I am going to be trying a few things to get my RX-7 to pass emissions (running a cat and air pump and no premix, then stepping up DA to trade HC and CO for NOx until I’m balanced enough to pass). To do this, I need to know how long it takes for my changed gas mix to hit the injectors from the tank. Here is a gross approximation. I am posting this because I thought some others may want to know, and a search revealed nothing on the subject.

Time = volume/rate = fuel system capacity/consumption rate

Fuel system capacity (estimate):
5/16 fuel line, 144” long. Vol = pi*5/32^2*144= 11.0 ci
Fuel filter = 6.0 ci
Fuel rail = 2.5 ci
Pump = 1.5 ci
Total = 21.0 ci

A gallon is 231 ci, and in my experience a car (like an FD/FC) burns around a gallon per hour at idle. So 231 ci/60min. To plug into the equation above:

Time = vol/rate = 21.0 ci/(231 ci / 60 min) = 21.0 ci * (60 min / 231 ci) = 5.5 minutes.

My car gets 17 mpg, here is the distance:
Dist = (17 mi / 231 ci)*21.0 ci = 1.5 miles.

Please feel free to discuss. Or if anyone has actually measured this, please describe your test method and results.

 

I had no problems passing a 2525 test with a Nikki carburetor, cheapy catalyst, and a checkvalve on the ACV blockoff plate.

I'm assuming you have a carbureted car because your calculations assume no fuel return. If you had a fuel injected car, the fuel cycles through in about a half second.

The problem isn't rich/lean, it's incomplete combustion. You can lean the mixture out so far that the HCs start climbing again due to lean misfire and they won't be low enough to pass an emissions test. Good driving mixture, proper ignition timing, a catalyst, and a little extra air to keep things burning in the exhaust manifold. That's all you need, and all the OEM system did.

 

Premix is normally 1oz to 1 gal. U can safely go as lean as 3oz to every 5 gal but its not as easy to measure.

I want to try .5oz to every gallon but Im not sure if its enough oil for the engine.
DON'T RUN YOUR CAR WITHOUT Oil.
Put an msd on ur leading and it will run much better and cleaner.

 

Premixing should have nothing to do with emissions. The oil burns as a fuel. BFD. No problem. I have passed with my above emissions setup while running appx. 80:1 premixing.

 

I passed just fine, didn't have to put anything in the tank excecpt oil-free fuel.

Oil doesn't burn completely. Clean combustion produces CO2 + H20 +N2, none of which are smokey. Gasoline burning cars that "burn" oil smoke. Some more or less than others. And I know a premix rotary doesnt smoke much, I am talking theory here. I am sure some cars that run enough compression or combustion temp can burn a lot more of the oil than others. My car isn't one of them, there are several symptoms to confirm this (oil in exhaust, oil on rear bumper, smells, etc). I normally run 128:1.

Next time I will probably run 1/8-1/4 oz per gallon premix and see if I can pass with a little oil. I had some margin on my HC and CO (150/220 and .6/1.0). First test was 1200/220.

 

Hmmm. Injected

Oops! Forgot about the recirc system thing. Well interesting thread for anyone with a carburator anyway

 

I also normally run 128:1
Pinapple racing runs 213:1 but that's more thinking at the pump
A half oz to gallon is 256:1 and is simple to rember. So I'm going try it.

First gen rx7s carburated and still use a return line so the fuel mixed quickly. U have a fuel bowl that takes 3 to 10 minutes to flush out depending on ur driving.

 

The factory metering pump runs on the order of 150:1 to 500:1 depending on the load conditions.

The biggest factor for the OEM is catalyst life, so they want to burn as little oil as possible.

I've found power gains all the way down to 60:1, for what that's worth. I can't have a catalyst on my car because it would slag in a heartbeat, so I just give the engine what it wants, 2oz/gallon in competition and somewhere around 1.5-1oz/gallon for highway driving.

 

as mentioned oil doesn't matter. blue smoke from the exhaust doesn't register on an emissions test.

why?

because emissions tests check for hydrocarbons, nitrogen oxides and carbon monoxide. poisonous gasses produced by the GASOLINE(namely hydrocarbons, the #1 reason why 95% of cars fail, the other 2 gasses are emitted from anything that combusts) during combustion. unburnt 2 stroke and engine oil does not register on any 3 of those readings. unburnt oil does affect octane and may result in higher than normal NOx readings but the decreased friction it allows also probably decreases it negating its effects.

i worked at a dealer that worked on mitsubishi's, ,the old 3 liter V6s would eat valve guide oil seals and smoke up the shop during tests but they always passed.

 

They will here - visible exhaust is an immediate fail.

Fortunately, this removed most of those infernal 3.0 V6s from the roads I remember one that burned so much oil that the glaze on the spark plugs would go conductive when the engine got hot. 10,000mi later, the new plugs would do it too.

 

Blue smoke might not be HC, but unburned oil contains HC. The historic basis of gasoline is octane, an 8 carbon HC (C8H18). Oil is atomically very similar, but with longer chain molecules, such as C36H74. They both come from crude oil, the source of the hydrocarbons, and selective refinement make the two different, but they both are still full of HC. 2 cycle oil has the same base as regular crankcase oil, just with more additives. Maybe the smokey cars you saw pass were having enough of the oil/gas HC burned up in the cat and leaving other components of the oil to contribute to the smoke?

Either way, some premix is probably a good idea when going through for emissions testing.

 

well i should say that is how is how it used to be, now most states will fail you if your car is smoking visually. but my point was, a moderate amount of 2 stroke oil can't be seen with a catted car.

you can believe whatever you want, i will stick to the fact i haven't noticed any detriment to emissions while premixing. any unburnt 2 stroke oil won't be picked up by the machine because the unburnt fuel is trapped in the unburnt oil molecule and the sniffer won't pick it up. the burnt oil won't carry a noticeable difference in hydrocarbons.

i smog these cars all the time and i never hesitate to say premixing even in 1 ounce or above levels is fine. if you're failing then it's simply other issues with the car or how it is tuned.

 

Yep. Again, running 60:1, my exhaust is clear except for when the engine is cold and running at up to 200% warmup enrichment. And even then, it's only until the coolant temps are up over 40F.

 

I passed anyway.

 

i've never tested it, but just because there is smoke, doesn't mean its going to show up as one of the tested gasses.

secondly, i would bet if there is an increase in HC's, its so small as to be insignificant, or not even show up in the data at all. maybe HC's go from 16 to 20, 4ppm is probably within the error margin of the machine.

 

i doubt it's even that high. my thought is any fuel that is going to be burnt is burned, any that happens to attach to an unburnt oil molecule isn't going to be picked up by the sniffer.