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Old 03-28-2006, 09:33 AM
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Caddy 472 with 10.1 pump gas

Will a 1970 stock caddy engine with 10.1 run on pump gas?

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Old 03-28-2006, 12:59 PM
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"70 Caddy C/R

In my motor manual the 472 caddy engine was born with a 10:1 compression ratio. In the '70's came the muscle car era and big engine power. Some of this power was derived from increased compression ratio which in turn was possible because of increased camshaft lobe duration, which in turn effectively lowers the actual dynamic C/R 1-1/12 points. In other words, the engine does not actually see 10:1 when running but more like 8.5-9.0:1. Good gas will work fine here if the timing is stock. A calculated "Static" ratio formula never gives the dynamic ratio but is always higher by 1 to 1-1/2 points.

The bottom line is the "Cranking Pressure"; fresh battery, carb. blocked wide open, ignition disabled, all sparkplugs removed. Connect compression guage to one cylinder and crank engine about five rotations. Observe reading and go to next cylinder. Record all readings and compare. They should all be within 15 lbs. of each other to indicate good condition. For preimum pump gas (92 octane), no cylinder should exceed 170 lbs. This 170 lb. cranking rule removes all the confusion about max. C/R on prem. pump gas. As you must know, Detonation is the problem to fear.

Caddilac's increased intake cam lobe duration closes that valve later as piston rises on compression stroke, this reduces the effective compressed volume of the cylinder thus lower compression ensues. The exaust valve hasn't fully closed either (overlap), this is used to help flush spent exaust gasses from the cylinder. You simply need to study up on camshafts and how they work in relation to the piston stroke to fully understand this delicate function as it's too much to write about here (intake & exaust reversion for example).

As a bonus I will tell you that correct trans. and rearend gearing is very critical to a competitive run. This is an involved issue also. Do yourself a favor and study up on this. KNOW WHAT YOU ARE DOING AND THE OTHERS WILL BE SCRATCHING THEIR HEADS. Pick your desired top speed and go from there using available calculator programs online.

Tom
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Old 03-28-2006, 01:12 PM
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depends on your altitude.I live at 6500 ft.I run 11:1 in my 427 on 91 octane gas with the stock .075 x .047 needles and .110 jet but change to .070 x .042 needles with the stock .110 jets using 91 octane gas(to control detonation at 3500) on my Edelbrock 750 carb and a bottle of Prestone 0 to 60 octane booster per tank of 91 octane for a total of 101 when I come of the mountian to the less than 2000ft altitude of Las Vegas for club cruises.I hope this helps.You can avoid the hassle if you just run 9:1 compression
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