Port velocities

[WPH]

I enlarged port entry volume before splitter and port dia to 28mm.
Velocity seemed to drop to acceptable range but I have to verify my FPS readings. If I "overtilt" the probe my readings go sky high,
I guess velocity pressure is doing something weird with static pressure holes (like in a spraygun, pulling more vacuum in static line)

[86rocco1]

Do you think the velocity effects are as simple as fuel drop out and wall wetting? If that's the case, one would expect to significant differences between fuel injected and carbed engines, is that occuring?

[106-1194218389]

I was reading on speedtalk.com today,3/25/08, in the advanced engine forum under port velocities there and Larry Meaux and Larry C. both have some very good comments there. Larry M. mentioned that when your are getting over 350 fps you are at .7 mach and 300 fps is .55 mach. Yes, I think I over simplified the problem. I know as you get to the speed of sound things get weird. You can imagine what my port would have been like at 392 fps. My understanding is the later model heads, as in 4 valve per cylinder and good port configurations as in motorcycles etc. tolerate higher speeds. I have not had any personal experience with that though.

[maxracesoftware]

[maxracesoftware]

[maxracesoftware]

From a previous Thread

too fast Velocity FPS can be a total disaster

Note=>all 3 of these Heads were tried on
the same Short Block with all the same pieces
and Dyno Tuned for best possible HP/TQ Curve
with those pieces.


#041x SBC Heads = 165.0 CCs
1.940/1.500 valves
these are the very Hi-Velocity Heads
with too much velocity everywhere inside
the Intake Port, same FlowBench numbers

and the "BEST" Dyno test with them
600 RPM/SEC , i don't have the Sheets
that we started at 3000 RPMs and all the
rest of the Sheets , but only kept the
Copies that stood out, and these are every
200 Hundred RPM increments as its too much Info to type
every 100 RPMs, but it should give you enough Info ?

note=> at 600 RPM/SEC you get a little Needle/Seat
action showing up especially with small gas bowl
chamber in Q-Jet, so look at Fuel Lbs/Hour trend
as well as rate (Same Q-Jet Carb all Dyno Tests)

RPM---TQ----HP----Fuel Lbs
4500-419.3-359.3--178.4
4700-438.1-392.1--171.5
4900-449.1-419.0--177.2
5100-451.0-437.9--169.8
5300-445.8-449.9--174.1
5500-443.2-464.1--188.3
5700-441.0-478.6--209.8
5900-429.6-482.6--222.1
6100-424.3-492.8--227.4
6300-413.9-496.5--214.9
6500-412.7-510.8--200.8
6700-407.6-520.0--210.3
6900-388.8-510.8--221.9
7100-363.7-491.7--236.1
7300-345.3-479.9--239.8
7500-325.1-464.3--233.4
7600-312.6-452.4--226.1

Avg=>406.5-464.9--206.0

--------------------------------------------------------------------------------

with #041x Heads back-to-back on same Short Block
same basic Flow CFM Numbers, same valves, same CC's
but with Port Velocity slower and more acceptable
throughout the entire Intake Port

RPM---TQ----HP----Fuel Lbs
4500-449.5-385.1--166.1
4700-444.2-397.5--164.5
4900-455.2-424.7--177.0
5100-456.2-443.0--158.3
5300-464.1-468.3--169.6
5500-471.1-493.3--192.9
5700-470.2-510.3--199.2
5900-468.2-526.0--199.3
6100-465.0-540.1--204.5
6300-459.8-551.5--209.7
6500-456.6-565.1--216.3
6700-442.6-564.6--223.1
6900-432.8-568.6--217.2
7100-426.6-576.7--215.3
7300-418.3-581.4--224.5
7500-401.8-573.8--238.2
7600-394.1-570.3--231.0

Avg=>445.7-514.1--200.4

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

with #462 castings 1.940/1.500 162.0 CC Ports
differences just 3 CCs can make when ground out in the
correct places, again FlowBench CFM between the
#462 and the other 2 #041x Heads were very close
and CFM numbers don't indicate the HP/TQ differences observed
and Ports had different Velocity Profiles.
Same ShortBlock and all pieces the same.

RPM---TQ----HP----Fuel Lbs
4500-443.0-379.6--168.3
4700-441.8-395.4--159.8
4900-450.6-420.4--164.4
5100-456.9-443.7--169.8
5300-459.2-463.4--183.9
5500-465.9-487.9--190.6
5700-464.1-503.7--192.0
5900-463.0-520.1--195.2
6100-460.6-535.0--196.6
6300-454.9-545.7--206.5
6500-446.8-553.0--216.1
6700-438.0-558.8--225.1
6900-428.4-562.8--220.8
7100-422.0-570.5--223.9
7300-410.1-570.0--219.5
7500-395.3-564.5--226.4
7600-388.8-562.6--231.1

Avg=>440.6-508.1--199.4

[106-1194218389]

Larry,
If my understanding is correct, from what I have read else where in your writings, I should first flow and test with the pitot before I touch the heads. That I am doing. Next I should run my combination in Pipemax for my combination and RPM range and find out what the piston CFM is. Am I correct so far? I have done that and come up with about 245 cfm. So what I think I should do then is port my heads to have around 245 cfm with the correct velocity. That should work for me, correct? What I think I gathered was if I put a head that flows more CFM say 300 cfm with the correct velocities, then I will actually only utilize 245 cfm of that head, but then it would have too slow of a velocity because you are now flowing less than the 300 cfm which would lower the velocity. So I think that what I need to do is aim for a 245 cfm head with the correct velocity.

