Injectors going static, Holley 670 mods
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Injectors going static, Holley 670 mods
I've got a Holley 670 on a modestly built 350 (more-or-less a 330 hp GM crate 350 w/ Vortec heads for a 8.75-9.0 CR, a Performer Vortec manifold, roller everything w/ a CompCams 264/274 deg, .480/.480 lift, and a vfpr). Two questions:
1) I am concerned that I am driving my injectors to static- fuel pressure is a steady 15psi, but my main fuel table (w/ a 7747) ranges from 43 to 99.6 (w/ the secondary table zero'd out). My WB indicates 12.5-13.5 in WOT. Do the almost-100-percent numbers indicate I need some more fuel pressure? After a year of tuning the BLMs are all in the 125-135 range, even at high MAP. Driveability isn't bad. Is some more fuel pressure and tuning called for, or should I be satisfied?
2) Has anyone ever tried to bore over a Holley 670, in the same way they did the old OEM 470 cfm units? Just eyeballing it, there seems to be a fair amount of extra room around the bores - perhaps 150, 200 mil or more. I'd like to get some more air into the motor, but the next step seems to be an expensive 4-bbl from Holley or Accel (along w/ ecu changes, mods, or additions) or an mpfi system (with its own round of ecu changes and reprogramming). It's an expensive hobby, but I don't want to make it any more expensive than necessary.
1) I am concerned that I am driving my injectors to static- fuel pressure is a steady 15psi, but my main fuel table (w/ a 7747) ranges from 43 to 99.6 (w/ the secondary table zero'd out). My WB indicates 12.5-13.5 in WOT. Do the almost-100-percent numbers indicate I need some more fuel pressure? After a year of tuning the BLMs are all in the 125-135 range, even at high MAP. Driveability isn't bad. Is some more fuel pressure and tuning called for, or should I be satisfied?
2) Has anyone ever tried to bore over a Holley 670, in the same way they did the old OEM 470 cfm units? Just eyeballing it, there seems to be a fair amount of extra room around the bores - perhaps 150, 200 mil or more. I'd like to get some more air into the motor, but the next step seems to be an expensive 4-bbl from Holley or Accel (along w/ ecu changes, mods, or additions) or an mpfi system (with its own round of ecu changes and reprogramming). It's an expensive hobby, but I don't want to make it any more expensive than necessary.
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You need the second AFR table. Thats the only control you have over the fueling when the motor goes over 3200 rpms. What happens is that the VE gets stuck at the last entry on the main table and if the motor needs more fuel, you have no way of adding it. The second table gives you at least a token ammount of control over the afrs when your off the main table.
If your getting to very high VEs and still no change in the actual AFR then thats a good sign that you need more pressure. You can also output the injector PW through the ALDL. Its a double byte value so you just place the two addresses in place of the PROM ID in the aldl address table and youll get the injector PW in your datalogs. This can tell you if your going static. I dont remember the RAM addresses of the BPW, though.
Before you consider overboring the tbi, run sans aircleaner and hook up a mechanical vacuum gauge. Run the engine through its powerband at WOT and note the largest ammount of vacuum reported. If its less then 3 inHg of vacuum, I wouldnt bother with overboring the tbi.
If your getting to very high VEs and still no change in the actual AFR then thats a good sign that you need more pressure. You can also output the injector PW through the ALDL. Its a double byte value so you just place the two addresses in place of the PROM ID in the aldl address table and youll get the injector PW in your datalogs. This can tell you if your going static. I dont remember the RAM addresses of the BPW, though.
Before you consider overboring the tbi, run sans aircleaner and hook up a mechanical vacuum gauge. Run the engine through its powerband at WOT and note the largest ammount of vacuum reported. If its less then 3 inHg of vacuum, I wouldnt bother with overboring the tbi.
QUOTE:
You need the second AFR table. Thats the only control you have over the fueling when the motor goes over 3200 rpms. What happens is that the VE gets stuck at the last entry on the main table and if the motor needs more fuel, you have no way of adding it. The second table gives you at least a token ammount of control over the afrs when your off the main table.
