boost loss
11-17-2018, 12:14 PM
#1
Teching In
Thread Starter
iTrader: (1)
Join Date: Jul 2004
Posts: 25
Likes: 0
Received 0 Likes
on
0 Posts
boost loss Ok maybe someone can help me on here im about to lose my mind with this car . I have a procharged trans am that has loss about 10 lbs of boost and I cant figure out why .so over the summer I had a power steering leak since then it have all been fix which is what I thought the problem was .Ive pressure tested all the intercooler pipes and found nothing .Ive pulled the bov apart and found nothing wrong with it . Ive made sure all the pulleys are aligned and ive even put a new pulley on the blower . Ive replace the tensioner and the belt. after fixing some little things I replace the belt again yesterday and it made 15lbs . When I put it in second it blew the elbow off . Well I fixed that and made another pass and it hit 10lbs this time and then went right to 5 lbs . Now it will hit 5lbs and stay there on the whole pass
here my setup
d1sc
7.65 crank pulley 8rib
4.25blower pulley
turbosmart big bubba bov
gates green belt
aster bracket
thanks Jason
here my setup
d1sc
7.65 crank pulley 8rib
4.25blower pulley
turbosmart big bubba bov
gates green belt
aster bracket
thanks Jason
11-17-2018, 01:33 PM
#3
My guess is belt slip. You should be able to hear a leaky BOV. Maybe cheap band clamps? Upgrade to locking style if your using the ones that came with the kit. If you spin a belt or get things like PS fluid on it, it’s toast. I had similar issues with belt slip.
11-17-2018, 01:35 PM
#4
15 lbs of boost with a 4.25 pully seems high. Bob at Brute recommended that I would have to downsize to at least a 3.9 pulley with a 7.65 crank pulley to make 12 lbs. But haven't put it on the dyno yet to see what it actually makes, still breaking in the engine.
But boost depends a lot of the engine efficiency. I rarely got to 10 lbs with a 4.38 pulley downsizing from the original 4.50 pulley which just barely made 8 lbs of boost.
When you blew the elbo off, did you examine the silicone for hairline crack? Any chance you have an extra to replace it? Seems odd the loss of boost is coincidental with the silicone connector blow off.
Out of curiosity, what is your belt length?
With a 7.65 crank pulley, 3.9 blower pulley and Aster Bracket center pulley on middle hole, my belt length is K080525HD (that's the green belt - not the RPM belt).
Any reason why you use a BOV instead of the bypass valve. I have the ATI big red bypass now since I have upped my boost (Over 12 lbs of boost, Bob suggested the Big Red).
It's my understanding a bypass valve is better suited for the D1 SC unless the BOV has a very light spring. Not as hard on the blower.
************************************************** *************
Bypass Valves vs Blow Off Valves
Blowers are always producing some amount of boost as they are belt driven, where a turbo spools up as the exhaust velocity is increased. Bypass valves are used with blowers since they always relieve the boost until near zero vacuum (heavy throttle) is achieved. Blow-off valves are designed to relieve boost at a set amount of boost, and can cause boost stacking when used with a blower. Light springs can be used with blow-off valves so that they can be used with blowers, and many have reported success with doing so. Unless a blow off valve is properly set up with a light spring though, the boost that is built up places a load on the blower that is hard on it, plus it will try to slow the blower down which can cause belt slippage. Stacked up boost will also try to find weak spot in the tubing and hoses to blow out of. This is why Bypass Valves are better than Blow Off Valves.
************************************************** *******************
But boost depends a lot of the engine efficiency. I rarely got to 10 lbs with a 4.38 pulley downsizing from the original 4.50 pulley which just barely made 8 lbs of boost.
When you blew the elbo off, did you examine the silicone for hairline crack? Any chance you have an extra to replace it? Seems odd the loss of boost is coincidental with the silicone connector blow off.
Out of curiosity, what is your belt length?
With a 7.65 crank pulley, 3.9 blower pulley and Aster Bracket center pulley on middle hole, my belt length is K080525HD (that's the green belt - not the RPM belt).
Any reason why you use a BOV instead of the bypass valve. I have the ATI big red bypass now since I have upped my boost (Over 12 lbs of boost, Bob suggested the Big Red).
It's my understanding a bypass valve is better suited for the D1 SC unless the BOV has a very light spring. Not as hard on the blower.
