**Understanding Compression Tests: A Closer Look**

As we examine our compression gauge, we notice a few different brackets - high, moderate, and low cylinder leakage. The goal is to land in the low range, which indicates that every cylinder has some leakage due to air passing past the ring. However, it's essential to note that you'll never have a fully perfectly sealed cylinder, and that's okay.

Now, let's talk about the problem I have with this tool. When following the instructions, the compression test actually tests the cylinder at around five to seven psi, which is likely enough pressure to sort out bigger issues. However, considering the actual running conditions of each cylinder, I don't think it's sufficient pressure to suss out smaller problems.

**Overcoming the Limitations**

When using this kind of tool, I tend to disregard the instructions and perform the test with a lot more pressure. Let me show you what I mean. With the instructions, we zero the gauge, bringing it up to only about seven psi. However, I think that's not enough pressure to really test an engine.

So, what I'm going to do is ignore this gauge altogether and crank the pressure up to around 40 psi. That's enough air to start sorting out some leaks. Since we can't rely on the gauge anymore, we'll have to rely on our ears and brains to detect any issues.

**The Importance of Listening**

Now, let's talk about listening for leaks. Depending on where you may or may not have a leak, that can tell you what's going on in your engine. If you hear air leaking out your dipstick, it means that air pressure is getting past your rings and pressurizing the crankcase. That's a sign of leakage.

On the other hand, if you're hearing air leak out your intake, it means your intake valve in the cylinder you're testing for some reason is leaking. If you're hearing air coming out your exhaust or out your exhaust port, it means for some reason or another your exhaust valve is leaking.

**The Final Test**

Now that we've completed a compression test and a leak down test on our old Miata, we've determined that apparently the pistons don't have any holes in them. Our cylinder walls seem to be in decent shape, our piston rings are still there, and the valves are operational condition. That's great news!

So now that we've got these tests done, I feel pretty confident that this little engine is going to be able to deal with the boost we're going to be throwing at it. And hey, being prepared for turbo is always a good thing! Get ready for an exciting next five weeks of turbo stuff on our car.

