Race Engine Forum UK

Guy,
I was wondering what dowelling method you would suggest for locating the inlet manifold on my 16v. The best method i've thought of so far is to bolt the manifold on leaving two studs out, then drill/reaming through the two open holes (using a depth stop of course!) so that i could fit a pair of tubular dowles.
I'm not planning on port matching at this current time as i'm not taking the head off, but i would like to riffle any positive steps in the head ports. Would this be a worthwhile quick fix (<-- i use the term loosely!) to a slightly improved flow, bearing in mind that with my new camshafts the valves will actually be opening! What would you suggest here?
Thanks,
Guy

Have a read of a feature in the GC V/W (Virtual Workshop) on this,

http://guy-croft.com/viewtopic.php?t=7

You would be wasting your time (I mean that as an observation not a criticism) dowelling the inlet manifold to the head. You would certainly get a lot of benefit from smoothing the manifold from as-cast to say, 80 or 120 grit and if there is much of a mismatch you can correct it.

That said, whether you correct a mismatch depends on:
1. how bad it is
2. which direction the mismatch is
3. what the relative flow in the head and manifold actually is

To illustrate point 3 above, if you have an inlet manifold that outflows the head but is actually smaller in exit section than the port, there is nothing at all to be gained by enlarging to match the port outer area. That would be what I would call an 'upstream' mismatch.

Frankly, modifying the port or inlet manifold over much (beyond smoothing) without a flowbench (which is why I bought one 3 years ago and thank goodness I did, a most alarming thing to use) is very hit and miss, you're as likely to generate a loss in flow and power as a gain..

GC

So my best bet would be to smooth the inside wall of the inlet manifold then, is this best done by hand in a linear fashion or with a rotary tool. Is it still worth making a template of the inlet ports and lining up to the head just to see if there are any upstream mismatches?
So dowelling is only worth doing if the head is to be flowed yes?
Thanks for your time,
Guy

P.s. Thanks for that link, i hadn't spotted that one before, should keep me quiet for a while!

Rotary tools, yes.

I will do a separate feature on tools.

G

Guy Croft wrote:Rotary tools, yes.

I will do a separate feature on tools.

G

Thanks i'd find that really useful, sometimes its hard to understand the results until you see the tool that they were done with. I assume you used one of those large air powered die grinders with a flap wheel.
Guy