S475 still having back pressure issues??
TECH Fanatic
Joined: Feb 2015
Posts: 1,080
Likes: 178
Current BP measurement location may not be ideal but should be sufficient unless you have some restriction between measurement port and turbo. If O2 port available on R side you could capture a comparative measurement.
Any pressure measurements pre and post IC?
Any pressure measurements pre and post IC?
I have nothing measured pre and post intercooler. Thus, i was thinking of bypassing the intercooler and donig a pull on the spring and see what the back pressure is. Thus telling me if the intercooler is a restriction.
The only restriction between one bank and the other would be where they merge. I plan on getting a measurement on the other bank before they merge. If it reads fine, then the problem is the merge of the two banks on the hotside. If the other bank reads ok, i may check the reading in a different spot on the bank the sensor is in now. Its odd because i have melted down two pistons - both in the same bank this sensor is in and never one on the other bank. This is whats leading me to think that this one bank is having pressure issues while the other is ok.
The only restriction between one bank and the other would be where they merge. I plan on getting a measurement on the other bank before they merge. If it reads fine, then the problem is the merge of the two banks on the hotside. If the other bank reads ok, i may check the reading in a different spot on the bank the sensor is in now. Its odd because i have melted down two pistons - both in the same bank this sensor is in and never one on the other bank. This is whats leading me to think that this one bank is having pressure issues while the other is ok.
Hey are u running flexjoints? What brand? I just put my new setup together and with 1 wot pass and a few idles i had a flex come apart and restrict flow big time. It was the one without the interlock liner inside. Just woving material. Glad it didnt make it to turbo.
I.ordered some new ones from mandrel bends for turbo app.
I.ordered some new ones from mandrel bends for turbo app.
Ultimately though, both exhaust banks meet at the turbine right? So really pressure should equalize throughout the entire system (hot side), so measuring at whatever point should be close enough to get an idea. I just wonder what effect wastegates could have in all of this.
This is a very comparable sized turbo (within 1mm on the exhaust wheel I think) and this shows the boost vs back pressure
http://onthedyno.com/GM-LS-motor/art...re-ls3-hybrid/
That website has a lot of interesting stuff, thanks to Stevieturbo for bringing it up.
http://onthedyno.com/GM-LS-motor/art...re-ls3-hybrid/
That website has a lot of interesting stuff, thanks to Stevieturbo for bringing it up.
Ultimately though, both exhaust banks meet at the turbine right? So really pressure should equalize throughout the entire system (hot side), so measuring at whatever point should be close enough to get an idea. I just wonder what effect wastegates could have in all of this.
Both banks may meet up, but if there is a restriction where the one bank meets the other, its possible for one bank to have more back pressure then the other. .. in my opinion
How sure are you that the transducer you are using is setup properly? Have you shop tested the sensor your using with a known calibrated gauge? Mine was way off on my MegaSquirt. MS expects a 0-5v sensor and I believe mine was a .5- 4.5v or something odd. Was an autometer 0-100psi transducer. I'd verify the transducer first.
Your "83mm" S475 has a 74/83 exh wheel. 74mm is the exducer diameter and how most turbo companies size the exh wheels. So you're running a 75/74. Not a 75/83. BW stuff is confusing that way.
74mm is still a pretty small wheel for a 6.0. With that same turbo I'd see 2.8:1 or so... at 24ish lbs on a 5.3. Your numbers are crazy high assuming your transducer reading are correct. Sounds like you've got a huge restriction somewhere. I'd take off the hot side and inspect it well. You also only need 1 sensor pre-IC as your map sensor is fine for post IC readings.
Last edited by Forcefed86; Jun 3, 2015 at 01:21 PM.
I take my pressure readings at the same spot basically. That's not the issue unless you have some huge restriction between the banks as you mentioned.
How sure are you that the transducer you are using is setup properly? Have you shop tested the sensor your using with a known calibrated gauge? Mine was way off on my MegaSquirt. MS expects a 0-5v sensor and I believe mine was a .5- 4.5v or something odd. Was an autometer 0-100psi transducer. I'd verify the transducer first.
Your "83mm" S475 has a 74/83 exh wheel. 74mm is the exducer diameter and how most turbo companies size the exh wheels. So you're running a 75/74. Not a 75/83. BW stuff is confusing that way.