WEBVTTKind: captionsLanguage: enso you want to turbo your car classic you want to make more power you want to make some cool noises and of course you want to make a bunch of dudes think you're super cool trust me i get it but turboing a car can seem so overwhelming there's so much to it there's so many parts how do you know what turbo's right for you how do you know if all your parts are going to work together what even is tuning and before all that most importantly is my engine even safe to turbo charge that's what we're going to be looking at today we're going to do a compression test and a leak down test so we can determine the health of this motor so we know whether or not it's gonna blow up i'm zach and this is money pit we're finally starting to do turbo stuff for the next six weeks baby are you ready thanks to ridge wallet for sponsoring this episode whoa whoa whoa i'm gonna have to see some id sir driver's license passport okay yeah i got uh you are screwed look james i gotta go it's me i gotta go host a b to b sorry pal rose's rules let's just skip on back to never never land mary poppins cause we ain't having it here okay that was easy that was easy the ridge wallet for sponsoring no no in a second you're gonna drop your wallet it's gonna ruin your life they're not going to let you onto the set and then they're going to let uncle jerry host bumper to bumper hold on what no nobody wants that i know man you got to use one of these it's a ridge wall and it's made with durable materials like titanium and carbon fiber so you only need one wallet for the rest of your life and they mean it it comes with a lifetime warranty uh ids please okay yeah i got uh wow that is durable uh here you go all right he's cool thanks for saving me future job sure jerry no problem but we can save even more people by telling them to go to ridge.com donut and if you use code donut you'll save 10 but you got to hurry because time is of the essence ah looks like i gotta go james is about to blow all his money all right first let's start with the basics of a turbo what is it and how does it work basically there are two sides to a turbo the hot side and the cold side the exhaust from your engine runs through the hot side comes in down here and it spins this little turbine in here real fast now that is on a shaft that is shared with this compressor wheel over here so when your exhaust is ripping through the hot side it's spinning the fan on the cold side which is sucking a lot of air in through this hole here compressing it in this housing and blasting it out this outlet over here essentially cramming a bunch of air into your engine now the point of cramming more air into your engine is that you can then burn more fuel and make more power but the flip side to that coin is that by making all that extra power and cramming all that extra air into the engine you're significantly going to increase your cylinder pressure and kind of the the beating that your engine is taking all the time so you got to figure out whether or not your engine can take the extra abuse that a turbo's going to dish out so here we can see some of our potential weak links in the engine potential weak links are going to be like your connecting rods your bearings the crankshaft itself the pistons or the piston rings and just looking at them like this you're not really going to be able to get a good understanding of whether or not they're strong or ready for a turbo that's where the internet comes in you're going to have to get on the forums do a little googling and if the engine you're thinking about has any weak links trust me there will be people talking about them so as long as all of the parts in our current engine are healthy we should have a great turbo car pretty soon but we're gonna have to do those tests and see whether or not that thing actually is healthy all right so we're gonna be performing two tests on the miata's engine here first we're gonna do a compression test and then later we'll do what's called a leak down test what a compression test is is a pretty quick and easy way to determine how well each of the cylinders in your engine are making compression your engine relies on the piston and your whole combustion chamber to compress the air fuel mixture in order to burn it efficiently and make good power so with a compression test you can quickly assess the health of each of your cylinders in terms of compression now you can't necessarily pinpoint what the issue is if you do see one but ideally you won't see an issue and then you'll just know everything's great so in order to perform our compression test i've got the engine warm we just turned it off so it's nice and warm next i'm going to go put the battery on a charger because we need to crank the engine a bunch of times and if you don't have your battery on a charger you can kill your battery which makes the test uh ineffective all right so now that we've got the battery on charge it's time to go back up under the hood we're going to pull out the spark plugs and we're going to disconnect our fuel system and our ignition system all together so now we're ready to perform our compression test so i've got my compression test kit here straight from the harborist of freights i think it costs about 40 bucks so not too bad something nice to have around to get this ready for the miata we've got our gauge we've got it connected to the hose that it comes with and then it's got a series of adapters depending on the size your spark plugs i believe this is the right one for us so we're gonna put this on the end of our unit here nice and hand tight and then we're just gonna go ahead and thread it in hole number one get that puppy nice and tight in there now the only thing left to do is do the test so i'm gonna get in the car remember we've got the battery charger on and i'm also gonna this is very important i'm gonna hold the throttle all the way open wide open throttle for a compression test so that there's no reason that the cylinder you're testing can't get air into it it should be able to get as much as it needs so wide open throttle while you do the test 10 seconds per hole then we'll see what the number reads on the gauge can i make a prediction sure i think cylinder 4 is going to be the lowest yeah me too that's my concern miata things baby cylinder one what'd we get about 125 or 130 yeah right in between the two we'll call it 130. so you might be wondering is that good is that bad well it's kind of tough to say i mean generally speaking you're going to want to see over 100 psi in any gas engine the higher the better but at the same time the specific number on the gauge