charlie31603

iTrader: (10)

whats the highest compresion ratio you can run on 87 octane? thanks for the help!

Air_Adam

I'd say no higher than 9.5:1 for 87...

jfreeman74

Would running straight 98 octane all the time burn up the fuel pump?

charlie31603

iTrader: (10)

So 10:1 is to high for 87. I was looking at geting the zz4 crate motor. thanks for the reply.

tilstad

Here in Norway we have 95 and 98 octane only. I really dont know what the max compression could be on 98 octane, but lots of cars have 10,5:1 and thats from the factory. Turbocars usually got 8,5:1, but I think you can safely go to 11:1 on 98 octane.

Whats really the reason behind having 87 octane?

charlie31603

iTrader: (10)

I wanted 87 octane becuse I know a v8 will suck down the gas, so I mite as will put the cheap stuff in it!

Tom84L69

The reason? Cheaper for the oil companies I suppose. They also may calculate octane using a different method in norway, here they use R+M or something like that. Is gas expensive in Norway?

Combustion chamber design and cylinder head material also determine minimum octane, not just compression. you may be able to get away with 87 on a ZZ4, but I doubt it. One example of head design affecting minimum octane is my Trailblazer, at 10:1 compression, it calls for only 87 octane and makes 270 hp/275 lb ft. Amazing.

As for the Aviation fuel, isn't that leaded? Not good for cats if you have them.

We use Torco 110 octane in the race car, it's $3.25 per gallon.

charlie31603

iTrader: (10)

so how do you get a high compresion motor to un on 87 ?

tilstad

You cant really get top performance on low octane. You would need the top of both i guess. Wasn't there a spesial Ls-6 'vette in the late sixties with a 13,5:1 compression ratio? Did you guys have higher octane in the old days?

I don't know how they calculate octane over here, but as I percieve it, the octane in the gas over here ( europa) is significantly higher. Sometimes they talk about raising compression on american cars, bacause of the availiability of higher octane.

Jep, gasoline are expensive here. It's not the octane that does it, perhaps a little, but there is ALOT of tax on gas. Like 70 % of the sale price which is approx. 5,5$ pr gallon. But that's a twelve year low, the last high was app. 7,8$ gallon.

The difference on 95 to 98 octane isn't that much, a couple of cents. If anyone needed cheaper gas it would be us!

My country is like the worst places in europa when it comes to taxes. Here they demanded 12800$ in tax, if I where to import a 1987 trans am. But thats not included registration and road tax, no, no...

Did you guys now there is actually a town here called "hell"?
And we actually have a dealer called " Toyota Hell" Lol..

tilstad

Here's a drwaing of the place; It can't be anything BUT hell, on the 25-30 thousand$, 2003 Z28, they slapped on a 100 000$ in tax, just for having a big engine and high weight. They really want us to have rubberbands-engine and that's a living hell, high octane or not.

Berlinetta82

I know I can tell the difference from 86-87 octane to 91-92 in my car, it runs smoother and generally better with the good gas.

BUT SERIOUSLLY, AVIATION FUEL! WHERE!?

z 28 jari

iTrader: (1)

Tilstad,
we have here in europe ron method in gasoline octaneratings.At US they have Ron+Mon/2.For example 98 oct ron gasoline specs are:Ron->99 mon->88.So US 93 is almost same as our's 98.

Jari

ctandc

As far as the older muscle cars with high compression engines from the factory, remember....the was LEADED gasoline at every pump. The lead in gasoline is just like the additive in octane booster. Even though the actual "Octane" rating wasn't that much higher, with the leaded gas the older engines could run much more compression without worrying about detonation.


I always caution people who run just 93 octane in their cars IF it doesn't call for it /need it. It's NOT easier on the engine if a higher octane is run, it's actually harder on the engine since more by products end up in the chamber. Run the LOWEST octane gas you can without any detonation etc. Most cars, ESPECIALLY anything with 50k miles or more on it, can GREATLY benefit from a little combustion chamber cleaning....suck some Seafoam, water, ATF ( insert your brand here ) into the intake tract, not enuff to hydrolock the engine mind ya, but enough for the detergents in these substances to clean the carbon from the engine. Water just "steam cleans" the engine from the inside out.

You'd be amazed at the difference getting rid of the carbon build up will make. When carbon builds up on the pistons or in the chamber, it actually RAISES the compression ratio a bit, and the uneven surfaces cause hot spots that will encourage deadly detonation.


As for me, my 9.3:1 L98 iron head TPI engine runs just fine on Citgo / Amaco 87 Octane with 12 degrees initial timing ( BTDC ). No audible or scanned spark knock.


