel while I climb to whatever altitude I want and thats it, tonight was a 3000 foot climb in excess of 8 gph and the cht never got over 320. I'm finally happy and hope this thing holds together. When I logged the trip tonight I took the time to actually go back total everything up, I've been estimating the times in some of my other communications. 
 The condition inspection is due the end of the month and I intend to take pictures of the combustion chambers if possible when I borescope the cylinders. I'll post them here if they work out.
 I have the steel to build the jigs for the dual plug conversion and 'll get on that after I get the inspection done.
 
     

Nice flight

The weather finally gave us enough of a break to allow for some flying today. So, I took advantage of Mother Nature and went for a spin. I have had several requests for updates but there has been nothing to report. Until today.

 I took some pictures of the panel so folks can see what is going on with the plane and engine to reinforce what I have been saying about my testing. Remember, when you look at the photos I have the sensors under the head stud by the exhaust port. I'll keep it short and let the pictures do the talking.  I apologize for the fuzz, it was pretty bumpy, enough so I couldn't get a good one in the climb.





My scratch built creation waiting to go.





 

The cht was 310 in the climb, about 45 degrees ambient on takeoff.

The switches are set to show the maximum temp, or hottest cylinder on both instruments. In this case number two is 275 and the egt is 1338. Just about at the limit I'll allow.



Those of you who know what a Ch701 is probably realize it is a high drag airframe. Mine has all the high drag stuff just like the factory plans (slats)  except I installed strut fairings. This picture shows that the vw pulls it through the air pretty well. You have to watch it in rough air and not throw it around.

Here is a good shot of my cruise power setting, I have it 1" lower than usual because of the rough air. It would normally be 5.5 to 6" and 3900 to 3925 rpm. It is worth noting that wide open throttle is 3", before I advanced the camshaft 4 degrees W.O.T. would result in a indication of atmospheric pressure, or 0 inches.  The fuel flow has settled down to 7.3 gph which means I don't go far, about 1.5 hours. That's about as long as I can sit still anyway. The gps is showing ground speed in knots. 

8 minutes after the shot above the engine has settled down and all the cylinders have stabilized at this point.  I run a ellison throttle body injector which I think is a fine piece but I have a slight imbalance with my induction system that I need to work on. I think it would improve my fuel efficiency slightly if I could get the right bank a little leaner.  



Number 1 numbers. As you can see, by comparing the pictures the cht is pretty even, I have to work on the egt. Unfortunately I didn't get a shot of number four ( the right front) , it runs cooler by about 30 degrees

I go back and reread these postings when nothing is going on and see things I want to add, today is one of those days. Relocating the sensor to the center head stud from where I have it ( under the head stud by the exhaust port) would result in a reading about 20 degrees cooler than those in the pictures. In the earlier posts I address this, but I still have folks asking why I run the heads so "cool".  To me, they are not cool. I am sure there are places in that head that are much hotter than what the sensor is showing. If there were a way to get the sesors mounted down under the head under the sparkplugs I'd do that just to see what is going on down there. I also feel that the sensors are getting a little cooling effect from being on top in the air stream. Look at the pictures in some of the earlier posts to see what  mean.
  I have folks asking about the summer temps, they generally run a little hotter but not much more. In hot weather the engine makes less power until you get up to altitude so the heat rejection is lower. I have flown with the temps in the middle 80's and the CHT will run about 320 in the initial climb. I usually climb at 65 to 70 when it's hot getting about 500 fpm and the cooling holds it own.
  If anyone has any questions let me know. I think the next posts will be how I did my own dual plug heads, anyone interested?    

I

More Thoughts.

I have wanted to get to the local Vw shop since I saw the article in Hot Vws magazine about the different heads on the market. I needed to buy a carburetor for my sawmill so I figured I wouldn't put it off any longer. While I was there I took the time to look at some heads on the shelf, unfortunately he didn't have exactly what I wanted in stock ( they will be in next week) but what was available will do for today's thoughts.