isn't the end-all be-all really what i'm going to be looking for here is to make sure that all four cylinders are roughly within about 10 percent of each other in terms of pressure if one strays farther away from the other three i know there's probably an issue with that cylinder so let's keep going and see what the rest of these cylinders make and then we can compare them to each other and then kind of get a general sense of how this thing is crank this thing for 10 seconds write down the number cylinder three you're up next so cylinder four here we go one twenty flat whoa 130. well that's good news this puppy must be healthy i have overheated it a few times okay and on the miata cylinder 4 tends to get extra hot so i was actually worried about cylinder 4 but so far so good seems to be making compression so we know it must be pretty healthy in there it's time to do a leak down test it's a little bit more accurate but a little bit more involved and you need an air compressor luckily i have one again you're going to want to do this on a warm engine if you can if your engine's running in this test we're not going to rely on the engine to make compression we're going to give the engine compression with our air compressor so the first thing we need to do is get the engine and cylinder one specifically to top dead center so to do that there's some marks on the pulley that i can use to visually check for top end center but i'm also going to drop something into cylinder one so i can visually see when it's at peak top dead center and that should be good enough all right we've got cylinder one at top dead center all the valves should be closed which means it should be able to hold compression right now so we're going to connect our tester to the spark plug hole and introduce our own compressed air see if we have any issues this is our adapter spark plug threads very similar to the compression tester thingy okay this is from harbor freight i forget how much it costs probably like 50 or so dollars we're gonna go through it using their instructions real quick so the first thing i want you to do is back this air regulator all the way clockwise all the way to the left so that's what we've got then connect your compressed air at no more than 100 psi so we are at 100 psi okay so now we can see our gauge is up there you see that little zero where it says set that yellow band the goal now is to turn this clockwise until we hit zero we want to zero this gauge out and it's important that when you do this you do it pretty accurately and try not to go past zero you wanna sneak right up on it perfect so now all we got to do is connect this to our spark plug hole and then we'll get a reading a little cumbersome okay so now on our gauge here we've got a few different brackets we've got high moderate and low cylinder leakage obviously we want to land in the low range and look at that we do at about 20 percent now every cylinder you're going to have some leakage some air will get past the ring so you're never going to have a fully perfectly sealed cylinder that's okay you just want to go and land in that low bracket but the problem that i have with this is that when you follow the instructions this actually tests the cylinder at about five to seven psi which if you have a big issue that's probably enough pressure to sort it out but that's such low pressure in comparison to what each cylinder sees when it's actually running that i don't think it's enough pressure to really suss out smaller problems so when i use this kind of tool i kind of throw the instructions out the window and i'll do the same exact thing but with a lot more pressure let me show you so with the instructions we zero this out which brings our gauge over here up to only about seven psi and that i just don't think is enough pressure to really test an engine so what i'm going to do is eventually ultimately ignore this gauge altogether and i'm going to crank the pressure up over here so that we're letting let's say 40 psi through i think that's enough air to really start sorting out some leaks but then since we're not going to be able to rely on the gauge we got to be relying on our ears and our brains so we'll explain that in a sec okay so now we've got about 35 psi in cylinder one right now so now what you want to do is listen for leaks and depending on where you may or may not have a leak that can tell you what's going on in your engine so if you hear air leaking out your dipstick that means air pressure is getting past your rings and pressurizing the crankcase that's where your dipstick goes pretty quiet but if you're hearing air leak out your intake that means your intake valve in the cylinder you're testing for some reason is leaking if you're hearing air coming out your exhaust or out your exhaust port if you have your manifold taken off that means for some reason or another your exhaust valve is leaking if you're getting bubbles coming out of your coolant overflow tank or your radiator that means your head gasket's leaking and really all we're doing here as we test all four cylinders is listening for anything that stands out you know a little bit of you know a little bit of leakage past the rings coming out your dipstick is normal but if cylinder three makes a bunch of noise coming out the dipstick well then cylinder 3 might have a problem with the rings we're going to go ahead and do that to all of our cylinders make sure we don't have any issues based on our compression test i don't think we're going to have any but just for good practice we're gonna check this thing out okay so we've completed a compression test and a leak down test on the old miata and have determined that apparently the pistons don't have any holes in them our cylinder walls seem to be in decent shape our piston rings seem to still be there and the valves are in operational condition so that's great so now that we've got these tests done i feel pretty confident that this little engine is going to be able to deal with the boost we're going to be throwing at it because again doing these tests was really just a precursor to being able to do this you know we've been getting ready to turbo this thing for a while and now it's really time now we've got the engine tested we are ready to go full go at the turbo stuff we're gonna be doing turbo things on this car for the next five weeks that's right five weeks of turbo stuff so get ready thank you so much for watching this video come back next week and the next several weeks after that to get into the turbo stuff with me don't forget to follow me on instagram zackjob and follow donut donutmedia i'll see you guys for an