I promised to touch on this in one of my previous threads and share with you guys why we do so and why it's so important...

First off, whats even MORE important than flow testing an exhaust port thru a pipe is to actually DESIGN the exhaust port thru a pipe....And the pipe should be curved and angled down to simulate a "typical" header as much as possible.

No exhaust port in any internal combustion engine that I'm familiar with exits directly into the atmosphere...There is always a header or tubular exhaust manifold to collect the gases exiting the port. This changes the entire dynamics of the gases rushing thru and exiting the exhaust port. Bolting on a header (or flow tube in this case) places "pressure" on different areas of the exhaust port which has a direct influence on "flow" and what avenue of attack you would use to try and re-shape the port so it could flow MORE.

When an AFR exhaust port is flowtested on a bench I usually see a larger gain with the use of a flowtube versus open....this is because the AFR exhaust port was "conceived" and designed with a pipe in place to simulate real world operating conditions....the path the airstream will normally encounter bolted to a set of headers.

Note the test below of a 225 Exh. port with and without a flowtube....I grabbed this off the production floor so some numbers might be a CFM or two up or down from what we "advertise".

.......LIFT.........200....300....400....500....60 0....700

CFM w/o pipe....116....172....201....215....221....224
CFM w/ pipe......122....182....219....239....249....255

At .600 lift there is a 28 CFM "loss of information" without the flowtube
At .700 lift its even greater (31 CFM).

Also, note the gains from lift point to lift point with and without the flowtube. More information that might be recorded in error had the head been flowtested "open".

Whats also interesting is the gains seen from the flowtube....I mentioned this earlier. They are MUCH greater than you would typically see from a Brand "X" SBC/LS1 cylinder head. I would say more the "norm" would be a 15-20 CFM gain with a flowtube in place versus open. I feel this stems from the fact the AFR port was designed with a pipe in place from its inception, and therefore "loses" more flow when tested without a pipe due to obvious changes in the dynamics of the port when the exhaust blasts out into the open air.

Some people feel its "cheating" when you flow an exhaust port with a "pipe".

I feel it's ludicrous not to....and ALL the exhaust port information that I document is with a pipe....(the same pipe by the way, so when I look to compare information from a test I might have conducted five years ago, I'm not worried about any "variables").

I was going to touch on the whole "flowing thru an intake situation" but I will save that for later...this post is already too long.

Regards to all,
Tony Mamo

 

interesting.

heres my head w/ flow tune and the PP was done the same way. to get the "higher' number advertised steve used a 2.25 straight pipe had lying around.

 

Tony, have you ever seen a port not gain any or worse yet loose flow on any of the heads you have flowed?

 

Also, like flowing the intake port with an intake on- the intake becomes the restriction but on the exhaust port were is the point were the tube becomes the restriction? I know in situations were you have to go up on header size but this may be a tech question answered were the "bigger" headers are needed- or not needed.

 

EXCELLENT info as always thanks Tony!!!!

 

Good point, this morning I was wondering if any companies would be willing ot produce intake flow numbers with various intakes (compare ls1,ls6 and fast intakes) to see how the intake ports flowed through them.

 

people use to bash TEA for using a pipe to flow their heads... They told me its a good idea to use a pipe since it helps give you an idea how they will work on the car with exhaust hooked up..

My old TEA 1.5 flows
Head Flow Numbers

- Exhaust ----Intake
.100----51.7----70.2
.200----111.2---138.6
.300----167.6---201.1
.400----216.3---250.9
.500----248.0---282.5
.550----258.5---294.5
.600----265.6---302.2


TEA 1.5's flowed killer on the exhaust side! Im gonna have them touched up a bit to help with the low end numbers some though

 

The only thing I don't like about flowing with a pipe is some companies will do it, and then mislead you to think they haven't used a pipe. I'd prefer to see with Pipe, W/O pipe, With the Intake, and W/O the intake become the industry standard but that's probably too much to ask.