 Bob Hoover always told me to use stock head castings, they would cool better than the aftermarket types. I wouldn't listen and bought the dune buggy heads the first go around. After I saw the magazine article I knew where Bob was coming from and so I wanted to get my hands on a few different examples for the blog. Here is what I found.    

The head casting that I originally started with and flew for the first 60 hours. I later modified these heads with the fat fin extensions.







The picture above is a well known 042 casting with 40 mm intake and 35.5 mm exhaust valves. I tried to open up the passages where possible but the thickness and shape of the casting prevented much improvement. The fins on the end of the head were nearly completely blocked due to mold shift and I did take the time to open those passages. As I said earlier, I tried unsuccessfully to add fin extensions to this head and just gave up because I was in a hurry and everyone told me it was not needed. Big mistake. I flew these heads for 60 something hours when the issue with the bottom plugs came up. See the earlier text. I went back to them later adding the fins and putting them back in service, that is where the fun began, literally. 



Here is a different casting that is like the original Vw, the difference between the two heads is clearly visible. 



When the two heads are compared you can see the wide open passages in the photo above that are filled in on most heads. How much better would this head cool ? I don't know, I would expect some improvement and in a aero application you need all the help you can get. I'm thinking that there is not a great amount of surface area added but the most important issue is the exhaust valve. Just above and to the right of the screw boss you can see the exhaust valve guide between the two port castings. More accurately I should say the valve guide is in the casting under the fin. Now look again at the top picture. Which guide is going to be cooler? The guide that is buried in the casting and getting heat soaked from the exhaust gasses passing through the head or the one that has air flowing all around it. The only way a exhaust valve is cooled is by heat transfer through the seat when the valve is closed and also up the stem into the guide where the heat is then transferred to the head. A little cooling is accomplished with oil bathing the stem. I have had folks argue that the stem will in effect be cooled better in a solid head because of more mass to absorb the heat. I  just don't buy it and neither did Bob, or Hot Vws.    



Here is what I'm talking about. How much air will get through this head?

Looking at the head above you can see how the two halves of the casting mold were not in alignment. There isn't alot of room for air to get through if this is perfect so with this kind of issue you can imagine how restrictive it will be. This MUST be corrected even if you do the fin extensions. I used a slitting saw in my mill but you can use anything that works, grinder, file etc. This head is the one with better passages down around the valve guide in the middle picture but they blew it on the ends. No free lunch. I would love to have the resources to buy a set of these and try them naked and then try the fat fin mod for comparison to my other data. I have been  tooling with the idea of building a test stand to measure engine performance and start trying different things to see what works best, but money is an issue..... maybe I could just build a MONSTER size motor and use these heads with the fat fin extensions, hmmmmmmmm.


I had to add this for inspiration, I hate winter and needed a pick me up. I flew over 4 hours this weekend on a cross country and doing a photo shoot for Kitplanes magazine. The work, effort and expense of the fat fin engine has paid off. I now just get in and go with much less worry than before.  

 I'd have to come up with a better redrive though. Maybe that will be my next project, I'm getting pretty bored this winter.

My Thoughts



Taking off from Crazy Horse International.



 The snow is flying and it's to cold to do much, my daughter is watching a chick flick on tv which means I am also so it's as good a time as any to post a few thoughts.

 The drawbacks of the fat fins:



 The extensions will keep the heads from fitting in many tools and machines used currently for repair. My engine machinist has no issues with the extensions at this time but problems may crop up later.

  The fins will be fragile, this means extra care in handling and they most certainly will have to be bolted to plywood for shipping.

 I'm sure there are other issues but I can't think of any at this time.

 Some of the frequently asked questions:

 I have have a buddy who knows somebody who doesn't have a cooling issue. Why did you?



 There are many reasons. One is the application. I'm using a Vw with a 1.6 to 1 redrive spinning a 70" Powerfin 3 blade prop. My engine is on a high drag slow speed airframe which requires much more power at a slower airspeed. Now look at the Sonex. They probably climb at an airspeed faster than I cruise and turn around 3000 rpm. I'm turning 37 to 3800 in climb and 3900 in cruise burning 7.2 gph so I'm making more power which means more heat. Apples and oranges.

