Summary

00:00 - Troy has asked, how much blow by is too much blow by? Is the best way to check by using a leak down tester? OK so really this question is a little bit hard to answer because it's going to depend on the particular engine.
00:12 Remembering that our ring end gap is going to depend on the sort of engine we're building, whether it's naturally aspirated or turbocharged.
00:20 And also when we're talking about turbocharged engines, we're generally, we will have more blow by.
00:27 It's inevitable we're going to end up with that blow by and as we increase the boost pressure, we increase the blow by level.
00:33 So I wouldn't say there's such a thing as too much blow by.
00:36 it's all about understanding and controlling that blow by which is why in very high boost and turbocharged engines, quite often there's a lot of work goes into increasing the size of the breathers from the rocker cover and the crank case in order to evacuate that blow by out of the engine.
00:53 There are a couple more things I'll add into this though.
00:56 It is possible to measure blow by.
00:59 There are actual gauges, it's not something I've used before.
01:02 Something that I do incorporate in some of our high boost drag engines is a crank case pressure sensor.
01:09 So in a round about way this kind of gives us an idea of how much blow by we've got.
01:13 And what we can do is use that to monitor the engine health.
01:16 So we've got data on that pressure sensor, when the engine was freshly built.
01:21 We can watch as the ring seal starts to deteriorate and as our blow by increases, and that pressure sensor will tell us when the engine is starting to suffer a little bit there.
01:34 By using a leak down test, as you've also commented there, yeah leak down testers or compression testers and leak down testers are really powerful tools.
01:43 A compression tester will give you a rough idea of the seal inside a cylinder.
01:48 However it's not gonna tell you where the problem lies if you are low in compression.
01:54 A leak down tester on the other hand can allow you to very specifically pinpoint whether the leakage is coming back past the valves, maybe into the water jacket to the cooling system, through a head gasket leak, or also down past the rings, so that'll give you an idea if your ring seal is problematic.
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