Re: [HSS] Timing

Unknown

sixforty wrote:

>

> A while ago, in a discussion it was mentioned by Geoff that the

> fuel that we buy today is different than the fuel that was used when

> our Hudsons' were new. Specifically, Geoff says that todays' fuel

> burns at a slower rate than the old stuff. So I was thinking, since

> the rate of burn is slower, do we need to change the timing for the

> spark? Or is the flash so fast that even though it burns figuratively

> slower, it is still fast enough that no change is necessary?

>

> Tony

>

Advancing the spark will help a little, but the problem is still in the

cam timing, as the charge is still burning as the exhaust valve opens.

There is not a lot you can do about this except get the camshaft

reprofiled, which does make a significant difference. I have no idea of

course what goes on inside the combustion chamber at the point of

ignition, but the octane rating of the modern fuel is much higher than

when our cars were made. Advancing the spark too far means that the

loading on the bearings and pistons is much greater, there is danger of

kick-back on the starter if you forget to retard when starting, and the

idling will be rough, necessitating fiddling with the lever. I'm not a

rocket scientist, but the octane rating is the anti-knock ability of the

fuel. That is, the ability to burn progressively instead of exploding.

Remember when cars used to "pink" under load? This is the fuel mixture

exploding inside the combustion chamber instead of burning progressively

as the piston travels down. Our cars will never pink because the

compression ratio is too low. The higher the pressure in the cylinder at

ignition, the faster the burn, hence our old engines burn the gas more

slowly. The instructions on my Essex distributor say to advance until

engine knocks at 10 m.p.h. with wide open throttle. This doesn't happen

with modern fuel, all that happens is the engine runs rougher, the load

on the components increases, and engine and starter life is shortened.

The ideal would be to shave the head by at least 1/16", and re-profile

the camshaft to take advantage of the modern high-octane fuel. Or you

can lower the octane rating of your fuel by diluting each tankful with

half a gallon of diesel, but be prepared for a bit of white smoke out

the back if you do this. Here endeth the lesson!

Geoff.