Adjustable Timing Curves and Heat Build Up

Heat build up in an engine is something that is a concern in several different motorsports. although different brand/make of engines/displacement/and fuel type play a major role in how to deal with heat, for arguement sake lets talk SBC with regular 89 octane pump gas for demo derby use, since that is the sport that seems to obsess about heat more than power.

 As a rule of thumb, i was always taught that less timing is less horsepower/more timing usually means more power to a point….which is usually 35 degrees at peak advance under heavy load or full throttle. so more timing-more fuel-more power- and obviously more heat as a result. remember from a previous blog i wrote about basic principles of performance: you don’t make horsepower without feeding the horse.

Now, so i don’t rehash something i already wrote about, here is a link to a previous blog describing advance curves and ignition. www.norespectracing.com/blog/?p=154 .so throwing real performance out the window i rethought a ignition set up.

a normal vacuum can advance will pull as much as 52 degrees of total advance at high vacuum like decelleration or high idle when base timing is set between 4-8 degrees on a stock engine. obviously at mid throttle this is reduced as it is usually plumbed into ported vacuum so it basically only pulls large amounts of advance at light load or cruising speed.

so what if we now use an adjustable vacuum can and plumb it right to the intake giving us full vacuum at everything but full throttle and cranking speed. we then use the can to crank the timing down to something more like 32-34 degrees. then set your base timing damn near stock at idle to just above zero (TDC) lets say 4 degrees, basically a low timing setting for cranking. lets leave the mechanical advance on the shelf for a moment and say it’s locked. Now, we have an optimum cranking timing setting for a hot engine, a quick response once it is started to a descent timing setting, and when you crack the throttle your timing goes into the toilet preventing any real power, which creates heat. so basically if you sandbag and feather the throttle you will build less heat than a stock distributor and have good response….longer overall run time. when you do open it up the 4.56 gear at the back of the car will make up for it. pair this with a loose bottom end and an absolute dog camshaft profile that will pull a high vacuum signal through a large part of the power band…… the thing may never overheat.

Now, if we include the mechanical advance it can be taylored to the rpm you want. a mechanical advance kit will give you the weights and cam to give you a broader range of rpm you can taylor your full throttle advance to. it also comes with different rate springs so the advance will be right where you want it at different rpm’s.

so lets say you use the springs and weights from your advance kit to conform your advance to come into full advance at 24 degree’s at 2000rpm. you obviously set it with the vacuum can unhooked running at above 2000 rpm with an adjustable light to verify the setting. you still have base timing set at 4 degrees remember. you then hook your vacuum can to intake vacuum and there you go.

you have good hot cranking-optimum low throttle timing for performance and heat build up- and and still have an option for full throttle timing adjustment. interesting theory right? well, to be honest i believe there might be something to it but i won’t do it. first off having a vacuum advance is just something else to go wrong and usually gets in the way of the distributor protector or at the very least makes it a pain in the ass. i still prefer putting the curve weights in and setting total timing with the mechanical advance changing around springs to come in at around your power band of your camshaft for full advance, then just chosing one total timing setting and leave it. BUT if you want to mess with multiple advance curves it’s something to think about.

Comments are closed.