Boost tuning today, big backfire/died, also temporary lifter clatter
02-25-2008, 09:12 PM
#1
Boost tuning today, big backfire/died, also temporary lifter clatter I've been creeping up on more timing, and on more boost.
Rear mount, low-comp forged pistons, fmic no meth, morels, automatic, 1998.
Running the manual boost controller that came with the STS kit originally.
3 turns = 7 psi, 4 turns = 9 psi, 5 turns = 11 psi.
Timing is at 22 degrees at peak torque, coming up to 24 degrees after peak.
Turned the dial to 6 turns expecting 13 psi. Timing and a/f checked out on a low boost run. Flipped it to high boost, got up to about 35 mph, and kicked it. Pulled strong, then a big KAPOW, some black smoke, and the engine died. Put it in neutral, coasted, hit the starter while it was still rolling and it fired right back up like nothing had happened.
The scan log (see post 15) didn't help much. I'm suspecting it loaded up the exhaust system rich while the timing was pulled for the 2-3 shift, then a lean pop set it off, but I'm just speculating on that. It also ran all the way up to 15.5 psi right before the pop - a lot more than I was expecting (later figured out this was just because the engine died and the throttle was still open). So that backfiring episode was weird thing #1.
I backed it back down to 5 turns on the controller, making 11 psi again. Everything looked good. Ran it up to 6600 rpms for the first time. Kept it in 3rd gear, let off, coasted/braked back down to 70 mph or so while still in 3rd. Lifter was clattering/ticking loud after it coasted back down. Drove it straight home to check it out, but 5 minutes into the drive, it quit making the noise. Got it home and can't hear it at all so I don't even know what side it was on. Kind of stumped on that one too. Valvetrain is early Morel lifters, PRC platinum springs, Harland Sharp stock ratio rockers, 581/588 lift, hardened pushrods 7.2 (7.4's wouldn't let the valves close all the way). Don't know why the lifter noise started up, or why it went away again. It was still pulling hard, and still making 11 psi, when I let off at 6600.
Any thoughts on either of these?
Rear mount, low-comp forged pistons, fmic no meth, morels, automatic, 1998.
Running the manual boost controller that came with the STS kit originally.
3 turns = 7 psi, 4 turns = 9 psi, 5 turns = 11 psi.
Timing is at 22 degrees at peak torque, coming up to 24 degrees after peak.
Turned the dial to 6 turns expecting 13 psi. Timing and a/f checked out on a low boost run. Flipped it to high boost, got up to about 35 mph, and kicked it. Pulled strong, then a big KAPOW, some black smoke, and the engine died. Put it in neutral, coasted, hit the starter while it was still rolling and it fired right back up like nothing had happened.
The scan log (see post 15) didn't help much. I'm suspecting it loaded up the exhaust system rich while the timing was pulled for the 2-3 shift, then a lean pop set it off, but I'm just speculating on that. It also ran all the way up to 15.5 psi right before the pop - a lot more than I was expecting (later figured out this was just because the engine died and the throttle was still open). So that backfiring episode was weird thing #1.
I backed it back down to 5 turns on the controller, making 11 psi again. Everything looked good. Ran it up to 6600 rpms for the first time. Kept it in 3rd gear, let off, coasted/braked back down to 70 mph or so while still in 3rd. Lifter was clattering/ticking loud after it coasted back down. Drove it straight home to check it out, but 5 minutes into the drive, it quit making the noise. Got it home and can't hear it at all so I don't even know what side it was on. Kind of stumped on that one too. Valvetrain is early Morel lifters, PRC platinum springs, Harland Sharp stock ratio rockers, 581/588 lift, hardened pushrods 7.2 (7.4's wouldn't let the valves close all the way). Don't know why the lifter noise started up, or why it went away again. It was still pulling hard, and still making 11 psi, when I let off at 6600.
Any thoughts on either of these?
Last edited by John_D.; 02-26-2008 at 03:59 PM.
