23 psi from a D1sc, up from 15 psi, yet no improvement in times...WTF!
03-10-2010, 01:26 PM
#1
23 psi from a D1sc, up from 15 psi, yet no improvement in times...WTF! This is the truck in my sig. The truck has been stuck in the 7.0 range in the 1/8 mile for over a year. Just recently, I upgraded the pulleys/tensioner to an 8-rib set up. The truck now makes a ton more boost, but still runs consistant 7.0's in the 1/8th. It did run 6.97 at 101 on the last pass I made this weekend but close enough. Here is a run down on the before and after boost levels:
Launch 3800 rpm: Before 5 psi, After 10 psi
Shift Point 6900 rpm: Before 14-15 psi, After 22-23 psi
After Shift Boost Drop: Before 10 psi, After 16-17 psi
The only other difference is the timing: Before 20* total, After 14* total
Everything else seems constant. AFR's the same, IAT's the same, 60' the same, converter stall and slip the same, shift points the same, no KR, etc. You can literally lay data logs from before and after over each other and they look identical, except for boost level and 6* less timing.
I do find it strange that it makes this much boost, but whatever. I was really expecting a significant improvement in times, but the truck doesn't even act like the extra airflow is even happening. WTF!
I called prochargers tech dept. and they didn't have a clue. Could my exhaust system be holding it back, or the intercooler? I'm out of guesses.
Launch 3800 rpm: Before 5 psi, After 10 psi
Shift Point 6900 rpm: Before 14-15 psi, After 22-23 psi
After Shift Boost Drop: Before 10 psi, After 16-17 psi
The only other difference is the timing: Before 20* total, After 14* total
Everything else seems constant. AFR's the same, IAT's the same, 60' the same, converter stall and slip the same, shift points the same, no KR, etc. You can literally lay data logs from before and after over each other and they look identical, except for boost level and 6* less timing.
I do find it strange that it makes this much boost, but whatever. I was really expecting a significant improvement in times, but the truck doesn't even act like the extra airflow is even happening. WTF!
I called prochargers tech dept. and they didn't have a clue. Could my exhaust system be holding it back, or the intercooler? I'm out of guesses.
03-10-2010, 02:14 PM
#5
9 Second Club
This is a pretty open ended problem based on the facts so far. I don't remember seeing anyone running at 23psi though on a D1SC before though? Your 4" exhaust is unlikely to be a restriction though unless you have a chambered muffler.
Remember, boost pressure is just a measure of airflow restriction and not a measure of power. It means generally speaking that there is more airflow up to a point but once you hit the efficiency limits of the blower/turbo all you really do is add more heat to the aircharge. More heat means less power in the actual burn events and potential for detonation to occur. The IATs might not show it yet if you are running in cooler ambient air temps than what you ran in before?
Valve float is certainly a potential problem at 23psi if that's a real number and not the boost gauge having an issue. You'll feel it around 5000-5500 rpm typically. The truck should feel more powerful up to that point and then fall on it's face and not roll up faster no matter what the boost pickup is.
Rick
Remember, boost pressure is just a measure of airflow restriction and not a measure of power. It means generally speaking that there is more airflow up to a point but once you hit the efficiency limits of the blower/turbo all you really do is add more heat to the aircharge. More heat means less power in the actual burn events and potential for detonation to occur. The IATs might not show it yet if you are running in cooler ambient air temps than what you ran in before?
Valve float is certainly a potential problem at 23psi if that's a real number and not the boost gauge having an issue. You'll feel it around 5000-5500 rpm typically. The truck should feel more powerful up to that point and then fall on it's face and not roll up faster no matter what the boost pickup is.
Rick
03-10-2010, 03:48 PM
#6
This is a pretty open ended problem based on the facts so far. I don't remember seeing anyone running at 23psi though on a D1SC before though? Your 4" exhaust is unlikely to be a restriction though unless you have a chambered muffler.
Remember, boost pressure is just a measure of airflow restriction and not a measure of power. It means generally speaking that there is more airflow up to a point but once you hit the efficiency limits of the blower/turbo all you really do is add more heat to the aircharge. More heat means less power in the actual burn events and potential for detonation to occur. The IATs might not show it yet if you are running in cooler ambient air temps than what you ran in before?
Valve float is certainly a potential problem at 23psi if that's a real number and not the boost gauge having an issue. You'll feel it around 5000-5500 rpm typically. The truck should feel more powerful up to that point and then fall on it's face and not roll up faster no matter what the boost pickup is.
Rick
Remember, boost pressure is just a measure of airflow restriction and not a measure of power. It means generally speaking that there is more airflow up to a point but once you hit the efficiency limits of the blower/turbo all you really do is add more heat to the aircharge. More heat means less power in the actual burn events and potential for detonation to occur. The IATs might not show it yet if you are running in cooler ambient air temps than what you ran in before?
