Fixing bad port work...
Posted: Sun Jan 09, 2005 3:02 am
I ported a set of 034 bowties for a friend about 7yrs ago and recently got them back to try to apply what I have learned here over the past few months. I bought pitot tubes and hooked them to a digital readout and made a few mods to my bench to read higher pressures/depressions.
The engine is 355 13:1, changing to roller cam 268/276 108lsa, Victor Jr, 750 carb., 1.875 heades, 5500 conv, 3200lb car, 5.13 gear, 9" tires, ran 6.89 @100 in 1/8 in ~ 1000ft DA weather with these heads and solid cam 264/270 .600".
The heads have 2.055/1.6 valves. Ports were ~198cc's. Avg CSA was ~2.29sq.in.
Problem #1:
The int. valve throat is 1.86" (90.5%)or 2.62sq.in., I know its too big. The pushrod area was 2.20 sq.in. (too small) and the area before the short turn was about 2.25sq.in.
Problem #2:
The intakes flowed 270cfm(28") @ .600" and gained slightly on up. When I flow the port @ 40" the flow goes down above .500" lift.
Problem #3:
The intake seats were radiused/blended not sharp on all angles.
To fix #3 The seats were redone but couldn't get edges under 60 in all places, but 45-30 in chamber and 60-45 in bowl are now sharp and some have 75-60 sharp. Are these the most critical edges? Will this help? Back cuts will be put on the intake valves since the bench showed with the new seats that back cuts were better. (they weren't before)
To attempt to fix #1 I opened the pushrod up as much as I can (~2.45sq.in now) and enlarged the area above the turn (~2.45 sq.in.). I can't get them as big as the valve throat without welding etc. (beyond the scope of this project). I also layed short turn back and bigger radius to fix #2. The port now flows 270+cfm when flowed @40" and converted back to 28" and doesn't "back up" at high lifts. I tested velocity (28" depression) and got a high of 322fps and low 264fps (avg 294, std dev 18) checking 9 places at the pushrod. The short turn is a high of 400fps and low of 242 (avg 309, std dev 55) checking 9 places also.
It appears that the short turn will have a choke problem according to Larry Meaux's previous posts on port velocity. The pushrod looks OK? Is there anything else I can do to correct this or at least minimize the effect of it?
Putting a bigger valve in would seem to be adding to problem #3 but would help problem #2. If a bigger valve went in the seat angles would be better and the throat % would be less. The disch. coef. would get worse since the flow can't pick up much with this CSA. Is staying with the 2.055" valve the best plan?
Lessons learned for next time, but what about these? Should we scrap them?
Sorry for the long post but I wanted anybody willing to help to have as much info as possible. Thanks for any help or advise. I haven't even started on the exhaust yet.
Thanks,
Rick
The engine is 355 13:1, changing to roller cam 268/276 108lsa, Victor Jr, 750 carb., 1.875 heades, 5500 conv, 3200lb car, 5.13 gear, 9" tires, ran 6.89 @100 in 1/8 in ~ 1000ft DA weather with these heads and solid cam 264/270 .600".
The heads have 2.055/1.6 valves. Ports were ~198cc's. Avg CSA was ~2.29sq.in.
Problem #1:
The int. valve throat is 1.86" (90.5%)or 2.62sq.in., I know its too big. The pushrod area was 2.20 sq.in. (too small) and the area before the short turn was about 2.25sq.in.
Problem #2:
The intakes flowed 270cfm(28") @ .600" and gained slightly on up. When I flow the port @ 40" the flow goes down above .500" lift.
Problem #3:
The intake seats were radiused/blended not sharp on all angles.
To fix #3 The seats were redone but couldn't get edges under 60 in all places, but 45-30 in chamber and 60-45 in bowl are now sharp and some have 75-60 sharp. Are these the most critical edges? Will this help? Back cuts will be put on the intake valves since the bench showed with the new seats that back cuts were better. (they weren't before)
To attempt to fix #1 I opened the pushrod up as much as I can (~2.45sq.in now) and enlarged the area above the turn (~2.45 sq.in.). I can't get them as big as the valve throat without welding etc. (beyond the scope of this project). I also layed short turn back and bigger radius to fix #2. The port now flows 270+cfm when flowed @40" and converted back to 28" and doesn't "back up" at high lifts. I tested velocity (28" depression) and got a high of 322fps and low 264fps (avg 294, std dev 18) checking 9 places at the pushrod. The short turn is a high of 400fps and low of 242 (avg 309, std dev 55) checking 9 places also.
It appears that the short turn will have a choke problem according to Larry Meaux's previous posts on port velocity. The pushrod looks OK? Is there anything else I can do to correct this or at least minimize the effect of it?
Putting a bigger valve in would seem to be adding to problem #3 but would help problem #2. If a bigger valve went in the seat angles would be better and the throat % would be less. The disch. coef. would get worse since the flow can't pick up much with this CSA. Is staying with the 2.055" valve the best plan?
Lessons learned for next time, but what about these? Should we scrap them?
Sorry for the long post but I wanted anybody willing to help to have as much info as possible. Thanks for any help or advise. I haven't even started on the exhaust yet.
Thanks,
Rick