Timing curve too slow? Needs to be advanced faster?

[onegonewild]

Here is what my current engine is running

383 internal balance
Mercruiser MPFI ported, 27lb injectors, ported throttle body
Iron 64cc vortec ported and polished
Comp Cams Beehive springs for 0.550 lift, Crane gold rockers 1.5 Camshaft:Comp Cams XFI 280 hydraulic roller, Comp Cams Magnum hydraulic rollers

Cam specs:
Operating Range: 2000-6000 RPM
Duration Advertised: 280° Intake / 288° Exhaust
Duration @ .050'' Lift: 230° Intake / 236° Exhaust
Valve Lift w/1.6 Rockers: .576'' Intake / .570'' Exhaust
Lobe Separation Angle: 113°


Also is the tune attached. What do i need to adjust the high octane table to to get the best power(if anyone has experience with these heads!)? I hear 32 total is the best but it feels pretty sluggish off the line. AFR is dead on 12.2 throughout the entire RPM band. Do i need the advance to come on stronger in the lower part of the RPM band and level off at 32 or ??? Any help is appreciated!!

[joeygc5]

Just a quick generalized statement.

Copy the high octane table and paste to the lower octane table, this will help in the initial tuning stages removing timing pull while dialing the setup in. You should (imo) then pull some of the high timing out of the upper kpa midrange cells to help with torque, then gradually bring the timing up in a smooth transition towards the higher rpm cells. Once that is all done and the response is better, go in and for example pull 5-6 degrees out of the whole table for a low octane map.

[WeathermanShawn]

When I initially setup my timing advance curve I took the 'inverse of my dyno TQ curve. Then I used Excel and at peak TQ values I had the least advance, and simply took the TQ percentage difference for various RPM's and adjusted (lowered) accordingly.

Like you I like to squeeze in as much spark advance in the 2000-peak TQ range to eliminate that sluggish feeling. Mainly in the lower-mid cylinder air cells.

[Goldfinger911]

Have you tried less timing? Try 26-27 degrees in the mid-high RPM ranges between 80 and 100kpa, and make sure your timing dip matches your torque curve peak, then adjust up or down watching for KR. Then ramp it back up to apex at peak power. If those heads are really efficient, remember that combustion efficiency allows timing retard, which then allows for combustion events at a later stage of piston rise.

Also, at least with my car, it is really sensitive to AFR at peak torque. 12.0 is sluggish, 12.5 pulls strong, and 13.0 is really sluggish. Log data and watch your RPM and MAP curves and where they flatten or stall out, see where that maps to in your Spark and VE tables.

I just went through this exercise yesterday with a hesitation/sluggishness right after I shifted from 1-2 and then 2-3... turns out I was lean at 13.0:1. Just richening to 12.5:1 cured my problem now it pulls hard.

[MSURacing]

you might want to look at B3644, you are not letting it go to PE at all.

[MSURacing]

use with caution. Only use with better than pump gas

it should get you where you want to be though