[maxracesoftware]

[106-1194218389]

The heads I am working on I will repeat are Dart Iron Eagle 180cc intake port heads. I have been reporting the very high port velocities they have. I just cc'd an intake port and they are not even close to 180 cc. I had read posted by one person that their heads only cc'd at 175 cc and I thought that they were doing it wrong. Well I just cc'd mine and they are 173.5 cc. Not very close to the advertised 180 cc. Beware! On the bright side it looks like I'll have plenty of cast iron to grind out and correct the problems. Here is a port map at the pushrod pinch and at the SSR all in FPS @28"
at Pushrod top port at SSR top of port
P 392 365 350 D | P 248 248 248
U 392 350 320 I | U 286 286 286
S 335 303 303 V W | S 392 392 392
H port floor I A | H at the SSR floor
R D L | R
O E L | O
D R | D

[larrycavan]

[maxracesoftware]

Are you referring to average or maximum piston speed?

just average Piston Speed in Feet Per Minute
using this Equation
Piston_Speed_FPM= Stroke * RPM * .166666

not the Instantaneous Piston Speed




The heads I am working on I will repeat are Dart Iron Eagle 180cc intake port heads

Sorry...i've been answering too many 4-valve topic Emails
i've got 4-valves on the Brain !

i don't see anything terribly wrong with the Pitot Profile.
its on the fast FPS side, its very possible you might be
just starting to loose HP , or maybe not

350 fps and 392 fps near the pushrod wall
is getting too fast

392's on the Floor's apex shouldn't be any problems

[maxracesoftware]

Your Port CenterLine Length should be somewhere around
the 5.500" Length , so 173.5 CC's = 1.925 Average CSA

a #041x iron OEM Head at 165.0 CC's
in Ported SS form at 5.168 CenterLine Length will be
about 1.948 average CSA

i know at 1.948 avg CSA ,
that 378 FPS is definetly hurting HP,
especially if it goes higher than 378FPS,
and if its in conjunction with 420+ fps
on short turn apex it can kill 50+ HP at 7500 RPM
on 363cid

[106-1194218389]

[maxracesoftware]

SplashZone (formerly known as KopCoat)
1 gallon Yellow
1 gallon Black
...mixes to dark green color

Purchase from Reher-Morrison or direct from Company
which their Name escapes me at the moment ??

Goodson sells this same stuff in smaller cans.

it takes some getting used to and don't use Water,
only use Dupont 3608-S Laquer Thinner to keep your Hands
only very slightly moist to work the Epoxy around.
Don't get carried away with the Laquer-Thinner.


pre-prep...you should rough up surfaces with a chipped
Alumna-Burr

you must use lite pre-heat just before applying,
then normal amount of Heat from a Electric space heater
for an Hour or more then just let cool a few hours to room
temp. Wait at least a full 24 Hrs before grinding.

after its shaped...i'd apply a very thin clear coating
ontop the SplashZone with your finger tip,
making sure you get a little up over the sides attached to walls

Darin Morgan uses Clear Spray Laquer paint coat ontop
of Epoxy . i just use Devcon 2-Ton Clear with my finger

be careful grinding the outside pushrod area walls,
the SBC castings have a "bias" on some cylinders,
...i max out the thiness of that wall..then i go shift the
port's pair center divider wall to make up the rest of the CSA

i use Metal custom bent Calipers with a custom made Stop
set at .040" thickness

[maxracesoftware]

jfholm......

i forgot to mention the very most important thing !!! =>

"Only" ...check your Port's Velocity at the Camshaft Lift
you are going to use or Run !!!!

Example only=>
it does you no good to check your Port's Velocity
at .700" Lift ...and you only run a .500" Lift Cam.
...that scenerio will incorrectly cause you to slow
the Port's FPS too much for .500" Lift

in fact i check Port's velocity FPS with Pitot
at .87 % PerCent times the Cam's Max Valve Lift

*************************

Also one more thing=> i know i harp a lot about how
important it is to use a Pitot Probe to measure actual real
local area port velocities !!!


jfholm......in your example,
you have a Port CenterLine Length= 5.510" inches
245 CFM @ 28" , and about 1.925 Average CSA
( or am i wrong in thinking you only have 245 CFM ??? )

that's a Theoretical FPS = 305.46 FPS
but your actual Pitot's Velocity Profile is much greater !!!

at Pushrod top port at SSR top of port
P 392 365 350 D | P 248 248 248
U 392 350 320 I | U 286 286 286
S 335 303 303 V W | S 392 392 392
H port floor I A | H at the SSR floor
R D L | R
O E L | O
D R | D