Mach .55 flow HP loss

[bill jones]

-Ok I got it, thanks...

[Walline]

maxracesoftware, Thank you for the wealth of knowledge. I am trying to understand all of this. In your calc. you use
"314.5 = Air velocity in Feet per Second " how is that measured, on the flow bench or engine?
Also I do not understand . . .
"goes back to some of same reasons SuperStock old style Cylinder Heads like 23 degree can only effectively use .37 to .39 L/D Ratios
whereas, modern Cyl Heads can use .41 to .42+ L/D Ratios
without Loss in HP or Torque"
Can you please explain L/D ratios

Thanks A million. I have learned so much from you allready!

Chris

[maxracesoftware]

360 = ( 12 inches * 60 seconds ) / 2 Revolutions ...for 4 Cycle

282.7433388 constant = 360 * .785398163

.003536777 = 1 / 282.7433388

2.4 = ( 144 Sq.Inches / 60 Seconds )

.416666667 = 1 / 2.4

rearranging equations around

RPM = ( FPS * CA ) / ( Bore * Bore * Stroke * .00353 )

where;
RPM = point of desired Peak HP
FPS = Feet per Second
CA = Cross-Sectional Area in Square Inches (smallest measured)


FPS = ( Bore * Bore * Stroke * RPM * .00353 ) / CA


CA = ( Bore * Bore * Stroke * RPM * .00353 ) / FPS


Example=> ProStock 500 cid

4.115 Sq.Inch Area = ( 4.687 * 4.687 * 3.62 * 9000 * .00353 ) / 613.9758744

where 613.9758744 = .55 Mach



Speed_of_Sound_FPS = (( 459.67 + TempF) * 2402.625624 ) ^ .5

1116.319772 fps @ 59 F

.55 Mach = 613.9758744 fps

Speed_of_Sound = (( 459.67 + TempF) * 1.4 * 32.174 * 53.34 ) ^ .5

Speed_of_Sound = (( 459.67 + TempF) * 1.4 * 1716.567377 ) ^ .5

and the easiest equation is

Speed_of_Sound = (( 459.67 + TempF ) ^ .5 ) * 49.02

TempF = temperature in degrees Fahrenheit

459.67 = Rankine degrees

=============================================

In your calc. you use
"314.5 = Air velocity in Feet per Second " how is that measured, on the flow bench or engine?

its calculated or guesstimated
306.7 to 314.5 FPS range is about 1/2 the .55 Mach number (613.98)
its represents the average port velocity baseline starting point
..you could use a number of your own to correlate your data

on the FlowBench, you would never "calculate or guesstimate" this
you would instead measure Port Velocity with a 180 degree or "U" or "J" shaped Pitot Probe attached to a 48" inch or so Vertical Manometer

the Pitot Tube would accurately account for Port's corner radius effects
..you can use equations to account for that, but the Probe is better/quicker/accurate

if your Pitot Probe Pressure in Inches of water "exceed" or equal your Test Pressure..theres are good chance you are already in or close to being into Choke under live conditions

you can get into a Choked port "sooner" than your Test Pressure number
..just depends how far the Choke's smallest-area is away from the
valve , and what are differences in pressure between the Short Turn Pressure and the Choke pressure

on the Short Turn's Apex you can flip the Pitot Probe upside down and attempt to measure localized velocity there on the apex...but that area seems to be worth 5 to 25 HP Losses if too high...but if the Port's Velocity in the smallest cross-sectional area is "too-high" its worth 50 to 100+ HP Losses..just depends on how far this area is from the valve

just like the Valve's Curtain Area in the Lift Curve will be the final Choke,
the Short Turn's Apex speed/pressure will be the next choke point,
then further up the smallest cross-sectional area Choke point

if you have a CA Choke point..it will control or dominate the port,..it will cause greater HP Losses than the Short Turn apex localized velocity

the straighter the Port (like a straight piece of tube)
the higher the velocity fps can be without flow separation or choke
the higher the fps...the higher the Volumetric Efficiency attainable

heads like #292 Turbo, #034 Bowtie, #461, #462, etc
all had "potential" pushrod area choke problems

Can you please explain L/D ratios

the L/D Ratio is just

Valve_Lift / Valve_Diameter

.3732 Ratio = .724 Lift / 1.940 OD Intake valve


.4215 Ratio = 1.060 Lift / 2.515 OD Intake Valve

if you look at any Flow Curve...the Flow rate increase is pretty good until you reach .25 L/D Ratio..then the Flow rate increase really drops off

the older style heads with poorer design/shaped Ports, can't handle the air velocity as well as modern shaped ports...so increasing L/D Ratio above .37 to .39 usually shows no Dyno gains, and most times HP Losses above .39 L/D ...whereas, ProStock style heads like .41 to .42+ L/D Ratios

all you'll do with older heads above .39 L/D Ratio is slow down the Curtain Area velocity and increase the pressure differential between a possible choke point further up the Port ..like at the pushrod area ...causing the Port to go into Choke sooner in the Lift Curve.