  400 to 410 doesn't seem that high. Well opinions vary. I know when I was hot rodding these things early in life 350  was about all I wanted to see.  See the text above about what Pratt and Limbach has to say.

  So and so says 450 is ok. Oh, really? How did they determine that 450 wouldn't hurt anything? Like I say, see the text above. The problem is nobody knows how hot is to hot on a vw engine. Who has done the testing? What was the power setting and how much power was produced and for how long?,  Where is the cht sensor? How many hundreds of hours did they get out of it? Did they fly it continuously at this temp????? I'll take Limbach and Pratts word for it though, I have a feeling they know more about what they are talking about. Since they have more at stake than a guy selling chinese heads over the counter I feel they have spent a little more on testing. I know what problems I had with the cht getting above 400.

 What about heat transfer across the joint?  What about it? Look, heat travels to less heat or cold. So what if heat doesn't transfer across the weld joint as well as a solid fin? Big deal! Any heat transfer at all is better than nothing isn't it?

 What about just doing every other fin? I don't know, I didn't try it. I am of the opinion to do them all. It's a lot easier to reduce the amount of cooling versus trying to increase it later. You see, to do this mod requires you to start on the bottom fin and work up one fin at a time, so if you do every other one and find out later you need more you have to remove the head, break off the fins you already have on down to the first one and start over. If you just go ahead and do them all and it proves to much cooling just cut down on the air flow through the fins. Think what it will take to pull the head and redo it.

 Is this mod needed on all conversions? I don't know about this either. To find out one would have to test each application with and without a fat fin mod. Right? In my opinion I would think it would be advantageous, like I said before, if it proves to much then cut down on the airflow which would reduce the cooling drag. I think this would be desirable for the go fast guys who want all the speed they can get. Ever heard of cowl flaps? I know I have had a bunch of the go fast guys talk to me about having to limit taxi time and step climbing to keep from exceeding redline.

  Why is your fuel burn so high?  Ummmm.... I'm making horsepower? I haven't been able to develop a carb that will make 100 hp on 2 gph. Kinda like the 300 hp 100 mpg car carburetor we all heard about back in the 70's that the oil companies supposedly stopped. Look at the claims made by some of these vendors. 100 hp and cruise fuel consumption of 3.5 to 4 gph.  Research brake specific fuel consumption. Ain't that about 45 hp? I could get about 90 to 95 hp for takeoff before the fat fin mod but had to limit it to 30 seconds or less then pull the power back. I interpret their claims to be just that, blast off for a few seconds and then run 45 hp which is about what a stock head fin is capable of cooling.  One other thing to remember, I have a egt sensor on each pipe so I know if I'm running rich or not. 

 Why isn't your climb better if you are making the power claimed? Maybe because I'm honest? Apples and oranges again guys, load up a 701 to 1075 lbs with a Rotax 912 and see what happens. I have static pull tested the plane and it produced 420 lbs of thrust BEFORE I hopped it up a little. With the high lift high drag wing on the 701 pulling the nose up just seems to increase the drag. It seems that my plane will climb at the same rate whether it is 55 or 65 mph.   Watch the youtube videos and see what you think. Search for "wclagg". There will be three short videos..... be sure to watch the end.
 What would happen if you turned more rpm for takeoff?  It would accelerate faster, climb somewhat better, and get hotter while climbing. I tried many, many, different settings of prop pitch all through out testing. At one point I had the takeoff roll about two thirds what it is now, it would get to rotation speed faster than I could think. Climb was a little better with the engine screaming at 4000 rpm and 55 to 60 mph. What really hurt was the cruise, it was down in the mid to upper 70's at 4100 to 4200 rpm. This is just to hard on the engine and prop and I only flew it  a couple of flights before I started setting it back the the way. Interestingly, I have guys tell me I had my prop set wrong, with the redrive I should be getting 4200 for takeoff and 3400 for cruise. Now, think about what I just said. HOW can you get more rpm for takeoff and climb than in cruise without a constant speed or in flight adjustable prop? Ever heard of static rpm? My plane will barely stay in the air at 3400 rpm, 2400 rpm is 500 fpm DOWN. I'm just stupid I guess, I haven't been able to figure out how to make my rpm go down as the plane accelerates into cruise configuration. The rpm on mine, and every other plane I have flown with a fixed pitch prop goes up as the plane speed increases.
 If you don't agree with me the next time you fly do a static rpm test and write it down. Then when you get to cruise write that down also. Sure you can make the rpm go down below static rpm but it will NOT be optimum cruise settings. I cruise my engine at 75 to 80 percent power continuously.        

