Total timing advance?

[Mac]

I put a freshened roller cam 305 in my pickup and I'm running a non-computer HEI dist.

It has an LT1 cam, Ed. Performer dual plane, Ed. 500cfm 4bbl, block huggers into single 3" pipe with straight thru mufler.
Apart from new springs and exh. valves the heads are stock 187 swirlies.
The HEI is one I ran in my old 283 and I fiddled with the advance springs and installed a limiter plate on the vacuum pull to keep vac advance to 8*.

For that 283 timing was like 12-14 base with 36 or so total. Now I'm reading that these fast burn heads are actually happier with 25-30 total advance.

I know this engine with these heads are among the least favorite SBC's. The mission is MPG and good low torque. I'm almost never a "wind it out" kind of driver and 4500 R's max suit me fine.

I'm just hoping someone can shed some "timing light" on this timing issue. I'm at the break in stage with maybe 25 miles on it and I'd hate to hole a piston.

[wayne petty]

you seem to be on the right curve in reducing..

but send a few minutes reading this multi page  detonation sensor article.


http://www.autospeed.com/cms/A_0348/article.html




i have seen similar knock sensor gauges... that will allow you do note the knocking.. even when its so light that you don't notice it...

http://www.summitracing.com/search/brand/caspers-electronics/product-line/caspers-electronics-knock-gauges
i would also install a vacuum gauge and a tachometer.. even though these are just for testing ...

this way you could monitor the vacuum signal to the Vacuum advance.. and the engine RPMs so you can see which of the advances you are going to need to adjust...

the vacuum advance.. or one half of the centrifical adavance at a time..



lastly... are the 5 and 7 spark plug wires really properly separated... as they fire 1/4 of a crank turn apart... too close will induce a ghost spark in the #7 cylinder when the piston is just below half way up...  this burns off some of the fuel mixture so when the compression builds and the real spark tries to ignite it..  that cylinder will be too lean and melt the piston but also knock slightly..

don't forget the oxygen sensor and air fuel ration display..   so you can fine tune the carb....  there are power valve spring sets... for different cruise manifold vacuums... so the primary rod pistons become  fully seated just below cruise vacuum....  so when you tip lightly  into it... that you raise the needles slightly...

there is also some tuning for MPG in the idle transition circuit restrictions and idle air bleeds...  these are hidden in the sides of the primary boosters..

the only way to get these corrected.. for best MPG.. is with the air fuel ratio display/gauge... so you can see as it comes off idle.. does it stay at the proper 13 or 14 to 1... or does it go lean or rich... then transition to the mains where the power valve springs and primary jetting/metering rods come into play at part throttle cruise...

most of these gauges can be mounted in a rubber gauge block and plugged into the cigar lighter socket for power and ground... with just a wire to the oxygen sensor, another to the detonation sensor. and a vacuum hose.. this makes them mostly easily removed so there is no need to figure out where to mount these gauges..   might be neat to be able to move them to the engine run in stand..  if you have one..

[Mac]

Thanks Wayne! All good info -with bonus extras, as usual.