The Soft Head
- Thread starter Pinhead
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Anonymous
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Interesting; thanks, Pinhead.
It strikes me that a lot more could be done, or done more easily, to aim and swirl and tumble the airstream and to get a homogenous mixture, if the intake poppet valve were replaced with a shaped rotary-valve, and if the fuel were port or direct-injected (NASCAR still uses carburetors, with restrictor plates, don't they?).
Notice how much importance Widmer reportedly attaches to the final "squish" event of the compression stroke. Notice that the pistons (those made available to be photographed, which may be significant) have fire-slots, a technique which was popular among racers for a while and has since declined, only to reappear recently in the guise of Singh's grooves. Food for thought.
It strikes me that a lot more could be done, or done more easily, to aim and swirl and tumble the airstream and to get a homogenous mixture, if the intake poppet valve were replaced with a shaped rotary-valve, and if the fuel were port or direct-injected (NASCAR still uses carburetors, with restrictor plates, don't they?).
Notice how much importance Widmer reportedly attaches to the final "squish" event of the compression stroke. Notice that the pistons (those made available to be photographed, which may be significant) have fire-slots, a technique which was popular among racers for a while and has since declined, only to reappear recently in the guise of Singh's grooves. Food for thought.
Widmer's website is at http://www.theoldone.com. It has copies of all of his old Hot Rod articles, look under articles.
He has some good stuff, that 500 hp Honda is something!
He has some good stuff, that 500 hp Honda is something!
I thought it interesting that both Larry Widmer and David Vizard stress the importance of a swirling spiral flow down and around the cylinder on the intake stroke. Vizard goes on to explain the use of the natural "biasing" of the flow around corners in the intake tract to accomplish this.
On our Ford 300 the rear three cylinders offer a natural biasing due to the intake valve being at the rear of the chamber. The airflow going around the corner will naturally hug the outside wall of the port and then flow around and down into the cylinder.
However, the front three cylinders will tend to flow more toward the center of the cylinder. I dunno which is better but they certainly have to give different results. It would seem preferable for them all to be the same.
I was envisioning a new type intake divided into two (or three) sections, each one pointing toward the front and slightly outward with a carb on each section. This would tend to direct the flow into all cylinders more evenly. You could get fancy and use sidedraft carbs for a more direct flow. I dunno what the linkage would look like
How's that for a goofy idea :roll:
Joe
On our Ford 300 the rear three cylinders offer a natural biasing due to the intake valve being at the rear of the chamber. The airflow going around the corner will naturally hug the outside wall of the port and then flow around and down into the cylinder.
However, the front three cylinders will tend to flow more toward the center of the cylinder. I dunno which is better but they certainly have to give different results. It would seem preferable for them all to be the same.
I was envisioning a new type intake divided into two (or three) sections, each one pointing toward the front and slightly outward with a carb on each section. This would tend to direct the flow into all cylinders more evenly. You could get fancy and use sidedraft carbs for a more direct flow. I dunno what the linkage would look like
How's that for a goofy idea :roll: Joe
Lazy JW":2qhn6foo said:I thought it interesting that both Larry Widmer and David Vizard stress the importance of a swirling spiral flow down and around the cylinder on the intake stroke. Vizard goes on to explain the use of the natural "biasing" of the flow around corners in the intake tract to accomplish this.
On our Ford 300 the rear three cylinders offer a natural biasing due to the intake valve being at the rear of the chamber. The airflow going around the corner will naturally hug the outside wall of the port and then flow around and down into the cylinder.
However, the front three cylinders will tend to flow more toward the center of the cylinder. I dunno which is better but they certainly have to give different results. It would seem preferable for them all to be the same.
I was envisioning a new type intake divided into two (or three) sections, each one pointing toward the front and slightly outward with a carb on each section. This would tend to direct the flow into all cylinders more evenly. You could get fancy and use sidedraft carbs for a more direct flow. I dunno what the linkage would look like
Joe
Reckon I'd get more response by asking how much more torque I can get by putting sparklers on my wheels :roll:
Lazy JW":3c6w4ho6 said:I thought it interesting that both Larry Widmer and David Vizard stress the importance of a swirling spiral flow down and around the cylinder on the intake stroke. Vizard goes on to explain the use of the natural "biasing" of the flow around corners in the intake tract to accomplish this.
On our Ford 300 the rear three cylinders offer a natural biasing due to the intake valve being at the rear of the chamber. The airflow going around the corner will naturally hug the outside wall of the port and then flow around and down into the cylinder.
