Quote: want to thank everyone for their replies. I just received an email from Extrude Hone and this is what they said for performace gains on exhaust manifolds: ""Rick says that after processing the average airflow increase is 15% with an approximate 15 to 20 horsepower increase. The cost to Extrude Hone process your exhaust manifolds is $675.00 (per pair) plus shipping. The turn around time will be approximately two weeks""
I just wanted to pass on the information.
For the record, "Rick" is the guy who helped me get my 340 manifolds done, after seeing the before and after results first hand I find his WAG of 15% - 15-20HP gains pretty optimistic, possible? sure, probable? Not IMO. But I do think you could see roughly half that amount of gain in many cases. They are nice and smooth inside which will help flow, but the volume has changed VERY little, not much material has been removed and I asked for the "Max" amount be removed. I'd dare to say that simply ceramic coating the insides could result in similar gains in flow. For the record I would go to Extrude Hone again if looking for every last bit of HP, I'm happy with the work, not so much with the price, but went in with a conservative hopeful outcome so regardless of how minimal the gain, I'm happy so far. Dyno run is next week, I'm going to try and have some stockers dyno'd during the same run.
