WickedFast555

Is there a calculation I can use to determine how many CFM of airflow is required to make a certain amount of power? For example, X amount of CFM is needed on a 327cid engine to make 400hp. I'm guessing there's probably no way to calculate this, but I thought I'd ask anyway. Thanks.

Mindgame

100% empirical cause there are just so many factors other than headflow at work, but you can come pretty close.

Here's a thread where we kinda got into this http://web.camaross.com/forums/showt...4&page=5&pp=15

Post any specific questions and we'll go from there.

-Mindgame

OldSStroker

There is a way. See these threads which are in addition to what Mindgame referenced.

http://web.camaross.com/forums/showthread.php?t=208830

http://web.camaross.com/forums/showthread.php?t=160037

Using the Vizard/Superflow calculations, to make 400 fwhp with a 10:1 CR, Hydraulic Roller 327, you'd need 230 cfm @28 in H2O IF you did everything right with the engine.

Since most people don't get all the inlet tuning and valve timing right on, let's say you 'd need 10% more. or something around 250 cfm.

If you are talking 400 rwhp you are asking a lot from a 327: lots of r's. lots of flow and probably no low-midrange. Drag engine only, IMO.

If you want to get in deeper, try this thread:

http://web.camaross.com/forums/showt...hreadid=102549

Remember it's always the combination that makes the engine perform. An engine has to be well designed and well constructed to get the most from it. There should be more goals than "400 hp".
My $.02

MaxRaceSoftware

Peak_HP = Flow_CFM * .257 * Number_of_Cylinders

is estimated potential Peak HP to expect
you multiply .87 percent times cam's theoretical max lift , round off to nearest .050" in Flow Test, then see what CFM is at 28 inches

example=> .700" Lift cam
.700 Lift times .87 percent = .609" Lift
Flow head at .600" Lift , then take CFM at 28 inches and calculate HP potential with above formula

.257 Factor = for beginning engine builders and engines near 10.0:1 Comp Ratio

.285 Factor = would be for Professional engine builders with wet sump pans, lightweight rotating assemblies, low tension great sealing rings, deep oil pans, etc.
excellent use of inertia/wave tuning with 9.5 to 11.5:1 Comp Ratios or
11.5 to 13.0:1 CR ranges without fully utilizing inertia/wave tuning effects

.300 to .310 Factor = Current ProStock Technology with dry sump, unlimited carburetion, Hi Comp Ratio, ultra lightweight rotating assembly, etc, max use of inertia/wave tuning, etc, 14:1 to 17:1 Comp Ratios
(usually no better than .3200 efficiency or no worse than .2980 eff %)

Mindgame

Larry,

Looks like those formulas could use some correction factors based on camshaft duration or piston speed. I don't rightfully know as I haven't really crunched the numbers.

The .285 factor looks a little extreme when you look at it based on "more streetable" engine speeds. I'd categorize those as engines where the avg. piston speed is ~4200 feet/min. Now bump that avg. ~700 feet/min and I think we're there with the .285 factor.
My combination in particular utilizes relatively mild camshaft timing. The potential is there for the .285 factor but I would probably need another 1000rpm to reach that, which turns my "street" ride into "race".

Just a thought.

-Mindgame

MaxRaceSoftware

Larry,

Looks like those formulas could use some correction factors based on camshaft duration or piston speed. I don't rightfully know as I haven't really crunched the numbers.
=======================================

.285 Factor works great with SuperStock Engines
usually 5500 to 8500 RPM ranges , 283 cid to 370+ cid
9:1 CR to 11.5 CR, Hi-Lift Roller Cams

.257 Factor..the majority of engine builders are capable of achieving

The Factors are only Quick BallPark for what HP might be possible

Farc

Hey max I ask you sometime ago about the formula to calculate CR from a test in CLY pressure, for a 300 psi in a LT1.
Coul you please tell us about

MaxRaceSoftware

Hey max I ask you sometime ago about the formula to calculate CR from a test in CLY pressure, for a 300 psi in a LT1.
Could you please tell us about
------------------------------------------

Sorry its part of a Computer Program i'm still working on

and i still need to refine it better

when i finish i might Post that part of the Source Code ?

