Optimal Timing Advance / Curve

[superstingray77]

I searched high and low on here before asking and other places on the net and found nothing.

Currently my tune has timing set at 32 deg advance, showing on the scanner while driving. ( I presume on OBDII this is total timing?) It will hit 37-38 while coasting but any amount of throttle appears to lock at 32 and just hold there from 1200-6500 part throttle or WOT.

These engines might be different than what I am used to building but typically I have made the best power with 36 deg all in around 2200-2400 depending on the weight/gearing etc. Would the 4.7 stroker be any different?
Large solid cam, ported, 9.5 comp, headers, fully forged and balanced.

[Cheromaniac]

Currently my tune has timing set at 32 deg advance, showing on the scanner while driving. ( I presume on OBDII this is total timing?) It will hit 37-38 while coasting but any amount of throttle appears to lock at 32 and just hold there from 1200-6500 part throttle or WOT.

That sounds about right for the Jeep engine computer and it's quite likely that this is all the timing you'll need. The dual quench design of the chambers in the 4.0 head and their small size promote a fast burn so you probably don't need much timing advance to maximize performance, especially if you keep the quench height tight.

[CobraMarty]

JET chips has an easy plug in chip on the ecu connector, they have added timing. Stage 2 requires 91 octane, so I am sure it will ping on 87, so it must have pretty close to the max timing advance in it.

[CobraMarty]

You can also do the CPS mod and add in 6* timing advance across the board quite easily.

[Cheromaniac]

JET chips has an easy plug in chip on the ecu connector, they have added timing. Stage 2 requires 91 octane, so I am sure it will ping on 87, so it must have pretty close to the max timing advance in it.

I had the JET Stage 2 for several years, and I didn't realise how much of a waste of money it was until I removed it.

[CobraMarty]

I had the JET Stage 2 for several years, and I didn't realise how much of a waste of money it was until I removed it.

That's funny. I never tried one.
What do you think that it did? Kept it 'cold' so that it would richen the mixture?

[superstingray77]

I already have a custom flashed PCM. Was curious if it was worth asking my tuner to bump up the advance on one of the files to test say 34 vs 32. Stock cruise timing was in the 40's now it just sits on 32, i figured if 34+ would provide more torque under low load I could obtain better mileage etc.
My head is majorly ported, has big LS-3 valves in it and unshrouded valves / chambers.. does that change or alter the dual quench or will that basic design principle remain static?

[Cheromaniac]

What do you think that it did? Kept it 'cold' so that it would richen the mixture?

Dunno how it did it but it only added torque below 1500rpm and above 3800rpm. Between those rpm points the JET Stage 2 produced a small torque loss so the overall effect was a flatter, wider torque curve with a lower peak TQ number and a higher peak HP number. The total area under the torque curve was probably about the same with the JET Stage 2 as it was without.

Was curious if it was worth asking my tuner to bump up the advance

If your engine doesn't ping at the existing level of timing advance, it's worth a try.

[superstingray77]

Have not heard any pinging or signs of it, pulled plugs and checked for aluminum or any other signs on the electrodes. However light detonation at full throttle often cannot be heard.

[Cheromaniac]

However light detonation at full throttle often cannot be heard.

Especially at higher rpm where it's drowned out by other engine noises. It might be a good idea to invest in a knock detector if you're going to play around with the timing.

[superstingray77]

I wonder... Is there a stand alone fully tuneable system that will integrate enough with the jeeps electronics for the trans etc to all work correctly? I've searched out plenty of stuff but not found anything definitive. Aem fic?

[SilverXJ]

The AEM FIC works, but its is not a stand alone fully tuneable item. It is a piggy back.

[superstingray77]

Will it work for both open and closed loop or must be forced to open loop? Sorry for the 20 questions but if its the best option to gain full control of this beast then I will order it and let the games begin. Overall my tune is not bad but he still has it richer than I feel it needs to be in the entire mid/part throttle area so i am using the MAP adjuster set at 4.80v to pull it back which leans out the idle/wot more than i would like.

WOT leans out at the 5k+ range to about 13.6 but if i leave the MAP stock its dead on at 12.8-13.0 however the rest of the range is like 11.8-12.4 so my tuner and I have been in an arguement about table resolutions because he tells me he cannot tune the entire drive range of the factory PCM which just seems like BS to me.

[CobraMarty]

The AEM should work just as you need it to. It can add or take out fuel which is just what it sounds like you want to do. If you need one I have one never used I can sell.

[superstingray77]

Thought I would reply back with the results from the past 2 tune files. I had him pull 20% more fuel out of the midrange (26.3HG vac) which is normal acceleration/lane changes etc however were still in the 12.4-12.7 range which is better than the 11.8-12.2 but not where I think we should be for best power/econ.

I did have him move the timing up to 35 degrees from 32 and WOW! major difference this thing screams off the bottom and pulls like a rocket to 6k, gone is the lugging feeling like im forcing it to rev that it had with the 32 deg of timing. Best of all even under full load with AC compressor engaged pulling a hill in OD at 80 I leaned on it pretty far but enough not to downshift and heard no detonation at all... or at 4,5,6k that was audible anyhow. I only run 93 so hopefully I will be ok at 35 deg. Seems i recall watching my scanner when it was in stock closed loop on the freeway and timing would cruise in the 40+ range without issue stock. Granted the PCM backed it down as you laid into it etc.

Anyone know why this thing doesnt seem to respond to fuel removal very well in the mid throttle range but yet responds quickly to WOT/Idle changes?