[ScottU]

Has anyone ever flow tested a complete head, intake and carb system? Is it possible. Trying to figure out were my restriction may be.

[Stan Weiss]

Do not know how many flow with the carb. But intake manifold and head combination is done all the time.

As far as the carb goes. What manifold vacuum do you have at WOT just before you shift?

Stan

[Skip Fix]

Yep some pictures and results here I did on a ported E head Tomahawk intake Holley and Q jet and even air cleaner. I think Jim Hand had some articles on his with heads ]

[Steve C.]

Within a related topic I provided this information....

Head flow and the intake manifold are interconnected. The intake effects the total air flow, as does the carb.
Rocky Rotella had some articles published in High Performance Magazine that involves the subject of total air flow thru the intake system. In conjunction with the article he tested the Performer RPM intake as cast on a stock SD-455 cylinder head that flowed an average of 237 cfm at .550" lift. Flow bench tested the RPM intake was just over 92 percent with the SD head. If the percentages stay true as flow goes up, you need head flow in the 260 cfm range to get 240 cfm into the engine. He also tested the flow through carburetors. His Holley HP950 and a Cliff Ruggles modified QJ reduced flow by about another 5 percent. If the QJ is stock, the reduction can be as much as 7 percent depending on the angle of the secondary air valves.
Anyway we can see it can get very involved when you consider the impact of the intake manifold and carb on total airflow.


.

[Skip Fix]

http://forums.maxperformanceinc.com/...t=flow+testing

[Jack Gifford]

This brings to mind the famous old photos of Mickey Thompson doing flow measurements with an assembled block/head/intake hanging on a wall! It wasn't a Pontiac- maybe the destroked SBC for his Harvey Aluminum Special car for the Indy 500 in '62.

[steve25]

It's done all the time to find out where the true restriction is .

I can't tell you how many people bring me heads to port and then after we discuss there build and that they are running a stock or mild aftermarket Intake I tell then them that I would even be wasting there money to port the heads!
There choke point would then be in the Manifold and all I woukd be doing by porting there heads would be to give there motor a smaller power band!

If you are running stock D port iron heads and a iron non EGR intake , your restriction is in the heads.

If you are running any of the normal aftermarket heads ( non High port and such ) these heads out of the box flow anywhere from 260s to 275 cfm@28" on the Intake side and then any iron intake be it 4bbl or tri power will be a restriction at a given rpm level and or CID .

Any of these heads in ported form will call for something better , and there are many choices to get there , but more info on what your motor is built like is needed!

[ScottU]

Not sure on the manifold vacuum just before the shift. Never monitored it. What would or should I be looking for.

Working with an NHRA stock eliminator engine as well as a street engine combo.

The NHRA combo is a 1971 455 HO. I am wondering if my choke point is the intake. The only option I have is to use another accepted intake(485640) or find another 483674 casting that is better. I am using the 71 single booster Q-Jet. I think I am at my limit with the heads for what is legally allowed. Intake castings are hard to come by. I have a couple but have never flowed the system before, just the heads.

The street engine combo is a stroked 455 with KRE D port heads modified by SD Performance to flow around 290 with an Edelbrock dual quad intake and two Edelbrock 600 carbs. I am thinking the manifold is the choke point here as well.

Thanks for the replies. I guess it has been done and should show where the choke point is. There should be some differences just from pipe loss along the length the more you add to the test. Just not sure what to look for.

Thanks, Scott

[Skip Fix]

ScottU as I am sure you know different castings heads and intakes can sure have different flow. If you can borrow a few intakes I would sure do that and flow them all on multiple ports upper and lower plenums. Rocky Rotella has some measurements on different year RAIV and HO intake plenum depths in a HPP article. My '72 SR intake cast in '76 was different than either.

Dual quad intakes look cool but generally don't flow that great. Heck even the Warrior/Nash TR I have does not keep up with a 320cfm head. But the cool factor sometimes is worth it on a street car

[Half-Inch Stud]

Pretty sure the Pontiac Vacuum gauge hits 0 mm Hg at WOT too easily for any fine flow evaluations.

