This is for the turbo guru's.

Current truck in sig has run 11.9s at 114.8 with a 1.80 60ft, MP70mm at roughly 10.5 psi on run. My 70mm has the .96 exhaust housing. I used to run a very loose converter and was able to cut 1.6 60fts with it leaving from about 2k rpms and no boost. I have gone to a much tighter ptc converter that seems to be about a 3200, but is so tight that usually spin the tires before I ever build boost. I realize i need about 3000 rpm or more to probably start spooling this thing on the line. I do not plan on really upping the power anymore until I add more fuel upgrades and such. The question is how bad will it hurt me to run a smaller exhuast housing at this power level on the big end. If I wont loose anything by going to a smaller exhaust housing, but gain some bottom end I think i would gain alot. If I ever go up in boost, I will switch it back. I just dont know at what power level, the .96 is needed. I know KB ran the .68, but not sure what boost level he was at. I love the way the truck runs, but would like to leave under boost without adding another converter/etc. Thanks for the responses. Im seeing a spike to 12 on shifts, and it stabilizes to around 10.5lbs. I may try to get a solid 12 out of it across the board, but I dont see going any higher then that.

 

have you tried to advance or retard your timing a little on the line to see what it does??

 

The timing is advanced right now down low to help spool it. I know I can hydroboost it, get a looser stall, etc. before 2 step, it would cut a 1.90, set 2 step at 2300, 1.83, set it at 2500, 1.80, but made no boost. set it at 3k, it would start to spin before hitting the 2 step limiter, so I know the converter is really tight. I had read for autos, to advance the timing, but i think we will be rerarding it to try it that way. I was just curious if wasting anything down low with the .96 and my power level, or is it needed at this point already. With loose 3600 converter, I was able to build 7lbs one time, but it roasted the drag radials badly. I was in the 1.6s with that converter, so I just raced it that way not building any boost on the line. Now with the tighter converter, I need to build somehting lol. The truck right now hits hard about 15-20 feet out lol.

 

hydroboost or transbrake

 

I had to change both mine out to a smaller ar and loosen the converter due to not being able to build a certain amount of boost off the t brake or the foot brake....it works great now

 

I would improve the brakes. Spending the money where it's going to help in the future is a better idea vs changing the housing which only helps the current build.

 

i personally would not change the AR that 70mm with its small turbine is already being choked up on the big end, going smaller AR will only hurt performance unless you were strickly doing 1/8 mile

 

Sounds like ur running a stock cam. Ur engine is able to make torque with that cam really early. I have a Circle D single disk that was built as a 1B (2500-2700) 10 1/4" converter. I have a small custom cam and i can brake stall it to 3500, by that time i've made 14# of boost and the tires break loose. U might want to look into a cam that's gonna benefit u on both ends of the spectrum.

 

Thanks everyone, its got a aftermarket cam in it, I will stick with what I have and upgrade the brakes. Truck is put away for awhile, putting in a 80e, new converter, bigger pump, and doing the brakes. I cut a 1.74 60ft last night off the 2 step at 2600 with no boost. I really think it needs more converter and some brakes that will hold it. Its all factory 2000 stuff. Im probably going to dual piston rear tahoe set up, and doing 05+ fronts, and if need be hydroboost. going with a 3600 circle D converter too. truck ran 7.67 at 91, and 12.01 at 113 with a 1.80 60ft. The 60e is done, hit limiter on 2nd, and wont shift to 3rd, so im happy with what it did. 10.5lbs of boost

 

You should do hydroboost before changing the brakes themselves out. Reason being, brake boosting on the line, you're vacuum is gone and you'll lose braking power. Hydroboost is cheaper too.