Premixed fuel: good idea?
 

Hey,
a friend told me, I should use premixed fuel for better lubrication inside the motor. He suggested to use a 1:100 (oil:fuel) mix ratio in this rotary engine.
what do you think about this?

I think you should start by reading and learning about the rotary engine. From the factory, MAZDA injected a small amount of sump oil in at the intake phase of the rotary. This was done to lubricate the hard seal/housing/side-plate interface and to aid compression.
*Some owners keep the factory system because it's relatively trouble free and requires little monitoring.
*Some people remove the factory injection system because it injects engine oil which they believe isn't as suitable, and substitute pre-mixing 2-cycle oil in with the fuel at a ratio of 1 oz. to 1 gal.
*Some owners keep the factory injection system and pre-mix at a reduced rate of ~ .5 oz. to 1 gal.
*Some owners opt for an adaptor on the factory pump which sources 2 cycle oil from an aftermarket tank.

Maybe after you learn more about how a rotary works you can then make a decision for yourself on the various merits and liabilities of those options.

I agree do a bit of research first before you make any decisions just coz someone else might do it and tells you to do it doesn't mean you have to.

what motor do you have?

pre-mixing in moderation won't hurt. what car do you have?

Frox, I have been pre-mixing for over a year now (using the 1:100 ratio and TCW-3 approved 2-stroke oil). I drove my car down to DGRR this past spring and had the revs wayy up most of the time while shredding up the roads, and the car performed perfectly. I then drove the 250 miles right back home haha. I have deleted my OMP and I pre-mix instead of using the OMP. Some people do both and use the pre-mixing as a fail safe.

using the OMP and premixing in the tank, would the octane rating in the fuel drop??

Premixed fuel: good idea?
 

In the appropriate quantities, no. This has been hashed out before.

I use a half oz per gallon and have a working omp. My car absolutely stinks though. I NEVER premixed my first fd. Car made 365 on stock turbos and motor and was more reliable than my dd Toyota avalon. I decided to pre mix this fd bc it has a ported motor and bnr turbos. A couple guys I respect suggested to do so including engine builders Ihor and Dave.

thanks DCSDaniel i might give it a go one day when my cars on the road,

what ratio is recommended for n/a still using the OMP? and does the ratio change for turbo motors?

Premixed fuel: good idea?
 

It comes down to preference. Most people will do as stated above, 0.5oz per gallon with a functioning OMP. The mixture is usually modified depending on demand, i.e. in a race application, more premix is recommended. I've never heard of the ratio changing specifically for an NA vs turbo.

yea a race prepped motor would need bit more oil as it will pretty much live in the high RPM range once its warmed up. thanks for the info

excuse me, but what does "OMP" mean?

my car is a RX 7 FB2 '85
(edit function doesn't work)

Oil Metering Pump (OMP). I second the 0.5oz of 2 stroke per gallon of gas when also running an OMP. I deleted mine and I use 1oz per gallon. I know it seems scary when you think about it, but it's tried and true. You will be very pleased.

^I think the Factory Service Manual (FSM) calls it the "Metering Oil Pump", so occasionally you'll also see owners refer to it as the "MOP"...but same thing.

If you are going to research about premixing, you will see that most of the guys here are doing it or at least ok with this method.

I recommend premix with a properly functioning OMP. I use 1 oz of premix per gallon of gas in all of my rx7s

Within reason the more lubrication you can get on the hard seals, the better. But as they say, 'there is no free lunch'. Premixing more than about .5 oz. per gal with a working OMP and you have to start thinking about carbon deposits. And if your car has a catalytic converter, I would think there might be some concern of fouling it. And that sort of brings me to those who have emissions testing in their State. I would, of course, NOT pre-mix if I had testing coming up.
FWIW, I don't have emissions and pre-mix, casually guesstimating .5 oz. per with the OMP. I also have a WI system on my car and carbon isn't much concern. I'm also running a BONEZ hi-flow cat and as a matter of practice when pull the car out of storage in the spring I pull it off and check the matrix. So far, I've seen no ill effects of the extra oil.

^ I have been premixing 1oz per gallon with a correctly functioning OMP on all of my rx7s for several years, and I do not have any carbon build up

This topic is sort of frustrating. I don't think there is much fact to back up anything.

For every one guy that says its a must and their rx runs like a top there is another guy that says they been running high hp and don't mix and have had great success.

I didn't mix in first fd and it was awesome for over a decade. I am mixing in the current one bc I guess my engine builder said to so I want to honor his wish. if a problem was to arise I can say I followed his direction.

Personally, I think it's a load of bs if u have a working omp. I worry that it's harmful in that it lowers octane rating. I bet you can dig up facts on that.

There are quite a few basic facts. The engine requires oil for the seals if any sort of longevity is desired. two stroke oil is MUCH better in a combustion process and leaves less deposits than engine oil. If your OMP or something in that system suddenly fails, as can happen on old cars, pre-mixing will save your engine. None of this is up for debate.

Take from this what you will but also keep in mind that people that have or have not found something useful also treat their cars differently. Also, you're adding oil at miniscule quantities compared to the fuel and the octane number on the pump is a minimum.

Premixed fuel: good idea?
 

You're welcome to keep thinking that. Name one reputable rotary builder/shop who's torn down a premixed engine and not noticed a difference.

There's very little need to premix with a working OMP at stock to moderate power levels. However, those of us tracking our cars, redlining every day, spinning high rpm, and put down 350, 400, 450whp have a very serious need for more protection.

Maybe so. As I understand it, octane rating is a indicator of the rate of burn. The higher the octane level, the slower that rate of burn. Seems like adding oil to fuel would slow the rate of burn...effectively raising octane. Regardless, there is so little oil added, and it drops out of the fuel during the intake/compression phase, that it's effect on octane level is miniscule.

agreed.
... and ... agreed. :)

The octane number is the volume percentage of n-Octane in the fuel and it don't indicates the rate of burn. It indicates how much the fuel mixture tends to knocking. that means how big the possibility of self-inflaming of the fuel is, because of pressure.

If you want to reduce that knocking, you have to use high octane fuel. I don't know which types of fuel is buyable in the USA but in germany there is 95, 98, 100 and 102.
102 is a kind of tricky extrapolated number that indicates that the fuel has characteristics of an hypothetical fuel with 102 volume percentage of n-octane.

Because oil won't inflame itself at a pressure under the one in a wankel engine, it should cause the mixture of fuel and oil to seams like having an higher octan number.
[This is just my gues: in reality I think it realy does not matter, because I think the oil and the fuel will mix in an heterogeneous way and the kind of how the fuel in that mixture acts under pressure is not affected. ]

So:
In my opinion you don't need to worry about the change of octane number when mix fuel with 2 stroke premix oil.

I think 2 stroke premix oil is designed to burn with very less carbone arrears in 2 stroke engines. The wankel rotary engine burns at very high temperatures, so the arrears sould be even less than in 2 stroke engines.