Just wondering what kind of octane boost I can expect from running a 100% meth injection on 93 octane fuel? Anyone with knowledge of this?

 

It is very simple math, but you need to know a couple of things that you may not.
Here are the basics:
Methanol has an octane rating of 119
Final Octane rating = (% of gasoline*93 + % of Methanol*119)/100

Now what you need to know: How much of your fuel charge IS being injected as Methanol?
That's the hard part. You can get a ballpark for how much methanol you are running by looking at your nozzles. Most people here are running either a single or a dual "10lbs/hr" nozzle. That figure is how much water the nozzle flows at 100PSI. The actual flow for Methanol will be slightly different due to its different viscosity, and also a lot of methanol systems run 130 - 150PSI injection pressure, so the flow will be a bit higher. Also, it is being injected into a pressurized pipe, so the effective pressure across the nozzle is the injection pressure minus boost. E.G. 130PSI (pump) - 15PSI (boost) = 115PSI effective.
For the sake of simplicity we will ignore this and just pretend that those 10lbs/hr nozzles really flow 10lbs/hr in our example.
Now you need to know how much fuel you are injecting into the engine. That is equal to your injector size * duty cycle * number of injectors. Here, again, you need to be careful: The effective fuel pressure across the injector is the fuel rail pressure minus boost. The industry standard is to rate injectors at 3BAR (43.5PSI). But your Corvette's fuel injection operates at 56PSI. At 12.5PSI of boost your 60lbs injectors will flow exactly what they should; 60lbs/hr at 100% duty cycle. Multiply by duty cycle to obtain actual flow (E.G. .8*60 = 48lbs/hr at 80% duty cycle).

This should allow you to work it out by yourself.
Now an example.

My car runs 2 lbs/hr injectors. That's approximately 20lbs/hr of methanol.
I run 60lbs/hr injectors. My fuel injector duty cycle at full throttle is 93%. That is 446lbs/hr of fuel (remember there are eight of them) at torque peak.
Thus, Approximately 5% of my fuel charge is Methanol

93*.95+119*.05 = 94.3
I.E. The effective octane rating of my fuel mixture on methanol is >95Ron+Mon / 2

Note that this number fluctuates since the methanol injection is a linear interpolation between no boost and full boost, whereas your fuel injection curve is not linear; it follows airflow which is roughly equivalent to your torque curve.

Moral of the story: Most of the gains provided by Methanol Injection are not coming from an increase in fuel Octane, but rather from the drop in IAT allowing more ignition timing to be run.

 

Wow Sam, thank you for the break down and explanation. That was fantastic reading. I do know the major benefit from the Methanol is the lower IAT's but I was wondering about the octane boost becauzse I do know Methanol is a fuel. My feeling was at most a 2 point increase in octane was probably about right. I recall someone starting a thread on using meth on a stock motor and claiming I think 110 octane or something like that which I knew was a bunch of bunk. Thanks again Sam

 

That's right... "ih4x4". Thank you for reminding me of why I normally don't post on the General forum... That guy had a BONE STOCK Corvette in which he never ran any fuel above 89 Octane. He drove it very gingerly going 5MPH under the speed limit, yet he somehow felt he needed methanol injection to "prevent carbon buildup."
The guy was so incredibly clueless it was like trying to talk to a child. He lacked any kind of foundation to understand why what he was doing was pointless so he just went back and forth saying the car needed it because back in World War 2 bomber planes (SUPERCHARGED bombers that is) used it for takeoff. It made my brain hurt so I retired from the thread.
Original thread here.

Every now and then I wonder how some people make enough money to buy a Corvette. There must be some pretty good money in extremely non intellectual jobs that I'm just not aware of

 

Meth should never be used as an octane booster. Safety, and as Sam mentioned, IAT lowering only. (unless you have alot of money to build a new shortblock)

 

I disagree. If you are going to use it take advantage.

 

But what happens when (or if) it fails under a WOT situation? If you are relying on that meth for adequate fuel for your motor, and it isn't there then you just blew up your motor. I guess I am just a little too conservative.

 

Mine is tuned for safety only. I never have my tune running on the edge. Blowing up my motor on a METH FAIL is not very appealing to me. Right now I have better things to do with the $10,000 it would likely cost me for a rebuild.

