Since I am finally getting around to ordering this thing I have some questions for you all. First off this will be matched to a 20B with a large street port and a big single turbo, at least a T-seventy-something. Looking for 650+ rwhp. This is a road race car, not a drag car so I want lag to be minimized.

I am probably going with the core from Spearco #2-182. Core dimensions are 20 x 15.6 x 3.5. Similiar, if not exactly like Evil Aviators.

My question is about inlet and outlet sizes. Spearco recommends a 2-1/2 inlet and a 3" outlet. I'm noty sure if they know about how much 20b's flow, so I was thinking 3" in and 3-1/2" out. I think most turbos have a 2-1/2" outlet standard and am wondering if this would be a bad match. I realize larger diameter tubes require more air to fill them, increasing lag, but am hoping a ported 20B can overcome this better than other engines. I am NO expert in this deptartment so peoples opinions are valued here.

 

corky bell's book "maximum boost" probably has the info you are looking for

 

Anyone with advice or input....

 

the stock cosmo and fd ic pipes are 2.75"....

mike

 

Thats weird, my 20b stock elbow before the tb measures 2-3/8".

I'm thinking that since the total area of the openings in the tb is just over 8.8 in.sq. and the area of a 3" pipe is 7.0 in.sq. and the area of a 3.5" pipe is 9.6 in.sq. the 3.5" pipe would be a better match. Does this make sense or does it not work this way?