Techie gurus, leak down tests,

[AdamT]

Hi guys,

Just had a leak down test done on the r turbo by Ruf, and it achieved 6% on all cylinders.

What is a leak down test exactly, and is 6% good for a car with 50,000miles?

thanks very much

adam

[Silver993tt]

If RUF did the test, didn't they say if was within spec or not?

[2something]

An old thread that might or might not be useful:

http://www.pistonheads.co.uk/gassing/topic.asp?h=0...

[phelix]

A quick and dirty explanation...

A leakdown test uses an air compressor to force a measured amount of air into the cylinder when it's at top dead centre and measures the amount of air that leaks out past the rings (worn rings or cylinder bores), valves (burnt seats or loose guides) and head gasket. Each cylinder is done in turn. Consistent numbers are important more so than the absolute numbers because they can vary somewhat depending upon the equipment used. A consistent 6% indicates a strong engine that's still got loads of mile left.

It's said that turbo engines can have fairly high leakdown numbers without much change in performance as the turbos just keep stuffing air in until the inlet valve closes so for each cylinder's intake, compression and ignition stroke the "leak" is only "relevant" for a shorter period of time than for a normally aspirrated engine.

For comparison my 993tt engine had numbers of 10-12% on 5 cylinders and 26% on 1. All cylinders had worn exhaust valve guides and the one high one had a piece of swarf (apparently factory installed but I couldn't find the option code) caught between the top of the barrel and the head that was causing the compression leakage.

Edited by phelix on Thursday 2nd August 10:01

[AdamT]

Thanks Phelix, much appreciated