[Joel Koontz]

I am getting the chambers enlarged to 80ccs on my 72cc Eheads and will probably get them ported to 310 CFM.

It is street only car(Convertible w/o Rollbar so I can't race it) .035" over 455 (Dougs Headers w/3" exhaust) I plan to run a smallish SR Cam. I currently have a 242/248 @ .050" cam but may go a bit larger, perhaps 255 @.050", probably nothing larger.

I could probably get them ported to 325 CFM for a relatively small additional amount.

If I was going to a much bigger cam, I would probably opt for the 325 porting, but I am wondering if this would be a good thing to do on a relatively mild motor like mine.

For my application, should I get them ported at all, 310 or 325 CFM?

[Steve C.]

The usual association of more air flow equals increased runner volume is of issue. That might be of interest.

My "310 cfm" 87cc chamber Edelbrock street heads were about 227 cc runner volume and seemed work well with a 254 solid roller that easly supported 580-600 hp at 5800-6000 peak rpm, depending on the intake, on a 4.210 stroke combo. The larger "330 cfm" 72cc chamber heads are about 234 cc's and supported 700 hp at 7000+ rpm on a 4.125 stroke combo.

A friends Butler ported 87cc "300" street heads are about 222 cc's, he's using them with a street combo and 242/128 solid roller.

[Steve C.]

Somewhat related, and fodder for conversation I suspect.

My 87cc Edelbrock castings were about 227cc's runner volume and based on a 4.7" port length that's 2.95 sq inches, they tested on our bench at 313 cfm at .600 lift. I have records on a Butler ported set of 87cc heads that flowed 316 cfm at the same .600 lift. But they were stated to be 222cc's, that's a smaller 2.88 sq inches. One might suggest it's a better head, not because it made 3 additional cfm air flow but because of the reduced intake runner volume. It effects the peak torque rpm.

Also interesting to see the effects of a 1.2 x 2.300 intake port verses a smaller port that might use the popular Felpro 1233 gasket that's about 1.180 x 2.200.
Noteing as it was pointed out in on similar thread these dimensions do not take into account the rounded corners of a port.

These calculators are of interest to see thrends:

http://www.wallaceracing.com/runnertorquecalc.php

http://www.wallaceracing.com/max-rpm.php

http://www.wallaceracing.com/csa-calc.php

http://www.wallaceracing.com/ca-calc.php

[steve25]

You can never have too much flow, just too low a port velocity from to large a port.
You basicly have to look at it like this, as your motor revs up you have less and less time to pack the cylinder with air, the faster the flow velocity, the better the intake system will be able to keep up with the revs, up to a point!
The key here being that in a non boosted motor the flow is always stopping and starting as the valves open and close. This creates a pumping loss factor, as it takes energy to stop and start the flow mass. And as you know their is no such thing as a free lunch, so the pumping factor becomes a restriction as the flow gets to aorund the 325 to 350 ft per second area.
Its totally possible to have a head for a 400 cid motor that when tested flows 280 cfm@28", and on that 400 cid motor makes the power you would expect from 280 cfm, but whan those heads are bolted on a 455 you find that your down some 25 HP due to the greater air demand and hence port velocity that the 455 places on the heads over what the 400 cid motor did.

[steve25]

When you see on a dyno sheet that the torque level has peaked, so has the given intake systems ability to feed the engine.
The only reason that the HP keeps going up is due to the fact that as the revs go up the cylinders are firing more times per minute.
HP will climb higher untill the motors own firction starts to eat up the HP.
If engines could be made to have no fiction, then as the revs continued to climb, so would the HP even though the heads where taped out way down lower in the rev range!

[Half-Inch Stud]

Indeed.

Factor-in the Exhaust signal at overlap being a stronger vacuum than the nearly 14 PSI manifold pressure at WOT and you have a rapidly-filling cylinder. <-- here here.

[steve25]

True, the exh tuning is a whole other story and a big part of why a well implemented race motor can hit VE numbers well over 130%.

[Motor Daddy]

Originally Posted by steve25

HP will climb higher untill the motors own firction starts to eat up the HP. If engines could be made to have no fiction, then as the revs continued to climb, so would the HP even though the heads where taped out way down lower in the rev range!

Friction definitely eats up HP, but the reason the power starts dropping after peak HP is because the engine can not maintain the torque at a higher RPM, because the piston is moving so fast. It's like trying to rear end the car in front of you when you are doing 59 MPH and he is doing 60 MPH in front of you. The lower the net force the lower the acceleration.

[PONTIAC DUDE]

Depends on if you think old school or NEW school and the torque and hp your after.

