Hi, Brendan,
I carried out some porting and polishing on a BMC A-Series engine some
years ago and did get a noticeable increase in power, particularly in
the mid range. being quite mildly tuned, the engine still ran sweetly.
Here are some do's and dont's I picked up along the way...
1. Just polishing is an academic exercise.
2. Polishing inlet ports to a high finish upsets the mixture
distribution-the rough cast finish helps the fuel droplets break up.
3. Work with the guidance of an expert-I used David Vizard's book for my
job.
3. After polishing and porting, balancing the combustion chambers for
capacity is very effective.
4. So is matching the manifold ports and gaskets.
5. So are radiusing the valve guides and any sharp bends and steps in
the casting.
So, what I did was...
1. Practised on a scrap head first.
2. Did the work slowly and carefully.
3. Used a fast road cam.
4. Replaced the twin SU HS2s with a single 28/36 DCD Weber.
5. Used a big bore, three-branch tubular header with free flow exhaust.
6. Made sure the ancillaries-distributor, fuel pump, oil pump, timing
chain, etc.-were up to the task.
Generally, factory engines are built to run but can be made to run
better. Hidden 'blueprinting' tasks, like having the
crank/flywheel/clutch assembly dynamically balanced, matching conrod
(end for end) and piston weights and lightening appropriate parts are
also beneficial. The main thing to remember is not to work blind because
it's laughably easy for horrors to happen. People have been known to
break through into oil/water galleries, take too much off conrods and
over-lighten flywheels to the point where they go bang and blow your
knees off.
IMHO, The best investment is a good tuning guide, preferably for your
particular engine-if you can find one.
Hope my experience helps,
Dave Hill
Brendan Shay wrote:
>
> I've got the urge to get a little more power out of my Fergeson 4-banger in
> my TR4 and was wondering if anyone could tell me if they've tried polishing
> the heads or ports, etc. Is there noticeable increase in power, and is this
> something I can do myself? Also thinking of purchasing second cam that
> would be mild street setup - how much power increase should I see (I've
> already got the 87mm bore piston & liner set and engine is freshly rebuilt)
> I figure why not take advantage for a little more 'pep'.... What do the
> wise LBC owners have to say about this?
>
> Brendan O'shea
> '64 TR4
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