Ford cvh 1600 cylinder head air flow speed verses volume
Discussion
Gentlemen
Is there any head porters that have experienced this ? And can answer you confirm the possibility’s
Background, I spent many years in the motor trade before studying refrigeration. Spent many a dirty weekend building A series / crossflow etc engines for buddys porting cylinder heads using a homemade flow bench using DV’s rules of thumb. All good fun drag racing at 2am around Brum.
Many years on a friend has asked me to build him a 1600 cvh for his 1989 Xr2 restoration. He has asked for a little more HP than standard. A supply of copious JD is supplied for my efforts. Everbodies a winner. It’s Looking real good so far, the shell was stripped back and rebuilt without any rust. Engine was low mileage and good for a rebuild all be it it’s a lean burn with kidney shaped combustion chamber. Keeping it cheap I’ve built another basic flow bench, sealed properly using 3x 1500 Watts vacuum motors and using accurate refrigeration vacuum gauge to measure vacuum pressure through the spark plug hole and a air velocity tool. Simple as it comes.
The 1600 rebuild will consist of minor blue printing, I can’t be arsed for the full monty. Kent cam 22 ,standard sized valves with angle cuts on a modified kidney cylinder head with possibly the orgianal carb or twin Webber’s . Using a 4-2-1 exhaust manifold. Lighter flywheel.
Using all the porting technics I can remember and reminding my self of David vizards rules and the written advise of others like puma racing and other cvh specialists. Ive never ported a cvh before but I always modify to achieve a balance between maximum air speed and least flow restistance for a street application. Nothing worse than a street engine that picks up poorly from low rpm to only enrage it’s self topend. I had a cracking 1100 mini that would beat many 1275 / 1300 with big everything off the line to 70!
After many hours I’ve porting, blending , cut different angled valve seats etc etc I’ve ended up improving all areas of valve lift using 3mm , 5mm and 11.5mm valve lifts as starting points. I use a coloured dye mix, flow balls etc to test how ports flow. I have no meaning full cfm numbers but my vacuum results follow in Kpa pressure.
Before any modifications 3mm lift = 21 kpa vac , 5mm lift= 17 -18 Kpa vac, 11.5mm lift = 14 Kpa pressure.
After all modifications I’ve ended up with
3mm lift = 12kpa , 5mm lift= 12kpa , 11.5mm lift = 12 Kpa vacuum pressure. Air speeds increased initially especially around 3 to 5mm lift but have decreased slightly since my thinking was I had more room to allow a better flow at 11.5mm lift and took a little more out the busy sides of the port. The vacuum restance of 12kpa stayed the same but it meant the air speed was decreasing. I know I have no meaningful cfms
My question is do I take the port further and try and increase the high lift flow volume or is a result of flowing as much at 3mm lift with good air volicites a good point to stop.
Regards
Shippers
Is there any head porters that have experienced this ? And can answer you confirm the possibility’s
Background, I spent many years in the motor trade before studying refrigeration. Spent many a dirty weekend building A series / crossflow etc engines for buddys porting cylinder heads using a homemade flow bench using DV’s rules of thumb. All good fun drag racing at 2am around Brum.
Many years on a friend has asked me to build him a 1600 cvh for his 1989 Xr2 restoration. He has asked for a little more HP than standard. A supply of copious JD is supplied for my efforts. Everbodies a winner. It’s Looking real good so far, the shell was stripped back and rebuilt without any rust. Engine was low mileage and good for a rebuild all be it it’s a lean burn with kidney shaped combustion chamber. Keeping it cheap I’ve built another basic flow bench, sealed properly using 3x 1500 Watts vacuum motors and using accurate refrigeration vacuum gauge to measure vacuum pressure through the spark plug hole and a air velocity tool. Simple as it comes.
The 1600 rebuild will consist of minor blue printing, I can’t be arsed for the full monty. Kent cam 22 ,standard sized valves with angle cuts on a modified kidney cylinder head with possibly the orgianal carb or twin Webber’s . Using a 4-2-1 exhaust manifold. Lighter flywheel.
Using all the porting technics I can remember and reminding my self of David vizards rules and the written advise of others like puma racing and other cvh specialists. Ive never ported a cvh before but I always modify to achieve a balance between maximum air speed and least flow restistance for a street application. Nothing worse than a street engine that picks up poorly from low rpm to only enrage it’s self topend. I had a cracking 1100 mini that would beat many 1275 / 1300 with big everything off the line to 70!
After many hours I’ve porting, blending , cut different angled valve seats etc etc I’ve ended up improving all areas of valve lift using 3mm , 5mm and 11.5mm valve lifts as starting points. I use a coloured dye mix, flow balls etc to test how ports flow. I have no meaning full cfm numbers but my vacuum results follow in Kpa pressure.
Before any modifications 3mm lift = 21 kpa vac , 5mm lift= 17 -18 Kpa vac, 11.5mm lift = 14 Kpa pressure.
After all modifications I’ve ended up with
3mm lift = 12kpa , 5mm lift= 12kpa , 11.5mm lift = 12 Kpa vacuum pressure. Air speeds increased initially especially around 3 to 5mm lift but have decreased slightly since my thinking was I had more room to allow a better flow at 11.5mm lift and took a little more out the busy sides of the port. The vacuum restance of 12kpa stayed the same but it meant the air speed was decreasing. I know I have no meaningful cfms
My question is do I take the port further and try and increase the high lift flow volume or is a result of flowing as much at 3mm lift with good air volicites a good point to stop.
Regards
Shippers
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