************************************************** *************
Bypass Valves vs Blow Off Valves
Blowers are always producing some amount of boost as they are belt driven, where a turbo spools up as the exhaust velocity is increased. Bypass valves are used with blowers since they always relieve the boost until near zero vacuum (heavy throttle) is achieved. Blow-off valves are designed to relieve boost at a set amount of boost, and can cause boost stacking when used with a blower. Light springs can be used with blow-off valves so that they can be used with blowers, and many have reported success with doing so. Unless a blow off valve is properly set up with a light spring though, the boost that is built up places a load on the blower that is hard on it, plus it will try to slow the blower down which can cause belt slippage. Stacked up boost will also try to find weak spot in the tubing and hoses to blow out of. This is why Bypass Valves are better than Blow Off Valves.
************************************************** *******************
Last edited by dlandsvZ28; 11-17-2018 at 01:54 PM.
11-17-2018, 01:37 PM
#5
Maybe a dumb question, but is the crank pulley keyed or pinned?
Yes - that's another place to check. Mine is double keyed at 180 since I upped the boost
Another place to look is free play on the tensioner. Is it bumping against full extension? It must have some gap to over extend. Easy to see. Adjust by moving the middle pulley in or out.
Yes - that's another place to check. Mine is double keyed at 180 since I upped the boost
Another place to look is free play on the tensioner. Is it bumping against full extension? It must have some gap to over extend. Easy to see. Adjust by moving the middle pulley in or out.
Last edited by dlandsvZ28; 11-17-2018 at 01:46 PM. Reason: Add additional info
11-18-2018, 02:14 PM
#7
Teching In
Thread Starter
iTrader: (1)
Join Date: Jul 2004
Posts: 25
Likes: 0
Received 0 Likes
on
0 Posts
15 lbs of boost with a 4.25 pully seems high. Bob at Brute recommended that I would have to downsize to at least a 3.9 pulley with a 7.65 crank pulley to make 12 lbs. But haven't put it on the dyno yet to see what it actually makes, still breaking in the engine.
But boost depends a lot of the engine efficiency. I rarely got to 10 lbs with a 4.38 pulley downsizing from the original 4.50 pulley which just barely made 8 lbs of boost.
When you blew the elbo off, did you examine the silicone for hairline crack? Any chance you have an extra to replace it? Seems odd the loss of boost is coincidental with the silicone connector blow off.
Out of curiosity, what is your belt length?
With a 7.65 crank pulley, 3.9 blower pulley and Aster Bracket center pulley on middle hole, my belt length is K080525HD (that's the green belt - not the RPM belt).
Any reason why you use a BOV instead of the bypass valve. I have the ATI big red bypass now since I have upped my boost (Over 12 lbs of boost, Bob suggested the Big Red).
It's my understanding a bypass valve is better suited for the D1 SC unless the BOV has a very light spring. Not as hard on the blower.
************************************************** *************
Bypass Valves vs Blow Off Valves
Blowers are always producing some amount of boost as they are belt driven, where a turbo spools up as the exhaust velocity is increased. Bypass valves are used with blowers since they always relieve the boost until near zero vacuum (heavy throttle) is achieved. Blow-off valves are designed to relieve boost at a set amount of boost, and can cause boost stacking when used with a blower. Light springs can be used with blow-off valves so that they can be used with blowers, and many have reported success with doing so. Unless a blow off valve is properly set up with a light spring though, the boost that is built up places a load on the blower that is hard on it, plus it will try to slow the blower down which can cause belt slippage. Stacked up boost will also try to find weak spot in the tubing and hoses to blow out of. This is why Bypass Valves are better than Blow Off Valves.
************************************************** *******************
But boost depends a lot of the engine efficiency. I rarely got to 10 lbs with a 4.38 pulley downsizing from the original 4.50 pulley which just barely made 8 lbs of boost.
When you blew the elbo off, did you examine the silicone for hairline crack? Any chance you have an extra to replace it? Seems odd the loss of boost is coincidental with the silicone connector blow off.
Out of curiosity, what is your belt length?
With a 7.65 crank pulley, 3.9 blower pulley and Aster Bracket center pulley on middle hole, my belt length is K080525HD (that's the green belt - not the RPM belt).
