MFI, cold start and K&N filters

[michel richard]

I'm fitting low profile K&N filters on my 2.2 E that runs MFI. That means I lose the brass lines inside the stock air intake housing.

I'm thinking of setting up something as was shown in a recent European Car article that featured a 911S with MFI and the same K&N filters and rain guards. Basically, small fittings through which fuel is squirted are screwed into the side of the intake stacks.

Does anybody know the size of the hole through which the fuel is squirted ? I figure it is critical to ensuring that the right amount of fuel is dumped in the intake, and I'm afraid that my brass lines are a little too beat up for me to take a reliable measurment.

Does anyone have experience with that kind of setup and its effectiveness ?

TIA

Michel Richard

[jkeyzer]

On the later MFI systems (2.4 for example) the cold start nozzles came from the factory as part of the air stacks. The nozzles themselves have a tiny pinhole through which fuel is squirted.

I can take a picture if you are interested but basically they are too small to measure with my calipers. About a thousandth in diameter perhaps?

[michel richard]

I was hoping someone might have a good set and try sticking different sizes of drill bits in the hole to figure out which bit goes in. It'd be one of the "number" drill sizes, perhaps somewhere between #50 and #60 ?

On the other hand, maybe there's a spec published somewhere.

Can anyone find this without too much trouble ?

Thanks

Michel Richard

[jluetjen]

My car's PO pitched the entire cold-start set-up related to those squiters at the top of the stacks and so I've never used it. He did wire up a clever arrangment that seems to work just as well (at least at freezing or above). It is a variation on what the factory apparently did to start the racing motors when cold.

Concept: If the MFI rack is pushed full forward when cold starting, that enrichens the mixture enough to allow an easy start.

Execution: Splice a wire from the MFI's cold start solenoid (gray wire off of the solenoid) to a switch on the dash and then to the start circuit at the ignition (key) switch (yellow wire in my car). I used the extra fog light switch on my dash for the new cold start switch. Close the new switch when cold starting. After the motor has started, re-open the new switch again so that you don't try to hot-start the engine by accident with it closed. If you try to hot start the motor with the new switch closed, it will be too rich to start.

Comments: When the PO made this change, he wired it through the relay that controls the solenoid. He also had the fog light indicator bulb still wired up. I'm not sure why, but there was some leakage which meant that the solenoid was always powered. I simplified the circuit by skipping the relay and removing the indicator bulb wiring from the switch. It works great now!

[304065]

My MFI pump (1971) only has one solenoid: the over-run cutoff.

I think the earlier cars (69-70) have a cold-start solenoid. I know they have two on the pump.

I would stick a little drill bit in the hole in the brass tube to get the size.

You would have to have the stacks OFF before drilling any holes, I would think. Don't want shavings down the holes.

Also, I wonder whether putting anything into the brass velocity stacks could mess up the flow. I would consider fabricating a clip that attaches to the lip of the stack, with a nozzle on that, but it would have to be pretty secure to avoid being sucked in.

Good luck and let us know what you decide and how it works.

[Paul Thomas]

I have a K&N setup on my car and it will not start cold with out the following mods. I ran a wire off of the starter solenoid to a switch on the dash (as mentioned above) then ran it to the cold start solenoid, so i wouldn't have the hot start flood problem. For the fuel squirters i used 1/8 inch T and L fitting mounted in the watershield directly above each velocity stack. That way the fuel goes directly down the hole. I think that my set-up actually works better than the factory one did. I can email a pic, or i can try to post it here but the BBS always says my pics are too big.

Paul

[michel richard]

Paul,

Thanks. How big are the holes in the fittings that are above the stacks, and how is the fuel line to these routed. I'm not sure how to get it past the filters and I would like to avoid drilling holes in the top of the watershields, to make sure I don't get water in the engine.

I'll take a hard look at it tonight and will try to devise somthing myself.

Cheers

[Paul Thomas]

Yeah, water in the motor would be bad. I think a little clear silicone would fix that though. I don't drive my car in the rain so i wasn't worried. Hopefully i will be posting a pic if it isn't too big. If anyone can tell me how to downsize a picture please do. The ones i take with my camera always come out HUGE on the CPU.

Paul

[CamB]

I will help!!!! I wan't to see pics of your engine - it sounds very very cool.

To reduce the size of the pictures you need to use an image editing program. I use Photoshop (lucky me). Another option is Microsoft Photo Editor (which might have come free with your computer).

Either way, you need a program to load the images which will allow you to change the size of the image down to about 640x480 pixels (which would probably be the lowest resolution on your camera). As a .jpg, this should be under the size limit.

Actually, the camera probably came with a suitable image editing program...

[Paul Thomas]

ok here goes....

[Paul Thomas]

ok here goes....

[CamB]

No picture there for me to see????

There is a faq on posting pictures... but I can't find it. I'll keep looking.

This has some good info:

http://www.pelicanparts.com/cgi-bin/vb/showthread.php?s=&threadid=53435&highlight=image+editing

[CamB]

http://www.pelicanparts.com/cgi-bin/vb/showthread.php?s=&threadid=63792&highlight=posting+pictures

This is better

[CamB]

I decided I should write down the steps - I have 20 mins to kill... (I am sure this was done before, but I couldn't find it)

Step 1 - Click "reply" or "New message", write some words, then click on "Attach Multiple"



Step 2 - click on "browse", find the file - a jpeg less than 100k (be nice to everyone and try and make it below 50k). Then click on "Upload Now!"



This will automatically upload the image and paste the correct UBB code for the image into your reply window.

Easy-peasy.

[Paul Thomas]

here goes ...

[Paul Thomas]

Cam, you are my new best friend. I have been trying to post pics for friggin ever. those velocity stacks are genuine Carrera 6. My buddy has a 906 and a 910. The stacks were an extra set that i had re-plated.
Paul

[CamB]

"Cam, you are my new best friend. "

Oh great!!! In New Zealand, best friends let each other drive their car whenever they want .

That engine looks awesome! I particularly like the way that because it is still MFI, a casual glance would not suggest the potential... (well, beyond the twin plug, etc etc).

What does the car look like (practice those new-found picture skills!).

Cam