Mid-range Timing

[Top Toy]

Killing time here in the winter months with some bench tuning. Have done enough dyno work to optimize 7000 rpm timing at 29 to 30 deg. Looking for mid range timing guidance. Has anybody optimized timing for max HP/torque around 4000 rpm (90 - 100 kPa MAP)? Stock displacement with full porting and cams.

Sent from my XT1254 using ZR-1 Net Registry mobile app

[mike100]

More than stock, but not as much as you have in the high kPa regions from 5000-redline. My car pings at sea level with CA 91 when it is hot outside. You may be able to do better with the gasoline in your area.

I think most engines get max hp with 27-28 deg total timing on the top end.

[Top Toy]

Thanks for your recommendations Mike! Thankfully, I've never had a problem with pinging or detonation with the 93 octane we have here. Stock for my '93 at 4000 rpm is about 24 deg. Have run as much as 30 deg. at 4000 without issues but made more torque/power at 28. Thinking I may need to drop even further. What's your timing at 4000?

[mike100]

Originally Posted by Top Toy

Thanks for your recommendations Mike! Thankfully, I've never had a problem with pinging or detonation with the 93 octane we have here. Stock for my '93 at 4000 rpm is about 24 deg. Have run as much as 30 deg. at 4000 without issues but made more torque/power at 28. Thinking I may need to drop even further. What's your timing at 4000?

I'll have to look. it is more about blending the values at part throttle for driveability and reliability. The car just feels better at part throttle with a touch more ign timing over the entire map from 2000 rpm on up. Just throwing in 27-28 degrees at the high end at full throttle kPa cells is the easy way. The sensitive region is around torque peak. Curiously, I don't have pinging issues if I can get to about 1000 ft elevation.

[Top Toy]

Agreed! The factory curves for spark and fuel are so rough, it's a miracle our cars even ran with them! Have spent many hours straightening things out across the whole range. Now just looking for that sweet spot for max torque in the mid range.

[Top Toy]

BTW, a N/A car will ping less at higher elevations because the lower density air also translates into a less dense charge in the combustion chamber. The spark travels slower in a lower density mixture which is also why our spark is advanced more at light engine loads.

[XfireZ51]

Dennis,

I think u need to look at the KC at each rpm level. I basically remove any Spark Retard so u see the actual amount of knock. Then progress the timing from conservative to more aggressive. U need to see where the knock occurs and for what rpm range. It may be so slight or so brief it makes little difference. It also may occur at an rpm level that is reached one time because WOT occurs and stays in a range beyond the point of knock.

[mike100]

Originally Posted by Top Toy

BTW, a N/A car will ping less at higher elevations because the lower density air also translates into a less dense charge in the combustion chamber. The spark travels slower in a lower density mixture which is also why our spark is advanced more at light engine loads.

I understand that...to give you more backstory... my LT5 will not ping in Phoenix (1200 ft ASL) at 100 degrees even with 91 octane. The barometric pressure seems to have a greater effect than temperature for spark knock. Drive down to the beach when it is 90...just get off the throttle when I hear the popcorn popping.

[XfireZ51]

There's a Baro Comp table that could help w that.