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Do I Have a Long or Short Water Pump?

Water Pumps and Cooling

Plenty of engines were built with two different water pump heights. Knowing which one is on your engine is what decides whether a set of pulleys, brackets or a full accessory drive will line up.

Overview

Short Answer

Measure from the face the pulley bolts to, back to the surface where the pump meets the engine. On a small block Chevy a short pump is about 5 5/8 inches and a long pump about 7 inches. Big block Chevy runs 5 3/4 and 7 1/4. Measure it, do not assume it from the year.

What long and short actually mean

The difference is how far the pump holds the pulley away from the block. A long pump pushes the whole accessory drive further forward, a short pump keeps it tucked back. Nothing else about the pump changes, but that one dimension moves every pulley, bracket and belt in front of the engine.

A short pump is usually chosen for clearance. Pulling the drive rearward buys room between the accessories and the radiator or core support, which matters on a tight engine bay or a car with a big radiator. A long pump trades some of that clearance for a more compact, factory style layout and is what most later factory engines used.

How to measure yours

One measurement settles it, and you can take it with the pump on or off the engine.

Find the two surfaces. One is the flat face the pulley bolts against, on the front of the pump hub. The other is the surface where the pump mates to the engine, which is the gasket face.

Measure straight between them. Lay a straight edge across the pulley mounting face and measure square back to the gasket surface. If the pump is still on the engine you are measuring to where the pump meets the block, so hold the straight edge against the hub and run a tape back from it.

Compare against the numbers below. You are looking for roughly an inch and a half of difference between the two types, so there is no ambiguity once you have the measurement.

Measuring water pump height on an engine with a straight edge and tape measure

On the engine: straight edge across the pulley mounting face, tape back to where the pump meets the block.

Measuring water pump height on a bench with a straight edge and tape measure

Off the engine is easier. Same two surfaces, straight edge on the hub face, tape down to the gasket surface.

Chevy small block and big block numbers

These are the two engine families we get asked about most, and the figures are well established. All of them are measured from the gasket surface to the pulley mounting hub.

Small block Chevy short pump: about 5 5/8 inches. Used on cars through 1968 and light trucks through 1972.
Small block Chevy long pump: about 7 inches. Used on cars from 1969 and light trucks from 1973.
Big block Chevy short pump: about 5 3/4 inches.
Big block Chevy long pump: about 7 1/4 inches.

There is one oddity worth knowing. Corvettes from 1971 to 1982 used a short pump at about 5.795 inches rather than the usual 5 5/8. It is still a short pump, but if you measure one and get a number that does not quite match, that is probably why.

Use the years as a sanity check rather than an answer. These engines have been apart and rebuilt for fifty years, and a 1972 block with a 1969 pump on it is not unusual. The measurement is what counts.

It is not just Chevy

Plenty of engine families were built with both heights, so this is worth checking whichever engine you are running. The ones that commonly come both ways are small block Chevy, big block Chevy, Oldsmobile, Pontiac, small block Ford and AMC.

The measurement method is the same on all of them. Only the numbers differ, so measure yours and tell us what you got rather than working from the engine family alone.

Why it matters for what you order

The water pump sets the plane the rest of the accessory drive works from. Order pulleys or brackets for the wrong pump height and nothing will line up, because everything in front of the engine has been shifted by an inch and a half.

Our pulley and bracket sets are listed by pump height for exactly this reason. You will see short water pump and long water pump versions, usually shortened to SWP and LWP. Pick the one that matches what you measured.

If you are running one of our kits and are not sure what it was built around, send us your order number and we will tell you.

We build kits for most of these variations, long and short, across the engine families listed above. If you are not certain which one you need, or you measure something that does not match, give us a call at 651.356.8593 and we will work it out with you before you order.