Hello all. I've got a bit of a thought experiment for any old experts familiar with the old OS Max-S 30 engines from the 1960/70s.

Suppose it's the mid 70s and you're into 1/8 RC drag car racing. You're at your workbench fiddling with your Team Associated RC100, Delta Super J, or scratch built car when you notice your OS S30.

In that instance does the thought ever cross your mind that you could make that OS faster than the Veco 19, or K&B 3.5 that were typically used in that era? If so what period correct mods could you do to get every thing out of the OS?

well you could buy 60% Nitro
when I was running RC boats guys started to put 80/90 size Tuned Pips on there 60 size engines. now for your 35 you could put a 50 size tuned pipe on it. yes yes T-pipes are long if you want to run the 35 in a car. but what you can do is buy a 50 size Ducted Fan T-pipe and run the pipe forward, I say this because the Exhaust Stinger on these pipe face backwards. slick, hu.

good luck.
Jim
PS, I don't know what size pipe this one is!

In the mid 70's we did exactly what you are asking to a close relative of your motor, a baffled iron piston O.S. 15. And as I recall, also briefly to a OS 35 S, an even closer relative. Although neither of these engines were really designed for high power...

On the 15, we removed the venturi entirely so that there was a gaping hole in the crankcase, probably twice the area of the original venturi. To compensate for the loss of fuel draw / suction, into one of the backplate bolt threads, we screwed in a "pressure tap" - a threaded hollow nipple. This was an O.S. option at the time and even today should not be too hard to find something that fits. In case you don't know, you connect the nipple to one of the vents on the fuel tank ( and seal any others off ). The crankcase provided a source of pressurised air and ensured a steady fuel supply to the engine, even during sudden changes of direction ( we flew combat wings at beginner level ).

I seem to remember the 15 screamed ( probably in protest ) after that. Today with a little more knowledge learned, I would use a larger venturi, even if I had to make one, as the air entry is far smoother and this is likely to give even more power than leaving the venturi out altogether.

I think on the 35 we used the larger of two available venturis but it wasn't much larger. I don't recall how much effect this had, probably because the plane didn't fly very long before it was crashed.

Of course even simpler is to raise the nitro content as said above. But if you go too high, you presumably will need to fit one or two extra head shims to bring down the compression ratio.

Pressure tap, as seen on this Taipan 15.

And lastly, I just remembered you said r/c cars, so you would be looking at larger / enlarged carburetors in place of the venturis. You would probably have your work cut out for you trying to get the mixture right throughout the rev range though. If your carb. is a good one, I can't see why it shouldn't be doable.