Valve float is certainly a potential problem at 23psi if that's a real number and not the boost gauge having an issue. You'll feel it around 5000-5500 rpm typically. The truck should feel more powerful up to that point and then fall on it's face and not roll up faster no matter what the boost pickup is.
Rick
The truck has meth on it so maybe that is masking my IAT's. All runs I'm comparing are in similar ambients and DA's.
Regarding your comment about valve float. I agree that could be a potential issue, however the truck feels the same as it used to no matter where I'm at in the rpm range. Even if the blower was becoming ineffecient you would still think that it would do something different in the first 60' before the blower really starts rolling. Looking at my logs it looks like its making 18 psi by the 60' mark with the motor at 5600 rpm and blower at 53,350 rpm which is well within its efficiency range. At 6900 rpm I'm spinning the blower around 65,000 rpm, which is not a great deal past its max recommended speed.
The boost numbers I'm quoting are converted from kpa readings in HPT, not off the gauge.
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03-10-2010, 09:54 PM
#11
I did actually stick on the dyno two weeks ago with this combo, however I only got to part of the story. The first pull I only went to 5000 rpm to make sure everything was cool. Then second pull I went to 6000 and it made 700 rwhp. After that it all started going downhill as the 2nd and 3rd clutch packs gave up in the tranny. I can tell you that the graph looked solid up to 6000 on the second pull.
I guess you guys make a good point about seeing exactly where the power might be falling off.
I guess you guys make a good point about seeing exactly where the power might be falling off.
03-11-2010, 11:02 AM
#13
9 Second Club
I guess I miss read this before... but I didn't see the pulling of 6 degrees of timing.
There isn't an exact relationship that I know of but for me, a pound of boost is pretty close to a degree of timing over all ET with my car. The difference is that timing is there for the whole curve and the pound of boost is at the mid to top end of the curve.
So based on the theory that you've traded boost for timing and your ET is the same it kind of fits. Did the MPH go up though with the increase boost with the theory that you might be seeing some more topend power?
Next question is what gas are you running? Then maybe try adding a degree of timing back if the meth is supporting it. That's were the dyno tuning can speed up the process rather than making a lot of passes at the track to do same thing.
Rick
There isn't an exact relationship that I know of but for me, a pound of boost is pretty close to a degree of timing over all ET with my car. The difference is that timing is there for the whole curve and the pound of boost is at the mid to top end of the curve.
So based on the theory that you've traded boost for timing and your ET is the same it kind of fits. Did the MPH go up though with the increase boost with the theory that you might be seeing some more topend power?
Next question is what gas are you running? Then maybe try adding a degree of timing back if the meth is supporting it. That's were the dyno tuning can speed up the process rather than making a lot of passes at the track to do same thing.
Rick
03-11-2010, 11:10 AM
#14
LS1Tech Co-Founder
iTrader: (34)
It's hard to figure out from your post OP.
Let's start by posting your best slip, power at that point, and your raceweight.
Could be valve float, that Vig 3600 might not be working that well, belt slip, something going on in your tune...etc.
I went 9.40@143, 1.35, 3500 raceweight, 680rwhp, 18 psi back in the day with my YSi. Had some belt slippage that hurt the top end. If you are 4000 raceweight I'd think you could run a best of 10.0 or a milder 10.5. MPH should be 130-135.
Let's start by posting your best slip, power at that point, and your raceweight.
Could be valve float, that Vig 3600 might not be working that well, belt slip, something going on in your tune...etc.
I went 9.40@143, 1.35, 3500 raceweight, 680rwhp, 18 psi back in the day with my YSi. Had some belt slippage that hurt the top end. If you are 4000 raceweight I'd think you could run a best of 10.0 or a milder 10.5. MPH should be 130-135.
03-11-2010, 12:50 PM
#15
The blower should indeed not be making anywhere close to that much boost on one of these engines. Do you have cats on there? If you do, I'll bet they are clogged up. Bob
03-11-2010, 07:32 PM
#17
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I would swap out your boost gauge... something isnt right here.
Second: any possibility you're blowing through the converter or your trans is giving up??
That big of a boost increase will change the exhaust note, does it sound any different or feel any different on the street?
Second: any possibility you're blowing through the converter or your trans is giving up??
That big of a boost increase will change the exhaust note, does it sound any different or feel any different on the street?
03-11-2010, 09:15 PM
#19
I would swap out your boost gauge... something isnt right here.
Second: any possibility you're blowing through the converter or your trans is giving up??
That big of a boost increase will change the exhaust note, does it sound any different or feel any different on the street?
Second: any possibility you're blowing through the converter or your trans is giving up??
That big of a boost increase will change the exhaust note, does it sound any different or feel any different on the street?
