[Steve C.]

Of interest, in the new HPP magazine there is a 1979 Trans Am with a built Olds 403cid motor and used primarily for street duty. They used Bulldog aluminum heads that have a 240cc intake runner volume as cast and flow about 290 cfm out-of-the-box. Motor cranked out a very nice 517 hp and it made it's peak power at only 5,700 rpm on the dyno. It used a 238 degree hyd roller cam.

408 cid - 240 cc runner - 238 degrees duration - 5700 rpm - street duty



( FYI the article was written by our good friend here on the board Rocky Rotella. As usuall another fine job by him )

[Cliff R]

"Cliff your new KRE heads are some of those "big high rpm "heads others talk about."

Hardly, they are unported versions, considered by many to be at best 230cfm, 220 by others!

We think they flow better than that, at least by looking at the improvements we saw with them on back to back testing, track and dyno.

We still consider our 455 a "tractor" engine. We shift at 5000rpm's for mid 11 second runs, using the strong/broad torque produced by our combination instead of strong top end power. Even though the engine pulls hard to at least 5800rpm's, I still choose to short shift it, rather than "grind" it up just to run just a tad quicker.....Cliff

[Skip Fix]

But most seem to think 180cc ports are getting out of "tractor" range Cliff, and you have those high rpm rods too
Next time I'm at the track I'm going to try short shifting a little also.

[Cliff R]

Skip, the Crower rods simply keep me from getting that "pucker factor" when we spin the big 455 up near 6000rpm's, I sleep better at night too!

I've tried shifting at at every rpm between 4800 and 5800. There is less than a tenth to be had between those points, so I simply shift at 5000rpm's for bracket racing. It also give me some room to work during the run, if the car slips a tad on the launch or I don't think my RT was that good. I can "buzz" the engine a bit harder and make sure I get to the end first, not giving my opponent any room to back off the throttle.......Cliff

[Skip Fix]

Just giving you a hard time Cliff!

I agree with the good reasonable priced rods out there now why use cast. I had a definite pucker factor when we dynoed my first 455 with the RAIV heads and buzzed it to 6200 with cast rods! It wasn't shifted that high but did see 6000 s few times.The next motor that got those heads got Crower billets-before the less expensive rods were around.


Often these discussion get "I ran 11s and even 10s with all stock pieces" yet most of use do prefer a little added insurance in durability as we has taken parts designed for very low rpm, 300-370 hp motors and are twisting 500+ hp out of them, and then suprised when a component(block,crank,rod) fails, or that a totally redesigned head can make it easier to get those extra HP, but then make them "expensive" race motors.

I hauled my car to several races borrowing a friend's utility trailer. It pulled crappy and with a short wheelbase full sized Bronco and two scarey experiences I felt it wasn't worth dying for the cost of a dedicated car trailer.Good rods, rear end parts etc are the same way if they fail at track speed-why risk your life for a few hundred dollars.

[blaktopr]

Oh my god. How bout we pull out our blanks and see whos is the biggest. There we go, problem solved. Where in this thread does it mention what the title suggests. Port velocity vs volume. It should say "whos car goes this fast with this head port size, big or small" How about some talk on how some ports are the same size cc but has anyone checked with a mold on the shape? Probably different shapes. How about the relationship between these ports and the size of the motor or how the engine speed can effect the size and shape of a port or vice versa. Why do some guys run better............the size, the shape, the flow??? MMMMMMMMMMM. How bout a question, can a 250cc intake port have the same velocity as a 175cc intake port. How and why? Answers lead to more questions. But here a discussion can be had to get all those answers and cross reference them to different combos. Not why somebody dont run a number with a cirtain combo. Cmon people!!!!!!!!!!!!!

[blaktopr]

Oh my god. How bout we pull out our blanks and see whos is the biggest. There we go, problem solved. Where in this thread does it mention what the title suggests. Port velocity vs volume. It should say "whos car goes this fast with this head port size, big or small" How about some talk on how some ports are the same size cc but has anyone checked with a mold on the shape? Probably different shapes. How about the relationship between these ports and the size of the motor or how the engine speed can effect the size and shape of a port or vice versa. Why do some guys run better............the size, the shape, the flow??? MMMMMMMMMMM. How bout a question, can a 250cc intake port have the same velocity as a 175cc intake port. How and why? Answers lead to more questions. But here a discussion can be had to get all those answers and cross reference them to different combos. Not why somebody dont run a number with a cirtain combo. Cmon people!!!!!!!!!!!!!

