PRP Velocity Lessons

[273]

Totally agree that velocity is the most important, but here’s the problem with the ‘chase velocity, not cfm’ arguement. There are two primary ways to come up with average velocity through the entire port. The difficult way is with the pitot tube. This requires lots of accurate velocity measurements and lots of accurate area measurements. Not easy to do.

The easy way is to take the port volume (measured with a liquid) and divide it by the port centerline length. This gives the average port cross sectional area. Then you take the cfm reading and divide it by the average CSA. This gives you velocity.

Since velocity is calculated from cfm, the way that you chase velocity is by monitoring cfm.

One question I got about ideal velocities for X cid at y rpm, is that an engines build level can vary somewhat wildly from mild to max effort and level of efficiency from 1 to 1.65 lbs-ft per cid. That would make the recommended port cc csa cfm is more likely based on a narrower level of build and efficiently, probably a more race level. Eg. making an ideal heads for 500 hp 360 @ 6500 rpm vs a efficient 600 hp @ 6500 rpm vastly different (1.25 vs 1.50 lbs-ft per cid).

 

[Hysteric]

Totally agree that velocity is the most important

Reminds me of this build:

Analyze This 316 cubes making 430 Hp and 430 Tq. All that with only 195 cfm peak flow, that's 2.2 HP per cfm and a 145 cc port

They filled the ports in from 152 cc to 145 cc

"The intake port is way smaller than the original. ,think the factory was 152 cc and now it's down to 145 and it's much higher. It's got a small cross section of 1.91 [square inches]." Final flow numbers ended up around 195 cfm on the intake and 170 on the exhaust. Though not huge peak flow numbers. he claims they were almost at those numbers by.200-inch lift. Just perfect for limited camshaft and rpm range applications.

 

[273]

Reminds me of this build:

Analyze This 316 cubes making 430 Hp and 430 Tq. All that with only 195 cfm peak flow, that's 2.2 HP per cfm and a 145 cc port

They filled the ports in from 152 cc to 145 cc

"The intake port is way smaller than the original. ,think the factory was 152 cc and now it's down to 145 and it's much higher. It's got a small cross section of 1.91 [square inches]." Final flow numbers ended up around 195 cfm on the intake and 170 on the exhaust. Though not huge peak flow numbers. he claims they were almost at those numbers by.200-inch lift. Just perfect for limited camshaft and rpm range applications.

Pretty cool build, any idea the velocity (fps) they be running?
How much time in effort and $$$ to R&D those heads and combo to get 2.2hp per cfm ?

 

[Earlie A]

Pretty cool build, any idea the velocity (fps) they be running?
How much time in effort and $$$ to R&D those heads and combo to get 2.2hp per cfm ?

If 1.91 sq inches is the average CSA, the calculation would be this:

(195 cfm)x(1m/60s)x(144ci/cf)x(1/1.91ci)=245ft/s velocity which is actually kind of low

145cc=8.848cubic inches so port centerline length would be (8.848ci/1.91si)=4.633 inches which is short for a SBM or SBC

My guess is the average CSA is actually lower than 1.91 which would raise the peak velocity and lengthen the centerline length.

Either way, that's a stout little engine.

 

[Earlie A]

Did he give a velocity range? From what I can find out in the 250-300 fps average.

Look at this chart. This is not my information, this is used by guys like Darin Morgan and Larry Meaux in their seminars and calculations. For the street 260-300 seems to be a sweet spot.

The Speedmaster head that I am working with can get to 285 cfm on a 186cc port with a 4.937in centerline length. That is pretty much max velocity/flow when the port starts shutting down due to separation/turbulence.

So, (186cc)x(1ci/16.387cc)=11.35 cubic inches port volume

(11.35ci)/4.937in=2.3 square inch average cross sectional area

(285cfm)x(1m/60s)x(144si/1sf)x(1/2.3si)=297 fps average velocity

This port is having problems before the 297fps point, so 260-285 fps would probably be better for this port and my porting skill level. Good racing heads would certainly have higher average velocities at the target rpm. Really good street heads could as well, but it would probably be better for a street engine to shoot for the 285 fps velocity at a lower rpm, which makes the CSA smaller for the street than for race.