02-25-2008, 09:26 PM
#2
Other info I just thought to include:
Plugs are TR6, .035, side-gapped.
Logged the fuel pressure (which is also boost referenced) and it was fine throughout.
Rev limiter is at 6900.
2-bar SD tune.
60 lb injectors.
IAT was 66F.
Plugs are TR6, .035, side-gapped.
Logged the fuel pressure (which is also boost referenced) and it was fine throughout.
Rev limiter is at 6900.
2-bar SD tune.
60 lb injectors.
IAT was 66F.
Last edited by John_D.; 02-26-2008 at 04:00 PM.
02-25-2008, 11:38 PM
#7
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I noticed with my stock trans between shifts it was so slow I'd get boost spikes when it hit the next gear... But never more than 7 or 7.5 psi when it was supposed to 6.
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02-26-2008, 10:12 AM
#10
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A couple things:
1.) If the manual boost controller is just the standard air compressor "regulator" type everyone uses, then you need to know that "counting turns" won't work. Because the closer it gets to "closed", the more sensitive it becomes. You'll get to a point where 1/8 turn may equal 3-4lbs of boost.
2.) Not sure what your compression is, or what fuel you're running, but that seems like an awful lot of timing. I've had 9:1 motors that didn't see that much timing with FMIC's and meth.
3.) From my experience, it's usually best to increase only boost or timing, not both. Find a good starting point where the engine makes good, clean power (flat a/f, etc). Then slowly come up on boost or timing. If you experiment a little, you'll find out what your combination likes best. IMHO.
1.) If the manual boost controller is just the standard air compressor "regulator" type everyone uses, then you need to know that "counting turns" won't work. Because the closer it gets to "closed", the more sensitive it becomes. You'll get to a point where 1/8 turn may equal 3-4lbs of boost.
2.) Not sure what your compression is, or what fuel you're running, but that seems like an awful lot of timing. I've had 9:1 motors that didn't see that much timing with FMIC's and meth.
3.) From my experience, it's usually best to increase only boost or timing, not both. Find a good starting point where the engine makes good, clean power (flat a/f, etc). Then slowly come up on boost or timing. If you experiment a little, you'll find out what your combination likes best. IMHO.
02-26-2008, 10:20 AM
#11
LS1Tech Co-Founder
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If you are running 22-24 degrees of timing, am I to assume you are running race gas? Sounds like you are getting aggressive with timing and boost as Rob noted.... Sounds risky, plus you are not sure how much boost you are actually getting.
Having the car shut off, could be a lot of things, was the car cutting in and out or was the engine fluttering, could be spark getting blown out?
Having the car shut off, could be a lot of things, was the car cutting in and out or was the engine fluttering, could be spark getting blown out?
02-26-2008, 01:12 PM
#12
1.) If the manual boost controller is just the standard air compressor "regulator" type everyone uses, then you need to know that "counting turns" won't work. Because the closer it gets to "closed", the more sensitive it becomes. You'll get to a point where 1/8 turn may equal 3-4lbs of boost.
3.) From my experience, it's usually best to increase only boost or timing, not both. Find a good starting point where the engine makes good, clean power (flat a/f, etc). Then slowly come up on boost or timing. If you experiment a little, you'll find out what your combination likes best. IMHO.
02-26-2008, 01:16 PM
#13
If you are running 22-24 degrees of timing, am I to assume you are running race gas? Sounds like you are getting aggressive with timing and boost as Rob noted.... Sounds risky, plus you are not sure how much boost you are actually getting.
Having the car shut off, could be a lot of things, was the car cutting in and out or was the engine fluttering, could be spark getting blown out?
Having the car shut off, could be a lot of things, was the car cutting in and out or was the engine fluttering, could be spark getting blown out?
The car was pulling strong, then one big boom, and it died immediately.
I'll pull a copy of the chart view off the laptop and post it up next. Might give some insight.