exciting next weekso you want to turbo your car classic you want to make more power you want to make some cool noises and of course you want to make a bunch of dudes think you're super cool trust me i get it but turboing a car can seem so overwhelming there's so much to it there's so many parts how do you know what turbo's right for you how do you know if all your parts are going to work together what even is tuning and before all that most importantly is my engine even safe to turbo charge that's what we're going to be looking at today we're going to do a compression test and a leak down test so we can determine the health of this motor so we know whether or not it's gonna blow up i'm zach and this is money pit we're finally starting to do turbo stuff for the next six weeks baby are you ready thanks to ridge wallet for sponsoring this episode whoa whoa whoa i'm gonna have to see some id sir driver's license passport okay yeah i got uh you are screwed look james i gotta go it's me i gotta go host a b to b sorry pal rose's rules let's just skip on back to never never land mary poppins cause we ain't having it here okay that was easy that was easy the ridge wallet for sponsoring no no in a second you're gonna drop your wallet it's gonna ruin your life they're not going to let you onto the set and then they're going to let uncle jerry host bumper to bumper hold on what no nobody wants that i know man you got to use one of these it's a ridge wall and it's made with durable materials like titanium and carbon fiber so you only need one wallet for the rest of your life and they mean it it comes with a lifetime warranty uh ids please okay yeah i got uh wow that is durable uh here you go all right he's cool thanks for saving me future job sure jerry no problem but we can save even more people by telling them to go to ridge.com donut and if you use code donut you'll save 10 but you got to hurry because time is of the essence ah looks like i gotta go james is about to blow all his money all right first let's start with the basics of a turbo what is it and how does it work basically there are two sides to a turbo the hot side and the cold side the exhaust from your engine runs through the hot side comes in down here and it spins this little turbine in here real fast now that is on a shaft that is shared with this compressor wheel over here so when your exhaust is ripping through the hot side it's spinning the fan on the cold side which is sucking a lot of air in through this hole here compressing it in this housing and blasting it out this outlet over here essentially cramming a bunch of air into your engine now the point of cramming more air into your engine is that you can then burn more fuel and make more power but the flip side to that coin is that by making all that extra power and cramming all that extra air into the engine you're significantly going to increase your cylinder pressure and kind of the the beating that your engine is taking all the time so you got to figure out whether or not your engine can take the extra abuse that a turbo's going to dish out so here we can see some of our potential weak links in the engine potential weak links are going to be like your connecting rods your bearings the crankshaft itself the pistons or the piston rings and just looking at them like this you're not really going to be able to get a good understanding of whether or not they're strong or ready for a turbo that's where the internet comes in you're going to have to get on the forums do a little googling and if the engine you're thinking about has any weak links trust me there will be people talking about them so as long as all of the parts in our current engine are healthy we should have a great turbo car pretty soon but we're gonna have to do those tests and see whether or not that thing actually is healthy all right so we're gonna be performing two tests on the miata's engine here first we're gonna do a compression test and then later we'll do what's called a leak down test what a compression test is is a pretty quick and easy way to determine how well each of the cylinders in your engine are making compression your engine relies on the piston and your whole combustion chamber to compress the air fuel mixture in order to burn it efficiently and make good power so with a compression test you can quickly assess the health of each of your cylinders in terms of compression now you can't necessarily pinpoint what the issue is if you do see one but ideally you won't see an issue and then you'll just know everything's great so in order to perform our compression test i've got the engine warm we just turned it off so it's nice and warm next i'm going to go put the battery on a charger because we need to crank the engine a bunch of times and if you don't have your battery on a charger you can kill your battery which makes the test uh ineffective all right so now that we've got the battery on charge it's time to go back up under the hood we're going to pull out the spark plugs and we're going to disconnect our fuel system and our ignition system all together so now we're ready to perform our compression test so i've got my compression test kit here straight from the harborist of freights i think it costs about 40 bucks so not too bad something nice to have around to get this ready for the miata we've got our gauge we've got it connected to the hose that it comes with and then it's got a series of adapters depending on the size your spark plugs i believe this is the right one for us so we're gonna put this on the end of our unit here nice and hand tight and then we're just gonna go ahead and thread it in hole number one get that puppy nice and tight in there now the only thing left to do is do the test so i'm gonna get in the car remember we've got the battery charger on and i'm also gonna this is very important i'm gonna hold the throttle all the way open wide open throttle for a compression test so that there's no reason that the cylinder you're testing can't get air into it it should be able to get as much as it needs so wide open throttle while you do the test 10 seconds per hole then we'll see what the number reads on the gauge can i make a prediction sure i think cylinder 4 is going to be the lowest yeah me too that's my concern miata things baby cylinder one what'd we get about 125 or 130 yeah right in between the two we'll call it 130. so you might be wondering is that good is that bad well it's kind of tough to say i mean generally speaking you're going to want to see over 100 psi in any gas engine the higher the better but at the same time the specific number on the gauge isn't the end-all