Extrude Hone ...

[DataMax]

Extrude Hone claims on their web site that they can improve the flow of exhaust manifolds by 80 to 90 percent ... has anyone tried this inplace of headers?

[ehostler]

Extrude honing is a great process. Even with extrude honing, an exhaust manifold cannot flow as well as a header, however you will maintain a stock appearance. Extrude honing is also great on intakes and heads.

The real problem is the price of extrude honing. Bend over and break out the KY.

[DartGT66]

I thnk the flow increase pretty much depends of the manifold you begin with. 80-90% is very much, and I sincerely doubpt that slot in most cases. A good exhaust, as you know, is also a lot of other things than just good flow, and those are properties that the extrude hone can not change. I believe having a pair of exhaust manifolds extrude honed will cost closer to 1000 than 500$. There was an article in Mopar Musclr where they did that and dynoed the before & after numbers. If I remember correctly the power increase was around 5 hp.

[451Mopar]

A few years ago one of the Mopar magazines extrude honed some magnum exhaust manifolds for a 440 powered Coronet (I think it was in High Performance Mopar Magazine.) Anyhow, the extrude honing helped a little bit, but I think it costs around $500+ to extrude hone the exhaust manifolds. A year or so later they installed headers and I think they reduced their ET's by 0.2-0.3 seconds.

The problem with the manifolds is not just restriction, it is the design that basically just dumps the exhaust into the manifold, so there is no tuning or scaveging effect with the manifolds that you get from correctly sized (diameter and length) headers.

[George G. Leverette]

I asked on another post about data in a controlled enviornment that verifies the actual horse power and torque gains on a street drive vehicle. Track times are determined on temperature, humudity, altitude, wind direction and intensity, surface of track, suspension setup....... reaction times and other uncontrolled factors and are probably not an indicator of adding headers without enriching the fuel mixture changing the timing and other factors therefore statements relating to improvements cannot be validated without repeatability over a dertimined period of time.