924Board.org

[-nick]

Hi Folks,
I'm trying to figure out the best way to install the EFI injectors. The stock injectors are pretty long and skinny and EFI injectors are short and stubby (that I've seen). I'm worried that the EFI injectors will just be squirting fuel into the walls of the injector hole since I don't think I could get the nozzle all the way down into the airstream (by a long shot). My only other thought is to install the injectors into the intake runners. The extra travel for the air/fuel mix bugs me too. Any thoughts on how to do this?

Best,
nick

[-nick]

Well, I might have had my question answered already (megasquirt board is great!).

Apparently, the VW EFI Digifant uses the same size/length injector hole as CIS Digi. If VW wasn't worried about the spray, then I'm not going to fret too much over it.

Below is a link I was sent too. Looks like the stock 931 injector sockets can either be replaced with EFI sockets, or modified to accept an EFI injector's sealing o-ring (ie chamfer the hole so the o-ring can seat itself). This may not be as bad as I thought.

http://www.not2fast.com/VAG/InjectorCup.html

nick

[leadfoot]

I had bosses made up that screw into the head the same way the phelonic inserts used to. These have a recess that accept an o-ring for the injector sealing.
I have been told that the spray pattern is narrower on a pintle style injector as opposed to a disc type injector and they also have a better spray dispersion as they atomiser finer.
I am using bosch 440cc injectors that are doing just fine. They are a little overkill until I fit the supercharger, but it won't be long now before I do.
Leadfoot

[-nick]

Thanks for the info Leadfoot. I ordered some of the Digifant inserts last night. At $2 each I don't think I can loose It would certainly make the conversion much easier if they fit easily.

For the N/A guys- I was given this link:
http://www.bitzracing.com/products/injector_bungs/injectorbungsdetails.html
Looks like this might be an easy solution for the N/A head.

PS- have a good source for the injectors? 440cc is good for around 250hp or so right? They're coming up on my shopping list.

nick

[simsport]

I found that the original holes were a little to close to the valve stem and the head's heat for my liking.
I wanted a good spray pattern and I wanted to fire the fuel into and along the airstream rather than across it.
Not scientific but I think was proven in the end.
To do so I welded small bosses into the intake runners to take the Bosch 944 injectors. These had enough duty for my needs.
I found the Webber caps with collets worked fine and held them into the holes by using an alloy retaining strip onto which I grafted 4 Fiat Uno injector holders.

If you do go direct into the head make sure there is enough heat protection or you may get injector fouling.

Cheers
Simon
_________________
Blown is always best!

[kidporsche]

[-nick]

Well, the Digifant inserts are coming today. I'll see how things fit up. Again, VW seemed to not have any worries about having the injector nose closer to the airstream so this may be a non-issue. Of course, I don't know how I would measure such an effect anyway?

nick

[Peter_in_AU]

for some applications, having the injector spray directly onto the runner wall is not a bad thing.

I have seen dyno comparisons of different injector placements and a setup where the injector was mounted at 90 degrees to the runner and therefore spraying directly at the runner wall actually produced more power than the more conventional mounting of the injectors at 45 degrees to the runners. The reason for more power was that the fuel hitting the runner walls was cooling the runners and therefore cooling the air flowing through. The downside was that low-speed running really sucked.

The comparison showed that the best injector placement for power was having the injectors mounted above the runner bellmouth firing straight down the runner. Take a look at the injector mounting on any modern race car. Of course mounting injectors this way is a total fire hazard.
_________________
1979 924 (Gone to a better place)
1974 Lotus 7 S4 "Big Valve" Twin-cam (waiting)
1982 924 (As featured on Wikipedia)

Learn to love your multimeter and may the search be with you

[-nick]

Interesting info Peter

I received the injector cups today, and they're the wrong size. I guess I could have measured our stock cups first...

It looks like our threads are 24x1.5mm rather than the Digifant's 22x1.5mm. If anyone finds some VW EFI cups in the 24mm size let me know! I know they're out there somewhere, I just need a part number.

nick

[endwrench]

Nick, I went thru the trouble of building some aluminum inserts for mine but in the end I beleive I would have been much better off to just take a stock set of CIS inserts and have them modified to fit the injector you plan to use. Using aluminum, I was able to seat my injectors clear to the bottem of the threaded hole thereby getting it as close as possible to the rather narrow opening. So far, I do not detect any problem from this set up other than the fact I beleive squirting directly on top of the intake valve creates some interesting enrichment maps (as in almost none!).

Todd

[kidporsche]

Power may be increased by firing onto the runner walls, but as you said low speed running cops it. The biggest problem is in transients though. It is much easier to map an engine for top HP than for low speed running and transients which are much more important on the road/track (unlesss you are only interested in top speed runs).
_________________
Chris
1981 924 - RoW (Australian) spec