i have been reading that a good improvement for a 4.9l is to change the BTDC from 10 to 12...now im new to the insides of motors.. so any knowledge on what exactly BTDC is and how to go about changing it, and WHY changing it would provide a little better performance would be nice, thanks

 

I'll take a stab at an explanation. BTDC stands for Before Top Dead Center. Top dead center describes the point at which the piston is at the very top of its stroke, so BEFORE TDC is the point where the spark plug fires. The earlier that the fuel/air mixture starts to burn, the better for power and mileage, up to a point. With too much timing advance, the flame front tends to collide with the top of the rising piston, leading to spark knock, or ping. This can lead to excessive heat on the piston top, which CAN melt it. So the general rule of thumb is to advance the timing until you hear spark knock, then back it off 2º.

One kinda handy thing about the 300 is that it came with a knock sensor starting with the switch to EFI in '87 (I think...might not have been until '89). It essentially senses vibrations in the block associated with spark knock, and retards the timing until the knock is gone. So theoretically you could dial in 50º of initial timing, and the engine would run without knocking, but I wouldn't!

Checking/changing the timing is pretty simple. Find the timing mark on the crankshaft pulley and mark it with something bright...paint pen, chalk, etc. Warm up the engine, then turn it off and hook up your timing light. Pull the SPOUT connector out (which I can't remember for the life of me where it's located) and loosen the distributor hold-down bolt. If it's been a while since the timing has been changed, it's possible that the distributor could be seized in the block...usually requires lots of penetrating oil and possibly some GENTLE persuasion with a hammer. Then start the engine, and pull the trigger on the timing light...on the 300, the timing marks are on the passenger side of the balancer. Ignore the marks on the left side. Now turn the distributor to get the timing you're aiming for (I THINK clockwise advances the timing...been a while!) Tighten the hold-down bolt, turn the engine off, and put the SPOUT connector back in. Viola, you've just changed your timing.

I personally ran my 300 at 14º BTDC with no ill effects...it did feel a bit spunkier, but that might have all been in my head.

Good luck...
Pat

 

thank you for the explanation!! im 18 and still learning these things. but i think ima go to work and ask one of my mech friends to help me out (40 year old certified ones that have done this stuff 200 times that i can learn from and not other 18 year olds!) and now knowing what it is, it makes sense to me, and i don't have a timing light but i no how to use one. so ima take a stab at it this week and let ya no how it turns out! but you say the 300 wont spark knock...how will i no if im to far then??

 

I'm 42 and been around the block a time or two, but I can't accurately answer that question! I would think that the engine would be a little less efficient if the computer is constantly pulling timing. Maybe you'd try to check the mileage before and after the timing change. Keep upping the timing until your mileage maxes out, but I wouldn't go much over 14º or 16º, as anything over that would be detrimental.

Pat