Well since my track layed the law down this month kicking me off track because I needed a cage a long time ago, I decided to drop timing via prom till the car slowed to 11.5ish.
I generally run 38* total all in by 2600.
First pass dropped 4* TO 34 -Ran the normal 7.11 in the 1/8 with the also normal and still present wheel spin. grrrr
Second PASS -8* TO 30 degrees total, after a horrible 1.65 60 ft from 1.52 last race day. 7.1 @ 96
Next dropped timing to 26 degrees total and installed restrictive SLP intake tube and stayed in gas.
Spinning again 1.55 60ft 7.3 1/8 -- 11.46 @ 117 < I think most of that from the air tube, as it has proved to lose 2 tenths + in the past .

So there you have it, dropped timing 12 degrees and not much change at all - I was hoping for great traction by cutting HP ...
I don't think I lost much at all.

Test and Tune nights they prep track very little.
Last race day I made 4 passes @ 1.52's 60 fts

I think I am going to drop timing to 20 total till 5000 for tommorow.

 

you are...

 

I think that proves that engines are not that picky. The engine just want's stable fuel/spark delevery. Really it's the s/a curve that is important(not the total).


slowing the car down, wish I had that problem

 

Well its depends on the effeciency more than anything.
So I guess my car is pretty effecient..

Not really, Had traction been there and I was letting it rip it would have turned a good time even with the 26 degrees total.

 

Sounds like you got a heck of a setup there and well thought out :-)

Did u keep track of your AFR as u dropped the timing down?

U can run cheap gas too lol(good thing right about now lol)

later
Jeremy

 

Wow..... Kind of a HUGE generalization taken from this one example. Unless the spark curve was optimized to MBT timing *everywhere* when you started, it's kind of difficult to know exactly what was going on.

All engines will respond to variations in spark timing in a very similar manner. Around MBT timing, you won't see much of a change in torque for relatively large timing changes. But, as you drop further away from MBT, the torque change is considerably more drastic. While the specific magnitude of MBT SA will change from engine-to-engine depending on MAP, RPM and EGR, the percent torque loss relative to retard from that point is very common among different engines.

So, in the example above, it may have been that some of the points on the "curve" were near (or above) MBT levels. Therefore, it's not surprising that there wasn't much loss with a 4deg change. However, the engine *is* sensitive to spark timing at each operating point. The objective to setting up the "curve" is to hit MBT timing as the engine is accelerating. If we don't hit MBT, we lose torque. And, it's lost in a predictable manner. The hardest part of this task is finding the MBT operating point.... If we don't start from there, all we can say is torque will *change* by changing spark advance. Maybe it will go up.... Maybe (well, very likely) it will go down.....

That being said, a stable spark/fuel delivery system is very important. There are just some other things that are important, too.

 

Not sure what you mean. I do stand by my statement. I have tuned several cars and it's not the total that's important. You can move the total around and not see much change in power,as proven here. BUT brining in the total sooner/later will show dramatic changes in power.

 

What does happen is folks miss the tune, and for them the timing can get ulltracritical. Talking street cars, here.

When you over fuel the motor, and start excessively raising the effective compression ratio, due to the fuel volume, timing can get overly critical. Not to mention, that doing that can also change the acoustic signature of the motor enough to fubar the K/S.

High turbulence, small chambers (highish CRs), also can help.

Notice no absolutes

Doc, says he's worked on at least 3 engines now. Or maybe he meant been working on internal combustion engines for 3 decades now.

 

Race motors are also very picky. Our little 600cc motor on 100 octane will buck to no torque if it's too rich by a VERY little amount. We're talking going from mid 13's to 12 and the motor just turns off. It's really amazing. I guess with 14.3:1 compression the extra fuel is just too much to even compress.... as for spark, it's not nearly as touchy. What's scary is how much timing these bikes can take under WOT... some places it's around 70^ other's it won't take anything above 50.
As for my car, it doesn't care what AFR there is, it'll just motor right through a huge 10:1 AFR and will spin lighter at a leanner AFR of around 16:1 ! My car is howerver much more senative to SA. 2 or 3 degrees not enough and the engine is sleepy everywhere, 1 degree too much at WOT and it'll tell you with 8 to 12 degrees of knock retard.... but it's all fun .
I can't believe you're taking that much timing out of the engine for WOT. I would have guessed a decrease in power if you're running only 20 degrees and it was fast at 38 total. That's a BIG difference. My car is a slug with less than 28 and it picks up knock at about 35 so I run 32 for the street and 34 with 94 octane... no knock counts but with 87 and 89 there is a hint.
Are you sure you aren't running more timing at WOT? What's the last line of your SA table at 100kpa?

 

Tom, could you send me your bin?