 

[pittsburghracer]

Reading textbook stuff like this makes it sound like you need X amount of space in any area and in some areas that may be true, but not all. I could grind for and hour and make more area and the only thing I did was hurt the port. When I hear guys say the airspeed is to slow for a street application how do you accomplish that in a small block Mopar head.

 

[273]

Look at this chart. This is not my information, this is used by guys like Darin Morgan and Larry Meaux in their seminars and calculations. For the street 260-300 seems to be a sweet spot.

The Speedmaster head that I am working with can get to 285 cfm on a 186cc port with a 4.937in centerline length. That is pretty much max velocity/flow when the port starts shutting down due to separation/turbulence.

So, (186cc)x(1ci/16.387cc)=11.35 cubic inches port volume

(11.35ci)/4.937in=2.3 square inch average cross sectional area

(285cfm)x(1m/60s)x(144si/1sf)x(1/2.3si)=297 fps average velocity

This port is having problems before the 297fps point, so 260-285 fps would probably be better for this port and my porting skill level. Good racing heads would certainly have higher average velocities at the target rpm. Really good street heads could as well, but it would probably be better for a street engine to shoot for the 285 fps velocity at a lower rpm, which makes the CSA smaller for the street than for race.

View attachment 1716205020

Thank you very much, great info, good to know these formula's aren't just based around applications way beyond the average dudes build.

I think Hysteric thinks I'm anti velocity, it just like his eg.. That's Olds combo is only something a dude with a flowbench and a dyno is gonna come up with and a lot of time, it's making 1.4 lbs-ft per cid beyond what most are capable of, most would build a 350 to get those numbers.

Plus most are dealing with of the stock or off the shelf heads and a few options at that, that engine is basic very similar to a 318 and the 3 400 hp combos gonna vary similar cam and cr wise and making peak hp around the same rpm but 35 hp less with EQ, Stock Magnum, ported 302. And probably at a more realistic around 1.18 lbs-ft per cid the one that ran EQ's they did a ported version of EQ's and got 425 hp (kind of a disappointment with the head flow #), I'm sure the velocities still probably fall in acceptable fps range. But these are all what I consider average street strip build level engines, basically 10:1 with 230 to 250 cam. A more street level cam under 230 generally needs airflow to makes it's hp eg. Modern truck engines like hemi and ls.


I'm just saying these engine are a lot less efficient than the Olds 1.17 to 1.19 vs 1.40 lbs-ft, but for the average dude this route probably makes more sense, especially since most would just go more displacement to hit these numbers, not that velocity shouldn't be thought of.


https://www.motortrend.com/how-to/0810phr-chrysler-318-engine/

"For our street performance small-block, we selected the most conservative of this line of camshafts, the XE275HL. Specs for this stick come to 231/237 degrees duration at .050, and .525-inch lift with a 1.5:1 rocker ratio, all on a 110-degree lobe separation angle."

On The BenchEngine Quest Ch318b Cylinder HeadsSuperflow 600 Flow Bench 28-Inch Water Depression Tested At Dr. J's Performance

LIFT:	INT:	EXH:	INT:	EXH:
. 100	68	57	69	60
. 200	124	114	138	124
. 300	179	155	200	169
.400	213	180	247	200
.500	227	187	273	219
.600	233	188	275	229

On The Dyno318 Mopar Street EngineSuperflow 901 Engine Dyno Stp Correction Factor Tested At Westech Performance Group

RPM	TQ	TQ	HP	HP
	BASE	PORTED	BASE	PORTED
3,000	335	335	192	192
3,200	342	340	208	207
3,400	351	356	228	231
3,600	365	369	250	253
3,800	374	379	271	274
4,000	379	384	289	293
4,200	378	383	302	306
4,400	375	383	314	321
4,600	376	382	329	335
4,800	375	386	343	353
5,000	372	384	354	366
5,200	367	383	363	378
5,400	361	379	371	390
5,600	355	374	379	399
5,800	350	371	386	409
6,000	345	365	395	418
6,200	341	360	402	425
6,400	329	345	401	421

