L29 454 Vortec with 0411 swap - Timing at WOT

[SiriusC1024]

Why hasn't the tune been posted?

[gtstorey]

He doesn’t own hpt and has been mailing his ECM off for updates.

[SiriusC1024]

This thread is a giant circle jerk.

[Scott-m]

K dooosh. Being a diik gets you nowhere. Maybe my 44 years of race engine building could have helped you with something.

[Scott-m]

I still feel like 28 is too much even on 91+ octane. 24-26 is about as much as I would dare on 91. No more than 22 on 87. Curve can be a little quicker at lower rpm and the negative values brought up to about 4-6*, but definitely needs a 4-6* dip near peak torque compared to timing at say 2,400-3,000 and over peak torque.

OK thanks, this is great info. The heads are ported and flow matched (295 cfm). I even flowed them with the manifold on. The chambers are unshrouded, polished, and cc matched (105 cc +- .2 after an .020 flat mill). The valves are mirror polished. Block decked .010 and compression heights are within +- .001 inch. Static compression is 9.08:1. The sharp chamber edges and protruding plug threads and other preignition points are gone. Does this suggest it will want more timing or less? Normally that kind of work lets you run more timing on a conventional chevy. Also I never saw even a trace of knock retard until they shot the timing up to 34. Then it was retarding 3-4 deg. What kind of timing would you expect at moderate part throttle, say 8 inches manifold vac? At light part throttle cruise its getting 30-35 deg at 2,000-2,400 with no knock. I will in fact buy an hp setup now that I'm coming to understand the tuning parameters.

[SiriusC1024]

K dooosh. Being a diik gets you nowhere. Maybe my 44 years of race engine building could have helped you with something.

Yeah ok then why are you asking about the timing curve on a BBC? I already told you.

You'll end up tuning it anyway if you want the most out of it. You did all those cool mods, but don't expect one of their cookie-cutter tunes will take advantage of them.

Guessing at WOT spark without a log is completely idiotic. Is AFR correct? What cylinder airmass? Knock sensors working? Well we can't tell without a tune and log. Buy HPT and start putting in work. Come back when you get serious.

[Fast4.7]

OK thanks, this is great info. The heads are ported and flow matched (295 cfm). I even flowed them with the manifold on. The chambers are unshrouded, polished, and cc matched (105 cc +- .2 after an .020 flat mill). The valves are mirror polished. Block decked .010 and compression heights are within +- .001 inch. Static compression is 9.08:1. The sharp chamber edges and protruding plug threads and other preignition points are gone. Does this suggest it will want more timing or less? Normally that kind of work lets you run more timing on a conventional chevy. Also I never saw even a trace of knock retard until they shot the timing up to 34. Then it was retarding 3-4 deg. What kind of timing would you expect at moderate part throttle, say 8 inches manifold vac? At light part throttle cruise its getting 30-35 deg at 2,000-2,400 with no knock. I will in fact buy an hp setup now that I'm coming to understand the tuning parameters.

Scott,

I would say at 8 in/hg vacuum, maybe 20-24* if it is over 3,000 rpm, like part throttle kickdown, running uphill kind of scenario. If its lower rpm, like 2,000 maybe as little as 16* Remember almost every vacuum advance can is down near zero by the time the manifold vacuum is down at 7-8 in/hg. Usually those start advancing about there and are full in 16* by maybe 12-14 in/hg. Stock Chevy distributor mechanical curves are also assymetrical, more advance rate at low rpm and tapers off at higher rpm. 22* HEI mechanical advance that is typical (GMPP HEI which is practically identical to the truck smog era stuff) is something like 0 @ 1,200, 12 @ 2,200, 18 @ 3,000 and 22 @ 4,000. Then add your initial to that, basic 454 was something like 4* initial for 26 total and that was on a 454 peanut port head engine with less than 8:1 compression. Keep in mind a higher compression engine, in a heavy truck, with a long runner EFI intake, using fast burn style chambers is not going to want as much timing by general rule of thumb. Personally for an 0411 or P59, I would start with the 8.1L timing tables and make small changes from there. The 8.1L has basically the same chamber design, better head flow and more compression, the cylinder pressure developed with the 8.1Ls greater VE is going to be a fairly decent match in my opinon to a 7.4L with head/intake porting, cam upgrade and more compression.

