MAX RACE......fps question......

[rewguy]

If the equation holds true........
FPS = (bore x bore x stroke x RPM (of peak hp) x .00353) / CA

that equates to 732 fps wich is WELL over mach .55 if you use 4.03 as a bore size, 3.48 as a stroke, and 7200 as a peak hp rpm, and 1.96 as a min CSA. I know some of these numbers I used are off of what a superstock 360ish cube is....But arent they kind of close? If so......how are you making peak hp so high if the fps is over 700 with this equation? Im sure Im missing something, but I thought Id ask.

[maxracesoftware]

If the equation holds true........
FPS = (bore x bore x stroke x RPM (of peak hp) x .00353) / CA

that equates to 732 fps wich is WELL over mach .55 if you use 4.03 as a bore size, 3.48 as a stroke, and 7200 as a peak hp rpm, and 1.96 as a min CSA. I know some of these numbers I used are off of what a superstock 360ish cube is....But arent they kind of close? If so......how are you making peak hp so high if the fps is over 700 with this equation? Im sure Im missing something, but I thought Id ask.

.55 Mach should be viewed as a "baseline Limit"

from memory, the highest i have Data for was .682 Mach

the SS350 was really 4.065bore 3.493stroke = 362.661 cid

753.07 fps or .6748 Mach (1.948 CSA)

PipeMax predicts=>
311 FPS Velocity CSA= 1.948 sq.in. at 7200 RPM Recommended Smallest Port CSA for a 362.661 CID engine @ 7200 RPM

and the 1.948 "average CSA" is just about exactly
what a GM Chevy #041X casting NHRA Legal =165.0 max CC
intake port volume


Formula=> Average_CSA = Port_Volume_CC / (Port_CenterLine_Length * 16.387)

1.9483 CSA = 165.0 CC / (5.168 Port Length * 16.387)


the problem with=>

FPS = (bore x bore x stroke x RPM (of peak hp) x .00353) / CA

and

Average_CSA = Port_Volume_CC / (Port_CenterLine_Length * 16.387)


are they are both based on an "average CSA" and "FPS"
and they are both "Calculated"

to measure Velocity FPS you need
a FlowBench and J-style Pitot Probe
..thats the bare essentials to get a ball-park picture
of whats going on or important in Cylinder Head Flow

one more thing,
the .55 Mach to .682 Mach is not the FPS you will see on your Pitot


what you see on Pitot , you can just about double that
relative to =>FPS = (bore x bore x stroke x RPM (of peak hp) x .00353) / CA

example if you measure 28" (350 fps) on Pitot while
FlowTesting @28" of Test Pressure
then 350 Pitot is just about 700 FPS in this Equation
FPS = (bore x bore x stroke x RPM (of peak hp) x .00353) / CA

350 FPS * 2 = 700 FPS
700 / 1116 = .627 Mach

this is all "ballpark" calculations
you will have to develope your own Database thru
experiences

[timdog]

What happens to CSA/FPS calculations when you have a 4-valve (or more!) per cylinder head?
Is it worth looking at the minimum CSA point to calculate FPS at this point? I have tried various different ramp profiles on the ports along with different size minimum CSA's, all having the same average CSA and seen quite different results.
If you were to look at minimum CSA then would this be twice its value for a split port?
Sorry if question sounds dumb, its been a long day and i'm struggling to write what my feeble brain is trying to say ......

[maxracesoftware]

What happens to CSA/FPS calculations when you have a 4-valve (or more!) per cylinder head?
Is it worth looking at the minimum CSA point to calculate FPS at this point? I have tried various different ramp profiles on the ports along with different size minimum CSA's, all having the same average CSA and seen quite different results.
If you were to look at minimum CSA then would this be twice its value for a split port?
Sorry if question sounds dumb, its been a long day and i'm struggling to write what my feeble brain is trying to say ......

you need to use a Pitot Probe to measure actual Velocity FPS Profiles
in 4 or 5 valve Heads, and not rely so much on theoretical Calculations.

usually you can successfully Epoxy up certain areas
in the 1 larger CSA before it transitions into the 2 or 3
smaller CSA areas ....somewhat like this Website
http://www.mototuneusa.com/
but if taken to extreme like in some of his Pics ,
on every 4 or 5 valve Head,
you'll probably loose HP in some instances

most of the Epoxy stuff he's doing won't work
on normal 2-valve Heads,
its mostly working for him because of the Speed FPS
transition between the larger siameze port going into the 2 individual ports
and both being closer to the Intake Valves relative to the
Total Induction Length.

[CMI Motorsports]

Larry,

The number I have been using is 614fps when I want to calculate minimum CSA. I think I got that number from a previous post. Is that what you recommend?

I also read that SAE technical paper(Japanese automaker ) that for engines with limitations on CSA relative to their stock castings and large bore and strokes, that duration is the way to exceed .55 Mach. Can you speak to those of us that have intake ports whistling Dixie above 0.55?

Lynn

[RT]

There was a previous post that said the port might whistle at high flow rates because the indivdual ports arn't flowing equally, mine whistle at 0.600" but one flows 7cfm more than the other

I think Larry's PipeMax CSA figures would be a good starting point

[larrycavan]

Larry,

The number I have been using is 614fps when I want to calculate minimum CSA. I think I got that number from a previous post. Is that what you recommend?

