Spark Table Suggestions

[bgott]

Having some issues with this tune I am working on regarding the spark I believe.

I have got my BLM values pretty consistent across the board at 128 or slightly below (rich) and am pleased with them at this point.

It is my understanding that the other thing that needs to be changed with a cam swap (Summit Racing 1102 which is the generic Edelbrock 2102 grind) is the spark table as the valve opening and closing events have changed and thus the spark needs to be sooner/later than stock.

I am running the BJYK BIN with adjusted fueling and have the base spark table advanced 4 degrees across the board. However, I am still getting knock counts at the upper RPM/load ranges which is causing the ECU to retard about 8° of timing out at those ranges and the engine feels sluggish at those RPM.

I know the Edelbrock cam calls for no more than 32° of Advance by 3500 RPM so I am assuming this cam will be about that as it is essentially the exact same grind.

This is my thought. I had a distributor put into the truck a while back and I have a sneaking suspicion it was installed at 0° BTDC. I want to verify this, and then set the timing at 14° BTDC at the distributor.

Then I will datalog and see what happens to the knock retard.

Any suggestions as to a good base for the spark table? Should I just use the stock BJYK spark table for now?

[steveo]

there are a ton of factors that affect optimal and maximum timing advance, the design of the cylinder head can be more important than the cam.

i'd start with a spark table designed for similar cylinder heads and fine tune from there.

spark advance is a lot of trial and error

when you modify an engine, the knock filter can start detecting quite a bit of 'knock' where it doesn't exist. i would remove a bunch of timing to see if the knock retard goes away, just to prove it's real knock caused by spark advance.

i would leave your distributor set to whatever your bin thinks the base timing is

[bgott]

there are a ton of factors that affect optimal and maximum timing advance, the design of the cylinder head can be more important than the cam.

i'd start with a spark table designed for similar cylinder heads and fine tune from there.

spark advance is a lot of trial and error

when you modify an engine, the knock filter can start detecting quite a bit of 'knock' where it doesn't exist. i would remove a bunch of timing to see if the knock retard goes away, just to prove it's real knock caused by spark advance.

i would leave your distributor set to whatever your bin thinks the base timing is

the heads are the stock 193 swirl ports, but the "knock" was being experienced with the base spark table from the BJYK bin. I suspect it is not a legitmate knock because the engine doesn't ping or have any other symptoms of detonation.

I will try removing some timing from the bin and seeing if the knock retard ceases. If I reset the timing at the distributor I will also change it in the bin and just let the computer control the advance. For now I will leave the distributor at 0° (stock) for testing purposes.

Thanks for your feedback!

[steveo]

i usually chuck 5 degrees from the knock area and if the knock counts persist, i call it fake. remember more aggressive cam lobes will cause noisier valve events, and valve clatter sounds a lot like knock both to your ears and a knock sensor. thats why knock sensors and solid lifters dont usually get along