125 | How to gap Piston Rings
One of the most critical tasks when it comes to assembling an engine is choosing and correctly setting your ring end gaps. In this webinar we’ll discuss what you need to know to choose your ring end gaps, and how to perform your ring gapping to get the best and most consistent results.
It's Andre from the High Performance Academy. Welcome to this webinar, where we're going to be discussing the techniques used to gap file fit piston rings. So what we're going to be doing here is we're going to be looking at what we need to do, why we need to actually file the piston ring end gap. And what exactly it is we're trying to achieve. Before we get into that though, I think it's important to get a better understanding of what the rings do.
And really when it comes down to it, the performance of our engine is really heavily hinged on how well the piston rings seal against the cylinder walls. It's really the key point there, it's going to affect the amount of cylinder leakage available, the blow by past the rings, the oil consumption, and that's also going to have an effect on the amount of power our engine can make. So really as far as our tasks go when we're building an engine or assembling a performance engine, really everything is focused on making the best possible seal between the rings and the bore walls. In terms of the rings, commonly when we're talking about the performance engines that most of us will be running, we're talking about a piston that contains three rings. It contains a top ring and a second compression ring.
The two top rings are both really primarily there for compression purposes. And then below that we'll have an oil control ring. So their tasks are a little bit broken down though. The top ring is primarily for containing the cylinder compression only, or the cylinder pressure I should say only. Of course because there is an end gap in our piston ring, some cylinder pressure is inevitably going to escape past that first ring and make it down into the cavity between the top ring and the second ring.
For this reason, the second ring is also partially responsibly for containing that cylinder pressure. But it is also playing a part in terms of oil control. So this is what I mean by this is it scraping some of the excess oil off the cylinder walls. And finally below our second ring we do have our oil control ring and the task of the oil control ring, as its name implies, is to remove that excess lubricating oil from the cylinder walls. And that will drain back typically inside of the piston.
So the three rings have a really important task to play and if they're not doing their job properly, we're not going to get the best possibly performance out of our engine. We're also going to potentially have problems with excessive blow by and possibly excessive oil consumption. Now a lot of this is out of our control. A lot of this is going to come down to the rings that we're using and the bore finish on our freshly honed cylinder walls. This is why this is not typically a job that we as engine builders are going to be involved in.
This is something that we are relying on our engine machinist to complete. So obviously if we want any hope of our engine performing how we would like it to or how it optimally could, we're really going to need to start with an engine that is correctly machined. So we want one where we have the correct finish on the bore walls where our clearances between our piston and the bore walls are optimal as well. Now it comes to the actual task at hand though, the subject of our webinar which is filing the piston ring end gaps. And if you've come from a background where you've maybe assembled some factory engines, then this may be quite a foreign topic because often or typically with a factory engine, if we are doing an overhaul and we're supplying a new set of piston rings, these come out of the box at the correct size, ready to fit and provided our cylinders are at the correct or specified diameters, then there's no work for us to do, we simply need to fit the piston rings onto our pistons and fit the pistons into the bores and we're ready to go.
With aftermarket pistons we're much more likely to have a set of what's known as file fit piston rings supplied. And as their name implies, the file fit rings are designed for us, the engine assembler or engine builder, to adjust the piston ring end gaps by filing the end of the piston ring. What we're trying to achieve here is important to understand. If we can understand the idea behind this, then we're going to have a much better chance of getting the right results. And really what we're trying to achieve is a minimal ring gap, particularly on our top compression ring, under operating conditions.
And that's the key point here. When we're assembling our engine here on the bench at normal temperatures we've got to consider that it's a very different situation to what the engine's going to be exposed to when it's actually running. Particularly when it's running at high RPM and wide open throttle and there's a lot of combustion temperature to consider. So when we're trying to achieve minimal ring gap at operating temperature we need to consider a few aspects that will affect this. First of all when the engine comes up to temperature, the bores will tend to expand slightly.
