I know this has been beaten to death here, but I have never had a clear understanding of how to blend leaded racing gas and 93 octane to produce 100 octane leaded gas. My current method- 7 gallons of 110 leaded gas with 10 gallons of 93 unleaded. Mathematically this should produce 17 gallons of 100 octane leaded. A simple proportion ratio apparently doesn't produce the right mix. Without all the technical info rehashed, how do I achieve the proper blend to produce the desired end result?

490 cid full roller motor. Yes, it needs the lead and detonates with only 93 octane. I do not want to adjust the timing. Why? Because. I like the tune up it has and don't want to bend to the rules. And, mostly, I live in Kalifornia and want to pollute the Bay area with raw, nasty leaded exhaust fumes.

 

MSD makes and in-cab timing adjustment **** that would allow you
to make timing changes from the drivers seat... just thought I would
mention it.... if you marked your timing points for 100 and 93 this
might give you the flexibility to run both blends of fuel w/out popping
the hood.


if no:

http://www.klotzlube.com

 

It's a big hit or miss as there are so many different blends throughout the country and no specific formula is good for every situation. Keep in mind that even today's NASCAR 800 HP engines are running on unleaded gas and not having problems. I remember many years ago (too many, in the mid '60s) you could blend the then available highest premium leaded gas with a lower grade of regular gas and get more power from the blend, then just the straight h/t leaded. Back then racing gas was unavailable and not allowed in NHRA. It had something to do with the specific gravity of the gas when tested. Find a match with the proper timing through experimentation with your own engine as "catch all" formulas will be too hit or miss.

 

67ratrag:

How did you determine that you need exactly 100 octane leaded gas for for car? I agree that blending leaded and unleaded gas for octane is not a straight proportion, but it should be close. For example: blending 5 gal of 93 octane unleaded and 5 gal of 110 octane leaded may not give you exactly 10 gallons of 101.5 octane mix, but it should be very close to this number (probably somewhere between 101 to 103octane). Certainly close enough to start with; then let you car be the final judge. There are just to many variables to be any more exact: engine timing, elevation, seasonal variation of the unleaded pump gas, air temperature, etc. etc.

I would start with a 50/50 blend of unleaded pump gas and leaded race gas and see how my engine performed. Then adjust up or down from there to control/optimize your overall costs without getting into engine detonation.

For additional information go to http://www.rockettbrand.com Then go to PRODUCT TECHNICALS, and TECHNICAL BULLETINS. You should find just about all the answers to your questions. They even have a technical bulletin specifically on blending unleaded pump gas and leaded race gas. However, their final recommendation is not to do it, but to buy unleaded 100 octane race gas instead.

Larry

 

As sick as this is, I am at work right now treating patients. I just did a root canal on a lower molar. Then I jumped back on the forum. Soon, my next patient will be here and it's back to work. Scaling and root planing 4 quadrants. Then some little monster, er, um, I mean a small child is coming in for me to see since last time she was here there was a scene with another DDS so I guess that makes me the default guy to go to.

Anyway, if there is the "universal formula", let me know.I'll check back in an hour.

 

I think you can just experiment with the mix to dial it in to your engines need, although you probably don't need to use any leaded fuel in the mix unless you are really flogging the engine on the race track.

You might want to save a little jingle and use regular unleaded fuel for the mix instead of the 93. I use 20-25% 110 octane unleaded mixed with 87 octane unleaded and run it in my 365 with an aggressive distributor curve, 12*initial and 11:1 compression with no problem. Mine will also knock like crazy on straight 93 octane fuel.

 

Well, out here in the Bay area gas is so expensive already- many stations have regular unleaded for 4.09 a gallon. For another .20 I get 6 more octane so it's no big deal overall. The cost of the racing gas is already so prohibitive that the little additional cost for the 93 is lost in the overall output of the coinage. Oh, to be back in Texas.......

 

Well, I'm done for the day at work, so I'm off on some other adventure. I'm still waiting for the magic equasion, so if you have any input I'd appreciate it.

Thanks.

 

there are a some articles from Tim Wusz @ rockett brand race gas (formally union oil race gas) that you can access thru the tech article link at www.olescarb.com . Tim was a fuel engineer for NASCAR and NHRA when union was selling race gas.


i hope this helps henry @ olescarb

 

Maybe someone else who was trying to keep their muscle cars going in the 70s when unleaded fuel came out will have a better memory than I. It seems like we were being told that when we mixed a few gallons of still available reular leaded fuel with unleaded, the resulting mix would have an octane value in excess of either one separately. I think several magazine articles tried to explain the chemistry of this but it's lost on me now. But I think this principal still lives on today in the practice of mixing about 5 gallons of racing fuel with 15 gallons of unleaded. The net results is a higher octane value than the straight proportions would suggest on a weighted average. Anyone else remember this?

Dan

 

i remember doing this, for the same reason you mentioned. not sure whether it actually worked as we thought, but it sounded good in theory....
Bill

 

Fuel Blending Chart

Here is another chart:

 

I'm currently running a mix of 5 gallons 110% to 10 gallons of 93% in my 327/365 HP with 11:1 compression. Mathematically this gives you a mix of 98.6% octane. My car is running out just fine. I may bump it up to get a mixture of 101-103% though. I have in the past ran a full tank of 110% and it ran great. The cost at the pump is what hurts!

 

So my take on this by looking at the chart is that I have been doing it right by mathematical averaging. Looking at the chart and taking 10 gallons of 91 and mixing it with 10 gallons of 100 yields 20 gallons of 95.5 gas, the same 'averaging' system I have been using. Also in my reading from one of the articles about octane they state "Using leaded racing gasoline on the street is illegal. The user and the seller can both be fined up to $10,000 each." Huh? I have antique plates for my car and it doesn't have to be inspected, but you can smell the difference when you approach the running car. Any Kalifornia peace officer will smell that and know something here is different. So I can't run leaded gas on the street in an antique vehicle?

 

The simple mathematical average works for unleaded fuels. Leaded fuels can have a different formula as the lead acts to boost the octane of the unleaded portion, so you actually need less. I do not have the formula and it is probably going to vary based on the actual PPM of lead in the leaded portion, so I'd stick with the simple formula and accept that your actual octane as blended is probably higher.

To your second point, it is illegal to use leaded fuels on the road. That said, I would not think a LEO would give you grief on this. Most high octane unleaded fuels are perfectly legal and there is no roadside test a LEO can perform to tell exactly what you are running.

 

careful now you just might offend someone....

 

Yeah, I will be erring on the side of caution and in all reality be running slightly higher than 100 octane gas as I use my mix. The car sure likes it so I'll stick with the old proven (useable) way until someone comes up with a better idea.

 

By memory I believe this is called octane response. The cuts of gasoline used to make the 93 octane fuel have more desirable traits and when introduced to the lead in the av gas or racing fuel it gives a kick in octane to the 93 unleaded portion of the blend. Lead in the old days was used to bring up the octane of poorer cuts of gasoline. Generally economics were the main issue. The blender would use the cost of lead and the cost of and availability of various cuts of gas to determine the type of fuel produced. Demand also entered into the equation. The sweet smell in the high octane fuels are aromatics and include benzene toluene and possibly cyclohexane. The aromatics have both high octane and low reid vapor pressure, good traits for av gas.
Regards