My engine I got runs as 9.1 comp ratio, and I've been using 91 octane, but there's only one place in this area where I live that has it with out going to North dekota to get 91 or higher gasoline.

I don't know much about these about the octane level and what comp ratio I can use with what.

I'm wondering if I bolted on more higher performance parts on to my engine, and it raises up my comp ratio, would it be fine to still be running on 91 octane gasoline? or do I have to keep on putting in octane booster to get it right? I don't know how much higher, but I don't beleive it would be any higher than 94 octane.

Thanks,

Tim

Are you up in the mountains of Montana? That's probably why 91 octane is so hard to find. Higher altitudes need less octane due to the lack of air.

Bolt-on parts will not raise your compression ratio. Only changing the pistons, the heads, or the head gaskets will change the compression ratio.

I'd say with 9.1:1 compression you'll be fine with the 89/90 octane you have available. Put in the 91 stuff if you plan on racing.

I live on the North - eastern side of Montana, where its mostly flat lands or just hilly. x-)

but its still hard to find good octane gas around here, because we don't have tracks or any type of racing up here. Even though a lot of the high schoolers around here like to have a fast car, and do a little street racing.
(I'm in my junior year of high school.)
I've talked to five7kid about the cylinder heads, I've iron TBI heads on my engine, and it would do so much better with vortec cylinder heads, (these are the ones five7kid pointed out for me.)
http://www.sdparts.com/product/SD806...merIntake.aspx
I do plan on getting those heads, and maybe get a root blower, but Im not sure about that yet.
I was really curious about how much those heads will raise me up on comp ratio.

And its good to know I can use 89 octane, i've been using 91 octane, because a bunch of my hot rod friends were worried and didnt want me to take a chance using 89 octane, because alot of them never used an engine I got.

You should only run the lowest octane available to prevent detonation. Any higher is just a waste of your money.
A 9:1 CR is nothing to worry about. You should be able to run 87 with no worries.
My own engines have shown that once you get to ~10:1 you need to start bumping up the octane.

your sig says you have an LT4. If this is so, then you have 10.5:1 compression, and at higher elevation a 10.5:1 engine will be like a 9.5:1 engine at sea level. Also, the LT4 has knock sensors and aluminum heads, so 91 octane should be just fine.

I need to change that.
its not an LT4 engine, I have the same parts out of a LT4 corvette parts, like the crank, pistons, cam, but I have Iron TBI heads with a pain intake with a carb.

Then plan on better heads.

???
Isn't the Vortec cylinder heads I mentioned earlier good enough?
As five7kid told me I would get the hp and tq as much as a ragular LT4.
has 575" max lift with a edlebrock performer intake.
I am looking at getting that eventually (trying to Finnish up on bills, rebuild my 6 speed, put 3.73 gear ratio with a posi, than get the cylinder heads package.)

Google "water injection."

Um....
explain to me why,
and what does that has to do anything with this topic?
(Im not being an A hole, kinda curious why.)

For what it's worth, I'm running 9.7:1 CR (calculated), 10 degrees base timing on the CC carb ignition system, no EGR, and the local 85 octane (R+M)/2 regular unleaded.

Wow. that's good to hear.
well.. I'll stop worring. I didnt want to be putting octane booster everytime I gas up if I decided to go with to raise my comp ratio.

Thanks for the info guys.

octane is really one of those hard things to say how much you need to use to prevent detonation. I've had cars with 8.5 compression only run on 91 or higher octane. any less and it would ping like crazy. my mazda on the other hand has I believe 9.5 compression and runs just peachy on 86 octane.

timing, what metal are the heads made out of, piston shape, head combustion chamber shape, cam profile, exhaust efficiency, cooling system, altitude, dynamic compression and so on. so it's really hard to give any exact you should use this octane since you have x.x:1 compression. the best most of us can do is just give you an idea of what to run but in the end but it is more of a starting point.

Do a little reading up on water (water/alcohol) injection. If the relevance to your situation and this thread topic does not become clearly apparent, then best you shut the hood and stay away from cars.

http://en.wikipedia.org/wiki/Water_injection_(engines)

Octane is the fuel's resistance to detonation. Gasoline in all grades has the same amount of BTU energy per gallon.

As mentioned above, you only need as much octane as is needed to prevent detonation. Those who claim more power with higher octane are probably only getting that extra power because the fuel isn't detonating and they're burning the fuel better which make more power.

A mechanic at work had his new 383 on an engine dyno last weekend. He had 91/92 octane pump gas and some C12 race gas. He made more power with the pump gas. The race gas burns slower and he lost power because of it.

Many years ago I was running a 10:1 454 on 91/92 pump gas and was running into the 10's with no problems. During the summer, the density altitude is also around 5000 feet so higher octane isn't required.

The majority of the "octane boost" stuff isn't worth the money. To significantly raise the octane, it would be cheaper to just buy higher octane fuel but as already stated, if your engine doesn't ping under load with a lower octane fuel, a higher octane won't make any more power.

If you have an EFI engine, use a scan tool and see how many knock counts it gets under load. If the knock sensor detects knocking it will retard the timing and you lose power. If the knock counts are high, use a higher octane fuel and try again. Once the knocks counts go away or are very minimal, don't go any higher in the octane levels.

Ok...
My shop teacher say it does work, he explained to me about it, but I still had a hard time beleiving it.
he had two of the containers that were used on his vehicles, and he said it would work if it didnt rust. (that with the wires running in circles inside the container with the water, rusted it out.)
I'll take a look at it.

Wires running around in circles in a container are not part of a water injection system.

www.snowperformance.net
http://www.alcoholinjectionsystems.com/
http://www.aquamist.co.uk/
http://en.wikipedia.org/wiki/Harry_Ricardo
http://www.kennedysdynotune.com/waterinjected.htm
http://autospeed.com/cms/A_107970/article.html
http://www.labontemotorsports.com/st...onSystems.html
http://www.rbracing-rsr.com/waterinjection.html
Google search for "DIY water injection"
http://www.alcohol-injection.com/

That should keep you busy.

. . . . wow?
I'm going to do some major studing on this stuff.
Thanks.

i'm gonna be running my combo on 89 octane.. 11:1, 385, AL heads, 260/260 @ .050 solid flat cam..