We have all discused which Headers to use on a 351W, but exactly which size tubes should we install on an engine with aftermarket Heads for High horsepower applications?
There is no answer written in stone for what your asking. Headers do not come in one size fits all, in order to properly suggest a size we really need to know what type of cam, valves sizes, carb, intake, transmission, gears, rest of exhaust, and more details about the type of driving you intend? city, race only, drag.
High horse versions of other engines in the 350 cube range use 1 3/4" to 1 7/8" primary tubes. With aftermarket heads and wide exhaust bolt pattern (or 4v 351c), you might hear of some using 2"+ diameter.
You have to know the cu" of the engine and the rpm it operates at to figure the best size and length for header primary tubes. You can then tune the diameter and length to give the engine a slightly lower but wider power band or a peaky higher power level. The math is fairly complex and I wouldn't recommend it for the average guy. A good example is the headers for my 357 cu" Windsor that has a peak power of 365 hp at 5500 rpm. The headers were selected for street use only and assist the power band in the low end so I get 425 ft lbs of torque with very high average torque from 1000 to 4500 rpm. This hurts the peak hp number but makes the car perform better in a wider range of speeds. My headers have a 39" long primary tube with a 1 5/8" OD (the ID is 1 1/2") and the primaries go into a 2 1/2" collector that is 19 1/2" long. My "H" pipe is 9 3/4" behind the end of the collector and the mufflers are 4 7/8" behind that. The dimensions are based on the geometry and speed of sound in the gasses as the temperature changes going down the pipes.
Thanks guys. In the past i used Tubular Automotive headers on my 351w with ported heads and 194 valves, with a 280 Competition Cam. I suspected the tubes were on the small side to allow for fitment. I have a set of Total Performance headers for my new project, anyone use these on a similar build?
A 1 1/2" ID tube will flow more than the 1.6" diameter valve. It will also keep the velocity up which can be used to improve performance. Just like with carbs, cams and intakes, bigger is not always better.
The OP specifically said "high horsepower"... Bigger is better for "high horsepower" vs "high torque"...
Define for me... What is high hp? The stock power is what... 190? Is 365 hp high? What cam is he using? What compression? What RPM? In my first post I mentioned that you have to know the cu" of the engine and the rpm it will run at to figure out what size tube is needed. Without a lot more information nobody can give a decent guess as to what he should use.
