I just acquired a decent used G60 that I plan to use in a Super Kaos. Here's one question, what carb venturi size is correct for this engine?

It currently has a throat diameter of 8mm.

I also have a Como 40 (history unknown) that has a 9mm throat diameter. I just put a ring in the Como and am running it in. After about 40 minutes it's starting to take leaning out, will hold an idle and seems to transition OK. So, the "big" carb works on the 40. I have no current use for this engine & if I did it would likely end up in a sport model that doesn't need every ounce of power. For information I have a Magnum GP 40 that has a 5.25mm dia carb.

So, do I switch the carbs and put the 9mm on the 60? Is the carb size muffler/pipe dependent? I'd like to find a vintage closed front Semco for it.

Also, the G60 head is stamped 20N; anyone know what that means? One just sold on ebay with same head stamping. I've posted this here because I figure there are a fair number of vintage pattern guys flying Super Tigres.

Jim

I just discovered that the two Supertigre BG60 Blueheads I have use different size throat diameters. The engines are identical other than that. I haven't measured them but the handle of my #11 x-acto knife will not go in the small one and goes in the larger throat very room to spare. I just measured the handle and it appears to be 8 mm. So one throat diameter is less than 8 mm and the other is more, maybe 9 mm. I flew both of these engines for years in the 70's and did not realize the difference in throat size or in power output. I flew them in my 78 Nats winning Fliteglas P-51 and another Flitglas P-51 that I flew over 1000 flights. Still have both P-51's by the way.
Ralph White, Neoga, IL

Ralph, thanks for input.

Maybe within a certain range on our model engines venturi size has little impact on performance. Certainly on cars/motorcycles a larger bore = more power and degraded low end performance. I have a Webra 61 Blackhead, and its carb bore looks to be about 8 mm, same as a Mark (Moki) 61 long stroke. I'm just surprised the Como 40 I have ran as good as it did with that 9mm carb.

I have to tell you how much I lusted after one of your P-51s. I never thought I was pilot enough to handle one, so I never got a chance to own one. Are you or is anyone else still making up the kits of the fuselages?

Jim

Jim,

Just measured both my G60 Blueheads. Carbs are both 9mm.

Derfly

So did I. Great version of the P-51 and I wish it were still available today. I believe the kit was based on Frank Baker's design published in the September 1967 issue of RCM.

Ray

I don't know of anyone producing the Fliteglas P-51 fuselage or kit. Every once in a while one comes available on e-bay. Right now I have 2 leads on kits in my area that where bought but never finished. I haven't had time to follow up on them to see if they could be bought.
I've been out of modeling for about 27 years, just getting back into it this summer.
I wonder how I ended up with a supertigre bluehead with only a 7mm (approx) throat in the carb? It seems to have plenty of power for the Aeromaster its in right now.
Ralph White, Neoga, IL

Yes the Fliteglas P-51 was based on Frank Baker's design. On my P-51's I thinned the wing airfoil at the tip for better scale appearance. I don't remember the actual amount I thinned the tip, but could measure the thickness if anyone is interested. That was the only modifacation I had on the stock kit.
Ralph White, Neoga, IL

Derfly, What muffler are you running on you Blueheads? I'm having trouble getting the correct muffler. The Mac muffler seems to lower the RPM on mine by about 2000 RPM. I just opened the exit in hopes of getting the RPM up. But afraid the noise will be up also.
Ralph White, Neoga, IL

Ralph, it is wonderful that you are back and active in hobby again. I always thought you did a great job with your kits.

Ralph,

I've attached a couple of picture for you.

The smaller muffler is the original that I bought back in 1983 with my first G60. It's a so called venturi type and rather small. The outlet is 6mm dia. and the front venturi "inlet" is also 6mm dia. The effect here is that the muffler exhausts at both ends (a bit like me) and doesn't muffle much at all. With the front venturi inlet blocked off, the engine looses considerable power.

The bigger muffler has about double the internal voume and an outlet of about 9mm. It is the muffler originally supplied with the first true 60 size schneurle ST, the S60 with the dished head. It is a good useable muffler.

The finned header was also sold with pipe as an extra to fit the S60 and is the combination I mostly use on my G60's.

Bear in mind that the the exhaust dimensions and the hole spacing on the current S61K is still the same as the G60 meaning that any ST 60 size muffler will suit your application.

