Build 327 w/ 350-375 horsepower - Impala Tech
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post #1 of 3 (permalink) Old 12-27-2010, 02:40 AM Thread Starter
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Build 327 w/ 350-375 horsepower

I am thinking about building my original 327 in my 67' impala and am wondering if 350-375 horsepower will be able to run on pump gas and be a good daily driver. I know that you can get 500+ horse out of a 327 but many people say they are not very good for the street. Also, if i can build it for the street, what should i do to make it with that amount of horsepower?
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post #2 of 3 (permalink) Old 12-27-2010, 09:42 AM
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The easy way to get that much HP is to add cubic inches. You can stroke it to a 383 and retain good street manners.

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post #3 of 3 (permalink) Old 12-27-2010, 11:12 AM
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David is correct.

The original 350 and 375 horse 327 motors which were driven on the street (at least 500 of them) where built by the factory to race in clandestine undocumented back door factory support of super stock racers. The engines had 11.0:1 compression which is too high for pump gas today, solid Duntov 30/30 cams and a Holley carb on top of an aluminum Winters manifold. They had 2.02 inch intakes and 1.60 inch exhaust valves with special stiff valve springs using camel hump (aka Fuelie) heads. Basically everything you would find in a 302 Z/28 motor out of a 1969 Camaro only with a slightly longer stroke of the 327. You will note that all Z/28 cars (which were sold in wholesale lots) came with only a manual transmission (because a high stall torque converter had not become available in the aftermarket) and 4.11 rear gears to get a 3,200 pound Camaro moving with a rather radical motor that had little torque but lots of peak horsepower.

This is what distinguishes torque from horsepower. NASCAR guys used to paint their horsepower on their hoods to promote sales of the cars on Monday if they won on Sunday. This is what you need to push a car through air at high speed; horsepower. This is why everyone who thinks they have the biggest baddest engine (or two, or four engines) attempts to proove how much horsepower they make on the salt at Bonneville (currently they are using two jet engines out of a B-58 Huslter supersonic bomber to propel a door stop of a wingless jet across the salt at super sonic speeds).

On the street you are not reving your motor to it's maximum RPM and holding it there. You want power from off idle to about 4,500 RPM which with rear gears designed for street driving (mileage and reduced engine wear) so that you can move a heavier than a race car from a stop sign with out having to rev to the moon and side step the clutch to get your car rolling (driving like that could also attract the interest of your local constabulary). There are two ways to get a heavy load accelerated. A big engine or a big transmission with a lot of gears inside.

A semi truck has a 350 horse engine under the hood to push the air out of the way of a big box driving down the interstate at 70 mph. It has 14 or more gears to shift through to get it up to that speed. Or you could put a big truck engine under your light weight (compared to a 38 ton semi) cars hood and reap the benifit of the torque generated by the big engine. This is why big block Chevy's are so popular. They make lots and lots of torque at very low RPM and across the whole RPM range. A small block makes more horsepower per cubic inch; but there are a lot more cubic inches inside a big block motor to more than compensate for the small block's efficency advantage.

This torque is generated by the big block's increased displacement and the fact that it has a much longer stroke which magnifies the amount of force applied to the crank just like a lever arm. This is why every one loves a 383 (your 327 bored 0.030 over and a 3.75 inch stroke crank installed in place of your stock 3.25 inch stroke crank). If you think a 3.75 inch stroke makes a difference you should try a 4.500 inch stroke in a standard height big block with a 4.500 inch bore (which will give you 572 cubic inches of grins). Go to a tall deck block and the stroke can grow out to 5.25 inches for motors displacing nearly a thousand cubic inches for power that will break the axel of a Mack truck.

Go as big as you can afford for fun on the street. If you want to race it only build a high reving small block and play the rule book margins to your advantage.

Big Dave
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