The only way your going to know if higher octane is going to give you more or less power is to put the engine on a dyno (or the machine on a chassis dyno) both are availible for small applications. There are to many variables (jetting, ignition timing, running temp, etc)to really be able to tell if any difference is made. I raced power boats for several years and always dyno'd the motors.Sometimes we thought we made power with a change or with some cool gadget only to find that in fact we did make HP, only it was in the wrong direction, regardlees of what we felt in the seat of our pants. As to av gas burning up engines at lower altitudes is wrong. Airplanes have either manual or in some cases automatic leaning to optimise air-fuel ratio and thus engine performance. I ran av gas in my race engines and the left-overs all went to my ATV's (100LL). We always read our spark plugs and after season engine tear downs always showed no problems associated with the use of 100LL. Couldnt tell any difference in the ATV's though. By the way 100LL does have some lead ( more than unleaded ) and the octane rating is higher than 100 ( somewhere around 104 )

 

PAPICO: Thank you, one more person that can attest to their good experience with Avgas. I think it's safe to say that Avgas is not harmful to the engine.

Rotorhead51: I have already made a bracket to mount the accelerometer to the grab-bar on my 400ex, I'm just waiting to get a few more miles on it's engine before I pin it through all the gears (I've only gone through two tanks of gas since I bought it, so it's not really broke in yet). Then I'll do some testing, and I'll be sure to post my results.

 

Guys,guys, I have the answer! No more discussion will be needed after you hear this! I was so motivated by the logic used to rebut Tree Farmer's point, that I quickly drained all the 87 octane fuel from all my machines. I then filled them with 93 octane fuel and ran those tanks through each machine. The results... LESS POWER. It's true. No, I have no dyno results or recorded elapsed times...who needs that useless information? The results that I obtained are universal for all internal combustion engines...because I said so. So guys, relax. The debate is over!
Dale

P.S. Motorhead, please, this topic would not be complete without a few more final posts from
you (grin).

 

Motorhead, you've already stated as fact that all engines develop more power with increased octane number fuel. Also, you've said you're so thoroughly convinced of this fact you needn't prove it further.

I wonder: why conduct any accelerometer test at all, then? Surely, the results seem predictable. Certainly, I don't think you'd "cook" the data, insuring it supports your pre-conceived conclusion, even though I presume your testing isn't "blind" (you'll know the contents of the tank), and you alone will be doing the riding.

Anyway, it seems your data would apply only to your machine; extending your findings from only one sample as a general conclusion applying to every engine ever produced seems a stretch.

Nevertheless, obtaining comparative accelerometer readings (assuming repeatability of your instrumentation) under different conditions appears most interesting, I look forward to reading your results.

Tree Farmer

 

My votes with treefarmer on this one, I have a 67 vet coupe with the original 327 300 hp in it if I don't run high test and every now and then put some 102 octane boost I start to get the ping and a little loss in power...if your engine is not designed for it your wasting your time running it.

 

Thanks for sharing your anecdotal experience, RidesanS!

I'd appreciate more information. Did the inverted curve of power vs. octane appear to the seat-of-your-pants to follow a linear, logarithmic, or asymtotic path?

Please respond; since your findings apply globally and universally to ALL engines, the clarification is IMPORTANT!

Tree Farmer

P.S. While I would hope this paragraph is unnecessary, I've found a number of Forum readers take posts quite, quite literally. Thus, I declare the contents of this post to be, just funnin'! A joke! Humor! Not serious!

Thank you for your previous post, adding some mirth to otherwise grim proccedings.

T.F.

 

Tree Farmer: I'm sorry I am not able to test every engine known to man, but I just don't have the resources and time for that. It seems as though you 'disbelievers' were telling me in previous posts that if you would have seen documented tests, you would be more open minded (as now you are obviously being very closed minded). Don't you think that what you have read could also have been 'cooked' results? Oh, wait, you've never actually seen any test results, you've only read speculation. God forbid someone actually goes out and tests this. Also, it wouldn't need to be a 'blind' test, this isn't a taste test, it isn't dependent on my oppinion, it is dependent on precision measuring equipment. I may do it alone, I may have a friend around when I do it, regardless, my results would be the same.

