I finally got back to the track with my turbo vette and I seem to be having a problem. I tried turning up the boost but it didn't seem to go above 9psi. It would spike in the shifts 1-2 psi but settle back down down to the 8-9 range and taper off slightly as rpm rose. This was data logged on my DFI.

Now here's the kicker. On my way home I popped it into 3rd and got 18psi according to my boost gauge before I let off the gas. My boost gauge seems to be with in a few psi of the map data log so its fairly accurate.

So the system seems to be clogging up somehow if I run through the gears as apposed to just nailing it on the highway. What would cause that? I managed to pull an 11.8@128 and when I turned the boost up the times went up from there. Any help would be greatly appreciated.



System:
Turbonetics T-76 BB .96 A/R
Turbonetics Racegate
Joe somebody's manual boost controller.
383ci 9:1 compression
224/218 cam on a 114 seperation
mild stock ported heads
stock headers to 2.5" to turbo
3.5" downpipe
2.5" intake pipe
Intercooled

 

Nice #'s for 9psi!!

Its like your not loading it enough when banging thru the gears at the track... but then you realy load it when you drop it in 3rd on the highway... wierd. You sure you werent spinning at the track (this would cause an unloading of the turbo)?

 

I had the same problem with an 87 GN. Call turbonetics, mine had the wrong spring in the wastegate???

 

that was my original thought, but the fact that he can get higher boost on the highway makes me think that isnt the problem.


when you boost in 1st and 2nd are you holding 9psi steady or do you shift as you get to 9 psi?



have you tried to roll on in 2nd and see if you can get higher boost then you were at the track?


fist thing i would do is check all your vacuum connections to make sure they are nice and tight,
nothing worse then chasing a boost creep/spike problem only to find out it is a vacuum line

 

Kelly, exactly!! Boost creep & spiking. Very erratic. one call to turbonetics problem solved............

 

deff worth a shot.
pull the WG off and take it apart, make sure the spring is ok and make sure everything else looks good,.

 

I checked all of my vaccume connections and everything looks just fine. I think I'm going to try and call turbonetics this afternoon and see what they say.

I managed to get the car to some remote location last night and gave it a good 4th gear blast starting at 45mph. I wasn't able to datalog the run but I did watch the boost gauge as closely as I could doing 5500rpm in 4th gear.

My gauge reads a few psi higher than my map sensor. The gauge spiked up to 16, quickly dropped to 15 and then slowly dropped down to 10 as rpm increased.

Could I be as simple as I'm maxing out the cfm on my intake track? I'm running 2.5" pipe with several bends in it. The IC should flow 1000cfm before it starts dropping any real pressure.

When I'm going down the track the datalog puts me at 5000+rpm the entire time from second gear on out. I guess a good test to this theory would be to do a 1-2-4 gear run and see if the drop in rpm in 4th does something for me.


My other fear is that the back pressure is getting to be too much for the system. Causing the system to not maintain the boost levles. I'm not sure what I could do about that except get a larger diameter header and maybe a larger exhuast duration on the cam.

 

i think this is the problem.
i was running a really small turbine housing and i was choking the car out.

what size is your DP ?

the problem i was having was i couldnt get all the exhaust out of the motor, so i was getting reversion (burnt exhaust gases leftover from the cumbustion process contaminating the next combustion cycle) which would kill my power and cause power loss.

you may also want to look into 3in charge piping to help.


is this problem new, or is this a new setup that you ve just discovered the problem on?

 

I'm running a Q-trim with a .96 a/r and a 3.5" down pipe. This is a newly discovered problem. I noticed it on a dyno before the engine was in the car, but that was with a p-trim turbine and I got a new turbo and I thought it was fixed, but I guess not.

I called turbonetics and they said check for intake leaks and that it may be too small of intake piping.


When I was at the track last year, and couldn't data log, my first run of the day with 7psi netted me a 11.5 @ 127. But my other runs with a higher boost attemp got me around 12.0 @ 128. This would make sense if the turbo would have to spin faster to try and force the air through the intercooler at a higher psi. And when the boost would drop the wastegate would stay closed causing more back pressure and more hp loss. Or maybe I'm making the symptoms fit the prognosis. It could be the other way around as well.

I wish there was an easy way to test to see if it is the intake piping.