is this true?

[dion]

okay I've heard this from a few different people now, if you mix 50/50 87 regular and 91 super in your take it makes 95 octane. I've asked a couple friends about it and they just looked at me like I didn't make it to the first grade and can't do simple addition.

anybody ever heard of this?

[gonebad2]

Nope, Never heard of it.

[MMGOODIE]

i searched "85 octane mixed with 91 octane" and came up with this site:

85 + 91 octane

[Randy70C-10]

If you want 95 octane, you'd have to blend aviation fuel (cam2) with 93. I did that alot when I was running a 12.5:1 compression 283 in my Model A. I should mention that if your engine doesn't ping using 93, there's no reason to run any higher octane. It won't make your truck any faster.

[cdowns]

WELL??? did you make it to first grade ???

[dion]

yeah, I figured it was BS. thanks for the link.

[cableguy0]

87 and 91 will be somewhere around 89 whoever told u that was either blowing smoke up your @ss or shouldnt be allowed to operate a car much less work on it

[dion]

randy, I'm not looking to go faster, just trying to get rid of the dentonation. I've tried boosters and marvel mystery oil, no change. Timed it way up and way down, still pings.

ORW sells race gas but it's $36 for 5 gallons

[Stocker]

How about getting rid of carbon buildup in the combustion chambers? That can lead to detonation partly because it increases the compression ratio, but mainly because the carbon will create hot spots. Dunno about other products, but Mopar Combustion Chamber Conditioner p/n 04318001AB ($5.75) works great - I just used it on our 95 Grand Cherokee and the pinging stopped. Sure makes a lot of smoke, though!

[Stroker]

Marvel oil is a great product but putting it in your gas is likely to create addition detonation problems not cure any. The octane boosters probably will help if you mix in enough to actually raise your octain level a point or two, but you'll go broke buying the stuff. I haven't personally used anything in the links below but you might take a look and see if it's something you want to try. If you try it let us know how it goes. Good luck.....Stroker



http://www.team.net/sol/tech/octane_b.html
http://www.vtr.org/maintain/gasoline-octane.html
http://www.gnttype.org/techarea/misc/octanebooster.html
http://www.gnttype.org/techarea/misc/Octanemix.html
http://www.syty.org/archives/syty/0112/msg00203.html

[Randy70C-10]

That would be an awfully large amout of carbon.
Dion- try backing down your timing. Turn clockwise (just a little) if it sounds a little better then turn a little more.

[Baradium]

Some gas stations sell race gas that's street legal, not a whole lot though. The legal stuff has the road tax...

There's one back in TN (in GA for turkey day).

In aviation 100 octane "low lead" (100LL, blue) fuel is extremely common, a lot of hot rodders love to get the stuff because not only is it high octane, the lead increasing the octane rating doesn't drop the power availible from the fuel as much as the stuff they use now does (100LL is supposed to increase power output from most engines, even if it's not to stop pinging). 80/87 AVGAS also has some lead, but it's lower octane, 100/130 octane avgas isn't very common place anymore. BTW, all fuel actually has two octane numbers, the one they tell you is devised by averaging them (the RM/2 method sign you see at all the gas pumps).

The thing is, it's not exactly legal to run 100LL in a street vehicle. It's legal to buy it for your ultralight, but not for your pickup.

Sorry for the basicaly offtopic ramblings...

[dion]

stroker, is that true? thanks for the info. I know guys who swear by that stuff, they say it slows the burn helping with the dentonation. It didn't help anyway. It did quiet down my lifters though!

thanks Randy, I did back the timing down and it didn't seem to help. just made the truck run like crap. this all started when I went from 76cc heads to 64 cc heads. the thing is though, the truck runs great, just sounds a little off.

I'm starting to think it might just be my mufflers going bad ??

[lux hauler]

What kind of pistons do you have.......flat top, dome, dish?

[dion]

lux, dished

[Spoof]

I had a prob with detonation that i thought was untreatable, a good mechanic changed the vacuum advance settings and the improvement was amazing. Just a thought.