 We'll cover some more later!

    

A Positive Test

I finally managed to get the engine on the plane without suffering frostbite and waited for a few weeks to test. One factor was the weather but another was my nerves. I was so worried that that this fat fin thing wouldn't work and I would be disappointed yet again. As usually happens I got up the nerve one day that I was in a good mood so I cranked it up to start breaking it in. I was not disappointed.
 Immediately I could see a difference, I thought the cylinder head temperature gauge was broken but I watched all the other instruments and all seemed well. I taxied up and down the runway and had trouble getting the temperature up. This was in March and the ambient temp was in the 40's but I at last got the cht up enough to do a full power ground test. I taxied around until I had the nose pointed uphill and the main wheels in a low spot so I could see what happened. My brakes wouldn't hold the plane before and I could tell the engine was more powerful so I knew I'd have trouble holding it........


Instrument panel showing the tach at the top, intake manifold vacuum gauge to the right and the fuel flow meter added after Oshkosh 2010 under that. 

 From the beginning of the design and layout of the panel a manifold pressure gauge, cylinder head and exhaust gas temperatures for all four cylinders were a must. I fully expected to have some trouble and I wanted to be able to see what each was doing to aid in troubleshooting but I had no idea how much trouble.
I wanted to use good instruments and I liked the features of Aerospace Logic, a Cherokee 180 I had been flying had a full compliment of them and watching ebay for over a year finally paid off. I had some new gauges at a really good price. I decided to install a vacuum gauge instead of a manifold pressure gauge after reading what Steve Bennett had to say about .
 Before I get into the testing I want people to understand something. This entire test program was done by a simple country boy who built a airplane in his shop with what was available or could be scrounged up. The testing was recorded by writing what I saw on the gauges on a piece of paper on a knee board with an ink pin. If you have a problem with that don't read any further.
 I have had calls asking if my instruments were calibrated, temperature compensated, if the data was corrected for atmospheric conditions, the same fuel used for all testing and on and on. The general answer.....no. Then they say the data isn't worth the paper it is written on. Just for the record, the Aerospace logic instruments are certified and they are "mathematically compensated over the entire temperature range".  You know, I don't give a _ _ _ _..... Here is what I do know. I had temperatures that I felt were above safe limits and I took it upon myself to correct that. The point here? The readings are a comparison, they show a difference from a baseline I had developed. There have been volumes written on Temp. compensated instruments and I won't pretend to cover it here but I didn't care if the ACTUAL compensated temperature was 410 or 420. What I wanted to know was what difference I could achieve between the original heads and the modified ones. The instruments are in the cabin and the temperature was close all through out the test. I have a heater ya know. Not being a complete idiot I had the good sense to establish a baseline ( about 75 hours of flying) and then make a change ( fin extension and camshaft) and keep all other things the same to see what effect it had. Here are the results using the same instruments, same sensors in the same location, same prop setting, same octane rating of fuel, timing, oil, and so forth.
 Before the mods:
1. Taxi time was very limited.
2. Full power for less than a minute no matter what airspeed.
3. Cht would be to 410 in 30 seconds after application of power, the manifold pressure would be at atmospheric pressure. Climb would be at best 600 fpm.
4. 65 to 70 in the climb and 4" of manifold vacuum resulted in 410 to 390 cht and about 400 fpm.
5. Cruise power setting of 6" of vacuum would result in a cht of 350 to 370 and 82 mph cruise.
6. Average fuel burn was 5.8 gph.