I must ask you, why do you think I would lie about this? Do you think I work for a gas company and WANT you to buy the expensive gas? No, I'm trying to share my experiences with you to better educate you on my findings on this topic. Yet you ridicule me for sharing my experiences and my reasoning. Looks like you were looking for a one-sided discussion, and are getting frustrated because I just won't give in to your 'reasoning' because I know otherwise due to previous experience (not speculaion). No, I have not tested every engine, but I have seen the results on a number of different engines, and all have been consistent with what I have been telling you. I guess, according to you, since I can't prove it helps on EVERY engine, only all the ones I test, then my results would be invalid.

I'll tell you what Tree Farmer, why don't you PROVE me wrong? After all, I'm proving myself right, yet you will not even listen to my tests OR my reasoning, you'll think I'd "cook the data", and disregard what I post as nonsense. Whatever, your loss. I guess if you can't listen to someone elses reasoning, and you can't listen to hard test numbers, then you truly are locked into your oppinion, and NOTHING can convince you otherwise.

I'm bored, think I'll go do some testing , and not because of you, but because I want to see HOW MUCH improvement Avgas gives my 400EX. I'll post my testing procedure and results once I've finished. You can read them and take them into consideration, or you can ignore them and continue in your closed-minded discussion.

 

Motorhead, I've no desire to prove you wrong. I may ask critical questions about your convictions and your basis for them, but you may be right; indeed you may convince me of that fact.

I am tolerant and respectful of diverse opinions; however, limited subjective experience and "because I said so" may be inadequate to change mine.

You have illuminated some interesting concepts and made intelligent comments in this discussion. However, neither RidesanS nor I deserve the lewd and vulgar comments you made in your personal attack.

Best wishes in your accelerometer tests with fuels of different octanes; I look forward to reading your results.

Tree Farmer

 

We'll I think this debate has gone on so long because both of you have some good points. I agree with Tree Farmer, if you run your engine with low compression stock timing and in a moderate climate with moderate engine loads and it is running fine with no ping or worse(a hole in the piston),then going out and getting 112 octane will not boost and might hurt performance because now your engine temperatures are cooler(too cold). HOWEVER, high engine load, and any modifications to compression ignition timing, too high ambient temperature,or increase engine load will make the engine run too hot. This will cause pinging and even worse it will make your cylinder swell a little too much away from the piston rings and you will lose cylinder pressure and this will make cause a power loss. This is really the point I think Motorhead is trying to make. In "real world" applications ( pulling a trailer up a hill in 110 degree heat lugging the motor out at 1500 rpm's in overdrive) will cause a noticable difference between the pump and race gas(much better in extreme cases). Also I think the AVGas discussion can go no where because he is talking of a big Low reving V8 that more closely models the type of conditions that Avgas was made for and WE in HERE are mostly talking about high reving 2-strokes in ATV's. A fuel designed for 2450RPMs might be the running RPM of a big V8 pulling a trailer down I-10 in overdrive, but not a TRX250R or Banshee Hill shooter. I just don't think you each are seeing each others points. There is ABSOLUTE true in BOTH your arguements. You guys are just arguing about 2 completely different things(situations) really and therefore this arument will never go anywhere but to frustration and then name calling, and finally to a locked forum.

CT250R

 

Here's one to think about.

You said it yourself Motorhead. "The human body is not a precision instrument" with this in mind, and the ears being a part of the body: Anyone familiar with engine tuning will tell you that all detonation/preignition is not audible. Maybe the source of the HP you've gained is from "inaudible" knock.... Just a though..

BTW... I *have* run race gas in my ATC250R (stock at the time except .040 over). I don't know exactly what kind of fuel it was (I can find out if you really want to know), but was very high octane that a buddy was running in his very modified, race Seadoo HX PWC. I lost immense amounts of power. The engine skipped much worse anywhere except when under high loads and wouldn't idle. Most of the power loss was in the bottom and mid ranges, with little noticible loss in the very top & meat of the powerband...

No, I didn't rejet, as it was just a spur of the moment thing, but your previous posts indicate that I wouldn't have needed to.

Just my experiences.