[Half-Inch Stud]

""""""but the reason the power starts dropping after peak HP is because the engine can not maintain the torque at a higher RPM, because the piston is moving so fast""""""

Whoa, a ball of confusion. How about "but the reason the power starts dropping after peak HP is because the engine cannot breathe well. The Torque per sparked CYL at higher RPM is reduced because of reduced inhale per cyl because the piston is moving so fast"... another way of showing VE going down after Peak TQ.

[Motor Daddy]

Originally Posted by Half-Inch Stud

""""""but the reason the power starts dropping after peak HP is because the engine can not maintain the torque at a higher RPM, because the piston is moving so fast""""""

Whoa, a ball of confusion. How about "but the reason the power starts dropping after peak HP is because the engine cannot breathe well. The Torque per sparked CYL at higher RPM is reduced because of reduced inhale per cyl because the piston is moving so fast"... another way of showing VE going down after Peak TQ.

If the piston was moving slower the crank would have more torque, but then the RPM would be different, wouldn't it? That means it's impossible to separate the two, RPM and torque. You know why?

VE% continues to increase after peak torque, and HP continues to increase after VE% starts dropping. BMEP is highest at peak torque.

[70 Lemans]

My head hurts No pun intended.

[Joel Koontz]

Thanks for the replies, but I would prefer a little less theory about when HP stops increasing and back to the question.

For my application, should I get them ported at all, 310 or 325 CFM?

I realize that too big of a port can be detrimental under some circumstances, hence my question. What I don't know is what amount of cam etc I need to make the bigger port/higher flow head advantageous.

Would I want the 325 CFM heads with an 068 Cam, I doubt it (but don't know for sure), but I don't know what level of Cam is needed to make the higher flow head preferable.

[steve25]

310 or 325 cfm E heads peak in flow at or well above .600" lift. a 068 cam even with 1.65 rockers to provide .447" lift at the valve will make for a very under used head as far as port area vs velocity goes, and this will translate directly into a motor with crappy throttle responce( torque!) over a wide rpm band.
I see this all the time here with guys who plop on a set of E heads or good flowing KRE D -ports and then drop there stock tri power on top.
I can not think of a better way to waste money other than what the government is doing with the bail out funding!!!
These tri power guys with anything less than 250 degree duration roller cams would have better performance with a set of big valve D-ports with 600 bucks worth of porting put in them.
May be this is the best way to resolve your question.
Stock E heads have some 38% more port volume than a stock high comp D-port, just this change will cause the motor to make peak torque and HP at a 25% higher rpm point. If you are not going to build the motor and the car to make use of that, than I would drop the E heads and go for a set of KRE D-ports.

[Steve C.]

He already has the Edelbrock heads and a 242/248 @ .050" cam.

While your having the chambers enlarged have them do a clean up which will bring them to about 288-300 cfm while not making the runner volume much bigger, probbly a few cc's. Or from the sounds of things maybe to a "310 cfm" port job max.

What type cam is it now, Hyd flat tappet ? If so and your stepping up to a hyd roller consider someting very similar in duration, presuming you like it now and it works ok. If stepping up to a solid roller then consider adding some duration, probably 6 degrees according to many.

How about info on the balance of your combination, converter, trans, rear gears, etc.

[Cliff R]

Also keep in mind here that the head intake runner is an extension of the intake manifold. Most intakes only flow 89 to about 93 percent of the port right to start with.

Depending on the cam chosen, static compression ratio, cid of the engine, just to name a few things, adding more port volume to the intake runners in the heads may not improve airflow or performance, at least not as much as one might be looking for?

Also, consider how airflow works in an engine, it isn't simply a smooth steady flow. Each time the intake valve closes, a pulse or shock wave is produced from the abrupt stop of the air moving thru the intake system.

Another thing to consider is the type of manifold and size of the carburetor. Single plane intakes with runners having a straighter shot at the valves will respond different to changes in port volume, than a dual plane intake will, with a divider between both sides of the engine. The carburetor plays a role here as well, more than most folks think. Pontiac engines in particular are fed by relatively "small" or conservative ports, intake and in the heads. This helps with port velocity, and has relatively large cid engines sucking pretty hard on the entire intake system.

Right on the dyno we've seen over 10HP lost simply by swapping an 850cfm carburetor back to a 750 cfm carburetor, on an engine making only 500hp with 455cid. Any formula used to compute CFM requirements, tells us that a 500hp 455 making peak power at 5100rpm's doesn't need 850cfm, or even 750 cfm right to start with. So why do we LOOSE power and see an increase in vacuum at WOT with a smaller 750 cfm carburetor? Probably because the entire intake system is "optimal" for the cid of the engine right to start with, at least at really high rpm's.

