Compression ratio - Team Camaro Tech
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post #1 of 12 (permalink) Old Dec 21st, 04, 03:35 AM Thread Starter
 
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As winter continues, my education is an ongoing process. My stroker has a compression of 10:1. What does this mean in relation to 9:1, 11:1, etc. Totally high performance and I'm curious as to whether this might be normal for my engine build,etc. Do you need to know other detail to answer? Also, the car has a line lock installed. As I just bought the car in July, so I really haven't messed with it much, but just before storing it, I tried to engage it to see if it worked, but didn't seem to hold the tires. How exactly do you engage it? Thanks.
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post #2 of 12 (permalink) Old Dec 21st, 04, 05:50 AM
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When a piston is at the bottom of the stroke there is a volume defined by the volume of the cylinder and the chamber in the head. When the piston is at the top of the stroke there is a smaller volume defined by the top of the piston and the chamber in the head. The ratio of the bottom of the stroke to the top of the stroke volumes is you 10:1 static compression ratio.

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post #3 of 12 (permalink) Old Dec 21st, 04, 08:20 AM
 
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And about a 10 to 1 CR. is approaching the max. compression a street iron-headed motor can be made so that it can run on good pump gas without fiddling with it, imho...

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post #4 of 12 (permalink) Old Dec 21st, 04, 09:48 AM Thread Starter
 
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Thanks. What is extreme and what is normal. The guy that built the engine and who I bought the car from, was leaning more towards strip, but also wanted the option of street. Which is basically where I'll be running it mostly. So I know that he built it right with the right parts, etc.
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post #5 of 12 (permalink) Old Dec 21st, 04, 10:13 AM
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Quote:
Originally posted by pdq67:
And about a 10 to 1 CR. is approaching the max. compression a street iron-headed motor can be made so that it can run on good pump gas without fiddling with it, imho...

pdq67
thats kinda odd considering the 302's came with 11/1's just remember not even the lil old 4 poppers run good on cheap gas......

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post #6 of 12 (permalink) Old Dec 21st, 04, 11:27 AM
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I agree that 10:1 is right on the money for pump gas. Some people get away with 11:1 on the street but it is tricky. For a normally aspirated ride you probably don't want any lower than 9.5:1

The thing about the 302's is that back when they were being produced you could get leaded gas with much better gas at the pump than you can today.

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post #7 of 12 (permalink) Old Dec 21st, 04, 11:58 AM
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Ahhh leaded gas was NOT a higher Octaine

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post #8 of 12 (permalink) Old Dec 21st, 04, 03:17 PM
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hmmm....Me thinks hundred octane was a few points higher than modern R+M/2 93. Me Knows Sonoco 106 was.

Max compression (mathematical static) is only 1 part of the equation. What really counts is maximum cylinder pressure, too much, it pings, and that's bad. Cylinder pressure needs to peak at the right time (piston location) and at a level that the fuel can handle (without combustion becoming uncontrolled {detonation}).

One measure used a lot is DCR (Dynamic comp. ratio) DCR takes into account when the intake valve closes, which is a huge factor. DCR's of 8:1-8.3:1 or so are considered "right".

Alluminum heads are less prone to detonation. Smooth chambers are too, as is small quench areas. Since "BIG" cams close the intake later, they are less prone to detonation, too. A rich mixture will too, because the unburned fuel keeps the chamber cooler, heck, that's the only cooling a top fuel car has.

The last factor is ignition timing. Retarding the timing will reduce pressure, and therefore reduce detonation, too, but at the expense of power, because peak pressure no longer happens at the right "time".

So the "trick" is to design a "package" that will turn as much of the gas into power as possible, right on the ragged edge, without ever going over, and without having to compromise ignition advance.





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post #9 of 12 (permalink) Old Dec 22nd, 04, 03:05 AM Thread Starter
 
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Thanks for all of the info, guys. The student salutes the teachers. [img]smile.gif[/img]
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post #10 of 12 (permalink) Old Dec 22nd, 04, 08:15 AM
 
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Way back when I was a "pup", you could buy SONOCO 260 for like .30/gallon and it was good in the high compressioned motors like the 12 and 12.5 to 1, 427L-88's and the 413 Max Wedge MOPARS at 13.5 to 1 or thereabouts CR. b/c of the large to huge cams they ran in those REAL Factory, hi-po motors ..

It was really like a true 97 octane, TEL containing gasoline so WAS GOOD STUFF back then, imho....

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post #11 of 12 (permalink) Old Dec 29th, 04, 08:24 PM
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To answer your other question at the beginning of the post on the line lock...

The ones that I have installed have operated by first pressing the brake pedal down (hard), and then pressing (and holding) the activation button. When you release the brake pedal, this should relase the line pressure to the rear brakes, but, holding pressure to the front brake lines, which allows you to heat up the rear tires.

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post #12 of 12 (permalink) Old Dec 30th, 04, 03:50 AM Thread Starter
 
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Thanks Skip.
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