Thread: Step Headers, what do you think?

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Here is what I have learned from David vizzard,
His opinion is that a 1 5/8 is good to about 375 hp ,then step up to 1 3/4.Short primary pipes favor top end power and long primary pipes favor the low end.He also states that equal leanth headers are of little use on a street ride and almost any engine for that matter ,based on the fact that each pipe comes into its own somewhere over the rpm band ,helping the overall power of the engine ,rather than one rpm area.
He also goes on to say that collector lenth and size play a much bigger role in making power than header configuration.A basic rule is that large short collectors favor top end and long small collectors favor the low end.A 2.5 inch collector is good up to about 375 and a 3 inch collector for 375 hp or more.He also states that a collector lenght of about 18 to 24 inches is best for the street,it can be made a little longer to help in the low end to get a heavy car under way faster.
Now this is where he stray from conventional wisdom ,He says that in order to have a zero loss muffled system that you need a terminator/resonator box after the collectors .The size of this needs to be 8 times the volume of one cylinder or 11 to 15 times the volume of one cylinder is better.Then you need a muffler than conformes to his 2.2 cfm per hp rule .One of these per header and hes sayes exaust system losses are under 1 percent of what open headers dyno out at.Its also good to put a balance pipe connecting the collectors or second choice is to connect the termination boxes with a balance pipe.
This system is suppose to look like open headers to the engine ,making everything down stream of the terminator box invisible to the engine and the dyno sayes less than one percent loss with this system over open headers.

His take on the balance pipe is that there are 2 possible benifits ,increased power and decreased noise.It sayes that dyno testing has shown it to be 100 percent effective at noise reduction of about 1 to 3 db ,with 2 being the most common.Power is more tricky,about 60 percent of the engines responded with more hp ,with about 12 being the max and 5 to 8 hp being the norm.The other 40 percent of the engines the power was unchanged,but none of the engines lost power .Theres no down side to a balance pipe.
The size and length of the balance pipe are not that cruicial,2.5 to 2.75 are fine on the diameter,with anything over 2.75 showing no gains on engines under 600 hp.Dyno tests showed that pipe lengths of 18 to 72 inches dynoed out virtually the same.
He sums it up by saying,although he has not exsplained the theory behind everything discused here,you should be well enuff informed to build a near zero loss exaust system,as long as you dont loose sight of the essentials and principals involved,good results will be acheived.He also warns that if you step outside these recomendations you are on yer own.......