[Rick360]

Wow! Thanks a bunch guys. This will take a while to absorb all of this.

Larry, If a head/port doesn't flow better, or has very small gains past .35 or .36 L/D will opening the valve further gain power if the disch coef. is dropping rapidly up there?

Rick

[maxracesoftware]

Larry, If a head/port doesn't flow better, or has very small gains past .35 or .36 L/D will opening the valve further gain power if the disch coef. is dropping rapidly up there? --Rick

looking at SuperStock years ago "before" NHRA allowed Porting...many Racers had from .630" to .660" to some with as much as .700"+ Lift...
even though on the FlowBench these SBC heads "in un-ported form"
stopped Flowing around .450" to .500" Lift, or made tiny increases after .450" Lift

Suppose your Flow increases stopped at .450" Lift
and you decided all you need is a .450" Lift cam
you might be at .450" Lift for less than 5 degrees or so
(not counting valvetrain losses)

...If you installed a .630 " Lift Cam..you'd access that .450" Lift Flow
for about 40 to 80 degrees more.
you would have more Flow Area available with the .630" Lift cam
and should be capable of more HP gains ..similiar like under the old SuperStock rules.

This is not the same effect as "Choke"
If you have a Pushrod Area Choke problem...then if you make the Heads flow more or increase valve lift....the speed thru the Choke will be higher
causing the Choke to be sooner in the Lift Curve

FPS = ( CFM / CA ) * 2.4

it seems the Choke further away from the Intake valve is the worst !

You "tune" the Intake System Length for a certain RPM range basing this from the Valve Seat angle -to- the Plenum Entry...as the Choke point is further away from the Curtain Area or Seat Angle, the more it seems Wave tuning is upset and greater losses....a Short Turn apex velocity problem doesn't loose as much HP as a Choke near the Pushrod area or higher up in the Intake Manifold runner

probably why its always best to have some Taper in an Intake System..to avoid a Choke in the middle...the Choke should be the Curtain Area, thats what your tunning the Intake Lengths from

[guest]

I am a newbie here, Love to hear the technical numbers and formulas.
Have acess to a dyno and mostly work on 9 to 1 390 cfm stuff. One thing I don't see in the above formulas is a consideration of mach numbers as realated to air pressure (Mach 1 varies with regard to air density,- temp, humidity and pressure)

When valve opens and piston travel tries to accelerate intake charge, the air column momentarily experiences reduced pressure at the valve opening or other choke point. Could this be the reason the above formulas use .55 mach as a limiting point??
I really look forward to some insight from such an experienced group, as the users of this forum

[maxracesoftware]

One thing I don't see in the above formulas is a consideration of mach numbers as realated to air pressure (Mach 1 varies with regard to air density,- temp, humidity and pressure)

in a total vacuum, the Speed of Sound = zero FPS

and the Temperature of the Mixture has a dominating influence
on the Speed of Sound

Speed_of_Sound = (( 459.67 + TempF ) ^ .5 ) * 49.02

TempF = temperature in degrees Fahrenheit

459.67 = Rankine degrees

With the Engine Efficiency in the past, a 500 CID ProStocker might of had
2.500 * 28" Header Primaries by 5.000" * 10-12" Collectors

now with Higher Engine Efficiency=> with lower Exhaust Gas Temperatures,
the Speed of Sound is slower in modern ProStocker, so Primary Header Pipes and Collectors will be smaller in diameter and shorter length than in the earlier years.

you would run a ProStock engine on the Edge of Choke or close to it,
by spreading the Centers and reducing Exhaust-to-Intake Flow and Valve Ratios...so as not to waste mixture during overlap period.

you would size the Intake cross-sectional area to keep the mixture speed as high as possible and as close to Choke as possible to get the greatest
speed possible for greatest inertia-ram effect at Intake Valve closing point
to increase Ve% , Torque, HP

too much overlap or too high a E/I Ratio will
waste too much mixture and create sooner/higher mixture speed ,
...in a highly scienced out Intake Port that you already have the fastest speed possible without Choke, if you increase E/I Ratio or close the Cam Centers, you can go into Choke or into Choke earlier than you were before, hurting top end HP

if you have Heads that have somewhat too large a Cross-Sectional Area for Engine CID and RPM...it might benefit to increase Overlap Period and E/I Ratio ( "Waste some ..to make some")
waste some mixture out exh during overlap to pickup port velocity in a too large Intake port....to make more HP, because Choke won't be such a problem.


