[Skippy597]

This is a topic that always interests me. Don't get wrong as most of you on here are probably smarter than I, but I think Pontiac guys have a some warped perception of head sizing. Even when talking to powell customs he said they speedmaster rounds ports 215cc runner are too small for a 460 stroker.

Lots of SBC guys run 200 cc runners on 383s that breaks down to 1.9 cubic inches per 1 cc of runner size

Yet you look at a 455 with 215 runners and that equals 2.1 ci per runner cc

You never here about SBC or sbf guys talking about runners being too large. But Pontiac guys tend to obsess over it.

Just interesting to me.

[Skippy597]

I will add that port velocity to a point is important but I feel it's over stressed on here.

[P@blo]

So would a 280cfm port be better on a 220cc or a 160cc runner? Looking for context here.

Also, modern transmissions skew things somewhat but a lower port volume would have got the horse and your wife there sooner Skip.

[Steve C.]

Magazine tid bit.....

"...a word about factory Pontiac heads in general: Pontiac heads were originally designed to get heavy cars up and moving. As such, they emphasize low-end torque over top-end power. Pontiac port volumes are roughly equivalent to a 350 Chevy small-block, yet most Pontiac engines are at least 50 ci larger. When it comes to porting the factory Pontiac heads, H-O Enterprises' Ken Crocie, a recognized Pontiac expert, says "You can't make a Pontiac head big enough. You can make it wrong, but not too big."


.

[Jay S]

Originally Posted by P@blo

So would a 280cfm port be better on a 220cc or a 160cc runner? Looking for context here.

Also, modern transmissions skew things somewhat but a lower port velocity would have got the horse and your wife there sooner Skip.

At peak power if those 2 engines have the same size valve the air speed past the valve is going to be the same, peak power would be fairly comparable. At the front side of the power band the smaller cc port will likely make more average power. Below the powerband trying to pull a big overdrive the bigger port might win. If the bigger port has a modern combustion chamber it can win by even more. The air mostly follows the port ceiling at part throttle on both those examples, neither use the entire port at part throttle. The bigger port takes longer to make the short side radius reactive. Below the cams powerband if the bigger port has less air velocity it can make more low end power than the small port. It doesn’t always, but the big port can causes less low RPM cylinder scavenging and positively influence very low end power.

Low end power loss from to much head is more of an issue when the valves are extra big for the bore and the powerband is risen higher from valve shrouding. For most people with at least a Pontiac 4.15 bore stroker engine with smaller than 2.19 intakes valves that is not much of an issue.
At some point with constant very low end load the bigger port will likely have extra carbon build up because the fuel can fall out of suspension. To much cam and putting around does the same thing, the reversion makes the fuel fall out of suspension. With some spirited driving and a cam that limits reversion to keep the air speed higher, that isn’t much of an issue for most street cars.

[Jay S]

It also made a difference what the heads flow at different valve lifts, not just the peak flow. I have seen plenty of flow bench tests that didn’t test below .2”, which make no sense to me because below .2” is where all the cylinder scavenging happens. Better low lift flows generally result in less low end power but more mid range, and pull the power peak back some.

[steve25]

My point is folks that Pontiac had it down in terms of off the show room floor street performance for the weight of the vehicle they were producing .

In terms of the pre 1971 high compression motors making between 350 to 390 hp ( there number not mine, I dont trust that 390 number! )
with a 4” stroke or more a they saw a hp peak rpm of around 5200 as being all that was needed, the 400 cid non RA4 motor was good to 5500, and the 153 to 154.5 CC intake port volume allowed this
All while them being able to hold a warranty on the motors and drivetrain.

Now adding a bigger higher lift cam that can make be full use of the air flow a 154 CC port can pass will make things a wash so to speak.
The greater duration ( hp aside ) increases rpm potential and the added air flow from the lift makes for greater average and peak port velocity as does the new rpm potential.

Pontiacs mandated use of 3.90 rear gears in all the 67 and up RA motors tell you flat out how the engineers wanted to keep street performance from just off idle up to the factory red line at the forefront.

What got me into the whole drag race deal and seeing what could be done with standard for the day hop up parts was a friend of my cousin in NJ.

He had a 69 WT motor in front of a 4 speed.

So this was a 350 hp motor with the 068 cam ( .406” lift. ) and no more then 155 CC intake ports

The motor had 75k on it and other then superb turning only had the timing chain replaced.

He ran 9” slicks , 4.33 rear gears , ladder bars and 1 5/8 headers .

The tall slicks brought the overall gear ratio down to about 3.90.


The car ran a best of 12.96 the last I heard back then.

So tell me again how placing heads with 215 CC intake ports would have made this 69 GTO faster?

[Formulajones]

Originally Posted by Skippy597

This is a topic that always interests me. Don't get wrong as most of you on here are probably smarter than I, but I think Pontiac guys have a some warped perception of head sizing. Even when talking to powell customs he said they speedmaster rounds ports 215cc runner are too small for a 460 stroker.

