Too much lag and only 5psi of boost! Please help!!!
12-09-2009, 03:12 PM
#1
Too much lag and only 5psi of boost! Please help!!! Here is the deal, I have a 02 F-body with a 408 iron block, Ported LS3 heads, LS3 intake, 230/240 .600/.600 114 cam, 3.70 rear gear ratio, 3600 stall, 4L60E,front mount intercooler, rear mounted GT-88 turbo, stock exhaust manifolds, 2.5" SLP Y pipe, 3" mandrel bent exhaust from the Y pipe to the turbine inlet, heat wrapped from the manifolds to the turbine inlet, no cats, 50mm Turbonetics race gate with 10psi spring in it, wastage sensing line is plumbed all the way to the manifold, the exhaust out of the turbo is a 5" large radius 90, once the 90 is pointing to the rear of the car it goes into two 3" exhaust pipes, one going straight out the drivers side of the car and the other going over and out the passenger side of the car, and the fuel system is set up to handle 1100hp. This is a DIY setup.
The turbo lag is bad. From a dead stop the car will not build any boost until right when it goes into 2nd gear. Once it is on boost it builds quick to 5.5psi and stops. I have pressure tested my cold air side and I have no leaks. I have pressure tested my exhaust side and have no leaks. I had it on the dyno Monday and while it was under boost we looked all over it to see if we had any leaks but found none. We checked to see if the WG was dumping (it dumps out into the open) and it was not dumping. We removed the sensing line to double check this and that did not help make any more boost. The K&N air filter is very loud.
The turbo is a T-6 GT-88 with a turbine section AR of 1.06. I realize if the turbine housing is too large it can cause allot of lag, but if it is too large can that also cause it not to build boost past X psi as described above?
We have been tuning it and nothing in the tune seams to help.
Could the air filter be causing this?
What else could be causing this? I am at my wits end with this. I am starting to think the 1.06 AR turbine housing is too large.
Thanks for the help.
The turbo lag is bad. From a dead stop the car will not build any boost until right when it goes into 2nd gear. Once it is on boost it builds quick to 5.5psi and stops. I have pressure tested my cold air side and I have no leaks. I have pressure tested my exhaust side and have no leaks. I had it on the dyno Monday and while it was under boost we looked all over it to see if we had any leaks but found none. We checked to see if the WG was dumping (it dumps out into the open) and it was not dumping. We removed the sensing line to double check this and that did not help make any more boost. The K&N air filter is very loud.
The turbo is a T-6 GT-88 with a turbine section AR of 1.06. I realize if the turbine housing is too large it can cause allot of lag, but if it is too large can that also cause it not to build boost past X psi as described above?
We have been tuning it and nothing in the tune seams to help.
Could the air filter be causing this?
What else could be causing this? I am at my wits end with this. I am starting to think the 1.06 AR turbine housing is too large.
Thanks for the help.
12-09-2009, 03:29 PM
#2
Are you saying you can pull the line to the gate and not see 10psi? what about in higher gears. are you hitting 10psi higher up in rpm and in third..? If you do pull the line off the gate make sure to watch you don't hit like 20psi but of course you can control boost with your right foot.
Obviously big turbo is going to have lag. If you have no boost leaks and don't like the lag then possibly still some help from tuning..if its pig rich then you could get a lot more lag..11.5 to 11.8 is good place to start for afr. Way too low timing likley would also not help..if still too much lag then consider small shot of nitrous like 50 or 75 shot to spool things up quicker. Boost leaks can be sneaky..blow off, piping. A good smoke machine can sometimes find them when other methods fail or you can make a boost leak tester from home depot parts. most dsm boards show you how.
Off the line a two step can help and high enough stall.
I have 408 and build boost quick but have two smaller turbos ,have two step and have py3400 yank. No complaints with my combo. Compression is 9.5 to 1. run around 11.5 to 11.8 range for afr. Run around 16 degrees max timing on pump 92 or 94 e10.
Course am also frontmount setup.
