Reply to "If you liked the 3 deuce intake manifold, you'll love this ..."

I agree that there is issue with aluminum blocks and dimensional growth but would not agree that the problematic issue is change in compression ratio or that the growth is .030".

The issue relates to maintaining appropriate lash on solid lifter mechanical valve train. The growth that is cited can be attributed to the difference in the coefficient of thermal expansion between the alloy block and (primarily) the push rods. It's true that the same occurs with the rotating assembly and CR, but as can be seen from the following discussion, this is less of an issue.

The range of coefficient of expansion in these materials is 8 to 13 microstrain, depending upon the materials in question, for a maximum difference in expansion coefficient of 5 microstrain; that is to say, at most .000005"/in/degree F x the length of dissimilar materials. In reality, I believe this is actually closer to 3 not 5 micro strain. –Those who argue 5 bias everything in the direction of more growth.

At any rate, if you say a push rod is at most 9" and the change in temperature is around 170 F (70 degree day going to 240 average engine temp), doing the math at 5 microstrain you'll get growth on the order of .0076". Yup. At most .008" or so. Probably more like .005” in reality.

Not much to worry about as far as compression ratio but not as pleasant of a thought for those running high lift solid cams and large rate valve springs. Set your valve train cold and you’re potentially loose or at minimum light. Set it hot (as is the practice) and be very tight cold.

It's certainly manageable but the issue is higher valve train loading at cold and the tendency to bend push rods when warming up, especially if you hammer it straight out of the shed.

You may be wondering: Why don't all modern alloy engines today have the same problem? Answer: some are overhead cam and all are hydraulic valve train. What do racers do? It's not uncommon to preheat engines with external heating and circulation prior to firing.

IMO, with the hydro roller grinds available today, there's plenty of power to be had with them when you consider the practical issues for street engines. If you don't mind maintaining mechanical valve train, to each his own. Just another one of the many trades and compromises that must be addressed in balancing the nature of race and street engines.

BTW, another “growth” issue exists for those of us running aluminum heads on iron blocks. This can be on the order of .025" or so because it’s over a much greater distance. The heads grow more fore and aft than the block and tend to work your head gaskets. But that’s another topic.

Kelly