HTH

tilstad

Here on Norway we have leaded on almost every pump. 98 with lead that's what i have used on my Harley, almost all my cars, No all of them now I think about it.Actually most of the cars say they run best on 98 in the manual, and that you will have to retard the timing if going with any lower. But I dont have the tpi, or computer controlled engine. The tpi has an automatic ignition retard, doesn't it? Allowing to use a variety of octane ratings?

camarogirl18

iTrader: (2)

that cheap gas clogs up my FI's.....i cant run the 87 in it....ive been told to once in a while run the 93 in it...my .02

rx7speed

figures I have to talk to you


but does it really clog up your fuel injectors?
if so it might be a sign that something else is wrong


your car should run just fine on 87 unless there is a problem somewhere else.

camarogirl18

iTrader: (2)

lol i dont know....just runs strange with it in the tank & then clogs the FI's up after a period of time.....lol could be just the driver

rezinn

I've had cheap gas clog my fuel injectors before. It's really annoying losing a cylinder because of it. I don't know if the place used a different supplier or what, but it has happened twice when I used the same texaco back home and never any other times.

To clear up something someone asked above, the octane of your gas has absolutely no relationship to the life of your fuel pump.

biff85ta

My instrutors actually recommende this to all of the students that this was good maintence as 93 contains basically the same thing as bottled injector cleaner to raise the octane. Oh and ethanol can work wonders to clean a fuel system.

IHI

iTrader: (1)

A few more things to condider when wanting to run lower octane fuel in a higher compression engine besides having good heads-aluminum heads as they disipate heat quicker so it gives so lee way as far as preignition is conserned, and you can retard the timing a few degrees also. Cam shaft grind is another factor, yes the older muscle cars had higher compression than what you'll find today in production, but they also had a little more overlap in some of the grinds which allows some of the compression to leak out before the valves completely close and while the staic numbers might say it's 11.5:1 they may really only be say a 10.0 or 10.5:1. The adage goes the lower octane you can burn the better off you are because lower octane actually has more BTU's than higher octane fuels so the 87 octane will actually have more bang than a 110. When we were having our race engine built for our Pro truck it was going to be a 11.5:1 Dart aluminum headed that could run on pump gas by taking some timing out, but we decided last minute to go with a 12.5:1 and just run the 110 octane. The key is in the combination.

omcrider

The highest octane you can get in California now is 91 we used to have 92 but a couple years ago it dissapeared. What states have 93 and does anyone know why our octane got lowered? I imagine it has something to do with the smog ***** here in Cali.

RustBucket

Here's what I know.

The LS-6 and other high compression big-blocks of that era had a powerful ally, tetraethyl lead. Lead as a fuel additive helped lubricate valves and valve seats, cooled the burn a bit so to speak, and let them run big dynamic compression numbers without needing alot of camshaft overlap.

The use of avgas, 100 lo-lead or its equivalents is illegal, but its still done. It's something that the EFI boys have to live without. Since avgas still contains lead, it wreaks havoc on sensors and catalytic converters. This stuff kills O2 sensors faster than Raid kills cockroaches.

Running low octane fuel in high compression engines is like stuffing a lit rag into a gas can. Its not a matter of if, it's a matter of when. Why? Since low octane fuel is quicker to ignite, it's easier for it do ignite from pure compression alone (the basic principal behind diesel engines). If the fuel ignites as the piston is traveling upwards on the compression stroke, the energy from the explosion compounded by the fact the piston is technically moving in the wrong direction when this occurs is extremely harmful to the pistons and other internals. This is how holes get melted through piston tops or skirts get broken and in extreme circumstances, how blocks get ventilated.

Higher octane fuels are colder burning. This is why an 8:1 motor runs poorly on a tank full of Cam2.

I've always been a firm believer that paying a little more at the pump is a good insurance policy on a high perf motor. Them parts ain't cheap, make em last as long as you can.

There are steps to take to help a high compression motor run on low octane fuel. You can retard ignition timing and/or valve timing, and possibly try a colder plug. All of this is fine, but the cost is performance. You'll be able to tune it to a "middle ground" but whether or not its a happy medium, is dependent on the particular case.

If the motor is stock, 87's not gonna kill it unless otherwise recommended from the manufacturer. Keep the filter changed, buy your gas from reputable stations, dump some fuel injector cleaner in every now and then and let it ride. Running 93 every few tanks IMO doesn't really do much. More often than not, the same additive package in the 87 octane fuel of a major brand is the same package used in the 93 octane fuels. Sometimes more additive is used, but that trend is slowly fading away.