[Randy70C-10]

Originally posted by dion
this all started when I went from 76cc heads to 64 cc heads.

Ahhhh, that will make a difference, but since you're running dished pistons I don't understand why you're still getting detonation. 93 octane should be more than enough to run properly, but you could add a gallon of aviation fuel just to see if that fixes the problem. Are you sure that those heads are still 64cc chambers, because if they've been machined, the chambers may be smaller now.

Spoof has a good point too.

[mikep684x4]

Just a thought on your detination problem, Have you checked the advance curve on your distributor? You changed alot from the stock components of your motor so the stock curve might be wrone,Hint,no change when you turn the distributor.you can turn it all you want but if the springs are wrong it will advance quicker or stay retarded longer than the motor reqires.Just asking

[Stroker]

dion, I can't say that I have any way to prove that it will cause detonation. But oil has a very low Octane rating and can be a cause of high rpm detonation. Normally this occurs because of poor ring seal and crankcase oil gets into the combustion chamber. Marvel is a lighter oil than standard motor oil and it may in some cases be of use when mixed in gas, for example to free a stuck ring. I don't believe it would be of any use to prevent detonation, but a mixture of water and marvel oil dribbled into the carb might be usefull if you have some carbon build up. I think I came across this method of carbon cleaning was suggested by a moderator on chevytalk..

most guys mix about 30% marvel mystery oil and 70% water, wait for the engine to get up to normal operating temps,and while reving the engine they shake the bottle violently to mix the two and very slowly dribble it in very small amounts into the carb, it turns to oily steam, this tends to break the carbon deposites loose and they blow out the exhaust as smokey exhaust mixed with carbon particals

You might find the info on this link helpfull if you suspect a detonation problem but are unsure. If it is detonation you need to get a handle on it, unless your looking for an excuse to justify a new engine soon. Sometime detonation can be a gearheads best friend. LOL

http://www.mg-tri-jag.net/tech6.htm

[Hooter]

I am lucky because my local Chevron and most chevrons in the area have 94 octane, the ole ls6 dont like much lower then 93 even if I back off the timing, the compression is around 12.2:1, but if you wanna have fun $$$$$$$

[gonebad2]

Someone mentioned it's not legal to run race gas on the streets. Probably because no road use tax was paid on it....Greedy government ya know.

[Hooter]

ya but who's gonna find out that you are running race gas anyways?

[Randy70C-10]

Originally posted by Hooter
ya but who's gonna find out that you are running race gas anyways?

It has a very unique smell when it burns. Nothing like the smell of burning av-gas in the morning.

[Vince M]

If I remember right..a while back I read somewhere about mixing the gases to boost the octane level. I remember it was 25% LEADED regular mixed with 75% 93 octane UNLEADED premium. The addition of the lead boosts the octane level of the premium. Can't substantiate this but the trick is to add leaded gas to unleaded premium. I don't know if this was clear on the original post. Obviously mixing the two as unleaded is going to decrease the octane level to something in between the two.

Like I said I can't remember where I read this or substantiate any of it.

[Baradium]

Originally posted by Vince M
If I remember right..a while back I read somewhere about mixing the gases to boost the octane level. I remember it was 25% LEADED regular mixed with 75% 93 octane UNLEADED premium. The addition of the lead boosts the octane level of the premium. Can't substantiate this but the trick is to add leaded gas to unleaded premium. I don't know if this was clear on the original post. Obviously mixing the two as unleaded is going to decrease the octane level to something in between the two.

Like I said I can't remember where I read this or substantiate any of it.

Doesn't make any sense to me, especially with the way that the octane ratings are done...


Race gas is legal on the streets as long as you get the stuff that has the tax paid on it, you *can* find it. There is a gas station in TN that sells it at one of its pumps, road tax and all and you can pump it directly into your car.

AVGas never has the tax paid on it at the airport since airplanes try to avoid roads!

I think there might also be an issue with the AVGas having lead in it too... don't remember if the stuff about leaded gas on the roads applies to vehicles that originally were designed for leaded gas.