02-26-2008, 01:25 PM
#14
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So you're doing this on the street, and not on a dyno? If so, I would really suggest you spend some time on a dyno 1st getting the basics dialed in. Then you can play with boost, timing, etc, and log it on the street later. But to try and tune it "safely" on the street, is almost impossible, IMHO.
Okay, about the 93 octane. I would have to say that you're running way too much timing and/or boost for 93 alone. Even at 9:1. If I were tuning the car, I'd lock the timing down at about 15 for anything over 4000rpm's. Then pick a boost level, say 10lbs, and tune it in there perfectly first. (BTW, when your engine backfired, did it show KR??) After that, come up on the boost a lb at a time, tweaking the fuel each time, and monitoring KR and A/F closely (on the street, w/pump gas you want about 11.5:1). When you add boost and notice power starts to level off, stop there, and then try adding (or even subtracting) a degree of timing.
That should get you pretty close.
Okay, about the 93 octane. I would have to say that you're running way too much timing and/or boost for 93 alone. Even at 9:1. If I were tuning the car, I'd lock the timing down at about 15 for anything over 4000rpm's. Then pick a boost level, say 10lbs, and tune it in there perfectly first. (BTW, when your engine backfired, did it show KR??) After that, come up on the boost a lb at a time, tweaking the fuel each time, and monitoring KR and A/F closely (on the street, w/pump gas you want about 11.5:1). When you add boost and notice power starts to level off, stop there, and then try adding (or even subtracting) a degree of timing.
That should get you pretty close.
02-26-2008, 01:37 PM
#15
After looking at the chart view again just now (not in the heat of the moment) it looks like I was right around 13 psi when it died (when the rpms fell off). The boost just continued to climb because the throttle was still open but the cylinders weren't firing anymore...
My afr was trailing the commanded but it always looks that way when I'm in transition because the wb is mounted in the tailpipe after the turbo.
The only clue I see is the big timing dip on the shift. As I've continued to advance the timing, I've had to add more fuel. When the timing is low, it appears to run much richer (on the same amount of fuel). A VE of 95% may run very rich (10.0:1) at 14 degrees, and needs 110%-115% VE just to hit 11.5 at 22 degrees.
As I advance the timing, it's burning it better and I have to add more fuel. So when the timing got pulled, it artificially got much richer (wb hadn't caught it yet though). Then when the timing recovered after the shift it may have lit off the rich mixture in the exhaust.
I've got it shifting way early, 4500 rpms, if I let the pcm shift it. That's to help save the transmission until I get my built one out of layaway... That's why I was letting it pull so much timing on the shift too.
When the attachment opens in IE, click on it to get it to normal size and it's easier to read.
My afr was trailing the commanded but it always looks that way when I'm in transition because the wb is mounted in the tailpipe after the turbo.
The only clue I see is the big timing dip on the shift. As I've continued to advance the timing, I've had to add more fuel. When the timing is low, it appears to run much richer (on the same amount of fuel). A VE of 95% may run very rich (10.0:1) at 14 degrees, and needs 110%-115% VE just to hit 11.5 at 22 degrees.
As I advance the timing, it's burning it better and I have to add more fuel. So when the timing got pulled, it artificially got much richer (wb hadn't caught it yet though). Then when the timing recovered after the shift it may have lit off the rich mixture in the exhaust.
I've got it shifting way early, 4500 rpms, if I let the pcm shift it. That's to help save the transmission until I get my built one out of layaway... That's why I was letting it pull so much timing on the shift too.
When the attachment opens in IE, click on it to get it to normal size and it's easier to read.
Last edited by John_D.; 02-26-2008 at 05:41 PM. Reason: more clear copy of chart
02-26-2008, 01:51 PM
#16
So you're doing this on the street, and not on a dyno? If so, I would really suggest you spend some time on a dyno 1st getting the basics dialed in. Then you can play with boost, timing, etc, and log it on the street later. But to try and tune it "safely" on the street, is almost impossible, IMHO.
