Question about the 2/3 mod "rule"
 

Hi All:

There seems to be some controversy over this "rule". The solution to "more fuel" always seems to be either an aftermarket ECU (PF, Pettit, M2, etc) or a standalone like the PFC or Haltech.

Why not just raise the base fuel pressure 5-10 psi? Can the stock fuel pump not keep up?

This will raise the pressure at *all* times (not just during boost). There will be more fuel pressure at cruise, but the ECU "should" be able to compensate for this. On the Honda ECU, this is known as "short term fuel trim" and "long term fuel trim". I'm assuming the FD3S ECU does something similar based on the way it also samples the O2 voltage.

:beerchug:

Sonny

Yes, you can use an aftermarket Rising Rate Fuel Pressure Regulator to add more fuel instead of upgrading injectors.. However, you still need something to "trim" the amount of fuel like a simple/cheap fuel computer. However, this is known as the "dirty" way of upgrading the fuel system now that technology has bigger and better things.

Actually as long as the boost is kept at 10 psi no ECU mod rule is required. Most agree on that.

It simply amazes me that people try to find a ghetto way around paying:

*$400 for a used ecu
*$300 for a new electronic boost controller (or less for a used one)
*less than $50 for a manual boost controller

There is no controversy about the 3-mod rule. There's either people who have the knowledge and know what they are talking about, and then there's the people that don't. If you can keep your boost at 10 psi with no spikes or creep, you can run all of the bolt-ons, period.

Ok, guys...good info. Thanks!

Sonny

You typed exactly what I was thinking.

Rynberg comes thru once again and I agree wholeheartedly. ;)
If you want to play the "more power" game without a safety net($$$) you have no room to bitch about the 13b-REW when it grenades on you.

I originally thought that keeping the boost @ 10psi would be o.k. for having all the bolt-ons, but am skeptical to that reasoning, because if it failed to do its job right you could very well mess up a good engine.

Also I don't think it is soo much as ghetto, but more looking for alternatives, as fmu's do work well in certain applications. It would be better than running stock, and certainly a cheaper route to go. But also agree that buying a performance ecu yields much more benefits. You don't here to much about people putting fmu's, instead of a performance ecu on Rx7's so it must not be the route to go. I posted a similiar thread a while back, and some apparently have done what your asking, but not many.

I wasn't talking about using a rising rate regulator (FMU)...just a simple upping of the base fuel pressure. I've done the FMU route before (not on an RX-7) and it sucks. I would never put an FMU on a car that came turbo from the factory!

I've also done the full standalone route. It was wonderful...complete control, but it took a while to learn that system and since it was on a piston-based engine, I'd be essentially starting over with a rotary-based engine and a Power FC or Haltech. It was a lot of time/work and before I go that route again, I'd like to drive the car for awhile but understand what the limitations of the stock ECU are.

On a car that I tuned before (a turbo Honda), we maxed out the 440cc injectors at 240 whp with a base fuel pressure of 35 psi. Injectors were seeing about 88% duty cycle.

We were able to drop the duty cycle into a safer area (about 78% or so) by upping the base pressure a bit and leaning out the part-throttle maps.

That was a completely safe and very viable alternative to dropping in a new set of $400 injectors.

I wasn't trying to ghetto or cheat anything...just seeing how you guys do things "over here" ;).

Cheers,
Sonny

You already know the stock fuel regulators can flow more, but how do you plan on increasing fuel delivery without adding or replacing something.

read this thread they unearthed it should help you out.
https://www.rx7club.com/showthread.p...threadid=27094

You can't simply "up the fuel pressure" as it's regulated by the Fuel Pressure Regulator. The only way that increasing the fuel pressure would cause "more fuel" into the A/F ratio would be if the stock FPR gets overrun by the higher fuel pressure and isn't doing it's job.