Don't run 87-89... compression ratio 10:1 requires 91-93.

 

yea thats a high cr for anything less than 91-93 unless your timing is set way back but everycar is different. i personally would just be happy for now or spend some money

 

Ya know I don't think I've ever seen 91 octane here in NC, but i will google it.

 

torco works , i used it and want to get a spare can sometime to have just incase.

 

I have been running 89 in mine for a long time and no knocking even in AZ weather. If everything is running right, the computer will adjust. I know I lose HP but Im not worried about that.

 

Yes, the PCM has an adaptive spark mechanism which reduces timing when knock is detected...

i.e. knock occurs, the knock sensors detect it and notify the PCM, the PCM immediately adjusts the knock slider toward the LO table, and when the knock disappears the PCM slowly adjusts the knock slider back toward the HO table, and then (because you're running low octane gas) knock happens again, the cycle repeats...

knock is a catostrophic event, each time knock occurs at lower loads a tiny piece of combustion chamber (head/piston) is chipped off... the size/volume of the knock is proportional to the load... at higher load the knock is huge and causes more damage (big enough to blow a hole thru the head gasket, melt a piston and blow a hole thru it, blow the ringlands off pistons, melt the spark plug tip, flatspot rod/crank bearings, ...);

a normal ignition is a burn (flame front proceeds with some relatively slow speed)... knock is an instant explosion (the shock front has a super high speed)...

consider this:
- normal ignition combustion chamber pressures are about 1200 psi;
- low load knock cc pressures are about 5000-10,000 psi;
- high load knock cc pressures reach about 20,000 psi;

if you go WOT on low octane gas the engine will knock and will continue to knock even tho the PCM has adapted spark (running from the LO table)... the adaptive spark mechanism is no guarantee to prevent knock, you don't want to rely on this to protect your engine (because it won't);

the Owner Manual and the Service Manual (and the decal inside the gas door) state to use 92 octane gas for a very good reason...

When you say you lose power you are implying that you're giving the engine some significant throttle (where else would power matter?)... not only will you lose power, you will lose your engine...

sounds pretty serious... because it is.

 

I think there are 3 kinds of people who use octane boosters.

1)FI guys to run more boost.
2)Guys who built a high performance pump gas engine, thats just a little too high a compression to run on 91/93 octane under all conditions, like hot days at low altitude.
3)People who think it makes thier stock engined grocery getter run faster.

People in category 3 should put the money they are spending on octane booster into thier 401K.

 

Here is a good read about race gas and tuning for it.. I copied it from someone that copied it.. Not sure who the original author is..




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I use VP MS 103. It has the same stoich ratio as 93 octane(e10). Which is around 14.2.

Which means I dont have to change the tune other than WOT timing adjustments. Where ms109 would require retuning. It has a stoich ratio of 13.41.

Heres a thread I copied from yellowbullet that explains this.

Race Gas Stoich Rating Tuning Considerations

Well I have seen questions from time to time about adding race gas without tuning which can be a very expensive experiment. I am going to explain how stoich effects AFR. Hopefully in simple format.

I am not going to get into MAF transfer functions or other tuning functions.This is just about fuel.

First lets define a few terms:

AFR: Air Fuel Ratio

Stoich Rating: In simple terms is the AFR to have chemically complete combustion that is neither rich or lean. For Example most pump gasoline is about 14.64 to 1. Which means 14.7 parts of air to 1 part of fuel.

Lambda: Is a term that is utilized when tuning. In basic terms think of it as an adjustment to your stoich rating when tuning AFR. For example with pump gas tuning .80 lambda, 14.7 x .80 = 11.76 AFR target.

Lets assume your car blower car has a nice tune that gives a perfect 11.8 AFR under WOT with pump gas.

So now it is race day. We add some timing to our tune, drain the fuel tank, and fill up with some high octane unleaded VP109.

We go for a blast down the 1/4 mile while datalogging and see the A/F is reading 12.8 then make a quick trip to the bathroom only to find out they are out of toilet paper.

There are a few factors here to consider.

The stoich rating of VP109 is 13.41.
Most wideband A/F modules are calibrated to 14.7 pump gas stoich.

So this is the formula to determine the true A/F for the run.
AFR/Wideband Stoich x Race Gas Stoich
12.8/14.7*13.41= 11.7 AFR on Race Gas

So you may think 11.7 sounds safe but we must remember the VP109 stoich is 13.41. So 11.7 AFR = .87 lambda. For the most part a safe lambda value is .80 to .82 for a forced induction mustang. I prefer .80

So we take VP109 stoich of 13.41 x .80 lambda = 10.73 AFR
This is the AFR (10.73) I am tuning for.

Keep in mind this is not what will display on your wide band as it is programmed to 14.7 stoich. You must convert the AFR.

AFR/Race Gas Stoich*Wide Band Stoich

10.73/13.41*14.7 = 11.76 AFR is what I want to see on my wideband when running VP109.

Just to reiterate 11.7 on the AFR display with VP 109 is really a 10.7 AFR.

Ok so hopefully you are not totally confused.

There is a simple solution to all of this madness. The SCT Advantage software has a Scalar for Stoichiometric Air Fuel Ratio. You simply enter the correct value for the fuel you are using and all lambda fuel calculations will be based on this value. Then just do the first formula conversion to determine what you should be reading on the AFR display. Some AFR modules may be able to be programed to the correct stoich.

Or leave the stoich in the tune and wideband at 14.64 and calcualte what AFR you need to read on the wideband for the fuel that is used. (This is how I did it in the past, but I find it easier to change the stoich scalar)

This is why you have to exercise caution when mixing race gas and pump gas as you do not know the true stoich of the mixture. The leaded race fuels have a stoich that is closest to pump gas. I always drain my tank before putting in the race gas. When I mixed fuels in the past I didn't notice a drastic change in AFR, but when I have 100% unleaded race gas it really leans out with a 14.64 stoich scalar in the tune.

The other caution is the winter (oxgenated) gas we get in Arizona. I noticed the car leaned out in the winter when it was tuned on the better summer blend. A 14.1 stoich scalar works for the AZ winter gas if your initial tune was based on the summer blend.




Race Gas Stoich Ratings

Sunoco MO2X UL – 14.5
Sunoco 260 GTX – 14.4
Sunoco 260 GT – 13.9
Sunoco 260 GT Plus – 13.7
Sunoco Standard – 14.8
Sunoco Supreme – 14.9
Sunoco MO2X – 14.5
Sunoco HCR Plus – 14.8
Sunoco Maximal – 15.0
Sunoco MaxNOS – 14.9

Turbo Blue Unleaded (100 octane) -13.9
Turbo Blue Unleaded Plus (104 octane) - 13.7
Turbo Blue 110 - 14.7
Turbo Blue Advantage - 14.9
Turbo Blue Extreme - 15.0

VP Street Blaze 100 - 14.16
VP C10 -14.53
VP C16 - 14.77
VP 110 - 15.09
VP MS109 - 13.41 bkjnn
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Original thread

http://www.yellowbullet.com/forum/sh...d.php?t=244066

 

That article is correct about the stoich AFR varying among racing fuels, but it does not address spark timing which is the main gist of this thread.

Adding a bottle of octane boost (which is what the OP is asking about) won't change the stoich AFR of the gas in the tank.

 

How much timing would you add then?

 

This is a Really Good Post!! Thanx guy's for the info I'm all in here please keep it going. You have my total attention.

 

See what I said about dyno...

 

its useless unless the computer knows its there....i have used it, and others simply because I thought that some of the 93 that I got was not up to par. Nowadays I always use shell 93...and now I am going to be using shell e85.