Saturday, May 3, 2014

Spare Engine - Porting the Head

As porting the head is simply a means of getting more gas through the ports, it should be fairly straight forward to make improvements. Just make the holes bigger! If only it were so simple. Porting seems to be an art-form that requires the skills of a sculptor and the experience and knowledge of an engineer. Neither of which I have at my disposal. Also I really need a flow bench to check how the modifications effect the Cubic Feet per Minute (so that's what CFM stands for!). I had a look around, and I don't seem to have one to hand. What I do have though is a scrap head to use for practice, some sub standard tools, a book and lots of determination.
The Big Yellow Bible.

After reading the chapters in David Vizard's Big Yellow Bible on porting, it seems that the A-Series head was designed with manufacturing ease in mind and not performance. So almost any modification should result in an improvement. I'm not really interested in massive performance gains here, so I am not looking to squeeze every ounce of power out I can. I just want to focus on improving the part of the head that is creating the largest obstruction and make some modest gains.

According the book, enlarging the ports where the manifold sits offers the least improvement as this is the area where the flow is at it's best. The area of focus to get best improvements is the throat area (just inside the valve seats) and increasing the size of the valve holes themselves. Apparently polishing also offers minimal performance enhancements as the emphasis is on shape and not texture. If absolute peek performance was the goal, I'm sure polishing might give that little bit extra, but it's not for me.

Looking inside the exhaust valve holes and down the throat, it's obvious that there is quite a lot of 'bottle necking' going on just around the area where the valve guide appears and then down into the port. The inlet holes don't look to be as badly constricted, but may benefit from a little work

Practice makes possible
I ordered a small set of mini grinding stones of Ebay quite cheaply and mounted them in my drill.

A Dremel type tool would have been perfect for this, but as I don't have one, I will have do make do with my budget power drill from Wilko. It may have been cheap, but it does have variable speed, which was essential. I found that if I mounted the grinding tool in the drill chuck with the minimum amount possible in the jaws, it was just about about long enough to reach through the valve hole and down into the port to do the grinding.

Using the scrap head for practice, it proved to be a very difficult job, maneuvering the stone to where it needed to be to cut away the unwanted metal without damaging the valve seat or the gasket surface. But I spent several hours practicing and worked out the best rotation speeds and angle of entry to avoid scuffing the head with the chuck. I also discovered that this job requires monumental amounts of patience as the stones hardly remove any metal at all, so progress was slow.

I wouldn't say that practice made perfect, but it did make it possible. Also the practice made me realise that there was a real risk of damaging either the valve seat or scuffing the gasket surface with the chuck of the drill, so less was indeed more for me here. It made me re-focus again on priority. So I decided to work on the exhaust throat area and leave the inlets alone. The inlet also has the problem of the valve guides being in the way, so another reason for me not to mess with them.

I found that one of these circular sand paper on a stick things (see pic below) seemed to work quite will on the inside diameter of the valve holes. I didn't do too mad here as the risk of slipping and damaging the valve seats seemed likely.

This probably has a name, but I'm calling it a thingy.

Putting practice to use.
Moving on to the working head, I used the experience gained and started work on the first exhaust port. Slowly, patiently I ground away at the unwanted metal and managed to get a much better shape without any mishaps. The picture below highlights the problem the exhause valves face. I'ts almost a step.

Chunky Step

After many hours (days it seemed), I ground the step down to a nice gradient that lead down into the port. As it turns out, photographing it is as difficult as doing it. I did my best to get a shot that shows the gradient sloping away into the port where the step once was.

No Step!

The other three exhaust ports were much the same story. But by the time I got to the final one, all of my mini grinding tools were pretty worn out, but I just managed to get the result I wanted with what was left.

Then it was just a quick skim around the internal diameter of all the ports, just to open them slightly and that was that. Total time on this project on and off is just too much to contemplate.

This is a proper 'have a go hack' and the big question is, will it make any difference at all. I guess I will never know until I try it out and see if there is any improvement to the performance. I'm hoping that there will be an appreciable improvement to the car when the head is tested Then at least this experience was of some use, but if there's not, well I'll just have to accept that this has been a monumental waste of my time and rethink my porting strategy.

Given the complexity and skill level porting demands, it's something that's probably best left to the professionals, especially if you are looking for high end performance. In my case, I'm just looking to make a few modest improvements, so I thought why not give it a go! Nothing ventured nothing gained.

Was it fun? Well it did start out as fun and the research was very interesting, but I have to admit that the limitations of the crappy tools I have and the sheer amount of time needed grinding, it did become more of a chore towards the end.

Would I do it again? If there's an improvement, definitely I would go through it all again on another head and might even experiment further on the inlet ports.

<Next Post> - 'Spare Engine - Rocker Refurb'
<This Post> - 'Spare Engine - Porting the Head'
<Previous Post> - 'Spare Engine - Lapping the valves'

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