74mm is still a pretty small wheel for a 6.0. With that same turbo I'd see 2.8:1 or so... at 24ish lbs on a 5.3. Your numbers are crazy high assuming your transducer reading are correct. Sounds like you've got a huge restriction somewhere. I'd take off the hot side and inspect it well. You also only need 1 sensor pre-IC as your map sensor is fine for post IC readings.
How sure are you that the transducer you are using is setup properly? Have you shop tested the sensor your using with a known calibrated gauge? Mine was way off on my MegaSquirt. MS expects a 0-5v sensor and I believe mine was a .5- 4.5v or something odd. Was an autometer 0-100psi transducer. I'd verify the transducer first.
Your "83mm" S475 has a 74/83 exh wheel. 74mm is the exducer diameter and how most turbo companies size the exh wheels. So you're running a 75/74. Not a 75/83. BW stuff is confusing that way.
74mm is still a pretty small wheel for a 6.0. With that same turbo I'd see 2.8:1 or so... at 24ish lbs on a 5.3. Your numbers are crazy high assuming your transducer reading are correct. Sounds like you've got a huge restriction somewhere. I'd take off the hot side and inspect it well. You also only need 1 sensor pre-IC as your map sensor is fine for post IC readings.
As far as sensor goes, yes mine is actually a .5 - 4.5v sensor. I have it reading 0 with key on and then to verify, i have ti 100psi with a compressor and its reading that correctly..
I do relaizse that the turbo is still small. However i see that it should be ok to run up to the 15psi max that i am shooting for. In my opinion - since i saw no change in swapping from the comp turbo to this one, that the restriction is somewhere other then the turbo at this point and at this low of boost.
Is it possible that i am getting my readings at to low of a boost setting? Should i test it at 8psi or even 10 psi? I jsut dont want to get crazy on turning this thing up because thats what caused my last motor to pop.
just bypassing the radiator should let me know if its a restriction. Thus i wouldnt have to weld in a bung in the aluminum piping and get a sensor up there.
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo If it’s a .5- 4.5 sensor what 2 values are you using on the MS. I can give you mine to try. I don’t remember off hand.
You can’t just measure the peak values. Mine read correctly this way as well, and was WAY off in between. Stick a push to reset tire pressure gauge on there to verify it quickly. I used a new paint gun regulator (prob still not the most accurate) To set mine up. If you plan to run 15lbs you want to make sure your gauge is accurate in the 15-40psi range. Screw any values higher than that, they aren’t important. A 3.5-4 bar map sensor would work much better and be much more accurate.
I agree that turbo should be fine. Stock48 ran one on his nova and his truck and they ran great. He didn’t measure back pressure, but I’m sure it was up there.
You can’t just measure the peak values. Mine read correctly this way as well, and was WAY off in between. Stick a push to reset tire pressure gauge on there to verify it quickly. I used a new paint gun regulator (prob still not the most accurate) To set mine up. If you plan to run 15lbs you want to make sure your gauge is accurate in the 15-40psi range. Screw any values higher than that, they aren’t important. A 3.5-4 bar map sensor would work much better and be much more accurate.
I agree that turbo should be fine. Stock48 ran one on his nova and his truck and they ran great. He didn’t measure back pressure, but I’m sure it was up there.
I believe the formula they gave me has me putting -12.5 in for 0 and 112.5 in for 100. I adjusted them a bit for that to get them to read 0 and 100 applying pressure.
I will do a little work on it tonight. Bypass the radiator and get that done and out of the way. After that, if its not the sensor, the only other thing to do is to check the hotside and see if its different from bank to bank and if the hotside is the restriction somewhere before the turbo
But yes, shoot me your numbers and i will see what my gauge reads.
I will do a little work on it tonight. Bypass the radiator and get that done and out of the way. After that, if its not the sensor, the only other thing to do is to check the hotside and see if its different from bank to bank and if the hotside is the restriction somewhere before the turbo
But yes, shoot me your numbers and i will see what my gauge reads.
So why are you so concerned with backpressure exactly? Backpressure doesnt melt pistons, detonation and poor tuning does that.
