ex-blower motor,pistons dished.... question. - Hot Rod Forum : Hotrodders Bulletin Board
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Old 04-18-2004, 01:00 AM
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ex-blower motor,pistons dished.... question.

recently bought a '49 gmc truck from a guy at work....he was running a cragar(old school) blower on it. 350 sbc, blower was too big to run hei dizzy,driveability sucked, so i decided to go w/ a complete over-haul of the top half. new intake( edelbrock performer eps), new carb.(edelbrock 600cfm),new dizzy(factory gm hei),and rebuilt heads( 1.940" I 1.500"E). okay so much for the plot-line! question is : blower motor was running 8.00:1 compression ratio w/ the pistons dished approx. 20cc (or so he said) will i be experiencing a sluggishness or a noticeable lack of power w/ the compression ratio being as low as it is? when the heads were re-built no decking of the mating surface was reported, which if that had been done would have reduced the combustion chamber size (i believe they're 76cc's). anyone think i'll need to drop the bottom end and replace the dished w/ flat-tops? this is not intended as a race truck, by any stretch....just want it to be able to get out of it's own way when i need to!! thanks for any and all responses....

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Old 04-18-2004, 03:01 AM
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you have ended up with a missmatched engine, you should either run forced induction like this setup (click here) or raise the compression. i dont have to tell anyone what i would prefer, but you could opt to install some flat tops or small dome pistons and a non-blower cam.. i actially think the price will be about the same for the two options
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Old 04-18-2004, 04:28 AM
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As Duce said your going to have to make a decision and build from there. several companies make supercharger or turbo charger set ups that are very street-able and your engine is already set up for that. To go normally aspirated your looking at a complete tear down and rebuild to get the compression 9.5:1-10:1 and a cam change to work with your new set up. No matter what you decide I would look into getting a set of 2.02 x 1.70 x 64cc heads as what you have now just don't flow all that well and your heads ultimately make or break your ability to make power in a small block motor.
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Old 04-18-2004, 12:01 PM
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Since you already have the bottom end for a blown application, why not use a blower of some kind? I might be a little biased. What made it have streetabilty/drivability issues? There are plenty of small bodied distributors out there that are much better than an HEI. If you still have the blower set-up and need help/suggestions tuning it, I think I would give it another shot.

If you are dead set on getting rid of the blower, then you will need to change the pistons or you will have a slug, you may be able to swap the heads for a set with small combustion chambers to get your compression up. Heads are more expensive but, are easier to change. Actually I know you can do it with a head change. Now you have to figure out what cam is in the thing, if it is a blower grind, then you would probably be better off with a different cam. If the engine was a mild blown engine then chances are it just has an RV cam in it and depending on your goals that might be just fine.


Royce
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Old 04-21-2004, 11:48 PM
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will it turn the tires? maybe that's easier......
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Old 05-02-2004, 09:47 PM
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posted an update on dilema...

i've decided to rebuild the engine starting w/ a new block (hey, new to me!) went w/ a '80-'85 style of block to retain the old flexplate,......and also to utilize the passenger side oil dipstick on these years of blocks. not much room for the oil dipstick on the drivers side w/ the steering linkage and all. got a block,all machine work will be done...freeze plugs installed,cam bearings,crank(1010) w/ the wrist pins installed on the rods w/ a domed piston that will give me the 9.0-1 c.r. i'm looking for...unfortunately i've got 76cc heads, so the domed hypereutectic pistons along w/ the proper head gasket will hopefully give me the "balance" that i was looking for in relation to the top end parts i've already purchased,...and the cam the previous owner had installed. supposedly a early Lt-1 cam profile.... so i guess it's back to the drawing board in getting this motor together.....i was just a couple of hairs shy of being able to fire up the engine when i started having my misgiving's.....luckily i had'nt put in the fresh oil and the anti-freeze yet!!

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