I DID JUST THAT. I ZEROED OUT THE MAIN FUEL TABLE #2. i did so to make the calculations easier after data logging. i would then only change the value in table 1 and need not be concerned about #2. i have not looked at my TC program since November so cant recall exactly how it reads. i think i only zeroed out the rpm's in table 2 that appear in table 1 but not the higher rpms in table #2 as those are needed. does this sound right? again this is CL only and not PE. i did log CL somewhat in high map high rpms with PE somewhat disabled. please explain why GM offerred 2 tables rather than one? i know this came up before.
ps i was running lean in PE last fall before i put car away 13.5/1. i attributed that to lack of FP as was set at 12 and should be much higher.
You need the second AFR table. Thats the only control you have over the fueling when the motor goes over 3200 rpms. What happens is that the VE gets stuck at the last entry on the main table and if the motor needs more fuel, you have no way of adding it. The second table gives you at least a token ammount of control over the afrs when your off the main table.
I DID JUST THAT. I ZEROED OUT THE MAIN FUEL TABLE #2. i did so to make the calculations easier after data logging. i would then only change the value in table 1 and need not be concerned about #2. i have not looked at my TC program since November so cant recall exactly how it reads. i think i only zeroed out the rpm's in table 2 that appear in table 1 but not the higher rpms in table #2 as those are needed. does this sound right? again this is CL only and not PE. i did log CL somewhat in high map high rpms with PE somewhat disabled. please explain why GM offerred 2 tables rather than one? i know this came up before.
ps i was running lean in PE last fall before i put car away 13.5/1. i attributed that to lack of FP as was set at 12 and should be much higher.
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From: Hurst, Texas
Car: 1983 G20 Chevy
Engine: 305 TPI
Transmission: 4L60
Axle/Gears: 14 bolt with 3.07 gears
The second fuel table is something that I don't fully understand yet. It looks to be just like the extended rpm spark, just with fuel?
The 400-3,200 rpm on the #1 fuel table really shows GMs intent for this engine to be a low rpm one.
As a side thought to this what would happen if you left the second table blank until the 3,600 rpm increment then added fuel above that? It just seems like at part throttle the ECM would be able to control the fuel better than having to use both tables. It also easier to tune the fuel that way.
The 400-3,200 rpm on the #1 fuel table really shows GMs intent for this engine to be a low rpm one.
As a side thought to this what would happen if you left the second table blank until the 3,600 rpm increment then added fuel above that? It just seems like at part throttle the ECM would be able to control the fuel better than having to use both tables. It also easier to tune the fuel that way.
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Yeah, it makes it a bit easier to tune if you zero out the 2nd fuel table from 400-3200. Just make sure you don't zero the whole table. All the second table is is an adder table that adds to the fuel in the first table.
I've zeroed that portion of the table out as well as the PE spark table, adding all my spark advance into the main table. Doing things like this just make tuning the engine a bit easier to visualize what's going on.
I've zeroed that portion of the table out as well as the PE spark table, adding all my spark advance into the main table. Doing things like this just make tuning the engine a bit easier to visualize what's going on.
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Car: 88 Camaro SC
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The problem with zeroing out the secondary table is that there is no way to reduce the AFRs after the engine passes its peak torque. You can zero it out, but the last row must have the AFR split between the primary and secondary tables.
This pic should help. At WOT, the green curve shows the overall VE that results from the two tables when theyre added together. Both the primary and secondary tables are added to get the overall VE. Once the engine passes 3200 rpm, the secondary table can be reduced, thus reducing the VE. If you didnt do this, the engine would go rich at higher rpms because the primary VE table is stuck at its last entry at 3200 rpm.
