Ranzo

That would be neat to read. Please hurry up and post that stuff.

Dragon

Ask and you shall recieve...



T-2 How to add a pair of additional 550 secondary injectors ^

o Plumb 2 extra series 5 (Gen2 T2 FC3S)-550 cc injectors into a

spacer between the inlet manifold and the plenum chamber,position

them to inject into the secondary runners.This Spacer /Auxiliary

injector holder will be available from FC-Datalogit soon.

o The series 5 (Gen2 T2 FC3S)550's are high impedance (15 ohm)so

they can be driven in parallel with the existing 850 secondaries.

o The injector drivers in the PFC are FETs.The IC contains 4

separate FETs,rated at 0.25ohm on

resistance and 3W max power dissipation for all 4.

o Driving 1 x 15 ohm injector at (say)15V BatV is 1A,so power per

FET is I ^2R =0.25W.Therefore the total power on the driver chip is

1W (at 100%injector duty)To drive the 2 secondaries together will

be 2A,and therefore power will be I ^2R =2 ^2*0.25 =1W.So the

total power for 2 primaries +4 secondaries will now be

0.25+0.25+1+1 =2.5W which is ok for the chip.

The result (FC-Datalogit team road test)was excellent.No

noticeable injector transition glitch's.Same smooth power at 1.0bar,

and injector went duty from 95%to 70%

o Note at 70%,the injector driver chip will only be dissipating

0.7*2.5W =1.75,which is fine.We plan to add a clip on heat-sink to

the chip though -all the same.You may wish to do that also.

o We also intend to scope the injector circuit -since you should really

modify the snubber circuit also.This consists of 33ohm in series with

0.47uF capacitor to ground.In theory we should halve the resistor

and double the capacitor to achieve the same.This could be modified

in the PFC,or added externally.We will explain more latter.

Dragon

now sombody who understand electronics better than me tell me if it can handle 3 low impediance (4 to 5ohm) injectors in series = 14-15 ohms (same ohms as the stock secondary) on each of the secondary power wires + 2 stock high (15 ohm) primary injectors... for a total of 8 injectors...

j9fd3s

thanks dragon. if i remember from skool right the formula works like this:

v

-------------- = watts

ohm * amp





mike

j9fd3s

bump

nschmidtjr

I tried running two stock 850's in the primary and 4 low impedence 850's on the secondaries and it would not work. I just bought a haltech for this reason. I know from experience not just guessing. And I also tried several different resistors with no luck. The low impedence injectors draw too much current and will not open properly. I can only assume that when you are just running a pair of 1600's in the secondaries, the circuit can handel the current but when you have 4 low impedence injectors you have doubled the current again and therefore will fry the PFC or not open the injectors. Don't know if this helps much but I thought I would share my experience.

Nick

3rdGen7

I am installing a set of 1600 secondaries as we speak but the only resistors I got locally were 10 ohm 2 watts ..not the 10 ohm 1 watt that most folks use.. I spoke to a friend who is a elector-geek and he told me that it shouldn't be a problem... the 2 watt just means that those resistors can handle more voltage.



any thoughts on this ??



TIA,

3G7

j9fd3s

the way it sounds like it works is you are using 1 watt, and the resistor can handle 2 watts.



mike

3rdGen7

Spoke to XS Eng and they said you can use the 10 ..heck even the 20 watt..just means that they will be able to handle more power.



Something interesting they said:



Even though most folks use 1 watt that is fine for most applications and driving around the street etc... but if you're running big boost and a drag launches.. you are better off going with something like a 20 watt ! ..it's an over kill but a safety margin you'd not have to worry about.



Just something to think about.



3G7

j9fd3s

yeah they are right, its not like the 20 watt one is a lot more $$ and if the 1 watt one fails?



mike