Don-maybe when you get your intercooler done, you can get away with 110. But you were talking about 20 lbs. boost???

With only 12 lbs., and this intercooler, I could probably take some timing out and run 92. But, am a little leary after all the isssues before. Just happy that it runs.

 

oh wow i thought you WERE running 92!

how are people geting away with 15 PSI and 92 octane?

could you use water injection to help that sort of thing?

 

King- I did run 92 in it and then went through a round of lean conditions until we got the "tune" where we wanted it-different pullies, boost levels,(12 vs planned 18) etc- the tune on the car was specifically for Road America, and not having any "real world" seat time, decided that 110 leaded would be the best defense against possible detonation if IAT temps got out of hand. I am positive that the IAT's at RA are in no way comparable to street driving, meaning that 92 is feesible for idling around town and the occasional blast.

 

We have 85,87, and 91 octane at the pump here. I might try 91 and 15#, but then again I tried 85 and 87 in my 13.8 to 1 iron headed 406. the 87 was ok but the 85 was no way. DO NOT TRY THIS! I only did it because I had a cam with a ton of overlap and 106 deg lobe sep and we are at 6000 ft altitude (lack of oxy dampens combustion).

 

Got the I/C covered, went with a air to liquid...

 

bbhunting you said you were runner 72pph injectors right?

I Still dont get why so big? with a BSFC of like .8 thats still like a 65pph injector... you DO have 8 injectors right? I just dont get it

please excuse my ignorance I thought that equation BSFC X hp / DC / #Inj was usually accurate

 

King- I think that the formulas are for recommended injector sizing. This motor has always moved more air and fuel than we anticipated. All I can tell you is that at 7k RPM, and 12.97 lbs. of boost, the 72's were over 85% DC. It also says that calculated A/F ratio is 14:7-1, where I am running 12-12:5-1, which would require more fuel. Don't know what else to tell you other than I am looking at 96's for future HP increases (18-20 lbs. boost).

 

wow i wonder if its got anything to do with the fuel octane? Doesnt higher octane fuel contain alchohol or somthing similar? that would probably change the demand for fuel... i know you need 2X as much alchohol as gasoline.

what do you think about that theory?

 

No, as a matter of fact, most current race gas has a little more energy content then pump gas (wasn’t always true).

I suspect what’s happening is that you’re using a lot of fuel to cool the chamber down and prevent detonation, but at that kind of rate you should be about at the point where his chances of detonation are going back up

 

83-please elaborate. That last thing I need is too replace another set of pistons!

Are you saying that too much fuel will cause detonation/pre ignition? My A/F ratio at higher rpm was trending lean (13), not fat.

 

that sounds a lil scary I figured in the 12's for a/f would be about right, anyone?

 

Sure, it’s fairly simple, to some small extent BSFC is dependant on your combustion efficiency (probably in the range of BSFCs of .35-.4, actually, that can be brought much lower through fancy chamber/port designs, but that’s irrelevant here), past that the biggest reason that your BSFC goes up is because you start adding fuel to slow down the burn rate and cool the chamber. A richer mixture burns slower and more importantly the pressure rise after ignition is slower.

Now most studies of detonation found that this works well in the BSFC .4-.6 or so range, and after that it’s effect on detonation drops off dramatically until around .75 where the curve starts turning back on itself. I’m not sure that I’ve ever seen a really good description of why, but I suspect it’s a combination of fuel burning off in places that it’s not supposed to (exhaust ports) adding heat to the process, and the combustion becoming less predictable and more likely to result in an end gas (after combustion) that is capable of supporting combustion, causing the secondary ignition to happen behind the flame front as opposed to in front of it like traditional detonation.

Basically, any time you end up with conditions that cause you to loose control of the combustion process is a bad thing.

Water injection has some very cool implications in these situations. Since water is just about a perfect anti-detonant, you can add water and replace all the fuel used above what the BSFC that the engine design will want if detonation isn’t an issue. In other words, if you’re running a of .65 to stay out of detonation and your engine really only needs .40… you can actually back off the fuel by that amount and replace it with water from a water injection system and the engine will make the same or better power and will be much less detonation prone.

BTW, your A/F ratio at higher rpm’s has little to do with this. Your duty cycle is highest at your torque peak. After that your engine efficiency (fuel and air use) starts dropping off per engine revolution

 

<b>72's were over 85% DC</b>

crossfire im just interested in that whole equation thing. what do you think about his 72pph's running 85% DC with only 13:1 A/F?

According to (650 X .6) / 85 / 8
he should only be using 57 PPH injectors

if hes using 72PPH injectors according to that equation he should be putting out 850 horsepower. say thats awfully close if that 650 is at the Rwheels, then he would be awfull close to 850 at the engine but with a higher BSFC huh?

 

Well, there’s a lot of fudging with #’s here but I’m not sure that he’s so far out of what would be considered an acceptable ballpark.

Look at it this way, 650hp at the wheels, with a 20% drivetrain loss works out to be about 812hp. Typically with that kind of power band you’re also dealing with some slippage on the rollers so you’re probably talking a little more then that at the crank even if you want to argue that he shouldn’t have that much drivetrain loss. Add to that that I bet that blower is pulling 50-60hp, and suddenly he’s over 90% DC with those 72# injectors with a BSFC of .60.

Based on those #’s and the fact that he said that he’s at about (possibly below) 85% DC he’s actually below a .56 BSFC, all said and done probably somewhere in the low .5x range, which is really reasonable.

Make sense?

To be honest, if I was looking to do some tuning on that engine, based on my previous experience I’d be looking for larger injectors also. When you end up with weird fuel problems when tuning it’s nice to be able to turn down your FP some and still have enough injector (fuel pumps are much happier at a few psi less), also, this lets you work around loads of other potential issues.

BTW, I know someone selling some a set of used 160’s

(sorry if my responses seem a bit confusing, my original response was based on you coming up with a BSFC of .8 and not really checking how you go there, to be honest, I probably read the beginning of this tread whenever it was started and then ignored it again till now so I may have missed or forgot stuff in between)

 

no you are dead on thats exactly what i thought you would say. i was just checkin

 

So, I am not crazy to think I need larger injectors? 160's huh-wow. So if I go from 12 to say 20 lbs. of boost-need more fuel?

 

Naw... sounds reasonable to me... It just confirms my belief that when someone says "it makes no sence" the problem is never an unexpecte situation, just not enough information/knowledge