More importantly though for us to consider is that the rings will also expand as the temperature, the combustion temperature is transferred down into the piston and then into the rings as well. The top ring also will be exposed directly to some level of combustion temperature. So when we're trying to decide on what ring end gaps to select or use for our application, one of the things we really need to consider is the amount of combustion heat that the rings will be exposed to. What I mean by this is in a low powered naturally aspirated engine the rings are going to be exposed to less combustion temperature, hence they're going to expand less than for example if we're running a very high boost turbo charged engine, where the physical combustion heat will be higher. So if we get our ring end gap correct so that we end up with a minimal ring gap at operating conditions, we're going to end up with some really big positives there.
First of all we're going to end up with improved ring seal. This is going to result in lower cylinder leakage. It's also going to result in a reduction in oil consumption. And along with our cylinder leakage being reduced, we're also going to reduce our blow by essentially one and the same. On top of all of this, which is obviously another key point that we need to consider, is we are likely to see a minor improvement in engine power.
This is one of the often heralded advantages of minimizing our piston ring end gaps. However it's important to be realistic here. We are talking about relatively small changes in our actual power. So that's what we can expect to get if we minimize our ring gaps and we have everything operating as we should. Of course the flip side of this is if our ring end gaps are too tight we can end up with catastrophic damage to our engine so we do need to be very careful when we're selecting and setting our ring end gaps.
The reason we can end up with a catastrophic engine failure is if the ring end gaps are too tight at normal room temperature, when the engine's under operating conditions, and everything's expanded with the heat, the ring ends can actually butt together. And at this point the ring has no opportunity to expand further and what it can do is essentially seize against the cylinder wall and in extreme situations this can almost instantly rip the top off the piston, resulting in obviously carnage as you could expect. So what sort of ring end gaps should we be looking for? Now this is going to depend on the bore diameter. So when we're talking about ring ends gaps, quite often what we'll end up doing is specifying the ring end gap in terms of a measurement per inch of bore. So in imperial measurements we would be talking about thousandths of an inch ring end gap per inch of bore.
A pretty typical rule of thumb if you didn't have any other data is around about four thousandths of an inch per inch of bore. That's a reasonably good place to start. However ring manufacturers fortunately will offer their own guidelines. Now if we can just jump across to my phone for a second. I just wanted to show you this is the information that is supplied with a set of JE piston rings to suit our Subaru FA20 engine.
So you can see that we have specifications for the top ring, the second ring and also the oil control ring rails. And we've got a range of different high performance street strip through to blown racer and nitrous et cetera. And you can see that we have a recommended gap, or end gap per inch of bore. So all we need to do here is take our actual bore diameter, and in this case for our FA20 our bore diameter is 3.405 inches. And if we wanted to run our high performance street strip recommendations we would go with a end dap of 0.0045 or 4.5 thousandths of an inch.
So all we'd do is multiply that by our bore of 3.406 and that will give us our recommended piston ring end gap. I actually don't have a calculator here on hand but off the top of my head I think that worked out to be somewhere in the region of about 15 thousandths of an inch. Now interestingly as well while we're still looking at this, we can see that the recommendations for the second ring are actually slightly larger by half a thou. Now the reason for this is that because we're still going to end up with some leakage past that top ring, if the second ring end gap is set excessively tight, what we're actually going to do is end up with that excessive pressure, the pressure that's made it past the top ring actually building up between the top ring and the second ring. And what this can do is destabilize the top ring and this can result in a massive loss of compression and hence power.
So what we want to do is make sure that our second ring is gapped slightly larger than our top ring to prevent that occurring. So it's typical to increase that by somewhere in the region of half a thousandth of an inch per inch of bore as JE recommends. Now just getting back to this, one last thing I wanted to point out is our oil rail ring. You can see that JE here simply offer or recommend a minimum ring end gap for our oil control rails of 15 thousandths of an inch. Now this is because these obviously as we've discussed, aren't involved with the compression process or retaining compression.
And the oil control ring is fitted so far down the piston, that it isn't exposed to as much heat. So the ring end gap for our oil control rails is much less critical and we simply want to make sure that it is at least 15 thousandths of an inch. OK let's move on and I will apologize for those of you who are more familiar with working in the metric system. As we discuss in our engine building fundamentals course, when it comes to building engines, it's really important or valuable if you can learn to work in both imperial and metric units. Even if you live in a country where you're primarily dealing with the metric system, it's almost inevitable that at some point you're going to need to be able to convert between imperial and metric units.