High backpressure doesnt mean anything is wrong....high back pressure means you are giving up high-rpm flow for quick spool, there is nothing wrong with that. Setups with low back pressure ratios typically are very lazy on the street without creative anti-lag techniques.
High backpressure doesnt mean anything is wrong....high back pressure means you are giving up high-rpm flow for quick spool, there is nothing wrong with that. Setups with low back pressure ratios typically are very lazy on the street without creative anti-lag techniques.
So why are you so concerned with backpressure exactly? Backpressure doesn't melt pistons, detonation and poor tuning does that.
High backpressure doesn't mean anything is wrong....high back pressure means you are giving up high-rpm flow for quick spool, there is nothing wrong with that. Setups with low back pressure ratios typically are very lazy on the street without creative anti-lag techniques.
High backpressure doesn't mean anything is wrong....high back pressure means you are giving up high-rpm flow for quick spool, there is nothing wrong with that. Setups with low back pressure ratios typically are very lazy on the street without creative anti-lag techniques.
I have had this happen to two different motors tuned by two different tuners. I have been chasing down this issue for about a year now trying to keep motors together and in the car. The car is fine on low boost.. say 5-10 psi. The first motor went on 15 psi at the top end of a long pass. The second motor went at 13psi at the top end of a 1/4 mile pass. Both worked great until the boost was turned up slightly.
This is why i thought back pressure and installed the sensor and the aftermarket ECU to monitor it.
Back pressure can cause reversion. Basically lowering the effective valve spring pressure.
A much easier way to test the Ic and the entire cold side would be to tap a barb fitting in the outlet of the turbo or really any pipe from the turbo to the inlet of the intercooler. All you need is a simple fitting, drill and tap. Then run that to a spare boost gauge, do a run and compare that reading to your reading off your map sensor or the boost gauge as long as its reference off the intake manifold.
Alex
A much easier way to test the Ic and the entire cold side would be to tap a barb fitting in the outlet of the turbo or really any pipe from the turbo to the inlet of the intercooler. All you need is a simple fitting, drill and tap. Then run that to a spare boost gauge, do a run and compare that reading to your reading off your map sensor or the boost gauge as long as its reference off the intake manifold.
Alex
Phish,
We uncannily (sp?) have pretty much the same setup (s475/83mm/t4/1.10), 3.5" DP to a dual 2.5" exhaust on a 6.0 (LQ9 in my case) and haven't melted it down yet despite 17+psi runs. Just curious on what fuel, AFR and timing your running. Water/meth?
I'm 11.5afr, 12* timing and water meth after 14psi. 93 octane here thankfully.
We uncannily (sp?) have pretty much the same setup (s475/83mm/t4/1.10), 3.5" DP to a dual 2.5" exhaust on a 6.0 (LQ9 in my case) and haven't melted it down yet despite 17+psi runs. Just curious on what fuel, AFR and timing your running. Water/meth?
I'm 11.5afr, 12* timing and water meth after 14psi. 93 octane here thankfully.
Phish,
We uncannily (sp?) have pretty much the same setup (s475/83mm/t4/1.10), 3.5" DP to a dual 2.5" exhaust on a 6.0 (LQ9 in my case) and haven't melted it down yet despite 17+psi runs. Just curious on what fuel, AFR and timing your running. Water/meth?
I'm 11.5afr, 12* timing and water meth after 14psi. 93 octane here thankfully.
We uncannily (sp?) have pretty much the same setup (s475/83mm/t4/1.10), 3.5" DP to a dual 2.5" exhaust on a 6.0 (LQ9 in my case) and haven't melted it down yet despite 17+psi runs. Just curious on what fuel, AFR and timing your running. Water/meth?
I'm 11.5afr, 12* timing and water meth after 14psi. 93 octane here thankfully.
I am sunsure of the afr and timing of the last two tunes/tuners/motors. However, all of them including this one have been on E85 (E70). I know right now, since i am trying to wait and have my back pressure issue figured out before my final tune i am running an 11.2 afr and 16 degrees of timing i believe. I would have to check the clogs to verify timing.... this is on 5 psi i remind you. There should be no issues at all with this setup. Thats why i think something has to be out of the norm.