[Steve C.]

It all goes back to Larry's initial post in this thread where on the first page of the article he posted it stated "flow quality is as important as flow quanity".

As already stated here, that statement is not new earth shaking news.
In the 2002 issue of Circle Track magazine Jim McFarland's tech article had this heading.... "Engine Airflow: More Than Just Numbers. Airflow quality can yield cost-effective performance gains."

Jim McFarland says, I recently asked a prominent engine builder, "What's the most frequent question you get when discussing cylinder heads with a customer?" His answer? "How much air will they flow or how many cc's are the ports?" Stop right here. Note, nothing was said about port shape, surface finish, airflow quality, cross section vs. torque range, combustion chamber shape, or any other characteristic of potential impact on optimizing power. Only "how much airflow" and "how big are the ports." What's implied is that more flow must mean the better when, in fact, both expectations can be misleading, if not wrong.


( 215 cc's is not too big for an honest street application and does not automaticly mean a high rpm "race" application. Some just like to step it up a bit )

[blaktopr]

Yes, airflow quality more inportant as airflow quantity. That should be the discussion in this thread not a pissing contest. Everyone is in the persuit of better times. What we can do is evaluate our own work and try new things to better ourselves in that persuit. Its funny cause the customers only want to know those two things about their heads, Steve, cause I feel we can be more than that. Educated customers. I hate seeing people get taken for a ride cause their machineist and magazine articles. Here we can discuss the facts and ideas to make good decisions and progress for ourselves. Maybe Larry is also trying to say through example is that for strong street motors, any cast iron head can me made to perform very well for the intended et that one is trying to persue, even some strip terrors too. That we dont need to go to the aluminum head yet if 10's, 11's, or 12's is your goal. Maybe im wrong, Larry. But, on the other hand, and with respect to the "example man" who is to say that his head is totally correct in respect to flow quality and quantity. How many items were changed in the past for the persuit of better times. Maybe he has been chasing the perfect setup to complement the cylinder head profile that he has. Maybe that is why not everyone can copy the same combo and get the same results? Depends on who ports the heads. Same cc's same flow but different?? Maybe thats why lots of people change so much. If you know what you are working with inside your head, a better idea of direction to take with selection of other parts. This even goes for the aluminum heads too. Any combo can work or appear to work for low rpm and high. Just cause a motor makes really good power under 6000 doesnt mean it works well. Proper port work may get even better results. We dont know cause not enough testing. We can only discuss our findings. I ramble, sorry. But seriously.......................I would beat all of u in a race....with a d-port 400. Just playing!!! lets get technical.............also without using magazine articles as the arguing points.

[Skip Fix]

blaktopr you bring up the same points I have in many of these discussions where smaller is automatically assumed to have better velocity and quality just based on port size alone. Even using the same head different porters are going to have different size and shape ports to get the same airflow, but as the Pro Stock guys(and the recent article on Chevy head testing I mentioned) found they may have varied power with similar flow due to those other factors. As you have stated it is just not that simple.

"the size, the shape, the flow??? MMMMMMMMMMM. How bout a question, can a 250cc intake port have the same velocity as a 175cc intake port. How and why?" Shape and entrance into the chamber are definite possibilities.

I've been called ignorant for suggesting that port cc is not the end all factor.You might get the same label for questioning that.

[blaktopr]

Skip, let them label us all they want. I'm not sweating it. You shouldnt either. This is a discussion. Next time someone labels someone for trying to discuss a point, not to say who is right or wrong but to discuss it even if it means going into SIMPLER terms for ALL to understand, think about how that someone PROBABLY is calling someone's shop to get something done that they CAN'T do. Its not like anyone calls to recomend a particular port arangement for THEIR OWN combo before it gets strapped into the CNC machine. Just that it flows a GAJILLLLLLION CFM (dr. evil ) Plus I am not going to write a novel about MY opinions on this topic to cover every last detail to take up pages and pages to explain. So label me.

