Lq4 ls6 intake bws475 92mm 1.10 t6
Im using a 3" to 2.5" 90 degree silicon reducer off the turbo to the intercooler.
how many inches in front of the throttle body should I step up from 2.5 to 3 inches and how many inches away should my bov and Iat sensor be from the throttle body
this is a speed density setup so no maf
thanks for your time guys I want to weld it up this weekend some pro input is definitely appreciated

 

use 3" throughout

 

Since you wrote that you are welding it up, I assume you can weld. Don't use any silicone for reducers or elbows if you can weld. Also, WTF with the baby intercooler? If anything, you want the IC to be bigger diameter piping than the turbo.

 

because the throttle body still needs a coupler at the end of the day. that is where I was going to place the step up and I've read plenty of topics here that state 2.5 is more than adequate for 750hp and to use the using the smallest diameter to reach your goals for the least ammount of lag someone more knowledgeable than me please chime in

 

You use the smallest diameter to reach your goals on the EXHAUST side, not the intake side. On the intake side you use the largest diameter you can tune. You absolutely never want your intercooler to be smaller than your turbo outlet diameter, and the only reason all of this is smaller than your throttle body is packaging issues. Also, you have to use silicone couplings, of course. What I was saying is that you don't want to use them for reducers or elbows. Make those from material that wont flex any significant amount during vac/boost transitions.

 

thanks for the info

 

too much plumbing slows things down, turbo will lag. There at what is called 'high mount' or similar, which utilize shorter tubes for example.

I use the same size as the compressor discharge for my hot side to keep lag and velocity optimal. You wouldn't want a large pipe to slow down the flow of the air coming immediately off the compressor, the main benefit of post-compressor air is its high temperature and high speed. Velocity of moving air in the plumbing is directly tied to engine response. Plus you wouldn't want to introduce any turbulence, ever, which might be induced accidentally by any kind of change in pipe shape. So minimal size changes and minimal bends are desirable. Never use a 90* bend always try to get 45* or less. If the discharge was 2.5" and you used 3" the sudden change in volume I believe would be an isothermic expansion, where pressure would drop, velocity would drop, volume would increase, and temperature would not change. There is no benefit to causing such a slowing of air and drop in pressure, that should be obvious. The temp isn't going to drop as there is no where for the heat to exchange to, besides the background rate provided by the aluminum throughout the entire system.

As the air is going through the intercooler it will encounter a bit of resistance as it collides with fins, and exchange energy (lose some internal energy as it cools), the pressure will change from one end to the other because any resistance to flow is going to take energy out of the air and the drop in temperature together with flow resistance will change the pressure and velocity by the time it gets to the other side. The outlet of the intercooler is therefore "resetting" the flow dynamic of the charge pipe, in other words, it no longer contains the same shape and structure provided initially by the compressor discharge. It is therefore reasonable to use the same diameter pipe on the outlet of the intercooler as is provided by the intercooler. You can "see" the outlet as another kind of 'compressor discharge' if you wish, where maintaining the same undisturbed exit flow dynamic (utilize the built-in smooth discharge pipe of the intercooler and match it's size to minimize differences) is a reasonable assumption.

 

Also the bypass should be on the compressor housing if possible, many turbo manufacturers are providing them as integral units now. If yours is not one such lucky unit simply place the bypass as close to the compressor as possible.