My setup...

third gen, 3150lbs, back-half, drag radials, 3.50gear
5.3 w/ 317's and studs,04 ls6 cam, hardened pushrods, pac springs
ls6 intake
th400 w/brake
93 octane and meth
gt66 t4 turbo
headers-1 3/4 primarys, 3inch colletors
crossover-2 1/2 into a small section of 3 inch at the turbo
down pipe is a 3-4 inch transition right on the turbine housing, 4 inch on out. no muffler.
cold side is 2 1/2 to the intercooler, 3 1/2 out to the tb.
intercooler is 18"x24"x4" air to air


That being said.... I have been running the car for 2 years now. After lots of tuning and data loging the car still takes too long to spool. I never dreamed this would be a problem with a 66mm turbo. After reading a ton of threads on piping size, turbo size, flow, ect.... I think I need to change a few things....Headers to manifolds because they are pretty big. Crossover down to 2" form 2 1/2" and make it as short as possible. Right now each leg is 5ft long. Maybe even shrink the cold side down to 2 1/2 from the intercooler to right before the tb, then step it up. My thinking is the way it is now there is just way to much volume to fill with hot air and low compression. This is far from a race engine. I never go over 7000rpm and thats even a rare thing. I want this thing to rip off the line. Planning on running 20-25psi if I can get it to leave. Current best, 1.41 60ft, 10.33 @ 135, 13psi-no meth. Want to go 9.50's.

Am I thinking correctly? Give me your opinion. Thanks

 

What are your afrs, and timing like before you get into boost? Do Not reduce the size of your cold side piping. Are your crossover/merge pipes wrapped or coated? The swap to manifolds is not a bad idea as they retain heat very well.

 

When are you seeing spool? What brand is the gt66? What are the specs of it? I was at full spool w/ a 70mm at about 2500rpm.

 

Why not?

 

With 2.5" into the intercooler and 3.5 inch out to the throttle body there is no reason for the reduction in the size of cold side piping. The OP has a problem spooling IMHO I would look elsewhere in the system, ie hot side/tuning.

 

+1. I think the issue is the turbo, or with the hotside(maybe exhaust leaks)

 

The low compression doesnt help, some E85 would help or a head swap.The headers are fine, not sure why you have the hotside flared at the turbo thats unnecessary. And how is each leg 5 feet long? It should be way shorter than that. Your intercooler piping should be at least 3 inches from the turbo to the intercooler. How much boost are you running? The low compression shines with high boost. And is your hotside wrapped? Wastegate springs?

 

My answer you will not like... 100 shot off the tree and shuts off at w/e desired PSI... Real talk, i have no idea how you arent spooling a 66mm with an auto no matter how fubar/gnar the piping setup. That baby girl should damn near spool revving in neutral. i used to run a 66mm in my civic, yah it didnt spool till 5000rpm, but it made power to 9200. 380whp, 10.6s pump gas, drag radial, NO BIG DEAL!

 

Thanks for the replies.....

My piping is all ceramic coated inside and out. The crossover piping is soo long because I had to go around other piping ect. ect... The afrs go from mid 13's to 12.0 at 0 vac. to 11.0 in full boost. They stay at in the the 11's pretty much the entire way down the track. The timing is set at 35 deg. on the brake. I tried lower and higher, I had no better results than 35 deg. The car acts like it makes no power on the brake. I have to start brake spooling it while rolling it in the beams to have it spooled in time. I have the 2-step set at 2500rpm. It makes about 6psi there. I shouldn't have trouble getting to 2500rpm imo. On the street you can start rolling into it and its spooling. This turbo has been around our shop for a while. Its an old innovative gt66, ceramic ball bearing, t4 p trim turbine w/ 3 inch exit. Front side is a 4 inch inlet, 2 1/2 outlet. I have a meth nozzle before and two after the turbo....havent been there yet. The turbo never gives up on the top end. IAT's are only 114deg. at the finish line. Im guessing the low compression is killing the power down low. I want to run high boost in the future, otherwise I would have left the stock heads on it. I could spray it on the line....but if I do I will most likely do it the entire way. Trying to stay away from that if I can. We had a bad explosion on another car in the past.....fire is no fun when you cant see where you are going at 7.80 @180 in a street roadster. If I don't need to mess with the cold side thats great. I really think doing the hot side with smaller piping and shorter distance will help. E85 is something I want to try when I go to high boost. I just want to be ready for it. I'm going to shoot for 9.50 with this setup. If the turbo will support that I will go for the stock 5.3 bottom end record. I think its a high 8 sec. as of now.

 

Im running a tial 44, with a 12psi spring. Exile boost controller set to 10psi on the line and 13 psi on out. I'm using BS3 to run the engine. I spared no expense on things other than the engine. We really want to push the stock rotating assembly and do it on pump gas. I'm no expert tuner at all. I know what I want under boost, maybe its my tuning out of boost. I can pm a log file if anybody wants to look at one.

 

Are you pulling timing or fuel when on the 2 step? So its only at the track on the brake that you are having trouble building boost?

 

I don't pull any timing...BS3 has a 2-step timing map...I just have it set to 35deg for all. I can roll into it going 25mph and its spooling, then it will take off like a rocket. I dont know if the converter maybe wrong..... I would think its ok since it runs like crazy other than on the transbrake.

 

How are the afrs when you are on the brake? It might be running rich which would slow spool. Lol phones are great, I type rich using swype, it somehow turns the word to day.

 

After looking at some of my log files....I see a trend. When on the brake, at the transition from vac. to boost it gets really rich. 10.0 afr for a split second then back to 13.0 and down to the 11's once boost builds. Looking at data from just street driving there is no rich spot at 0 psi. I wonder if that is because its not at 100% throttle in that area on the street. Its pretty easy to spool on the street with the car already rolling. I rarely just stomp the go pedal on the street. When I use the brake I roll into the gas pretty fast. I should be able to just stomp on the gas and be pounding the 2-step right?

 

I am not familiar with BS3, but I would see if you could lean it out a little before transitioning into boost. Just the lean afr alone will raise heat in the exhaust gasses, resulting in a quicker spool. What is the stall speed of the converter? have you tried upping the rpm a bit? I reread your post, does it slowly make its way up to your 2 step limit when on the brake?

 

The converter is supposed to be 3800 stall. Its from a builder I have never had a problem with. I doubt its a converter issue. It is slow slow slow to reach the 2-step no matter where I set it. I have gone as low as 2000 up to 4000. I can tell at 4000 its in the converter, not really rapping the 2-step just holding rpm. Once its on the 2-step it builds boost fine. It just has a hard time getting there.

 

What is your lower 2 step limit set to? is it far below the upper limit? If so try moving them closer together like lower at 2300-2400 and upper at 2500.