1958 392 Hemi 10.5:1 compression - blower - Hot Rod Forum : Hotrodders Bulletin Board
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Old 08-10-2008, 06:54 PM
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1958 392 Hemi 10.5:1 compression - blower

Hey guys,

I came across a rebuilt 1958 392 Hemi that was already complete. I jumped on the deal. I already had one but it needed to be rebuilt.
Here are the specs on the engine I bought.
This motor was rebuilt and has a .030 overbore mild lope cam and adjustable Pushrods. This was thoroughly rebuilt with new valves , springs , cam, pistons 10.5:1, pushrods, lifters, oil pump ,timing chain, copper head gaskets, and all bearings with the best available. The block was align bored, decked /trued , crank was mag'd , polished, drilled for 1/2 flywheel bolts and heads were re surfaced. No money was spared in this rebuild. The motor is already broken in and currently has less then 5,000 miles since rebuild this was built for a cruiser so it has never been raced .

Now I know a blower motors are usually 8.5:1 compression. I would like to save a lot of time and grief by not tearing down this motor to get 8.5:1 compression. How much boost can I run with 10.5:1 compression? If possible, which size pulleys would be required for motor and 671 blower (tooth count on pulleys) to achieve desired boost.
Thanks for the input.

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Last edited by rattub; 08-12-2008 at 12:38 PM.
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Old 08-10-2008, 09:03 PM
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I would say NO BOOST at that compression!

Sorry, but I would replace the pistons if a blower is what you want, why not run it the way it is for now?
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Old 08-10-2008, 09:37 PM
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Its a lot less hassel to put the right pistons in it now than later.

Shane
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Old 08-10-2008, 09:50 PM
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You could always run a dummy blower.
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Old 08-10-2008, 10:14 PM
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According to Blower Drive Service, you can run 2 lbs with 92 octane fuel.....
http://www.blowerdriveservice.com/techcharts.php
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Old 08-10-2008, 11:33 PM
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You can run quite a bit of boost on a high compression engine, if you run high octane fuel. eg: methanol, ethanol 110 to 114 octane racing gasoline.

Water-Methanol injection.
www.snowperformance.net
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Old 08-11-2008, 12:25 AM
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Why not run E-85 with what you have .??? It's rates about 105 octane. It should run great. It was $2.85/ gal today.
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Old 08-11-2008, 12:36 AM
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.............

Last edited by rattub; 08-12-2008 at 12:38 PM.
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Old 08-11-2008, 08:26 AM
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Even 2 pounds of boost will get your attention on the street especially with the compression. You really should get something like an MSD with a retard function related to boost.. 450+ would not be unreasonable.
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Old 08-12-2008, 03:45 PM
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Re: pistons

If those are PAW/egge/hot heads cast pistons do not run a blower on them even at 2 lbs of boost. 392 & 354 (early Chrysler) hemi forged pistons are "pricey" roughly $600-700.00. If you plan on running more boost than 2% you may wish to run "o-rings"
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