Richard,

I do have a model for the injectors. the problem is the interference with the runner to the body if you want an acceptible entry angle for the runner. I dont think you had the same challenge, since you placed the runners in-board in your model. I do agree it is easy to have the modeler do an offset automatically, but doing so killed the shape of the internal port and exit angle when trying to keep the stock positions.

I think your design is great too, but it didnt have the same challenge (plenty of other ones though). The challenge all related to injectors in the original location.

Regards,
Hans

This may help illustrate the challenge, and also show where I had a problem that I didn't catch (corrected now, but just showing some of the hard parts).

As you can see in this drawing, the clearance between the fuel rail and the tubular runner measures at 2.2mm

The clearance between the injector body and the recess made for the injector is only 1.4mm

Trying to keep the injector in its stock location, the necessary recess for the body, exit angle of the port, and transitioning the port geometry to a round bore, PLUS still having room for a fuel rail was incredibly difficult. It did take over a dozen revisions (lost track) before coming up with a design that even had that 2.2mm clearance between the rail and the runner with port geometry that I found acceptable.

Please note that the o-rings on the injector are the smaller diameter, as it was something I was playing with earlier, but you will notice the bore on the rail and manifold is setup for the standard 14mm. Also, please note that this is a cross-section taken from the middle of the runner, so you are seeing the injector boss protruding into the runner. the runner is much more open than this cross-section portrays.

https://lh5.googleusercontent.com/-0...824/Intake.png

Regards,
Hans

Hi Hans,

Got it... I can see what issues you are having better now..

Like I said, everyone is having different issues. What I meant by it not being difficult, was relative to the other things that were set as parameters relative to injector position in the design...

I did a sketch like you have it, but I moved the injectors inboard to solve that and some other issues.. I did not want to run up against those clearance issues, and I wanted to keep the ability to place a larger compressor in the valley at a later date...

Cheers,

Hans had previously mentioned the difference dimensionaly between Generation III and Generation II injectors. By using a Gen III injector, you can lesson the intrusion into the intake runner required for the injector because they are skinnier.

But using an injector that is thinner is not enough all by itself, we found.

We also canted our intake runners away from the injector, again so that the intrusion into the air stream could be as small as possible. This gave us a secondary benefit: we were aiming for max power between 4000 and 6500 (road racing) and needed slightly longer intake runner lengths to bring in the power there. When calculating intake runner length for Helmholtz effect, measure from apex of bell-mouth to reflective surface (back of valve). There is about 2.5" of intake runner in the head of a 928 all by itself - so getting a "long" intake runner for mid-range power isn't that hard!

Note the taper from top to bottom of intake runner. You want to design-in some intake runner taper, or you are leaving some HP on the bench.

80#/hr injectors are straight up-and-down and aimed at the back of the valves, aluminum fuel rail, fuel rail stand-offs/mounts are Delrin.

I may have finally found an affordable foundry to get these manifold flanges into existence. As much as I love domestic quality, in the volume the 928 community would use, the tooling was just too expensive. Best quote I got was around $5000 for the tooling and then another $1500 or so for the machining fixtures.

I have been in touch with an Asian foundry, and the numbers are considerably better. Smallest run they would do is 50 pieces (equals 25 manifolds). I thought I should check and see if anyone is still interested in something like this before going any further and paying for the tooling to get a sample.

Thanks
Hans

What type of a cost would we be looking at per pair?

I am still working out a few things with the foundry, and just have an email with pricing, not a formal quote. I am very hopeful though, that I would be able to meet my original benchmark goal of around $500/pair.

I should know for sure by the end of the week.

If this initial casting goes well, I will approach them about casting the plenums for the intake as well.

Thanks,
Hans

Hans
At $500, I am in for at least 1 set up fornt, and probobly a few more down the road.
Victor

Same here Hans...in for 1! Great work!!

After a short delay due to a holiday overseas, I have heard back from my contact at the casting facility. They are willing to comply with my requests, despite the small production run for a small fee (quite reasonable and well worth it in my opinion). They will pour from A356, which is considered to be one of the more easily weldable alloys, and provide a T6 heat treatment to the part. The raw body will be cast, and all critical features machined.

I will probably start another thread to gauge interest, but would need to do a run of 50 parts (25 sets) I can sit on some of those for personal use, mockups... etc, but for me to even consider laying out the funds for the molds, I would want to make sure I had 10 sets pre-sold.

It will be very difficult for me to estimate the exact price for these, as shipping and import duties are yet to be determined. My original design goal was to offer these for $500/set, and reasonably certain I can still do that, even with the upgraded material and heat-treat. As with all my projects, that is with a VERY small margin, so not much room to absorb any unforeseen shipping issues. If there are, I would increase the price of each set according to the total amount over budget divided evenly across all 25 sets, so any deviation in price should be reasonable, and cant see any scenario where it would adjust the price more than 15%

Can I get a show of hands who would be interested in a pre-order at $500/set I will have a current version sent out for SLA to triple check both against the 928 head, but also against several types of current injectors for clearance if we get to that 10 commitments.

Thanks
Hans

Sounds good, i'm interested.

How about running it as a kickstarter project

I wanna go to ITBs next year so scratch me down for 1 set Hans.

Good news. I had to get a couple things machined this morning, so while we were waiting for some Sharkwoofer bits to come of the CNC we took the mounting surface of the lower intake int0 the CAM program, and cut out at test piece from 1/16" clear plexi. The file for lack of a better word was perfect. It fits on all my loose head here better than any factory part.

I designed the new part to be symmetrical with tight tolerances, here are some interesting findings:

The factory port profile/outline is remarkably close along the entire head both in centering and overall shape. *However* the centering of the injector itself is skewed/offset on most of the ports. The variation here is actually quite startling. I need to digitize a fuel rail, but this does beg several question, such as are the fuel injectors perpendicular to the head (properly seated with a good seal at the o-ring) or is the fuel injector spraying into an obscured/blind part of the head.

I am close to the number of interested people to green light the casting. I am going to hold up the purchase order until the Ford Cobra injectors https://rennlist.com/forums/928-foru...discusion.html get here for me to include in the model. I will try and center these injectors over the average center of the ports in the head and modify the lower manifold if necessary.

That said, I will have disposable templates made to assist in port matching for those interested. I will also have silicone intake manifold gaskets cut. I may even make a rental drill jig for truing the injector portion of the intake.

Getting closer, can we get any more names on the list?

Thanks
Hans

Still $500/pair right? Ah what the heck, I'm in.

Dan
'91 928GT S/C :eek: 475hp/460lb.ft