Merge collectors

[Exhausted]

Originally Posted by Alan Nyhus

- Is backing up the exhaust duration by 4 degrees is a good place to start. Your thoughts? -Al

It seems that 10-15 years ago, most engine builders all had more exhaust duration than needed. (I think this is a result of relying on dynos, IMO). It is less the case currently, but I am getting less feedback these days.
Going from a 4into1 to a 421 it is a safe bet. I am always willing to discuss those decisions with folks if they would like,and I do often, but the cam grinders are probably more up on direction to go there.
I will say that a 421 header will almost always add bottom end power no matter what size you make it. But horsepower upstairs is very easy to lose or miss by breaking flow rules and using wrong tube size. (read; you should get what you pay for)