GRANTED, i have not tried turning up the boost with this setup. The two motors that went had the Comp 8079 strapped to them and we know they are horrendous for back pressure issues. Maybe this one will live. Do you have any way to check back pressure on your S475 setup?
So, i went out and changed up my pipng so it bypassed the intercooler. When i pulled out of the garage and headed down my street the car seemed to be a bit more peppy... which i thought was odd... long story short, did a pull and the car made 5 psi. (its been makeing 3.5 on the 5lb spring). went back and looked at the logs and backpressure was at 2:1. at 5 psi i had 9 to 11 psi back pressure. I looked back at an old log and at 5psi i had 18psi in the manifold. Thus, i am thinking that the intercooler is being a restriction in the system. I will pull it off tonight or tomorrow and see if something is blocking it, however it may jsut be the intercooler? Its one of the cheap CX racing intercoolers that most guys run but its a tough smaller then guys usually run in the camaro. Not sure if its the intercooler itself, or something on the inside of it thats messed up.
There are a few of us running that same exact turbo, except in trucks and it's enough to propel a 5400 lb truck to an 11 flat quarter mile, with more left. I've also probably got enough exhaust pipe length to wrap around an rx7. Yes, backpressure is high, however, it's not hurting anything.
I am sunsure of the afr and timing of the last two tunes/tuners/motors. However, all of them including this one have been on E85 (E70). I know right now, since i am trying to wait and have my back pressure issue figured out before my final tune i am running an 11.2 afr and 16 degrees of timing i believe. I would have to check the clogs to verify timing.... this is on 5 psi i remind you. There should be no issues at all with this setup. Thats why i think something has to be out of the norm.
GRANTED, i have not tried turning up the boost with this setup. The two motors that went had the Comp 8079 strapped to them and we know they are horrendous for back pressure issues. Maybe this one will live. Do you have any way to check back pressure on your S475 setup?
GRANTED, i have not tried turning up the boost with this setup. The two motors that went had the Comp 8079 strapped to them and we know they are horrendous for back pressure issues. Maybe this one will live. Do you have any way to check back pressure on your S475 setup?
Did you check the sensor? How are you doing this testing? While driving or on the foot/trans brake?
It's known there are big pressure drops across the cheap china cores. 2psi seems excessive at 5lbs. But even your BP numbers without the IC are still strangely high for 5lbs IMO. Nothing wrong with 2:1. Did you try 10lbs or so without the IC to see if it goes over 2:1?
Just drill and tap a manifold with the engine running. Few tiny metal burrs in the exh. aren't going to damage anything. I've done it many times.
It's known there are big pressure drops across the cheap china cores. 2psi seems excessive at 5lbs. But even your BP numbers without the IC are still strangely high for 5lbs IMO. Nothing wrong with 2:1. Did you try 10lbs or so without the IC to see if it goes over 2:1?
Next time I have the hot side off I'll weld a bung in there to check. But I would imagine BP will be high. But its real responsive and I wouldnt want spool any slower so it is what it is and its going to stay as is regardless of what the readings are. I am curious though....
Did you check the sensor? How are you doing this testing? While driving or on the foot/trans brake?
It's known there are big pressure drops across the cheap china cores. 2psi seems excessive at 5lbs. But even your BP numbers without the IC are still strangely high for 5lbs IMO. Nothing wrong with 2:1. Did you try 10lbs or so without the IC to see if it goes over 2:1?
It's known there are big pressure drops across the cheap china cores. 2psi seems excessive at 5lbs. But even your BP numbers without the IC are still strangely high for 5lbs IMO. Nothing wrong with 2:1. Did you try 10lbs or so without the IC to see if it goes over 2:1?
I have not checked the sensor since we last talked.
I am testing by acctually driving the car. Doing a seond gear "pull" from around 40mph. not staying in it to long, just enough to get it to the boost level and hold it for a couple seconds.
I jsut went out and tried it on 7ish psi. 7-8 psi shows 16-17psi backpressure.
From my reading, i am finding that a small percentace of the cxracing intercoolers have had restrictions in the cores of them. Looks as if guys swap them out for the same intercooler and the problem is solved. I guess quality control is not the best in china. That being said, whats the next step from here. Same intercooler, different type/brand intercooler...?