Any reason why you use a BOV instead of the bypass valve. I have the ATI big red bypass now since I have upped my boost (Over 12 lbs of boost, Bob suggested the Big Red).
It's my understanding a bypass valve is better suited for the D1 SC unless the BOV has a very light spring. Not as hard on the blower.
************************************************** *************
Bypass Valves vs Blow Off Valves
Blowers are always producing some amount of boost as they are belt driven, where a turbo spools up as the exhaust velocity is increased. Bypass valves are used with blowers since they always relieve the boost until near zero vacuum (heavy throttle) is achieved. Blow-off valves are designed to relieve boost at a set amount of boost, and can cause boost stacking when used with a blower. Light springs can be used with blow-off valves so that they can be used with blowers, and many have reported success with doing so. Unless a blow off valve is properly set up with a light spring though, the boost that is built up places a load on the blower that is hard on it, plus it will try to slow the blower down which can cause belt slippage. Stacked up boost will also try to find weak spot in the tubing and hoses to blow out of. This is why Bypass Valves are better than Blow Off Valves.
************************************************** *******************
Trending Topics
11-18-2018, 02:27 PM
#8
I guess belt slip as well. The power steering pump sits above the blower on an fbody so any leak will coat the belt and pulleys. The fact that you replaced the belt and had 15 psi 1 pull and then blew a coupler may also indicate slip since the belt wither stretched or was recoated from residue on either the crank pulley or blower pulley.
11-18-2018, 04:13 PM
#9
I am sure you know about Bob's chart and belt lengths.
https://ls1tech.com/forums/forced-in...t-lengths.html
The tensioner plays a big role for belt slippage. If it is bumping up against the bump stop, it's not effective. You can't imagine how that thing jumps around when going to full throttle especially when the blower is approaching max boost. So it needs some clearance to move around.
A large screwdriver will tell you if the spring is broken inside. Just leverage it back and forth to make sure it isn't binding. Sxxx happens
Your belt has a one year warranty - never hurts to ask if they will warranty it. The man at the counter is sometimes your best friend.
11-18-2018, 06:59 PM
#10
Teching In
Thread Starter
iTrader: (1)
Join Date: Jul 2004
Posts: 25
Likes: 0
Received 0 Likes
on
0 Posts
I guess belt slip as well. The power steering pump sits above the blower on an fbody so any leak will coat the belt and pulleys. The fact that you replaced the belt and had 15 psi 1 pull and then blew a coupler may also indicate slip since the belt wither stretched or was recoated from residue on either the crank pulley or blower pulley.
11-24-2018, 11:43 AM
#13
Suppose it's possible you have developed an intercooler leak.
A shop here who have done tons of FI cars told me best way to check if my OCX intercooler was leaking was to remove it, fill it with water and let it sit for a couple of days. If it leaks, he said that the water will find its way out. Even though it didn't leak I replaced it. Whether what I have now is better??????
The water method is the way he tests when making modifications to the tanks such as standoffs etc for mounting brackets on the side as opposed to top and bottom.
No need to cap the ends and pressure test with air although you can test that way. It it holds air it's good.
What type of intercooler - bar and plate or tube and fin? The tube and fin type are more easily punctured from road debris because the tubes are exposed compared to the bar and plate type.
OR:
Have you checked the vacuum line to the bypass valve and the line to the gauge. Over time the ends can dry rot.
It's possible that the valve isn't closing on boost or positive pressure is leaking to the gauge so not measuring the actual positive pressure. You say it jumps to 15 and then bleeds off down to 5 psi.
My line to the gauge is nylon and secured to the gauge with a compression fitting. No zip ties.
For example: My ATI Proflow low boost bypass valve was controlled with a push on vacuum hose. I replaced with a Big Red ATI bypass valve and it contain a nylon vacuum line that is attached to the valve with an NPT compression fitting.
Why the difference on the line material and type of connection? The nylon line and NPT fitting is less likely to blow off from positive pressure over 15 lbs of boost compared to the rubber line that is perhaps secured with a zip tie or not. So ATI provides a nylon line instead of synthetic rubber.
The same applies to synthetic rubber vacuum lines that might be starting to dry rot and could burst at 15 lbs + of positive pressure.
