Q on flow testing cylinder heads

I was wondering, when you flow test heads on a supercharged car don't you need to test them with the same psi as the blower is going to make? If so, wouldn't having higher exhaust cfm be better then having higher intake cfm? you can always crank up the boost a bit to make up the difference, right? Thanks for any responses.

-Darrel

D-bird said:

I was wondering, when you flow test heads on a supercharged car don't you need to test them with the same psi as the blower is going to make? If so, wouldn't having higher exhaust cfm be better then having higher intake cfm? you can always crank up the boost a bit to make up the difference, right? Thanks for any responses.

-Darrel

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Derrel

On my Dads flow bench he flowed my heads with max flow rate to see if he was gaining or loosing when porting. He did the exhaust with the Kooks header on the head and than without. Wish he was still here he would give you a complete run down on head flowing. He flowed it with intake and exhaust valve in the head with dial indicator open the valve to the cam max lift same with exhaust valve

D-bird said:

I was wondering, when you flow test heads on a supercharged car don't you need to test them with the same psi as the blower is going to make? If so, wouldn't having higher exhaust cfm be better then having higher intake cfm? you can always crank up the boost a bit to make up the difference, right? Thanks for any responses.

-Darrel

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No the standard way is the way it's done. at 28 inches of water.

Jeff

J57ltr said:

No the standard way is the way it's done. at 28 inches of water.

Jeff

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That doesn't make sense to me. Wouldn't the pressure difference change the rate of flow?

-Darrel

Jim Demmitt Jr said:

Derrel

On my Dads flow bench he flowed my heads with max flow rate to see if he was gaining or loosing when porting. He did the exhaust with the Kooks header on the head and than without. Wish he was still here he would give you a complete run down on head flowing. He flowed it with intake and exhaust valve in the head with dial indicator open the valve to the cam max lift same with exhaust valve

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My thought was similar to your Dads except I was thinking through the entire intake system from the blower to the exhaust manifolds/headers. If I only had money, time, and more know-how.....That's what I get for going to college....


-Darrel

Yes but you are compairing it to a standard. Cylinder head flow is measured in inches of water (the standard). You use this standard to determine how much airflow is restricted.

Jeff

J57ltr said:

Yes but you are compairing it to a standard. Cylinder head flow is measured in inches of water (the standard). You use this standard to determine how much airflow is restricted.

Jeff

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That makes sense now, but wouldn't better balance in I/E numbers be achieved testing under higher pressure for a boosted car? I completely understand the use of a standard for a N/A car, but boosted cars are in a completely different world, so to speak. To me that'd be like having your car dyno tuned at 5000 ft, then racing it at sea level....

-Darrel

D-bird said:

That makes sense now, but wouldn't better balance in I/E numbers be achieved testing under higher pressure for a boosted car? I completely understand the use of a standard for a N/A car, but boosted cars are in a completely different world, so to speak. To me that'd be like having your car dyno tuned at 5000 ft, then racing it at sea level....

-Darrel

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E would not really be affected by boost pressures, and math can be used to detrimine airflow at X CFM.There are correction figures for alititude.

I haven't seen exactly how the air is drawn through the head or how it's blown out. The only one I have seen I think had a regen type blower(Sounded like a vacuum cleaner). I can imagine that at those pressures that it would take a much larger unit, or a roots at a MUCH higher cost, plus the cost of the motor. Also when your exhaust is done sometimes they use a tube on the exhaust and on the inlet clay to give the head a nice entry. There are a lot of varibles.

Jeff