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OK, class. Some of you know this and some of you don't. So, for the sake of everyone in the room, it's science review time.
Got the itch for some extra power? Often times that extra power can come from the ability to run more timing in your car or truck. BUT....octane is the key. Whether or not your have knock sensors, you need to be aware of the risks of running race fuels or e85 without the proper tuning.
If you're already a Venomous Tuning client, you can add a race tune to your arsenal with just a couple of clicks and providing us with critical information. Every fuel has a stoichiometric value. That's the "air/fuel" ratio at which the fuel burns most completely and efficiently. Here are a few examples:
93 octane (pure) 14.67 (or 14.67:1 as represented as an air/fuel ratio)
93 with 10% ethanol 14.08
VP MS109 13.34
At "no load", or idle/cruise, the vehicle should be running at that "stoich" figure respresented as AFR or air/fuel ratio. If you have a wideband air/fuel monitor in your car and it reads in air/fuel, you'll see the figures above on your gauge at no load. At full throttle, however, we often times command 80 or 81 percent of that. (Math starts to become a pain in the butt here, so we have an answer for you!)
Let's take 93 octane as our example. Idling around 14:1, we know we're all good and it's operating correctly. Now, remember that we command around .81 or 81% of that at wide open throttle. The end result is 11.88:1 air/fuel ratio.
Simple enough. But do you really have to remember all these numbers? And do multiplication? At wide open throttle am I really going to be looking for 7.97:1 with e85? The answer to the last question is yes. But here's how we deal with multiple fuels.
The stoichiometry of a fuel is called Lambda. Regardless of the actual stoich figure for any fuel, the normal vehicle will command 1 Lambda at idle and cruise (no load). That's 1 X 14.67. 1 Lambda is 14.67:1. 1 Lambda on e85 is 9.85:1 and so on.
Let's say we almost always use .80 Lambda as a target for wide open throttle. Perfect. If we're using a Lambda gauge rather than an air/fuel gauge, we just look for an average of 1.00 at cruise and .80 when we mat it, regardless of the fuel that's being used.
.80 Lambda on 93 with 10% ethanol represents 11.22:1 AFR
.80 Lambda on straight 93 represents 11.78:1 AFR
.80 Lambda on e85 is 7.88:1 AFR
So, it's incredibly important that you have a monitor that can show you Lambda and not just AFR. And it's equally important that you do your homeword and provide your tuner with the exact stoich value for the fuel you will be using. That number gets plugged into the calibration and if it's wrong you can be incredibly lean or rich, neither being good and perhaps extremely dangerous for the vehicle.
When you order your race gas or e85 tune you need to let us know the stoich value of the fuel. It can be found on the manufacturer's website. NOTE: The stoichiometry of e85 changes with variances high or low from 85% alcohol! Thus you must test every tank of fuel. If it's not correct, your car will be richer or leaner than intended. Learn the differences.
Below is an example of one of VP's race fuels. It is the propery of VP and we are using it as an example only because they do great work but this is not an endorsement for any brand or octane rating of any fuels.
We will provide ONE idle/slow rev and ONE wide open throttle datalog review with this service. Additional logs or revisions are available upon request on an ala carte basis. Call us to discuss.
ANTICIPATE TWO BUSINESS DAYS FOR PROCESSING AND SHIPMENT OF YOUR STAGE 1 TUNE OR SHIPMENT OF IN-STOCK ORDERS. STAGE 2 AND 3 CUSTOM TUNING WILL TAKE A MINIMUM OF 5-7 BUSINESS DAYS.