Most of the time its pretty close
but just a few days ago we checked a 14:1 CR engine that only
cranked 180 psi after 7 to 10 needle pulses because of such poor ring seal
when it should have cranked 235 psi with the particular cam specs it had

Joes94TA

was that 14:1 engine warm or cold engine temparature can change readings upwards of 30-40 psi in some cases.. making deriving at a formula tough to do on all out race applications...

WickedFast555

Thanks guys. I'm not really building a 327, that was just a random example. I'm on the fence between a pair of RMRE ported Big Chiefs or their new 12deg 'Raptors' for a big block, I was hoping to quantify the difference in airflow into a rough estimate of power potential.

MaxRaceSoftware

was that 14:1 engine warm or cold engine temparature can change readings upwards of 30-40 psi in some cases.. making deriving at a formula tough to do on all out race applications...
=============================

we had just finished making a couple of Dyno Pulls , so engine was around 150 deg F

i usually always check at least the #2 Cyl on Dyno (Passenger Side), as thats usually easiest to get to spark plug w/ Header Pipe out the way, and its also the side with the Dyno Starter Button close by...so it can be a one-Man operation

the Cranking Psi then becomes part of Dyno Data

MaxRaceSoftware

Thanks guys. I'm not really building a 327, that was just a random example. I'm on the fence between a pair of RMRE ported Big Chiefs or their new 12deg 'Raptors' for a big block, I was hoping to quantify the difference in airflow into a rough estimate of power potential.
==================================================

.300 to .310 Factor = Current ProStock Technology with dry sump, unlimited carburetion, Hi Comp Ratio, ultra lightweight rotating assembly, etc, max use of inertia/wave tuning, etc, 14:1 to 17:1 Comp Ratios
(usually no better than .3200 efficiency or no worse than .2980 eff %)

For a "State -of- Art" type engine with those Heads from Reher/Morrison , if you know how to build the rest of the Engine you should get
around .300 Factor if you have 15-16:1 CR,etc

Backwards calculation =>

Current ProStock 500 cid = 1345 to 1350 HP "Quote Bill Jenkins"

1350 / 8_Cylinders = 168.75 HP per Cylinder

562.5 Potential CFM @ 28" = 168.75 / .300

544.4 Potential CFM @ 28" = 168.75 / .310

pretty close to what they claim as Head Flow numbers

Darin Morgan claims as high as 116.5 CFM/Sq Inch Valve Area
a 2.525" od valve = 583.4 cfm

583.4 cfm = 168.75 / .289271 Factor (Sounds too high)

562.5 cfm would be 112.33 cfm/sq.inch sounds more reasonable ??
and that would be a .300 Flow Factor on that sort of engine

Some of the Math descrepencies are due to the fact that often Dynos and FlowBenches don't all read the same ...some read High , some read Low, so the Flow Factors might seem off a little

Ucantcme57

John Lingenfelter always said that with a EFI engine there is no difference with CFM. you could put a 1300cfm monoblade on a stock TPI the engine will only use the air it can, there might be some port velocity differences but he put 48's 52's 58's and a 1300cfm butterfly tb on a 383 and it kept building power the bigger the TB you put on it.. There might be changes you would have to do to get you TPS to go WOT... The same is not true for Carbs..

OneFlyn95z28

We have always showed gains with larger TB's on LT1s

This weekend I spent four-five hours on a flow bench with a few intakes on a LT1 ported head. The stock intak showed the worse losses. A stock intake with the port raised as far as you can with out welding was fairly close to my radicly modified intake and then my modified intake showed the most.

so then we popped the top off the modified intake and I quicly learned why top draft intakes seem to work best. there was a large improvment when we took the top off. we tried a few thing but the air liked going straight into the port that was for sure

As mentioned A flow bench can only tell you so much If you play some you can get better idea's though