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Low Compression Street Engine's & Tuning Techniques Idea's...How Too's on low compression Engines.

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Old 10-08-12, 09:20PM   #1
KINGPIN
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Default Pump Gas Lesson

I learned the hard way. Raced recently with 91 octane pump gas and ran my fastest times. I had 5 gallons of 110 so when I got low, poured it in and slowed down. incredible. 10.5 compression e heads, 472 ci.

my son had a shop teacher show them an experiment. he had a small amount of diesel fuel, regular gasoline, high octane race fuel. tossed a match in the diesel the match went out, tossed into the gasoline flame on, tossed into the race fuel match went out. all I need to know!
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Old 10-09-12, 04:30AM   #2
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The 110 Race gas will be a slower burn than 87 with lower(operating/dynamic) compression but will be less prone to detonation than 87 will be at higher compression & boost levels.
You can get away with 10.5:1 static CR & 87 octane using the aluminum heads.
The aluminum heads draw the heat out of the chambers faster than cast iron and that can kill power too if too much heat is dragged out of the expanding gases during the power stroke before the piston gets to BDC.
If you were trying to use that 10.5:1 with iron heads you would have a tough time on 87 octane without doping the 87 or even 91 octane gasoline with race gas.
The cam would have to be set up to bleed off a lot of compression at low speed just so you could switch the engine off.

Nitromethane burns that way too until you compress it.
Throw a match to it and it will burn real slow and lazy.
Pour a small spot of it on the garage floor , strike the spot with a hammer and "pow"
There will be a small divet in the concrete floor where the nitro was detonated.
Where safety goggles and gloves shoud you attempt that trial test.
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Old 10-09-12, 08:39PM   #3
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Quote:
Originally Posted by sprint250 View Post
The 110 Race gas will be a slower burn than 87 with lower(operating/dynamic) compression but will be less prone to detonation than 87 will be at higher compression & boost levels.
You can get away with 10.5:1 static CR & 87 octane using the aluminum heads.
The aluminum heads draw the heat out of the chambers faster than cast iron and that can kill power too if too much heat is dragged out of the expanding gases during the power stroke before the piston gets to BDC.
If you were trying to use that 10.5:1 with iron heads you would have a tough time on 87 octane without doping the 87 or even 91 octane gasoline with race gas.
The cam would have to be set up to bleed off a lot of compression at low speed just so you could switch the engine off.

Nitromethane burns that way too until you compress it.
Throw a match to it and it will burn real slow and lazy.
Pour a small spot of it on the garage floor , strike the spot with a hammer and "pow"
There will be a small divet in the concrete floor where the nitro was detonated.
Where safety goggles and gloves shoud you attempt that trial test.
Yep. I was running the highest octane pump gas available here. 91. should i run again using the 110 I figure on experimenting with mixing 2 gallons 91 with 1 gallon 110.
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Old 11-21-12, 02:19AM   #4
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Basically the higher the octane, the more it resists burning. The lower the octane, the easier it burns, thus more prone to detonation. I tell people, don't run any more octane than you need to not detonate. Like Sprint250 said, higher compression ratios generate more heat that can help burn the higher octane fuel.

As far as race gas goes for power, we have found that the Shell racing fuel makes the best power of any we tested.
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Old 11-21-12, 04:05PM   #5
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When I dyno. First pulls. we use Mobile. Then stop and got Shell as near as we could tell the Shell gas was worth 8 HP.
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Old 11-21-12, 04:57PM   #6
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that's about the same difference we found with Shell.
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Old 11-21-12, 09:42PM   #7
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There is more energy in pump gas. The additives in race gas that raise the octane just take up space in a gallon of fuel. What they do is raise the flash point of the gas, it does not burn like gasoline.
There are more BTUs in pump gas than race gas.
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Old 11-21-12, 10:10PM   #8
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Quote:
Originally Posted by gtofreek View Post
that's about the same difference we found with Shell.
Good I feel better, knowing we where pretty close then on what we figured it to be.
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Old 11-22-12, 11:40AM   #9
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Shell anything is a higher standard period. I use Rotella exculsively in heavy equipment and all the big trucks we maintain. My dad worked for Shell in several capacities for 27 years in California. IMHO they make some of the best products same goes with Auto-
lite, Mystic.......several others
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Old 12-07-12, 11:38AM   #10
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As others have alluded to, octane is a parameter of "burn rate". Lower octane, higher rate.