Lag might be blessing if it helps with traction. I have massive traction problems even at low boost on current setup. Am trying a few things to help out in that department next year. Ramping boost by rpm, time or gear, variable add on traction control to name two ideas.
Obviously big turbo is going to have lag. If you have no boost leaks and don't like the lag then possibly still some help from tuning..if its pig rich then you could get a lot more lag..11.5 to 11.8 is good place to start for afr. Way too low timing likley would also not help..if still too much lag then consider small shot of nitrous like 50 or 75 shot to spool things up quicker. Boost leaks can be sneaky..blow off, piping. A good smoke machine can sometimes find them when other methods fail or you can make a boost leak tester from home depot parts. most dsm boards show you how.
Off the line a two step can help and high enough stall.
I have 408 and build boost quick but have two smaller turbos ,have two step and have py3400 yank. No complaints with my combo. Compression is 9.5 to 1. run around 11.5 to 11.8 range for afr. Run around 16 degrees max timing on pump 92 or 94 e10.
Course am also frontmount setup.
Lag might be blessing if it helps with traction. I have massive traction problems even at low boost on current setup. Am trying a few things to help out in that department next year. Ramping boost by rpm, time or gear, variable add on traction control to name two ideas.
12-09-2009, 06:32 PM
#3
It might be your wastgate. I know I had the same problem in my 89 tta. Same motor as the Buick GN. Replaced the wastegate and that fixed the problem. Have you ran any race fuel?
12-09-2009, 07:49 PM
#4
Are you saying you can pull the line to the gate and not see 10psi? what about in higher gears. are you hitting 10psi higher up in rpm and in third..? If you do pull the line off the gate make sure to watch you don't hit like 20psi but of course you can control boost with your right foot.
Obviously big turbo is going to have lag. If you have no boost leaks and don't like the lag then possibly still some help from tuning..if its pig rich then you could get a lot more lag..11.5 to 11.8 is good place to start for afr. Way too low timing likley would also not help..if still too much lag then consider small shot of nitrous like 50 or 75 shot to spool things up quicker. Boost leaks can be sneaky..blow off, piping. A good smoke machine can sometimes find them when other methods fail or you can make a boost leak tester from home depot parts. most dsm boards show you how.
Off the line a two step can help and high enough stall.
I have 408 and build boost quick but have two smaller turbos ,have two step and have py3400 yank. No complaints with my combo. Compression is 9.5 to 1. run around 11.5 to 11.8 range for afr. Run around 16 degrees max timing on pump 92 or 94 e10.
Course am also frontmount setup.
Lag might be blessing if it helps with traction. I have massive traction problems even at low boost on current setup. Am trying a few things to help out in that department next year. Ramping boost by rpm, time or gear, variable add on traction control to name two ideas.
Obviously big turbo is going to have lag. If you have no boost leaks and don't like the lag then possibly still some help from tuning..if its pig rich then you could get a lot more lag..11.5 to 11.8 is good place to start for afr. Way too low timing likley would also not help..if still too much lag then consider small shot of nitrous like 50 or 75 shot to spool things up quicker. Boost leaks can be sneaky..blow off, piping. A good smoke machine can sometimes find them when other methods fail or you can make a boost leak tester from home depot parts. most dsm boards show you how.
Off the line a two step can help and high enough stall.
I have 408 and build boost quick but have two smaller turbos ,have two step and have py3400 yank. No complaints with my combo. Compression is 9.5 to 1. run around 11.5 to 11.8 range for afr. Run around 16 degrees max timing on pump 92 or 94 e10.
Course am also frontmount setup.
Lag might be blessing if it helps with traction. I have massive traction problems even at low boost on current setup. Am trying a few things to help out in that department next year. Ramping boost by rpm, time or gear, variable add on traction control to name two ideas.
12-09-2009, 08:06 PM
#6
I think your problem is your exhaust size and t-6 flange. YOur trying to build alot of pressure in a big area trying to push a big turbo. A pt88 t-4 would have been a better choice. I don't have a good way of explaining how it works but your gonna have trouble pushing the gt-88 in the rear. Good luck and hopfully someone with more knowledge can step in.
