Pre-Mix
 

So I am going to disconnect my OMP, and I need to know how Pre-Mix to run. I have heard several different ratios, 75:1, 100:1, so anyone done this and what works best? Thanks, Dave

I do between 1/2-1 oz per gallon, works fine.

Wow, That is not much at all. I was thinking of using a half quart per tank.

i'm doing 1/2 oz per gallon right now, but i still have my factory OMP and 720/1600cc injectors on street ported FD engine... just over 800 miles on break in.

What year is your RX-7?

The reason I ask is, if you have an S5 (89-91) you can't just 'disconnect' the OMP. It is electrical and will put the car into limp home mode.

You can physically unbolt it, and take the OMP lines off, but you still need to leave the OMP plugged in to the harness, and tie it back somewhere.

The only way around it is a standalone EMS, or an Rtek ECU upgrade.

If you have an S4 (86-88), yank it all off and put on a block off plate. Easy.

It is an S4 engine, I upgraded to a S5 manifold and turbo when I did my rebuild.

1/2 qt/tank is about 1 oz/gal or 1:128 which is honestly what most people run. Some say way more, some say less.

Personally I run Idemitsu premix at a ratio of about 1/3oz/gallon in the tank and I also have it injecting it through the OMP. That works out to 384:1 in the tank and whatever the OMP injects. I really should start to measure it.

I've done this before and I'll do it again...... lets look at the factory system

Think about how much sump oil that a rotary burns. These are pretty crude numbers but hear me out. A quart every 3000 miles is "normal," so lets just say that you're burning a qt every 1,000 miles becuase you drive around pretty heavy footed. Ok, so you're using 32 oz of oil every 1000 miles. How much gas are you using? How about 15mpg? Ok, so in 1000 miles you're burning 66.67 gallons of gas. 66.67 gals = 8533 ozs. So that equates to 266:1 of SUMP oil on the high side. Being a qt low after 3,000 miles is roughly 1:800...... think about that for a minute. The factory system will inject sump oil at a rate of 800:1 and some people are saying to mix 4oz/gal or 25x the amount that the factory saw necessary.

Now, some people will say that the stock OMP will burn a qt in 500 miles of heavy driving. Ok, so lets think about heavy driving...... how does 5mpg sound :rofl: At 5mpg and a qt every 500 miles the stock system is injecting it at a rate of 400:1. Keep in mind this is still sump oil, not really fancy designed for the task at hand 2-stroke oil.

Run Idemitsu, follow thier rec's and enjoy. They rec 1/2 oz/ gal or 256:1

I do run Idemitsu oil. I did this yesterday and put in 16 oz. in the tank. Way too much, it was smoking a bit when it was cold, so I think next tank I will try 8 oz. and see what happens. Sounds like that should be the number!

I usually end up with about 110:1. It's a bit rich for my driving habits, but no harm in that.

Idemitsu should be run at a ratio of 1/2 oz oil to 1 gallon fuel. You did put to much in. Go for 7-8 oz and you'll never have to worry about it again.

When I tank up tomorrow before the dyno I'll prob put a weeee more in than I usually do..... just becuase that's the way I am

TT writes it up good on the stock system. Note that every body change there was a change in metering rates. 68/78 used a ~quart in a thousand. (One of the reasons we had so many motors go off back then. Drove it for 5k miles and the light came on then the motor stopped. Bad idea having the low level sensor in the bottom of the pan and having these Americans that traded their 66 chevys in that had 150k where they never changed the oil.
But that is another story.)
79 to 85 were suppose to use quart in 1500/2000.
86/91 quart in 3000.
93/95 US quart in 4 to 5k Far to lean for my liking especially here in the desert.
I set up all my client motors to use more and if they drive hard, use premix.
TT's suggestion is fine.
All race motors from here run 100:1 Redline two-stroke race oil. From Showroom stock to GT. Never had a lean burn condition or abnormal wear issue.

What I found in over 35 years building motors (30 out here) is that the metering system on all client cars was sufficient, as long as they used mazda oil filters, quality oil and changed it every 3k miles for NA and 1500 miles or when the oil takes on any color for those with hair dryers. Never let it go black. Seeing 150/200k on client cars is not uncommon. Original equipment or built new.
For those using sticking with electronic injection, easiest is to just use TT's formula. Use mazda filter and change your oil. They are your cheapest insurance.
BTW: Castrol GTX 20/50 for NA and Castrol 30HD for turbos.

Thank you for the kind words.

What are your suggestions for those of us using Synthetic oil in turbo engines. Currently I'm using Mobil 1 10w30 and thinking about ordering a case or two of Idemitsu engine oil.

I have been running 10w30 in the engine and Idemitsu pre-mix, My oil pressure took a huge jump when I disconnected the OMP, is this normal? My Gauge is metric and is running at 5 kg/cm2 at 3000 rpm. Previously it was at about 3kg/cm2, so nearly doubled. I suppose it could be the cooler temps, but even when the engine is at operating temps it is still this high.

TT- Use synthetics only on sealed motors. ie no metering pump. Problems with them are that they do not mix with fuel and they do not serve as a lubricant under combustion. I do not know of any that are made for two stroke oil savaging use.
When Mobil 1 first came out I had a car come in that was using it for 3000 miles, it was forming hard silica like deposits on the rotors and spark plugs. Went back to petroleum and eventually they went away. He was lucky none broke loose.
Save your money and stick with oil if you still have metering system. If someone does guarantee that their synthetic was made specifically for two stroke use then that may be an option.

Raleigh- Should not make any difference in O/Pressure when disconnecting the metering system unless it was puking a lot of oil. Didn't have big temp change recently have you. Pressures can show higher here in the winter, but not that much. Different oil filter? Non-Mazda? I have used Mazda only since 72 and never had a problem. Remember everyone I am a factory freak.

Normally that could indicate a blockage somewhere, something going on with the oil filter, pressure regulator or relief valves. Would not think failure of part more something in one. I have never seen a failure of either. Have found foreign items.

Way back the way of changing oil included punching a hole in the oil filter to drain it. Trick was hitting it off center and just going through the can. Quick lube places were hammering them in the center and going deep. They bought a lot of motors because they knocked the check valve that is in top center down to the inlet oil port for the motor. The valve was a circular black plastic piece that if you did not look closely sat on top of the port. If you looked quickly everything looked fine. Put filter on customer drives a few miles and motor locks up.

TT - I will give kudos to those that think things out and are willing to try different things after doing a good bit of research, and they do not think they know more than factory engineers. (granted there are some exceptions) We have bantered before and I respect what you do. If anyone goes to my forum you will find my philosophy. If it ain’t broke and rarely does etc etc, KISS if one has to make a change and 99% of the time the factory know best. In my opinion the FC is the exception at 40%. Don’t flame me here my reasons will be posted on my forum.

This was a problem with the older synthetic oils, the new synthetics burn just fine and is perfectly safe to use with cars running the OMP