However, the front three cylinders will tend to flow more toward the center of the cylinder. I dunno which is better but they certainly have to give different results. It would seem preferable for them all to be the same.
I was envisioning a new type intake divided into two (or three) sections, each one pointing toward the front and slightly outward with a carb on each section. This would tend to direct the flow into all cylinders more evenly. You could get fancy and use sidedraft carbs for a more direct flow. I dunno what the linkage would look like
Joe
It probably wouldn't gain much unless a) your side-draft carbs atomize the fuel much better or b) you port bias the head to swirl even more (or both).
You probably would gain volumetric efficiency down low since it would inherently give you a longer intake runner resulting in more "ram air" due to the added air momentum. You could also customize the intake runners to be more of a funnel than the original intake manifold.
Combining port biasing, long funnel intake tracts, and well-atomizing side-draft carbs would probably help quite a bit.
A
Anonymous
Guest
How long a straight section, after the turn in the manifold, does it take for the intake charge to get itself centered so that the swirl in the front three cylinders is the same as the swirl in the back three, Joe? An early factory manifold forces the air to make hard turns, which intuitively looks bad, but the the runners all go straight to the ports, which we are guessing is a good thing as far as uniform swirl effects. My Clifford manifold, the design of which may have been guided as much by intuition as anything, has big sweeping turns that look impressive, but what if by keeping velocity up, inertia keeps the charge piled up on the side of the runner? Let's see, could you help the swirl situation with all of these single-carburetor manifolds by getting a piece of solid 2 X 2" aluminum barstock and milling ports in it, to space the manifold out from the head by 2"?
The more you think about this, the better three side-draft Webers look, not to mention the fuel injection set-up. Vizard cast up some manifolds to mount three SU slide-valve carbs on a 292. He is very enthusiastic about that set-up, claims it pulls like a steam engine from 400 rpm up. Aside from the problem that SUs have a poor reputation here, that is food for thought as well. But if a straight run to the head is important, even these siamese manifolds of Vizard's are sub-optimal.
The more you think about this, the better three side-draft Webers look, not to mention the fuel injection set-up. Vizard cast up some manifolds to mount three SU slide-valve carbs on a 292. He is very enthusiastic about that set-up, claims it pulls like a steam engine from 400 rpm up. Aside from the problem that SUs have a poor reputation here, that is food for thought as well. But if a straight run to the head is important, even these siamese manifolds of Vizard's are sub-optimal.
happens to be a tripple SU manifold on Aust ebay at the moment:
http://cgi.ebay.com.au/FORD-FALCON-170- ... dZViewItem
this one you need to cut off the log and braze weld a plate to the inlet ports(runners).
the manifold is ported for 3 x 13/4" Su's ( or 1.5 " Su's ( with a step in the manifold) .
could also fit 2 " SU's if you ground out the ports.
Not sure that SU's deserve their reputation - cant over carb and give good atomisation . - maybe its a result of the english cars they were attched to...
i picked up one of these on ebay - just havent got around to doing the plate mod.
although for simplicty sake i think i prefer the twin SU's - as per AK millers hot rod article.
a lot of people assume that this is for the separate manifold aussie 2V head. ( of which there is also SU manifolds available).- but manifold but faces dont match
Brett
Melbourne
http://cgi.ebay.com.au/FORD-FALCON-170- ... dZViewItem
this one you need to cut off the log and braze weld a plate to the inlet ports(runners).
the manifold is ported for 3 x 13/4" Su's ( or 1.5 " Su's ( with a step in the manifold) .
could also fit 2 " SU's if you ground out the ports.
Not sure that SU's deserve their reputation - cant over carb and give good atomisation . - maybe its a result of the english cars they were attched to...
i picked up one of these on ebay - just havent got around to doing the plate mod.
although for simplicty sake i think i prefer the twin SU's - as per AK millers hot rod article.
a lot of people assume that this is for the separate manifold aussie 2V head. ( of which there is also SU manifolds available).- but manifold but faces dont match
Brett
Melbourne
I'm not sure that I'm adequately describing my thoughts here. The stock 300 already has the REAR three cylinders biased so the intake flow swirls around the outside which is desireable according to Mr. Vizard and Mr.Widmer. The front three cylinders simply cannot achieve this when fed from a single, centered carburetor, be it a one, two, or four barrel unit. Feeding two cylinders with a carb centered between them won't do it either.
Envision cutting the front three cylinder runners off a stock manifold and feeding the rear three with this unit. Take another stock manifold, cut it EXACTLY the same as the other one, and use it on the front three cylinders with its own carburetor. This very crude setup would accomplish the desired biasing of flow to all six cylinders.