 

uh oh rob your not going to like me this summer

 

http://www.snowperformance.net/product.php?pk=13

here you go this is what i use it opens up the bypass valve causing boost to bleed off

 

That's why I had Doug at ECS tune my car when I decided I was going to bite the bullet and run Meth.
I was sold on it when my buddy Dave had a Meth pump fail on his 9 second drag car. All it did was run two back to back 11 second passes. Mind you, this was a maximum effort, 18+ PSI build relying extremely on pure methanol injection, and he took it down the drag strip not once, but TWICE with no meth. After it didn't blow up I figured there really was a way to keep those from blowing up when the Meth fails.
I found out first hand just weeks after the tune. I was on a 1500 mile roadtrip and about 860 miles into it I got on it leaving a toll booth and my car fell flat on its face. It felt like a hose had popped off the induction system. I knew what it was right away, drove normally to a gas station, purchased 8 bottles of "HEET", dumped them in the meth injection tank, and continued the drive.

The explanation of how it works has been pasted before so I won't re-type everything, but essentially once the meth stops spraying the ECU commands an extremely low amount of ignition timing and the air/fuel ratio goes very lean (13s), so the engine loses a massive amount of power and doesn't detonate.

I still really dislike meth (its a pain in the butt when you drive as much and as far as I do). If there was any way I could make 700RWHP on this setup without it, I'd ditch it in a second... But since there isn't, I stick with it, and at least I know it is safe.

 

Sam, how long does a fill up on Meth last you? It sounds like you are saying you have to fill it frequently. I have gotten many tankfuls of gas (probably 10 or more) on a single fill up of Meth. Now I probably dont lean on my car as much as you do with yours but I do usually get 1 or two WOT pulls in 2nd/3rd gear every time I drive. It is interesting when I hear of people having to fill their meth frequently. Sometimes I wonder if maybe my meth is not spraying as much as it should.

 

Your meth sprays when you are under boost, and in direct proportion to how much boost you are making. I.E. The harder you drive the car, the more methanol you will use.
A high HP car on street tires will see the methanol last almost for ever as going into high boost is completely pointless. I have the traction to use full boost and I drive my car very hard, so I can go through my 1.7 gallon tank in 4 fillups. Conversely, when I drive in cold or bad weather it lasts almost indefinitely since I can't lean into the boost as much.

I.E. It depends entirely on how hard you drive the car.

 

Good information here. I just got my car back from ECS so I was wondering about methanol myself. Is the windshield washer tank 1.7 gallons, or did you put the methanol elsewhere?

I was really curious myself since I was playing with my car how quickly I would need to refill the tank. I am also curious if I can purchase some and store it in a tank, but will it be okay to store outside in a shed? Will it keep, or does it go bad like gasoline will?

 

Your washer reservoir is 1 gallon. I have a tank on the back of my car that's 1.7Gals.
No fuel "goes bad" (OK, except Biodiesel). Gasoline can lose its more volatile fractions when stored in a non gas tight container (such as your fuel tank), and, similarly, Methanol can pick up moisture when stored that way, but either one will keep indefinitely if stored in a gastight fashion.
I keep my Meth in a 2 gallon gas can. Works fine.

 

My methanol came in a 5 gallon pail. I just leave the lid on tight and store it in my garage on a couple of pieces of wood to keep it off the floor where it is most susceptible to absorbing any water.

 

It absorbs water from the air, not through the floor. What happens is that during the day when the ambient temperature rises, a vented cap allows some of the methanol vapor to escape. At night once the temperature drops the pressure in the meth container drops and if the lid or cap is vented it will take in ambient air. Any moisture from that air will then condense inside the methanol container. A similar mechanism is responsible for the octane lowering in gasoline when it is stored; the vapors escaping are the most volatile fractions and those are responsible for the high octane in gas.

The simple fix is to keep it in an air tight container. It doesn't matter what you put under it.

 

You are probably right but its one of those old school habits I can't break. I never leave anything sitting directly on the floor.

 

You're tidier than I am... My garages always look like a bomb went off inside them. The only place I keep organized is my work space

 

Once your car pulls timing do you need a retune to get it back to the A/F that it was?