12-09-2009, 08:38 PM
#7
I had a PT78, but was told it was too small do to the turbine housing being a t-4. I went to the t-6 as drasticly suggested. This is due to the 408 ci up front. I am not doughting you, but there is no way I am going to buy a different turbo unit this one fails and I have run out of attempts to get the boost up. I am thinking I need a smaller AR housing. Say go from a 1.06 to a .9x.
Forgive me if i sound sh!tty, there is a long story behind the selection of the turbo that i do not want to get into because I bought both times what a sponsor here told me to buy. So any sh!ttyness on my part is not toward you.
Forgive me if i sound sh!tty, there is a long story behind the selection of the turbo that i do not want to get into because I bought both times what a sponsor here told me to buy. So any sh!ttyness on my part is not toward you.
Trending Topics
12-09-2009, 08:47 PM
#8
TECH Addict
iTrader: (8)
Join Date: Oct 2008
Location: toronto ontario canada
Posts: 2,047
Likes: 0
Received 2 Likes
on
2 Posts
usually rear mounts require a smaller a/r on the turbo then you would normally install on a front mount. and the t6 flange is a little overkill for a rearmount. i would of went with a t4. that would of created a little more back pressure and help the turbo spool.
the sponsor that sold you the turbo, did he know this is for a ream mount project ?
what diameter are the pipes going out of the turbo to the intercooler?
the sponsor that sold you the turbo, did he know this is for a ream mount project ?
what diameter are the pipes going out of the turbo to the intercooler?
12-09-2009, 09:01 PM
#9
Yes they did in both instances. Enough about that. I am not here to bash a sponsor.
The piping running from the turbo to the intercooler is 2.5". From the intercooler to the TB is 3". I was told by them this would work fine. I wanted to run 3" but that is not possible with the room under the car, at least for me to do with the limited exhaust pipe tooling I have.
The piping running from the turbo to the intercooler is 2.5". From the intercooler to the TB is 3". I was told by them this would work fine. I wanted to run 3" but that is not possible with the room under the car, at least for me to do with the limited exhaust pipe tooling I have.
12-09-2009, 09:06 PM
#10
I has been known that in some wastegates race fuel will screw them up an not work like they are suppose too. That it what I was told back then and that is why I bought another one. But before I bought me another one I had a friend to let me take his off and put it in place of mine. So it worked fine, then I got me another one. If you can find someone to let you try that then you can rule that out.
12-09-2009, 09:24 PM
#12
TECH Resident
iTrader: (1)
Join Date: Jan 2002
Location: ATX©
Posts: 798
Likes: 0
Received 0 Likes
on
0 Posts
Just re-read. You have a problem. No doubt about it. If you have a 10psi spring and it's making 5.5psi, there is an issue.
Look over this...
http://www.turbosmartonline.com/inde...ownload&id=231
Especially the vacuum reference.
-W
Look over this...
http://www.turbosmartonline.com/inde...ownload&id=231
Especially the vacuum reference.
-W
12-09-2009, 09:36 PM
#13
The exhaust housing is a 1.08 AR. I have looked at all of those things. My sensing line is SS braded all the way to the front. I have even gone as far as to disconect it to make sure the waste gate does not open. I have even brought home from work a calibrated test pump/gauge for testing regulated valves like the Racegate and Raceport to test the cracking and full open pressure. It is all good (and all new). Maybe I just have not gone far enough up in the rpm band to get full boost yet.
The lag I am not worried about, I can work around that with a transbrake or a tangent housing with a boost activated gate. Plus I can use the lag on the street.
The lag I am not worried about, I can work around that with a transbrake or a tangent housing with a boost activated gate. Plus I can use the lag on the street.
