Do new cams automatically raise the octane of fuel you have to use?

[kaisersouse]

I know, prob a very stupid question. Was wondering if there was any cam upgrade that still allowed the use of 87oct?

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[Assassin4457]

I wouldnt assume they need higher octane. I mean I your not changing compression. But im not an expert, could someone confirm?

[Master2192]

You could possibly get cams that leave the intake valve open longer while the piston starts the compression cycle. This would lower your Dynamic Compression ratio enabling you to use lower octane fuels.

But that would also most likely reduce your power output as well

[kaisersouse]

yah see i didnt know if there was a way to get more power via cam upgrade without having to change to 89 or 93

[Master2192]

Oops, I figured you were increasing the compression on the engine and wanted to use lower octane still.

I don't think there are any cams currently that require you to use higher octane in a motor that previously didn't need it. But I could be wrong.

[kaisersouse]

well im already at 10:1 (2.2l)

and I honestly don't know a lot about cams, I just know its a good upgrade and virtually everyone ive seen here who has touched the inside of their engine, uses cams.

I thought I read something about either NEEDING higher octane or EM if you get new cams...i cant remember which.

[bannerd]

No, a cam upgrade doesn't mean you have to use a higher octane. Upgrading the cam's all depends what style you get. If you get a mean cam that was made for racing you will see little increase in horse power. Why? Simple stock cam's will push the vavle down allowing the air/gas mixture into the combustion chamber. So with what air/gas mixture is in the combustion chamber compression takes care of the rest causing it to explode thus leaveing you with power. With a street cam it will push the valves down a hair more and longer allowing more gas/air mixture into the compression chamber which in returns gives you a better power rate.

Using a higher octane will also give you more HP (not a whole lot) The higher the octane the better it responds to igniting inside the compression chamber via spark plug.

Ps with the above information know that you compression will change when installing performance cams. To get even better compression look at buying performance heads that allow more compression and in return more horse power.

--Bannerd

[ballitch]

you dont need to use higher octane gas, thats silly. if anything, when/if you knock, your ECU will pull timing, which will rob a ton of power anyway, it will be even more pronounced with better cams, since your new cams are designed for more lift and duration. you could just go to medium grade after a while and see if that helps or hurts performance. but unless you change your CR, or boost it, you shouldnt need to use higher octane gas..........at least thats what i think is theoretical....in the real world, it might be a different story.

~Josh~

[FalconRS]

Originally Posted by bannerd

Using a higher octane will also give you more HP (not a whole lot) The higher the octane the better it responds to igniting inside the compression chamber via spark plug.

Actually, unless your ECU is setup (tuned) to advance timing or lean out the mixture to take advantage of the higher octane, you'll most likely LOSE power. Switching to higher octane alone won't make power, and in many cases has a negative effect.

If you guys want a technical write-up on why, let me know.

[Patrick Olsen]

Originally Posted by bannerd

No, a cam upgrade doesn't mean you have to use a higher octane. Upgrading the cam's all depends what style you get. If you get a mean cam that was made for racing you will see little increase in horse power. Why? Simple stock cam's will push the vavle down allowing the air/gas mixture into the combustion chamber. So with what air/gas mixture is in the combustion chamber compression takes care of the rest causing it to explode thus leaveing you with power. With a street cam it will push the valves down a hair more and longer allowing more gas/air mixture into the compression chamber which in returns gives you a better power rate.

Using a higher octane will also give you more HP (not a whole lot) The higher the octane the better it responds to igniting inside the compression chamber via spark plug.

Ps with the above information know that you compression will change when installing performance cams. To get even better compression look at buying performance heads that allow more compression and in return more horse power.

I think if we just pretend this post never happened this thread will be much better off. It would be too much work for me to refute every sentence, so I'll just throw out a blanket, "bannerd, you're wrong." Then again, maybe I'm just misunderstanding what you wrote, since it's a bit hard to figure out.

Pat Olsen
'97 Legacy 2.5GT sedan

[NW OBS]

Originally Posted by FalconRS

Actually, unless your ECU is setup (tuned) to advance timing or lean out the mixture to take advantage of the higher octane, you'll most likely LOSE power. Switching to higher octane alone won't make power, and in many cases has a negative effect.