Lots of SBC guys run 200 cc runners on 383s that breaks down to 1.9 cubic inches per 1 cc of runner size

Yet you look at a 455 with 215 runners and that equals 2.1 ci per runner cc

You never here about SBC or sbf guys talking about runners being too large. But Pontiac guys tend to obsess over it.

Just interesting to me.

Powell would be correct.
Hell I put 195's on a 327 I recently did and it made 447 ft lbs. It made over 400 ft lbs for the entire pull from 3000 to 7200. It has a really nice flat torque curve. Throttle response is instantaneous, and it drives fantastic. That's a peanut motor compared to what we are talking about here.

Are you guys trying to tell me a 455 Pontiac with a 4.210 crank is incapable of that if we put 200cc heads on it?? If that's the case it doesn't say much for Pontiacs.

[Half-Inch Stud]

Optimal Runner length and port volume have a complete dependency on shape. Best example for "varied CSA for flow" is the funnel-to-nozzle optimized into a venturi.

No intake and head have an optimal venturi. Motorcycle engines come closest.

Dave Vizard shows that an optimized BBC head can make better power by filling the lower 1/4 area to be even better. That data is key to understanding the PMD tall runner shape as a means to make power, while under load.


In other tech:
Still Intrigued that nitro-methane engines make MUCH MORE HP under heavy load than mildly loaded, for same WOT setting.

[PAUL K]

I didn't read much of this but when a brand X guy, or anybody else explains what port volume is too small, large or just about right, take it with a grain of salt unless it was a first hand in depth conversation. Intended application is the key. 215cc maybe too small for a max effort 455 build requiring a 5,000 stall and 4.11 gears but a well tuned 160cc runner would would drag the 215 cc runner in a street/strip application using a 3,000 stall and a 3:55 gear.

There's a reason a well tuned 455HO TA would have its way with a LS-6 Chevelle using a close ratio and a 3:36. The LS-6 would win the dyno race.

When watching videos of experts explaining headers beat with a hammer make more power than undented headers, figure out why before you start pounding on your $1200 headers.

[Jay S]

I have a rectangle port 454 BBC out on a stand with 340 cc intake runners that will probably only make 30 more HP power than my 461 Pontiac with a 185cc port. It gets humorous when you start to look at port volumes only and talk across platforms. I chuckled when I read Powells claim that Pontiac has a deficient heads when he compares it to a LS head. The LS is a cathedral port and the port entry is much higher, which is very different than a Pontiac. SBC has a 23* head and a completely different intake port shape than a Pontiac. Big Block Chevy has about another inch of port length on the head side than a Pontiac and a narrower intake manifold. Ford FE is exactly the opposite, the intake gasket is underneath the valve cover, the intake is really wide. A 426 HEMi has a 245cc intake port and can flow over 400 cfm with no increase in port volume. Oldsmobile 455 has a low port with a shallow 6* valve angle, wildly different than the HEMI, and difficult to compare. The Oldsmobile 455 often used their big valve heads like the W30 engine on low RPM industrial applications. Opposite of what you would expect. Ford did the opposite and used really small valves on industrial engines. Yet on most low RPM applications the Olds kicks the snot out of the Ford. We have good reasons to be confused. lol

[Stan Weiss]

Originally Posted by Stan Weiss

Steve,
Do you know what head that is based on? Port volume can be an indicator of average CSA, but only when the ports have the same port center line length. So a High Port would have a longer port center line length that a standard location port.

Stan

Does anyone know what the Pontiac "D" port intake port center line length is? The number I have is 5.0" which would be shorter than a SBC or BBC. For reference the number I have for a CV-1 intake port is 5.5".

Stan

[Jay S]

Originally Posted by Stan Weiss

Does anyone know what the Pontiac "D" port intake port center line length is? The number I have is 5.0" which would be shorter than a SBC or BBC. For reference the number I have for a CV-1 intake port is 5.5".

Stan

5” sounds close to correct on a standard d port. A SBC is about 5.3”, but also the intake manifold angle is different (10*) and makes it even more misleading. I think a BBC is about 6”. The modern LS has an even more shallow intake maniflold face angle and cathedral ports throw the port length comparison way off. It is not like comparing Apples and Oranges. It is closer to comparing Apples and Carrots. LOL

[Steve C.]

Posted here for conversation.....

Out of interest in 1998 Jim Hand did port modification to a Edelbrock 87 casting with the goal being to improve low-and mid-lift flow while maintaining adequate high lift flow.

Reduced port volume from the original 215-216 cc to 196cc
Reduced inlet port height from RAIV configuration to standard D port dimension
Changed inlet valve seat angle to 30 degrees
Reduced maximum bowl/throat size to 1.70" diameter

Measurement and verification was done using a Superflow 110 bench; final tests were performed on a Superflow 600 operated at 28" of water.
A control port was left as-received to use as a standard.

