Originally posted by RoadRacer
I've heard both sides of this issues, and don't know what to do. Will big duration cams cause blow through on a boosted motor, and then not produce as much hp? Would running a larger duration intake cam and a regular exhaust cam produce better results? I guess a vtec motor is a good example of this, as the vtec lobs have a pretty big duration. I think John said 290 deg? Don't b18 turbo motors make pretty decent hp....250hp+
Thanks,
What is the application? As far as big intake and small exhaust, thats just as bad. The problem most fail to realise is that you generally have twice the pressure in the exhaust tract that you do the intake. If you are making 10psi at the manifold, you have 20psi (or more!) before the turbo. So if the intake and exhaust are open at all, you will get exhaust "blowing back" into the chamber, pushing fresh air/fuel out, and really hurting combustibility.
I've heard that turbo'd VTEC's usually don't make as much HP as a non-vtec will if all else is equal. So the long duration VTEC cam could be hurting performance there too.