7747-7427 Swap

[Scooterwrench]

Maybe add 5% across the board then, run the spreadsheet calcs?

OK, this is something I've discovered. Do not interpolate your VE tables. It will have you chasing your tail. Find a VE table that is close to the engine you are running and log BLM's and run them through dave w's spreadsheet a few times. If you think about it the A/F demand changes in a non-linear manner with RPM and load. There is always going to be an area in the rev/load rage where the engine draws the most air and that is going to create a hump in the VE table. When you interpolate it flattens the entire table and and you wind up back lean or rich in areas where engine doesn't like it. Interpolating does seem to work better on the spark tables, it smooths out the timing curve.
Once I get a new KS installed I'll start bumping up the advance then retard the cells where it shows knock.
You mentioned turning off your PE. Mine is running great right now with the PE off but once I get the VE's right that will change. I was looking at the PE A/F ratio in the .bin and they have it at 12.1, seems a little rich to me. I'm thinking more like 12.8

Aright, back to it!!!

 

[PlayingWithTBI]

Interpolating does seem to work better on the spark tables, it smooths out the timing curve.
Once I get a new KS installed I'll start bumping up the advance then retard the cells where it shows knock.

You'll probably find that you need to reduce SA at higher MAP/RPM than when "All In" closer to the middle. Here's an interesting thread where @84Elky explains SA on post #3 and made a spreadsheet to help with your SA tables. It is a direct copy and paste for the EBL but, IIRC yours should be about the same. Down on post #8 @Sharp38 corrected a loop in the table and attached his .xls

I had to lower my SAs some at higher MAP/RPMs than his formula did due to my aluminum heads' "Fast Burn" design. Check it out and enjoy!
www.thirdgen.org/forums/diy-prom/761049-spark-advance-table-example.html#post6301288

Spark Advance table example needed - Third Generation F-Body Message Boards

DIY PROM - Spark Advance table example needed - Trying to understand the sa tables vs actual engine excelleration vs mph at the foot pedal. Found this graph from older thread here and compared it to my bin which is a lot different. Can there be a good/simple reason?...

www.thirdgen.org

 

[Scooterwrench]

You'll probably find that you need to reduce SA at higher MAP/RPM than when "All In" closer to the middle. Here's an interesting thread where @84Elky explains SA on post #3 and made a spreadsheet to help with your SA tables. It is a direct copy and paste for the EBL but, IIRC yours should be about the same. Down on post #8 @Sharp38 corrected a loop in the table and attached his .xls

I had to lower my SAs some at higher MAP/RPMs than his formula did due to my aluminum heads' "Fast Burn" design. Check it out and enjoy!
www.thirdgen.org/forums/diy-prom/761049-spark-advance-table-example.html#post6301288

Spark Advance table example needed - Third Generation F-Body Message Boards

DIY PROM - Spark Advance table example needed - Trying to understand the sa tables vs actual engine excelleration vs mph at the foot pedal. Found this graph from older thread here and compared it to my bin which is a lot different. Can there be a good/simple reason?...

www.thirdgen.org

Hmm, that's pretty interesting. I'll have to give that a whirl.

 

[L31MaxExpress]

OK, this is something I've discovered. Do not interpolate your VE tables. It will have you chasing your tail. Find a VE table that is close to the engine you are running and log BLM's and run them through dave w's spreadsheet a few times. If you think about it the A/F demand changes in a non-linear manner with RPM and load. There is always going to be an area in the rev/load rage where the engine draws the most air and that is going to create a hump in the VE table. When you interpolate it flattens the entire table and and you wind up back lean or rich in areas where engine doesn't like it. Interpolating does seem to work better on the spark tables, it smooths out the timing curve.
Once I get a new KS installed I'll start bumping up the advance then retard the cells where it shows knock.
You mentioned turning off your PE. Mine is running great right now with the PE off but once I get the VE's right that will change. I was looking at the PE A/F ratio in the .bin and they have it at 12.1, seems a little rich to me. I'm thinking more like 12.8

Aright, back to it!!!

On E10 fuel, 12.0 at peak torque and 12.6 at peak HP is about right.

 

[Scooterwrench]

On E10 fuel, 12.0 at peak torque and 12.6 at peak HP is about right.

With a worn out, low compression 305?

 

[Scooterwrench]

You'll probably find that you need to reduce SA at higher MAP/RPM than when "All In" closer to the middle. Here's an interesting thread where @84Elky explains SA on post #3 and made a spreadsheet to help with your SA tables. It is a direct copy and paste for the EBL but, IIRC yours should be about the same. Down on post #8 @Sharp38 corrected a loop in the table and attached his .xls

I had to lower my SAs some at higher MAP/RPMs than his formula did due to my aluminum heads' "Fast Burn" design. Check it out and enjoy!
www.thirdgen.org/forums/diy-prom/761049-spark-advance-table-example.html#post6301288

Spark Advance table example needed - Third Generation F-Body Message Boards

DIY PROM - Spark Advance table example needed - Trying to understand the sa tables vs actual engine excelleration vs mph at the foot pedal. Found this graph from older thread here and compared it to my bin which is a lot different. Can there be a good/simple reason?...

www.thirdgen.org

I tried that timing table builder and failed horribly. I built this table the old fashioned way, it looks like it will work. I took MaxEx's advice and limited all out timing to 30deg. I'll take it easy and watch for knock and trim back where needed.

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[L31MaxExpress]

With a worn out, low compression 305?

I tried that timing table builder and failed horribly. I built this table the old fashioned way, it looks like it will work. I took MaxEx's advice and limited all out timing to 30deg. I'll take it easy and watch for knock and trim back where needed.

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Cruise timing can be low 40s. I probably have a good TBI head based advance table on my old Netbook.

 

[Scooterwrench]

Cruise timing can be low 40s. I probably have a good TBI head based advance table on my old Netbook.

That's a pretty steep ramp rate.
Sure man, thanks. I'll give it a try.
I tried a more aggressive curve earlier today and got lots of audible knock when trying to accelerate at 40 MPH. Sounded like a 300lb rattlesnake under the hood. I went and got a KS today and am going to install it in the morning. Maybe if I'm lucky the drain hole will be clogged with scale, not a fan of green showers.

 

[L31MaxExpress]

That's a pretty steep ramp rate.
Sure man, thanks. I'll give it a try.
I tried a more aggressive curve earlier today and got lots of audible knock when trying to accelerate at 40 MPH. Sounded like a 300lb rattlesnake under the hood. I went and got a KS today and am going to install it in the morning. Maybe if I'm lucky the drain hole will be clogged with scale, not a fan of green showers.

This was a stock pull out of a LF3 4bbl 305 van eprom. Had an added 4-6° at WOT. This was before GM neutered the cruise timing advance. I used this timing map as a starting point for a 305 with 601 and later 081 heads under TBI and later TPI.

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[L31MaxExpress]

This is what I run as a starting point for a Vortec head engine. It is probably 4° too much for a swirl port head above 80 kpa. Neither TBI or Vortec heads like much of an actual curve in my experience. A vast majority of the WOT timing will be in in the curve by 2,400 rpm. If you are cruising ~2,000-2,400 rpm and under ~60 KPA will likely want high 30s and low 40s for timing advance. At TDC or 0° on the distributor initial advance you are limited to 42° advance.

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