[howieschoon]

Hello all,
It’s my first post anywhere on the internet so hopefully I don’t do too terribly. I found this website about a month ago while I was looking for information on 4-cyl exhaust headers and was quite thrilled that David Vizard was the “director of technical writing.” The car/engine this is for is a 1991 Pontiac Sunbird with a 2.0L 4cyl. While this is not a common car to modify, I have had it for about 10 years and am quite attached to it. I would like the header to mainly improve torque and gas mileage as this is my daily driver and doesn’t need high RPM horsepower, most of the time. I would like it to be tuned for about 4000RPM. For this reason and for packaging constraints I would like to use a tri-y design with the first sections about 20”-24” long and the overall primary lengths to be between about 72”-76” (unequal lengths). I used 1400FPS for the speed of sound and a cam with 214deg duration at 0.050” lift (yes, it is a rather small cam). Hopefully my lengths are right, if not please correct me. I wasn’t sure if I should use 180deg or 214deg. or whaever the cam timing is at 0.006” lift to get the time. What I wasn’t sure about was the pipe diameter and if I should have it step up in size or not. I read somewhere that on an even fire 4cyl that the collector should only be about 20% larger (not sure if this was diameter or area) than the primary since the pulses are evenly spaced. Has anyone here heard this before, or even better tested it? Also, should I have the tube size increase by 10% or so at the first “Y” and then another 10% at the collector? I was thinking about using 15ga stainless steel pipe which would give me about a 1.35” ID (I got this size recommendation somewhere, a while ago) with 1.5” OD pipe for the primaries and I think the rest of my exhaust is 1.75”, which I could make larger if it would be worthwhile. I am going to coat the pipes inside and out with Tech Line’s Black Satin (baked in an oven @ 750deg). I want to keep as much heat in the pipes as possible and to have it last a long time. Sorry this is so long and thanks for any and all help.
Howard