Revisiting spark advance to optimize ...NEED SMART EYEBALLS....

[Josh]

Oops. I was already with you on the why...didn't mean to imply cutting the advance off totally.
I was wondering about the how using Megasquirt -- I got ya with the emulating... Thanks!

=============

Maybe this will help-
This is a from the first warm run on a thoroughly beefed up engine in son's street car.
(Definitely not a PRV, but if something can go wrong, it will ;-).
Note the advance climbs after the accelerator is released and the advance drops sharper (for the first half).
It turns high 10s and is very well behaved (no exhaust/engine braking problems).

Attachment 58505

Your screencap from VCMscanner isn't very relevant here. Especially if he is just reving the engine in neutral.

[opethmike]

Owen, you need to dial your timing WAY back; you are far, far into danger territory.

[FABombjoy]

I'll offer the dissenting opinion and post my "so far so good" table, along with the corresponding Volvo distributor curve which corroborates the service manual specs. Have about 2000 miles over the last year on this table.

[dn010]

I think it will be difficult to judge our tables because we all seem to have different setups. 3.0 vs 2.8, turbo vs NA. I don't know if injector size or how fueling is based will effect it, I'm still trying to learn more about this when I have time. I run MAF based fueling and my table hits at most 36.5 degrees. My engine runs and gets me where I need but it needs work, it certainly has points where I can hear a knock, especially on a rev from idle or hitting the pedal a little hard from a stop causing the RPMs to drop. I will be taking it to the dyno in a few weeks, again when I can free up some time. This is an interesting thread and I will definitely keep my eye on it in hopes of learning more.

[FABombjoy]

I wouldn't be surprised if the 3.0 needed less timing. A turbo 2.8 vs n/a 2.8 should be able to share tables though. You just have to drive below sea level to hit the 100+kpa cells

Maybe you could dig up an OEM table from one of the later PRVs for comparison?

[Drive Stainless]

I used this to generate my table for 94 octane, which is all that I use.

http://www.useasydocs.com/theory/spktable.htm

[Spittybug]

Owen, you need to dial your timing WAY back; you are far, far into danger territory.

????? Do you disagree with the spreadsheet results? Mechanical in to quick? Vacuum out too slow?

[FABombjoy]

it certainly has points where I can hear a knock, especially on a rev from idle or hitting the pedal a little hard from a stop causing the RPMs to drop

Are you sure its knock? Pre-EFI I discovered just how much K-jet leans out when cold. Even with a turbo running discerningly lean AFRs into boost I never heard knock. I did chase a mystery sound for some time that turned out to be a loose exhaust clamp.

????? Do you disagree with the spreadsheet results? Mechanical in to quick? Vacuum out too slow?

15 degrees base is a little more than the spec but your table doesn't seem too far from stock. I've seen at least 3 corroborating sources regarding the stock advance curves. Compared to a modern (or even semi-modern) motor it seems like a lot.

Pre-turbo install, before I re-plumbed the cold advance setup I could tell with 100% certainty when the vac advance system was shut down. It makes an already anemic motor feel like there was a birds nest stuck in the intake.

The B28F seems to run with so much timing I suspect you could run fairly well without an IAC valve and live exclusively on MS's idle advance / idle timing curve correction.

To dial in a timing map without excel, you can just:
-Take the DMC timing specs, set the advance specs at your RPM breakpoints, and interpolate.
-Find max vac advance kPa row, add the max timing value to that row, and copy/paste down. Use a gauge vacuum -> kPa conversion formula
-Interpolate between max advance row to 100kPa
-Add 13 deg base across the board
-Create your idle landing zone

I've looked for any hint of timing on B280/3.0 but nobody seems to have posted any data.

[dn010]

I am pretty sure it is a knock because if I play with the table I can either get rid of the noise or make it worse. For instance, I can reduce the advance at lower RPMs and the knock on rev or take-off is gone but that makes the engine buck on takeoff. I can increase the advance and the bucking stops but then knocks on takeoff. I really need to get to the dyno.

I've also tried finding timing curves for the B280F since that is what I am running. Of course, I came up with no documentation. I also looked in the Dodge/Jeep PRV 3.0 diagnostic book. The Monaco repair manual. The Chilton's manual for the 780. I could find tables for the B230 or B28 but never the B280 E/F or the 3.0. I ended up creating a table using the same link that Matt posted above but it needed work to be usable.

Similarly, it was also impossible trying to locate MAF sensor readings for the B280F and associated Bosch hot wire sensor. I came close with a few test readings at one point but not enough to create a usable table even with calculated numbers in the rest of the boxes. I scrapped that Bosch and went with a different MAF sensor altogether.

It seems like that info is either lost, not documented or locked away in some obscure vault somewhere!

[FABombjoy]

Locked away in the ECU calibration. Would have to find out if anyone has reverse engineered the ROM format. Load cell dyno testing would definitely be a better use of time & resources!