First off, I've been reading/ searching for a couple of days on this topic, but can't find what I need. I've read Rober Raucher's article on using a 7747 for spark only. This was an excellent read and explained a lot that I had questions on.

Here's the basic question-
What do you guys do for your spark curves on warmed up motors? What's your "all in" advance & at what RPM? What's your advance at idle?
more importantly, what affects these numbers? Static Compression? Dynamic Compression? Head type? Octane?

I helped dyno tune a motor for a buddy of mine... basically 10- 10.5;1 static CR, L31 Vortec heads, 383 stroker, offorad roller cam (this is in a rock crawler) His motor guy told me to set the spark curve at 38* all in @ 2000 RPM. It seemed to work well, and we didn't have any knock on 93 octane.

Now I want to juice up my timing curve, since I set it really conservative when I built my motor and kind of forgot about it. Here's the specs-
355 SBC, 58cc swirl port heads (this motor never goes above 5K RPM and is intended for torque), 10.5 to 11:1 Static CR (not sure on the deck height), Comp Extreme Energy Cam (CS XE256H-12).
I was thinking that I should run about 19* at idle and 28* all in by 3000 RPM due to the CR. Is this still way too conservative, or too aggressive? I'm trying to learn how to build a curve. Anybody have tips or links to articles?

 

see my sig for motor specs.

I am at max timing at 4800 rpms 40 MAP at 38.5. From there it tapers down to 25.7 at 100MAP 6000 rpms.

At 3200 rpms 40 map I am 35.1

At 3000 rpms " 33.0.

Once WOT 100 MAP it flashes from 22.0-25.7 as RPMs climb 3000-6000.

92 octane. no KC's WOT. False KC at around 2400-50 MAP

 

Maybe it's my settings, but I don't see your sig.

 

its gone?
350 CID Edel rpm alum heads 64cc....-6cc forged pistons. static 10.1/1 CR. cam 224/230 @.05 114LSA bleeds off some CR dynamic.
I use EBL-ECU.
Soon adding NOS universal system 100 HP controlled by ECU.

 

This can be difficult to answer. There are many aspects of what defines the engines spark advance at load/RPM points. One of the most important things to understand is that just because an engine doesn't detonate, does not mean that the timing is OK.

It is easy to have a lot more timing then proper, and be losing power, and the engine doesn't knock. If the engine starts getting rough (butt dyno is real happy), then there is too much timing.

Head design is the first item that affects the required timing. Look at some swirl port headed engines (L03/L05) calibrations. The timing is so low that I've had people tell me that it can't be correct. Yet just a few degrees more and they ping like crazy.

Heads are either detonate limited or timing limited.

Cams: more overlap means more self-EGR'ing, means more timing required at lower RPM.

Octane: goes hand-in-hand with static/dynamic compression ratio. The higher the compression the higher the required octane. Better for a head to be timing limited then to be detonation limited.

And, for driveability it isn't always best to make the max power. It can be helpful to pull timing a bit at low/low-mid RPM so that the car is driveable without attracting the wrong type of attention.

Same for overrun. Too much timing and the engine doesn't want to slow down. A lean mix such as highway mode and more timing is required. A lean mix burns slower. A cold mix burns slower. A hot mix burns faster.

Many times the fastest way down the 1/4 is on the edge of detonation. But not a good street or road course tune in doing that.

For WOT SA, easy enough to use acceleration runs. Look at a graph of RPM in 2nd and 3rd gears. Any flat areas? Add a little SA and see if it picks up. If not, then reduce the SA a little in that area. Or, try adding 2 degrees across the WOT area and overlay the former graph with the new graph.

Note whether the acceleration picked up or dropped off.

RBob.

 

Is that a typo?
Did you mean 28* instead of 38* ?

 

No. Not a typo. 38* @ 2000 RPM.
On the dyno, we tried 36, 38, & 40* all in by 2K. Made the most power at 38*.

RBob,
Thanks for the info.

 

Little clarification on above post ^^^^^^

The motor that we had 38* all in on was running L31 Vortec heads, which I understand can tolerate that kind of SA.

My question relates more to the 58cc swirl port heads. How much SA can they tolerate when running flat top pistons on a 350 (compression bump)?

 

Just a clirification. On dyno how do you monitor for detonation (audible) ? Is it best to look for Max HP and/or when finding it retard a couple degrees. I recall oil temp plays a role as well. I know this is different but A/F that creates max HP is not the way to go.

 

On the dyno, we watched knock sensor, WB AFR and individual exhaust port pyrometers. The motor is rigid mounted in a rock crawler, so once we determined that there was no knock, we decided to eliminate the KS, since the chassis will be slamming off of things all the time and ringing the block.

 

Read the plugs.