924Board.org

[Kenodog]

[Lefty]

Cedric, many thanks for your response,
Lefty
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One less beige car

[MikeJinCO]

The valve seats were definitely hard, sliced thru them with a mini grinder cutoff wheel, then took to the bandsaw. I think the valve seat leaded fuel issue was primarily for the use of unleaded fuel in cast iron heads with no seat inserts, JMHO.
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Mike


'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild)

[MikeJinCO]

I would like to see any ideas on improving the flow in the 931 head as I would like to use on on my track car. The exhaust side is much better than the NA exhaust due to the larger valve and port volume. With out looking at my data at least 15% greater with numbers similar to the stock NA intake or 140cfm range. The 931 port shape is difficult to improve as the offset kidney shape is better than a round port for a NA application as it directs the airflow toward the center of the cylinder rather than toward the cylinder wall with its valve shrouding. With a pressurized intake I thank all the old literature which concentrated on NA applications can get thrown out the window although I may well be wrong about that. 6 or 7 psi thru the entire valve cycle compared with a variable negative pressure from 0 to minus 2psi is like comparing apples to oranges.

One of the local racers and a well respected Datsun motor builder who has a flow bench told me that on a NA head like ours and apparently the Datsun 240Z type with rather poor head designs with tight radius ports the problem is more often exhaust restriction more than intake flow.
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Mike


'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild)

[ideola]

[gegge]

[MikeJinCO]

OK, I'm not totally sure I'll buy that. I'll just continue on with what I'm doing and I'll see how it turns out.
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Mike


'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild)