Port and Polish by Comiittee thread (Cool pics throughout)
05-11-2017, 04:33 PM
#408
05-11-2017, 05:20 PM
#409
Rainman
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Thanks.
Was trying to calculate (via right triangles
) how far down "vertically" the valves stick out at max lift without having a head in my hands...for valve relief planning.
Was trying to calculate (via right triangles
) how far down "vertically" the valves stick out at max lift without having a head in my hands...for valve relief planning.
05-12-2017, 11:07 AM
#410
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It is damn hard to measure if it 28 degrees or 27.4 degrees. Greg, from where did you get that information about the combined included angle? My thinking is why has Porsche chosen such an awkward angle as 27.4 degrees if it is correct?
Åke
Åke
05-13-2017, 03:40 AM
#413
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Found this at Jenniskens. Seems, when introducing the S4 compared to the precursor the S3/86.5, Porsche changed the combustion chamber to 3mm shallower, with larger valves and a slightly change of the valve included angle (27.4 degrees versus 28). I can see two reasons for changing the angle. First the head of the valves will be better adapted to the combustion chamber wall. Two there will be a slight increase in distance between the seated intake and exhaust valves. However the increase is minimal about 1.2mm which cannot be justified as there is hardly no overlap.
Åke
"Amazingly, an even better 928 was on the way. It arrived for 1987 in all markets except Australia as the Porsche 928S 4 (denoting a “fourth series”). “Porsche raises the price and rewards of automotive hedonism one more time,” said Car and Driver.
And how. Emissions-legal horsepower was now 316 at 6,000 rpm, torque 317 pounds/feet at 3,000 rpm. This was accomplished with revised cylinder heads with larger valves, combustion chambers that were shallower by 3 mm, a narrower valve angle (27.4 degrees versus 28), altered valve timing, and a new, more compact two-stage intake manifold. The last comprised twin resonance chambers or tracts -- one long, one short -- feeding air to the intake pipes via a Y-shaped passage from the throttle body. Below 3,500 rpm the engine breathed only through the long tract; above that, depending on throttle position, a butterfly valve in the second tract opened to increase airflow. Porsche claimed this setup ensured at least 300 pounds/feet of torque from 2,700 to 4,750 rpm, a “fat” torque curve, indeed."
http://jenniskens.livedsl.nl/Evoluti...%20history.htm
Åke
"Amazingly, an even better 928 was on the way. It arrived for 1987 in all markets except Australia as the Porsche 928S 4 (denoting a “fourth series”). “Porsche raises the price and rewards of automotive hedonism one more time,” said Car and Driver.
And how. Emissions-legal horsepower was now 316 at 6,000 rpm, torque 317 pounds/feet at 3,000 rpm. This was accomplished with revised cylinder heads with larger valves, combustion chambers that were shallower by 3 mm, a narrower valve angle (27.4 degrees versus 28), altered valve timing, and a new, more compact two-stage intake manifold. The last comprised twin resonance chambers or tracts -- one long, one short -- feeding air to the intake pipes via a Y-shaped passage from the throttle body. Below 3,500 rpm the engine breathed only through the long tract; above that, depending on throttle position, a butterfly valve in the second tract opened to increase airflow. Porsche claimed this setup ensured at least 300 pounds/feet of torque from 2,700 to 4,750 rpm, a “fat” torque curve, indeed."
http://jenniskens.livedsl.nl/Evoluti...%20history.htm
Last edited by Strosek Ultra; 05-13-2017 at 04:21 AM.
05-13-2017, 12:48 PM
#416
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Erkka has been so kind to provide us with a sectional image of the S3 head but is there a similar image of the S4 head which is supposed to be different? When I get the time I will try to measure the angles on a S4 head using more sophisticated equipment.
Åke
Åke
05-15-2017, 03:49 PM
#419
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For you guys who want the exact figures fetch a pen and paper. In order to be able to measure the angles correctly I had to turn a long rod with a perfect fit into the lifter bore. I have some advanced angle measurement tools which I hardly ever use because it is time consuming. I did the measurement on two different S4 heads but only at one cylinder of each head. The 928 S4 intake valve inclined angle is 14.2 degrees. The exhaust valve inclined angle is 13.2 degrees. Adding it up I find the combined included angle to be 27.4 degrees which is the same as stated by Porsche so I believe my measurements are correctly made.
Åke
Åke
05-15-2017, 05:26 PM
#420
Ake, All of Porsche's modern engines like the GT3 up to the 997 model used 27.4 degrees. It in magazines like Race Engine Technology. Also I did a rough measurement with rods myself. When I got to a bit more than 27 degrees I thought it must be 27.4 degrees.