Nice that you bring up the subject of porting, David. A little shaping where the intake ports come closest together, some sanding rolls to smooth things out (no polishing, ruins the boundary layer) can make a significant improvement in both power and smoothness on Solex or Weber motors. Even Zenith motors can be improved, although liking slightly different contouring as I remember. I hope Vic will offer some help here because he has a flow bench and he's good at explaining things. Photos don't show the subtlety very well.
Proper parts, clearances, combustion chambers, so forth, are of course all critical to assembling good-running motors, and are talked about a lot on this forum and all sorts of the old literature. I know some people say a little porting won't help for street use (and too much WILL hurt), but I've made some super running motors by paying attention to porting.
22degree heads with 30degree big bore kit?
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Re: 22degree heads with 30degree big bore kit?
Craig; I will chime in on Zeniths on a racing 1300 engine. The heads took an incredible amount of work and development. One thing I did do was to use B heads; small ports. 3/4 of the port was left alone. The inner radius was turned into a literal "D" shape. With HIGHLY modified Zeniths, the engine pulled 8000 rpm at the end of the Mid-Ohio straight with a 3C top gear. Horsepower about 140.
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Re: 22degree heads with 30degree big bore kit?
The only thing I will add to the conversation regarding porting is that keeping up the velocity of the charges was probably the most important aspect that had to be aimed for. Hogging out the inlet tract and putting in bigger valves and ports hurt the flow but correct shape of the whole of the inlet tract and matching of flows from carb on down gave the best results.
If I had known I would live this long I would have pushed the envelope a little harder.
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Re: 22degree heads with 30degree big bore kit?
Vic, excuse a dumb question: when you say the inner radius was turned into a D shape, which side was the flat side, the inner radius? I have read that the flow typically bounces off the inner radius and hits the outer side of the valve opening, and that much of the valve circumference experiences very little flow.Vic Skirmants wrote:Craig; I will chime in on Zeniths on a racing 1300 engine. The heads took an incredible amount of work and development. One thing I did do was to use B heads; small ports. 3/4 of the port was left alone. The inner radius was turned into a literal "D" shape. With HIGHLY modified Zeniths, the engine pulled 8000 rpm at the end of the Mid-Ohio straight with a 3C top gear. Horsepower about 140.
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Re: 22degree heads with 30degree big bore kit?
And that's why the inner radius is so important; if you get that right, the valve experiences very good flow. As I said, and you repeated, "the inner radius was turned into a D shape". You need to read better books.DaveErickson wrote:Vic, excuse a dumb question: when you say the inner radius was turned into a D shape, which side was the flat side, the inner radius? I have read that the flow typically bounces off the inner radius and hits the outer side of the valve opening, and that much of the valve circumference experiences very little flow.Vic Skirmants wrote:Craig; I will chime in on Zeniths on a racing 1300 engine. The heads took an incredible amount of work and development. One thing I did do was to use B heads; small ports. 3/4 of the port was left alone. The inner radius was turned into a literal "D" shape. With HIGHLY modified Zeniths, the engine pulled 8000 rpm at the end of the Mid-Ohio straight with a 3C top gear. Horsepower about 140.