Testing was done throughout the entire lift curve thru 0.600" lift

Edelbrock port:

.100" lift 69 cfm
.200 139
.300 200
.400 245
.500 268
.600 272

Modified port:

.100 87
.200 164
.300 213
.400 250
.500 267
.600 273

If memory serves me right modifications were conducted to one port only and never ment for any production and/or track testing.

( Side note: The above modification was 27 years ago. A lot has changed within our Pontiac community since then.
Larger cubic inches, improvements in intake manifolds, "larger" camshafts becoming more of a norm, as are 500+ horspower combos dedicated to street use, etc, etc.
To many today their opinions have changed revolving the use of cylinder heads. )

.

[Steve C.]

I forgot to mention the Jim Hand modifications to the Edelbrock head was with the cooperation and approval of Edelbrock. It was done in order to improve low and mid rpm response and performance for street and street/strip engines, to provide improved power in the lower rpm ranges, and to eliminate the need to operate the engine at higher rpm in order to realize significant performance gains with the Edelbrock heads. Noting it was done to provide good performance on basically STOCK Pontiac engines.
Edelbrock furnished a new ready to run 87 cc head (actually two cylinders of a head – cut so as not to be used on a car). The modifications were for research only for both Jim and Edelbrock. As Bondo was used as the fill material.
There were some minor sources of possible error listed in his report to Edelbrock. But the comparison was considered valid.
The report was sent to Edelbrock along with the modified head. They found it interesting, but informed him that since their foundry was running at full capacity, there would be no second Pontiac head for better lower RPM street use.
Again, keep in mind this was 27 years ago.


.

[Stan Weiss]

Originally Posted by Jay S

It also made a difference what the heads flow at different valve lifts, not just the peak flow. I have seen plenty of flow bench tests that didn’t test below .2”, which make no sense to me because below .2” is where all the cylinder scavenging happens. Better low lift flows generally result in less low end power but more mid range, and pull the power peak back some.

Jay,
Time is money. So less testing at less lift points is cheaper. I know that David Vizard like to start testing @ 0.050" lift and does every 0.050" until around .400" and the goes by .100" increments

Stan

[Jay S]

Originally Posted by Steve C.

Posted here for conversation.....

Out of interest in 1998 Jim Hand did port modification to a Edelbrock 87 casting with the goal being to improve low-and mid-lift flow while maintaining adequate high lift flow.

Reduced port volume from the original 215-216 cc to 196cc
Reduced inlet port height from RAIV configuration to standard D port dimension
Changed inlet valve seat angle to 30 degrees
Reduced maximum bowl/throat size to 1.70" diameter

Measurement and verification was done using a Superflow 110 bench; final tests were performed on a Superflow 600 operated at 28" of water.
A control port was left as-received to use as a standard.

Testing was done throughout the entire lift curve thru 0.600" lift

Edelbrock port:

.100" lift 69 cfm
.200 139
.300 200
.400 245
.500 268
.600 272

Modified port:

.100 87
.200 164
.300 213
.400 250
.500 267
.600 273

If memory serves me right modifications were conducted to one port only and never ment for any production and/or track testing.

( Side note: The above modification was 27 years ago. A lot has changed within our Pontiac community since then.
Larger cubic inches, improvements in intake manifolds, "larger" camshafts becoming more of a norm, as are 500+ horspower combos dedicated to street use, etc, etc.
To many today their opinions have changed revolving the use of cylinder heads. )

.

I think there is no question with the way his car was set up it would have went a little quicker with those port mods he did than a stock E head. The average flow was more after the mods. But he could have went a lot quicker if he would have been willing to change his engine more and put that effort to porting the heads to 320cfm, especially running an AOD. We would be talking about his 10 second car instead of it running in the 11s.

[PAUL K]

Originally Posted by Jay S

I think there is no question with the way his car was set up it would have went a little quicker with those port mods he did than a stock E head. The average flow was more after the mods. But he could have went a lot quicker if he would have been willing to change his engine more and put that effort to porting the heads to 320cfm, especially running an AOD. We would be talking about his 10 second car instead of it running in the 11s.

He tried a pair of aluminum d-ports and slowed down. He probably could've gotten in the tens if the car weighed less. He had an idea of how he wanted his car to perform and stuck with it. It's easy to fall into the little bit more gear, little bit more RPM, little bit more nitrous trap.

[Jay S]

Originally Posted by PAUL K

He tried a pair of aluminum d-ports and slowed down. He probably could've gotten in the tens if the car weighed less. He had an idea of how he wanted his car to perform and stuck with it. It's easy to fall into the little bit more gear, little bit more RPM, little bit more nitrous trap.

He was not a young man by the time he was trying that stuff either. I think if you sent Jim home in his younger days with a 535 AI2 block and some wide ports all I would have ever seen was his tail lights.

[p4msi1]

I don't know what all the fuss is about using a big port on the street. Most of us have 455ci+ engines. I just built a .060 + 455 for my son-in-law with 360cfm Edelbrocks. They are ported pretty big but show no signs of being sluggish at low rpm. It also fries the tires at 50 MPH in 2nd gear with 3.08 rear gears. I don't think iron heads can compare.