Torque falls in the upper RPM of the power band.Easier install due to smaller dimensions.Spool faster providing more torque lower in the power band.While 90% of the internet would tell you to pick the smallest turbocharger that meets your horsepower goals I would like to offer a different point of view after we go over the pro’s and con’s of each. It would be nice if turbocharging was like many other decisions where bigger is better, but not so.
So you have decided to turbocharge your car or upgrade your existing turbo, but are stuck on what size of turbo would be right for you. Does a large turbo car make a terrible streetcar? The quick spool timing should only be adjusted to fine tune the flame-front position and expansion into the scroll when you know where it's at and the fueling is known to be correct (not too rich).Things to consider when picking and deciding on a turbo size for your build. This avoids hammering the piston and rod bearings when the crank throw is straight up and the energy has no where to go except into rocking the piston OR into the rod bearing/journal. If you can adjust the quick spool timing, avoid zero degrees and stay greater than +2 degs or below -2degs, before or after TDC. This means the turbo spool can actually suffer due to the cooling affect of un-burnt fuel that's igniting in the elbow or down tube. If the wide open throttle fueling, prior to boost, is too rich then the retarded timing can send the flame-front too far down the exhaust. These cases make going to a lower over-lap cam a good direction if decreased spool time is your goal.Īnother consideration with regards to "quick spool" timing is knowing where the flame front is. 63 turbine housing with S-II wheel remains slightly elevated and this typically does not go well with a cam that has significant over-lap, due to the risks of exhaust reversion back into the combustion chamber. This reduces exhaust gas velocity and results in a decrease in spool response.Īdditionally, the delta pressure across a. 63 housing and a stage-II wheel, the turbine inducer scroll opening is widened slightly, due to the machining process.
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