12-09-2009, 09:59 PM
#14
10 Second Club
iTrader: (27)
Join Date: Sep 2008
Location: Lake Tapps, WA
Posts: 2,229
Likes: 0
Received 0 Likes
on
0 Posts
3.70 and a stall are going to make it hard to build boost, they don't put much load on the motor, lots of rpm but no much load. A good test is to get the car into 4th and roll into the throttle, if you have a long grade to climb that's even better.
12-09-2009, 11:08 PM
#15
This is true. I am building a 4L80 for it and I do plan on going to less stall, probly 3000. I am not to worried about the lag, I can work around that with a transbrake in the 4L80 and some lag will help me on the street. It is the 5 psi of boost that I am trying to correct.
12-10-2009, 11:09 AM
#18
On The Tree
Join Date: Dec 2004
Posts: 187
Likes: 0
Received 0 Likes
on
0 Posts
https://ls1tech.com/forums/forced-in...ke-graphs.html
Change the turbine housing to a twin scroll and get a quick spool valve.
12-10-2009, 11:47 AM
#19
I don't think brake makes as much difference as a two step for building boost on the line. And thought with too low a stall you won't build boost as even with t brake or footbrake it can't go up higher than stall allows. eg you can't get to 6000rpm like manual car can on a 3000 stall.
So thought stall had to be closer to turbo spool up rpm..so if you turbo spools at 5000 you would need like a 5000 stall?? Again new to turbos and autos just swapped my car over and put it away for winter without being really able to test it out yet.
Manual cars can use antilag to help build good boost on the line but autos don't benefit as much from it .I can build great boost in my 91 race talon with stock small turbo and stock stall just on two step no t brakes made for those cars. Can leave line at like 15psi.
Two step is the key.
Also as said bigger turbos can benefit from small shots of spray 50 ,75 even 100 shot to really get them spooling up quick. LIke you said slower spool and more lag can be good on street in helping out traction problems although too much lag bugs me . I also hate gearing in the under 3.42 range for street use. I have 3.54 in mine they seem to load up my turbos just fine. As does the 3400 stall also seems to work well.
You should be fine to go wot on street in higher gears with tune even reasonably close if you have high octane and are only talking 10psi or so. Keep timing down a bit if you are concerned, keep afr to 11.0 and timing to 12 max or maybe 14. You mostly just want to see if its hitting max boost at higher rpm and /or gear. Yeah it may not be possibly to build full boost in lower gears .
So thought stall had to be closer to turbo spool up rpm..so if you turbo spools at 5000 you would need like a 5000 stall?? Again new to turbos and autos just swapped my car over and put it away for winter without being really able to test it out yet.
Manual cars can use antilag to help build good boost on the line but autos don't benefit as much from it .I can build great boost in my 91 race talon with stock small turbo and stock stall just on two step no t brakes made for those cars. Can leave line at like 15psi.
Two step is the key.
Also as said bigger turbos can benefit from small shots of spray 50 ,75 even 100 shot to really get them spooling up quick. LIke you said slower spool and more lag can be good on street in helping out traction problems although too much lag bugs me . I also hate gearing in the under 3.42 range for street use. I have 3.54 in mine they seem to load up my turbos just fine. As does the 3400 stall also seems to work well.
You should be fine to go wot on street in higher gears with tune even reasonably close if you have high octane and are only talking 10psi or so. Keep timing down a bit if you are concerned, keep afr to 11.0 and timing to 12 max or maybe 14. You mostly just want to see if its hitting max boost at higher rpm and /or gear. Yeah it may not be possibly to build full boost in lower gears .
12-10-2009, 06:46 PM
#20
Even though I dont have an LS motor I have a custom rearmount. I can tell you that your turbine housing is gorilla huge for where the turbo is located. Try to get a turbo blanket to help spool a little quicker maybe a few hundred RPMS. You should also talk to Zombie about his setup.
https://ls1tech.com/forums/forced-in...ke-graphs.html
Change the turbine housing to a twin scroll and get a quick spool valve.
https://ls1tech.com/forums/forced-in...ke-graphs.html
Change the turbine housing to a twin scroll and get a quick spool valve.