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Old 03-18-2009, 02:13 PM
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comprestion ratios

what comprestion can i run with pump gas? 87 octane, 90, and 92.

i have aluminum heads with the fast burn chambers.


thanks

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Old 03-18-2009, 02:18 PM
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compression tolerance also depends a lot on the cam timing events.

and to a lesser extent, on the gear, stall, cooling system, and load.

what cam do you have???
what is the rest of the car setup like?
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Old 03-18-2009, 03:13 PM
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dont have anything except for the afr heads and edelbrock performer rpm intake. and a all stock 1958 chevy 1/2 ton truck. so its really heavy.

i will be getting a comp cam 286H or maybe 286HR cam.

.037 quench distance, 5.7 rod, 400 crank, 400 block, 4 speed manual tranny, whatever rear gears the cam works best with (3.90?), and the best cooling system i can get for it since chevy 400s seem to run hot anyway.
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Old 03-18-2009, 03:34 PM
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I would guess the following if you use the 286H cam and afr heads

with 9.5 to 9.75:1 cr you could run 87 octane

9.75 to 10.25:1 cr you could run 90

10.25 to 10.75 cr you could use 92

3.73 gears would work well with 28 or 29 in tall tires. if you plan to use taller tires then use more gear.

get steam holes drilled in the heads.

use zddp oil additive if you use a flat tappet cam. and use the additive all the time (at every oil change).

check this out

http://www.chevyhiperformance.com/te...ild/index.html
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Old 03-18-2009, 05:02 PM
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are those static compression ratios?



thanks
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Old 03-19-2009, 08:30 AM
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Yes. static ratios
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Old 03-19-2009, 09:09 AM
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so i would be running at about 7.5 dynamic compression. that seems really low.

this is the calculator i used.

http://kb-silvolite.com/calc.php?action=comp
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Old 03-19-2009, 09:24 AM
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check out this site.

http://www.empirenet.com/pkelley2/DynamicCR.html

The above article says 7.5 to 8.5 dcr is good with 91 octane. so I went with the 8.0:1 with 92. Maybe a little conservative, but why build the engine on the edge for a few extra hp. not worth it in a street engine as you will not be able to tell the difference but tuning will be much easier with lower cr.

In get the following dcr with the 286 cam
10.75:1 cr goes to 8.03 dcr
10.25:1 cr goes to 7.71 dcr
10.00:1 cr goes to 7.5 dcr
9.75:1 cr goes to 7.35 dcr
9.5:1 cr goes to 7.15 dcr

here is another site. they recommend 8.0 dcr for an old school sbc

http://www.hotrod.com/pitstop/hrdp_0...ion/index.html
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Old 03-19-2009, 10:34 AM
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what type of power could i get with the 286H cam, afr 195cc heads, 400 block, 400 crank, and the 87 octane 7.15:1 dynamic ratio.

and what rpm range would it be in?
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Old 03-19-2009, 11:52 AM
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go back and look at post #4. click on the link. go to the last few pages to see dyno run. the cam they are using is the 280H with 180cc afr heads. I would guess the bigger heads and cam would make 20 more hp and the same amount of torque at maybe 300 rpms higher.
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Old 03-19-2009, 12:11 PM
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yeah im making some changes to that build but its about the same.


thanks for the help!
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