I am running:

LQ4 w 317 heads
LS9 gaskets
LJMS Stage 1 cam

F body driver's manifold, 2" OD crossover pipe to KB Racing log manifold

On3 7875
ebay Godspeed 50mm gate
2.5" intercooler piping into 3" cxracing intercooler

Wastegate only, vacuum line from the compressor housing straight to the lower port.

Hptuners and in-car gauge both report 3-4 psi of boost.

I took the wastegate apart - it was a standard POS where the shaft was rough and the bolts were half backed out. I cleaned all that up and loc tited the bolts.

I bench tested the wastegate with a harbor freight regulator off my air compressor and it seems to take 8-10 psi to open the valve.

I hooked up the regulator to the boost reference on my turbo and pumped air through the system and I cannot hear any leaks.

I can pump 20+ psi into the top port of the wastegate and it holds so I think the diaphragm is good.

Is it possible my exhaust pressure is high enough to where it is pushing the spring open that much earlier on the street? I really don't think I have a boost leak, I can hear that turbo is not working very hard. If I hook the boost reference up incorrectly to the top wastegate port, it will start making all kinds of boost (with the pressure holding the valve shut).

Should I rig up a home depot smoke machine and pump it through the cold side? I have checked and double checked my couplers and clamps - I think it would have to be an intercooler crack if it really is a boost leak.

Thanks for any help

 

It takes 8-10psi with only air, add back pressure and it sounds like your gate is doing the right job. You cant install an X PSI spring and expect it to open at said PSI due to too many factors.

Time to add spring or Air on top

 

I would try it referenced after the intercooler and see what it makes.

 

^ what he said. Measure boost at the compressor cover and compare it to intake manifold psi. 2.5" cold side sounds small.

 

add a manual boost controller. Hallman MBC is proven boost controller. I have used it in all my setup. one even held good at 34psi using 20psi spring.

Ive also experience same issue as you said, I tossed it up as WAY to big of a wastegate for what i needed.
so now I go with something smaller. im running 38mm and no issues.

 

People greatly underestimate pressure loss through an intercooler. Even in a perfectly 100% efficient world, when you cool down your charge air, pressure is reduced. Add to that the real world flow restriction of even the best Treadstone has to offer, and I don't know why anyone would try to boost reference from the compressor cover.

 

I swapped to the supposed 12 psi spring for the 50mm gate. I also resealed the front housing on the turbo.

I am now making about 8 psi...car runs great.

I have tried using a manual boost controller but I really wanted to get it to where I could keep it simple...no more points of failure. I also picked up some appropriate sized shims from home depot and may shim the spring for slightly more.

My IATs are very reasonable, but I tried looking up some math and the air is probably very turbulent through the 2.5" hotside. I got another box of bends to make 3" - I will update this thread once I change over. I am thinking I may gain 1 or 2 psi.

 

Thats 1 thing I noticed when I first got my On3 turbo.I had to reseal the housing and then made it perform. I thought of using manual boost controller also and wanted to keep things simple.I then bought a gofastbits e-controller and works great.I had first boost reffed from the turbo directly and as others said...that pressure drops considerably from there to the intake itself and I got my refference at the intake. The controller displays vacuum and boost and allows to fine tune power delivery. I highly recommend a controller regardless ...there are nice features you get with them for things like overboost etc.

 

Yup he is right on

 

Your wastegate will always open earlier if referenced from the compressor housing. Your boost gauge and wastegate should be referenced from the same point.

 

Time to go to home Depot and buy a air compressor regulator and t it inbetwedn your lower wastegat port and your top. Close the regulator all the way and then just give it a half turn open. Slowly start opening it until you get the desired boost level. Spend the rest of the money that you would have used on a big $$ boost controller on hookers and blow!!

 

I hate when I google threads and people never post replies so I wanted to post my results. I tune the car myself and have not dynoed before or after but the difference was obvious. I was disappointed in the power of the car before for a turbo v8, now it is the opposite.

I ended up redoing my piping. I tried to eliminate as many turns as possible. I have 12-18" of 2.5" coming off the turbo, stepping up into 3" going into the FMIC, then 12-18" of 3" coming off the intercooler stepping up into 3.5" running to the TB.

The difference is dramatic. I see very close to spring pressure in terms of boost when measuring at the intake. It spools sooner and the car is all over the road from spinning them so hard.

I was also using at least 1 90 degree silicone connector in both sides before, which are eliminated. So piping does matter on a turbo setup to some degree, particularly if you are not using a boost controller.

 

If you do the math, it sure looks like 2.5" piping is better suited. I'm not saying all the complex bends and 90's you had in place before were correct. Or that what you have now doesn't work better than the previous setup with your installed parts. Just that a properly laid out 2.5” setup (with the correct IC) should increase response while not causing turbulence/drag issues on most mild SBE LS engines.

