Mixing Fuels - Pros and Cons
Mixing Fuels - Pros and Cons
(OP)
G'day all,
I have just completed build a Nissan RB30DE (3 ltr twin cam)with approx. 11.5:1 compression ratio.
I am trying to determine what the best fuel to run this on would be. I was thinking a 50 / 50 mix of Avgas (100 RON) and PB Ultimate (98 RON).
However, I am unsure of the pros and cons of mixing fuels, especially seeing that Avgas is a leaded fuel and BP Ultimate is an unleaded fuel...
The car is designed for track use only so the use of leaded fuels is permissible.
Thanks in advance!
I have just completed build a Nissan RB30DE (3 ltr twin cam)with approx. 11.5:1 compression ratio.
I am trying to determine what the best fuel to run this on would be. I was thinking a 50 / 50 mix of Avgas (100 RON) and PB Ultimate (98 RON).
However, I am unsure of the pros and cons of mixing fuels, especially seeing that Avgas is a leaded fuel and BP Ultimate is an unleaded fuel...
The car is designed for track use only so the use of leaded fuels is permissible.
Thanks in advance!





RE: Mixing Fuels - Pros and Cons
It will have enough octane where the mix may not and it is a lot easier to control. ie just add fuel from the drum to the car.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: Mixing Fuels - Pros and Cons
You did not mention whether or not you still have a catalytic converter in place (not likely), and whether carburetor, (carburettor, or carburetter, or carb depending on what part of the english speaking world you hail from) or fuel injected, closed loop or open loop.
If you have a carb, then realize you need to tune for different fuel densities (avgas vs street pump gas.) If you are tuning for a given track at a given altitude, then this isn't too much of a problem. This is less of an issue, or possibly a non-issue, if you are closed loop fuel injected. If you are still running closed loop fuel injected with a catalyst (i.e. some sort of controlled street car class) then low-lead or regular leaded avgas is not going to work.
Here's some good info:
http://www.osbornauto.com/racing/race2avgas.htm
-Tony Staples
www.tscombustion.com
RE: Mixing Fuels - Pros and Cons
RE: Mixing Fuels - Pros and Cons
RE: Mixing Fuels - Pros and Cons
I presume his part of the world is Australia based on the G'day and the 3 litre Nissan, which is a common motor here.
Avgas will be made to a consistent tight spec whereas pump gas will be whatever is cheapest and meets the octane and SG requirements and maybe some evaporation rate requirement. I would much rather tune to avgas due to it's very consistent standard, even if it is not optimised for road use.
I guess the lack of optimisation refers to evaporation rate and SG.
To buy leaded avgas in Aus, you need to produce a race drivers licence and sign a statlatory declaration about use.
Last time I looked, it was A$1000.00 per cylinder fine if caught being used on public roads. It is only allowed by the EPA at special sanctioned events. The lack of availability and the potential fines is why I changed from avgas to methanol on our street class race car.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: Mixing Fuels - Pros and Cons
RE: Mixing Fuels - Pros and Cons
RE: Mixing Fuels - Pros and Cons
RE: Mixing Fuels - Pros and Cons
Yes, I am in Australia.
A few more details:
The motor is fuel injected and is using an Autronic SM4 for the EMS.
There is no catalytic converter installed as it is not required for racing. The car is to be used for club days and the occasional drag race and does not have to meet any specific criteria.
What unleaded race fuels are available (in Australia)that are reasonably easy to source?
RE: Mixing Fuels - Pros and Cons
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: Mixing Fuels - Pros and Cons
RE: Mixing Fuels - Pros and Cons
I am now thinking it may be a better idea to use the unleaded fuel as then I can tune the car on the raod as well and not have to take it to the track everytime I want to use it.
RE: Mixing Fuels - Pros and Cons
VP make some fine racing fuels, but they are very very expensive, with a great deal of hype about brand name. I know their methanol is over twice the price of "industrial grade 99.9% pure. They claim an advantage due to purity. I never found a difference in the 0.01%. I very strongly suspect that at least some grades are just traded by them from outside suppliers with a change of drum and a huge mark up.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: Mixing Fuels - Pros and Cons
However, I have read that BP Ultimate with 10% Tolulene will push the octane towards ~102...
Several members of Skylines Australia have used it in High Boost applications with good results. This should work nicley in a high compression N/A motor. Some people have also siad that Avgas does not work well in high RPM motors due to the burn properties. I'm not sure what thay class as 'High RPM' but I am expecting around 7500 rpm out of mine, would this be too high for Avgas?
I hadn't chase any prices on VP fuels yet but I was expecting I'd need to be sitting down when they told me!
What would be the ratio of 98 and Methanol (not sure if I can get ethanol) required for this sort of application and would methanol be acceptable?
RE: Mixing Fuels - Pros and Cons
It was used extensively as a fuel in touring car racing, boat racing and drag racing in Australia up until about year 2000 when it was effectively banned by the EPA.
The Shell fuel with the ethanol is a standard Shell retail pump product, well at least it is in Sydney.
I just looked it up. There are 2 products, one is a LRP at 10% ethanol and 94 octane and another is a blend of their 98 octane premium unleaded and 5% ethanol to give a 100 octane racing fuel. It is only available in Sydney, Melbourne, Brisbane and Canberra.
http://w
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: Mixing Fuels - Pros and Cons
When running oxygenates (like alcohols) with an open loop fuelling control system you will actually be running leaner than and may need to richen to compensate.
The oxygenates you add reduce the calorific value of the fuel but *may* allow you to usefully increase the spark advance without knocking - thus restoring bsfc.
MS