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Thread: TPS vs MAP AE 7427 $0E

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    Fuel Injected! CDeeZ's Avatar
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    TPS vs MAP AE 7427 $0E

    I'm still working on getting the AE acceleration enrichment to play nicely on my TBI. I'm still getting a lean pop when the throttle is planted open quickly.

    I have copied over every AE parameter from BMHK 454 bin into my bin. I did this because I figure these AE parameters ought to be a closer start for me since I also have a large throttle body and even more plenum volume from the single plane intake. Additionally, This bin was setup for the higher pressure 454 TBI, which also ought to be closer for me since I'm running about 28 PSI..

    I have been increasing the Delta TPS and Delta MAP AE tables by 20% or 30% at a time, and also reducing the filter tables ($4B3A and $4B62) values by 10%... RBob mentioned this.
    These changes have helped with the lean pop, some, but the issue is still there. Also, this has made the engine bog down way rich (10 AFR on WB02) when just tipping into the throttle from a start.

    I'm thinking that I need LESS TPS AE at this point as indicated potentially from the rich bog on tip in. AND, that I need MORE MAP AE to cure the lean pop..... Sometimes It will even lean pop when climbing a hill at interstate speeds as the load and MAP increase....

    Thoughts?

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    In the beginning of my tune learning I chased what I thought was a lean pop. After install WB realized it was not lean pop but anticipated spark retard. I lowered the amount of spark retard allowed and increased advance in the 60-85 map area and haven't had a pop in years. I had a friend with mod 454 that had similar results. Your mileage might be different.
    6395, BHDF, 7.4 BBC lightly modded now 6395 BMHM back to BHDF

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    I've run into the same problem. Popping is not rich, it's lean. IIRC there is a max PW size that needs to be increased. Then you'll probably end up reducing values in the other two tables.

    You'd think the high pressure cal would be closer but the high pressure 454 had a TBI specific manifold which had a smaller volume than the old carby manifold plus adapter.

    Increasing spark advance or changing the spark retard limit can increase how quickly the engine accelerates which in turn draws the fuel/air mix out of the manifold before it can ignite.

    Edit: Yes, the maximum Async pulsewidth value will limit total AE.

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    Quote Originally Posted by 1project2many View Post
    I've run into the same problem. Popping is not rich, it's lean. IIRC there is a max PW size that needs to be increased. Then you'll probably end up reducing values in the other two tables.

    You'd think the high pressure cal would be closer but the high pressure 454 had a TBI specific manifold which had a smaller volume than the old carby manifold plus adapter.

    Increasing spark advance or changing the spark retard limit can increase how quickly the engine accelerates which in turn draws the fuel/air mix out of the manifold before it can ignite.

    Edit: Yes, the maximum Async pulsewidth value will limit total AE.
    Lack of timing advance can also cause popping.

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    Fuel Injected! CDeeZ's Avatar
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    Quote Originally Posted by myburb View Post
    In the beginning of my tune learning I chased what I thought was a lean pop. After install WB realized it was not lean pop but anticipated spark retard. I lowered the amount of spark retard allowed and increased advance in the 60-85 map area and haven't had a pop in years. I had a friend with mod 454 that had similar results. Your mileage might be different.
    Interesting. I know this is a lean pop because I can see it on the WB02 gauge itself, as well as the logs. I have wondered if I don't have enough timing now though.

    Quote Originally Posted by 1project2many View Post
    I've run into the same problem. Popping is not rich, it's lean. IIRC there is a max PW size that needs to be increased. Then you'll probably end up reducing values in the other two tables.

    You'd think the high pressure cal would be closer but the high pressure 454 had a TBI specific manifold which had a smaller volume than the old carby manifold plus adapter.

    Increasing spark advance or changing the spark retard limit can increase how quickly the engine accelerates which in turn draws the fuel/air mix out of the manifold before it can ignite.

    Edit: Yes, the maximum Async pulsewidth value will limit total AE.
    Well what I was saying is that increasing the Delta TPS and MAP AE seems to help lessen the lean pop when you smash the throttle open quickly, however, those same changes appear to have made it overly rich on very light throttle tip in pulling away from a stop. It literally pegs my WB on 10 AFR for a second or two. I've read several threads on TGO where Dewey talked about having a similar/same issue... Here's one I stumbled on
    https://www.thirdgen.org/forums/tbi/...ifold-big.html

    Where is this max PW you speak of? Do you think the 350 AE parameters would be closer??? I thought with the big throttle body and single plane carb intake it would be closer, but now that you mention the 454 manifold was smaller.......

    Quote Originally Posted by Fast355 View Post
    Lack of timing advance can also cause popping.
    I was running the stock L05 timing table from the $0E bin I started with. I then copied over the timing table from Brian, (sturgillbd on here). His timing table IIRC has a little more advance in it. It seemed to help mine with the lean pop when you smash the throttle open....

