Performance Timing Table Chevy 5.7 Liter TBI ECM 1227747

[tolow4phathoes]

Bin is the same. The issue is the XDF from this website automatically removes the Spark Bias so what you see in spark Advance table is actual timing. Not timing with 9.84 degrees added to it. (if small block, if big block there is no bias so any XDF will show actual timing)

Sorry still a lil confuse, please bear with me. But why is there a big timing difference between the two tables?

[Fast355]

Figures below the "Lift @1.5" are valve lift, using 1.5 ratio rocker arms. Cam lift multiplied by rocker arm ratio = valve lift.

dave w

Dave the 350 TBI uses the 274 aka gm 929 cam. I was a little off on the lift, but that is due to the goodwrench advertised specs being wrong. I was confusing 156 and 773. They are basically the same with 1* wider lsa on the 156.

[dave w]

Sorry still a lil confuse, please bear with me. But why is there a big timing difference between the two tables?

The .xdf file can be configured to display the spark table in several ways. The "Spark Bias" parameter can be subtracted in the (if the .xdf author so desires) and that's why there is a difference between the two .xdf files.

dave w

[dave w]

Dave the 350 TBI uses the 274 aka gm 929 cam. I was a little off on the lift, but that is due to the goodwrench advertised specs being wrong. I was confusing 156 and 773. They are basically the same with 1* wider lsa on the 156.

Fast,
I often use re-ground camshafts ( http://www.oregoncamshaft.com ), so I'll measure the camshaft to make sure I have a good core. I've only needed to measured a few TBI camshafts. It's been a few years since I last measured a TBI camshaft, but I'm remembering the lift of the three or four I measured was something close to .350 / .380 @ 1.5 rocker arm ratio.

I've used the TBI performance timing table I posted on several different EFI friendly camshaft profiles, up to about .423 / .443 lift @ 1.5 rocker arm ratio. Depending on the vehicle I'm working with, I've needed to make adjustments to the timing table, that's tuning. Camshaft profiles effect cylinder pressures, so there is not a "one size fit's all" performance timing table.

The intent for posting the TBI performance timing table was to help others learn spark tuning by experimenting with a decent / proven timing table to begin with. My method to develop a good timing tables involves using data log analysis with Excel. I use Excel to trend spark advance Kpa vs. RPM vs. MPH. Ever look at Kpa vs. high knock counts?

dave w

[Fast355]

Fast,
I often use re-ground camshafts ( http://www.oregoncamshaft.com ), so I'll measure the camshaft to make sure I have a good core. I've only needed to measured a few TBI camshafts. It's been a few years since I last measured a TBI camshaft, but I'm remembering the lift of the three or four I measured was something close to .350 / .380 @ 1.5 rocker arm ratio.

I've used the TBI performance timing table I posted on several different EFI friendly camshaft profiles, up to about .423 / .443 lift @ 1.5 rocker arm ratio. Depending on the vehicle I'm working with, I've needed to make adjustments to the timing table, that's tuning. Camshaft profiles effect cylinder pressures, so there is not a "one size fit's all" performance timing table.

The intent for posting the TBI performance timing table was to help others learn spark tuning by experimenting with a decent / proven timing table to begin with. My method to develop a good timing tables involves using data log analysis with Excel. I use Excel to trend spark advance Kpa vs. RPM vs. MPH. Ever look at Kpa vs. high knock counts?

dave w

Understand that completely. I use TPS vs MAP vs MPH/RPM alot myself.

I have run the Mellings MTC1 and Federal Mougal CS1014R in TBI engines with no more than a slight fuel pressure and timing tweak with good results.