A shop here who have done tons of FI cars told me best way to check if my OCX intercooler was leaking was to remove it, fill it with water and let it sit for a couple of days. If it leaks, he said that the water will find its way out. Even though it didn't leak I replaced it. Whether what I have now is better??????
The water method is the way he tests when making modifications to the tanks such as standoffs etc for mounting brackets on the side as opposed to top and bottom.
No need to cap the ends and pressure test with air although you can test that way. It it holds air it's good.
What type of intercooler - bar and plate or tube and fin? The tube and fin type are more easily punctured from road debris because the tubes are exposed compared to the bar and plate type.
OR:
Have you checked the vacuum line to the bypass valve and the line to the gauge. Over time the ends can dry rot.
It's possible that the valve isn't closing on boost or positive pressure is leaking to the gauge so not measuring the actual positive pressure. You say it jumps to 15 and then bleeds off down to 5 psi.
My line to the gauge is nylon and secured to the gauge with a compression fitting. No zip ties.
For example: My ATI Proflow low boost bypass valve was controlled with a push on vacuum hose. I replaced with a Big Red ATI bypass valve and it contain a nylon vacuum line that is attached to the valve with an NPT compression fitting.
Why the difference on the line material and type of connection? The nylon line and NPT fitting is less likely to blow off from positive pressure over 15 lbs of boost compared to the rubber line that is perhaps secured with a zip tie or not. So ATI provides a nylon line instead of synthetic rubber.
The same applies to synthetic rubber vacuum lines that might be starting to dry rot and could burst at 15 lbs + of positive pressure.
11-24-2018, 12:43 PM
#14
Teching In
Thread Starter
iTrader: (1)
Join Date: Jul 2004
Posts: 25
Likes: 0
Received 0 Likes
on
0 Posts
Suppose it's possible you have developed an intercooler leak.
A shop here who have done tons of FI cars told me best way to check if my OCX intercooler was leaking was to remove it, fill it with water and let it sit for a couple of days. If it leaks, he said that the water will find its way out. Even though it didn't leak I replaced it. Whether what I have now is better??????
The water method is the way he tests when making modifications to the tanks such as standoffs etc for mounting brackets on the side as opposed to top and bottom.
No need to cap the ends and pressure test with air although you can test that way. It it holds air it's good.
What type of intercooler - bar and plate or tube and fin? The tube and fin type are more easily punctured from road debris because the tubes are exposed compared to the bar and plate type.
OR:
Have you checked the vacuum line to the bypass valve and the line to the gauge. Over time the ends can dry rot.
It's possible that the valve isn't closing on boost or positive pressure is leaking to the gauge so not measuring the actual positive pressure. You say it jumps to 15 and then bleeds off down to 5 psi.
My line to the gauge is nylon and secured to the gauge with a compression fitting. No zip ties.
For example: My ATI Proflow low boost bypass valve was controlled with a push on vacuum hose. I replaced with a Big Red ATI bypass valve and it contain a nylon vacuum line that is attached to the valve with an NPT compression fitting.
Why the difference on the line material and type of connection? The nylon line and NPT fitting is less likely to blow off from positive pressure over 15 lbs of boost compared to the rubber line that is perhaps secured with a zip tie or not. So ATI provides a nylon line instead of synthetic rubber.
The same applies to synthetic rubber vacuum lines that might be starting to dry rot and could burst at 15 lbs + of positive pressure.
A shop here who have done tons of FI cars told me best way to check if my OCX intercooler was leaking was to remove it, fill it with water and let it sit for a couple of days. If it leaks, he said that the water will find its way out. Even though it didn't leak I replaced it. Whether what I have now is better??????
The water method is the way he tests when making modifications to the tanks such as standoffs etc for mounting brackets on the side as opposed to top and bottom.
No need to cap the ends and pressure test with air although you can test that way. It it holds air it's good.
What type of intercooler - bar and plate or tube and fin? The tube and fin type are more easily punctured from road debris because the tubes are exposed compared to the bar and plate type.
OR:
Have you checked the vacuum line to the bypass valve and the line to the gauge. Over time the ends can dry rot.
It's possible that the valve isn't closing on boost or positive pressure is leaking to the gauge so not measuring the actual positive pressure. You say it jumps to 15 and then bleeds off down to 5 psi.
My line to the gauge is nylon and secured to the gauge with a compression fitting. No zip ties.
