Fuel Additives for High Compression Engines

[Richard L.]

I am running approximately 10.5:1 compression in one of my vintage cars and have been advised by the engine builder that it would be good insurance to add a can of VP Racing Fuel Additive 2855 to each full tank of gas, even if it's premium, given the uneven quality of today's gasoline. I trust his advice as well as his technical and mechanical expertise although I wonder if his specific brand recommendation needs to be followed implicitly. VP is a trustworthy brand used nationwide by racers and builder of high- performance engines but are there other brands equally effective in raising octane ratings? I want to stay clear of the fake, snake-oil manufacturers with unsubstantiated claims and shaky reputations. Can anyone here provide some additional expert recommendation and advice.
Thank you in advance.
ric

[Leif A.]

Re: Fuel Additives for High Compression Engines

Richard,
If your car is tuned correctly (timing, A/F adjustments, correct vacuum cannister using manifold vacuum, spark plugs, and wires) you don't need any additional additives to your gasoline. If you have 93 octane with no more than 10% alcohol you shouldn't have any issues whatsoever.

[Duke W.]

Re: Fuel Additives for High Compression Engines

Most original "high compression" engines (and most have been rebuilt with "lower" compression") will operate detonation-free on the highest locally available PON and many will operate on less.

Each case is unique, so in order to make an educated guess more information is needed about your SPECIFIC engine configuration and operating conditions.

What's the make, model, year, and engine option? Is it original? Rebuilt? Modified?

How was the CR arrived at? Was a compression ratio calculator used with all the requisite accurately measured input data like head chamber volume. piston dome or dish volume. deck clearance, and head gasket thickness?

What is idle vacuum? Measure in neutral if a manual transmission and Drive if an automatic, Report as XX" Hg @ yyy RPM.

What is the altitude range you drive in and typical highest ambient temperature?

What are the PON ratings for locally available gasoline and which one are you using.

Are you hearing any detonation (knock, ping) and if so under what operating conditions?

If you can report all the above I can give you some guidance, but it ultimately requires some testing and perhaps some modifications to the spark advance map.

Duke

[Richard L.]

Re: Fuel Additives for High Compression Engines

Thank you both for your considered replies. The engine in question is far from stock and in high state of tune so none of the usual considerations apply. It needs higher octane fuel than gas pumps provide though not quite the ratings that race gas provides.

[Duke W.]

Re: Fuel Additives for High Compression Engines

Engines with "big cams" can tolerate higher compression ratios than mild cams. It's not the overlap, but the late closing inlet valve that causes reversion resulting in low VE (and low torque) at lower revs, which is when detonation is most prevalent. Exhaust gas dilution due to the high overlap slows combustion propagation, so they like and can tolerate more low rev spark advance than mild cams. If you don't understand this you will learn more from my tuning seminar, which is attached to the "restoration documents" thread near the end of the sticky section.

Though specifics apply to Chevrolet small and big block V8s, other American V-8s are pretty much the same having wedge combustion chambers, so optimum spark advance maps aren't that much different. The Chrysler hemis might be one exception.

... sounds like you'll have to do your own experimentation, but a lot of so-called "octane boosters" are snake oil and their "points" are 0.1, not 1.0. Good luck!

Duke

[Joseph W.]

Re: Fuel Additives for High Compression Engines

I have a buddy that swears by this stuff.
H runs it in his Hemi Cuda and his 70 Z28
He buys it by the case
Anyone on the board ever try it?

http://www.wildbillscorvette.com/OctaneSupreme01.htm

[Rocco S.]

Re: Fuel Additives for High Compression Engines

I have been using the Octane Supreme for about 9 years in my original 1967 L79. The engine has 11:1 compression ratio. It seemed to have helped the slight pinging problem I had when climing a hill or when it was extremely hot.

I am currently working with member, Duke Williams to modify my VAC and distributor mechanical advance springs in the hopes I can run straight 93 octane. He seems very knowledgeble on the subject. I was originally thinking of mixing 50/50 93 octane (10% ethanol) with 100LL aviation fuel which is available locally to eliminate the octane booster. Hopefully things will work out.

As a side note today a new service center opened in my area offering 3 grades of non-ethanol fuel. 87, 89 and 93. and the price is not bad for the 93. I plan on switching to this non-ethanol in the future.