I'm on tune # 61.
AFR, KR, and timing are all spot on at 5 psi. Also good at 7, 9, and 11 psi now. Up to 6000 rpms anyway. It only has one run to 6600 and that's when the lifter? started acting up.
Okay, about the 93 octane. I would have to say that you're running way too much timing and/or boost for 93 alone. Even at 9:1. If I were tuning the car, I'd lock the timing down at about 15 for anything over 4000rpm's. Then pick a boost level, say 10lbs, and tune it in there perfectly first. (BTW, when your engine backfired, did it show KR??) After that, come up on the boost a lb at a time, tweaking the fuel each time, and monitoring KR and A/F closely (on the street, w/pump gas you want about 11.5:1). When you add boost and notice power starts to level off, stop there, and then try adding (or even subtracting) a degree of timing.
That should get you pretty close.
That should get you pretty close.
But with 22 degrees it's pulling as hard in 3rd gear on the interstate at interstate+ speeds as my stock TA pulls in first gear at first gear speeds. (gains 10-11 mph per second at wot)
That's 40% more power being applied at 22 degrees vs 15 degrees, for the duration of a 30-40mph increase from the starting speed of the wot blast.
7.5 mph vs 10.5 mph per second. 3 more mph over the initial 7.5.
3/7.5 = 0.40
You've described my approach, except I've come up 2 psi at a time. I also was shooting for 10.5 on the fueling in the initial stages. It's just in the past ten tunes that I've let it come up into the mid 11's.
Last edited by John_D.; 02-26-2008 at 07:56 PM. Reason: clarify the observed performance difference of 15 degrees vs 22 degrees
02-26-2008, 02:02 PM
#17
p.s for additional loading I've been doing some hill climbing under boost and logging it too. That should really bring out the KR if there's going to be any. I've gotten past blowing off pipes, blowing out the dipstick, re-working the pcv, etc.
It's just the big backfire when I got it over 11 psi that worried me. I'm pretty sure this is the first time I've let it upshift while under big boost too.
Normally I get it into a gear (2nd or 3rd), boost through that gear, and let off around 6k or before. My shift tables are set so if I'm turning more than 3000 rpms it won't downshift. I must have been just under 3k for this test and it downshifted to 2nd, then upshifted back to 3rd right away. Looks like from the log I was doing 32mph and I needed to have been going 35mph when I got on it, to keep it in 3rd gear.
It's just the big backfire when I got it over 11 psi that worried me. I'm pretty sure this is the first time I've let it upshift while under big boost too.
Normally I get it into a gear (2nd or 3rd), boost through that gear, and let off around 6k or before. My shift tables are set so if I'm turning more than 3000 rpms it won't downshift. I must have been just under 3k for this test and it downshifted to 2nd, then upshifted back to 3rd right away. Looks like from the log I was doing 32mph and I needed to have been going 35mph when I got on it, to keep it in 3rd gear.
02-26-2008, 02:12 PM
#20
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Being sluggish, wouldn't be because of the 15 degrees of timing. It's more than likely the A/F is rich on spool-up. Understandably, because you are trying to tune it safely. For right now, I wouldn't worry about the lower rpm's. I'd tune the WOT from about 4000 up. The lower rpm's are much easier to tune, and require a lot less road.
You actually want the A/F to 'ramp' down to 11.5:1 (or whatever your target is) as boost increases. In other words, seeing 12.8:1 with 1-2psi, is okay. Richening up to your target A/F by about 5psi.
Also, by running less timing down low, you can actually make it spool quicker. Less timing equals hotter exhaust, faster spool.
You actually want the A/F to 'ramp' down to 11.5:1 (or whatever your target is) as boost increases. In other words, seeing 12.8:1 with 1-2psi, is okay. Richening up to your target A/F by about 5psi.
Also, by running less timing down low, you can actually make it spool quicker. Less timing equals hotter exhaust, faster spool.