running AV 100octane gas on a N42/N42 flat tops combo...

[olie05]

I have a n42 head on a flat top pistoned block. I can hear detonation on the higher load gears... (4 and 5) today, someone offered to bring me some AV 100 octane gas the next time I go autoxing. Is there anything to becareful with? What I have heard is that it will mess up O2 sensors and Catalytic converters. Since I don't have either, i should be ok right? This will not mess up my injectors or eat through my hoses will it?

 

-Oliver

[1 fast z]

It will only plug up cats, if its leaded, I dought it is. It will also only shorten the life of the O2, not ruin it instantly. I use leaded gas with my WB, numerous times and still havent ruined it.

[madkaw]

100LL has a lot more lead then auto leaded gas ever had. What damage it will do ,I'm not sure. When I use to work at an FBO I would fill up my 240z every once in a while(hope my old boss isn't reading this) and the car ran fantastic.

[Thumper]

Other than clogging up cats and o2 sensors leaded gas won't hurt your engine. And if my memory is correct you don't have either currently so you are good to go.

[olie05]

yep! sounds like I will be running the next autox on AV gas!

[JMortensen]

If you run more octane than you need you can actually lose power. You can buy AV gas from just about any airport that deals with small prop planes. It's not legal for street use, and you can't pull your car up to the pump, but they usually have self service pumps and you can just walk up with a gas can and fill it.

 

What I did was to keep cutting it with regular gas until I found out what octane I needed to run the timing I wanted and not ping. Turns out in my case it's about 95 octane, so I basically just split it 50/50 with supreme unleaded from the pump and that's it.

[rztmartini]

i have a 55 gal barrel with 110 leaded we used to use on our quads. so if i put this stuff in i will actually lose horsepower? what is the calculations needed to figure out octane by cutting it with 92?

[olie05]

Hey jon, What is your setup again? what head/block combo are you running?

 

I remember you saying you had upped compression somewhere.

 

I'm just trying to see how close your combo is to mine.

[JMortensen]

L28/E31, about 11:1 compression, .490/280 cam, ported and polished (chambers too), 280 valves, 44 Mikunis

i have a 55 gal barrel with 110 leaded we used to use on our quads. so if i put this stuff in i will actually lose horsepower? what is the calculations needed to figure out octane by cutting it with 92?

Yes, that's what I'm saying. I think Dan Baldwin had some hp figures on race gas vs street gas that proved my point. He made about 10 hp less on the higher octane gas.

[BRAAP]

FWIW, the currently available 100 LL AV gas has far less lead than it used to, pretty negligible any more, (I am a FAA certified Air Frame and Power plant technician a private pilot SEL, also professional engine builder specializing in L-series cylinder heads).

 

AV gas is fine for auto engines. At Sunset Engine development, we used AV gas in pretty much all of the Gasoline powered white water race boat engines we ran on the Dyno as well as the 2/3 scale and ¾ scale P-51 Mustang kit plane V-8 engines.

 

As has been mentioned by 1fastZ, AV gas is hard on Cats and over time will take its toll on O-2 sensors, though an O-2 will run for quite a while with AV gas.

Our personal L-28 autocross car runs strictly AV gas and an Innovate LM-1 Wideband O-2. The engine is a Flat top piston L-28 with the MN-47 head, right at 12:1 comp ratio with around 42 degrees total ignition advance, no pinging or detonation, AFR at WOT is between 12.3-12.8:1

 

Now there is something that you DO need to be aware regarding AV gas. AV gas has less specific gravity than auto gas and race gas. This means you must either jet a little fatter or scale your EFI fuel map “up” just a skosh. If you plan to run it long term, definitely make it a point to retune your AFR as AV gasses lower specific gravity can burn a valve or worse. I’m sure many of you have heard horror stories that just by switching from auto or race gas to AV gas, you will burn up your engine. Yes, that is true and has been documented, but not because AV gas burns any hotter. AV gas burns valves due to the fact that theses same people didn’t recalibrate their fuel metering, i.e. fatten up the mixture due to lower specific gravity of AV gas so their engines were running too lean, that is what burned up their engine.

Short term use like an autocross here and there most likely wont hurt anything, especially if your engine is running a little on the fat side with auto gas to begin with. If you are running on the lean side with auto fuel, then I would suggest you make a mixture adjustment, even if it is short term. Not only will this protect your engine from running too lean, but your AFR will be more ideal for maximum performance with that fuel.

 

 

Octane rating an be viewed as a number that refers to the stability of the gas under certain conditions, Octane does not indicate power available in that fuel. In fact, as jmortenson mentioned, the more octane a fuel has, the less BTU’s available, i.e. less available power, but this is very slight. The trade off is that a higher octane rating is more stable and less prone to detonation, a trade off worth making for high compression race engines. In short, for maximum performance, run only as much octane as you need with ideal full ignition advance for the compression ratio of your engine.

 

Hope this helps…

[JMortensen]

Oh yeah, the math. Well lets say you're adding one gallon 110 to 5 gallons 92 octane. All you have to do is add all the octane points up and divide by the number of gallons. So 92 x 5 = 460 + the one gallon of 110 = 570. Divide that by 6 and you get 95 octane.

[rztmartini]

oh cool. thanks for that...i am amazed at the collective knowlege between just a few guys, let alone the entire forum!

[olie05]

Thanks Paul!

