Just incase there are any confusions about pump octane grades

[rjfguitar]

Higher octane = less power.

Martin

This rule only applies when you are using fuel with an octane level greatly exceeding what the engine in question needs to run without pinging.

For example, 100 octane with a 350 with 8.5:1 comp.

The rule would not apply on an engine with say a 9.1:1 comp and 91 octane gas.

 

[rjfguitar]

I guess 400's suck, because my 406 with a measly 9.2:1 compression will ping with anything but 91 octane. When I would tow, I'd even have to dump in a bottle of boost on top of that to keep it from pinging. My timing is at 12* advance @idle.

 

[Chief Brody]

I remember when the pumps around here had 96 Octane premium....then 94....I think we are down to 92 now.

I use premium in my small truck because my valves clatter or "ping" when I use regular...

I think gas was about 1.00 a gallon when they sold 96 octane around here...my dad always bought Amoco Premium for the Buick...so I did too.

Back in the 70's when Carter was President was the first time we went around with ethanol...I remember that my dad's shop was backed up with cars because the ethanol cut all the crud loose in the tank and lines...

If you are going to use ethanol, you need to use it from the beginning, not after the vehicle has run for years on gas....at least that's the way it used to be.

 

[K85 Octane]

compression ratios don't mean a whole lot, it's hard to go by those. I know it's a different engine entirely, but 12:1 and 13:1 dirtbike motors are running 91 octane.

Also, when I say a vehicle only needs 87, I'm talking about your run of the mill vehicle that comes off the assembly line. Not some zz4 or 400sb. Compression ratios don't mater a whole lot anyway, it's actual psi compression after the cam changes everything.

personally, I'm not paying 3.60 for 91, when 87 @ 3.30 will get me anywhere even with a trailer. Actually that's a slight lie, if I'm going on a long trip w/trailer, I'll run 89 in my DD s10.

 

[Hogback Fabrication]

The higher the compression ratio the more efficient the engine is: more power and better fuel economy. That's simple thermodynamics.

Now, as to whether the added cost of premium fuel makes up for the gains you could see vary but generally the cheapest cars to operate still use regular fuel because it's cheaper (even if they could get another couple mpg on premium). Performance cars use premium because it makes more power (of course on an engine that's meant to use it, as mentioned an engine that isn't meant to need premium won't make more power by using it).

The bottom line is that in the compression ratios we deal with (say 8:1 to 12:1) there is roughly a ~1-2% gain in power and efficiency for each point in increased compression ratio. As mentioned, static compression ratio isn't what is actually going on inside the motor.

 

[cuervo]

hahaha
where I live, the tankers all drop by the big stations every other day, sometimes more often. The Big Chevon station near me said every night. wow, that's 9,000 gallons if the tank is empty.

I'd say the 91 octane helps you run a more advanced spark timing. That would help with some power and more than likely run a little cooler. Maybe carbed vehicles benefit cause they can't compensate for fuel changes. Computers can.

Well, I guess gas sits at marinas a bit longer then in LA.

I'd bet even in my small town gas is only in the ground 3 or 4 days max but it can sit in my boat for a week or two at a time.

 

[cuervo]

I guess 400's suck, because my 406 with a measly 9.2:1 compression will ping with anything but 91 octane. When I would tow, I'd even have to dump in a bottle of boost on top of that to keep it from pinging. My timing is at 12* advance @idle.

Do you have a 30 degree curve? I would think 42 total timing might be a bit too much.

 

[cuervo]

Around here, its all ditch water and kerosene, so ya might as well buy the cheap stuff.

^^^ That would make a nice sig quote!