Here's one to confirm port velocity a set of ported 302 heads 215 cfm (size ?) made the most torque and made 400 hp with a smaller cam xe268h, besides the leaking problem is most can't port even if they trying don't mean their gonna get the same results. This does have the best efficiency out of the 400 hp builds 1.26lbs-ft per cid.

https://www.motortrend.com/how-to/318-small-block-build/

Junkyard Jewel 318 Power Curves
RPM	TEST 1		TEST 2		TEST 3
	Torque	HP	Torque	HP	Torque	HP
3,000	334.9	191.3	354.1	202.3	349.1	199.4
3,500	360.7	240.4	378.2	252.0	380.7	253.7
4,000	376.6	286.8	402.3	306.4	401.5	305.8
4,100	379.3	296.1	402.4	314.1	401.6	313.5
4,500	374.0	320.4	402.5	344.9	400.1	342.8
4,600	374.0	327.6	403.1	353.0	400.6	350.9
4,700	373.5	334.2	400.6	358.4	408.0	365.1
5,000	363.9	346.4	389.7	371.0	402.0	382.7
5,500	344.0	360.2	368.3	385.7	386.5	404.8
5,900	331.1	372.0	347.1	390.0	361.4	406.0
6,000	328.3	375.0	344.0	393.0	353.8	404.2
6,100	319.4	371.0	339.2	394.0	347.8	404.0

Might as well, here the magnum one, the easiest to build just add cam cr 4bbl headers to a 5.2l

https://www.motortrend.com/how-to/mopp-0409-318-engine-build/

Mopar 318
RPM	HP	TQ
3,000	190	332
3,500	241	376
4,000	286	376
4,500	321	375
4,900	357	382
5,000	363	381
5,500	388	371
6,000	398	348
6,200	400	339
6,500	393	318

Might as well add one more here's a 477 hp 323 built for engine masters challenge more inline with the Olds, making similar tq but more hp, ported R/T Magnum's and 247 cam.

https://www.motortrend.com/how-to/0901phr-mopar-318-magnum-engine/
On The Dyno DTS Dyno Data Performance Crankshaft 323CI Small-Block Mopar

RPM	TQ	HP
2,500	337	161
2,600	350	173
2,700	357	183
2,800	357	190
2,900	356	196
3,000	351	201
3,100	345	204
3,200	339	207
3,300	343	216
3,400	356	230
3,500	371	247
3,600	385	264
3,700	396	279
3,800	404	292
3,900	410	305
4,000	415	316
4,100	418	327
4,200	420	336
4,300	422	345
4,400	421	353
4,500	420	360
4,600	421	369
4,700	425	380
4,800	426	390
4,900	427	398
5,000	427	407
5,100	427	414
5,200	426	421
5,300	425	428
5,400	423	435
5,500	421	440
5,600	419	446
5,700	417	453
5,800	415	458
5,900	412	462
6,000	407	465
6,100	401	466
6,200	397	469
6,300	393	471
6,400	390	475
6,500	386	477

 

[Hysteric]

I think Hysteric thinks I'm anti velocity, it just like his eg.. That's Olds combo is only something a dude with a flowbench and a dyno is gonna come up with and a lot of time, it's making 1.4 lbs-ft per cid beyond what most are capable of, most would build a 350 to get those numbers.

You would need to understand my point for me to think you have an issue with velocity.

At what point in the pistons travel does the port reach peak velocity? What's the velocity in the intake port when you open the intake valve and the exhaust residual heads straight up the intake runner and up through the intake manifold?

 

[273]

You would need to understand my point for me to think you have an issue with velocity.

At what point in the pistons travel does the port reach peak velocity? What's the velocity in the intake port when you open the intake valve and the exhaust residual heads straight up the intake runner and up through the intake port?

Like I said before if you want a real convo where you make a point the I respond and vise versa then fine, not playing your bread trail game.

 

[fishmens67]

 

[Earlie A]

Reading textbook stuff like this makes it sound like you need X amount of space in any area and in some areas that may be true, but not all. I could grind for and hour and make more area and the only thing I did was hurt the port. When I hear guys say the airspeed is to slow for a street application how do you accomplish that in a small block Mopar head.

Hard to do on big inch stuff for sure. Trick flows on a 318 might be a little overkill.

