I'm trying to gather up as many formulas, and thier proper uses as I can. I'm not looking for calculators. just the on paper stuff.

also Mindgame did you get this finished?

if so I would like to know first what a GUI is, and if you could post it.

I'm looking for things sim. to these kinds of foumulas that I have already found posted by various members. sorry for not giving credit.

flow factors for a given engine

Hp per cylinder/cfm at 85% of given lift at valve=flow factor

exampel
You take Kaase and his SCJ heads that had a .675 lift cam,
take 85% of that lift and you come up with .575. Take the flow
of his heads at that lift (360cfm) and you can figure out the
flow factor of that motor..... 745hp / 8 cyl = 93.125 Hp per
hole / 360 cfm = a flow factor of .258

Max power rpm = (min cross sectional area x 185,000)/(stroke x bore^2)

formula for hp rpm peak through a given cylinder head
(Min Cross Section x 185,000) / (Stroke x Bore ^2) = HP RPM Peak

example
2.10 x 185,000 / 3.75 x 4.03 ^2 = 6379rpm Max Power

forumla for airspeed through min. cross sectional area of a given head

(.00353 x RPM x stroke x bore^2)/min cross sectional area = Max Port

example
The 355 with LT1 heads @ 7000rpm....
(.00353 x 7000 x 3.75 x 4.03^2)/2.10 = 665 fps or around .55 MACH!

The formula for determining volumetric flow rate at different
depressions.

Flow at new depression=sq rt (new pressure drop/old pressure drop)xflow
rate at old pressure drop

Airflow demands (cfm)...
((rpm x displacement)/3456) x VE

or the one from Pro Systems...
(cid x rpm x VE)/2820


CAM formulas
AID = Advertised Intake Duration
AED = Advertised Exhaust Duration
ICA = Intake Centerline Angle
ECA = Exhaust Centerline Angle
LSA = Lobe Separation Angle
IO = Intake Open (BTDC)
IC = Intake Close (ABDC)
EO = Exhaust Open (BBDC)
EC = Exhaust Close (ATDC)

ECA = (2 * LSA) - ICA
IO = (AID / 2) - ICA
IC = (AID - IO - 180)
EC = (AED / 2) - ECA
EO = (AED - EC - 180)

 

GUI = Graphic User Interface.

No, I haven't put anything together that I'd want people to download and use yet.

Looks like you've done a bit of searching already. Spend some more time looking at the formulas MaxRaceSoftware has used in his posts. If you have specific questions then that might help. There are also a number of books on automotive formulas. The Automotive Math Handbook by Forbes Aird ISBN 0-7603-0696-6 is a good book that deals with everything auto... not just engines. Check it out.

-Mindgame

 

thanks mind game I'll look those up

here is another one I have anyone know how reliable this one is?

.257 x airflow x number of cylinders = potential HP

 

The flow factor based example and it's general engine type guidelines are a better way to go than that.

Bret

 

It's pretty close,used as a rule of thumb.But that is presuming everything else is correct. This is only the HP level the heads will support.

 

Depends on the combo....

A set of 260cfm that make 600hp works out around .290 and that's a real life combo.

Or a set of 268cfm heads that make 592hp = .276

These heads would have been good for only 530-550hp with the .257 example.

Bret

 

Like I said "rule of thumb". It's not like putting an engine on a dyno and then figuring out the HP level from flow or crunching a bunch of numbers to "try" to get spot on.

 

Bret's correct ..it depends on the Engine Combo !!

most all the NHRA SuperStock Cyl Heads i port make an average .285 Flow Factor value relative to a conservative FlowBench and Dyno.

an old pair of #041x SBC heads 1.940/1.500 valves 165.0 CC port volume
Flows 250 CFM on a conservative FlowBench and makes 565-585 HP
runs 10.00's ET at 3330 Lbs. ( 250 CFM @ 585 HP = .29225 Flow Factor )
( 250 CFM @ 565 HP = .2825 )

i noticed same Flow Factor ranges on NHRA 283, 327, 350 and Chrysler
318,340,360 engines

usually the "minimum" HP to expect from Cyl Head Flow numbers
is between .2000 to .222 Flow Factor

and normally most people can achieve .257 Flow Factor

on the opposite end like Professional type engines, they can achieve
Flow Factors of .2900 to .3200

if you applied the .257 Flow Factor to ProStock , you would calculate
that it takes 656.6 CFM = 1350 HP ...thats a mile off .

1350 HP needs approx 563 CFM or around .3000 Flow Factor

the "Standard" Flow Fator of .257 , changes up or down relative to ;
Piston Speed, Wave Tuning, Compression Ratio, Carb CFM, Rotating Weights,
ValveTrain Dynamics, Camshaft Specs, Oil pan design, oil weight/vicosity,
Block/Ring seal, etc and a host of other factors.

 

Thanks for letting us know how far the formula spreads.
I use the .2571 on my "normal" street/strip type engines and it seem's to get me close when some body asks how much HP will "this"make.Never built a Pro engine but have done a couple of "mountain" motors(700+CID)but wasn't predicting any HP just knew it was going to be a bunch.And Was.

 

a big Factor in the FlowFactor is piston speed...
and a 700+ or any engine around 500+ the Flow Factor will increase with increases in piston speed.

i have a 632 CID BBC engine making a Flow Factor of .3175
on a conservative Dyno and FlowBench....this same Engine was Dyno
tested on another well known Dyno and made 80+ HP more .

applying a Curve Fit thru all my Dyno and FlowBench Data
it looks like .3200 to .3300 would be the Limit for N/A gasoline Engine ???

it would be interesting to see Data from NASCAR Engine combos

 

Thanks Larry.
Do you have any easy to get to dyno info on a 383CID with 4375 ft/min@7000 with head flow #'s 338@.700 lift a 248CC runner.


What would the flow factor be on the above?

 

Was talking with Mr. Crower yesterday and he kept on trying to teach me a calculation and I couldn't figure out what the hell he was talking about.

We were talking about cams, valve train, etc. and he kept telling me to take .00250 (I assume this is half lift of 500) and mutiply it by 1.6 (rocker ratio) times rpm.

I don't know if he was talking about spring pressures or what. I realize that this doesn't give you much to go on, but thought perhaps you might know what he was getting at. BTW, he was also the one who claimed that it was ok to use guide plates along with SA rockers (a claim that we decided here to be untrue).

Just thought that what he was talking about might come in handy, since my "new" mechanic is attemping to put together a top end that will actually last (since the current top end has, in my opinion, been responsible for killing 2 motors.

Thanks