Oil in the Gas Reduces Octane
 

I'm no engineer but I know that some of you guys are mixing some form of oil with your gas to aid in the seal lubrication process. In fact, I know some folks who do a lot of track days do this. I have talked to some folks who are concerned that this might lower the overall octane rating and thus increase the operating temps of the Renesis. Can anyone shed more light on this subject and if you are mixing what are you using and are you seeing higher temps. Thanks.

Lower octane means it ignites easier (at lower temperature). I can hardly see a mixture of 0.2% oil in gasoline making any difference in ignition temperatures (and if it would, it would increase it anyway). So no, there are no effects one can measure from having a small amount of oil added to gas (engine temps). I use high RPM motorcycle (2T) oil. Why is used? To supplement the weak OMP our engines have (I have a 4AT, so the 4 port engine).

Most likely the rotary engine is only a VERY, VERY small part of this . A manufacturer cannot possibly keep up with the government regulations when they design a engine. Gas companies are under constant pressure to reduce emissions. One of the key things they now take out in the refing process is sulfur. However, sulfur is also one of the main lubricity factors in gas and diesel. In Jan 2006 the EPA has mandated that all on road highway diesel will be "ultra low sulfur", we will have to inject a lubricity additive to compensate for the removal of the natural sulfur lubricity to prevent possible dammage of diesel engines. Gasoline has seen a sharp decline in sulfur content over the last 5 years as well and we are being asked to reduce further the sulfur content of gasoline. You may be adding alot more than a little oil in a few years. Adding that small amount of oil you mentioned will effect only the end point of gasoline, nothing else.

The people that are premixing oil into the gas are typically not using the stock oil metering system anymore. Those that are shouldn't be. A very small amount of oil is injected into the engine to lubricate the apex and side seals. The source of this is the engine oil. We are only talking about a quart or so every couple of thousand miles. This varies depending on how hard the car is driven. When you factor in the amount of time and the amount of fuel used in this time, that is a nearly miniscule amount of oil. Some people disable this oil metering system and opt to use 2 stroke oil that is designed to be mixed with gas. A 4 oz bottle will easily suffice for a 16 gallon gas tank. Even this ratio is adjusted by many as it needs to represent the amount necessary for the worst case scenario. This is such a small amount that the octane level isn't going to be affected to any measurable degree.

Oil in the gas
 

Thanks Rotarygod. Here's why I am asking. I am building a racecar powered by a stock renesis engine. The engine builder is using a gear driven oil pump rather than the ECU controlled pump which is on the stock car. He also recommends mixing a two stroke oil at 100:1 with the gas. I am interested in why people are disconnecting their stock pumps. I also see that you folks are using a 500:1 ratio with the oil/gas mix. Clearly there is a very big difference between what is being done to my engine and what you folks are doing to yours. I am used to questioning everything which is why I came here to get some other opinions. Incidentally , the prototype setup has been run for 20 hours on the track and dyno with that fuel mix and pump and a recent teardown shows no visible wear on the apex seals or anywhere else in the engine. The engine does run 230 degrees F at wot on hot days so I was wondering if the oil mix might be lowering the octane and potentially causing the engine to run hotter. I'm still new to the Rotary so I am looking for all of the information I can get. Thanks.

why do you say the MOP is weak?

The Renesis oil pumps are technically gear driven. There is a physical connection from the crank to the pump itself. The ecu steps in to vary the amount of oil that gets to this pump. The oil metering pumps from '88 and earlier were only mechanical. They like yours did have a physical connection to the crank. The difference is that the amount of oil getting to this little worm gear pump was controll by a mechanical linkage that was tied into the throttlebody. The more gas you gave it, the more oil it receives. I personally prefer the old mechanical system.

I see no reason to premix and use a metering pump. If your engine runs at high rpm's and loads all the time then you will definitely need a richer oil ratio than the average street car. Understand that the supply to the engine is always changing based on rpm and load. In your case with premix, you use a fixed ratio that accounts for the worst case scenario. I personally feel that a 100:1 ratio of premix AND using a functioning oil metering pump is way too much oil being dumped into the engine.

Yes, and no.....
 

Oil can definitely reduce the total average octane your engine sees - some of the kerosine/diesel range oils have 'octane' ratings as low as minus 150!

The good news is that two-stroke oil makers can avoid most of these really bad components, so two-stroke oil is a little better, overall.

Motor oil is a different story, it was never intended to be a major fuel component; it can really reduce your overall octane.

Worst case, what is the highest consumption rate from the stock pump setup? (Just guessing here...) Under race conditions the pump is probably maxed out - the worst I have seen is a quart every 1000 miles, so maybe racing would double that consumption, to maybe half a quart per tank of fuel? That is a lot of oil, on an octane basis, but even if we take the motor oil as 'zero' or 'minus 10' octane, the net effect is only to lower your 91 octane fill to an average 90 octane, so not TOO bad.

The 100:1 two-stroke pre-mix is perhaps a bit rich, the net effect of this would also be in the 'one octane number' range, and together with the stock oil, you would be looking at serious reduction if you ran boost or any timing advance.

A good synthetic stroker oil, that meets the ISO EGD standards for clean burn and deposits, at about 200:1, might be a more suitable choice..... ;)

S

Thanks
 

I appreciate all of this really good input. StealthTL can you help me understand where you got your info on the octane of oils and how you computed the effect on the overall effective octane rating of the fuel oil mix. Also can you steer me to more info on stroker oil. I've never heard of tha before and would like to know more about it and what products are available. Thanks

the Formula Mazda guys are running premix with no MOP... maybe you can check with one of the teams on the mix

Stroker....
 

