7427 upgrade tuning help understanding

**dave w** · 06-08-2019

Link I posted to the Stock 1998 Vortec L31 Timing Table: http://www.gearhead-efi.com/Fuel-Inj...-Throttle-ONLY!

There might be other gearhead-efi posts with better performing (NON STOCK) L31 timing tables??? Perhaps those members will post in this thread with a READABLE L31 Performance Vortec timing table??? A copy / paste version of a L31 performance timing would be best for ALL members!

dave w

**typhoonss92** · 06-08-2019

Thanks dave. I have seen the thread you linked. with the 7747 I started with the vortec bin you posted and changed the timing table to fit my motor, I had it running without knocks. So when I swapped over to this computer I copied the timing table and VE for the starting point. Just wondering about these what I want to call false knocks since there is no timing removed.
I just ordered a standard ks6 knock sensor will have it tuesday.
Here is my SA table right now. I started in wot high kpa in the 30-32 range and have slowly brought it down from knock. I could run 30 degrees around 3400-3600 on the 7747 but seem to get knocks with this 7427. vortec_sa.PNG

**dave w** · 06-09-2019

Timing tables can be challenging. Most of the time, I start tuning with a factory timing table, like the Vortec L31 table I posted a link to and tune from there. Once the stock timing table has been tuned for a good fuel table, then I adjust the timing table for optimal spark advance / optimal fuel tables / optimal performance.

Depending on the engine modifications, it might take several or even dozens of data logs to get achieve optimal performance.

Tip, sometimes adding spark advance will reduce knock retard.
Tip, sometimes spark advance changes of 1 degree or less will have a significant change in performance / knock.

I authored an Excel WBO2 spreadsheet to help others tune the 16197427: http://www.gearhead-efi.com/Fuel-Inj...g)-Spreadsheet

dave w

**typhoonss92** · 06-09-2019

Dave thanks for the input. I am using the excel wbo2 sheet. I have been trying to read as much as I can and search as much as I can before I post because there is alot of information on this site, if I do not find what I am looking for then I ask the great set of minds that are on this site. I have tried running the stock vortec tables, and that is where I started with the 7747, the bin you posted for that system. I have had to agressivly add spark to get any power. I installed the 7427 last weekend and have burned about 25 chips so far trying to figure everything out. Your wbo2 excel sheet has helped alot with the VE tables and they are pretty close.

So is knock without timing retard already low and needs to be raised and knock with timing taken out needs lowered?
I usually get 400-600knock(not retard in timing) when I start tunerpro connection but have dropped that with adding a little more timing at 400-600 rpm and last datalog it was 188. I did ad some timing where the knock without retard was and my knock counts have dropped but still there so guessing more timing. I am closing in on 30-32 in the higher map mid to higher rpm and I know that is what the max should be for 93 octane with vortec heads.

I just set up another chip and going to head out for another datalog, lets see how it does. As always thanks for the help.

**tayto** · 06-09-2019

what plugs are you running? i had maxed out knock counts in a short drive similar to you. went from R44LTS to R42LTS and knock counts when down drastically.

**typhoonss92** · 06-11-2019

I am running since I put in my msd 6AL a acdelco 41-993(19256067) iridium plug. I had acdelco rapidfires before that #14's. I had no knock issue when I was running the 7747 computer with these plugs. When I swapped to these the motor ran smoother. I know to stay with acdelco or ngk since they make the acdelco plugs. I would not be opposed to trying these just need to get to the parts store and get them.

I will have the new knock sensor (ks6 standard) tomorrow so hopefully get it installed tomorrow night.

I tried a starter timing table that Fast355 posted on TGO for vortecs, he said that he uses it as his starting point for stock to mild cam motors. I tried it and seemed to work well except high rpm high map, upped the timing there and just from one adj seems to run pretty good, still needs refined. Here is what fast355 posted and I modified it for my spark table. maybe this will help others as it was pretty good for the first drive. fast355 starter vortec timing stock-mild cam.PNG

Fast355 if you are around maybe you can chime in on this and if you have made any changes over the years on this for your starting point for the vortec heads. I would think 30* is high at idle but I did not get knock.

**tayto** · 06-11-2019

i know knock sensor torque plays a part in knock sensitivity (IIRC, 30 ft-lbs) along with using the already applied thread locker that comes on the ac delco brand. have you tried regular copper plugs? I recall fast355 supporting this some years ago...

**Fast355** · 06-13-2019

Originally Posted by typhoonss92

I am running since I put in my msd 6AL a acdelco 41-993(19256067) iridium plug. I had acdelco rapidfires before that #14's. I had no knock issue when I was running the 7747 computer with these plugs. When I swapped to these the motor ran smoother. I know to stay with acdelco or ngk since they make the acdelco plugs. I would not be opposed to trying these just need to get to the parts store and get them.

I will have the new knock sensor (ks6 standard) tomorrow so hopefully get it installed tomorrow night.

I tried a starter timing table that Fast355 posted on TGO for vortecs, he said that he uses it as his starting point for stock to mild cam motors. I tried it and seemed to work well except high rpm high map, upped the timing there and just from one adj seems to run pretty good, still needs refined. Here is what fast355 posted and I modified it for my spark table. maybe this will help others as it was pretty good for the first drive. fast355 starter vortec timing stock-mild cam.PNG

Fast355 if you are around maybe you can chime in on this and if you have made any changes over the years on this for your starting point for the vortec heads. I would think 30* is high at idle but I did not get knock.

I use the PE adder to add 4-6° up top. Actually starts adding 1-2° as low as 2,600 when its in PE. I have found situations where you will be at high Kpa for a while and not need the fuel enrichment. If you run full timing without the PE adder after a period of time the engine running at stoich will build some heat and start knockinh.