99 L29 454 build

[Supercharged111]

You guys that are adjusting your own tunes, what is your idle, full throttle and part throttle ignition timing? When I was driving around recording data on the laptop, I thought the timing was low across the board. I wrote to BB and asked them if they would add a couple degrees advance at idle and part throttle. They didn't refuse to, but said they didn't think it was necessary.

I have been building carbureted/distributor chevys since 1981. They idle best with 12-14 degrees initial timing. It takes half as much throttle opening for a good idle with 14 degrees initial compared to just 5 or 6 degrees for typical stock. But of course they need no more than 34-36 degrees at high rpm and wot, so you must limit mechanical distributor advance to about 20 deg total. That's what I do on my race engines, 14 initial and +20 mechanical.

Street engines also need vacuum advance for part throttle conditions. It's good for 3 mpg and much cooler running. I use vacuum adv msd dists, which give +10 degrees at 15 inches of vacuum. I use ported vacuum rather than direct manifold vacuum, because manifold idle vacuum would push total advance to 24 deg at idle and that's too much. Plus you will often get part throttle ping when running direct manifold vac. So part throttle cruising at say 2000 rpm would be 14 initial plus 5-6 mechanical plus 10 vacuum for 29-30 total. At 2,500 rpm cruise there would be about 10 mechanical for 34 total.

The highest advance I recorded when driving was only 37 deg, and that was when coasting down from a wot run. At that moment of max vac and high rpm, timing should have peaked at about 44 deg by my method (14 + 20 + 10). Of course the efi is more sophisticated and maybe it knows best but I'm not sure.

My question is, what do you see at idle, wot, and cruise? Do you mess with it? Do you bump it up until it pings? I have matched and polished my chambers and polished the valves to mirrors to reduce preignition. When I was recording, the ecm never saw anything from the knock sensors. So I think it can use a little more timing and get better mileage.

You're talking on the 454, right? Any of them are starved for timing with a stock tune, but I don't even think I see 20 degrees WOT on the plow truck (454 Vortec stock for now). And let's not forget about that evil 60 second PE delay. If you're thinking a 454 Vortec is just begging for timing, you're right. But the one I have tuned is supercharged so runs less timing than yours is gonna want. A lot less. Were I to keep the stock PCM on the plow truck, I think I'd start with a global 4 degree bump (akin to twisting the distributor) and go from there. When I do tune a PCM I'll do global bumps until I start to see traces of knock, then work on bumping the lower end stuff to bring it in sooner (think lighter springs in an HEI here). The end result is a much more responsive truck that gets along with less throttle input. The grade of gasoline you run will factor into the answer of how much timing and where.

 

[BeXtreme]

You guys that are adjusting your own tunes, what is your idle, full throttle and part throttle ignition timing? When I was driving around recording data on the laptop, I thought the timing was low across the board. I wrote to BB and asked them if they would add a couple degrees advance at idle and part throttle. They didn't refuse to, but said they didn't think it was necessary.

I have been building carbureted/distributor chevys since 1981. They idle best with 12-14 degrees initial timing. It takes half as much throttle opening for a good idle with 14 degrees initial compared to just 5 or 6 degrees for typical stock. But of course they need no more than 34-36 degrees at high rpm and wot, so you must limit mechanical distributor advance to about 20 deg total. That's what I do on my race engines, 14 initial and +20 mechanical.

Street engines also need vacuum advance for part throttle conditions. It's good for 3 mpg and much cooler running. I use vacuum adv msd dists, which give +10 degrees at 15 inches of vacuum. I use ported vacuum rather than direct manifold vacuum, because manifold idle vacuum would push total advance to 24 deg at idle and that's too much. Plus you will often get part throttle ping when running direct manifold vac. So part throttle cruising at say 2000 rpm would be 14 initial plus 5-6 mechanical plus 10 vacuum for 29-30 total. At 2,500 rpm cruise there would be about 10 mechanical for 34 total.

The highest advance I recorded when driving was only 37 deg, and that was when coasting down from a wot run. At that moment of max vac and high rpm, timing should have peaked at about 44 deg by my method (14 + 20 + 10). Of course the efi is more sophisticated and maybe it knows best but I'm not sure.

My question is, what do you see at idle, wot, and cruise? Do you mess with it? Do you bump it up until it pings? I have matched and polished my chambers and polished the valves to mirrors to reduce preignition. When I was recording, the ecm never saw anything from the knock sensors. So I think it can use a little more timing and get better mileage.

This is someones response on an HP tuners forum post from @yevgenievich while he was working through his E38 tune.

"I've done a setup like this with a 502 but with a '411 PCM.

Have you done much tuning before? This is going to be a pretty advanced job. The 502 and the SBC's I've done like this have all eventually took quite a lot of OL cold tuning.. They run quite a lot dirtier than a LS. So I'd ignore what it does short of fully warmed up for now.

Make sure the injector data is proper and work on the tune while it is fully warmed up since the cold stuff is just adders on top of that anyway.

Also I'd probably not use more than 46 degrees advance in decel/low load and at wide open its going to take somewhere between 28ish on the low side but likely low to mid 30's."

 

[Supercharged111]

This is someones response on an HP tuners forum post from @yevgenievich while he was working through his E38 tune.

"I've done a setup like this with a 502 but with a '411 PCM.

Have you done much tuning before? This is going to be a pretty advanced job. The 502 and the SBC's I've done like this have all eventually took quite a lot of OL cold tuning.. They run quite a lot dirtier than a LS. So I'd ignore what it does short of fully warmed up for now.

Make sure the injector data is proper and work on the tune while it is fully warmed up since the cold stuff is just adders on top of that anyway.

Also I'd probably not use more than 46 degrees advance in decel/low load and at wide open its going to take somewhere between 28ish on the low side but likely low to mid 30's."

That sounds like a bit much for a 454. I forget what heads @yevgenievich was running on that engine?

 

[yevgenievich]

I have been working on my timing table for some time trying to figure out what the motor likes. Attached is my current base high octane table, but with my low compression 8.9:1 it works on 87 octane. Brodix race rite 270 heads. Always looking for recommendations on the timing table. There are a lot of various adaptives on e38 ecu for timing table based on conditions.

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[Supercharged111]

I have been working on my timing table for some time trying to figure out what the motor likes. Attached is my current base high octane table, but with my low compression 8.9:1 it works on 87 octane. Brodix race rite 270 heads. Always looking for recommendations on the timing table. There are a lot of various adaptives on e38 ecu for timing table based on conditions.

You must be registered for see images attach

Without knowing what kind of air you pull it's difficult to know how much advance that thing sees at WOT.

 

[L31MaxExpress]

Without knowing what kind of air you pull it's difficult to know how much advance that thing sees at WOT.

I would assume it is somewhere between 0.68 and 1.00. Kind of the range I see on N/A stuff..

 

[yevgenievich]

Without knowing what kind of air you pull it's difficult to know how much advance that thing sees at WOT.

Logs show starting at 0.8 and goes up peaking about 5500rpm slightly over 1 when at wot

 

[Supercharged111]

Damn so you see as much as 35 degrees on that thing. I was thinking stock 30 or so might be the max and that I may end up closer to 28 on the plow truck. But I want to run cheap gas in that so we'll just see where it starts to get into KR.

 

[BeXtreme]

Everything I've ever seen for max power total timing is usually between 34-38 degrees for both BBC and SBC. More timing for leaner and low load conditions. You can see them do this even with high quality aluminum heads and high compression on engine masters all the time. Its a function of how efficient the combustion chamber and overall engine design is. If you can get to those timing values without detonation, you should. If you have to back all the way down to 28-30 to keep it from detonating with low compression and stock heads, you probably are masking something wrong with it.

 

[Supercharged111]

Everything I've ever seen for max power total timing is usually between 34-38 degrees for both BBC and SBC. More timing for leaner and low load conditions. You can see them do this even with high quality aluminum heads and high compression on engine masters all the time. Its a function of how efficient the combustion chamber and overall engine design is. If you can get to those timing values without detonation, you should. If you have to back all the way down to 28-30 to keep it from detonating with low compression and stock heads, you probably are masking something wrong with it.

I've always been under the impression that the 454 Vortec doesn't like as much timing as the 350. My 350 took I want to say 32 degrees here in CO before it started to pull a little timing. And the 350 Vortec does not take as much timing as an older 350. The chambers burn the fuel more quickly.