    I'm running TrickFlow aluminum heads https://www.summitracing.com/parts/SUM-162108

    Maybe with these new heads and the single plane, flat top pistons and everything else I don't have near enough timing advance for this combo? Anyone have a timing table for such a combo that might be closer in the ball park vs what I've tried?

    Initial spark advance is 3*
    Last edited by CDeeZ; 03-02-2019 at 12:22 PM.

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    I have the same heads and a 46mm TB with 18LB spring on a 3704 intake (bored out to 48mm).

    AMUS 2.JPG

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    How's yours running? My TB measures nearly 52 MM... One of the reasons I suspect AE is what is causing this lean pop.

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    How's yours running? My TB measures nearly 52 MM... One of the reasons I suspect AE is what is causing this lean pop.
    It's getting better, Dave helped me get the Main Fuel table dialed in so my BLM is ~127 ave. Now i'm adjusting VE and PE with data logging. Of course mine's an '88 with 7747 and I'm guessing my cam (207/213 @.050, .466/.484 with 1.6 rockers) is milder than yours. Here's where I am so far;

    PE-AE bin 06.JPG

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    Well what I was saying is that increasing the Delta TPS and MAP AE seems to help lessen the lean pop when you smash the throttle open quickly, however, those same changes appear to have made it overly rich on very light throttle tip in pulling away from a stop.
    The first 25% of throttle angle change makes a greater difference in air density than the next 50%. I tend to ramp MAP AE in faster than TPS on a larger plenum. Then I'll increase the MAP difference to enable AE as a limit to MAP contribution at low throttle angles. This helps prevent rich surges when load changes without much change in throttle.

    Are those heads a fast burn style? They might require a fair amount more timing.

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    The first 25% of throttle angle change makes a greater difference in air density than the next 50%. I tend to ramp MAP AE in faster than TPS on a larger plenum. Then I'll increase the MAP difference to enable AE as a limit to MAP contribution at low throttle angles. This helps prevent rich surges when load changes without much change in throttle.

    Are those heads a fast burn style? They might require a fair amount more timing.
    Thanks 1p2m, Good info! These heads (SUM-106108) have 170cc intake runners, from what I understand "fast burn" heads are 210cc which come into power at higher revs. Although these heads have bigger valves (2.02/1.60 compared to ~2.00/1.55) I'm wondering if they are a good match for a single plane manifold with a 7.4 TB on a SBC???

    CDeeZ: do you have a 5.7 or is it stroked? A 350 @ 6,000RPM only needs a little over 600CFM (check out the "Carburetor Sizing" at the bottom")

    http://www.tciauto.com/tc/racing-calculators

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    I thought fast burn was just another name for the OEM vortec castings? Yeah the heads are linked in post #5.


    It's a 355, (.030" over) The Holley TB is probably a tad overkill, but I found it for $5 at a swap meet... It measures a tad larger than a BBC TB. Stock unmodified 4.3/5.0/5.7 TB probably wasn't quite enough for this engine?

    Shannen , sounds like you're saying more MAP AE might be the answer..... But you're also saying that you increase the filter table values? This is in contrast to what I had read RBob post about? He was saying to decrease the filter tables. More than one way to skin a cat I suppose?

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    Chamber design has come a long way since the days of the first smallblock. The size, shape, depth of the chamber all play a part in efficiency. Today engineers are looking for faster and more complete combustion and heads with a well designed chamber need less spark advance. Look at some of the old and new designs in this link: https://www.chevydiy.com/chevy-small...-fundamentals/ If the Summit heads are a copy of an old design head, you may need to add a bunch of spark timing. If they are a newer fast burn type chamber the increased efficiency may work to balance the heat loss through the head in a way that lets the stock L05 timing work. My comment wasn't necessarily about curing popping with timing changes, but more of a comment on how close the stock L05 tables will be to correct.

    For AE in a wet manifold you need to increase fuel delivery with an increase in air density. The amount of increase has to be greater at low rpm when the manifold air charge has more time to be exposed to the intake valves, the primary heat source responsible for popping. As rpm increases the fuel/air charge spends less time in the manifold so there's less chance for popping. And when throttle angle is greater there's less change in density with a given change in throttle angle so less fuel needs to be delivered.

    The AE tables don't care what RPM or throttle angle the engine is at. They deliver fuel based on change. So you could go from 0% to 20% TPS or 60% to 80% and both changes get the same amount of fuel from the delta TPS table, even though the 0-20% change should get more fuel.

    Decreasing the filter values makes AE respond faster. For most engines I don't feel this is the first step. For a larger plenum engine I try to shift AE fuel delivery so MAP is responsible for more of the job at low rpm. At higher rpm or lighter loads, too much AE shows up as a rich reading on O2 and possibly as soggy performance. If AE is correct when you stomp on it, but it's showing as rich with a small throttle change, then you might try increasing the MAP difference to enable AE and/or the TPS difference to enable AE. The 7.4 cal I'm looking at now (BHDC) shows a 2% difference in TPS to enable AE, an 18% difference in MAP, and a 14% difference in MAP to enable idle AE. I might try increasing the TPS difference to 4% and increasing the MAP at idle to 18%.