be-all really what i'm going to be looking for here is to make sure that all four cylinders are roughly within about 10 percent of each other in terms of pressure if one strays farther away from the other three i know there's probably an issue with that cylinder so let's keep going and see what the rest of these cylinders make and then we can compare them to each other and then kind of get a general sense of how this thing is crank this thing for 10 seconds write down the number cylinder three you're up next so cylinder four here we go one twenty flat whoa 130. well that's good news this puppy must be healthy i have overheated it a few times okay and on the miata cylinder 4 tends to get extra hot so i was actually worried about cylinder 4 but so far so good seems to be making compression so we know it must be pretty healthy in there it's time to do a leak down test it's a little bit more accurate but a little bit more involved and you need an air compressor luckily i have one again you're going to want to do this on a warm engine if you can if your engine's running in this test we're not going to rely on the engine to make compression we're going to give the engine compression with our air compressor so the first thing we need to do is get the engine and cylinder one specifically to top dead center so to do that there's some marks on the pulley that i can use to visually check for top end center but i'm also going to drop something into cylinder one so i can visually see when it's at peak top dead center and that should be good enough all right we've got cylinder one at top dead center all the valves should be closed which means it should be able to hold compression right now so we're going to connect our tester to the spark plug hole and introduce our own compressed air see if we have any issues this is our adapter spark plug threads very similar to the compression tester thingy okay this is from harbor freight i forget how much it costs probably like 50 or so dollars we're gonna go through it using their instructions real quick so the first thing i want you to do is back this air regulator all the way clockwise all the way to the left so that's what we've got then connect your compressed air at no more than 100 psi so we are at 100 psi okay so now we can see our gauge is up there you see that little zero where it says set that yellow band the goal now is to turn this clockwise until we hit zero we want to zero this gauge out and it's important that when you do this you do it pretty accurately and try not to go past zero you wanna sneak right up on it perfect so now all we got to do is connect this to our spark plug hole and then we'll get a reading a little cumbersome okay so now on our gauge here we've got a few different brackets we've got high moderate and low cylinder leakage obviously we want to land in the low range and look at that we do at about 20 percent now every cylinder you're going to have some leakage some air will get past the ring so you're never going to have a fully perfectly sealed cylinder that's okay you just want to go and land in that low bracket but the problem that i have with this is that when you follow the instructions this actually tests the cylinder at about five to seven psi which if you have a big issue that's probably enough pressure to sort it out but that's such low pressure in comparison to what each cylinder sees when it's actually running that i don't think it's enough pressure to really suss out smaller problems so when i use this kind of tool i kind of throw the instructions out the window and i'll do the same exact thing but with a lot more pressure let me show you so with the instructions we zero this out which brings our gauge over here up to only about seven psi and that i just don't think is enough pressure to really test an engine so what i'm going to do is eventually ultimately ignore this gauge altogether and i'm going to crank the pressure up over here so that we're letting let's say 40 psi through i think that's enough air to really start sorting out some leaks but then since we're not going to be able to rely on the gauge we got to be relying on our ears and our brains so we'll explain that in a sec okay so now we've got about 35 psi in cylinder one right now so now what you want to do is listen for leaks and depending on where you may or may not have a leak that can tell you what's going on in your engine so if you hear air leaking out your dipstick that means air pressure is getting past your rings and pressurizing the crankcase that's where your dipstick goes pretty quiet but if you're hearing air leak out your intake that means your intake valve in the cylinder you're testing for some reason is leaking if you're hearing air coming out your exhaust or out your exhaust port if you have your manifold taken off that means for some reason or another your exhaust valve is leaking if you're getting bubbles coming out of your coolant overflow tank or your radiator that means your head gasket's leaking and really all we're doing here as we test all four cylinders is listening for anything that stands out you know a little bit of you know a little bit of leakage past the rings coming out your dipstick is normal but if cylinder three makes a bunch of noise coming out the dipstick well then cylinder 3 might have a problem with the rings we're going to go ahead and do that to all of our cylinders make sure we don't have any issues based on our compression test i don't think we're going to have any but just for good practice we're gonna check this thing out okay so we've completed a compression test and a leak down test on the old miata and have determined that apparently the pistons don't have any holes in them our cylinder walls seem to be in decent shape our piston rings seem to still be there and the valves are in operational condition so that's great so now that we've got these tests done i feel pretty confident that this little engine is going to be able to deal with the boost we're going to be throwing at it because again doing these tests was really just a precursor to being able to do this you know we've been getting ready to turbo this thing for a while and now it's really time now we've got the engine tested we are ready to go full go at the turbo stuff we're gonna be doing turbo things on this car for the next five weeks that's right five weeks of turbo stuff so get ready thank you so much for watching this video come back next week and the next several weeks after that to get into the turbo stuff with me don't forget to follow me on instagram zackjob and follow donut donutmedia i'll see you guys for an exciting next week