Porting

[Tom Coates]

I know this subject has been discussed a few times previously, but probably ripe for another airing...
 
My engine has a new block from Tony which was fitted a couple of years ago with only minimal cleaning up of the ports which are therefore fairly rough and probably not very efficient. I’d like to improve it as much as is worthwhile for a for a fast road engine.
 
Firstly I don’t really want to take the engine out if I can avoid it, is it feasible to work on the ports in situ? Access is obviously not as good as having it up on a bench, but I think I can cope with that if I maybe take the front NS wing off. The other issue is stopping crud from going down into the valve chest and bores – these could probably be masked off and the valve guides plugged. Has anyone done this or is it daft? At least I wouldn’t need to clamp the block down!
 
The other question is how far to go, is it worth adding epoxy putty to the bottom corner on a road engine with a single carburettor, or better to stick to just smoothing out the inside radius and lumpy bits?

At the moment I can get up to about 38mph in 1st gear at the bridge at Prescott, which is about 5300rpm, it would be nice to squeeze a few more MPH out of it, but it is probably also limited by various other factors such as cam and carburettor which I don't want to fiddle with.

[Chris KC]

I'd leave it alone...

[Alan]

I wouldn’t even think about it without the block off the car. If you are going to do it, you need to do it properly and that probably involves big inlet valves and recut valve seats.
But, why do you need to do it anyway? What carb are you running and what manifolds?

[Speedex750]

Hi Tom,
I know we all like doing this putting our own bit of magic into the engine but frankly it doesn't make any difference. Flow bench testing has shown that the port is if anything already too big. If it's running OK as it is I'd be tempted to leave it alone, especially if you're wanting to do it insitu but taking the wing off? At most three angling the seats with a bottom 60 degree cutter to narrow the seat is about as far as you need to go and could be just about done without taking everything out. I tried building the ports on one of my engines with plastic metal as they did in the 750 days, even with a twice blasted port I subsequently found a bit missing though it seemingly hadn't done any damage. If you're wanting a bit more; try the things Jack French advised in In Sheeps' Clothing, it's a good read.

Dave

[Stuart Giles]

Not worth doing a lot of work on the ports unless you have decent carburation and exhaust; factory valve springs won't go any/much over 5000 RPM either. As Alan says, getting a really decent shape in the valve throat -the biggest restriction in the port area- really involves increasing the valve size. If you do any work on the inlet ports, the "short side radius"  -which is actually a sharp right angle on factory blocks is where the bulk of the flow happens, so is the best place to be concentrating on. This is a block I did some work on where you can see that there is now a short side radius rather than a near knife edge right angle at the valve throat.

[Special Bits]

I was fiddling around with blocks yesterday, trying to find a decent one out of several we have, not overly successfully.

Anyway, sticking my finger down the inlet of a standard block (like you do) from the valve side, reveals the nasty pocket and step next to / behind the stud web. I did wonder if filling that with plastic metal would be advantageous?
Some of this is cut away and opened out with big valves, but far from all of it.

looking at Stuarts lovely block above, its amazing how much can be removed from the short side (top) to produce a nice radius where there is a nasty sharp edge as standard.

Stuart Palmer.

[Bob Culver]

The Willaims book recommends removing the reinforcing ribs for the studs and in the naievety of youth I did this years ago. but it seems cruel and the port is very large there anyway. Would not dream of doing to a new block.

[Tom Coates]

I wouldn’t even think about it without the block off the car. If you are going to do it, you need to do it properly and that probably involves big inlet valves and recut valve seats.
But, why do you need to do it anyway? What carb are you running and what manifolds?

Alan, I have already got big inlet valves and double valve springs. It has a Solex 30MOV carb and tubular exhaust manifold.
Seems like a job best done off the car though!