 

[K5dreamer]

octane by definition is a resistance to detonation or auto ignition. That is its primary relation to engine operation. any effects in mileage or power are consequential.

lower octane burns just fine as long as the engine can handle it, but can cause fouling of the engine if used on a car with higher operating temperatures. In some cases, such as the Audi 3.2L V6, which runs on the ragged edge of efficiency and has a 12.5:1 compression, you may even see carbon deposit build up despite running 91 octane. We advise people to run a fuel additive like BG 44K every couple of tank fulls to prevent this carbon build up. Also the fuel here in the states is notoriously dirty. coupled with EGR systems, they can leave quite a mess on the combustion chamber, intake manifold, and valves. the benifit of the higher octane is it does tend to burn cleaner, and produce fewer carbon deposits, which tends to keep mileage and performance at a level closer to stock.

regarding ethanol - its a great fuel, on many levels. but us hippies that are in the know realize we need a different method of producing it before its worth hugging. Its current production is via corn, which has displaced other crops, which are being outsourced to south america, which is cutting down rainforests to produce the cropland to grow these displaced/outsourced crops.

quite frankly, algae based biodiesel is the future of long range transportation. and home based hydrogen production for fuel cell vehicles via solar or wind powered electrolysis is the future of in city transportation.

just my two cents.

 

[TexasSilhouette]

I love ethonal, so much I retuned my 91 GTA to run E85. You can't make that stuff detonate. I have a 200 shot of N2O as well. We are putting a supercharger on the Suburban, we will be building an E85 tune for it as well for those days we want to run the small pulley. Awesome fuel if you ignore the source.

 

[Yo]

Do you have a 30 degree curve? I would think 42 total timing might be a bit too much.

This all depends on what dizzy he's running and what spring rates he's using.

I mean, let's say it's an MSD or a factory GMPP; these setups are typically factory calibrated using heavy springs and a 21* bushing, he may not even be hitting full advance since the mechanical advance doesn't even open to total until 4K rpm. IDK ab alot of you all, but I rarely hit over 4k RPM in my truck, even w a 5800rpm redline zz4. Running it offroad is another story, but how long you gonna keep an engine spooling at 4K+ unless you're in a mudhole? I guess we should also consider whether the dizzy has vacuum advance or not.

I find that for 4x4s that aren't mud boggin trucks and see daily driving duties w at least 9.5:1, 12* initial and 33* total with 92 octane keeps em running well. I am still playing around with springs and bushing in my MSD, but I'm thinking I want all in advance around 3K rpm. The Boss Hoss motorcycle forums has great info on the ZZ4, and they are saying the 10* initial, 32* total as speced by GMPP is not ideal, and bumping initial up 2* helps out a lot.

 

[Chief Brody]

I don't know about anywhere else, but here the premium is about 20 cents higher a gallon....for 30 gallons that's only $6.00 more.
That's less than the cost of one bottle of Octane booster...why not just run premium?

 

[rjfguitar]

This all depends on what dizzy he's running and what spring rates he's using.

I mean, let's say it's an MSD or a factory GMPP; these setups are typically factory calibrated using heavy springs and a 21* bushing, he may not even be hitting full advance since the mechanical advance doesn't even open to total until 4K rpm. IDK ab alot of you all, but I rarely hit over 4k RPM in my truck, even w a 5800rpm redline zz4. Running it offroad is another story, but how long you gonna keep an engine spooling at 4K+ unless you're in a mudhole? I guess we should also consider whether the dizzy has vacuum advance or not.

I find that for 4x4s that aren't mud boggin trucks and see daily driving duties w at least 9.5:1, 12* initial and 33* total with 92 octane keeps em running well. I am still playing around with springs and bushing in my MSD, but I'm thinking I want all in advance around 3K rpm. The Boss Hoss motorcycle forums has great info on the ZZ4, and they are saying the 10* initial, 32* total as speced by GMPP is not ideal, and bumping initial up 2* helps out a lot.

I'm running a stock HEI vacuum advance distributor. When I had my K5 on the dyno about 5 years ago, the guys said it wasn't advancing right, and put a new spring kit in it for me. Ran much better after that, and I seem to recall them saying something about it being around 36* full advance, but I could be wrong.

Regardless, 400's are a PITA. The Siamese cylinders run warmer than a regular block, obviously making fuel pre detonate easier.

