The head is hopefully going to be one which I can run for a long time. It began it's life as a low compression emission head on a European triumph 1500. It has no air injection ports which is rare for North America. The head has the larger but not largest valves as standard but it does have hardened valve seats installed. Once the majority of the porting and I decide which valves I am going to the use, the head is going to get a massive .165" skim which should bring me up around 10:1 compression. I will them work on removing some of the shrouding from the inlet valve. Minimal modifications though. Just enough to help it a bit as it will almost be toughing the wall of the combustion chamber.
To start of this head I needed a better depth gauge. Here is v2.0 which has a much nicer point, adjustment and grip. Depth is set to 2.0mm for the first pass on the short side radius.
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| Depth Tool v2.0 |
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| End is profiled to sit flat against port walls |
As far as actual port work. Today I concentrated on smoothing the manifold side of the intake ports. For this I just take one of my 1.250" (1147cc inlet) valves which is coincidently the exact same diameter as the entrance to the port and the inside diameter of the valve seat AND more importantly is perfectly within the 81-83% of the intake valve
diameter as outlined by A. Graham Bell in Four-stroke performance tuning (Chapter 2, Page 16). I work this down the port until the beginning of the short side radius. It would fit clean through the port although there is a bit of a pinch about 1/2" in similar to the other manifold, once I worked through this section it was clear sailing to the ssr. This should give a much smoother path keeping the port velocity very similar to what it is in the manifold.
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60 Grit Flapper Wheel Finish on the long side of the port
(least important but easiest to photograph) |
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| No More Pinch Area |
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Core Shift. I chose not to remove the material needed to
smooth this surface in order to keep the port volume and
diameter consistent. Goal wasn't to remove material |
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| Core Shift wasn't as noticeable on these two ports |
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| But they did have some on both side unlike the others |
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LARGE step right below the valve seat.
I'm deciding how to go about it. |
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| Another shot of this step which is present in all intake ports. |
I also got the second dash-pot back today which had been shortened .100" the same as the other which brings the piston perfectly flush with the carb body at the REAR of the piston. I will install these in the morning. I am also running springs which are shortened to give 2.5oz force at 2.625" which is very close to 2oz of pre-load when installed. (~1.25" shorter than standard 4.5oz @ 1.625 springs). Modification was done using a nice digital scale which has come in very handy. Pistons are also within a gram of each other.
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| Unaltered on Left, Altered on Right |
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I don't run dampers. Incredible change in pickup.
No negative effects so far, no flutter or lean. |
The only modification I have made to the actual casting bodies was to clean up the casting in this area. The piston bore is straight down and clear but the through bore has a bit of a casting ridge where it meats the piston bore. I smoother this ridge out both before and after the piston bore. What a bore, and it probably don't make much of a difference but it looks much cleaner and shouldn't rub again the piston.
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| Casting Cleanup Area |
My philosophy is that if I do 10 things which only gain 1hp each that's 10 hp. On their own each is insignificant but in the whole picture they each contribute. Make all the small gains as well as the easy one. The small gains are usually much cheaper and DIY too.
