Just a quick question.

If an engine is being tuned and modified for, say theoretically 300 HP at the crank at 100% duty cycle injectors would need to be about 43#/hr at 12:1 AFR.

If 55# injectors were installed in this setup, assuming the same AFR of 12:1 would the injectors need resistors? Also what approximate duty cycle would that be?

Thanks.

 

I would use resistors (and do use resistors with the 55lbers in my car, from the advice of Tim Richards). They are easy to install and good insurance. I bet a DME is quite a bit more than the resistors.

How was the drive?

 

last time I checked you don't have a 951......

 

i dunno i have 4 DMEs lol...how many ohms?

the drive was a blast! flying up palomar mountain was a workout on the hairpins without power steering...average speed up the mountain for the group (about 20 cars) prolly around 60 or more.
preparing for a build...

 

Mine are Siemens and are (I think) 2.5 ohm injectors. Stock injectors (at least on a 951) are 5 ohm I believe.

 

so i need a pair of 2.5 ohm resistors wired in there to be safe?

 

No, I forget what ohm resistors I put in, there are two injectors per driver circuit. Someone else on here can explain it better, but if you search for "injector resistors" you'll find several good threads on it.

-Darwin

 

You need two 1ohm resistors (one resistor on each injector wire coming out of the DME).

 

This is the rig I built, heat sink may be a little over the top, thermal paste included. The sink does help protect the assy. I got all my info through search.

 

Resistors are easy to install and required for reliability with low impedence injectors.

The ECU driver is rated at 16 amps.

Without resistors:
0.625ohms. 12v/.0.625 = 19.2amps.

With two 1ohm resistors:
2.5 ohm + .5 ohm resistance(a 1ohm resistor on each of the two injector dirvers) = 3 ohms each
4 injectors would be 3ohms/4 = 0.75 ohms
12v/0.75 = 16 amps.

I'm running on 3 hours of sleep this morning so if the above is wrong, please correct.

...and with that, here's where I installed mine:

 

can these be mounted in the engine bay somewhere closer to the injectors or should i keep them close to the dme?

 

Technically the closer to the DME(injector drivers) the better. They can be mounted anywhere however it's easier to get to the wires closer to the DME. Plus being near the DME, the resistors are protected from outside elements and won't be subjected to the extra heat from the engine.

I would suggest either mounting them under the dash or near the battery if you don't want them inside.

 

Spence, an early car is NOT laid out for this type of work...

 

you do not need it if you are going to run 55 lbs injectors

 

If you don't then you're running the risk of burning out the drivers.