Extrude honing is a process whereby a coarse, abrasive putty is pushed through a metal part, like an upper intake manifold. In so doing, the putty widens out the ports, and smooths the interior. It also has the benefit of optimizing flow because it itself flows, and thus puts greater grinding force against anything obstructing flow (like strange nodules in the flow stream).
Power gain for <= 98.5 SVT UIM? Maybe 7-10hp.
Power gain for 99-2000 SVT UIM? Maybe 11-14hp MAYBE...
Not by itself! Increased and more laminar air flow doesn't do a thing for you unless your LIM and intake ports are clean, and you've got an exhaust system that can support the flow! I would say headers, intake, UIM, and catback system will net you 25-30... Probably along the lines of 20 to the wheels.
So the lesson here is, if possible, pick up the later model SVT UIM as opposed to the 98 version? The difference between them (honing) justifying a slightly higher price for the newer UIM. I recently picked up a 98 SVT LIM not realizing there was a difference between years, so I don't want to make the same mistake with the UIM.
actually there have been several threads debating that topic. Are the later SVT UIMs actually better then the 98's? The reason for the debate is because the later model SVT's produce a couple of extra horsepower, and many believe its because of the UIM. I'm going to have to disagree with them, as I recall there was a thread on either here or ceg.org where someone actually contacted the owner of extrude hone, and he called back leaving a voice message, which was then posted to the web, saying the extrude hone process was exactly the same between all years of the SVT, and that the hp difference had do with something else. I don't believe anyone has flow benched the UIMs between the different years to compare, but I seriously doubt there is a difference.
Now there are SVT UIMs out there that are better then stock, as many people sent theirs back to extrude hone about a year ago as part of a group buy to have the process performed again to maximize the flow, these have been proven to be better. But these would be hard to find, as I doubt anyone is going to be willing to give it up.
The 2000 SVT manifolds were supposedly "dual honed". The external difference was that the powder coating (or whatever they used) was crazy smooth compared to the stock manifold, even compared to the '98/'99 SVT UIMs. It's pretty easy to tell the difference just by looking at them. If you still see bumps through the powder coating, chances are it's a '98/'99. If it's smooth as a baby's butt on the outside, it's probably a 2000 UIM.
As for power difference, can't say- Sounds like the guy from EH knew that there was no difference between years.. But there is definitely an external difference.
<Sigh> Seems not so long ago that I was the first one to do the SVT UIM/TB swap to my original 2.5L... :biggrin: :tongue:
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