 

[K5dreamer]

I don't know about anywhere else, but here the premium is about 20 cents higher a gallon....for 30 gallons that's only $6.00 more.
That's less than the cost of one bottle of Octane booster...why not just run premium?

octane booster usually also includes fuel stabilizer, injector cleaners, and other additives not found in regular fuel. the octane boost would be probably very close to the 4 point difference from regular unleaded to premium.

 

[djtejas]

octane by definition is a resistance to detonation or auto ignition. That is its primary relation to engine operation. any effects in mileage or power are consequential.

lower octane burns just fine as long as the engine can handle it, but can cause fouling of the engine if used on a car with higher operating temperatures. In some cases, such as the Audi 3.2L V6, which runs on the ragged edge of efficiency and has a 12.5:1 compression, you may even see carbon deposit build up despite running 91 octane. We advise people to run a fuel additive like BG 44K every couple of tank fulls to prevent this carbon build up. Also the fuel here in the states is notoriously dirty. coupled with EGR systems, they can leave quite a mess on the combustion chamber, intake manifold, and valves. the benifit of the higher octane is it does tend to burn cleaner, and produce fewer carbon deposits, which tends to keep mileage and performance at a level closer to stock.

regarding ethanol - its a great fuel, on many levels. but us hippies that are in the know realize we need a different method of producing it before its worth hugging. Its current production is via corn, which has displaced other crops, which are being outsourced to south america, which is cutting down rainforests to produce the cropland to grow these displaced/outsourced crops.

quite frankly, algae based biodiesel is the future of long range transportation. and home based hydrogen production for fuel cell vehicles via solar or wind powered electrolysis is the future of in city transportation.

just my two cents.

If we got rid of our ridiculous hemp laws, we could use hemp as a fuel source...beats corn or any other source for alternative fuels.
Our hemp laws weren't really put in place to stop the smoking of marijuana...the law protected William Randolph Hearst and the Dupont company. They saw what could be produced by hemp and their businesses would have died if hemp was used. Hemp would have taken over the timber and plastics industry.
We need to reform hemp laws....there are such many more uses than just getting high from marijuana...most hemp can't even get you high.

 

[K5dreamer]

If we got rid of our ridiculous hemp laws, we could use hemp as a fuel source...beats corn or any other source for alternative fuels.
Our hemp laws weren't really put in place to stop the smoking of marijuana...the law protected William Randolph Hearst and the Dupont company. They saw what could be produced by hemp and their businesses would have died if hemp was used. Hemp would have taken over the timber and plastics industry.
We need to reform hemp laws....there are such many more uses than just getting high from marijuana...most hemp can't even get you high.

on point good sir.

 

[sweetk30]

Regardless, 400's are a PITA. The Siamese cylinders run warmer than a regular block, obviously making fuel pre detonate easier.

i run a 400 sbc for few years. was built for 1/4 mile car before i got it.

swaped it in my 1ton. LOVED that motor. ran 210 all the time. empty on highway or slingin mud on 38" swapers for 10-15 min stright. 3 core rad stock h20 pump and NO fan shroud with 7 blade clutch fan.

 

[cuervo]

I'm running a stock HEI vacuum advance distributor. When I had my K5 on the dyno about 5 years ago, the guys said it wasn't advancing right, and put a new spring kit in it for me. Ran much better after that, and I seem to recall them saying something about it being around 36* full advance, but I could be wrong.

Regardless, 400's are a PITA. The Siamese cylinders run warmer than a regular block, obviously making fuel pre detonate easier.

Ok, that's what I was hoping for. 42 degrees seems like to much for just about anything.

 

[82355]

Most 400's I have been around loved what seemed like excessive timing.

Martin

 

[cuervo]

Most 400's I have been around loved what seemed like excessive timing.

Martin

I think the most I've ever seen was 38 on a 406 but it was a strip strip car. Mid 10s if I remember right. That was some 30 years ago.