Max power and cylinder head flow
Thread Starter
TECH Fanatic
Joined: Nov 2001
Posts: 1,347
Likes: 1
From: Freeland, MD
Max power and cylinder head flow In the latest Car Craft, there is an article on porting cylinder heads that gives the following formula:
max hp = cyl head cfm * 0.2575 * # of cylinders
This formula is supposed to give the maximum power a well set-up street engine would give per level of intake flow. Does anyone know what this is based on? One thing that seems clear to me is that this could vary between EFI and carb engines. Car Craft, unfortunately like most of the rodder mags, has not switched its emphasis over yet to the EFI world.
If this is roughly true, then all motor setups and a 0.550" lift cam should be able to yield the following power levels (head flow numbers adjusted by intake manifold):
Heads Intake Flow at 0.550" Ptnl Max Power
LS1 LS1 229 cfm 471 hp
LS1 LS6 241 cfm 492 hp
LS1* LS1 251 cfm 517 hp
LS1* LS6 277 cfm 570 hp
LS6 LS6 263 cfm 542 hp
LS6* LS6 280 cfm 577 hp
* Ported heads
(Thanks to kewlbrz for originally posting the heads/intake flow numbers used above) Obviously, cubic inches have to factor in here as well, since a smaller diplacement motor can only flow the full head potential if it is really spun up. This is likely why some of the 422s are exceeding 577 hp in very driveable form, while I have not seen too many (any?) LS6 heads/cam/LS6 intake 346s getting 500 RWHP.
[ January 17, 2002: Message edited by: WeatherGuy ]
[ January 17, 2002: Message edited by: WeatherGuy ]</p>
max hp = cyl head cfm * 0.2575 * # of cylinders
This formula is supposed to give the maximum power a well set-up street engine would give per level of intake flow. Does anyone know what this is based on? One thing that seems clear to me is that this could vary between EFI and carb engines. Car Craft, unfortunately like most of the rodder mags, has not switched its emphasis over yet to the EFI world.
If this is roughly true, then all motor setups and a 0.550" lift cam should be able to yield the following power levels (head flow numbers adjusted by intake manifold):
Heads Intake Flow at 0.550" Ptnl Max Power
LS1 LS1 229 cfm 471 hp
LS1 LS6 241 cfm 492 hp
LS1* LS1 251 cfm 517 hp
LS1* LS6 277 cfm 570 hp
LS6 LS6 263 cfm 542 hp
LS6* LS6 280 cfm 577 hp
* Ported heads
(Thanks to kewlbrz for originally posting the heads/intake flow numbers used above) Obviously, cubic inches have to factor in here as well, since a smaller diplacement motor can only flow the full head potential if it is really spun up. This is likely why some of the 422s are exceeding 577 hp in very driveable form, while I have not seen too many (any?) LS6 heads/cam/LS6 intake 346s getting 500 RWHP.
[ January 17, 2002: Message edited by: WeatherGuy ]
[ January 17, 2002: Message edited by: WeatherGuy ]</p>
TECH Addict
Joined: Dec 2001
Posts: 2,298
Likes: 2
From: new england
Re: Max power and cylinder head flow I dont have the answer to your question but i have made some observations, those HP #'s are not rear wheel hp, if they were stock motor would be putting out 492hp based on stock head flow .They must be accurate when max power is built into combo, not mild street set ups. IMO
Thread Starter
TECH Fanatic
Joined: Nov 2001
Posts: 1,347
Likes: 1
From: Freeland, MD
Re: Max power and cylinder head flow [quote]Originally posted by LS1derfull:
<strong>I dont have the answer to your question but i have made some observations, those HP #'s are not rear wheel hp, if they were stock motor would be putting out 492hp based on stock head flow .They must be accurate when max power is built into combo, not mild street set ups. IMO</strong><hr></blockquote>
Oops - should have made that clear. Those are flywheel HP numbers . . . can only guess those factoring in the usual 10-18% driveline loss.
<strong>I dont have the answer to your question but i have made some observations, those HP #'s are not rear wheel hp, if they were stock motor would be putting out 492hp based on stock head flow .They must be accurate when max power is built into combo, not mild street set ups. IMO</strong><hr></blockquote>
Oops - should have made that clear. Those are flywheel HP numbers . . . can only guess those factoring in the usual 10-18% driveline loss.
FormerVendor
Joined: Nov 2001
Posts: 3,065
Likes: 6
From: Houston, Tx.
Re: Max power and cylinder head flow That's a fairly good formula for estimating POTENTIAL power at the engine with a fairly optimized setup. <img src="graemlins/burnout.gif" border="0" alt="[Burnout]" />
