The rule of thumb for the stock-block 302 is no more than 500 hp with the stud girdle. I'm paranoid about the limitations of the 2-bolt mains, and would use a stud girdle on any stock 302 block if the engine will see more than 300 hp or 6,000 rpm.
there is only 1 girdle on the market that is worth anything and it costs about $300. It does work. I have used them in supercharged engines producing over 600hp and 800lbft of torque. I have also used them in 8500 rpm vintage race engines. To date I have never had a problem from a girdle related failer.
A steel girdle is the way to go. The one I use in cut from a 5/8" piece if hardened billit steel. the aluminum ones will deflect and bend. Also, you can't just bolt it on. The block have to be machined and line bored with the girdle on and torqued. If you try to add it to an existing engine that hasn't been machined with it, it will distroy the bottom end of the engine.
Are they not making the aluminum girdles thick enough? It seems you can achieve the same stiffness with either material.
quote: Again, for the sake of an easy to follow comparison, we might say that "one inch" of steel plate will yield beyond its ability to recover its original shape at approximately 36k psi, and will fail at approximately 60k psi.
A "strength-equivalent" aluminum structure, having used deflection (stiffness) as the design criteria, will have been built using roughly 50% greater plate thickness. We might then say that this strength-equivalent "one and a half inch" thick aluminum plate will yield at around 51k per square inch of surface area (around 29% greater yield strength than the "equivalent" region of steel plate), and will fail at around 67.5k psi (around 12.5% greater ultimate strength than the "equivalent" region of steel plate).
Of course these broad generalizations are intended only as a way of illustrating the approximate relative strengths of the materials. However, from these considerations we can see that the aluminum vessel will have a greater overall strength than the steel vessel per square area of plate. The reason for this is that the aluminum plate will, for the sake of stiffness, be 150% the size of the steel plate.
quote: The following table gives a quick point of reference when you need the approximate thickness of aluminum sheet to use in replacing steel sheet. The designated aluminum thickness will give you about the same stiffness. Or, putting it another way, the deflection will be about equal. As a rule of thumb, plan on using an aluminum sheet about 40% thicker than steel. Since aluminum weighs only 1/3 as much as steel, this means that the equivalent aluminum sheet will weigh only half as much as the steel sheet it replaces.
I would assume an identical coefficient of thermal expansion is very important, unless the whole thing is prestressed in some complex way?
This would suggest that alloy would therefore not be the most suitable material?
I doubt that the temperature swings of the main cap area are large enough to present a problem once the engine is up to temp.
So if an alloy girdle is properly dimensioned, it should be OK.
It appears to me that the added bulk of alum required to achieve the same stiffness
benefit of a steel girdle would translate into additional time and material costs.
In other words, a steel unit should cost
significantly less, which I think Gordon mentioned. However if you are willing to spend the extra $$$ for a small weight savings, I have seen aluminum girdles running in high HP drag cars.
I have seen aluminum girdles on drag cars, they will work well because they only run hard for a few seconds at a time and everything doesn't heat up as much. An aluminum girdle in a road race engine would concern me a bit. with the hard running for 20-30 minutes or a hour or more, I feel more comfortable with a good billit steel piece.
Bill, I do sell the parts. Give me a call.