Wade

iTrader: (1)

I can't say this for certain about the Gold boxes, but I'm pretty sure this aspect has not changed with Gold/Purple boxes.

0% fuel added with the PMS means 0% fuel added over stock. There are two things that need explained about this.

1) This might make you wonder why some cars, when tested with a wideband lambda, don't need any fuel added over the stock ECU. The biggest reason is the boost level. If boost is kept at 10psi, usually no extra fuel is needed. This is because the stock ECU delivers so much fuel that the a:f ratio is 10:1 on a stock car. Even a bunch of mods won't usually lean that beyond the target of 11.X:1 that most people use to tune their RX-7. Yes, this implies that if you run 10 psi of boost and you are tuning for max power, you might actually be removing fuel from the stock settings.

2) Above 10psi, all bets are off. Since the stock ECU causes an overboost fuel cut when the boost level stays above appx 10psi for a certain length of time (around 3 seconds), there is no way to do a direct comparison above 10 psi between the stock ECU fuel settings and the PMS. The stock ECU simply won't allow it. I'm pretty sure the PMS clamps the incoming boost signal to the stock ECU to appx 10psi (below the overboost fuel cut). This is supported by my car that running 10psi with the PMS gives a 10:1, and raising the boost gradually increases the a/f ratio (the mixture gets leaner). So if you want to run 15psi of boost, chances are you will need to add some fuel at max boost (probably no more than 10% with typical bolt-on mods - intake, exhaust, IC, etc).

Wade

Donovan

whoa!! I've got like +20% at only 12lbs of boost. I was using the 02 readings on the key pad to tune to close to .82 rich EFI uses %0-100 right? I have a down pipe mid pipe and cat back as well as intake but now it seems like that is too much.
Wade your saying I may only need as little as +10% at 15 psi?????

Wade

iTrader: (1)

If you have 20% at 12psi then you are definitely running far too rich, assuming nothing is wrong with your car that would cause it to deliver less fuel than it should. I'm kinda surprised it doesn't stumble and poof black smoke at WOT (or does it?)

For 12psi, I didn't have to add any fuel and I still had an acceptable 11.X:1 a/f ratio indicated on my wideband at WOT in 4th gear. And yes, I think most cars wouldn't need more than about +10% for 15psi, but it will vary by setup. Though I wouldn't recommend running 15psi without a big intercooler and some special care.

You should be able to drop your fuel to +10% for 12psi without any worries, but the bottom line is you really need to spend about an hour on a dyno or with a wideband. It is worth the money, it's silly to spend thousands on modifications and then throw away 50 horsepower by running a 10:1 a/f ratio.

Wade

Donovan

Dang it your right! I need to find a place where I can put it on a dyno, Problem is it is about a 2 hour trip at least.I guess I should not pay attention to the stock 02 readings that come up on the hand held then correct?
Hey Wade did you take out any timing? I've heard to take out 1 degree for each lb over stock boost and I've heard to take none and actually add some at 4k to help the transition smooth out?

Wade

iTrader: (1)

You should be able to rent a wideband lambda if a dyno is too hard to get to.

Yes, I subtract some timing. I use the general rule of subtracting about 1 degree at max boost for each psi of boost over stock, or -5 for 15psi of boost.

Wade

sbrx7

Wade,

When you subtract the timing, does it have an affect on A/F ratio, or is it just a safety issue to prevent detonation? Also, being the wideband king you are, did backing the timing down affect HP figures on the dyno? BTW, for the readers of the thread, can you go over some of your fuel system mods? As I recall, you have only optimized the stock particles, and added an aftermarket pump, correct?

Always looking for a few more ponies

Steve Bertok
94 MB touring
319 RWHP, no added fuel!*

*substantial modifications, including some fuel system items.

Wade

iTrader: (1)

Subtracting the timing doesn't have a significant effect on the a/f ratio. It might at extremes but the small changes I have made (5 degrees) were not detectable. The big reason for doing it is just to reduce the chances of knock.

I own a wideband but I don't have a local dyno. So I don't know how much the timing changes will effect power. You'd be better off talking to crispeed, riceracing, or one of those other guys with very high horsepower cars that have spent lots of time on dynos. I could tell you how much of a difference I think it would make but it would be only a guess. To me, any gain in power is moot because my primary concerns are keeping a safe a/f ratio, timing, and air temps.

Fuel System:
Stock sized 550/850cc injectors
AN-6 lines and pretty AL fittings
SX adjustable fuel pressure regulator
Walbro GSS-341 high pressure pump

My fuel pressure is set higher than stock which gives me approximately 10% fuel. I would guess that a car with no fuel modifications at all would need 10-15% extra fuel to run 15psi with a relatively conservative a/f ratio. A car with a pump but stock regulator would probably need less added (or none) because the fuel pressure might raise slightly.

As usual, I suggest everyone use a wideband to be sure.

Wade