What often comes into discussion in these particular threads, is how much performance is lost, or how much overal power suffers, simply by adding more port volume than the engine requires. If you have enough head flow, for the total combination of parts, and add more head flow, does it hurt low end power, average power, total power and peak power producton?

This discussion has folks sitting on the fence, and on both sides of the fence. The same thing can be said of camshafts. Once you have a large enough cam, or have found an "ideal" cam for your combination of parts, will going to a bigger cam help anyplace in overall vehicle performance?

Let's complicate the discussion even further by dropping the static compression ratio a bit (for some reason that is mentioned in the thread), adding more head flow, larger cam, even possibly on a tighter LSA. If your combination of parts and overal vehicle performance was optimized with the original set-up, will it improve anyplace with the new set-up, without changing anything else in the "recipe"?..........Cliff

[Steve C.]

"...adding more port volume to the intake runners in the heads may not improve airflow..."

A source located in Canada that does a lot of Pontiac heads did a set of Edelbrock 72cc castings for a customer that were reported to flow 323 cfm at .600 lift with the use of a 2.190" intake valve. It was stated the intake runner volume on these piticular heads was 225 cc's. Yet another source that does a lot of Pontiac heads located in Ohio did a set of 72cc Edelbrock heads for a customer that used the same 2.190" intake valve size and they were stated to flow 309 cfm at .600 lift but they had a bigger 236 cc intake runner. If the info is correct that's 14 less cfm airflow dispite having 11 additional cc's of intake runner volume.

[Skip Fix]

As Cliff said intake choice will make a decision for you. My pump gas motor has 320 cfm CNC heads and a massaged T2.(the 320 is not on a Superflow bench).

As far as intakes being "corks" on Edelbrock heads. My last 455 in the TA had hand ported 320+ E heads. To rush it together for a Southern Nationals I used my HO intake to use the Shaker. Later after modifying a Shaker base for a Holley/Demon I used a Torker 2. It picked up 0.4 seconds and idled better than the HO intake with its 3/4" Holley adapter(which picked up 0.3 seonds over a Carb Shop modified Qjet on the HO intake and a 1/2" spacer).

Back to discussions in the past I really think the velocity of a 225cc port on a 455+ ci motor is negligable, figure even the old Vortec heads Chevy put on their truck 350 ci motors had bigger ports than our Pontiac iron D ports. Lots of torquey 383/400 ci Chevy motors(almost the same dimensions as our 400s) use 215-230cc port heads.

[Cliff R]

"Lots of torquey 383/400 ci Chevy motors(almost the same dimensions as our 400s) use 215-230cc port heads."

Skip, having decades of experience with SBC engines, I can tell you for certain that a 200cc intake runner World Products Sportman head will easily make 700-750hp on a well prepared 355cid engine. Even the very best factory heads, 461X castings only have 171cc intake runners, the better "Vortech" heads are close to that size, and the vast majority of the famous "double hump" castings are only 165cc. I have a customer running SS to low 9's at over 150mph using the 165cc 041 castings! How much head flow do you need for 355cid, or 383 or 400 for that matter?

The guys installing 215/230cfm heads have WAY more head flow than they need for most street and street/strip applications on those little "mouse" engines.

I can tell you for certain, a 355cid engine at 10 to 1 SCR and a 230 @ .050" cam, is pretty "sluggish" using a 200cc runner head, at least in comparison to using a set of 165cc heads on the same engine with the same camshaft.

I throw this at you since we've moved to discussing SBC's, the intake manifold can be a BIG choke point on them as well. We've picked up significantly at the track with quite a few combinations moving up to the Victor Jr with the larger castings, mostly on full race set-ups using big cams on extremely "tight" LSA's, which those combinations really seem to enjoy.

Completely different philosophy, and approach to making respectable power with a Pontiac engine, here in the street section, at least if you are trying to keep up with the SBC crowd.....IMHO.....Cliff

[Steve C.]

How much does the intake & carb effect things, for those who like to play with numbers...

Flow data is an accurate predictor of an engine's potential power output if the rest of the motor's components are matched to the cylinder head's flow characteristics.
Air Flow Resarch developed a formula that predicts horsepower potential based on intake-system airflow, or the TOTAL airflow to the cylinder thru the carburetor, intake manifold and cylinder heads (at 28").
It is: horsepower = 0.25714 x cfm x number of cylinders
( there are a few caveats required to reaching the predicted power level, but let's keep it simple ) Example:
Cylinder head flow- use a head that flows 260 cfm.
Intake flow efficiency- with flow bench testing on a unmodified Performer intake it was in the 88 percent range.
Carburetor efficiency- reduce flow by another 5 percent.
The result is 460.38 hp

This calculator provides almost the same results:
http://www.wallaceracing.com/calcafhp.php