stunthanger.com
Engine basics => Engine set up tips => Topic started by: Herman Green on January 12, 2017, 09:30:42 AM
-
I read a number of threads regarding the TT GP 42. General conclusion was that pretty much everyone liked it. Opinions ranged from as good/better than a LA 46 to not as good as a LA 46, but good anyway. Anyhow, I've acquired several.
Installing the venturies, on the first two I put in the OS FP 40 venturi, which measures about 0.282" or 0.283". Then, reading the instruction sheet for the motor, the dang thing isn't a 42 after all, it's a 40 (0.396). So, the question on the venturies. As I said, the large OS venturi is about 0.283". The FP 20-25 size I previously bought measures 0.268". The current FP 20 size they're selling now measures 0.259".
So which size have you guys used? I always put the 0.268 size on the LA and FP 40 engines.
I'd appreciate your thoughts/experiences.
Thanks,
Herman
-
In looking a little further and digging through my "stuff", I find I have two different spec sheets for the Thunder Tiger GP-42. One list the bore as 0.835" and the stroke as 0.724" for a displacement of 0.396 ci. The other sheet lists it as 0.846" bore and 0.748" for a displacement of 0.421 ci.
Well, I have five of these engines on hand and I couldn't stand not knowing, so I pulled the heads and measured the bores. All five measured 0.8445". I figured this equates to the 0.846" since ABC/ABN cylinders are ground with a slight taper to expand at the top when hot (and my digital caliper hasn't been calibrated).
So, believing that all mine are indeed 42's, I think I'll plan on the larger OS venturi unless someone has a better idea.
Herman
-
I don't have some, but Leonard Neuman wrote that the venturi boss/bore is tapered, so it takes some extra PITA to make venturi inserts fit. Have you looked into that delightful feature? ??? Steve
-
The first one I did had a tapered bore in the case and I had to slightly taper the base of the venturi. Not a big deal with a fine file. None of the others since have been tapered. They do, however have a small cast in boss near the bottom that limits the insertion depth. I had to file off about 1/16" from the bottom of the venturi to get a good tight compression of the o ring.
Herman
-
Veturie size'd depend on prop , plane size & weight , Line Length , and altitude at field .
A venturie that works at 3.000 in the mid thirties C ( about 90) does about 80 mph at sea level in the teens . %^@ mw~