During the past years, I read a lot of BenR's (Angelworks) posts about inlet manifold porting and his results were always very good!
He wrote this:
-"A properly done inlet manifold can gain between 8-12bhp"
-"The 172/182 manifold responds well because its not a great shape and the casting quality is poor. There are 2 levels to the 172 manifold mod, one is working the areas you can (which is about 90%), reshaping, matching and generally optimising the flow path. The second level reuqires cutting off the plenham top, welding it up (to give me more meat to work with) and starting from scratch, its substantially more expensive, but substantially better."
-"Gains are typically between 6-15bhp, averaging 8-10bhp for the cheaper modification. However, if your manifold is a good one to start with, gains will be in the lower end of the scale, i cannot gaurantee gains due to the nature of the work."
-"The design we ended up with was the result of CFD analysis and allowed us to generate a profile that aids flow control greatly. Infact, the actual perfect design requires material to be added to the casting so there are areas which are not touched as they are already 'oversize', and you will see this vary with batch casting used." [This is referred to CNC manufacture]
-"Gains will still be in the region of 8-13bhp depending on which cylinder head/ex manifold combination your car happens to be stuck with"
This is a dyno test [Ph1 car with AWT inlet manifold, Magnex exhaust, ITG Maxogen]:
View attachment 134924 Why are there these differences beetwen BenR works and others?