DerFly

Thanks Derfly. Guess I'll have to keep my eyes open for a used supertigre muffler. Right now I'm going to keep using the Dubro baffle plate muffler even thou it is a little louder than the other mufflers being used at the flying field. The Bluehead is running real nice with the Dubro muffler on it.
Ralph White, Neoga, IL

Jim,
With regards ST G60 Blue Head, I do have a small collection of these engines and they all have the 9mm choke. Smaller chokes were certainly produced but I think it was on the much earlier models that did not have the 'mag' type carb. One of the pictures I have posted shows the most recent muffler produced by ST and it will fit the G60. I must admit it is not the prettiest of mufflers but works very well provided you do not push the muffler fully home, if you do the peak RPM will drop by about 2000. For those of you who have a keen eye you will notice that one of the G60's has the 'present day carb,' the motor is a bit a a hybrid, it was made for me by the UK ST agent and enjoys PDP porting and ABC construction. This PDP/ABC engine was quite a rarity in the UK, I believe only about 10 were ever imported, how about the USA?
They are great engines and they are still sitting in boxes out there somewhere in peoples attics!
John

I have a Bluehead PDP, ABC, Perry carb with pump, new in the box in my attic! Will be putting in a Phoenix 5 thats also in the attic.

Jeff

Windy,

A lovely collection and all of them cleaner than my two! FYI, both of mine are also PDP, abc. One was bought in Sweden and the other here in Australia.

DeFly

John: Thanks for the information confirming the venturi size. I have switched my 40 and 60 carbs and now have them where they belong. I did get a modern swivel ST muffler with my G60 so at least I've got something for it. But I can't bear to use it on a vintage plane, whether pattern or sport, so I've been searching for a closed front Semco with no success so far.

That is a nice collection of G60s. In a perfect world I'd be mounting my NIB Bluehead on my just-completed Ralph White Fliteglas P-51.

Jim

Thanks Jim, There are still some Fliteglas P-51's out there. They are just hard to find. I have leads on 3 in my area.

I forgot to mention. After opening up the Mac's muffler exit to 11/32" (Also opened muffler intake as much as possible) the muffler still reduced the RPM by 2000 compared to the Dobro baffle plate muffler. The noise did not go up a noticable amount. But the Aeromaster just doesn't fly the same with 2000 RPM taken off the top. So I plan to use the Dubro muffler until I find something better.
Ralph White, Neoga, IL

I picked up some old magazines at the LHS today. Model Airplane News Nov 71 has a Peter Chinn article on the G60 Bluehead.

Some of the information: in 4 years more than a half dozen variants; 4 different heads; six different carbs, latest has effective choke area of 20 sq mm, which is same as fitted to the less powerful ST60 (small case) and ST51 - this choke area is smaller by 20% compared to the then average 60. Chinn says it is reasonable to suppose a larger carb would deliver more power but that Super Tigre must have their reasons. The 71 engine did not yet have the bosses on the sides of the exhaust for the muffler bolts. They recorded a 400 rpm drop on the open front muffler, which they said was very loud. 11500 on 11x7

If I get the math right, the 20 sq mm equates to an 8 mm choke diameter (effective area = area of choke less the area of the spray bar). The spray bar averages 3.725mm wide, so its 3.1416 x 4 squared less 3.725 times 8, answer about 20.5.

The 9mm carb bore gives 30mm choke area, a 50% increase.

Based on this article it would seem either 8 mm or 9mm is OK, the 9mm being for later versions. My G60 does have the later crankcase and the later crank, but no Bluehead, so who knows what carb it originally had.

Jim

Thanks Jim for that information about carb sizes. The 9mm I have is busted, so guess I'll start looking for a 9mm carb to try in the Aeromaster to see if there is a difference in power.
Ralph White, Neoga, IL

Don't forget the flat or round spray bars that made a volume difference.
I have one of the ST pipe finned elbows ,NIP , pictured in post # 10. It is for sale.........It does not come with an extention..........

More carb venturi sizes for those who may be interested.

My Super Tigre addiction resulted in a NIB G60 Bluehead. This one has the 8mm carb and it came with the exhaust baffle. It does have the muffler lugs on the side of the case, and they are slightly different in shape than the other G60 I have.

Also got a nice, excl+ compression V56 (small case 60 size). This on has the 9mm carb. Go figure.

Jim