After the mods:

1. Unlimited taxi time. Full power runs on the ground were possible.
2. Full power can be maintained indefinitely.

3.  Cht at 300 or less with full power in the climb, manifold at 3" of vacuum with wide open throttle. The engine is really pulling harder on the injector and a larger TBI could be used. Climb at least 600 fpm usually over 700 fpm.

4. 65 mph in the climb, again at full power, 550 fpm. Cht less than 300.
5. Cruise power at 6" , 84 mph with cht of 270, some cylinders about 210 to 220 .
6. Average fuel burn undetermined but I know it was higher.

Cruise power, 7.2gph. 272 degrees.

332 degrees in the descent, reduced power.

  










These two pictures are somewhat comparative. The one on the right is with the Generation Two version of heads with the smaller fins. There is a video on Youtube that shows me taking off with a heat soaked engine and climbing 2000 feet. I'll let the video speak for itself. The heads in the video are the original developmental " Generation One" version and they performed much better than expected other than the crack that showed up between the intake and exhaust valve on number two cylinder. I contribute this crack to the heads having been cooked for 60 some hours before the plug holes pulled out. From the beginning of the fat fin test the number two exhaust valve required adjustment every 1.5 hours and it had always tightened up when checked. I flew these heads for a little over 11 hours to obtain good data but it became obvious that the valve was not going to settle in and closer investigation was required. I pulled the head and discovered the crack. I was actually relieved because I worried about the bottom plugs blowing out due to failure of the Helicoil inserts I used to repair the threads.
 I used the data from the original test to come up with a redesigned fin extension. I eliminated one fin by the exhaust port due to interference problems with the exhaust pipe and made the fins all the same length but slightly shorter than the short genertion one fins. The Generation Two heads have been on the engine for about 32 hours with zero difficulties, no valve adjustments or loose head studs, nothing. I put the heads on the engine and flew it one time, cooled it off and adjusted the valves again. So far I have had no issues, but only extensive testing will tell!! 

 The Generation Two head stats with slightly more prop pitch:

1. Unlimited taxi.

2. I have to watch full power runs on the ground.

3. Unlimited full power climbs, 320 max cht. All other statistics about the same.

4. 65 in the climb is about 300 to 290 and the climb rate is about the same.

5. Cruise at 6", 270 to 280, 230 to 240 on the cooler ones, 88 to 90 indicated.

6. Fuel burn is 8.5 to 9 gph in climb, 7.2 in cruise. Based on my calculations using the formula for brake specific fuel consumption I think I'm getting about 100 hp once established in the climb and about 86 in cruise.
 The difference in the two sets of heads are small. I used the "new" $1000.00 heads mentioned before that failed at just over 10 hours. Remember, I took them to my local engine builder and he "rebuilt" them using silicone bronze guides, new exhaust valves and a 3 angle valve seat cut. Both sets were 042 designs with 40 mm intake and 35.5 exhaust but were by different manufacturers. The intake ports appear to be the same between the two manufacturers but the exhaust ports were slightly smaller on the current heads. I also went down to about 8.2 or 8.3 with the compression but this does not seem to effect performance.

The factory fin to the left  didn't get an extension on round two.

The original baffle extends below the extension in this picture showing how much shorter the current version is.

 The reason I went with fewer fins on the new design? Like I said before, I had trouble getting the pipes on and off and testing showed me that I didn't need that much cooling.  I  had a few fins crack off on one head due to the Durafix failing and I noticed no reduction in cooling in those cylinders. I am confident that I am responsible for the Durafix joint failing since the fins that came loose were on the first head I started working on. The second head I did with this material had no loss of fins. I am sure it was due to the fact I had not developed the proper procedure for success early on. I decided to try and tig weld the fins on this time as I fully expected these new heads to be on the plane for some time, and I was told that it couldn't be done. Look below, what do you think? 

These fins were tig welded on. Another thing that I was told " can't be done" 

 Is this Fat Fin Mod necessary? You have to be the judge of that but for me it was essential. Just the piece of mind was worth the effort and for sure my reliability has gone up. We'll talk about the drawbacks of the fat fin mod and answer some frequently asked questions the next time.