If you guys want a technical write-up on why, let me know.

I am fairly curious myself. Seen this argued into the ground here and other boards. Enough so, that I stopped using 91 in my OBS and have done 2 tanks of 89. I actually feel it's a little quicker when pushed hard. But, I also leave a stop sometimes at low RPM's and heavy foot and it does detonate (rattles a bit ~ the noise I feared in my trurbo cars).

It never did this on 91. There isn't enough change (good or bad) to convince me I am loosing anything on power while running 91~

So...?

[FalconRS]

Alrighty then. It's a little more indepth than this, but what it comes down to is heat control. Within the combustion chamber, you get optimal burn and optimal performance within a temperature window of 500-850*C. Where in that window depends on some factors, but below that level you get misfiring and fouling plugs, above it and you get detonation and stuff breaks.

Any car setup (as in, tuned) for 87 octane will run best on 87 octane. Headers/exhaust contribute to reduced combustion chamber temperatures and reduce knock tendencies. Cams do much the same, increasing flow through the engine and reducing cylinder temperatures, and in turn tendency for knock. Increasing octane also reduces knock tendency by introducing a cooler burn, which (you guessed it) lowers cylinder temperatures yet again. Incidentally, octane level can have the largest effect of any of these other factors on cylinder temperatures, which is why guys are able to run so much more boost and hammer down such incredible horsepower numbers as soon as they switch to race gas.

Now, the reason your car runs better on 89 than on 91, is because with 91 cylinder temperatures are becoming too low and you're no longer getting a complete burn. This will also lead to fouled plugs. If you switch UP a heat range or two on your plugs, I'd bet your car would run a lot better on 91 octane. Plugs by design are there to pull heat out of the chamber, thus the different heat ranges. A colder plug pulls out more heat, a hotter plug pulls out less. So if you want to run 91 for the Big Baller lifestyle, go hotter on your plugs. But why would you do that? The stock ECU has timing and fuel maps setup for 87 octane.

Manufacturers will often tune their cars to run at the hot end of the temperature window to heat up catalytic converters faster and get a more complete burn, improving emissions and fuel economy. This is why you can usually bump a level of fuel OR drop a heat range on the plugs with no ill effects. Do both, OR drop heat ranges of plugs too far, OR go too high on your fuel's octane rating, and performance will start to suffer.

Me, I'm dropping a heat range in plugs, and keeping the nice cheap 87 octane.

If you want to make it as simple as possible:
Stuff That Makes Things Hotter:
Intake mods (anything that happens before the intake valves)
Decreasing Octane
Increase Spark Plug Heat Range
Advancing Timing

Stuff That Makes Things Colder:
Exhaust mods (anything after the exhaust valves) remove heat.
Increasing octane
Decreasing Spark Plug Heat Range
Retarding Timing

DISCLAIMER:
You can factor a hell of a lot more factors into how an engine behaves and runs and different things that affect your engine. I'm going with a very simplistic approach. I believe in balance in an engine.

As for my background, my dad owned a bulk fuel depot for about 40 years so I kinda grew up around this stuff. One could say this could increase my credibility....or on the flipside one could say I've sniffed so many gas fumes I'm completely out to lunch. My suggestion: Take what I said, and go research it deeper.

[bannerd]

Originally Posted by Patrick Olsen

I think if we just pretend this post never happened this thread will be much better off. It would be too much work for me to refute every sentence, so I'll just throw out a blanket, "bannerd, you're wrong." Then again, maybe I'm just misunderstanding what you wrote, since it's a bit hard to figure out.

Pat Olsen
'97 Legacy 2.5GT sedan

Okay to sum up what I said, yes buying better cams will increase performance. I might have been drunk that night but reading it over it sounds okay...maybe the entire part about fuel to air mixture might confuse people

[pingpong]

Originally Posted by bannerd

Using a higher octane will also give you more HP (not a whole lot) The higher the octane the better it responds to igniting inside the compression chamber via spark plug.


--Bannerd

The higher the octane, the less it respondse to igniting. The lower the octane, the easier it ignites.