Discussion in 'The Garage' started by big_truxx, Jul 21, 2005.
whats the highest compression ratio usable with reg gas?
The answer is.........that depends. It depends on what the dynamic compression ratio is. There are online calculators to figure that out.
d'oh! id have to be smart to use one lol
quality of gas, combustion chamber design, piston design, finish of parts, they are all factors.
plain ole gasolina
When you say "regular gas" that indicates to me a octane level of 87.
With 87 octane fuel it's a safe bet that you can up to 9:1 with Iron heads w/o fear of pinging if the engine is tuned correctly.
With aluminum heads you could run 1 full point higher at 10:1 with 87 but you may have to pull the timing back a notch.
These are just my personal opinions and do not necessarily reflect those of CK5 or it's staff.
so whats the diff w/alum heads?
heat absorption and dissipation. Hot spots don't pop up as much or quickly. My understanding of it anyway.
you are sio cool
im not worthy! im not worthy!
I'm wrong sometimes too, human nature, I'm too quick to turn things I hear around as things I know, bites me sometimes, often enough I expand on those things with added info.
Aluminum dissipates heat quicker than Cast Iron.....
I am kinda conservative in this area. I take the octane rating and put a decimel point in the middle ie 87=8.7. I know thats low, but it keeps me from torching any motors. Altitude also plays a big factor. Where I'm at (8000ft), I know guys who run9.5-10.0 to 1 on 87 octane and their motors survive.
Yep yep, that's a good formula......there are so many variables involved here such as combustion chamber shape, piston to head clearance, ignition system, camshaft selection...but i still believe 10:1 is the upper limit for any combination of parts on 87 octane.
please refer to this post, i believe it will help you answer your question.
i am not running 33's on porsches so... no it didnt help but thanks.
so if reg gas is 87 octane, what is mid grade and super at for octane?
depends on the area. Where I live right now, at the Sheetz down the street, its 87, 89, 92. Back home at any station its, 87, 89, 93, and at Sunoco 94.
The search function comment was that we've had threads asking this same question in the recent history, maybe even under the same name.
Mid grade is typically 89 octane, super / premium can be 91 / 92 / 93 / 94.
The thing to remember is that these numbers are derived from the adding the research and motor octane numbers together, then dividing by 2.
Motor octane testing is done with a load on the test motor, research octane testing is done with cooled water and no load on the test motor.
It's possible to get a high R+M/2 octane designation, (premium fuel ) by having a high research octane number in the equation, and the fuel won't resist detonation under load any better than say 87...
The key to self protection here is to read the stickers on the pumps, and search for a brand that has the highest motor octane in the equation. Beyond that, the vehicle will tell you what it likes, when it's not hammering like a woodpecker, or dieseling on shut down. On the other hand, much of the destruction is inaudible anyway, so to me, running 87 is playing russian roulette with my motor, no matter what I hear or don't hear coming from under the hood.
While I'm on the subject-
It kills me when an owners manual states that a computer controlled vehicle's octane requirement is 87 or " regular ". A more honest statement would be to say that today's vehicles are designed to compensate for the crap fuel being sold, in that timing is retarded in the presence of detonation - you save your engine, but power suffers, as does mileage and emissions.
Personally, we run 87 in the trucks and dad's C5 , and my 10:1 small block camaro gets 89, and they all get treated with a booster that raises both octane by 10 points and BTU of the fuel, and we don't worry about fuel anymore. learn more here : TK - 7
I know bro but had to make he comment apon the comment recieved lol have you ever tried to search for something? I look and look sometimes and still do not have the answer. then post and still get flamed on cuz supposedly there was a post... so I most of the time stop caring and post first skiping the wasted time searching and getting directly to being flamed apon! I like it! lol
so basically after I read another post... i guess that many questions spark arguments lol oh and that I will need to just simply build the engine the way I want then find out what octane fuel it wants after it is built. hopefully not blowing it up in the process.
build it with iron heads, run a 7.5:1 dynamic compression ratio, and 87 octane and be happy with it.
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