I finally got my Hogan manifold for my SB2.2 4-cylinder. I'm going to flow the manifold on the head, but I have a few general questions. What am I looking for? Should or will the flow drop. Are you trying to get it not to drop? Should all the runners flow the same. I've never done this before, so I need to seem stupid. I have no clue what I need to "try" to accomplish by doing this. Any help, like always, is appreciated.
Chad
Manifold Guys.. HELP!! Basic questions
Moderator: Team
-
bill jones
- Guru
- Posts: 2650
- Joined: Sun Sep 05, 2004 6:38 pm
- Location: salt lake city, ut
- Contact:
-you can test the manifold several ways, either at all the same increments you test the head, or at set the heads to flow some predetermined rate (and use that same high flow rate for each cylinder) and then pull the radius off the head and slip the intake on the head.
------------------------------------------
-Personally I feel you need to do all three, flow the head first to get all the normal numbers, then flow it again with the manifold and carburetors to see what that does, and then I'd pick some flow number about 10% down from what the head flows at max---so it flows 400----I'd pick 360 and adjust each port to flow 360 with the radius---don't care about the what the lift is---and compare head vs manifold at 360 every cylinder.
---------------------------------------
-I work mostly on heads that flow in the 275 cfm range so I chose 268 as what I test manifolds at when I'm looking for a baseline for a manifold.
--------------------------------------
-Real racing head people might be able to get the same airflow thru their manifolds as they get just thru the ports, but I have yet to find ANY manifold that doesn't cost something in airflow and I see about 1% flow loss for each .100" lift point I check but this is mainly on cast aluminum single four barrel manifolds and individual stack injection.
-----------------------------------------------------------
-I would think you should be seeing all of the sheet metal manifold runners flow within onesy-twoseys of each other and the total losses I would expect to be less than 8% at .800" lift.
-------------------------------------------------------
-I would not waste my time flowing the manifold with NO carburetors or throttle bodies because the position of the throttle bores affect the end results.
----------------------------------------------------------
-I feel like you want all the flow you can find but you have to have some empirical data to know what is acceptable, and if you have swirl meter or a charge motion system make sure you pay attention to what that's telling you because it may all make some sense some day
------------------------------------------
-Personally I feel you need to do all three, flow the head first to get all the normal numbers, then flow it again with the manifold and carburetors to see what that does, and then I'd pick some flow number about 10% down from what the head flows at max---so it flows 400----I'd pick 360 and adjust each port to flow 360 with the radius---don't care about the what the lift is---and compare head vs manifold at 360 every cylinder.
---------------------------------------
-I work mostly on heads that flow in the 275 cfm range so I chose 268 as what I test manifolds at when I'm looking for a baseline for a manifold.
--------------------------------------
-Real racing head people might be able to get the same airflow thru their manifolds as they get just thru the ports, but I have yet to find ANY manifold that doesn't cost something in airflow and I see about 1% flow loss for each .100" lift point I check but this is mainly on cast aluminum single four barrel manifolds and individual stack injection.
-----------------------------------------------------------
-I would think you should be seeing all of the sheet metal manifold runners flow within onesy-twoseys of each other and the total losses I would expect to be less than 8% at .800" lift.
-------------------------------------------------------
-I would not waste my time flowing the manifold with NO carburetors or throttle bodies because the position of the throttle bores affect the end results.
----------------------------------------------------------
-I feel like you want all the flow you can find but you have to have some empirical data to know what is acceptable, and if you have swirl meter or a charge motion system make sure you pay attention to what that's telling you because it may all make some sense some day
Bill is right, most manifolds kill flow.
I have seen some instances where the manifold will actually help the flow however. The runner entry to the head allowed the flow pattern at the entrance to the port to be more favorable.
Bill is also spot on because the manifold used will possibly change the mixture motion in the cylinder.
Just start doing it and see what you find.
SWB
I have seen some instances where the manifold will actually help the flow however. The runner entry to the head allowed the flow pattern at the entrance to the port to be more favorable.
Bill is also spot on because the manifold used will possibly change the mixture motion in the cylinder.
Just start doing it and see what you find.
SWB
Just so you know - this can be done.
My intake runner shape picked up 9 cfm over the head alone, (with a radius port entry,) and 6 cfm with the carb.
Translated to a solid 12 to 15 hundreths and 1.5 mph 1/4 mile increase over a ported Victor. Runner angles are crucial. Naturally aspirated.
Don't ask. (Are you nuts?) It can be done.
I'm sure I can do better. Hell, I'm still learning.....
My intake runner shape picked up 9 cfm over the head alone, (with a radius port entry,) and 6 cfm with the carb.
Translated to a solid 12 to 15 hundreths and 1.5 mph 1/4 mile increase over a ported Victor. Runner angles are crucial. Naturally aspirated.
Don't ask. (Are you nuts?) It can be done.
I'm sure I can do better. Hell, I'm still learning.....
Function - the hidden math.
http://www.pontiacengines.com
http://www.pontiacengines.com
Also, if you are trying to determine if the manifold runner is the specific cause of a flow loss, flow it with the plenum-top removed. Often, a sheet metal intake will show a bad loss, and part of this is due to an "unnatural" condition of flowing through the carb, or carb opening into a large plenum with only one runner creating the signal. This condition can show big expansion losses as the air flows from the carb at hi-speed into a vast open space (plenum) The condition with all the cylinders pulling would be much different. Maybe someone like Darin can help with what is, and isn't valid in such a test. This condition isn't nearly so bad in a single plane manifold as the plenum shape(similar width of the carb base) doesn't compound the losses under the carb as does a sheetmetal type plenum. ( wide and long) . Emperical results in flow-test vs dyno/track results would be vaulable in giving a real value to your test results.