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  #1  
Old 12-19-2001, 06:36 PM
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Default What makes it a swirl port?

All the modern generation engines make a big deal of the fact that the heads are high swirl, because it makes the engine more efficient and more knock resistant etc. I've never heard a good explanation of how the head is shaped to make the swirl phenomenon occur however. What are the differences between a regular closed-chamber head and a swirl-port head? For example the 318 heads from the late 60's vs. the "302" castings.
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  #2  
Old 12-19-2001, 09:44 PM
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I don't think I can get this totally right. So i'll explain it like this.
Swirl is whats happeing to the air & fuel in the chamber after it pass's through the head and valve. It's incorparated in the design. The older heads do not swirl the air & fuel in the cyclinder. It just rush's in and the gas reforms into droplets. Not so in a swirl port head. Or at least not alot.
You may not recognize any real diff in the heads even if there laying next to each other.

Anyone have pic's of there heads. Weather swirl or not so we can get a veiw? Thanks all.
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  #3  
Old 12-19-2001, 10:23 PM
moeflo moeflo is offline
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Worth mentioning, this being a performance site, alot of the swirl"tech" is based around part-throttle emmisions/driveability. Like in the Ford 4.6, with the purpose-shrouding of the intake valve for swirl, the damn things ran faster when they were unshrouded.(they quietly dropped it) I've never seen any meaniful change in mixture motion ,in the chamber, from port-only modifications, without taking a hit in cfm. I think you'll find it to be a function of chamber design, over port design. The "hi-swirl ports" have alot to do with engineers justifing their existance to their non-engineer bosses, and it's something the marketing dept can work with. if you take away the superior exh. ports of these new "hi-swirl" sb heads, I think you might a well be running a "J" head, at least at WOT.
my 1.5 cents

If it helps my case, the last Chevettes featured "hi-swirl" intake ports.
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  #4  
Old 12-19-2001, 11:30 PM
skankweirdall skankweirdall is offline
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Lightbulb

i think your right about the swirl and wot. however having said that i think that quench areas have made the most advances. some early heads had problems when ported because the volume of air that was trying to make the short side turn would just shear across the valve. so we got "swirl port" heads with improved short side radius' or is that radii, any way the only swirl
part of any of these heads is the small bump in the combustion chamber by the spark plug.
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  #5  
Old 12-20-2001, 12:01 AM
FASTDARTCHESTER FASTDARTCHESTER is offline
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Typically, it's the combustion chamber shape. The 302/308 and some others have a heart shape to them, to induce swirl on the intake charge. It aids in mixing the air and gas. They're great heads when you port and take advantage of them. You can find the 302 head in plentiful supplies in junkyards on mid 80's and up 318 engines. Intake port design changed little from standard to swirl heads but the exhaust port is superior in that it features a much improved short turn radius. It reduces airflow stall above certain valve lifts at certain rpms.

I have a set fully ported and polished 302 heads on a 0.030 over 318 with a Hughes cam and some other stealth goodies and it was running consistent 12.50's with a 4.56 gear in a '70 Swinger. This was with the 1.78/1.50 valves with no power adder.

Magnums have this combustion chamber shape to them too. It is a smaller more "quenched" version, but achieves the same effect.
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  #6  
Old 12-20-2001, 05:03 AM
DartGT66 DartGT66 is offline
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...Except that the 308's do not have heart shaped chamber, nor quench areas. They are just regular open chamber heads with a good exhaust port. Some flow benches are equipped with a swirl meter, and according to the results I have heard all the factory Mopar wedge heads have a good swirl, so I guess they are all 'high swirl' heads. The intake port in the 308&302's isn't that much different, so I believe too it's pretty much just a marketing hype.
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  #7  
Old 12-20-2001, 11:04 AM
gthomas gthomas is offline
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I bought a set of swirl heads for the 360ci I built in 1999. We visually compared them to the old style heads and noticed that the center exhaust ports were very restricted. Flow bench tests were not very good on them and they were returned to the dealer. Basically I agree with moeflo in regards to engineers justifing their existance (I'm an engineer). I can't argue with FASTDARTCHESTER in regards to the exhaust port short radius turn, but in stock form they did terrible on the flow bench. And no I do not remember the flow numbers but I stuck with the older heads and had them ported.
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  #8  
Old 12-20-2001, 11:52 AM
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Biggrin Swirl "PORT" definition