Hope I shed some light on this.

89transam

Here is what i have heard, it may or may not be true. Supposedly all the time that the 92 was being used the company that had the patent on "california smog legal 92 octane" was not receiveing any royalties. One day they demanded 5 cents a gallon, judge ruled with them.

So...Insted of pay them thier 5 cents a gallon, all of california now uses 91 octane.

Air_Adam

From what I know, the highest compression engines Chevy ever made were the Corvette 427's from '66-69. The L88 427, which was an iron block, aluminum head 4bbl had 12.5:1 compression. The ZL1 427 was basically the same engine, but with an alumunum block.

They both needed 103 Octane (leaded) to stay in one peice because of the 12.5:1 compression.

My friend's '69 Chevelle, which has a 350 with about 10.25:1 compression, runs perfectly fine on 87 octane. Nothing exotic on it either, just the factory pistons and cast iron heads.

Alot of it is how you drive it too.. if you drive the car really gently (as in keeping your foot out of the throttle) you could probably get away with 87 in a 11:1 engine. Its when you "put it to the wood" that you will have problems, like pre-ignition and detonation.

1bad91Z

iTrader: (1)

I run super unleaded (93 octane) pump gas on my 10.5:1 motor and it runs great with-out detonation.

Of friend of mine has an 11:1 motor that he runs 93 in.

Anything over 11.0:1 , I would recommend stepping up to the lowest grade of race gas (which is 98 octane I think).

SSC

Most engines run fine on 87, here in Co is considered mid grade fuel. If you have ran this fuel at full engine operating temprature with no detonation then you will continue to be ok. Alot of us with higher compression setups do have pre-ignition/detonation problems with most pump gas because our timing will not be automaticly retarded by the ECM via the knock sensor the old HEI doesnt much care the engine is about to explode.

omcrider

I was just watching a history channel special on fuel last night. As long as your just cruising you will be fine. Its when you open her up and try to cram more fuel in that you will have problems. So if you don't hear any knocking or pinging your fine. Just when you know your going out to play and not commute to work you should run a higher Octane. I wish I could get 93 here. I run super and its costing me over $2.30 a gallon for lousy 91. Of course I don't have to commute so it doesn't hurt to bad.

Dante93GTZ

iTrader: (5)

A couple of points:

My '93 Beretta GTZ's engine has a CR of 11:1 and the best pump gas I can get here is 91. I run just fine with it, no ill effects. When I built the engine I was worried being that I was told that 93 was the minimum for it, but 91 works fine.

As far as octane vs. "clean" gas...

Octane is the resistance to burn. The more octane, the harder it is to predetonate. 87 octane will not CLOG injectors unless its dirty or bad gas.

Gas out here in Idaho SUCKS. Highest is 91 unless you get 10% ethanol gas which is 92. I filled my tank with 91 octane yesterday for $2.09/gal. OUTRAGEOUS.

Back in TN we regularly had 93 available it was nice...

Bulldog92

iTrader: (1)

Thanks for the input, guys...wonder where my last post went?

Anyway, I can totally feel your pain on these gas prices...but I'm apparently not paying as much! The cheapest I've seen is $1.65/gal for Raceway 87 octane and about $1.90 for 92-93 octane.

ME Leigh

Thats only in southern Idaho, where they have smog problems in the cities. North of Boise you can get 93 all over the place. With 87 being the lowest grade, instead of the souths 85.

seek007

is it better to only get gas from one gas station cause i usually just fill up where ever i am at and i don't know if it would make a difference or not

i know to never get gas when the station is filling up cause it can run up some **** from the bottom of there tank, even hours later you could end up with bad gas...

whatcha think?

SSC

Well if you were to think of it. Rust and dirt sink to the bottem of the tank anyway so full tank or not your pickup is located at the bottem of the tank so you going to get dirt and other crap reguardless of the fuel level.

I'm convinced that certain places just get crap for gas or the condition of the holding tank is sub par. Older gas stations do tend to have more issues with bad fuel then newer ones, might be water seeping into the tank or just the owner pulling out the hose at 3am and making that special super clean "hydrogen" mix. An example would be my truck engine 10.5:1 that runs fine on 87 @ altitude when I get fuel from certain gas stations, other gas stations I'm just wasting 10 cents more per gallon for the 87 mid grade when it runs like its got a tank full of 85. Amazing how 2 octaine points can make that much of a difference.

rx7speed

I have seen 12.3:1 compression on a 502 and it ran just fine using around 12:1-13:1 a/f ratio