RX7Elmo

I"m curious if having an upgraded fuel pump and a FPR such as SX would lower the duty cycle of the injectors? I've searched and read that many people are in the 90% duty cycle on stock injectors running higher boost. Will getting a fuel pump and a RRFPR help to reduce the d-cycle to a safer margin level? I figure more pressure = more flow. I assume some engine management would be needed as well to tune for the extra pressure etc since the ECU has no clue there is more fuel being pumped in.

Any comments, thanks!

Danny

j9fd3s

iTrader: (3)

those things can be used to make the car run richer, but the only thing that affects duty cycle on the stock ecu are rpm and boost. the stock ecu runs about 90% duty at high boost anyways, so i dont know if this is even a problem. http://www.newwave.net/~flanham/wlan.../3modrule.html

mike

RX7Elmo

the logic i see is we're deallign with something mechanical vs sometthing electrical. Sure adding more pressure gets more fuel, and the ECU will still see high duty cycles. What can be done is to add high fuel pressure, and then lean out teh ECU more, thus resulting in lower duty cycles, but the same fuel flow as before.


Thoughts/comments?

mjw

iTrader: (1)

This will work, but the SX regulator will not do it.. you need an adjustable rising rate regulator. The SX allows you to adjust idle pressure, and it increases 1:1 on boost from there. You would need something that would allow you to adjust the amount of pressure increase per psi of boost(eg. 1.5:1, 2:1 etc). Personally I would not go this route for a couple reasons, first off it can be a pain to tune this way, and second you are putting a lot more strain on the fuel pump.. increase that pressure too much and your GPH will drop like a rock. If you have an aftermarket ECU that is tuneable (ie PFC, Haltec, TEC-II) it would be easier to just drop in larger injectors in my opinion.

Matt

Wade

iTrader: (1)

Yes, your thinking is correct. You can increase fuel pressure with a different regulator and a good fuel pump, and retune your ECU to drop the duty cycles. As Matt says though, you might have some tuning problems. Whether or not those problems are worse than trying to deal with larger injectors depends on a lot of things.

Wade

RX7Elmo

Matt,

With the 1:1 ratio vs the rising rate, the RR is better as you stated since you add much more fuel on the high end of boost. I figure the 1:1 could work, but using the ECU, you could keep the duty cycle higher (closer to normal) on the high end of boost. Of course i'd run an aftermarket fuel pump which should be able to take this load of fuel.

The main reason why i'm not doing larger injectors is b/c i'm going to be running the PFS PMS which can't support larger injectors unless i increase both primary & secondary (too much fuel) and possibly even harder to tune. Thanks for the comments.

I think in the end it comes down to sitting hte car on a dyno and tuning things out.

Danny

duboisr

With the PMS you can run bigger injectors if both pri and sec injectors are inlarged keeping the 39% differance in the pri drop when the sec come on . you can lean idle and other ranges out , this will run well if you can set the unit correctly .You can not change the 39% drop

PVerdieck

Hmmm This looks to be an interesting thread about inj. duty cycles.
You see my mods below. Given what I had heard about high duty cycles, I was under the impression that getting a better pump would help.

Is that not the case?

fdracer

wtf are you talking about. a 1:1 regulator is a rr regulator. i.e. fuel pressure rises 1 psi per 1 psi of boost, hence a rising rate.

j9fd3s

iTrader: (3)

you can make the stock regulator a rising rate (1:1) by plugging it into the manifold, instead of the solenoid

mike

mjw

iTrader: (1)

Mike:

I thought the stock regulator was a rising rate (1:1).

Matt

j9fd3s

iTrader: (3)

it is but they have it hooked up to the solenoid, so that it only "sees" manifold pressure when its cranking

mike

Wade

iTrader: (1)

Wrong²...

Stock regulator is a 1:1, and it sees manifold pressure EXCEPT when the FPR solenoid bypasses it. This is for hot starts, it uses atm pressure instead of vacuum from the engine... more fuel pressure for hot starts, this is detailed in the manual.

"Rising Rate" is a regulator with a rate GREATER than 1:1. A standard adjustable pressure 1:1 regulator is usually called a "boost dependent" or "boost/vacuum compensated" regulator.

Maybe this will clear up some of the confusion.

Wade

RX7Elmo

I'm not sure what SX regulator i have to be honest, i know that SX makes a 1:1 and a rising rate unit. the part number I have is 15404 I believe. I went to SX's website but found no info on part numbers.
Also, what should i set the pressure to be at idle??

Its at 43psi at idle currently. Thus making my idle run pretty rich as well as the rest of the power band. Mods are intake/dp/cb with a fuel pump/regulator. I'm running 10-11psi of boost currently. Should I go a head and lower the fuel pressure down to stock levels?

Danny

Wade

iTrader: (1)

Are you positive SX makes a rising rate unit, because the 3 I've seen from SX were the same 1:1 style but with different ports. Never, ever seen or heard of a true RR from SX.

I'd set idle to be about 43psi with 0 boost (just disconnect the hose from the reg, set it to 43, then plug the hose back up).

Wade

RX7Elmo

IF you go to SRmotorsports website, they list a rising rate fpr from SX. there is no picture attached either.

And isn't 43psi at idle a bit rich for stock boost?

danny

Wade

iTrader: (1)

It says "new product", so it looks like SX starting making one more recently.

43 psi is about right for 0 psi. I don't remember offhand what stock is set to, but I believe it is somewhere between 40-43psi at 0psi boost. At idle, the actual fuel pressure would be lower once the control hose is reconnected (by appx 1psi for every inHg on your boost gauge).

So if you let your car idle, you removed the FPR control hose, the boost reference would be 0psi. Set your fuel pressure to be 43 psi. Then when you reconnect your boost/control hose, the fuel pressure will drop to about 35psi assuming your car makes about 16inHg vacuum at idle. Know what I mean?

Wade

RX7Elmo

Wade,

I understand. I had to read it about 3 times but i get it I'll do the adjustment when i get home. And i believe stock fuel pressure is 38psi.

You are right, i probally have the 1:1 regulator. Still better than nothing right.

Also, i looked at your website and it showed the 3 myth rule page. On it was a lamda test of a car iwth a fuel pressure regulator "+10psi" Could you clarify if that is +10psi at idle? or at what boost? Thanks!

Danny