So far no one has given the real definition of a swirl port design. A cylinder head WITH the swirl "PORT" can be identified by the ramp that is directly under the valve. You must remove the valve to actually see this. Under the intake valve is a inclined ramp that forces the incoming air/fuel charge to spin just prior to meeting the valve. The idea is that this action makes it easier for the incoming charge to clear the valve and therefore make more effecient power. It is not just a way for some engineering group to justify their existance. There actually is a major difference between swirl and non-swirl heads.
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  #9  
Old 12-20-2001, 12:11 PM
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My take on it was the port is shaped to induce a " swirling motion to the air fuel charge to keep the two evenly mixed. I assume for a better, more complete burn, with no hot spots and keep the detonation to a minimum. From what I have read- the old BB heads, ( 915 thru 452s all basically the same ports) had very good charateristics for this-( unfortunately coupled with poor plug placement that washed the plug out)- The chamber/ piston design also contributes to keeping this going once inside the cylinder.
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  #10  
Old 12-20-2001, 12:56 PM
mr_340 mr_340 is offline
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Lightbulb Swirl

Swirl is designed into the port to enhance the combustion process. Swirl and tumble speed the rate of combustion. This can reduce the octane requirements for that engine and the compression ratio can be increased for more efficiency.

The new Magnum manual goes into this a bit further. I had a set of #302 heads and all I could see different was the combustion chamber. The ports looked the same to me at the time.
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  #11  
Old 12-20-2001, 01:38 PM
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So the physical differences in the heads are...? I've heard of some heads (not Mopars) that have runners in the intake ports to cause swirl, also I've heard the case that shrouded valves cause swirl. Both these sound like a poor method to me because of losses at high port velocities. I've also heard that it's mostly the combustion chamber shape, hence the heart-shaped chambers. Flat-top pistons also are usually used, probably to keep the swirl going (and to reduce the number of hot spots on the combustion area). I guess the point of my question was to see if a non-swirl port engine could be modified to increase the swirl greatly, either with machining or the addition of new material via welding.
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  #12  
Old 12-20-2001, 02:36 PM
sanborn sanborn is offline
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"Swirl" is just a term. The engineers discovered it in the 70s. It helped to keep the fuel/air mixture in suspension as it went in to the combustion chamber at very low mixture velocities. There are a number of ways to achieve it;IE, small ports, restricted intake valves, combustion chamber shape, ramps in the intake ports, etc. Different companies use different techniques. You use whichever technique needed to achieve "swirl". If you talk to real automotive design engineers they will admit it is really new jargon for "turbulence". It is very useful for part throttle operation.

Remember, everything we do with an engine is a compromise in some form. If "swirl" is useful in part throttle or low velocity applications it is probably detrimental in WOT(Wide Open Throttle) applications. I had one well respected cylinder head man(who does CNC race heads for a living) tell me the only accomodation for swirl he will make is the shape of the combustion chamber around the intake valve. It is very critical in keeping the mixture in suspension at part throttle racing applications.

I don't claim to be an expert in this area, I just ask questions and listen very closely. Who's right? Don't know. But I would look at Moeflo's response real close. Maybe his "handle" might give a clue as to what he does for a living.
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  #13  
Old 12-20-2001, 08:12 PM
moeflo moeflo is offline
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gthomas, I'm not shocked at the bad exh ports you ran into, on the later heads. I think it may have been part of a "ugly run" of castings. Every now and then, you can run across some that should have been re-melted for another try. We checked a set of 302's for a k/stock guy, who was considering switching from his old style heads, and they were up, 30 cfm over the older ones. They were nice castings, but, you can run into anything.

goose, any 340/360 head you choose, will have pretty good swirl. It's the nature of the beast. this is due to the valve to bore location, relative to the port's direction. The bore on the long side of the chamber, creates a near perfect "ramp" to aid this. So you can see how the shape of the chamber, can be used to help this transition to the bore wall's ramp. but in the case of a SBM, it naturally occurs. Having done two sets of, equally flowing, w-2's, one early(open chamber) and one set late(closed), with the same chamber CC's, that went on the same flat-top motor, on a dyno, on the same day, the results were within error. So a least in this case, the chamber types didn't seem to be an issue.
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  #14  
Old 12-20-2001, 09:51 PM
CudaMike CudaMike is offline
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Question

Moeflo, do you have a full set of flow numbers (I & E, at the various lifts) for both stock 302 heads, and 302 heads with oversize valves and porting, that you could share with me (or us). Any info you can share would be helpful.
Thanks
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  #15  
Old 12-21-2001, 08:28 AM
moeflo moeflo is offline
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Mike, I got them, around somewhere. I'll dig 'em out and post them.
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  #16  
Old 12-21-2001, 02:18 PM
HankL HankL is offline
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Almost any head with a heart shaped combustion chamber like these Magnum RT heads:




will create some swirl in the intake charge of air/fuel as it first enters.