For example: My ATI Proflow low boost bypass valve was controlled with a push on vacuum hose. I replaced with a Big Red ATI bypass valve and it contain a nylon vacuum line that is attached to the valve with an NPT compression fitting.
Why the difference on the line material and type of connection? The nylon line and NPT fitting is less likely to blow off from positive pressure over 15 lbs of boost compared to the rubber line that is perhaps secured with a zip tie or not. So ATI provides a nylon line instead of synthetic rubber.
The same applies to synthetic rubber vacuum lines that might be starting to dry rot and could burst at 15 lbs + of positive pressure.
12-01-2018, 06:22 AM
#15
Have you actually checked the intercoooler for a restriction, flow test ?
Many people have complained of lower boost conditions as a result of a less flowing intercooler compared to another.
Possibly In your case something ( I wouldn’t know what or how) could have lodged in it & is causing a restriction. When I hear “ hit 15lbs then blew off the elbo” I’m thinking the intercooler has a blockage & elbo couldn’t hold. When you tightened it up the restriction allowed only 5lbs. Are you hearing any compressor surge at the same time ? Unusally high IATs ?
Just a thought.
Many people have complained of lower boost conditions as a result of a less flowing intercooler compared to another.
Possibly In your case something ( I wouldn’t know what or how) could have lodged in it & is causing a restriction. When I hear “ hit 15lbs then blew off the elbo” I’m thinking the intercooler has a blockage & elbo couldn’t hold. When you tightened it up the restriction allowed only 5lbs. Are you hearing any compressor surge at the same time ? Unusally high IATs ?
Just a thought.
12-01-2018, 10:51 AM
#19
I'm going to go out on a limb and no doubt will get a lot of pushback, but I don't think your initial readings was ever 15 psi.
The reason I say that is because if we go back to a stock engine, which isn't nearly as efficient as those that are mildly modified, with a D1 and a 4.5 pulley boost was usually in the 6-8 lbs range, maybe 9-10 at most.
If that weren't the norm, I don't think ATI would have been pushing DI's out the door, knowing that they might be going on stock engines, and would easily make 15 lbs of boost. Of course, there are those that will argue that you can run 15 lbs of boost on a stock LS1 and never have any issues. Whether ATI wants to take that risk, that's for another discussion.
Bob at EPP experimented with 15 lbs of boost on a stock and the engine eventually failed. I don't recall, however, what pulley he used to get to 15 psi. You might ask him. Maybe it was a 4.25.
Another thing not mentioned is the size of your air filter. Can't imagine you still have the tiny original filter that comes with the D1 kit. It's for sure more restrictive by 1 or 2 lbs compared to larger filters.
Have you tried removing the filter?
Do you have catch cans? Full or empty?
The reason I say that is because if we go back to a stock engine, which isn't nearly as efficient as those that are mildly modified, with a D1 and a 4.5 pulley boost was usually in the 6-8 lbs range, maybe 9-10 at most.
If that weren't the norm, I don't think ATI would have been pushing DI's out the door, knowing that they might be going on stock engines, and would easily make 15 lbs of boost. Of course, there are those that will argue that you can run 15 lbs of boost on a stock LS1 and never have any issues. Whether ATI wants to take that risk, that's for another discussion.
Bob at EPP experimented with 15 lbs of boost on a stock and the engine eventually failed. I don't recall, however, what pulley he used to get to 15 psi. You might ask him. Maybe it was a 4.25.
Another thing not mentioned is the size of your air filter. Can't imagine you still have the tiny original filter that comes with the D1 kit. It's for sure more restrictive by 1 or 2 lbs compared to larger filters.
Have you tried removing the filter?
Do you have catch cans? Full or empty?
12-01-2018, 12:05 PM
#20
9 Second Club
So you've pressure tested the system properly...
From supercharger inlet, right through to either the throttle itself, or better still remove rockers and test against the closed intake valves ?
Or have you done some other sort of test ?
And history...this exact setup used to run 15psi reliably ?
You mention a tensioner....exactly what are you using for a tensioner, details or pictures of belt system ?
From supercharger inlet, right through to either the throttle itself, or better still remove rockers and test against the closed intake valves ?
Or have you done some other sort of test ?
And history...this exact setup used to run 15psi reliably ?
You mention a tensioner....exactly what are you using for a tensioner, details or pictures of belt system ?