Head flow, Positive boost vs. Flow Bench
#552637
12/13/09 01:13 PM
12/13/09 01:13 PM
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turbobitt
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Here is a question that is bothering me. How does flow bench under vaccuum relate to positive boost pressure flow ? Example, if my head flow flattens out at .600 lift on a flow bench, could I expect a different reaction under boost pressure ? Would flow increase ? Allan G.
1970 Challenger w/572 Hemi street car and my pride and joy.
1986 T-Type with 272 Stage 2 Buick V6 engine - True 8 second street car. Just updated the engine and put down 928 HP @ 35# boost to the ground on chasis dyno.
1976 Cee Bee Avenger Jet Boat - 460 Ford powered.
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[Re: Cab_Burge]
#552639
12/13/09 02:19 PM
12/13/09 02:19 PM
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Re: Head flow, Positive boost vs. Flow Bench
#552640
12/13/09 04:03 PM
12/13/09 04:03 PM
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turbobitt
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I undestand the relation between HP and boost. Just wondering if I should consider more lift on my cam. AG.
1970 Challenger w/572 Hemi street car and my pride and joy.
1986 T-Type with 272 Stage 2 Buick V6 engine - True 8 second street car. Just updated the engine and put down 928 HP @ 35# boost to the ground on chasis dyno.
1976 Cee Bee Avenger Jet Boat - 460 Ford powered.
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Re: Head flow, Positive boost vs. Flow Bench
[Re: turbobitt]
#552641
12/13/09 04:12 PM
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gregsdart
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Maybe another way to look at the situation is absolute pressure. 0 being a total vacuum, 14.7 psi is normal atmospheric pressure at sea level, 30 psi (14.7 plus 15.3 psi boost) about two atmospheres of pressure. Horespower will rise about the same as absolute pressure, if the efficiency of the blower/intercooler is high enough. The valve lift can remain the same, heads can remain the same, the extra pressure will put more air in the cylinder.
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
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Re: Head flow, Positive boost vs. Flow Bench
[Re: turbobitt]
#552643
12/13/09 07:37 PM
12/13/09 07:37 PM
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polyspheric
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Can't really answer the question, because some of the blower discharge is expanded into volume at low pressure (only slightly higher than normal low vacuum in the manifold), but some may still be under higher pressure between boost pressure and zero, depending on manifold volume and boost level. A 3-71 producing 5 psi into a 500" RB with a tunnel ram manifold will get the entire flow as CFM at zero to low vacuum, a 14-71 producing 30 psi into a 300" LA with a simple base plate to the manifold will have over 20 psi. Flow benches don't test density. HP will not increase linear to boost regardless of blower efficiency, because there is heating and expansion just due to the temperature rise in the engine. The Wallace calculator simply multiplies existing power by (14.696 + your boost input) ÷ 14.696, and it's wayyy too high (yes, the same mistake appears elsewhere, even on blower manufacturer sites - and still wrong). Read my article: http://victorylibrary.com/mopar/blower-c.htm
Boffin Emeritus
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Re: Head flow, Positive boost vs. Flow Bench
[Re: dodgeboy11]
#552649
12/14/09 01:54 AM
12/14/09 01:54 AM
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DakFink
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Quote:
Flow would increase, but you're thinking about it wrong. The motor doesn't know it's boosted mechanically or not. Vacuum is often used incorrectly. The engine doesn't see vacuum, it sees reduced pressure. N/A the engine sees atmospheric pressure. If you add 1 bar under boost, that's a total of 2 atmospheres. So the flow bench would have to have the pressure drop increased. I've done it out of curiosity and a port that went turbulent at 28in did indeed flow more air at 35in. I don't know what the numbers are exactly, but more pressure will force more air through the same size hole UNTIL you've got the port saturated. Which is why I go for volume on engines I know are going to be boosted.
THIS ANSWER RIGHT HERE IS ABOUT AS CLOSE TO ANY I HAVE HEARD COME FROM PROFESSIONAL TURBO RACERS ABOUT HEADS!!!!
I've had the privilege to hear and pay attention when questions about building Turbo Motrs were brough up and HEADS was always the HOT TOPIC!!
Everyone of them said your heads is where it's at! Buy the best flowing heads you pocket $$$$ can stand and go from there. The turn radius and stagnant port flow that N/A guys worry about doesn't apply as much to Boost.
Look for Port Volume and Flow the more the better.
I wish more people would flow their heads like dodgeboy11 did, especially when they know they are being set-up for Boost.
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Re: Head flow, Positive boost vs. Flow Bench
[Re: dodgeboy11]
#552650
12/14/09 11:04 AM
12/14/09 11:04 AM
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Joined: Oct 2006
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Shaker223
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Quote:
I expect it to drop your boost numbers and increase your mph:)
Believe me...I realize the stock cam and head are an obstruction!! I've always wondered bow much of the boost was making it into the cylinders with a .380"(after lash cam)
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