[johnta1]

I could care less if it's the biggest, fastest, or whatever as long as it makes me go faster.

[Bruce K]

I think it is a combination of head & cam. My new combo has 235cc runners & a much larger cam than my previous combo of ported 6X's (230/202 flow) & 224/230 cam. I have notice a considerable shift in the rpm range, the old combo came on from 2500 to 5000 whereas the new combo is much higher at 3800 to 6200. I believe the cam has as much or more of an influence on the rpm range as the heads.

[Cliff R]

Bruce, no doubt about it. The cam must compliment head flow, or we end up with tennis ball size ports and sluggish velocity thru them, then not enough duration and overlap to really use their potential. It's always been about the combination of parts. This particular topic continues to come up, and it clearly shows that folks can run well with large port heads as well as small port heads.

The discussing usually leads into how much large port high flowing heads hurt low end power? The cam in those scenarios would have as much to do with it as the runner volume!......Cliff

[uneasyrider]

Originally Posted by Larry Navarro

Very interesting info but not necessarily limited to "street" cars.
Use "zoom" feature to enlarge the pic for your reading pleasure.

An example:

Theoretical cfm (total for engine) = (rpm x cid)/3456

Q (flow rate in cfm) = V (velocity in ft/min) x A (area of the inlet/port/carb in sqft.)

So theoretically (not taking in factors like ram tuning, friction etc.) for a 467cid engine with a 4.25in stroke will need at 6,000rpm a flow rate of,

Q = (6,000rpm x 467ci)/3456 = 811cfm total (carb size)

Now divide that by 8 and you need 101.4cfm(ft^3/min) per cyl.

Q=VA, 101.4 = VA.

At 6,000 rpm your piston velocity for a 4.25in stroke is equal to:

piston velocity(V) = (stroke(in) x rpm)/6

V = (4.25in x 6,000rpm)/6

V = 4250ft/min

Q = VA

101.4ft^3/min = 4250ft/min x A

A = 0.0238ft^2 = 3.42in^2

So you need an intake port 3.42 square inches to feed each cyl. at 6,000rpm. That's an intake port 1.848in x 1.848in.

That is just an example of the port size you need to get the right velocity to match the velocity needed to fill the void left by the piston at 6,000rpm for the above engine in theory. That doesn't say a thing about how well the port will work at lower or higher rpm or about friction, ram tuning etc, it's just straight flow rate at 6,000rpm but that is the basic relationship of flow to "volume" (port area) vs. cid and rpm.

[Skip Fix]

So then the biggest SCE gasket that is 2.350"x1.135 od 2.66" sq in, and the "big" Edebrock throat area that is 1.92 diameter (pi x r2 3.1416x0.96x0.96) of 2.89 sq in can't feed 467 at 6000 and should have peaks below that then?? Maybe back in the tractor rpm range?

[Skip Fix]

Sorry for the multiple posts, server gave me errors as it did trying to delete the extras.

[Skip Fix]

Sorry for the multiples server fatal error, as it did trying to delete them.

[uneasyrider]

Originally Posted by Skip Fix

So then the biggest SCE gasket that is 2.350"x1.135 od 2.66" sq in, and the "big" Edebrock throat area that is 1.92 diameter (pi x r2 3.1416x0.96x0.96) of 2.89 sq in can't feed 467 at 6000 and should have peaks below that then?? Maybe back in the tractor rpm range?

What I gave above was a rough calc. not to be taken as anything other than a way to come up with a number that should be a base line without friction and other dynamic factors that occur in the real world. It's a way to show a trend not an exact port size if you see what I meen? It's "close" a SWAG.

[Steve C.]

http://www.wallaceracing.com/chokepoint-rpm.php
Calculator for cross section based on rpm

Fun to play with numbers...

A truck motor 4.180 bore 4.210 stroke at 5000 rpm = 2.33 sq inches.
Use a factory 2.05 x 1.30 intake gasket at 2.31 sq inches.
Same bore & stroke taken to 6000 rpm, Felpro 1233 gasket at 1.180 x 2.200 or 2.596 sq inches.
A truck motor 505 at 6000 rpm, SCE #128103 gasket, 2.320" tall.