YOu are right I don't need the volumetric expansion from the venturis with FI. I wonder if anyone has tried to incorporate this to help atomization.

I wonder what that barb on teh secondary plate is for. The injector seems to be aimed right at it. I wonder if it introduced turbulance to help mixing.

Randy, I would think that the screw heads would be in the interface layer (boundary layer) at the surface. They probably do not matter much with the density of air. Let me go back to some text books and I will try to give you a better answer.

Looking carefully at the picture, there is a dark line around the point at which that brass tube meets the throttle bore. There is also a barb on the outside of the throttle body at that point. I think that tube is a vacuum tap or something, I don't think it is connected to that secondary plate at all.

I guess what I'm saying is this: No, you don't need the vacuum you get out of venturis. But more importantly, the main benefit of small ports and runners is to keep your intake velocity up. If you just squeeze down the size at one point, as with a venturi, you only have higher velocity in one little spot, which does not give the benefit. Thus I don't think a venturi would do anything good on an efi/mfi setup.

I think the GSXR 600 38mm throttle bodies would be a good match with the stock 39mm early SC intake ports. In fact, I think using 40mm throttle bodies and tapering the adapter you use between the throttle body and the head would be good too. But of course I haven't done any of this let alone dynoed anything, so take my opinion with a grain of salt. It's just that mechanically or electronically injected velocity stack type systems tend to have nonincreasing diameters between the trumpet and the beginning of the intake port. The area of the intake port increases toward the valve(s), but this is because the airflow into the cylinder is partially blocked by the valve(s).

that is a great bit of information. Correct me if I am wrong, I am still trying to learn all this. The intake track (meant to be from the top of the stack to the valve) has a tapered setup. That is, the diameter is always decreasing. In effect this will cause the intake charge (air and fuel) to speed up and compress as it enters the combustion chamber, thus creating the volumetric efficiency.

Should this taper be confined to the last section of the intake? This would mean inside the head. What about a gradual taper? Taper at the top and then columner all the way down? Just throwing out food for thought.

btw, I too think the 38mm 600 TBs will be a good match for my engine, and I suspect the larger ones will work just as well.

I also think the 38's should be fine. However, the smallest that TWM sells are 46's. Are we thinking too small?

Would the on-center spacing still be 93 mm if you bolt directly to the manifold?

93mm if the weber manifold is used. It will be much greater if they are bolted on the head. I will then have to clear the heater ducts or move the linkage to the back and clear other items in the engine bay.

Jamie says... "will cause the intake charge (air and fuel) to speed up and compress as it .."

Bernouli says that as velocity increases, local pressure decreases in the area of reduced diameter...

Just a little fluid-dynamics-engineer-nerd humor....sorry...

--Wil

In my previous post, I edited to clean up that last sentence a little, and added information about inside the head.

Mike, TWM sells smaller than 46. Their site says;

"Throttle sizes available 40, 44, 46 48 mm"

Jamie, as far as not using the weber manifold, all I'm saying is that a straight vertical shot to the intake port, as seen on the TWM 3006 throttle bodies for 3.6 and 3.8s, is more desirable. For an engine that is not strictly a race engine, there may be negligible difference in practice, I don't really know.

They would not have to mount directly to the head, the height of the throttles and injectors is a question for the other thread. If they were high enough, the linkage might still work. based on the way these throttles are made, I don't really think that spacing them out further should be too much trouble.

However, if there is just as much fab work that has to go in to adapting to the weber manifolds, you might as well make some straight risers. all you'd need is two plates welded onto the ends of a proper diameter tube for each cylinder. Plus you save the cost of weber manifolds if you don't already have them. and I think it would look really cool, like the TWM 3006s. :D

http://forums.pelicanparts.com/uploa...1093554148.jpg

You may find it easier to use the weber manifolds and just a slightly modified weber linkage, and that would be just great, I'm sure.

Bernoulli's principle or the Euler equations are frequently misused - there are a lot of restrictions on their use: - flow at rear of bluff body, viscous flows, etc.

jp - Any thoughts on the flow velocity? The Re will need to be calc'd - looks like the injector is downstream so the viscosity for air can be used.
The Cd for a short, erect cylinder at Re around 40k will be about .76 - see Hoerner, SF. Fluid-Dynamic Drag. Greenbriar.

Of course, the engine spends little time at full power (with the plate parallel to the flow), so the big effect will be the plate itself.
But it is a fun exercise....

Jamie, Your statement on the taper is true. However, inside the head things are a little more complicated because there is a big valve blocking the mixture's path into the cylinder, so the port needs to be bigger around the valve.

Also, on the head, when a head's ports are opened up but the valve sizes are not changed, most of the material is removed near the entrance of the port where the manifold bolts up. I don't think you'll be changing valve sizes, so you're in this boat.

Here are some port size specs (measured where the intake manifold bolts up), from BA's book:
78/79 SC worldwide:
Intake port 39mm Exhaust 35mm
80-83 SC worldwide:
I 34, E 35 (I thought the RoW were the same as 78/79 US but I Guess not)
Carrera 3.2 worldwide:
I 40, E 38
2.8 RSR, 3.0 RSR, 3.0 SC/RS:
I 43, E 43

Note that _all_ of these engines have 49mm intake valves and 41.5mm exhaust valves.

This means that the intake ports are always quite a bit smaller by the intake manifold, because near the valve the port is the same size as the valve, minus the thickness of the seat.

If I were you I wouldn't worry much about the head near the valve, and would keep my head stock size (39mm) if I were going to use the 38mm bodies. If I wanted to use 40mm bodies I would probably still keep the ports where they are. heck, if you had any manifold length at all you could neck down from 42mm throttles to 39mm ports pretty easily. Considering where the RSR engines are at 43mm, I wouldn't be in a hurry to enlarge your intake ports very much, if at all, for a partly street use car, even though yours will be a 3.2.