Agreed with above stock iron intake port comment. Yet intake is easily swapped so i tend to assure the head is "ported" for future growth.

"Ported": minimum best effort is to blend the bowl-seat-chamber, and thaat's it.

"properly ported"; include sanding smoothing roof & floor for attached flow, yet maintain original FACTORY port shape, around guide boss. Modifications with a grinder: open CSA across the pushrod bulge to be 10-15% larger than the blelded valve-bowl minimum CSA result, gring open the valve curtain, assure pushrod hole is ovaled to accomodate 1.65:1 ratio, deburr the oil drain-back. DONE.

HIS (6-pack influenced porting) Raise the roof (HO Racing shows an excellent guide), Lower the runner floor, do not lower the short-turn. Have a Gasket opening in-mind, ans a series of CSA goals for bowl, valve curtain, turn, pusshrod bulge, and opening. Rather uncheek the short-turn firt, THEN carefully consider the short-turn bowl blend to be as high a turn radius you can muster (4" turn radius is Bravo, while <\= 1" turn radius is Bravado Stupido. HIS

[v869tr6]

If you flow one port in the head and intake I would think only a single barrel of a 8 pack would give any accurate data.

[johnta1]

I always liked the 71 intake better than the 72 intake.

I'd look for an original 483674, not a service replacement.

[ScottU]

I have two original 71 intakes. I also have access to an original 72 intake for test purposes. Time will tell. How much of a difference will be noticeable. Does a stock intake always restrict flow?

[Tom Vaught]

Originally Posted by v869tr6

If you flow one port in the head and intake I would think only a single barrel of a 8 pack would give any accurate data.

I built a rig for Ford and gave the same info to Wilson Manifolds on how to flow and read multiple cylinder flows at the same time to make the data more accurate and also define the distribution in the intake tract.

Tom V.

[Skip Fix]

The difference Rocky saw in plenum depths was very minimal I want to think 0.050! My SR was a about halfway between. So probably very minimal I would look more at core shift and casting flashing since you can not legally port to correct it.

For quickie flow checks I do two ports outside and inside and then flip a dual plane so those same ports get an upper and a lower plenum test. If I was looking for every last CFM like the heads up guys and Engine Masters guys and probably some of the Stocker and Super Stockers I'd do every port and have a wide band in every tube on the headers.

[steve25]

A stock non EGR iron intake has been shown to allow 500 hp to be made, or a tad better , but a big part of the key is to modified the plenum to take a atleast a 1/2 tall open spacer.

The shallow side of the plenum badly needs slower velocity out of the bottom of the Carb ( the big secondary's on a Q - jet are a plus in this regard ) at high revs to get the air mass to turn into the runners, and since the best way to do that is a bigger Carb, the next best way is a spacer.

On the other end of the motor The right lenght collector extension and a merge type collector at that really helps in allowing the Exh pulse to restart the Intake flow mass during the end of the Cams overlap period.

The Intake cycle is only 180 degrees and at 5000 rpm that cycle only last .006 second, so if you think that it's not important to keep the Intake flow mass once it enters the manifold runners moving as fast as possible without hitting the sonic brick wall in your motors peticular power band , you've got some learning. To do !

[Half-Inch Stud]

Originally Posted by v869tr6

If you flow one port in the head and intake I would think only a single barrel of a 8 pack would give any accurate data.

Surely you be correct. Tiz why Smokey had engine block mules: From what i heard, one was an 4-hole flow bench, another an 8-hole flow bench, and an upgrade featured a rotaing assy with highly modified "pistons" to simulate flw timing. Told youz more thani i know; need details to go any further.

[Half-Inch Stud]

Steve25, great insight on the shallow side affect to the Primary. And yea we all need to attain 3:1 or 4:1 merged Collectors for better results across the RPM ranges. The legacy 4:1 Collector is deplorable.