[ted]

I've still have a Milodon gear drive on one of my Fe's but it's still there only because the engine was initially set up for it. It is quite though and has remained dependable over the years.

I've dyno'ed both this gear drive against a double roller chain with the camshaft being degreed in identically and the chain does still make more horsepower than the gear drive. Whereas the ignition timing with a gear drive remains constant throughout the rpm range, the ignition timing using the chain can be seen to start retarding after 3000 rpm (that's where my total ignition timing is all in) and will retard up to 4° at 6000 rpm. Timing comes right back in place at the lower rpm's.

The retard effect using the chain is due to chain elasticity where the chain actual stretches longer at higher rpm and comes back at the lower rpms. This is congruent to horsepower production and is in a sense variable cam timing.

My experience with the circle track engines is that they do like the gear drives over the long haul as the cam timing remains constant over the course of the season. The timing chain on the other hand tends to stretch over the course of the season and requires the ignition timing to be corrected in order to compensate while ignoring the fact that the camshaft is slowly retarding away from its optimum initial setup earlier in the season. Timing chains do not appear to like the constant up and down acceleration that's seen in this type of racing. Of course this is using roller valve spring pressures which puts an additional amount of force on the valve train not normally seen with engines using valve springs of much less pressure.