Does anyone know for certain what the measurements are for the placement of the injector holes in a piece of custom fuel rail extrusion for a home made fuel rail? So far as I can tell from some measurements I have done on '95 factory fuel rails and the matching intake manifolds, the distance between each of the first and last 3 cylinders is 4.15" and 3.12" between the groups of 3 (between cyls #3 and #4). If the upload feature is working for me (first attempt), the following drawing should produce fuel rails that can be interchanged from side to side, i.e., identical machining. When reversed, the injector holes are given a .75" offset (I THINK that’s the correct amount of offset between banks) and the ends should be even with each other.
I have the fuel rail out of my wife’s 1990 XJ-S convertible (5.3L V12 w/ Marelli ignition) now and it would be relatively easy for me to take these measurements on the fuel rail and intake manifolds on that car. You don’t mention what year and model you are working on (or even if you are working on a Jaguar). Before I go and take those measurement, please confirm that it would be helpful to you to have this info from a 1990 Fuel Injected 5.3L V12.
Thanks for the offer Paul. Very kind of you. As I mentioned in the original post, my manifolds and fuel rails are from a '95. I will be installing the injection setup on my '71 E Type. I have already done measurements using an electronic caliper, but I have doubts about the absolute accuracy of it. What I was looking for was perhaps a pointer to some published information that could lead me to the exact centers for the intake valves since the injectors are centered on them. I have already found the “official”, that is, published information for the cylinder centers and the intake valve offset from the cylinder center, but the one value that has eluded me so far is the difference in the cylinder centers between #3 and #4, which are wider to accommodate the larger center main bearing where the thrust washers are installed. Also, this is where the order of Intake and exhaust are reversed.
After more careful measurements and ascertaining that the fuel injectors are NOT centered over the intake valves only the port mating surface between head and manifold, I have revised my drawing and will proceed with machining the new fuel rails to these dimensions. Perhaps this information will be of use to others.
The bore spacing is 105.4mm (4.15") on all engines. The centre bore spacing is 111.2mm (~4.375"). The spacing on the centre inlet ports is 3.5" so far as I am aware (actual data to the nth decimal place not immediately to hand). Bore offset side to side is 19.05mm (0.75").
The injector is located exactly in the centre of the inlet port and is directed at about 12 degrees to the back of the inlet valve.
So perhaps you should double check that 3.125" measurement?? I’ll double check my figures when I get the opportunity. My computer model is from a Group C head, and there is a slight possibility that they straightened the ports slightly which would have made the centre ports further apart. I have some standard heads on the bench and can check them tonight also.
Steve, Just re-read your post and noted your comment that the injectors are NOT in the centre of the port. I’ll double check this, because on my inlets they are! Sorry if I have added to the confusion!
Rgds
Mark
Thanks for the information. I originally was working under the assumption that the injectors were centered on the ports and began calculating from published figures, e.g., bore centers, inlet valve offset from bore center, etc. I then realized after a bit of scrutiny that this wouldn’t work since the ports in the heads themselves are angled with the front 3 toward the front of the engine and the back 3 toward the back of the engine.
Looking at the injector bores in the intake manifold I can see that they are NOT in the center of the port in the front to back plane and definitely not in the side to side plane. It appears that the offset places the injectors more toward the center of the valve, but I cannot tell if it is actually over the center or just somewhere close to it, maybe centered to the side of the valve stem. I just don’t know if the offset of the injector in the manifold port is equal to the offset of the head port opening from the valve center. If they ARE supposed to be centered on the intake valves then I could still use my original method of calculation once I find out what the bore center distance is between #3 and #4. That’s about the only dimension I haven’t been able to locate. It’s larger in the center due to the thrust bearings being located there.
The 3.125" measurement was taken from both the injector bores in the manifold and the matching cups on the fuel rail, so I am fairly confident that I am at least close within 5 or 10 thou since they agree.
I was hoping that someone who has already made custom fuel rails would chime in with exact, proven dimensions.
I’m interested in any conclusions you may have after checking your own hardware.
Checked what I have here and you are absolutely correct. The injectors are offset 0.1875" from the centre of the port. The centre ports are spaced 3.5" apart. The injectors are biased towards the centre of the head. Therefore 3.5 - 2x0.1875 = 3.125" as you stated.
The non-HE inlet manifolds that I checked are a little frightening. The internal finishing is all over the place. Especially around the injector opening. These manifolds had injectors fitted, some of which are poking out into clear air, others are partly shrouded by aluminium “break outs” from the injector machining operation. Probably looks worse than it is.
I wanted to start a thread on the port design at some point, as I have just finished some CFD analysis on it with some surprising results.
Now that WOULD be interesting. I’m wondering what the offset is between the center of the port at the head/manifold interface and the center of the valve. We already know that the inlet valve center is offset from the bore center by 0.825", but there is some confusion about the middle bore spacing. This quote is from one of Roger Bywater’s posts:
“Strangely Walter Hassan’s well known paper gives the middle bore
spacing as 4.25” which presumably must be an error because the main
bearing widths conform to the EPA figure of 4.375”.”
my V12 is a 1978 preHE ,and you are correct about internal finishing, humps and bumps, lumps around the injector hole!
so i had them EXTRUDE HONED 1994, besides opening them up it reduced many of them and opened up the internal volume by guessing 10/15%, including runners, i then port matched to head!
the offset in the head port to valve bowl is to increase swirl into cylinder, and taper is to increase velocity at same event!
I had suspicions about that taper and so I did not tamper with that when doing a cleanup on my heads, so thank you for confirming that. I read this in one of Roger Bywater’s posts many years ago and wondered just exactly how to decipher it:
“Porting the heads is largely a waste of time (or money) unless the engine has very
advanced induction and exhaust modifications to reap the benefit. We found
years ago that with production based inlet manifolds the best thing to do
to the inlet port is to slightly scoop out the outer port edge below the
joint face to continue the curving flow down towards the valve throat.”
From seeing your past postings, I would hazard a guess that you may have experience in this area. Do you think he is talking about the outer port edge of the head or the manifold? I’m leaning towards the head. What say you?
Yeah, it took me a while too when the new software was put into the forum. When you reply, look at the top of the box and you will see a small horizontal bar with an arrow pointing up from it’s center. When you click on that it opens a file selection box for you to load your picture.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
20
The non-HE inlet manifolds that I checked are a little frightening.
The internal finishing is all over the place.
Roger Bywater of AJ6 Engineering once offered a conversion in which the
OEM manifolds were cut open, little trumpets installed, and then welded
back together. He once reported that the things he’d find within those
manifolds were frightening. He said he once found some aluminum flashing
that basically blocked off about half the passageway of one runner. And I’m
pretty sure he was talking about H.E. manifolds; the pre-H.E.s might be even
worse!
If one has a manifold in hand, perhaps the thing to do would be to use a
string or wire to drag a wad of sandpaper or something back and forth
through each runner a coupla dozen times. Or perhaps a “butterfly” of
sandpaper on the end of a flexible shaft chucked up in a drill.
