Alrighty then, going to ship out this small port manifold to be extrude honed. Expensive process, but let's see if it's worth it. Going to go all the way and have the mani pushed out to match the gasket. See how much of a difference it makes. The head already has some work so I'll start from there with the head. Waiting for parts from Battle Garage and MRP so this is going to be a bit of a wait.

Extrude honing is an interesting process... results (and opinions) will vary as the saying goes
It really is a honing process designed to smooth, clean and polish surfaces rather than remove
a lot of material. Although there are industrial applications where the workpiece is pressurised
and the flow direction of the medium reverses with every stroke of the pump.

That allows the medium to be forced against the internal surfaces of the workpiece. By using
several different grades of grit the amount of metal removed can be increased. Single direction
flow with the exit at atmospheric pressure will remove progressively less material as the medium
travels thru the workpiece (your manifold).

Just putting this ^^^^ here for anyone not familiar with the process. It would be great to see
some before and after pics if you could post them up when the manifold comes back.

Cheers... jondee86

before & after pix, say nothing about the impact on performance unfortunately..... just like head porting pix
Risky.... expensive mod, for possibly very little to no gain
If head/intake union, is 'poor' quality, benefits from smoothing the transition alone is commom
CA18 for example show 'significant' gains here, but.... process is a 'low-buck' mod, and "boost", amplifies the performance improvement

jinx wrote:before & after pix, say nothing about the impact on performance...

True... there are a lot more factors involved in improving the performance of a manifold
than just smoothing the passages. Even making the passages bigger is not always helpful
if it reduces velocity at a critical point. Mirror finishing offers no advantage due to boundary
layer effects, and these days dimpling is getting good results in comparative testing.

All that is interesting but getting the basic manifold design right is the first step. This page...
https://www.musclecardiy.com/performanc ... manifolds/ has
some good comment. I always thought that the smallport manifold worked fine... pulled
smoothly down to 1500rpm and did not seem to be restrictive at 8000rpm. The stock cams
were running out of puff by then....



From memory, stock unopened smallport engine, stock intake (FWD converted to RWD and
cast iron AE86 exhaust manifold. Might of had an Apexi cone filter but otherwise no mods.

Cheers... jondee86

will be interesting to see.... I'm running essentially a stock smallport intake, and I'm making 140whp with 10.7:1, and Web 577 cams....