This pic should help. At WOT, the green curve shows the overall VE that results from the two tables when theyre added together. Both the primary and secondary tables are added to get the overall VE. Once the engine passes 3200 rpm, the secondary table can be reduced, thus reducing the VE. If you didnt do this, the engine would go rich at higher rpms because the primary VE table is stuck at its last entry at 3200 rpm.
Last edited by dimented24x7; Mar 9, 2005 at 08:55 PM.
DIMMENTED: are you saying it is OK to zero out the table 2 at low rpm as i did? and maintain the table 2 higher rpms? my issue after manifold/cam swap is i went from 12.3/1 to 13.3/1 but used a diff WB after swap.
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it would be ok, I suppose. The last row must be a mix of the two tables so you can scale down the VE at higher rpms after the motor passes peak torque. Its not ideal as teh computer interpolates between values and it will cause some error when you transition to the last row.
The best way is to use some constant value in teh adder table when below 3200 rpms and after that, use the adder table to control the afrs with the VE. I illustrated this in the pic. above.
The best way is to use some constant value in teh adder table when below 3200 rpms and after that, use the adder table to control the afrs with the VE. I illustrated this in the pic. above.
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OK, now I'm confused ( though I suppose I should be used to it by now, eh?)
Some time ago, I had a thread going about tuning a different motor, and the VE table 2 thing came up. I was doing what Ronny is talking about, and RBob suggested (I thought) that I zero out the table all the way - here's the pertinent section:
So I'm confused - I've kind of got two algorithms spinning around in my head. Clarification, please?
Some time ago, I had a thread going about tuning a different motor, and the VE table 2 thing came up. I was doing what Ronny is talking about, and RBob suggested (I thought) that I zero out the table all the way - here's the pertinent section:
I have another question, though it probably should be a separate thread, concerning the VE tables: it has to do with how the system transitions from Table 1 to Table 2. Table 1 "runs out" (or becomes linear) above 3200: Table 2 continues to 6400. If I wanted to incorporate T2 into T1, I understand I'd simply add the numbers (keeping them below 100), and "0" T2. However, what do I do above 3200? Just leave the values alone? So T2 might look like this:
RPM % Vol Eff.
0 25.0
400 0.0
800 0.0
1200 0.0
1600 0.0
2000 0.0
2400 0.0
2800 0.0
3200 0.0
3600 33.2
4000 27.3
4400 27.3
4800 31.3
5200 33.2
5600 33.2
6000 33.2
6400 33.2
Then, if I scale T1 10%, I'd also scale T2 10%. Or would I "0" the whole table? I've tried to study the hack, but I'm just not a machine-code kind of guy.
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07-23-2003 05:44 AM
RBob
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<snip>
The two VE tables are always added together. Once engine is greater then 3200 RPM the 3200 RPM row is used. You don't want to do what you have above. Once you go past 3200 RPM you will be adding a lot of fuel. Along with no way to reduce the fuel below the 3200 level.
It comes down to how much lower will the VE be at 6400 RPM vs. 3200 RPM. You need to have at least that much room to remove fuel via the VE table.
RPM % Vol Eff.
0 25.0
400 0.0
800 0.0
1200 0.0
1600 0.0
2000 0.0
2400 0.0
2800 0.0
3200 0.0
3600 33.2
4000 27.3
4400 27.3
4800 31.3
5200 33.2
5600 33.2
6000 33.2
6400 33.2
Then, if I scale T1 10%, I'd also scale T2 10%. Or would I "0" the whole table? I've tried to study the hack, but I'm just not a machine-code kind of guy.
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07-23-2003 05:44 AM
RBob
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<snip>
The two VE tables are always added together. Once engine is greater then 3200 RPM the 3200 RPM row is used. You don't want to do what you have above. Once you go past 3200 RPM you will be adding a lot of fuel. Along with no way to reduce the fuel below the 3200 level.
It comes down to how much lower will the VE be at 6400 RPM vs. 3200 RPM. You need to have at least that much room to remove fuel via the VE table.
