I've been reading a lot on the forums lately, regarding folks running a PFC with 1600 cc secondaries, without the resistors.
So what's the deal, run with them or without them?

 

I've HEARD of people having problems when trying to tune high boost (like 24psi+) and using resistors. In addition in a pm Ralph from Xcessive told me the same thing, he then went on to say when he pulled of the resistors all was great and he turned it up to over 30psi. He's been running like that for around a year with no known effects to the injector drivers in the PFC.

Personally, I'm on the fence cause so many people run them. I'm probably going to leave them off though and trust Ralphs opinion. Hopefully it'll be ok

I was going to make a selection for the 2nd choice BUT since I dont have personal experience I decided to just post this instead.

STEPHEN

 

Great post thanks Stephen! I'm still on the fence and waiting more folks to chime in regarding this issue. At this point between the cost needed to update to a 3 bar map sensor and datalogit to control everything, I'm thinking about jumping ship and going Haltech.

 

Surf the haltec forum for a bit before you take that path. I was initially sceptical about the PFC but after tuning with the datalogit and a wb I am thrilled with my decision to go with the PFC.

Thanks to the clever guys down under!

Almost forgot, i run resistors up to 19 psi with no ill effects.

Might we assume that a track car would need resistors since the secondary injectors will be going all the time, street car will rarely run the secondaries and therefore not push the PFC drivers to their thermal limits. Dunno.

 

I've used the 1680cc injectors in my PFC with no resistors, and haven't had any problems, in actuality the more load(higher boost) the LESS chance that something will go wrong, this is because resistance actually gets slightly higher as the load on the injector gets higher. Every 1680cc injector I have measured resistance on has been about 5ohms with no load, do the math. Me and other people I know have tried this with no problems. A side benefit from running no resistors is that the injector reacts faster, giving you better control. On a side note, Ralph from Ground Zero also wrote this on another thread:

"I have found that the 1600s with resistors, under higher boost 26psi+ and 70+ duty cycle makes the car surge under long lruns, this is with 43psi base fuel pressure constant. The best way I found to test this was I boot strapped the resistors with ong wires hanging out of manifold, then ran the care some good pulls then cyt the wire putting the resistore back in use
and did some more pulles. It was amazing the difference
between the two. Think about it this way,manufacturer
specs= low impedence= 4+amp switch and 1 amp hold
(peak&hold) High imp.= 1 amp switch (saturated)
this means to me that the low impedence requires 4X
the current to make injector work to specifications.
sorry for the length, I have tried to get RC and others to measure the diff, but they just act like they dont care."

Someone else I know did have this surging problem and when they removed the resistors, the problem went away. If anyone is worried about running the 1680's with no resistors, don't be, some guys have been running w/o the resistors for 2+ years with no problems, some of them are daily driven cars that would've do doubt fried the PFC by now if there was a problem. Ralph, Boostn7, and Waynespeed can also chime in on this if they like, they've mentioned this to me before when I was doing research on this before I attempted it myself.

 

From what I gather the PFC injector drivers have a maximum rating of 3W total for both channels. Because the 1680's have a higher resistance than normal low impedence injectors, the combo of stock primaries and 1680 secondaries will put it close to the limit.. something like 2.5W at 70% injector duty. This sounds like it could exceed 3W at 100% but since several have reported that the impedence of the 1680's increase when hot, it may not. Pretty close though. Maybe adding 3 or 5 ohm resistors would still keep the current draw down but interfere less with delay times.

From that I'd assume that it would definitely be bad to run a typical low imp injector (2-3 ohm) anywhere in there with no resistors.

On the other forum someone (IGY or Dragon I think) spoke of Apex'i offering a mod to install better drivers in the PFC to support more current but I'm not sure if that's realy necessary unless you're doing something like running 6 low-imp injectors or something.

That said, I run 550/1680s with 10ohm resistors on the 1680s and have never had any transition hesitation. Perhaps it's because my rails are plumbed in parallel. Most people that I have seen complain about transition problems have been plumbed in series.

I don't see this as a compelling reason to go haltech. Particularly when the PFC does things like run the MOP.

 

Don't get me wrong, at this point I have couldn't be happier with an ECU. Though, now that I'm starting to get some serious modifications, the cost of updating the PFC to run the boost I want and do the things I want to do with are running close to the top of the line Haltech (E11) which controls the omp and has much better resolution with more features and you don't have to worry about resistors as far as the injectors go.

How do I get some of you new fangled injector seats?
How much do the run?

 

I hear ya. It's a more full-strength solution. I'm curious, in what respect in the resolution better? Also, does it have a 2nd timing map for the split? I haven't really looked into it.

If you're interested in the injector seats, there's more info at http://dave.newbern.org/rx7/InjectorBushing/. I have a few sets left and I'll probably make another batch when I get some time.

 

I wouldn't even stress the resolution, the PFC is a 20X20map, it's enough. AEM's map is only a 17X21 and people are running 4bar map sensors with no problem. Remember, the PFC can adapt to any map sensor you want, so running boost won't be a problem. Because of it having only 4 injector outputs though, you'll be at the limit like I am currently. We need to talk to Ralph(Xcessive) from Ground Zero, he was working on finding a way around this, I think it was a different injector driver strong enough to handle 4X1600 secondaries, but I'm not sure how far along he's into it. I myself am running into this problem because I'm at my limit as far as injectors go, and I want to run more boost, BUT with my 950pri and 1680sec injectors it's not gonna happen unless I find a solution to this, which I don't think will be that much of an issue, let's see what happens.

On a side note, how come no one else has voted on this threads poll? C'mon people, we need opinions here, that's what this forum is about, helping each other and the Rotary community.

 

I ran the 1680cc injectors for a year without any problems.

 

A Haltech Map is 32X32 instead of 20X20, and it can control split timing, even on a 3 rotor!

 

I could see where that might be helpful to run > 2 bar of boost but I don't see the need. (desire, perhaps.. need I'm not so sure of.) There has been plenty of big power made on the PFC.

To each his own.

 

I know this glass_man, I'm just stating that you don't need a larger map reference, if the guys with AEM are getting away with it, as well as other ecu's with less resolution with no problem, you won't have a problem with the PFC, that's what I'm refering to.

 

I am thinking of actually taking the resistors off my 1680's. I have researched and it seems you can get away with it. Even with the proper lag time settings I still get a split second of lean afr's when secondaries come online. I think it could be partially due to the added resistance, slowing the injector response time.

 

I'm running with the resistors for now.

 

I have noticed a split second lean condition when the secondaries come online. I recently upgraded my primaries to 870cc injectors with rx7.com resistors. I can really see and feel the lean condition now.

For those with upgradded primaries what are you doing?

Chris

 

This is happening due to the fact that you should move your transition point over to about 60-65%, this will cure your problem.

 

Transition point is 64 but I still have the problem.