I work for a 'large' oil company, making gasoline.

You can look up the octane rating of any hydrocarbon easily, the problems come with finding the right ones - all motor oils are mixtures, often hundreds of different chain formations, each with its own attributes.

No one could reliably predict how the oil/gas octane would be affected, and my estimates are just that, even if based on 30 years of refining. I could run a mixture of gas and motor oil thru the knock engines to test the actual octane, but even if you got the same brand of oil and the same brand/grade of gas, you would not get the same results; different crudes, different batches, from different refineries.

The two-stoke (stroker!) oils are much more predictable - standard brands are mostly 'bright stock', a fine cut of the crude, and a decent lubricant, but smoky and a little dirty when burned.
Modern synthetics rely heavily on polyisobutylene, which burns clean and actually helps clean out deposits. Some of the 'combustion chamber' cleaners you can buy contain it.

The strictest test of a modern stroker oil is the european ISO test, and the highest rating is EG-d, to pass, the oil must burn clean, have low deposits, and be absolutely smoke free. Any oil made from dead dinosaurs is not going to pass!

Personally I would use any EG-D rated oil at about 200:1 if your stock oil pump is in use at all. Our motors are not two-stroke, and won't seize due to lack of lube, the oil is just there to provide a tiny microscopic film in the housing, something the two-stroke oil was designed for, and will do much better than the stock pump.

S

(Interesting, but off topic - I was having a hard time estimating how much oil the stock pump injects, (how many miles per quart) because mine uses ZERO. I have used a premix at about 250:1 since day one, and it seems the oil scraper seals must be very efficient, because my oil level actually goes UP. If I take dipstick readings, the level rises slowly over the 3000 miles, until it is about a quarter inch above the start point when I change the oil! 25,000 miles, mostly highway, so I know it's not gas getting into the oil. :D Your mileage may vary! :D )

While oil gets consumed (burned, evaporated) or simply injected in the chambers, water (from combustion) and gasoline (back-flow from the chambers) come to the oil pan. For most people, the result is lost total oil volume.
In your case it would be hard to know what is going on unless you run an analysis for gasoline in the used oil and check the used oil after it drains out for water separation (so you'll have to change it yourself - analysis is misleading as the water will separate, so you cannot get an homogeneous sample to give the lab).

Thanks
 

TYhanks to all for the really good input. Special thanks to StealthTL for the education on octane ratings for oil and gasoline. This is a great site. Once I get the finished chassis I will experiment with all of this info and see what happens. I will also talk to the pro Formula Mazda teams and see what they are doing in this area.

you have any pics or more info on your project (racecar powered 13b-msp)? inquiring minds want to know :D

Info on race car
 

http://www.diasio.com for photos of the car.

CS

You got yourself a mini LeMans car!

Diasio R
 

Your right! I have been running motorcycle powered Diasio's since they were first built. Both Chris and I have felt that a rotary powered car with the attributes of the new R model would be an incredibly fast and very reliable platform. I think it will be all of that and more. Now I just have to wait for my chassis. Thanks to all of you for the excellent information. I'm sure that I will be back for more as the development continues.

Any idea what was behind the choise of the Renesis Engine?

Andrew

Why Renesis
 

Sure. The main premises of the Diasio have always been safety, reliability and performance. The R model was intended to take the equation to the next level to compete with the best chassis available. The rotary engine represents great performance for a racing package but was limited by the need to build the 12A /13B engines to the max to get 250HP targeted output. The prototype was originally tested with a race built 12A engine and clearly proved the superiority of the rotary powerplant in this chassis. The problem was that this engine requires rebuild every 25 hours. The Renesis makes the same HP in stock trim and we expect it to last many time longer between rebuilds. The fact that the Pro Formula Mazdas have been using the same powerplant for several years reinforces our belief that this is the right engine. Incidentally, we are using the same transmission as the Pro Mazda guys as well- Hewland FTR 6 speed sequential.

You might consider adapting an oil reservoir for your engine. Check out RotaryGod's comments:


https://www.rx8club.com/showthread.p...=Oil+reservoir

Thanks KWS. The engine will be drysumped. That's one of the things which is important in a roadrace car to enhance reliability.

WOW! Every 25 hrs. I am guessing thats 25 hrs of race time? does that roughly translate into KM's or Miles?

Andrew

Rebuild times
 

Most racers keep track of engine use in terms of hours run under racing conditions. Most of the cas have hour meters installed as oart of the dash system but we all log the actual racing hours to manage the need to replace specific wear items. The miles/kilometers can be more or less depending on how fast you are going on track. Some engines ( klike the Tpoyota 4 cylinder engines used in the Formula Atlantic series in the SCCA use mileage on track between rebuilds. In that case it's 750 miles. The most competitive people rebuild these recips between every race. I am trying to be at the other end of the spectrum.

Guestimating that a F1 car has average race speeds of 125 MPH(?), 25 hours would be around 3125 miles.

What speed would these cars average over a race?

Andrwe

Diasio R
 

That depends on the track but it usually runs from 85- 100 MPh. However, our races are sprints and usually last 25-30 minutes each.