Quote:
Originally Posted by hillshooter
so really, is that low AR number for more of a street/daily application? I just want to know the science behind it.
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No, that is not low for these types of twin applications. All depends upon the set-up, engine size, use of the vehicle, etc. This kit uses larger T4 turbine housings, where a larger a/r is not needed to correct for higher backpressure. We can use a/r to hone in where the customer wants the turbos to light depending upon their use. I run billet 5858's on my car with the T4 .68 housings. Street car that just went 9.92's on the stock bottom end, turbos come on nearly instantly and have enough efficiency to still make excellent power up top! Most commonly we use .68 or .81 housings, rarely .96 for the big boys but this comes down to engine specs, goals, RPM range, use of vehicle, etc. A/R is simply the space available inside the housing. Smaller number = less space, therefore quicker to fill and have the exhaust hit the exhaust wheel and get business started. Larger A/R is more space = more space to fill with exhaust and a slightly delayed response to get going, but the end result is more volume to be able to hold, thus more efficiency in the higher RPM range where the engine feeds more exhaust. Good example would be a car driven on the street with a manual trans wants quick spool vs a similar car in auto with a cam that likes slightly higher RPM shift points. We may bump the a/r up to be a happy match with the camshaft.