I also read that SAE technical paper(Japanese automaker ) that for engines with limitations on CSA relative to their stock castings and large bore and strokes, that duration is the way to exceed .55 Mach. Can you speak to those of us that have intake ports whistling Dixie above 0.55?

Lynn

A port that whistles like that can be misleading. In recent testing on an early Kawasaki 4V head -900 Ninja- I used a modified stock rubber intake boot on the port entrance. When the port started whisteling, it could be stopped by simply placing a finger on the edge of the intake boot. Touch it anywhere on the leading edge and the whisteling stopped completely.

[shawn]

I could be wrong, but I don't think he's actually refering to the port making a whistling noise, but asking what to do with a port that has exceeded .55 mach in running conditions without having any cross section left. Much like you have with a super stock style drag head.
Shawn

[larrycavan]

I could be wrong, but I don't think he's actually refering to the port making a whistling noise, but asking what to do with a port that has exceeded .55 mach in running conditions without having any cross section left. Much like you have with a super stock style drag head.
Shawn

Might be the case Shawn...I don't know for sure either. Still, it's worth pointing out the discovery...don't you think?

The .55 mach figure is relavant to the engine design as to just how closely you must adhere to the value. If, a situation developed where you were already at the max velocity the port would effectively work at and you had no room for more CSA, then adding duration may well be the answer. If it were me, I'd try some lobe center juggling first. It should give an indication if it's going to work before you lay down the $$$ for the cams.

Raising velocity through epoxy build up on the floor and spreading lobe centers has been done for years in motorcycle performance shops.

JMO

Larry C

[CMI Motorsports]

Shawn is right. This is an NHRA SS motor. "Whisting Dixie" was just my poor attempt at humor. Yes we have a Pontiac motor with a 2.37 CSA at the push rod with a 4.210 bore and a 4.223 stroke.

If I use 614 fps, then:

CSA(minimum) = bore * bore * stroke * rpm * .00353/fps

or

rpm = 2.37 * 614/(4.210 * 4.210 * 4.223 * 0.00353)

rpm = 5507

This engine makes peak HP at 6300, wonder what it would do without choke? Seems to be the limiting HP on all big Pontiacs.

My questions is 614fps the right number to use? Alot of SS guys are running that way because NHRA allows aftermarket castings to some, but others must run 35 year old castings.

Lynn

[larrycavan]

How closely does this formula work out to your actual data?

Intake Runner Area = Cylinder Volume X Peak Torque RPM / 88200

[CMI Motorsports]

How closely does this formula work out to your actual data?

Intake Runner Area = Cylinder Volume X Peak Torque RPM / 88200

Please clarify:

Intake area minimum? or the choke point?

Peak Torque times RPM in calcuation?:

Why would I be interested in peak torque? Our cars always perform better running off of peak HP. My peak torque is 4800 RPM, and the car never sees less that 6000 RPM down the track. Anytime we cram the motor down, the car slows down.

We have been doing tons of work on acceleration values. I believe that due to the "choke" of the intake ports our engines work very well at low accelerations rates 300 RPM/Sec and below. When we cram the motor down, we are asking the engine to accelerate the car.

Lynn

[larrycavan]

Intake Runner Area = Cylinder Volume x Peak Torque RPM / 88200

I just recently came across that formula. I'm going to figure it's average area. Curious to know how accurate it is.

[maxracesoftware]

Why would I be interested in peak torque? Our cars always perform better running off of peak HP. My peak torque is 4800 RPM, and the car never sees less that 6000 RPM down the track. Anytime we cram the motor down, the car slows down.

We have been doing tons of work on acceleration values. I believe that due to the "choke" of the intake ports our engines work very well at low accelerations rates 300 RPM/Sec and below. When we cram the motor down, we are asking the engine to accelerate the car.

Lynn

Why would I be interested in peak torque? Our cars always perform better running off of peak HP. My peak torque is 4800 RPM, and the car never sees less that 6000 RPM down the track. Anytime we cram the motor down, the car slows down.


....yes, HP is correct answer !...ask Comp,ProStock,NASCAR,F1 Guys
(Torque times RPM, which is = HP)...not just Torque

6300 RPM = looks about 702 FPS or about .629 MACH

lets say you find a way to be able to use 753 FPS like in the SS350
example

the SS350 was really 4.065bore 3.493stroke = 362.661 cid
753.07 fps or .6748 Mach (1.948 CSA)


then for 753 FPS it would be = 6754 RPM capability

the pushrod choke is really severe in Pontiac older style SS Heads
and most probably legal Carb size also becoming limiting factor.

857 CFM at 6300 RPM
919 CFM at 6754 RPM

QJet will usually show 1.5" Hg plenum vac at 750 to 800 CFM
and anything higher than 1.5" is definetly
going to start limiting HP

[CMI Motorsports]

When we were in Augusta, KS 15 years ago, Daren Morgan and Kip Martin bent the flaps and got our Q-jet from flowing 800 to 1000 cfm. It made no difference on a 400. I wonder if we need to revisit that with the 455's?

These SS Q-jet 454's & 427's are making big power. So we hope that we have a way to go with the cylinder heads yet.

My next step is to pound the push rod tubes flat on the port side. I think we can get 2.84 square inches that way. It has become a matter of art now instead of science,

We also just recieved a regrind of our old cam. We are going from a 276 lobe on the intake back to a 284. Lobe separation is 110.

Lynn