Question about 1972 Chevrolet Corvette

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What is the longest stroke crankshaft can you put in a L71 chevy engine ?

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  • Chevrolet Master
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I'm a smallblock guy but the BB is pretty much an over-grown SB.
You can probably get away with a 1/2" stroke in there...The limiting factor is when the rod assembly starts getting in the way of the bottom of the cylinder bores. Big Block engines make tons of torque but are not high RPM friendly. Increasing the stroke will make even more torque but sacrifice even more top end RPM'S so, why would you want to do that?
If you are building an engine, my opinion is that you would be better served getting yourself a really good set of heads and intake manifold and matching the cam to your intended application and expected rpm range.
The key to building a strong engine is to match the parts you intend to use to what you intend as the end result. Most good aftermarket manufacturers have done extensive testing and if you actually call them and talk with an engineer, they can give you an "off the shelf" combination that will work, or, can actually develop a combination to fit your needs.
Even though there are far more available combinations to work with than ever before, one thing remains constant. That is what's called volumetric efficiency. Simply put that is what goes in has to have a way out, and, needs to be completely burned before escaping. Really good heads go a long way towards that, along with an ignition system that can light your fire.
Unless you intend to run a blower and nitromethane, where all the rules change, you are better spending your $ on making the engine breathe!

Posted on Aug 23, 2010

Testimonial: "Thanks for your sollution i was trying to get a few more cubic inches out of it my engine is a402 with a 376 stroke looking at a425 crank was wanderin"

  • Richard Scordino Aug 24, 2010

    Two things to remember....1. the further away from the center pivot, the easier it is to break something (try breaking a long stick and a short one of the same diameter). 2. The more cubic inches you have the harder it is to keep mixture flow moving.... Increasing CID can often result in more unburned waste. Therefore there comes a point where you can make lots of torque but little in the horsepower department, and will break lots of parts as well. Don't forget that a fuel engine comes apart regularly after each round, and often comes apart before it reaches the other end of the track!!!
    Sometimes your application will force you to build "grenades" but if you intend to use a combination that is exceptionally radical on the street it will eat your bank account alive!!!!

    Good luck with it!!!



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Two major things wrong with this answer: First: NEVER insert a screwdriver into the spark plug hole to find TDC. You can nick or scratch the top of the piston head, which will cause hot spots which in time will crack the piston head which in time will mean you will be paying for a major engine rebuild! Instead, use a plastic (not wire, not wood) coat-hanger cut along it's longest length. Second: You need to know more than just where TDC is for most applications. What most people really need to know is where is TDC on the COMPRESSION stroke. (The stroke where the spark plug fires, rather then the exhaust stroke where the piston pushes the waste gasses out of the combustion chamber at TDC). You do this by putting your thumb against the hole where spark plug # 1 goes. Then rotate the engine by hand (ALWAYS clockwise if you are standing in front of the vehicle, facing it) and wait until you feel a large puff of air escaping. THAT is TDC on the compression stroke. Pull off your Distributor Cap and look at where the rotor is pointing. It should be pointing to Cylinder #1. If not, you either mistook the small puff of air that happens on the exhaust stroke for the big puff of air that happens on compression, OR, your distributor is not seated right in the engine.
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