With a 9:1 CR engine, you'll have a lot of Clearance Volume that can act more as a Dampner, reducing the "Hit" on the Intake and Exhaust Systems...and creating a greater volume where exhaust gas residuals can
be if you get the Header Pipe dimensions and Wave tuning wrong.
you can loose a lot more Torque/HP with low CR than with high CR if
things are wrong, especially at lower RPM range like under 4500 RPM when there's more Time and slower velocities

390 CFM carb will be a great restriction
usually an Engine will make its Peak HP when plenum vacuum will be in a range from .8" to 1.2" inches Hg vac

anything above 1.2" inches of plenum vacuum, and carb will hurt Peak HP

with a 390 cfm Carb, you're probably seeing at least 7+" inches Hg of vacuum, and thats about 80 to 100+ HP lost on a V8 engine

[Guest]

With a 9:1 CR engine, you'll have a lot of Clearance Volume that can act more as a Dampner, reducing the "Hit" on the Intake and Exhaust Systems...and creating a greater volume where exhaust gas residuals can
be if you get the Header Pipe dimensions and Wave tuning wrong.
you can loose a lot more Torque/HP with low CR than with high CR if
things are wrong, especially at lower RPM range like under 4500 RPM when there's more Time and slower velocities

Funny you should say that.

The first time we ran an engine on our dyno we were working on in the car exhaust systems. Previous to this point we always rented someone elses dyno and used their dyno headers. Well, eight sets of headers, four collecters and five mufflers later, we had found 30 HP. That is a HUGE number for our type of racing (Nascar Elite touring series). Funnier still is the fact that the most expensive headers- Dynatech and the McCabe's performed the worst on our particular combination. A $185.00 set made the best numbers, and gave the most area under the curve!!

[maxracesoftware]

we had found 30 HP. That is a HUGE number for our type of racing (Nascar Elite touring series).

was that +30 HP gain from your previous best combo ??

or was that +30 HP gain from the worst -to- the best Header-Muffler combo ??

everyonce in awhile i'll start a Dyno test at 3000 or 3500 on a SuperStock engine and see whats happening with Collector lengths at very low RPMs

i've seen as much as 80+ HP gains at the very low RPM range
like on a low-CR SuperStock engine , [around 3000 to 4500 rpm,
with cams in the 280 deg at .050" range] with around the same peak HP or within 10 HP ... testing various Collector lengths. Luckily these SS engines don't ever see anything below 5000 rpm, most have +5500 stall converters.

[Guest]

Back in the mid eighties some one ( heddman I think) came out with an Anti-reversion cone mounted to the header flange against the heads, that was good for 200HP at rpm that the motor wouldn't pull down to with standard headers ( it wouldn't run WOT that low RPM but with new headers would make 200 hp@WOT at same rpm. Would have probably made a great start on road race exhaust. Didnt seem to change peak #'s.
Our 30 hp was over what we were running in the car before. We had Dynatech and McCabe headers and collectors, pretty stuff!! but apparently more suited for unrestricted applications. Spent several days on the dyno trying almost all of the combinations, plus it had to pass a Db rule.

We had a hard time believing 30 hp, so we took the engine back over to the rental dyno, just to make sure that the output hadn't somehow changed. Apparently it was all in the exhaust. As a sidebar this team has LOTS of victories in Nascar's touring series.

We haven't raced in two years but we have rented out the car and motor, and it was second fast qualifier for a SWS race. At this point I am trying to get ideas, and maybe put another enginge together.

I saw something in jeg's EMC about enclosing the cam journals and lifter bores to control windage, has anyone tested this?? would you be willing to speak on this forum about what gains were found??

Would the 390 cfm carb be the choke point or would it be the valve opening?? Brodix 10X WT

[Guest]

Hi all, New here and I think I have the perfect example of a choked intake port.
My engine is a 540 mopar with B1BS heads that have raised floor for better short side radius.
The cross section area next to the pushrod is very narrow (1.2") and is the smallest CA. CA is only 2.33" here.

Engine is dynoed with 6400 peak hp.
LPV= 0.00353x6400x4.25x(4.5x4.5)/ 2.33= 834fps
I calculated the max rpm given with 660fps.
RPM=660x2.33/0.00353x4.25x(4.5x4.5)=5062rpm

I can switch intake rockers to Indy 440-1 to get more offset and make the port much wider, a guess would be to have new CA in the 3.0 sq inch range.
I might have to switch to offset lifters also to get there.
This area increase will make the LVP in the 660-670fps.

