So I have a 75 250i6 maverick, and ive heard that running a little higher grade gas can do good for your engine. I have always ran 87, but now that the car isnt a daily driver, ive started to do work to it, and I was wondering if switching grades will do any good. Its fairly stock, ive thrown a glasspack on there, blaster coil wire new wires, disc brake conversion, suspension upgrades (not that it applies) and a few minor upgrades (in college, pretty broke at the moment). So will putting 89 or higher damage the car or have any benefits?
Generally speaking.. higher grade fuels allow more aggressive ignition tunes(more timing lead) and give slightly more leeway for extending tuneup intervals. IOW, it basically allows more margin of safety if things aren't exactly perfect with the current state of tune. It certainly won't hurt the motor.
I agree with Jamie. if it were a higher compression motor...maybe... it's like setting your watch 5 mins. fast so you will be on time... let someone take it to the gas station and put gas in it and not tell you what grade they put in. then without knowing what grade drive the car and see if you can tell any difference...
Back in my stock car days, our class always had a 10.5 to 1 compression limit and the higher up classes were at 11 to 1 so we all burned CAM 2 or VP racing gas - then somebody comes in selling Turbo Blue at something like 107 octane - the rush was on to get this "more power" gas into their fuel cells - our engine builder would just laugh and say "you don't have a car on this entire property that can use that stuff"
Read this............. http://blog.hemmings.com/index.php/...the-fiction-behind-those-higher-priced-fuels/
Informative article I was actually waiting to read how everything came out of the same tank and only cost more if you hit the wrong button
Another fun and highly misunderstood subject. The basic fact is this. Higher octane fuels reduce the likelihood of pre-ignition. This allows for more aggressive tunes while still controlling and maintaining consistent flame front speed/pressure rise during the power stroke. For those that would think that a low compression(8:1 or even lower) motor cannot be made to knock?.. well.. they probably haven't tuned enough motors to the edge of their fuels cylinder pressure/temperature rise capability to make such statements in the first place. We must keep in mind that the ignition event begins as the piston is rising and pressure/heat waves can wreak havoc for lower rated fuels. Try locking the timing at 40 degrees and load the car up with friends in your 3.00 geared car to get an idea. It'll surely knock your socks off and rattle your fillings. then add a little bit of combustion space contamination?(oil and carbon).. the more likely you wont like the result. Then add the fact that combustion chamber deposits can affect running compression(dynamic compression ratio) more so than static compression and burn rates/pressure rise gets out of hand even quicker. Another aspect about octane that some are not considering is this. Many octane improving compounds are aromatic in nature which can cause slight octane losses over time. Especially in the old style vented systems. Higher octane fuels also allow a slight bit more margin of octane loss for those who drive/fill their cars tank less often. But.. it is very true that any basic marginally tuned engine shouldn't see any gain unless something else is off in the first place.
Quite simply ... higher octane means the gas burns more slowly. I want the gas to burn as fast I as can, and be able to use it, with out tearing things up. Running more octane that you need for a long period of time can lead to excess carbon in the combustion chamber, which then fuels more pre-ignition, and eventually can create it's own need to run the higher octane. My 351W has a rowdy cam, headers, and a 4 bbl carb. It is quite happy with 89 octane when drag racing it. If going out for a long highway drive, I would drop down to 87, and not run it at more than about 2/3rds throttle, and it was fine under those conditions too. It doesn't like being pounded on hard while running 87.