Since all six cylinders are evenly spaced, and each one has the intake to the rear, it would be simple to cast a small intake manifold with either two or three runners. The two-runner unit would require three per engine, each identical and interchangeable. Just a slight sweep outward and to the front, bolt a suitable sidewinder carb on, and have fun!
Working on this theory, a straight run to each port is not as desireable as a biased run. According to Vizard and Widmer anyway. I dunno. Just thinking (way out of the box) out loud here.
Joe
Envision cutting the front three cylinder runners off a stock manifold and feeding the rear three with this unit. Take another stock manifold, cut it EXACTLY the same as the other one, and use it on the front three cylinders with its own carburetor. This very crude setup would accomplish the desired biasing of flow to all six cylinders.
Since all six cylinders are evenly spaced, and each one has the intake to the rear, it would be simple to cast a small intake manifold with either two or three runners. The two-runner unit would require three per engine, each identical and interchangeable. Just a slight sweep outward and to the front, bolt a suitable sidewinder carb on, and have fun!
Working on this theory, a straight run to each port is not as desireable as a biased run. According to Vizard and Widmer anyway. I dunno. Just thinking (way out of the box) out loud here.
Joe
The sidedraught SU's tend to be a problem with long duration cams and thus the preference for Weber DCOE etc. With SUs, proportional air velocity over the range is a problem. Erratic modulation arises because, to have the right size at high revs, means the velocity pressure at low to medium revs isn't enough modulate the choke. If the cam is relatively mild and the engine is operating over a moderate rev range then it's not so much of a concern = like the 260Z
I wouldn't know an SU carb if it jumped up and bit me; the only side-draft carb I have much experience with is the Marvel-Schebler on my 1941 John Deere tractor so this is obviuosly way out of my league. Just had a goofy thought that applying some of the Vizard/Widmer theory could be useful to someone trying to get more out of the 300. But what do those guys know :roll:
Joe
Joe
I've been toying around with the idea of using some Honda CV motorcycle carbs from the early '80s on a car engine. It'd definitely have to be one carb per cylinder to be able to get enough CFM for any decent horsepower, but they can be modded pretty easily to produce very well atomized fuel, and parts are extremely plentiful.
The SU's/Hitachis are a nice bit of kit, but they do require TLC. If you are looking at putting them on youir six, then maybe the Datsun setup is for you. For me EFI is the only way to go, unless it's like my rally engine and then the rules dictate I have to use a carb, which is where the Webers come in.
Pinhead I'll give you the heads up on the Mikuni type individual setup = make sure you have some control over the runner lengths, because it will be prone to behave like a dog if you can't get the rarefaction right. I'd investigate dual choke like on the GSXR750/1000
Lazy I haven't read the Windmer article, mainly because I'm stuck in my own world
The gyst from reading the member posts is that the idea is to send the air in so that it vortexes around the pot chamber and burrows down to the piston tops? Well that isn't anything new and way back in the 60/70's we were doing just that by modding the port runners and bowls to increase the angle of attack. The manifold runners were angled too, then three carbs thrown on to give good distribution.
Pinhead I'll give you the heads up on the Mikuni type individual setup = make sure you have some control over the runner lengths, because it will be prone to behave like a dog if you can't get the rarefaction right. I'd investigate dual choke like on the GSXR750/1000
Lazy I haven't read the Windmer article, mainly because I'm stuck in my own world
The gyst from reading the member posts is that the idea is to send the air in so that it vortexes around the pot chamber and burrows down to the piston tops? Well that isn't anything new and way back in the 60/70's we were doing just that by modding the port runners and bowls to increase the angle of attack. The manifold runners were angled too, then three carbs thrown on to give good distribution.XPC66":aepzz7o6 said:Pinhead I'll give you the heads up on the Mikuni type individual setup = make sure you have some control over the runner lengths, because it will be prone to behave like a dog if you can't get the rarefaction right. I'd investigate dual choke like on the GSXR750/1000
Lazy I haven't read the Windmer article, mainly because I'm stuck in my own world
"Rarefaction"??
Widmer obviously does more than that, 'cause you definitely didn't see anything in the 23:1 CR range back in the '70s...
XPC66":2t1cju8s said:....
Lazy I haven't read the Windmer article, mainly because I'm stuck in my own world
OK, so is it worthwhile? Because in order to accomplish this, some special effort needs to be made as there is no way that it works on both ends of this engine as-is. Am I the only one who has noticed this apparent design flaw in the 300?
Joe
