srgould41

I have an '83 305 and converted from carb to a '7747 based TBI. The engine is cammed (RV cam) and uses an Edelbrock Performer carb intake.

The tune is coming along nicely. Now that the VE tables are looking good I want to move on to timing. I have read that my engine timing table will differ from that of swirl port heads and have read some posts about needing more initial advance, but what I lack is a good comparison.

Can some post two main timing tables, one for swirl port heads and one for non-swirl port heads? I need an idea on where to begin.

Thanks much!

Steve

RBob

iTrader: (1)

For the swirl port SA, just look at a L03 '7747 BIN. Image is for an LG4 engine with '416 heads in a '85 Camaro.

For initial SA, try 4 or 6* BTDC. It is only used during cranking and when malf code 42 is active.

RBob.

srgould41

Thank you for your answer. I explained "initial advance" incorrectly. What I mean is the timing curve. I am currently set to 0* base timing. My old HEI was recurved so I was all in by about 1800 RPM. I ran with 18" base timing for a total base and mechanical of about 38*. Vacuum was reduced and slowed somewhat, but I had a total of about 54*.

So, what I really meant was I read that my heads like more timing early on than SP heads.

Fast355

iTrader: (2)

Very similar to the CCC Q-Jet spark maps I have for nearly identical engines. Have one for a 83 LG4 Grandprix, 85 L69 Monte Carlo SS and 83-84 LF3 305 Van.

LG4


L69


LF3


My 059 head TPI 310


She would move on the freeway for being a brick with 3.08s and a 305.

srgould41

My engine is actually in a 4,500lb 1971 FJ40. More of a barn door than a brick.

This is helpful and gives me some ideas. Thanks guys.

srgould41

Here is what I did and what did and didn't work.

I altered the main spark advance table to look similar to the LF3 table above. The engine was way down on power, no knocks.

Switched back to my stock spark table and instead added 2 to all cells in the PE Spark Advance table. Wow, what a difference. It was or almost back to carb/HEI performance. Hard to tell exactly since that was a couple months ago. It was a huge improvement, though. My PE %TPS was lowered which makes this work.

Next bin was added a total of 4 degrees to all cells in the PE spark table. Even better lower RPM response, but possibly worse at higher RPM. I need to do some more testing here to know for sure. I will play around with different values like 4 degrees added at lower RPM tapering to 2 or 3 degrees at higher RPM. Testing will tell.