 

Not bad

My TEA heads flow 272 cfm through the pipe with a stock exhaust valve

 

Pipes are great, but the type type of pipe can dramatically change the flow w/o touching the heads. just look at my PP results. i believe TEA uses a straight pipe.

just like flowing on a bigger bore will yield a higher flow rate

 

jrp, thats the reason im having mine looked over since they are off the car. I know no to flow benches hardly read the same, but im just curious to see how they do in a different shop

 

Gosh, were's all those PIPE BASHERS now??

 

Pipe bashers? Linda Lovelace???

How about showing us your pipe Brian?

Boy does that sound X rated...

Ed

 

I do not believe in flowing with a pipe. Flowing with a pipe smooths out a turbulent port. It's better to get a port to flow smooth without a pipe. Also, flowing with a pipe lures head porters into quitting on the exhaust ports sooner than they should because they think they've reached the magic intake to exhaust ratio.

Better to have 270 cfm before a pipe than 270 with one.

Just my .02

 

I guess everyone wants to see Tooley's Tool

 

Any legit 270 cfm exhaust port is awsome,with or without a pipe.

 

Any of you guys develop a really efficient exhaust port, and then lower the compression ratio of the motor?

 

Very good post! Actually, most model airplane engines used to dump exhaust directly into the atmosphere, but now most of them have mufflers or tuned pipes. If the muffler or pipe falls off one of these engines in flight, it changes the tunning so drastically that they will sometimes stop running.

 

Greg Good, have you ever got a port to flow smooth w/o a pipe and then reflow it with to compare your results? That would be a nice comparison, but I am thinking not since you havent posted the details of such flow test.
I like the idea of testing with variables as close to possible as its going to be used. I dont forsee myself removing the headers to race, even if it smoothed out the flow that little bit!
Good info everyone, thanks Tony.

 

It has been done by many race car builders. NASCAR and other such racing proved years ago that in this environment, by reducing compression, one picks up horsepower due to an increase in volumetric efficency in engines making over 100% due to scavenging the exhaust completely out of the combustion chamber.

Let me explain. Lets compair two compression ratios in a road race small block chevy with a bore of 4.125" and a stroke of 3.25" (347 destroker).

Our first comparison is a 13.6:1 compression. Let's say we are using an 18" head with a 62 cc combustion chamber, a deck hight of zero (piston crown is level with the deck at tdc .000"), with a felpro gasket (3 cc volume) and a 10cc dome. At TDC of the compression stroke, the air/fuel mixture is compressed in a 55cc space. If the intake and exhaust are tuned close to perfectly for the rpm we are spinning, the exhaust will scavenge ALL of the exhaust from this area at the top fo the exhaust stroke, and the leading edge of the intake stroke, and will probably pull some freak air/fuel through the exhaust valve (over scavenging). THis means that our limit of space with which to fill air and fuel is approximately 7.9% larger than the displacement of the engine (which could be slightly above atmospheric pressure due to inertia in the intake ports creating a slight pressurized effect (much like having a couple lbs of boost in a highly tuned engine).

Lets compair this to an engine that is 10.2:1 compression. This would be the same engine with a 10 cc dish instead of a dome, brining the compression volume up to 75 cc. This yields a 10.7% larger space than the engine's displacement to fill with air and fuel, and actuall this gives us 2% more inductoin flow than the larger compression engine. Not only that, remember we are dealing with a wedge shaped chamber. A flat top or a dished piston produces better burn efficency with a wedge shaped chamber. THere is a good probablity that in this case the lower compression engien will actually make more horsepower, and will definately yield more mid-range torque. In road race applications or classes with limited carburation or induction, this will yeild more gas milage, and more horsepower due to 2% more of your fuel to remain in the combustion chamber during the overlap period in which scavenging occurs.

This is why NASCAR didn' lose any horsepower when they hanged the rules limiting the engines to 9:1 compression
Any questions?