Note that the intake valve is shrouded on one side which also helps.

In the Magnum truck engines apparently even these features are not enough to create as much swirl as the engineers want. To increase swirl even more, the runners of the 'beer barrel' intake manifold are slightly twisted too.

More pictures of the RT Magnum head at:

http://mid-mich-mopars.org/dakheads.htm

CF Taylors big textbook on engines called 'IC Engines' has a chapter on how combustion chambers and valve shrouding increase swirl. In general more swirl=less ignition advance needed.

The less ignition advance you need to create maximum torque, the less 'negative work' is done when the rising piston has to force itself up against the pressure of already started combustion.

In the ideal case, a combustion chamber with 'super swirl' would burn the fuel so fast and completely that the ignition timing could be set to 0 degrees top dead center.

If the combustion did not start until the piston was already at top dead center - there would be no 'negative work' at all and the engine would produce more horsepower.

The famous engine designer Harry Ricardo is given a lot of credit for understanding how the tornado like swirl could speed up combustion.
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  #17  
Old 12-21-2001, 04:14 PM
Jesse Lackman Jesse Lackman is offline
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Moeflo is right about the 308 head's intake port being pretty much the same as the X, J etc, even the TAs. Of course the pushrod bulge is bigger on the 308s and that may have some effect on swirl but that is not why it is bigger. It is bigger because of more clearance needed with the roller cams the 308 head engines came with. Now if you compare a Magnum intake port to a pre-Magnum port, you see a difference in the port design. The Magnum's intake port is not a rectangle all along it's length, it is "pinched" (narrower) on the bottom. In theory this pinch changes the pressure in that section of the intake port and again, in theory, creates a rolling effect in the port itself. The velocity would increase in the pinched section of the port, an increase in velocity lowers the pressure, the result being a flow shift from the lower velocity non pinched section to the pinched section. In other words a rolling effect or swirl.

I'm not sure how all this works in reality.

Engineer; One who sees something working in actual practice and wonders if it would work in theory.
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  #18  
Old 12-21-2001, 10:49 PM
moeflo moeflo is offline
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Cudamike, it seems I don't read too well. All I've ever done with these heads, is for that guy with the stocker. I've never ported any. I can't answer your question, about the ported comparison.
I just checked his early, and the late ones, back-to-back. As I recall, not a big difference on the intake side, but a huge difference in exh.

Jesse, I'm aware of the theorys concerning the pinched-off area, you describe. Strictly from a pressure/velocity point of view, it makes sense, and if massaged, just so may work. Our observations(attempts,shot-in-the-dark,SWAG's)have almost as often worked in reverse, though. As the incoming flow approaches this pinched area, we've seen it, react to the small area as a localized restriction, instead of flowing,neatly into this area and speeding up, and dropping the pressure. the flow can "stack-up" a little, actually slowing, and raising pressure,. Then it climbs towards the lower pressure, anywhere it can see it. As much climbs over the pinched-area, disrupting upper-half flow, as pushes through the pinched-area. Have never done any of this on these heads, but looking at it, I doubt it works all that well. They are aiming, I guess, at some sort of venturi-effect. That is quite a challenge, if it does not include a 360-deg X-section of the port.(I think). But as alot of wet fuel is on the floor by that point in the port, it may be a good thing, for helping to re-atomize it some. I don't know, but it sounds good.
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  #19  
Old 12-21-2001, 10:53 PM
CudaMike CudaMike is offline
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Thumbs up

Moeflo, if you can still come up with the numbers for the stock 302's that would still be a big help to me. Thanks
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  #20  
Old 12-21-2001, 11:28 PM
moeflo moeflo is offline
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Mike, this was tested for a stock lift cam, so we only went to .500" lift
head mounted to a 4.030" bore slider-plate, that locates head with dowels, for repeatability


FLOW BELOW


The intake was flowed with a clay radius inlet.
The exh., with a header pipe, that exits straight, for 4" and turns down at a 45-deg angle(total 10" long

Sorry about the spotty checking(no .300" on exh, and only a spot-check on the old exh.

