We seem to be talking as if I should be using both systems on my car. The greddy kits used to come with a BDFPR, but they switched to controlling the injectors, why? Because the blue box controls pulsewidth like a standalone would, without messing with the FP. This is the better way to provide fuel enrichment, right? Anyway, regardless of the fuel setup-

I guess what I'm really asking is if my a/f ratio reads 12.5:1 at WOT on the wideband O2 at 42 psi FP and 7.5 psi of boost, how could I be leaning out? The wideband says the fuel is perfect!

Or is 12.5:1 not the correct a/f ratio? (Turbo Tech said that is the a/f ratio they shoot for.)

Why does my car run perfectly at 12.5:1 a/f ratio at 5.5 psi, but not 7.5 psi?

Do higher boost levels require richer a/f ratios than lower boost levels?

Am I going crazy thinking about this too much?!?!? There must be a simple explanation.

 

You're right, there is a very simple explanation. Higher boost requires higher fuel pressure. The same fuel pressure that allows you to run a/f of 12.5:1 at 5.5 lbs of boost is not adequate for 8lbs of boost. So, what you need is MORE fuel to run the SAME a/f (12.5:1) at higher boost. THat same fuel presure (that you used at 5.5 lbs of boost to get 12.5:1) at 8lbs of boost would probably be in the 14' or 15s on a/f even though its perfect at 12.5:1 at 5.5 lbs of boost.

So remember, hihger boost requires higher fuel pressure at the injectors. 50psi may be fine at 5.5 lbs of boost and give you 12.5:1, but you need about 80 psi at 8 lbs of boost to still run 12.5:1. Thats why you need a BOOST DEPENDANT fuel pressure regulator, or FMU (fuel management unit) as Vortech calls it.

Let me know if thats still not clear.



[Modified by greyzone, 10:39 PM 12/12/2001]

 

I said this in my post, but maybe it's clearer this way- we've been misunderstandng each other.

On the dyno this is what happened...

Boost level = 7.5 psi
Fuel pressure = 42 psi
Wideband O2 reading at the above settings = 12.5:1 a/f ratio!!

See, what I was saying is that my a/f ratio was 12.5:1 at BOTH 5.5 PSI AND AT 7.5 PSI. That is why I don't understand why it was pinging at 7.5 psi. Even with 5 degrees retard and 99 octane fuel. My a/f ratio was obviously perfect.

So why is it that now when I raised FP from 42 psi to 62 psi and only run 2 degrees retard and 92 octane fuel that it runs fine? My a/f ratio must be really rich now, like maybe 11:1 or something.

Thus I reach the question- do higher boost levels require richer a/f ratios? (this doesn't sound right to me)

 

No. Regardless of boost level the correct a/f is 12.5:1, its just at higher boost levels it takes MORE GAS to keep it there. Sounds to me like the sensor may not have been reading correctly, or perhaps some problems with your plugs or ignition/wires. Perhaps the gas wasn't 99?

 

OK. I highly doubt the wideband wasn't reading right.

If it was an ignition problem it would've misfired, not detonated.

The gas was like 6 gallons of 92 octane mixed with a bottle of NOS octane boost which I was told works well. Maybe it wasn't actually 99 octane, but it should've been high enough.

I just dont get it because I've had countless people tell me that they boost 8-10 psi with the same setup and have no detonation on pump gas with anywhere from stock to 2 degrees retarded timing. Are they full of it? I don't think so, my bro runs 9 psi at 2 degrees retard with no problems. My car seems to be a special case. Oh well, no use in dragging this out anymore- its been beat to death.

 

Im not so sure thats true...bad wires, weak spark, cracked distributor, bad rotor...many things can be off with the ignition that may not necessarily cause a miss but can still be ignition related and cause problems...

NOS is about the best, but one can (size?) in 6 gallons may increase you from 92 to about 93 or 94...also, if the 92 is from ARCO or some small brand outfit its not good gas. Its important to stick wwith the majors, like Shell, Texaco, Chevron etc.

The bottom line is if you're having these "wierd" problems that no one else seems to be having there is definitely a reason for it...personally at anything less than 5 degress retarded I detonate. Im going to add the MSD BTM soon to help with this and probably add the MSD knock sensor to boot, but havent decided yet for sure.

Its like Im getting so far into this everything is just becoming a cheap substitution for a stand alone so Im getting real tempted to just go that route.

Anyway, I think its good to "beat this stuff to death" and not leave any stone unturned or leave things to assumption...especially when mistakes can run into the thousands of dollars in a only a few seconds of ignorant bliss.

You do bring up a real good point...if you're detonating with an a/f of 12.5:1 AND your timing is appropriately retarded AND your gas is high-enough octane, then WHATS causing the detonation? I dont know but Im gonna post that as a question...lets see what response we get.


[Modified by greyzone, 7:04 AM 12/15/2001]