Piston rings need to be kept cool or local oil films start breaking down

But how much, I look at the water jackets and they are huge compared to the rest of the piping, surely it is more beneficial to have less water more iron in the block?

I have seen some water jackett filler products, can one fill half the block with that?

Probably, on a drag race engine that doesn't run very long.  But think of the distortion the block would probably get if you don't provide cooling to some areas.

Casting an engine block requires that wall thicknesses be controlled to minimize distortion upon casting cooling.  A thick section next to a thin section can distort dimensionally.  Cast iron costs money, so adding iron to fill a jacket would be a financial penalty.

Heat transfer is a function of flow rate, flow geometry, and heat transfer coefficients.  In the cylinder area, the apparently large voids may be required to provide enough coolant mass with lesser flow.

Drag racers that fill or partly fill the block tend to run methanol as the fuel. Methanol runs a lot cooler than petrol.

There are several purposes of filling the block. They are

1) To keep some heat in to improve thermal efficiency of the motor for a short time.
2) To improve the strengthy and avoid splitting the bores under very high stress.
3) To keep the bores round and straight so as to aid in ring seal

Regards
pat

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I know alcohol is a much cooler fuel, however you also burn much more of that, making more power, surely this creates more heat?

On drag engines they fill the whole thing, since they don't run radiators, and billet heads, however on oval racing they fill them half way as far as I know... According to Hardblok you can fill a street engine 1/3.

I don't know that 1/3 or even half does that much for you, as the cylinder pressures are much higher in the top 1/3.

In fact, the exhaust valve will be opened for tha bottom 1/4.

Alcohol runs a lot cooler in the inlet manifold, and somewhat cooler in the chamber. This equals somewhat lowwer cooling system requirements, but bigger heat difference between inlet charge and power stroke, which means more power.

Regards
pat

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

Here is a question for this discussion.  How is the size of the radiator calculated? What formulas are involved? Does anyone have the design criteria for laying out a new radiator or the factors to determine if a radiator is to small or too big for a given engine and application? When manufactures of car design a radiator for a given engine what determines the overall size and volume for one engine versus a larger or smaller engine? I am writing an article and I need references, does anyone have a web site that can provide the factors?

rob98801
I suggest you read SAE Publication SP-1541 "A Systems Approach to Engine Cooling Design".  That will tell you how the OEM's do it.

PJGD

I don't know that 1/3 or even half does that much for you, as the cylinder pressures are much higher in the top 1/3.

One thing that it does for you, which I haven't seen mentioned, is that it increases the coolant velocities in the upper (remaining) part of the jacket, and improves cooling in that region.  

It still stiffens the block, therefore increasing strength reducing chances of blow by and cylinder damage? ... I would think even half on a street engine is fine since most of the heat is in the head isn't it?

InHiding's point seems very pertinent to me.

I would fill it to 1/2 the stroke length down from the top of the deck, which is probably to about the water pump inlet holes on a SBC

Regards
pat

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.