Intake used a legal replacement stainless 1.88" intake valve, with no back-cut
the old head had a oem, back-cut intake(2.020)
both exh were 1.600"
To bring about legal CC's the intake seat was sunk .020" and exh was sunk .030"
you would avoid that sinking, if the rules were not in the way.
Intake seat was cut with a Peterson seat & guide machine using a #4038 cutter, exh was cut with a #4005 cutter. The exh chamber was cleaned up with the legal (valve dia.+.250") wide 15-deg chamber cut.

No doubt, more can be had, but this was a hurry-up job, and,as usual, there's little funding for that last little bit.
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Old 12-21-2001, 11:36 PM
moeflo moeflo is offline
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Damn! once posted my neat little columns were squished up.
try it this way:
old intake
.200 /127.7
.300 /175.5
.400/199.9
.450/197.5
.500/196.6
---------------
new intake
.200/125.6
.300/178.8
.400/199.3
.450/206.4
.500/210
----------------
old exh
.450/136.6
----------------
new exh
.200/127.6
.400/172.3
.450/177
.500/181
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  #22  
Old 12-21-2001, 11:49 PM
CudaMike CudaMike is offline
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Moeflo, were these numbers for the 308 casting (360 swirl port) or 302 casting (318 swirl port)? Just wondering from the size of the valves and the numbers look a little high for 318 heads.
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  #23  
Old 12-22-2001, 12:11 AM
moeflo moeflo is offline
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Mike, Now you dunnit. I'm confused. All I remember is they are legal replacements in nhra stock, for 340-360's. They may be the ones with the early,open chambers, but with late exh ports. I went to the dungen(storage-room) and found a new pair of 302's but I can't recall who they belong to, or why they're here.

But, what ever the hell it was we flowed is some sort of 340/360 replacement, not 318.
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Old 12-22-2001, 11:13 AM
CudaMike CudaMike is offline
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Biggrin

Moeflo, sorry for trouble :-(
Yeah, those were 308's. If you ever do flow some 302's please pass the numbers on to me. Lot's of people have used and dealt with the 302's but nobody seems to have flow numbers.
Thanks a bunch for your help!!!
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  #25  
Old 12-22-2001, 05:34 PM
George G. Leverette George G. Leverette is offline
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Is there any data on the 340, 2.02" swirl port 574 heads available? I am runninng these heads on my 72 340 engine and would like to know the value of porting the heads. There is considerable comment on CFM numbers indicating power output, would this be true if the velocity was increased with the same volume?
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  #26  
Old 12-22-2001, 05:36 PM
DartGT66 DartGT66 is offline
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No comments yet about the 2.02 vs 1.88 benefit in moderate applications?
In our country there are not many flowbenches around and the porters do not usually use them. I have felt that since the intake/ exhaust flow relatioship in the SB heds is pretty poor there is not much need for th bigger intake valve in moderate engines. My experience with the 308 heads pretty much support this theory. The intake port unported is very narrow in the pushrod area, and i wonder why the Cc's still needed the valves to be ground deeper if the ports are otherwise about the same as in the earlier heads. It's about ten years since i had those heads but i kind of remember that the bowls were a bit more generous in the 308's than in the earlier heads and didn't actually need a lot of blending.
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Old 12-22-2001, 08:02 PM
moeflo moeflo is offline
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Dart, It was chamber CC's, that was the problem on those. They were for a stocker, and uncut, the chambers were already too small to pass tech. I believe you're right about the 1.88" valve being just as good. You can help the very low lifts with the bigger valve, but at higher lifts, the port, obviously becomes a bigger problem than the valve size, and a little more room on the wall-side, never hurts, either.

George, if you increase velocity, with the same volume, you're flowing more, and that's good. In general, I don't think you have to worry about getting one of the intake-ports too big, on one of these heads, at least for bracket-racing, or hi-po street motors. As I'm sure you're aware, while port sze, shouldn't be a concern on one of these, you can get some shapes wrong in a few places, and lose flow. So you end up with a bigger port, and less flow, and that's bad
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Old 12-22-2001, 11:34 PM
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What I vagely remember from school was that in some instances turbulance gave more velocity and better flow and in some it didn't. It depended on the coefficient of friction of the surface (casting vs. polish), temperature, density of the air, velocity, and cross-sectional area. Obviously too any variables to predict outcomes without years and years of experience.

But I do know that with pure laminar flow the velocity of the air is zero at the metal surface and it gets highest in the center.
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