[buster]

OK, not a C3 question but, I read that the new C7 will have a SBC with a comp ratio of 11.5:1. How can that run on street gas of CA 91 octane?

 

[PalmBeachVette76]

Computer control. Spark timing, fuel mix, etc. is all controlled by the computer and changes constantly based on the atmospheric and engine conditions from pressure to temps the computer is changing injection patterns, advancing and retarding timing, killing cylinders on the C7 and sense spark knock. Bottom Line, serious high tech engineering.

In addition to that I can only guess that they have machined the cylinder head combustion chambers smooth so no hot spots from metal burrs occur. All the things we have to manually do they have incorporated. Of, course this is part of the hefty price tag on these cars but for the most part they're turn key and worry free. No offense but look at most of the people who drive them, gasing up is the extent of their mechanical capability, not a bad thing just something that separates those who own old school from new school.

 

[vettex2]

direct fuel injection and chevy also machined the top of the pistons in a special way

http://www.ncminsurance.com/corvette-c7-lt1-engine.html

http://www.autoblog.com/2012/10/24/meet-the-lt1-the-corvette-c7s-new-6-2-liter-small-block-v8/

 

[[email protected]]

heres what GM says..they ve brought back the legendary LT1 nameplate...."The all-new LT1 engine also utilizes Active Fuel Management which is a first for the Corvette. This helps save fuel by very slightly, but gradually, reducing half the engines’ cylinders in light-load driving conditions. Also a first for Corvette is Direct Injection, which is the primary contributor to the greater combustion efficiency of the engine. This allows a more complete burn of fuel in the air-fuel mixture by precisely controlling the mixture motion and fuel engine spray pattern. Direct injection keeps the combustion chamber cooler, which allows for the higher 11.5:1 compression ratio"... theres your reason why it works Buster

 

[vetteoz]

How can that run on street gas of CA 91 octane?

Camshaft selection can have a big effect on the true (DCR ) compression which is always lower than the static CR

http://members.uia.net/pkelley2/DynamicCR.html

 

[[email protected]]

good article ..very informative

 

[toobroketoretire]

Yes, that is a very good article as it clearly spells out why there is a huge difference between compression ratios and actual cylinder pressures.

That is why I advanced my 220/220 duration marine cam 4 degrees. By closing the intake valves 4 degrees earlier more of the air/fuel mixture gets trapped in the cylinder which then provides more torque down low where I needed it the most because of my overdrive 4th gear.

Cams will provide better low and mid-range power when advanced a few degrees and is the reason why most aftermarket timing chain/sprocket sets have the advance/retard keyways cut into the cam sprocket.

 

[[email protected]]

remember Steve, back when we could build street motors and pop 12.5:1 domes in them? , buy 100 or 105 octane Premium gas at the Amoco on the corner for 79cents/gallon ...run for years.. ah, the good old days!!! now I ve got 10.5:1 CR and can just get by on 93 Octane E10 gas .. altho, I am still cranking out big power..but premium is $4/gal now .

 

[Pappytinker]

remember Steve, back when we could build street motors and pop 12.5:1 domes in them? , buy 100 or 105 octane Premium gas at the Amoco on the corner for 79cents/gallon ...run for years.. ah, the good old days!!! now I ve got 10.5:1 CR and can just get by on 93 Octane E10 gas .. altho, I am still cranking out big power..but premium is $4/gal now .

Gee, I remember paying like 34.9 for Premium that I put in my '59 Ford Sunliner (about $3300.00 new) with the Interceptor 390. And, I remember 23.9 that I put in my '51 Pontiac (about $2000.00 new) before that. But, if you adjust up for inflation since then you wont be too many pennies away from the $4.00 for today's gas. In 1967 I was making about $80 per week take home and today, if I were still working, I would be making about 30+ times that. Inflation since 1970 to 2010 has been about 1800%. That is one thousand eight hundred percent. That is a multiplication factor of 18. In 1970, the price of a gallon of regular gas was about $0.36. Multiply that by the factor of 18 and you get $6.48. So, relatively speaking, gas is cheaper now than it was then. Therefore, IMHO, the "Good Old Days" were not that good.

 

[Shattered]

Gee, I remember paying like 34.9 for Premium that I put in my '59 Ford Sunliner (about $3300.00 new) with the Interceptor 390. And, I remember 23.9 that I put in my '51 Pontiac (about $2000.00 new) before that. But, if you adjust up for inflation since then you wont be too many pennies away from the $4.00 for today's gas. In 1967 I was making about $80 per week take home and today, if I were still working, I would be making about 30+ times that. Inflation since 1970 to 2010 has been about 1800%. That is one thousand eight hundred percent. That is a multiplication factor of 18. In 1970, the price of a gallon of regular gas was about $0.36. Multiply that by the factor of 18 and you get $6.48. So, relatively speaking, gas is cheaper now than it was then. Therefore, IMHO, the "Good Old Days" were not that good.

You make some interesting points Pappy. I started out at 3.60 an hour in '73, just 21yrs. old, thought I was steppin' in high cotton. I stayed for 37yrs, and when I retired I was up to 39.00. I guess everything is relevant, but those were the days being much younger!

 

[[email protected]]

the cheapest I remember paying was around 35 cents/gallon for reg when I started driving in 69.....when I bought my first Corvette in Jan 73, it was around 49 cents/gallon here .. but the 105 octane was about 79 cents ... boy to be that young and foolish again eh?

 

[bluedawg357]

In addition to what others have pointed out, since 95 gm started cooling the heads before the block. Keeping the heads cooler allows a higher compression ratio. Same as aluminum heads and there cooling affect. my aluminum l92 6.2l in my truck has 10.5 to 1 compression.

 

[toobroketoretire]

the cheapest I remember paying was around 35 cents/gallon for reg when I started driving in 69.....when I bought my first Corvette in Jan 73, it was around 49 cents/gallon here .. but the 105 octane was about 79 cents ... boy to be that young and foolish again eh?

I clearly remember seeing regular gasoline for only 25 cents per gallon and 10 Mc Donalds hamburgers for a buck. That was back in about 1958 or so.

 

[[email protected]]

I remember 6 burgers for a buck,now they are $6 for 1 burger.... but it wasn t Mc Donalds, we had Burger Chef here ..they went under few years later