obj1, I'm setting up a 1973 superstinger for grass drags and then ovals in our BEVRA series here in Michigan. This sled was my dads old personal sled, so getting it to run it's best is paramount.
What are your basic recommendations in regards to clutching and carburation? I would like to run a PT II primary and the stock secondary, I have access to several different versions of the PT II, including the 77 black face from the 77 sting. I also have a selection of 102's and 108's that I can use. Our rules require I use a diaphragm carb, but it doesn't have to be a walbro, I can go with tilly, keihin, mikuni bn, all of which I have as well.
I saw a post where you were taking 8500 rpm shift out out of your 73, how did you get the points motor to pull that many rpms without the points giving up and floating? And where were you timing it at?
Totally understand if you would rather not give away your setup, but thought I would ask.
"Be who you are and say what you feel..because those that mind don't matter and those that matter don't mind" ~ Dr. Suess
Post by mooreperformance on Jul 3, 2012 11:41:55 GMT -5
Back in the day I asked the same question at a Scorpion service school. The reply was the WDA6 Walbro. They also recommended the black plastic air horn from a 1972 Super Stinger. This was the best combo they saw on their dyno.
Of course this was before the Power Thrust II clutch so they had no recommendations on that. I would go with the much more modern Comet clutch (if it is legal).
Point bounce with a twin cylinder Magneto has never been an issue, as far as I know. The points open and close much more smoothly with a two cylinder cam than they will with a four, six or eight cylinder ignition cam. A mag is completely different than a battery ignition. Breakerless ignitions provide no performance advantage other than the points won't get dirty or rusty. Magnetos use AC current, Battery ignitions use DC current. AC current will not burn points like DC current and Magnetos never need the points replaced for any reason other than dirt and rust. ;D Because of the lack of points burning (with AC Current), the points can be opened more slowly and closed more slowly eliminating points bounce.
Post by mooreperformance on Jul 4, 2012 11:27:43 GMT -5
I certainly hope you are going to use the large port cylinders (with the 6 studs) and the center spark plug heads. There is a huge difference in horsepower. I also strongly suggest using the dual inlet Donaldson muffler to eliminate the restrictive "Y" pipe in the exhaust system.
When we attended the 1973 Scorpion dealer meeting (back in the day) we were told that the 400TK (Rockwell/JLO) Super Stinger was the fastest Scorpion in the model lineup. Much faster than the 440 (Rockwell/JLO) Super Stinger. The 400 TK had the large port cylinders and the 440 had the standard port cylinders. In 1974 all 400 and 440 Rockwell/JLO engines had the large ports.
The 1973 400 TK would run away and hide from the 1973 440 Super Stinger in a drag race. They even had a promotional movie racing the 400 TK against the 440 Super Stinger.
The 400 TK (Trail King) was the yellow 1973 Scorpion.
The obvious difference between a 440 with standard ports and a 440 with large ports is the 6 studs attaching the heads and the bolt-on exhaust manifold. The standard port cylinders have 4 studs attaching the heads and the exhaust manifold is clamped onto the pipes (muffler clamps) extending from the exhaust ports.
The difference in intake port size and exhaust port size is VERY obvious when they are sitting side-by-side.
Post by mooreperformance on Jul 8, 2012 19:31:56 GMT -5
The guys that raced Scorpions in stock class grass races back in 1973 were stuck with a Donaldson "Silent Power Tuned" can style muffler. It was pretty restrictive compared to the previous years "Power Tuned" muffler. (The 1971 and 1972 standard "Power Tuned" muffler was much louder than the 1973 "Silent Power Tuned").
For extra performance on the 1973 "Silent Power tuned" muffler we would cut the bottom off of the muffler and cut a hole (with a hole saw) into the baffle that sits below the mufflers megaphone.
Cut the hole the same size as the megaphone. The baffle has many exhaust holes cut into it from the factory (it is swiss cheese already) and cutting it with a hole saw is a piece of cake.
If you re-welded the muffler carefully nobody would know.
It was good for a few extra horsepower but didn't increase the sound much. I doubt that it would be necessary to do it now because you could just install a 1971 or 1972 "Power Tuned" muffler and nobody would care (nobody would know the difference).