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Debating on bov upgrade or not

2K views 7 replies 5 participants last post by  drtalon123 
#1 ·
Hello , i’m debating on whether upgrading the blow off valve or not .
I’m experiencing what feel like surging. Between gears changes , it take about 2 long seconds before i get throttle respond which feel like forever considering my larger size of turbo falling out of momentum.
I’m currently running a gtx3582 bb replica/ anti surge cover with 2.5” piping and a hks ssqv bov. Im wondering if upgrading to a tial 50mm would help the cause. Im away from home for a moment and can’t measure porting size myself.
Here a short youtube video of a dyno run. Made 420whp and 309wtq @27 psi

 
#2 ·
Hmmmm the SSQBOV is a pull type unit I thought it was "leak proof" compared to the push type greddy style. I have one of those SSQBOVs too...before replacing it i'd check for a boost leak or significant difference in boost pressure from the compressor housing (if you have a port there) and post bov (like intake manifold). That way you could see if you were losing boost or if it's just your mind.
 
#4 ·
If you feel like surge is significant enough to prevent re-spool when back on the throttle, check the pressure drop across the intercooler as well.

Depending on where your plumbed in for pressure measurements, you might not know that you're making significantly more boost pressure on the inlet side of the cooler compared to what's present on the outlet side of the cooler. Depending on where your referencing boost pressure measurements from for your boost gauge and MAP sensor, you might be measuring 25 pounds of boost at the intake manifold, but if your intercooler is too small for your application, it could be up in the 30's on the inlet side of cooler before you lift off, then when the throttle slams shut, you spike and surge back through the turbo, especially being ball bearing turbo, you've got very low friction so the rotational inertia keeps things making pressure, and the flow is exhausted back out the turbo compressor housing instead of through the intercooler and finally the blow off valve.

Just one more place to check before dropping a bunch of money on a new bov!
 
#5 ·
Also, what are the build specifics? Unless this throttle response issue is new and just recently popped up, the way you describe throttle response being too long, could just be good old turbo lag.

What is your compression ratio? Pistons and rods? Valvetrain upgrades at all?

Also, at that power level I'm surprised you didn't go to something like a 3" exhaust all the way? Any particular reason for doing 2.5"?
 
#7 · (Edited)
Thanks for all the suggestions . I’m just trying to make an educated guess on what feel like constant granny shifting. I always low key had this issue going on of one sort , even with a smaller frame turbo but always at high boost levels. I had a talk and few revisions of the tune concerning this problem with my tuner but no improvement on this side at the time. Im really starting to believe something about the setup is holding me down. Pressure pre and post intercooler should be first checked as mentioned. I do realize this *********** special could be the root of my problem but many had success using them. Same with the ssqv bov.. didn’t see many high hp setup using those.

Here some of the specs
Z6 bottom end wiseco(9.1-1)eagle rod
Y8 cylinder head , stock ports , bisi 3.6 ,supertech spring/retainers.
If i remember correctly, it will idle around 23psi on vacuum.
Junk2 intake manifold/66mm alpha throttle body
2.5” charge piping , 3” exhaust
Turbo measured to a 86.5mm exducer billet wheel. 4”in / 2.5” out

I was looking a some data log and don’t look like there any wheel spin or lost of speed between gear change.
Shifting at 8000rpm (27psi) pick back up at 5400rpm (5psi) on a second/third gear change .I average 0.400s between closed throttle-wot.
 
#8 ·
Yeah, check the drop across the cooler. If its OK, this sounds like just lag to me honestly. Maybe try getting the full throttle shift function tuned in?

This way you wouldn't have to lift off during shifts, just clutch in and shift, power will cut or retard for split second preventing banging the rev limiter, then when you finish shifting and release the clutch, ECU reengages full power.

Will take some time to get used to shifting that way and tweaking the clutch pedal and clutch switch position, but doing this you wont have to lift throttle meaning your BOV never opens and you don't have as much of a pressure loss in the intake tract during shifts. It should reduce your boost loss between shifts.
 
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