If you went up to 41mm or 42mm you could use GSXR1000 42mm bodies or even Hayabusa 45mm bodies.

I thought that was only for incompressable fluids like a liquid. Gases act outside these boundary conditions.

Sorry I didn't refresh for a while.

Randy, using a 40mm size, 6k rpm gives me a flow of 2970 L/min per cylinder assuming 495 cc/cylinder for a 3.0. My calculated N(re) is 1127 which is in the Laminar flow region. This is without the injector, valve stem or throttle plate blocking flow. It is corrected for a 13:1 AFR adjusted density/viscosity. Time to go back and add some more terms.

Andy, I have a single manifold that I can try and fit to. I think the straight adaptors may be easier. three flanges connected to three pipes connected to one flange for rigidity and then the TBs sitting on top with stacks on top of those. I could even use that Silicone tubing to attach them. I guess I have to see if I can still gas-weld Al since I don't have a tig welder. Anyone want to donate to the cause for some new tools? :D

AN Re in the 1,000's doesn't sound like an issue (off the top of my head). What air speed did you get from the 2970 L/min?

I don't understand your comment before the last one.

Randy, I think Jamie was answering my little barb about Bernoulli's principle....which BTW....indeed does work for gas flow....

---Wil

Wil, I was making a comment regarding your reduced pressure through a venturi and Bernoulli. I took a fluid dynamics class in grad school but it was outside my major and .. well, I learned enough to be dangerous by not knowing enough. This is why I ask lots of questions.

Randy, I get an intake gas speed (linear flow rate) of 39.6 m/s using the above air flow and the cross sectional area of the intake (40mm). I know that this would increase at 39mm and is likely even smaller when you consider the head ports with the valve stem.

Jamie, for air at 20 oC, I get Re > 1^6. So the bdy layer is not gonna be very large.... I may fiddle with this later on some more if I can get the boring editing done on a brief I need to file. This is more fun, but ....


Wil - Bernoulli's principle is valid only under ceratain conditions, gas flow or liquid flow, whatever. It is frequently abused. I see it bandied about on this forum quite a bit, and expect that many of those using the term know less about fluid flow than a sand dollar (altho they are supurbly designed for their fluid situation...). That was the reson for my admonition.

G'day fellas SmileWavy
Mike sent me an email asking me to give you all some insight as to how I fitted GSXR TBs to an Alfa engine.
Only too glad to help, so here goes.
The bakerlite I used was 20mm thick electrical busbar insulation from in a chlorine plant that was being scrapped where I work.
I used the earlier TB's which are eccentric (like me!!) at their outlet. This proved to be a real PITA when machining them up.
What I did was cut each block in a rectangular shape and center bore them 40mm using a lathe with a 4 jaw chuck. I then bolted each one to the alfa manifold and aligned the bores. Then I placed the TBs on top and scribed their outline into the bakerlite. Then it was back to the lathe and after carefully lining up the scribed lines on each block I machined a 12mm deep recess in them. The TB's sit inside this recess and are bonded in using Dow Corning 730 fuel resistant sealant. Exy stuff too!! You'll notice that on these early TBs there's a groove around them for the rubber boot to bite onto. I made use of this by drilling and tapping 4x4mm holes in each block and used grub screws to help pin things in place and take some of mechanical stress off the sealant. This proved very handy when trying to align things up as the sealant was going off. Might I suggest that you also use some sort of temporary aligning guides as well as this proved to be a difficult process.

The advantages of using these blocks were:
a) it cost me nothing because I could source everthing at work and use their machinery
b) it kept the injectors as close as possible to the intake valve.
c) I needed to keep things as short as possible due to space limitations.

I've seen it done another way and that was to weld the TBs directly to a 10mm thick mounting plate. I didn't want to do this because I wasn't sure as to the effect of heat on these TBs and the costs of having the welding done. I've seen it done on another website tho and so it should work. If you want I'll see if I can try and find it again.

Hope this has been of some help to you all and you can see more details of my setup here http://www.msefi.com/viewtopic.php?t=895

Thanks so much for joining us, Brett! I hope we can make this a viable option for 911 engines too, for those that are willing to do a little special work.

Basically it sounds like you had to use a fabricated adapter between the alfa weber manifold and the TBs, right? I'm not sure if I understand how the grub screws (what are they?) interact with the boot groove.

Best Regards,

Ah, I did a little research, and we dumb 'mericans would call grub screws "set screws". So it sounds like you had the part of the throttle body that the boot went over fitting into the plastic injector block, then had set screws holding the throttle body in the boot groove. then the sealant filled the gaps. I think I understand this arrangement.

That's right, grub screw ,set screw same thing different lingo.
Look at this pic and you'll se what I mean
http://members.optusnet.com.au/bcalv/tb9.jpg
You can see the holes where the screws are inserted. There are allen type (you do call them allen right?)
That recess the TBs sit into is slightly larger than the OD of the TB to allow room for the sealant. The grub srews help to align them in the first instance and they also give some mechanical support. The screws line up with the grooves around the TBs.
I'm not sure what you're on about re plastic injector blocks. Don't forget these are the earlier 98/99 mikuni TBs and they are quite different to the latter kehein (sp?) type. They are better IMO because the injector angle is more accute and the Toyota denso injectors fit them. Also they are a bit less plasticy.
Only draw back with them is the eccentricity of the outlet.
Inlet is 48mm tapering down to 46 at the trottle plate and 40 at the outlet. Ideal for upwards of 250cc per pot at 7000 rpm. Makes you think about how much air this bikes need to rev as hard as they do.