Well Fellas,

I finally had a chance, the next day, after my bachelor party to play with the pump shot and timing. I was experiencing tons of knock with an AFR ~12.5 off my WB. In addition, I was noticing that when I would initially floor it, the AFR would dip to ~18.5 and then transition to 12.5. Takouts even with the 3200 vigilante were sluggish and no tirespinn was evident.

I doubled all the values in the accelerated enrichment vs LV8. Along with taking my timing back to 25.1*. Well guess what. No more knock counts through the 1/4 and major wheel spin! First is pretty much a waste Not a bad thing. Also the car feels much stronger with no hesitation, except for a bog after wheelspin stops. I think, this is due to the vettes bad design of their gas tank pickups. When the tank is low, near 1-2 bars from reserve, the gas sloshes to one side and starves the engine of gas till it stettles. I did not have a chance to get a new tank of gas yet to test my theory.

Here are my questions.

1. I am still experiencing the transition to lean when I punch the gas. What methodology do you guys use when adding pump shots? Perhaps someone can explain what it is the AE tables do, then I will have a better idea of what I am trying to accomplish. I realize they are multipliers, but don't know when they are activated, etc. The searches I performed are more along the lines of of people recommending the addition of the shot, not a details explination of what it actually does.

2. I am going to play with the timing tables some more along with the fuel curves. How soon should I bring the total timing in? should it all be there by TC stall speed? In other words if 25.2* is where the best performance is without knock, should the timing table vs LV8 be set up to reach 25.2 before the stall speed? Could someone give me some advice or rational on how this is usually done.

I appreciate all your help in getting this critter straightened out. I have been battling this thing for the last 4 months and now I feel I am getting close. The roughing work I am pretty straight on, but the detailing I have not yet had the experience to know answer the above questions.


Thanks for the help again.

 

lv8 accel inrich vs delta lv8 is the "pump shot".Some moderator from another board wrote an article on spark advance.He has seen up to a full second off his 1/4 mile time by bringing in the total by 2800 rpm.He did state that was for racing only.But I would suggest try to bring in the total by 3600rpm.

 

There is also some Delta TPS AE stuff.

You want max WOT timing in by peak Torque. You might add a couple degrees above that, but that's usually just cause your going a lil too rich to cool the chamber.

You want to run as little timing as possible below the stall speed of the converter. unless you like tire spin and going slow. I'll typically run 8-10d pre stall and then immediately ramp quickly to 18ish as I hit the stall of the converter then max HAPPY timing by peak torque and then maybe add a few degrees as I get to peak HP. With stall usually at about peak torque it takes a couple chips to get it all sorted out.....

 

Good news on the progress! I had the same problem on my 355 TPI and played with the AE (pump shot) quite a bit.

I added to the values in the AE vs. change in LV8 table, more so for the upper values. I also increased it in the AE vs. coolant temp table in the area where my engine normally operates. To lengthen the effect of the AE, I lowered the AE decay factor vs. coolant temp in the normal operating temperature range.

I have my timing coming all in a good bit after the stall speed of the converter, but that's because my engine is detonation-sensitive at high-load/low-rpm and the converter is only stalling at ~2500 rpm. I need a converter that stalls at around 3200 rpm, but the money tree isn't growing fast enough. You'll need to strike a balance between how much timing the engine can take below/near the stall speed and how much traction you have. If you can't hook up with the tires you're running, lowering the timing below/near the stall speed will help reduce the low-end torque that tends to blow off the tires when launching.

 

Thanks guys. I will use that advise wisely. I realize that traction is key to fast ETs, but I like to hit the gas and hear them smoke for now. You remember I had the bad TC that was stalling at 1100 RPM! For the life of me I couldn't get them to really spin. I will detune to lower RPMs and come up from there.

Grumpy you are only running 10* at idle? Or did I read wrong? It sounded like you said 10* at idle up to ~18 till stall, then bring in the max timing?

Please let me know if I read correctly. Thanks

 

Heheheh, smoking the tires is sure a lot of fun on the street, just not at the track when you're trying to hook up.

I think he means 10 degrees at low-rpm/high-load, so if you look at the timing table at, say, 1000 or 1500 rpm, going from low-load (idle) to high-load (launching), the timing would drop down from 20+ degrees to 10 degrees. Higher-performance engines don't like much timing at low-rpm/high-load conditions anyways, heck, most engines don't like it. I've seen the spark advance data from a '95 Caprice that had timing as low at 1 degree at 800 rpm, and only increasing into the teens up through 2500 rpm, but that's with a low-stall stock converter.