Non Ethanol Gas.jpg

Rocco

[Mark E.]

Re: Fuel Additives for High Compression Engines

Agree with the comments above. Under 11:1 you can tune the engine to work with the fuel available. Select an advance curve and adjust static timing to achieve no detonation at full throttle with VAC disconnected. Then select a VAC that works at cruise and light loads. I recommend a variable VAC for this.

[Larry E.]

Re: Fuel Additives for High Compression Engines

Can not understand why you guys go through all the trouble WITH these "gimmicks".(Changing timing/head gaskets/adding
additives and etc.. Just buy the gas that is available now that is the closest gas THAT WAS AVAILABLE WHEN YOUR
CHEVROLET ENGINE WAS MADE namely>100LL at your local airport + that fact it last so much longer with out gumming
up and getting bad. Of course>JMHO. Larry P.S. Your car will Start/Idle/Run so much better and you keep your engine
ALL ORIGINAL

[Mark E.]

Re: Fuel Additives for High Compression Engines

Can not understand why you guys go through all the trouble WITH these "gimmicks".(Changing timing/head gaskets/adding
additives and etc.. Just buy the gas that is available now that is the closest gas THAT WAS AVAILABLE WHEN YOUR
CHEVROLET ENGINE WAS MADE namely>100LL at your local airport + that fact it last so much longer with out gumming
up and getting bad. Of course>JMHO. Larry P.S. Your car will Start/Idle/Run so much better and you keep your engine
ALL ORIGINAL

Gimmick is harsh. I would say "tuning". It’s more convenient than filling up with Jerry cans, less expensive and yields good performance.
Plus no lead deposits in the combustion chamber, valves, plugs and exhaust (remember that problem?).

[Larry E.]

Re: Fuel Additives for High Compression Engines

THAT'S THE WAY CHEVROLET DESIGNED YOUR ENGINE; FOR THE MILES MOST OWNERS PUT ON IN
A YEAR THIS PROBLEM IS IRRELEVANT. OF COURSE JMHO

Mark: Thanks for your comments; let me respond under your comments above.

[Terry D.]

Re: Fuel Additives for High Compression Engines

For those who only put a few miles a month on their car 100 aviation fuel is an easy fix, but for someone like me who puts 5 to 7 thousand miles a year on their car it is not so good. I'm preparing for a fall foilage trip from Ohio to Statesville by way of The Tail of the Dragon. If I had to rely on airport fuel I'd be done for. I agree with Mark and Duke if you take the time to tune your motor correctly there is no need for 100 octane fuel. But that's just my old two cents!

[Duke W.]

Re: Fuel Additives for High Compression Engines

I have been using the Octane Supreme for about 9 years in my original 1967 L79. The engine has 11:1 compression ratio. It seemed to have helped the slight pinging problem I had when climing a hill or when it was extremely hot.

I am currently working with member, Duke Williams to modify my VAC and distributor mechanical advance springs in the hopes I can run straight 93 octane. He seems very knowledgeble on the subject. I was originally thinking of mixing 50/50 93 octane (10% ethanol) with 100LL aviation fuel which is available locally to eliminate the octane booster. Hopefully things will work out.

As a side note today a new service center opened in my area offering 3 grades of non-ethanol fuel. 87, 89 and 93. and the price is not bad for the 93. I plan on switching to this non-ethanol in the future.

[ATTACH=CONFIG]123854[/ATTACH]

Rocco

It's great that you have the three grades of NON-ETHANOL gasoline, but the prices are about as bad as California, especially the 93 PON. The highest PON we have in CA is 91 and non-ethanol is rare.

Duke

[Patrick H.]

Re: Fuel Additives for High Compression Engines

It's great that you have the three grades of NON-ETHANOL gasoline, but the prices are about as bad as California, especially the 93 PON. The highest PON we have in CA is 91 and non-ethanol is rare.

Duke

Those prices seem great to me for non-ethanol, and similar to the usual 10% ethanol swill they sell.

[Bruce M.]

Re: Fuel Additives for High Compression Engines

I used the Octane Supreme for years to boost the non-ethanol 91 to 93 in my original, unrestored L36. It's nasty stuff (tetra ethyl lead) but it eliminated the occasional ping on WOT. Now we have the non-ethanol 93 locally and it behaves the same.

Bruce