We proved it to the local circle track crowd. By rule, they had 9.2:1 iron headed 358 CID small block Chevy. Most were using 109 or 110. I challenged one of my customers to drain the race gas and put straight 93 in it. Knocked nearly .2 seconds off his lap times (1/3 mile oval). That is significant.

As Paul said, always run the octane correct for the compression ratio and "environement"

Jim
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Old 12-07-12, 09:26PM   #11
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Also don't they change the flash rate between winter and summer months. Now that I'm thinking about it what's that got to do with, well guess for those who didn't know it.
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Old 12-13-12, 01:55AM   #12
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WE saw an 18 HP increase in a 406SBC 9.9CR going from Sunoco Purple to Sunoco 93 true pump gas.Bill C.
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Old 12-13-12, 12:06PM   #13
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Always used the Sunoco 93 on my engines that had 10.5:1 with no problems
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Old 01-26-13, 09:03PM   #14
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Guys, there is simply more energy in lower octane gas. The stuff they use to raise the octane just takes up space in a gallon of gas.
Pump gas engines will ALWAYS make more power with just enough octane not to pings some high octane race fuel.
The only way to realize more power with high test is to have enough cylinder pressure to put the race gas to work.
There are more BTUs in pump gas than race gas. Heat is energy.
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Old 09-12-13, 08:19AM   #15
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Quote:
Originally Posted by KINGPIN View Post
I learned the hard way. Raced recently with 91 octane pump gas and ran my fastest times. I had 5 gallons of 110 so when I got low, poured it in and slowed down. incredible. 10.5 compression e heads, 472 ci.

my son had a shop teacher show them an experiment. he had a small amount of diesel fuel, regular gasoline, high octane race fuel. tossed a match in the diesel the match went out, tossed into the gasoline flame on, tossed into the race fuel match went out. all I need to know!

low octane fuel burns faster, and has more energy, than high octane fuel. That's something most hot rodders don't know or realize. This is why it pays to crack a book once in a while, and research things first- no reason to repeat the R/D mistakes of the past. Car mfgrs. knew this back in 1930.

the higher the octane, the slower the fuel burns, and the less energy the fuel has in it- inert ingredients such as lead are added, just to retard the flame front and make the fuel burn slower and more gradually- where the power increase comes from first and foremost, is ultra-high static compression ratio- the slower burning, high octane fuel is then used with high cR, to stop detonation, so the engine can run the high mechanical compression ratio without engine damage

once the high static compression ration is taken away, and you're building a true "pump gas" engine that can run on the 93 octane at the gas pumps today, there's absolutely no advantage to racing fuel, and there's actually a disadvantage- because the low octane fuel will burn faster and make more power in a low compression engine- the high octane fuel will make less HP in a low compression engine

that's why pushing CR up for a street car on pump gas, is counterproductive, the pump gas available doesn't have enough octane to prevent detonation. Likewise, putting high octane fuel in a low compression engine is also counterproductive, it's like putting wood into an oil furnace, it can't burn it efficiently.

how much HP an engine can make, it totally dependent on what fuel it can burn, that's the limiting factor, once the airflow and CID are maximized, the fuel and compression ratio relationship becomes the governor.

running 13:1 with 116 octane fuel, makes more power, but it's 2 steps ahead with the compression, then one step backwards with the high octane fuel needed, to prevent detonation. Octane is added for one reason only- to prevent detonation, thereby letting you run more compression. The result is a net gain in some HP. If you start with more cylinder pressure in the beginning during the compression stroke, there will be a net gain in cylinder pressure during the power stroke, but the fuel has to be high enough octane to suppress the detonation, and slow the burn down and make it burn evenly- otherwise the engine blows apart.
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