when to turn on 5th injector

Roastin944 · 01-02-2003, 07:45 PM

hey guys,

as you know i am supercharging my car right now and would like to know your thoughts on when i should have the 5th injector activate. Will the n/a feed it a little more fuel as the first lb or two of boost come on? Should i have it turn on right at 1 lb of boost? I was thinking at 2 lbs, would that make it run to lean before it turns on? Thanks

John

ae1969 · 01-02-2003, 08:18 PM

If I were you..... I would have it turn on at 1 lb ....

in your case its better to run to rich than to lean...........

944freak · 01-03-2003, 06:39 AM

Shouldn't the car recognize the extra air being pushed in it, therefore increase the fuel. Couldn't you just raise your fuel pressure and add a bigger fuel pump. Im supercharging my car aslo. Im upgrading to 951 injectors.

ae1969 · 01-03-2003, 08:23 AM

There is only so much fuel your stock injectors will pump out..... regardless of fuel pump size.

The other issue you mention is that the turbo injectors (quoting marksportscts)...the injectors use different impedance so they actually do not work properly (who would of known that??)

You will have to add a 5th injector or custom injectors from RCengineering...

1.2gees · 1.2gees's Garage

Quote:

Originally posted by 1.2gees
A 5th injector is not a good idea for several reasons, one of the most important being placement. There's not an efficient way to position a 5th injector to get good fuel atomization across all 4 runners. If you put it on one end of the manifold, it'll richen some cylinders more than others, this is not desirable obviously. If you put it closer to the throttle body, the fuel mist is likely to condensate, and drip on the manifold this time not only richenning some cylinders more, but also adding to the atomization problem. There's another issue, when the 5th injector opens, you're giving it fuel from the same supply as the other 4, so yes now you have 1 more open injector, but also less pressure for the other 4!

A turbo fuel rail will come with the rising rate fuel pressure regulator (boost dependant) that you want, along with the injectors, hence I say get the whole rail, it'd probably be cheaper too.
Ahmet

But this time I have a couple more things to say, with ballast resistors you may be able to use stock 944 turbo fuel injectors which I still think is the best way to go. I will also do a shameless plug and let you know that I currently have a 2.5 bar fuel pressure regulator (almost new) out of a 944 turbo on e-bay, and it is a "rising rate" meaning it will increase the fuel pressure, as boost rises. If you have a late model 944, it should bolt up to your fuel rail if you choose to do that (if I remember correctly).
Ahmet

944freak · 01-03-2003, 12:24 PM

Both Huntley Racing and Speed Force Racing have supercharger kits for the 944 na. Both of them include stock 951 injectors as part of the kit. Does anyone know if theres any special reason why they will work with their kits and not a home made kit. (I have a HR kit) I emailed Tim Richards at SFR for a specific answer but in the meantime while Im waiting for a response what does everyone here think?

944freak · 01-04-2003, 01:13 PM

Chris at Powerhaus told me on the phone that with stock 944 na injectors that you can push up to about 300 hp at the wheels with a fuel pressure regulator. I dont know the exact setup you need but Im sure he can help you. He was real helpfull talking on the phone. The # is 480-948-4788
keep me posted on this supercharger kit as Im gonna supercharge my 83 as soon as I get home. I'm in the ARMY currently overseas in Afganistan area, but the HuntleyRacing kit is waiting at home for me.
steve
stevensmithnc@yahoo.com

1.2gees · 1.2gees's Garage

That doesn't sound right as stock fuel injectors on a turbo (which flow a lot more than 8v NA injectors) top out around 300.

I would still prefer to push the stock injectors with higher pressure (as long as you don't go too far as this'll cause them to start locking up) rather than a 5th injector, or swap all 4 injectors for something with higher capacity.
Ahmet

Roastin944 · 01-04-2003, 02:11 PM

so how should i make the stock injectors push more fuel? A FMU, or an adjustable fuel pressure regulator, a stock regulator from a turbo, could someone explain to me clearly how to accomplish this. Thanks alot,

John

944freak · 01-04-2003, 03:22 PM

Get an adjustable fuel pressure regulator. It is installed after the fuel rail. When you adjust it it will restrict the flow of fuel back to the fuel tank therefore increasing your fuel pressure. I would also recommend a better fuel pump for good measures. As far as how much the stock injectors will flow, Chris Carroll at Powerhaus told me that stock 944 injectors will hold for up to 300 hp at the wheels. I know that these injectors are not rated for that but he explained that with the increased fuel pressure they will work. He recommended me to use Powerhause's 3.0 Bar pressure regulator which is $85 from Powerhaus. I told him I was installing a supercharger kit and was going to install 951 injectors and he said thats not necessary unless Im going over 300 hp to the wheels. Im still going with the 951 injectors because the huntley supercharger kit I have is designed to use them.