What can I expect to gain by doing this ??
CA Area after this choke is significant larger and valve is 2.20" right now but will soon be 2.25" with 89% throat area.

Greatful for any advice.
Tom J, Sweden

[comp]

Back in the mid eighties some one ( heddman I think) came out with an Anti-reversion cone mounted to the header flange against the heads, that was good for 200HP at rpm that the motor wouldn't pull down to with standard headers ( it wouldn't run WOT that low RPM but with new headers would make 200 hp@WOT at same rpm. Would have probably made a great start on road race exhaust. Didnt seem to change peak #'s.
Our 30 hp was over what we were running in the car before. We had Dynatech and McCabe headers and collectors, pretty stuff!! but apparently more suited for unrestricted applications. Spent several days on the dyno trying almost all of the combinations, plus it had to pass a Db rule.

We had a hard time believing 30 hp, so we took the engine back over to the rental dyno, just to make sure that the output hadn't somehow changed. Apparently it was all in the exhaust. As a sidebar this team has LOTS of victories in Nascar's touring series.

We haven't raced in two years but we have rented out the car and motor, and it was second fast qualifier for a SWS race. At this point I am trying to get ideas, and maybe put another enginge together.

I saw something in jeg's EMC about enclosing the cam journals and lifter bores to control windage, has anyone tested this?? would you be willing to speak on this forum about what gains were found??

Would the 390 cfm carb be the choke point or would it be the valve opening?? Brodix 10X WT

200hp ????

[maxracesoftware]

The cross section area next to the pushrod is very narrow (1.2") and is the smallest CA. CA is only 2.33" here.

Engine is dynoed with 6400 peak hp.
LPV= 0.00353x6400x4.25x(4.5x4.5)/ 2.33= 834fps
I calculated the max rpm given with 660fps.
RPM=660x2.33/0.00353x4.25x(4.5x4.5)=5062rpm

I can switch intake rockers to Indy 440-1 to get more offset and make the port much wider, a guess would be to have new CA in the 3.0 sq inch range.
I might have to switch to offset lifters also to get there.
This area increase will make the LVP in the 660-670fps.

What can I expect to gain by doing this ??
CA Area after this choke is significant larger and valve is 2.20" right now but will soon be 2.25" with 89% throat area.

Greatful for any advice.
Tom J, Sweden

usually you will start to loose the very bottom end Tq/HP numbers
and by 3500 to 4500 rpm you will be pretty close to same numbers as you were before , and 4500 rpm and higher you should be picking up HP
if your LPV was as high as 834 fps

usually its pretty safe to go ahead and enlarge that Choke Area if your
LPV was 600 or higher fps, but different heads have different shapes with higher or lower localized spots of velocities...so this should be double-checked with a Pitot Probe

another similiar example=>
sort of like if you let a 1350 HP ProStock engine idle
you have a large pressure differential at the throttle plates
with very high velocity there but it can't make 1350 HP idleing ,
its throttled or choked.

[Guest]

usually you will start to loose the very bottom end Tq/HP numbers
and by 3500 to 4500 rpm you will be pretty close to same numbers as you were before , and 4500 rpm and higher you should be picking up HP
if your LPV was as high as 834 fps

usually its pretty safe to go ahead and enlarge that Choke Area if your
LPV was 600 or higher fps, but different heads have different shapes with higher or lower localized spots of velocities...so this should be double-checked with a Pitot Probe

Thanks Larry, I have doubble checked CA and meas. some more CAreas.
Port entry is 3.64 sq in and pushrod choke area is realy 2.33 to give 834 fps at 6400rpm.
From 2.33sq in. the area expands to 2.85 sq in just before the short side radius turns down.
I do have a homebuilt (by me) flowbench for intake flow only, with a 11kW fan that can easy pull over 32"Water...
I have never tried meas. flow(in intake port) with a probe but will do that, In the early days (15 years ago) when I started working with ventilation we used pitot tubes to meas. airflow.
Even if the spots are high or low, what I plan to do is to straighten out the bend curve thats there for the pushrod so the port will be wider (the side wall will be straighter) and that shouldn´t be bad for flow.
Maybe the port needs to have some of the raised floor removed, I will try to meas. spot velocity before start.

Port flow-28" is now 328@600 and 350@700-800 dyno data for engine when built is not to bad for a 540 with so little CA ports 810hp@6400 and 726ft-lb@5400.

Will this intake port see any gains going from 2.20" Int. valve to 2.25" without opening up the CA ?? Or is the choke holding back any portflow hp gains ??

My goal is to keep these heads but improve them as much as possible, because I like the low rpm with low maintance for Super class racing.

Larry thanks again for helping me with advice.