Tumble Fixture

Swirl and Tumble are 2 different types of motion the air/fuel charge can exhibit as it enters the cylinder on the intake stroke.  Generally, swirl is measured on 2 valve engines and tumble is measured on 4 valve engines.  However, if you are looking for that extra 1-2% power, understanding idle stability or engine efficiency, you would want to measure both.  Then you can completely measure the effects of different Head modifications.

Illustration of Swirl Motion               Illustration of Tumble Motion

(+ directions shown are not necessarily an industry standard)

Swirl meter is now the smaller USB swirl meter.  The swirl meter produces a positive swirl (tumble) reading when it spins clockwise when viewed from the top.  In this picture, the top of the swirl meter faces the tumble fixture on the right.  For a typical 4 valve head to read a positive swirl number in this picture, the intake ports would have to be facing the operator, and the exhaust port would be facing back, toward the flow bench.

Close up of optional Swivel Adapter, to measure tumble in 360 degrees of head orientation.  This pic also shows head bolt adapter plate with special nuts to attach head.  The 2 larger nuts are to locate the head precisely like dowel pins.  You will use much smaller diameter bolts than the head bolts to hold the head in place.  Note pointer on right side for measuring degrees of turn (swivel).  

You need our Swirl Meter to measure tumble.  The tumble fixture lets you mount the swirl meter sideways so you can measure tumble motion.  Tumble fixtures are all custom for different bore sizes and head bolt patterns, and are quoted individually.  Several options are available for the tumble fixture, including:

• Individual, inter-changeable bore sleeves and head bolt adapters so one tumble adapter can be used for several engine designs.

• Piston Adjuster to see if Piston Dome/top shape influences tumble.

• Swivel Adapter to check tumble at several different orientations (and it changes "big time" in different orientations).

Call 248-473-9230 or email  sales@performancetrends.com  to discuss these options.