Also read you size the piping based on the engines NA flow. As you said… because of turbulence around 450 FPS (.4 mach) is the commonly accepted do not exceed point for airspeed in a cold side pipe. Tube size can roughly be checked by calculating the maximum airflow attainable, dividing by the area of the tube in square feet, and dividing again by 60 to convert to feet per second. So If we use a 400hp NA engine (roughly 600CFM) as an example. Airspeed is about 293FPS (.27 mach) in a 2.5” pipe. Of course more restriction/turbulence will be added when you add additional bends/length.. But for the typical LS making sub 400hp NA, it sure seems like 2.5” piping should lower the volume of the system and improve response. According to rough math anyway.

 

Still referencing off the housing?

 

One item NOT stated above IS the pressure in your exhaust manifold. (EMAP)

FORTY YEARS AGO, I purchased a B-24, yes the plane, Manifold Pressure Gauge.
This I then had restored by an AP house with ONE pointer painted Blue AND the other pointer painted RED.
These pointers ARE "over top" of each other, thus an easy read of Delta Pressure.

My FIRST Turbo was a 351-C, Twin Turbo, in a FORD (Pantera)
This car would "spin" the rears @ 100 MPH, a Mid-Engine CAR !
I removed the "speedo" and fit my B-24 multi engine gauge in its place.

WHAT I LEARNED that day was greater than ALL OTHER Turbo experience combined in the past.

THAT FACT : When the Blue pointer (MAP) was greater than the Red pointer (EMAP), the engine made EXTREME POWER.
When the Red needle would "climb" with RPM increase, Torque would drop.

Today I use this tool for turbo "match" purposes.

I would be one who could provide this type of tool, any interest ?

Lance

 

Very good idea. Super simple as well. Dual needle pressure gauge.

 

Manifold pressure is never going to be higher than exhaust drive pressure on the OP’s 6.0 with a single 78/75 t4. My 6.0 with the 1.32 T6 and 87/96 exh wheel is still at 1.4:1 around 19lbs. You’d need a large frame turbo to hit 1:1. Not very common or practical on the average single street strip setup and response would be poor.

2 $16 pressure transducers tied to any decent aftermarket ECU you can data log would make for better clarity than a gauge IMO.

 

The SIMPLE FACT IS when one measures, records, Delta-P in REAL TIME a GREAT amount of knowledge will be learned.
Those who HAVE NOT take the time to do so, would NOT have the insight !

The "art" of being "fair" can also be considered.
The ability of an engine to run in "crossover" for a period of time IS affected by tune.
THAT "tune" includes, Cams, Intake/Exhaust Port Sizes, RPM, etc.
WHEN we state "the engine has a good song" we know that tune is of a well constructed engine.

NOW, lets rule that out.

Lets OBSERVE simple laws, the law of Angular Momentum.

The Turbosupercharger is "seen" to have a great amount of momentum at 70K RPM, the inertia of the compressor/turbine.
NOW the EXAMPLE : When the engine "drops" RPM as when a "shift" occurs,
the compressor/turbine speed will be high, E-MAP will be low.
This is one case of a "crossover" period.

This is why a Dash Gauge helps a great amount in understanding engine operation.

My case : Many times I have used a rolling road to do the final tune, a well designed engine.
I make my own exhaust with an E-MAP port if allowed.
I fit my Gauge, do the runs, observe the "crossover" window almost every time.
MY engines have a good turbo match, thus proven, a VERY GOOD "spool"
and make good power for the observed MAP/engine size/engine design.

I manufacture the Redline ECU-882/422 WITH board mounted pressure sensors that measure manifold pressures.
This allows the measurement of MAP/E-MAP AND the information is "saved" in a 1 mbit flash chip for future views.

NOW the last comment, this concerns DRIVING a turbo car at Riverside Track in CA.
MY gauge, a dash Delta MAP/EMAP gauge, allowed me to predict when the engine torque would greater than the ability of the rear tires to transmit that power to the ground.
This allowed me to win most of my races in my Twin Turbo Pantera. (1970's)

The original question : 2" valve = pressure area = 1 x 3.14 x EMAP (19 .lbs?) = ? all trying to open that valve !

Lance

 

Wasn’t disagreeing with you. Less back pressure is better.

Just stating that your described ideal conditions aren’t going to happen on 99% of the “Street” single turbo V8 setups. Most will be lucky to see below 2:1 ratios at any decent amount of boost.

I’d see as high as 2.8:1 on my first 5.3 with a T4 1.10 housing S475 at 26lbs. Despite the 73psi in the manifolds, the car still ran a solid 8 sec ¼ mile and used a very mild PAC1218 valve spring. (130 closed, 318 open pressures.) -21* of overlap @ .050 cam profile. 100% factory original valve train. (including OEM push rods)

 

OK, thanks for that friendship remark.

Your case, I wonder HOW close you are to the SAME THING except with the Exhaust Valve.

Lets do the Math :
Exhaust Seat Pressure = 130 .lbs
E-MAP = 79 psi.

NEXT 1.6 divided by two = .8 x 3.14 x 79 = Valve Seat Float

My guess is about 180 .lbs of Force trying to push your valve OPEN.

THIS item is also NEVER stated here, my original direction. (thanks)

Lance