Originally Posted by
Big Lee
AFM you are the bomb. Great wealth of knowledge.
MY question is : I race offroad buggy with a .21 GRP tuned mill and have been running 20% Nitro ( Oils - 10% Synthetic, 5% Castor ) and an O'Donnel 97T (medium) Plug, with good results. Was lacking bottom end so went lookig for answers and found RCTECH and the wealth of knowledge to go with it.
Since reading the GRP thread have learned that the usual tuning meathod of tuning the hsn first then the lsn was not a good way to tune these motors, that they loved having a rich top end and very lean bottom. WOW what a difference. Still working on the tune.
Thinking of uping the Nitro content to 25% as used by the majority of racers at the local club. Was lead to beleave early in my rc life that past 16% was only decreasing the life of the motor, so was always hesitant to go any higher than the 20% originally recomended by my lhs when I started out.
BUT these motors come head shimmed for 30%. Alot of racers also use a P3 ( hot ) glow plug.
Go for the 25% on the medium plug ???????????
How different will I find the tune, power, temps, ease of tune ???????????
Yes, off road engines work well and safely at 25% nitro, but since moving to a higher nitro will increment compression, I would go to a 99T plug, to compensate for the extra heat. You will find the extra low end punch you were lacking. You will have to retune your carb.
As per your method of carb tuning, I desagree with leaning to much the LSN. I work the opposite, rich but not bogging LSN, and lean appropiately the HSN.
AFM