 

[273]

You would need to understand my point for me to think you have an issue with velocity.

At what point in the pistons travel does the port reach peak velocity? What's the velocity in the intake port when you open the intake valve and the exhaust residual heads straight up the intake runner and up through the intake manifold?

I'm not necessarily debating velocity obviously it matters, Just working out/debating how it fits with an average non highly competitive racing engine that may never see the track with vague desired results and or with a non porter without a flowbench and no dyno that's not gonna regularly test on the track or even it they do but are not willing to invest time and money in R&D to get the extra little bit.

How does these formulas and metrics that even the pro's even debate how useful are they, how does this stuff translate to the average dude the 99%?

Eg.. Like with that Olds most would just add 30-50 cid to get that torque and powerband. How many builders do a 408 to get around 500+ lbs-ft when a 1.4+ lbs-ft per cid 360 could get that, is build a bigger less efficient engine really a worse way to go for 99% of the builds out there?

That's what I'm trying to workout.

 

[Hysteric]

I'm not necessarily debating velocity obviously it matters, Just working out/debating how it fits with an average non highly competitive racing engine that may never see the track with vague desired results and or with a non porter without a flowbench and no dyno that's not gonna regularly test on the track or even it they do but are not willing to invest time and money in R&D to get the extra little bit.

Until you talk to some one who is a head porter and tells you he did a set of heads that only flow 215 cfm with tiny ports for a 450 ci Buick that runs 10.9s @ 3500 pounds. According to the Moroso slide rule that's 480hp with 215cfm of flow. 2.23 hp per cfm.

In my view trying to calculate intake port velocity is a waste of time as a flow bench is not a running engine. Maybe a better way to view the problem is how does too much port velocity manifest itself as a problem in a running engine?

 

[273]

Until you talk to some one who is a head porter and tells you he did a set of heads that only flow 215 cfm with tiny ports for a 450 ci Buick that runs 10.9s @ 3500 pounds. According to the Moroso slide rule that's 480hp with 215cfm of flow. 2.23 hp per cfm.

Yes that's impressive, but for the average dude meaningless, cause their not gonna be able to replicate it in anyway, I'm not an engine builder but I feel pretty confident that I could build a 1.8 to 1.9 hp per cfm engine, so I'd feel I need about 270 to 280 cfm head to make 480 hp, and try to make that with 10.5:1 cr and 240 ish cam. And if wanted to build for a similar rpm powerband and torque add about 50 cid to the build.

What's the main advantages of building a highly efficient engine?
Especially for the average guy?

In my view trying to calculate intake port velocity is a waste of time as a flow bench is not a running engine.

Probably true to some extent, I guess you'd find the formulas and programs some of these builder useless/little value too?

Maybe a better way to view the problem is how does too much port velocity manifest itself as a problem in a running engine?

And that would be?

 

[Dale Davies]

Reminds me of this build:

Analyze This 316 cubes making 430 Hp and 430 Tq. All that with only 195 cfm peak flow, that's 2.2 HP per cfm and a 145 cc port

They filled the ports in from 152 cc to 145 cc

"The intake port is way smaller than the original. ,think the factory was 152 cc and now it's down to 145 and it's much higher. It's got a small cross section of 1.91 [square inches]." Final flow numbers ended up around 195 cfm on the intake and 170 on the exhaust. Though not huge peak flow numbers. he claims they were almost at those numbers by.200-inch lift. Just perfect for limited camshaft and rpm range applications.

All about port energy and where the flow is. It wants to flow more on the top and that provides a better shot into the cylinder and promotes swirl if the port is widened going past the valve and guide on the cylinder wall side.

 

[Dale Davies]

Until you talk to some one who is a head porter and tells you he did a set of heads that only flow 215 cfm with tiny ports for a 450 ci Buick that runs 10.9s @ 3500 pounds. According to the Moroso slide rule that's 480hp with 215cfm of flow. 2.23 hp per cfm.

In my view trying to calculate intake port velocity is a waste of time as a flow bench is not a running engine. Maybe a better way to view the problem is how does too much port velocity manifest itself as a problem in a running engine?

Time to catch up reading DV.