Hi Octane Fuel Alternatives

[Jim V.]

I am one of those "old school" types still running 11:1CR. Yeh, I know PITA.. Here in the western burbs of Chicago I can get various grades of so-called racing fuels, 100 octane with MTBE from Citco, and 110 octane with TEL from Sunoco. Anybody know what the scoop is on MTBE? Sorry, I'm not bright enough to remember what the MTBE acronym stands for.

BTW.. Although I have been in the NCRS for about 9 years, I'm new to this site. I just want to thank all you guys who provide so much useful help and insight, wish I found you guys earlier.

Thanks
JimV

[Duke W.]

Re: Hi Octane Fuel Alternatives

First, does your car really need higher than commercial pump octane? Many owners are running 11:1 engines on the highest pump premium they can find and are not experiencing any detonation, which is the symptom of inadequate octane.

Mild detonation can often be eliminated by dialing back the initial timing a few degrees or slowing the centrifugal advance curve. Lost intitial timing can be regained at higher revs by modifying the distributor to increase total centrifugal advance an amount equal to the lost initial timing. You'll lose a bit of low end torque, but the solution is usually permanent, and you can buy gasoline anywhere without having to brew up your own blend.

MTBE - methyl tertiary butyl ethylene - is an "oxygenate" used in reformulated gasoline (RFG), and it is also and octane enhancer.

If you experience detonation that cannot be eliminated with small timing changes then developing a blend of high octane racing gasoline and pump premium is the next best alternative, and no more than a 25 percent mix of 100 to 110 octane racing gasoline with pump premium should do the trick.

Duke

P.S. A lot of California guys are complaining that the highest pump premium we can get is 91 octane. I think the reason is that the lower volatility (vapor pressure) required in CA has forced refiners to lower the aromatic content. Aromatics are octane enhancers, but they are more volatile and result in higher vapor pressure. MTBE is an octane enhancer, but can only be mixed to a maximum of 15 percent, so the limit on MTBE concentration and aromatics has placed an economical limit of 91 octane on CA premium grades, even though in some parts of the country, 93 and even 94 octane is available.

The good news is that the lower volatility California RFG should have less tendency to vapor lock.

Duke

[Joe L.]

Re: Hi Octane Fuel Alternatives

Jim-----

I agree with Duke. Also, observe this following simple, basic, "rule-of-thumb":

If your car does not experience significant detonation or pre-ignition using a particular grade of pump gas, then you ABSOLUTELY DO NOT REQUIRE HIGHER OCTANE. In that case, higher octane fuel will do NOTHING more than cost you more money. It is ABSOLUTELY NOT otherwise "better" or beneficial for your engine.

[Duke W.]

I'm in complete agreement with Joe *NM*

[Duke W.]

Re: Hi Octane Fuel Alternatives

I made an error in my definition of MTBE. It's methyl tertiary butyl ether. Sorry for the error. Just don't ask me to sketch out the molecular arrangement.

Duke

[Clem Z.]

Re: Hi Octane Fuel Alternatives

if you have side pipes you will never hear it so learn to read plugs to check for pre ignition. there is a lot of talk about the cam helping lower the cly pressure but if the pistons are not deburred and the head chambers not polished you are in a grey area with anything over 9.5:1 with a iron head engine. early iron BB have hot spots that develope in the chambers because of the water passage design that allows for stagnet water flow. we found this out when building 14:1 drag race engines as we had to tap into the water jacket on the valve spring side of the head and install fittings and tubing to get the hot spots out by having the air/water bleed out thru the tubing into the water outlet passage in the head. this was corrected with the later aluminum heads

[Patrick H.]

Re: Hi Octane Fuel Alternatives

Duke,

Oh, come on. That's an easy one to sketch out.

Patrick

[Jim V.]

Re: Hi Octane Fuel Alternatives

Duke,
Some follow-ups.
First, what good is dialing back initial timing only to make it up at the high end. Is'nt the high-end where detonation becomes more of the issue?

Second, speaking to RFG, are other oxygenators...ethanol any different, better, worse, similar, to MTBE? Can all oxygenators be grouped under the same evil or good banner?

Lastly, since I have access to TEL (110 Octane) and MTBE (100 Octane) is one better than the other in any other aspect other than octane?

Thanks again.
JimV

[Chas Kingston]

[John H.]

Re: Hi Octane Fuel Alternatives

The EPA has already published new regulations which make MTBE illegal as a gasoline additive, as it has been shown to be a carcinogen; don't know when they take effect, but the corn lobby loves it

[Duke W.]

Re: Hi Octane Fuel Alternatives

Agree with Geezer. On the detonation issue, detonation is primarily a LOW rev phenomenon.

Say your engine operates detonation free at high revs with 36 degrees total WOT timing. If you have a very quick centrifugal curve that gets it all in at 2000 you will probably have some detonation at low revs. That's one reason why cars have centrifugal advance.

Detonation is a function of how much clock time the last part of the unburned charge spends at high temperature and pressure before being consumed by the advancing flame front. The longer it sits before being consumed, the greater the tendency that it will react spontaneously before the flame from arrives, which is detonation. At 2000 revs it sits there waiting to be consumed for twice as long as at 4000 revs. That's why detonation is more of a low rev than high rev issue.

If the engine makes peak high rev power at 36 degrees, and you have to reduce your initial to excorcise low rev detonation, you will have less than optimum high rev timing and loss power. You can make up for this and maintain the optimum high rev timing by adding centrifugal in an amount equal the amount you had to dial back the initial.

Juggling the initial, total centrifugal, and rate of centrifugal advance is what you should first do if you have detonation, but if you end up with no torque or power because you don't have enough timing, you have to mix up a higher octane blend of fuel.

Duke

Duke

[Jim V.]

Re: Hi Octane Fuel Alternatives

Hey fellow C-Town West Sider and thanks for the reply... I am way west in Glen Ellyn. There is a U-SAVE station on bloomingdale rd just north of North Ave in Glendale Heights that has a Sunoco race fuel pump (just one towards the back). This is the 110 stuff with TEL. Can't pump into any drive-up vehicle since the stuff is labeled for off-road only. They get $4/gal.

The Citgo stuff (MTBE 100 octane) is available at several Clark Oil owned stations like Road Pilot in Lombard.

Sounds like PB Premium with 10% of the Sunoco 110 is the ticket for a target 96 octane..

Where are you located.?

[Theodore K.]

Re: Hi Octane Fuel Alternatives

I have been using a fuel mixture of 25% 100 Octane low-lead Av Gas with pretty good results. The balance is 91 Octane no-lead. I have successfully also tried the Jack Podell TEL additive. The other octane boosters such as 104 does not idle well with my engine (57 with dual 4, duntov & solids, domed pistons). One other thought on the ethanol additives. The older cars do not have a fuel recirculation system. I learned the hard way that vapor lock on hot days was a reality with the alcohol fuels. I stay away from them now.