[Fast4.7]

The 2nd issue if datalogs were not made, it is impossible to know where your engine is operating at a given point in the spark timing map. A stock engine may see a cylinder load of 0.64 gm/cyl at peak torque and taper off to 0.54 gm/cyl at high rpm. Mild engine may see 0.78 gm/cyl at peak torque and taper off to 0.64 gm/cyl. An engine like my 383 sees over 1.00 gm/cyl at peak torque. That number is very close to a VE%. It is a basically a real time measurement of VE based off dynamic airflow from the MAF and VE table that is being used as a load reference for the spark map. The OE timing curve was calibrated to run within the operating range of the OE engine. Once you exceed that GM merely dropped the advance numbers to extremely low values because they did not calibrate the whole table because the stock engine never ran there. A stock L31 Express tune sees about 24-26* total timing at WOT when it is in PE. Assuming IATs are under 90F and the CTS is under 194F. With IATs in the 180F range and CTS in the 210F range they often see in hot weather, PCM pulls as much as 10* of that timing out.

[Scott-m]

Thanks fast4.7! I am making data logs and sending them to black bear. I tried to post pictures of the graphs but apparently the pic files were too big to upload. I can still upload the dot efi files, but it's irrelevant now until the new adjustment comes back.

[gtstorey]

Thanks fast4.7! I am making data logs and sending them to black bear. I tried to post pictures of the graphs but apparently the pic files were too big to upload. I can still upload the dot efi files, but it's irrelevant now until the new adjustment comes back.

So you/they are tuning in EFI Live?

[Scott-m]

They are using efi live, and they loaned me a V2 data cable (with my cc of course). I email the logs and send the ecm up for adjustments. Here are a couple screenshots of the most recent tune. My phone takes pics that are too big to upload, so these are with my old cannon with permanent water marks on the lens. First one shows a half throttle run through the gears, no trace of knock with 28-30 deg timing. Second shows a wot run through 2nd and 3rd, with advance jumping to 33-34 and knock retard kicking in, especially in 3rd gear. Obviously more timing at wot than at half throttle is wrong, but it is my fault for asking for too much at wot.

[gtstorey]

I’m not sure that anyone is going to be able to do much with screen shots. But what is going on in the middle of the screens with o2 voltage (500 on time scale of first screen?

[Scott-m]

Right, I know no one here can help until I get the hp myself. Yeah they glitch out, often right after a wot run. And it's right when spart timing drops to zero too, if there is any connection. I don't know if it's really happening or not. There are glitches with the map numbers and afr too.

[Fast4.7]

Scott,

I am also going off first hand experience tuning that engine in everything from a 26K motor home to a friends 99 K3500 dually towing a large travel trailer. If you are ever towing with it, hitch the trailer to it and datalog. You will run into detonation a bit earlier towing than you will running empty, especially on a hot day. I actually have 2 tunes for the 383 in my Express and can change tunes in about 60 seconds, I have a hot tune for running the van itself around town and long distance and a tune that required about 4-8* less advance under load for towing 8K. After you elimonate the detonation currently found in your tune, if you are going to tow anything long distance, hook up to the trailer, then datalog the truck for 30 minutes or more and head uphill with a hot engine to make sure it is not detonating when towing. The knock sensors and low octane timing table are meant to protect the engine but I loathe relying on that system to save a hard working engine. I tune the engine for the maximum load it will see and retain the knock detection and low octane spark stuff for a tank of bad gas or the like.

With the old TBI systems I had a couple of switching boards that held multiple EPROMs or Memcals depending on the year model and had a rotary dial on it in the dash board. I had about 4 different tunes for my L31 TPI 383 and 4L60E combination. One that was optimized for highway fuel mileage, one that was great for running around town that locked out overdrive, one that was optimized for power and another that was setup for towing as well as an anti-theft position that would not even start and run.

[Scott-m]

Thanks Fast. I do tow a trailer and in the AZ heat. The old black box in the 97 would kill power down to nothing in hot weather, like barely able to climb highway hills in second gear. My 1982 454 carb'd rv could pull my trailer better than the stock 97. I think the ecm was killing off power due to trans temp. But how would it cut power? By backing off timing? That would put a lot of unburned fuel into the exhaust. And coincidentally, I found a ton of burned wiring when I swapped engines and did the 0411 rewire. Everything within 6 inches of the exhaust was crispy. BB says the new tune will not do that. This pic is from June last year.

Anyway I'm suprised they want so little timing. Now I'm feeling stupid about demanding more from BB. I thought I read somewhere the 0411 can use multiple spark tables.