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Ok, here's the deal. Let's say you zero the 2nd table out for everything up to and including 3200RPM. So you must have added the values from the 2nd table into the 1st table to accomodate for the zero's right? right. Now when the ECM goes beyond 3200RPM and off the charts of the 1st table, it holds the 3200RPM values from the 1st table constant and adds in the values from the 2nd table at 3600, 4000, etc.
Now, if you've zeroed the 2nd table and corrected for it in the 1st table you'll have a value of something like say 95 in some of the 3200RPM cells in the 1st table. Now after 3200RPM your 2nd table is no longer zeroes, but as you posted, 33.2 at 3600RPM. That means essentially that at 3600 RPM, your VE value is 128.2! Do you see why that can be bad now? Because your VE isn't going to be nearly that high at those RPM. Hope that didn't come out too confusing.
Now, if you've zeroed the 2nd table and corrected for it in the 1st table you'll have a value of something like say 95 in some of the 3200RPM cells in the 1st table. Now after 3200RPM your 2nd table is no longer zeroes, but as you posted, 33.2 at 3600RPM. That means essentially that at 3600 RPM, your VE value is 128.2! Do you see why that can be bad now? Because your VE isn't going to be nearly that high at those RPM. Hope that didn't come out too confusing.
now i get it. peak TQ= high VE. the adder table #2 can produce VE in excess of what is needed above 3200 rpms as VE can/does reduce. thanks for the info. i need to reapproach my "zero" and check peak TQ as was on dyno with prior set up. maybe i can compare VE in that regard.
only comment i can make is it is diificult to get good VE above 3200 rpms unless you disable PE. i ran my car in third gear at high rpms (3200/3400/3600/3800) and the commoners on xway thought i was over the edge. duals with aerochambers make some nasty noise.
only comment i can make is it is diificult to get good VE above 3200 rpms unless you disable PE. i ran my car in third gear at high rpms (3200/3400/3600/3800) and the commoners on xway thought i was over the edge. duals with aerochambers make some nasty noise.
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OK, I think I'm getting the idea, too. Effectively, the "Sum of VE" would look like this:
So what I need to do is at least split the difference between the 3200 VE1
and the 3200 VE2
So, to get back to my very original question, yeah, I probably *am* driving my injectors to saturation.
Code:
RPM VE2 VE1@100kpa Sum 400 0.0 45 45 800 0.0 50 50 1200 0.0 55 55 1600 0.0 60 60 2000 0.0 65 65 2400 0.0 70 70 2800 0.0 75 75 3200 0.0 80 80 3600 33.2 80 112.2 4000 27.3 80 107.3 4400 27.3 80 107.3 4800 31.3 80 111.3 5200 33.2 80 113.2 5600 33.2 80 113.2 6000 33.2 80 113.2 6400 33.2 80 113.2
and the 3200 VE2
Code:
RPM VE2 VE1@100kpa Sum 400 0.0 45 45 800 0.0 50 50 1200 0.0 55 55 1600 0.0 60 60 2000 0.0 65 65 2400 0.0 70 70 2800 0.0 75 75 3200 40.0 40 80 3600 33.2 40 73.2 4000 27.3 40 67.3 4400 27.3 40 67.3 4800 31.3 40 71.3 5200 33.2 40 73.2 5600 33.2 40 73.2 6000 33.2 40 73.2 6400 33.2 40 73.2
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From: Hurst, Texas
Car: 1983 G20 Chevy
Engine: 305 TPI
Transmission: 4L60
Axle/Gears: 14 bolt with 3.07 gears
Oh I get it the 3,200 rpm on the 1st table has to have something in it to keep from going rich at higher speeds.
No wonder I have been having problems with the 307 I am tuning @ WOT and about 3,200 rpm, it goes so rich that the engine litterally bogs down and stalls.
Thanks for this insight.
No wonder I have been having problems with the 307 I am tuning @ WOT and about 3,200 rpm, it goes so rich that the engine litterally bogs down and stalls.
Thanks for this insight.
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