FredR

Well I guess you don't get too many of those to the pound [avoirdupois]!

Fred

FredR

Mark,

You have to get the fuel presssure up to the proscribed amount-[52 psig or so] -it should stay constant more or less irrespective of being at tickover or full load. Only then can you begin to analyse other variables- apologies if I am missing something. At 20 psi the injectors do not atomise correctly [probably no where near correctly].

Best wishes

Fred

heinrich

What is this mystery car, Mark?

John Speake

Yes, set by the LH EPROM, as I said "The (GT) LH EPROM has almost identical fuel maps to the S4 and GTS. The only significant difference is the 775rpm idle speed setting, as opposed to the 675 of the other models."

brutus

the redline cut off is higher RPM for the GT.

mark kibort

6800rpm, if i recall

mark kibort

Thanks!!

so, im thinking. since the timing is less, might i not gain some HP at the top rpm, where i mostly use my engine with the racer?? 4000rpm to 6600rpm?

Rob Edwards

There are 2 question marks there, so I interpret that you're asking a question about a GT map gaining you hp-sec at high rpm. Since you're asking that question, given the imperfections in communicating over the internet, I interpret that you don't know the answer. So I am going to answer that if you sharktuned your racer, you could maximize your hp-sec in that rpm range by optimizing those cells of the fuel and timing maps to a good safe AFR of 12-12.5:1 and either no or very few minor knock events, respectively. Any other approach to tuning in that range is just guessing, which leads to more question marks, which is a vicious and unpleasant cycle for the rest of us.

John Speake

I wouldn't recommend that as a sensible way to go about seting ignition advance..... you need to data log knocks versus load and rpm and correct the EZK map ONLY after tuning A/F ratio to be safe. A 30# EPROM or PEM
with stock fuel pressure would be a good starting point, plus a WBO2 to confirm.

mark kibort

Well, thats the next step for me. I might take the GT brain and dyno it vs my set up. then we will know if any thing special is happening with the current Holbert brain. If it is close, that one can be used to put in the custom chips and optimize the settings for my "racing" rpm range.
my fuel air ratios are in the 11.5 to 12:1 range in my use range. I dont know the gains you could get on that narrow RPM range of 4000rpm to 6600rpm, but coupled with some timing pull back or advance, i suspect that there would be some gains. how much, thats what i dont know. Ive played with fuel pressure to change ratios from 11:5 to 13:1, and didnt see very much change, but i have no clue what the hp gains would be if timing was also changed. one thind I DONT want to do ,is get to the edge , where my operational conditons change (as I run in 50 degree temps, as well as 110degree race days), and end up over the edge on those days. thats one of the reason, i like the state of tune my car is in now, as it seems to be safe. However, i would like to see how far its off optimum when i can afford the time and expense of doing so.

Thanks for the help!

Now, i just got off the phone with the owner of the 6.0 liter, and he told me the story of the shops that have been pulling fuel pressure out for years . not ever knowing what the pressure was, and only going off the soot from the tail pipes, and an observation off the street after going through the gears that it was a "flame thrower" between shifts or on downshifts, he kept on turning down the fuel pressure to get less carbon in the pipes. I personally believe that the soot is maybe due to it being , was being , rich initially under WOT. But, under idle, and warm starts, the car needs more fuel and i imagine it is running out of fuel under WOT now, at 20psi.
im going to pump it up to 40psi and see what it does. that way, it is not too far off my car's setting, besides the 400cc difference.

Speedtoys

Yer 8th post has to copy mine?

-2?

Dave928S

I smell a spammer/serial PIA ...check other posts ... done the same in other threads .. reported.

911SLOW

It was a spambot.
Thanks for the heads up.

dprantl

This car needs a wbO2 installed. Convince him that the ~$300 is worth it. Is it really that much to pay to see exactly what the AFR is at all times/situations instead of blindly trying to set base fuel pressure?

Dan
'91 928GT S/C 475hp/460lb.ft

jcorenman

Mark, this is the data that I think you are looking for.
I honestly do not know what possible use you can make of this, because these two curves are optimized for different motors than either yours, or the 6.0L.



John, this is a good suggestion, but without knowing the AFR or knowing what the EZK's knock-detection is doing, it still seems like stumbling around in the woods, in the dark-- just not as deep.
I could do this easily, but the reality is what Greg pointed out:

This engine (the 6.0L) was built with higher compression, and without being able to change the ignition timing. That seems nuts to me, but that is all there was, then. And it's been running around for quite some time with uncontrolled detonation and unknown AFR's, with the only (apparent) attempt at tuning being blindly fiddling with fuel pressure. Is this engine somehow undamaged, or a ticking bomb? I have no idea.

Mark, if you want help with Sharktuning, I would be all over that. Because I think that is the only thing that makes sense, here, for this engine. You need to get the fueling right, and more fiddling with fuel pressure won't get you there. And you need to be able to back out a bunch of timing while doing that, and then monitor the EZK's knock-detection before you start putting any back in. And then check your fueling again, because everything is connected.

You have obviously not spent much time at sea. Fortunately, the car gods seem much more forgiving of hubris, but I would not count on that extending very far to other people's cars. Be careful.