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2.0 Head Tuning

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2.0 Head Tuning

I bought a second-hand but unused and "as new" 1.9 Ascona CiH cylinder head a few years ago and it's still sitting in my garage since I went all V8 Manta powered. With the new cylinder head I also got some photocopies from an old car magazine of some Manta head tuning articles. There's a lot of talk, testing and speculation but I managed to glean some items of info from the pages that I thought you might find useful...

The article mainly goes into the cfm (cubic feet per minute) of airflow and ways of improving horsepower for road-going vehicles with bigger valves and trick cams.

  • The valve guide boss on the injection head is smaller than on the GM carb head - 10mm on the inlet side.

  • Standard valve sizes are 42/37 (inlet/exhaust) but can go up to 45/40 for a road-going car.

  • Manta cylinder heads can be (apparently) prone to split across the seats (inlet to exhaust) and a wider valve (46mm+) will only accentuate this on a high-mileage road car.

  • Standard Flow on an injection head is virtually identical to the carb head - 85 cfm on the inlet at 400 thou lift

  • A well-flowed head can achieve over 100 cfm on the inlet at 400 thou lift (30/45/60º cut seats, removing most of the valve guide boss.)

  • Beware - over-shortening the valve guide bosses can lead to rapid valve wear.

  • Often, by using bigger inlet valves (Carlton 2.2) and leaving the exhaust valves as standard will suffice. The standard Manta exhaust valves are very efficient anyway (flowing 75-82% of the inlet) and bigger exhaust valves are purported to only add 1-2 bhp.

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