    If you opt to lower the filter values then you may end up redoing the AE tables. With a faster response time on AE there may be noticeable differences "all over." The filters delay AE reaction time so it may be easier to increase AE on a 0 to WOT transition, but I would expect the rich surge at light load, small throttle changes to get worse.

    Then again, I'm only on my first coffee so who knows...

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    Just finished my 2nd cup and starting to understand some of this great info, LOL

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    It seems like I'm getting somewhere with wrastlin' this AE into submission. I'm starting to get a better understanding of the what/how/why. AE is just to compensate for the drop in manifold vacuum when the throttle is opened quickly. Much like pump shot in a carburetor since TBI is also a wet manifold... AE is just to get you into PE then PE is in play from then on out.

    My throttle only opens 60%, I need to adjust the throttle cable or something, possibly move the home-made bracket that mounts it. Most of the time, when I slam the pedal down to 60% it is no longer lean popping. I'm still getting some lean pop occasionally.

    Once I got rid of most of the lean pops, I was also seeing the WB02 pegged on full rich 10 AFR. It was sluggish going off the line, especially when lightly stepping into the throttle. I have reduced some of the TPS AE and that seems to have helped.

    Does it stand to reason that with a large throttle body, and all the open plenum space of a carbed single plane, that MAP AE is going to probably be the main requirement to get AE in line? It seems that way in my case. I have read about other people having similar experiences with needing more MAP AE than TPS AE in similar setups.

    Really makes me appreciate my LS truck.... A dry manifold that comes off in 5 minutes, No distributor to hassle with, no AE to have to tune. Just slug the PE right into the 11.5 AFR range, turn up the boost and let it eat.

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    Quote Originally Posted by CDeeZ View Post
    It seems like I'm getting somewhere with wrastlin' this AE into submission. I'm starting to get a better understanding of the what/how/why. AE is just to compensate for the drop in manifold vacuum when the throttle is opened quickly. Much like pump shot in a carburetor since TBI is also a wet manifold... AE is just to get you into PE then PE is in play from then on out.

    My throttle only opens 60%, I need to adjust the throttle cable or something, possibly move the home-made bracket that mounts it. Most of the time, when I slam the pedal down to 60% it is no longer lean popping. I'm still getting some lean pop occasionally.

    Once I got rid of most of the lean pops, I was also seeing the WB02 pegged on full rich 10 AFR. It was sluggish going off the line, especially when lightly stepping into the throttle. I have reduced some of the TPS AE and that seems to have helped.

    Does it stand to reason that with a large throttle body, and all the open plenum space of a carbed single plane, that MAP AE is going to probably be the main requirement to get AE in line? It seems that way in my case. I have read about other people having similar experiences with needing more MAP AE than TPS AE in similar setups.

    Really makes me appreciate my LS truck.... A dry manifold that comes off in 5 minutes, No distributor to hassle with, no AE to have to tune. Just slug the PE right into the 11.5 AFR range, turn up the boost and let it eat.
    AE is still in effect in a LS truck and there are substantial throttle response gains to dialing them in as well. All the Wall Wet/Evaporation tables in the PCM are how they do it. I got it all dialed in the way I wanted on my L31 too.

    I found my old setup liked more bias toward the MAP AE. You can run into driving conditions were the manifold vacuum will suddenly drop from fairly high to almost non-existing with zero movement of the throttle pedal and need to have the MAP AE to keep the engine from experiencing a lean spike. Watch your part-throttle upshifts effect on the 02 sensor voltage and short term fuel trim. If the 02 voltage and narrow bands spike lean on a part throttle upshift at say 25% throttle you need to add more MAP AE. My old 350 Vortec Single Plane setup on the G20 van had 3x the MAP AE of a stock 454.

    If you are at 10:1 and it is still popping you have issues that are not AE related. Retarded spark timing as well as overly tight valves can cause popping and even fireballs out of the TBI unit.

    In my experience the L03/L05 spark maps only work well on the swirl port heads. They do not have enough timing in them to work well with other heads. Most other heads want more timing in the low rpm/high map area than the TBI heads work OK with in factory form. Most L05 timing maps actually have negative timing values off-idle at WOT. I have tuned cammed LS engines with 3,000+ rpm stall converters that like 20* of timing at 1,200 rpm @ full load and only run 26-28* of total timing at high rpm.

    With a loose converter you can typically advance the timing substantially under the stall speed. I usually use the PE spark added to ensure the extra timing is only there at WOT. I use 4-8* in my PE adder. When you are cruising around with a locked converter, out of PE the same timing values that help spool the engine up at WOT from a stop would cause spark knock.

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