Author Topic: Nitro/No Nitro puzzle (Read 1019 times)

Terry Caron · « **on:** June 14, 2015, 02:20:25 PM »

So I've been benching a Forster .35 (OS 6/A3 plug) with different props/fuel mixes.
There's no rpm drop when igniter is removed with 14.5/60.5/25 mix, ~200 rpm drop with 0/75/25 mix, as might be expected.
The puzzler is that 0 nitro will peak the various props at 2-300 rpm higher than 14.5 nitro.
Not what I expected.
Is it just something I didn't know about/haven't seen before or is this strange?

FWIW, it has a c/r of ~9:1 and recommended "hot fuel" was 37.5/37.5/25 (!).

Terry

Tim Wescott · « **Reply #1 on:** June 14, 2015, 02:28:41 PM »

Are you sure about that compression ratio? In my only-moderate reading, and very limited experience (a few heads for Cox 049's), an RPM drop with nitro only happens if you've got lots and lots of compression, and the motor is actually overcompressed for nitro.

(BTW: if you build a glow plug adaptor for a Cox reed-valve 049 that just barely clears the piston it'll run all day on 5% nitro, where it wouldn't even start before with a standard plug).

Terry Caron · « **Reply #2 on:** June 14, 2015, 02:50:48 PM »

That spec comes from the engine review posted on SpectreFlight Tim - I know it's the ratio of cylinder + combustion chamber volume to combustion chamber volume but I don't know how to accurately measure them.
FWIW, performance data reported in the review are way above what my engine will do.

Terry

Author Topic: Nitro/No Nitro puzzle (Read 1019 times)

Terry Caron

Nitro/No Nitro puzzle

Tim Wescott

Re: Nitro/No Nitro puzzle

Terry Caron

Re: Nitro/No Nitro puzzle