So after some reading this is what I feel I have come to understand more or less please correct me if i'm wrong it helps me learn and I appreciate the feedback.


wastegate / bov work of spring pressures

high boost motor can get away with running a smaller gate because it doesnt need to vent as much boost because its using most of it.

low boost motor requires a bigger gate because unlike the high boost motor its using alot less of the boost meaning it needs to vent more boost off.

im assuming the bov work in the same fashion.


my question here is could you not just run overly big BOV and WG and would it not be healthier for your motor ?

here is my thought process behind it the ''mm'' attached to these is simply the diamater of the gate inlet/outlet. The bigger the outlet the faster/more boost it will vent which means less chances of surge and back pressure? The smaller the inlet/outlet the longer it will take to vent away that surge or back pressure. So why not go bigger and reduce those negative effects?

is this out to lunch ? and is surge and back pressure the same thing ? stalling the wheel and making it turbulant ?

 

smaller wastegates have a harder time controlling high boost levels. that's why most people go with 2 44s or a single 60mm. bov you need to match the spring to your boost level if its to light it will push open under boost.

 

if going twins is a single 60 sufficient for wastegate? they will be 61/65mm ON3 T4. I think thats right ? 61 compressor inducer 65 exhaust exducer ?

Cold Side

Compressor Wheel 61mm
.70 a/r
4” Inlet and 2.5” Compressor Outlet
Inducer- 61mm
Exducer- 99mm
Exhaust Side

Exhaust Housing T-4 Flange
.68 ar Exhaust Housing
3.0″ Vband outlet
Inducer- 74.5mm
Exducer- 65mm

 

A single 60 would work and I have seen it done but for twins it is much nicer to do dual 44mm gates. To do the single gate you have to merge the two banks to use one gate and the pipes to the gate usually get long and it doesnt control boost as fast or as well. Plus two 44 usually cost about the same as one 60mm honestly.

 

if its twins I would use dual 44s. I wouldn't want to plumb a single gate .

 

Smaller wastegates have a harder time controlling LOW boost levels, because they can't divert enough exhaust gas to keep boost at a low level, so it will climb/creep above spring pressure.

A wastegate too large can prevent you from making high boost without a good boost controller, because it will crack open below spring pressure and be large enough to bleed off enough exhaust to keep boost from rising.
A 38mm gate might open be fully open at 1", but a 60mm gate will only have to crack open 5/8" to flow just as much.

A good boost controller that prevents the wastegate from seeing boost will help with a large wastegate, but if your backpressure is high enough to force the valve open, you'll make much less boost than spring pressure regardless.

 

Thought you'd want to match the spring on the BOV to the vacuum then engine pulls?

 

Instead of trying to memorize what every person is doing with their setup,

try to learn what these devices do. What is the purpose of the "BOV"? How does the factory implement a "BOV"? All factory turbo cars come with a BOV but we call it a BYPASS instead, because it bypasses the compressed air back to the compressor inlet where it increases the kinetic energy of incoming air to the compressor, which is helping save fuel, and reducing lag. The first thing many new owners do is remove the "bypass" and replace it with a "BOV" which only means they have removed the recirculating portion and replaced it with an open atmospheric 'vent' so they can hear the noise it makes.

From a performance point of view, anybody who is doing it 'that way' is 'in the dark'. They probably do not understand the negative result of venting an atmospheric 'bov' just to hear it make noise. Please spend some time examining the factory's way of setting up a turbo engine, and if you can find the time to study a little thermodynamics and kinetics, specifically the kinetic energy of moving objects and the rotational/inertial aspects.


Next, the wastegate and it's purpose is somewhat discontinuous with the bypass. That is, it functions to perform a completely different feature, and if the two ever interact it is merely a coincidental incidence which we generally dismiss or do not consider.

The gate is a device which we would prefer not to need. An engine would run better without one. This is because a gate interrupts the flow of exhaust gas, forces it to turn, bend around a corner, compete with other cross-sectional areas for flow.

Unfortunetelly, once the turbine is "up to speed" we have to throw away the excess exhaust gas. This is quite unfortunate since hot exhaust gas contains energy, both internal energy (enthalpy/entropy) and kinetic energy. Since our combustion engines are open mass (burnt fuel and air leave and are not re-used) every scrap of hot exhaust gas energy should ideally be used somehow, until that energy is gone. So we don't want to throw away the exhaust gas at all; but that is exactly why it is called a "waste gate". Once the turbine has enough energy to spin the desired speed (turbine speed -> compressor speed -> Exact compressor flow volume is known) any additional exhaust gas energy is "wasted" out the wastegate. boost "creep" occurs when the gate flow is maxed, and no more exhaust can fit out the gate, so the extra energy goes into the turbine where it speeds up "out of control" and increases boost, thus the "creep".