Ok so when the throttle is open, manifold vacuum will be low and the gram/cyl flow will be high. On a carb/distributor engine, the lack of vacuum at wot will cause the vacuum-advance mechanism to stop adding additional timing. So the timing the engine sees is the initial timing of say 10-12 degrees, plus the additional timing coming from the centrifugal advance mechanism, which increases with rpm. At 2,000 that would be 12+10 for 22, at 3,000 it would be 12+18 for 30, etc. How do I get BB to tune it how I want?
99 L29 454 build
- Thread starter Scottm
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L31, these heads are not stock. The detonation inducing sharp edges and protruding plug threads are gone. They are cc matched and polished and the valves are mirror polished. They will look to the engine like a good aftermarket head with cnc cut chambers. That means they will like as much timing as any chevy v8 in history with good aftermarket heads, which is routinely 34-36 degrees. ANd that's with the poor fuel distribution of a carb, plus the wandering spark timing of a conventional distributor. Obviously I don't know efi tuning like you guys do, but I see nothing about this engine that contradicts 70 years of chevy engine setup.
L31MaxExpress
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Have one word, swirl. Both the intake port and chamber design create loads of it. The more swirl you have, the less timing you need. Take a swirl port 350 head for example, no matter what you do to it short of grinding out the swirl ramp, it is going to like about 26* of total WOT timing. By the time you run into detonation with those heads you were already down on power because your timing was too advanced for the mixtures burn speed. Even if you ground the swirl vane out of the L29 heads, port bias and chamber design are still going to give a quicker burn than older or aftermaket chamber designs. The 454 vortec has a very similar chamber design to a 350 vortec and as such has a much quicker burn than a normal 454 head, especially the older design smog era open chambers the aftermarket tend to favor for increased flow. My 8.1L does not need more than about 22* total timing to make its peak power and the 8.1L chamber is similar to the L29s.
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Alright good points. But I still don't understand why BB advanced timing on it everywhere, resulting in part throttle ping, when I was clear that part throttle timing was good. I also don't understand why the in the previous tunes, going wot dropped the advance to 22 deg, regardless of rpm, 2k to 5k. Again ignoring or contradicting the pretty-well established norm of timing increasing with rpm. Maybe that's my lack of understanding of efi, but if you can't adjust specifically the wot timing curve, then efi IS less tunable than a $200 msd distributor.
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L31MaxExpress
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Has to be how the timing table is programmed. The 0411 has a large spark map with what I want to say is over 120 values.
I have not made data logs yet, plan to today, so I don't know for sure if they advanced wot timing or not. It does need to stop pinging at part throttle though, so it's going back at least one more time.
Here is a screenshot from the instructions for an MSD 6014 controller, used for running the ignition on a gen 3 LS when switching to a carb. It shows an example of a custom advance curve that a person can set by picking points themselves, if they want something other than the available pre-set curves. Notice it ramps up with rpm, like every other timing curve in history, plus it tops out at 32 deg total.
Here is a screenshot from the instructions for an MSD 6014 controller, used for running the ignition on a gen 3 LS when switching to a carb. It shows an example of a custom advance curve that a person can set by picking points themselves, if they want something other than the available pre-set curves. Notice it ramps up with rpm, like every other timing curve in history, plus it tops out at 32 deg total.
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Finally made logs today including wide open. BB did advance the wot timing alright, all the way from 22 deg to 34. And.. It pings and knock retard is kicking in. So L31, you were right, I was wrong, 34 is definitely too much. (I will punish myself later). At least they finally changed something. But a couple things are getting dialed in. Cruise timing is good and fuel trims are down to just a couple %, down from 16% plus. Also wot timing is ramping up with rpm, as I requested. Before it was 22 deg flat, no change from 2,000 to 5,000. So I take credit for educating them on this simple concept. It goes back up tomorrow for hopefully the last time. I will ask them to dial back wot timing, and if possible, have it ramp up from about 20 deg at 2k to a max of 28 from 3k and up. What do you think L? Also what do you think of the injector duty being only 50% at wot and 4200 rpm? Are the injectors way too big?
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Got it back again today after asking them to limit timing to 28 at wot. It was actually still getting 30, but that was ok for a long time through 2nd gear. Then it started to ping right before the shift to third. Then it pinged pretty hard in 3rd, even after 2.5 deg of retard kicked in. So 27 is still too much. How about 24? I'm baffled by this, but so be it. Sorry again to you guys who know what you're talking about!
Also it's flowing 32 lb/min air at 4900 with 55% idc. It will never rev much higher than that. Are the injectors too big or ok?
Also it's flowing 32 lb/min air at 4900 with 55% idc. It will never rev much higher than that. Are the injectors too big or ok?
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L31MaxExpress
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Injectors are good to to IMO. As long as the injector data is good for that injector there is no issue running them at a lower IDC. All the flex fuel vehicles running on gasoline run at similar IDC. They need the headroom when they run on E85. A lot of people buy flex fuel vehicles and never run anything but Gasoline in them.
L31MaxExpress
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Hows the revision coming Scott?
I was looking through some of the datalogs I have on my tuning laptop, some 950 of them, lol. This was my buddies all stock 99 K3500 crew cab short bed dually. Looking at the calibration and datalog after tuning it, I had about 24* in the timing table and it was running about 22* from the IATs and still occasionally blipping 1-2* of knock retard. Truck was getting run hard at the time, towing a heavy trailer on a hot summer day. I pulled it back to 22* in the next revision and the next log it was running 20* with no knock retard. Appears I was only able to put 2* of added WOT timing into it. I also definitely suspect the MAF flow table is off on your truck or the MAF itself is reading low. My buddies truck was pulling the same airflow all stock that yours is reading. Did you happen to log the MAF frequency, if your MAF is showing more hz than the 8,900 hz my buddies truck was logging, it means the MAF curve in your PCM is too low at that point. Hope it helps.
I was looking through some of the datalogs I have on my tuning laptop, some 950 of them, lol. This was my buddies all stock 99 K3500 crew cab short bed dually. Looking at the calibration and datalog after tuning it, I had about 24* in the timing table and it was running about 22* from the IATs and still occasionally blipping 1-2* of knock retard. Truck was getting run hard at the time, towing a heavy trailer on a hot summer day. I pulled it back to 22* in the next revision and the next log it was running 20* with no knock retard. Appears I was only able to put 2* of added WOT timing into it. I also definitely suspect the MAF flow table is off on your truck or the MAF itself is reading low. My buddies truck was pulling the same airflow all stock that yours is reading. Did you happen to log the MAF frequency, if your MAF is showing more hz than the 8,900 hz my buddies truck was logging, it means the MAF curve in your PCM is too low at that point. Hope it helps.
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