 

you always seem to clear things up for me!

 

Projects for this week before the autox:

install NB O2 sitting in my room and make sure i'm running on the rich side

-and-

adjust afm if i'm not running rich already.

 

I cant wait until I have megasquirt on this car!!!

[BRAAP]

Thanks Paul!

 

you always seem to clear things up for me!

 

Projects for this week before the autox:

install NB O2 sitting in my room and make sure i'm running on the rich side

-and-

adjust afm if i'm not running rich already.

 

I cant wait until I have megasquirt on this car!!!

 

 

 

Oliver' date='

Since you are running the OE EFI, your best bet for across the board fuel enrichment is alter the water temp sender value. A 250 ohm resistor in series with your water temp sender might be enough to fatten your mixture for AV gas, if your AFR was pretty close to being with. As for using the AFM for adjusting the AFR, The AFM will only affect the AFR up to 4000-4500 RPM only and it doesn’t affect the AFR linearly. At WOT, the AFR has considerably less influence on the fuel map than it does at part throttle and idle, there fore the AFM would not be an ideal way to adjust your AFR for a swap to AV gas.

 

For tuning OE EFI equipped cars, I use my little black box. This little black box is wired in series with OE water temp sensor for tuning purposes, (I even use it for diagnosing drivability issues some times as well). This black box consists of a small 3” x 2” plastic electrical box, a 1k ohm “linear taper” potentiometer, a fixed 1k ohm resistor, and a single pole double throw switch. All parts bought at Radio Shack, (I’d take a picture of the black box for you but it is currently in use in Ron Tylers ’78 280). Using my Fluke DMM, I then graduated the dial of the POT in 250k increments. 1k increments would be better, especially when dyno tuning. This little black box is a neat little tuning aid for the OE EFI. One position of the switch is just the POT, 0-1k ohms plus the OE water temp, the other position adds 1k ohms to the POT for a range of 1k-2k plus the water temp. This allows for VERY coarse adjustment, (if you are dyno tuning, just a 1k POT is MORE than enough adjustment.)

 

Here is a picture of an example resistor with the bullet connectors on the ends and also a potentiometer allowing analog adjustment of the fuel curve on the fly. (The resistor pictured is just for example purposes, its ohm value is NOT desirable). You just unplug one of the water temp sensor connectors, either one it doesn’t matter, that is just behind the thermostat housing, (not the one with the red tape, that is the thermo time switch), and put the resistor in between the connectors and wa la, you will have a little fatter AFR. DO make sure that you protect the resistor from touching any metal parts as that could ground out the water temp signal causing the engine to run very lean, i.e. wrap it in electrical tape, heat shrink, etc.

 

Hope this helps.

 

 

 

BTW, did you get the E-mail I sent?

 

 

 

[img']http://i17.photobucket.com/albums/b81/BRAAPZ/Rusch%20Motorsports/ResistorMedium.jpg[/img]

[olie05]

I got your email paul

 

I will be heading over to the radio shack. Is there any complication with running the resistor into the cabin? (i.e. wire resistance/ foot of wire?)

 

thanks for all the replies guys! This thread has proven to be very informative for me.

 

-Oliver

[BRAAP]

Oliver,

You should not have any issue with running the resister in the cabin. In fact, the little black box sits on the center console for on the fly tuning/diagnosing.

 

I was able to get in to Rons car to get picture of the little black box sitting on his center console, just in ahead of the 280 Z ash tray.

 

 

 

Not that it has any relevance to what you are doing, but as for “ball park” OE water temp sender values, when the engine is dead cold, ambient temp of 70 degrees, the water temp sender value is typically between 2500-3000 ohms. With the engine at full operating temp, approx 180 degrees F, water temp sender value is typically 250-350 ohms.

[BRAAP]

EXACTLY! I’m glad I’m not the only one whos L-28 was so finicky that it had to have separate summer and winter resistors. LOL A bone stock L-28 will tolerate quite a spread in AFR, but the more finely tuned for performance the engine is, the more finicky it becomes to AFR and even fuel quality. Finicky enough that during extreme temp swings from morning to the afternoon on some days, the engine will have slight misfires that you can ever so slightly feel/hear unless you reset your values.

There is a little air temp sensor in the AFM, (that little white probe-nub looking doohickey), that is supposed to compensate for air density caused by temp variations, and it does a great job on stock engines, but for finely tuned performance cars, the ECU needs to have a more aggressive adjustment MAP in regards to that little sensor. FWIW, that little sensor in the AFM works just like the water temp sender, and that little air temp sender responds VERY VERY fast. It responds so fast in fact, I have used it as a tire pyrometer with a DMM. I did this back in the early ‘90’s. I just attached it to the end of an old ball point pen with the leads coming out of the back of the pen. I didn’t get actual temp values, (though it would be easy to calibrate it for that), I just used it to check for misalignment of toe and camber at the track when I used to run my cheesy 195 60HR 14” daily driver tires… (those were the days… LOL).

 

have we gotten far enough off topic yet? LOL.

 

I just love these discussions that get off on interesting tangents.

[olie05]

I made up the pot and wired up to the water temp sensor.

 

I went and "tuned" just by listening to the engine for the tell tale rattle in 4th gear, and I got it to almost go away. This will be good, because I won't even be getting out of 2nd at the autox. I should have a nice margin of safety for the lower specific gravity of the av gas.

 

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