And a great example of this is what we've just looked at. The piston specifications and the piston ring specifications from JE are all supplied to us in imperial units. All we need to do here to convert though is to remember that there are 25.4 millimeters in an inch. So that's our conversion factor if we need to go between metric and imperial. Now my experience over a career of building engines now for probably the better part of 12 or 13 years, is that the ring manufacturer's guidelines will often be a little on the large side.
And there's not specifically anything wrong with that. It's always safest when we are selecting ring gaps to be a little on the large side. The worst case scenario if our ring end gaps are a little bit large is that we might end up with a little bit more blow by. On the other hand as we've already discussed, if our ring end gaps are too tight this could result in catastrophic engine failure. So obviously if we know nothing more, it's always best to start with our ring manufacturer's recommendations.
What I do find though is if you are building a lot of the same engine and an example I'll give here is from my own career. I was building a lot of Mitsubishi 4G63 engines, and a lot of them were based around drag applications. So what this gave me was the opportunity to test and also see what the ring condition looked like when these engines came back to me for a tear down. And one of the things we want to always look at when we strip down an engine is the condition of the ring end gaps. Now if we can just pull a ring out here.
I'll try and just show what I'm talking about here. What we want to do is look particularly at where the ring ends will butt. And what we want to do, I can't get too much closer than this and stay in focus, but what we want to do when an engine has run, is we want to be able to inspect that ring end gap. That's one of the first things we want to do when we strip the rings off the piston. And we want to look for any sign that those ring end gaps are polished.
Now if we are getting very very close to our ring end gaps butting together this is going to be the first sign. And there's a very very narrow room for error here. We go very quickly from the ring ends just butting together which will give that polished appearance. If we go much further that's where we're likely to have the rings actually seize against the piston wall and that's when we end up with engine failures. So that's one of the things we want to look at.
If we've got no sign of our end gaps butting together, and we want to really push the boundaries and try and improve the performance of our engine, as I was with our drag applications, then when we put the engine back together with a new set of rings, we can slightly reduce our end gaps. And if I'm going to do that I'd only be reducing those end gaps in the region of about half a thou, to a thousandth of an inch overall. I'm not talking here about per inch of bore. So in other words if I'd sent an engine out with a ring end gap of 15 or 16 thou, it came back in, there was no sign that those rings ends had been butting together, I might reduce that by a thousandth of an inch perhaps at the absolute most. So what this gives us is the ability to build up some knowledge and experience with a particular type of engine under a specific application and find out what's going to be best suited for that particular engine.
Now when it comes to our rings, there are a few considerations as opposed to just purely our ring end gap. One of the key aspects that's really easy to overlook is not only do we want a ring gap to be at a specified size, we also want to make very sure that our ring end gaps are parallel when the ring is fitted into the bore. And quite often what we'll find is that straight out of the box if we install a set of fresh rings that are ready to be file fitted, we'll find that those ring end gaps aren't quite parallel. Now if we can jump across to my laptop screen for a second I've just got a photo that shows this really nicely. So this is a ring from our FA20 engine.
And what we are looking at here, hopefully you'll be able to see, is the inside diameter, or the inside edge I should say, of that piston ring, the end gap is slightly wider than if we go out to the cylinder wall. And this is a pretty common scenario. So this is one of the first things we want to be looking at when we install our fresh rings into the bore, we want to visually inspect the ring end gap and make sure that it's parallel. And if it isn't parallel then we're going to be correcting this when we start filing the ring end gap. We also want to take this into consideration when we are measuring the existing ring gap with our feeler blades because if the end gaps aren't parallel we're going to end up with one side of that end gap larger than the others.
OK so how do we actually go about measuring our piston ring end gaps? It's pretty easy really. What we want to do is simply use a set of feeler blades. And our feeler blades are a relatively cheap tool that we're going to be using for a few tasks in the engine building arena. So it's definitely a tool that you're going to require. What we want to do is start by installing our rings into our bores so we can actually measure what we've got.
Before we do that though, once we have filed our rings, then we're going to be filing them to suit the specific bore and once that's done we need to make sure that our rings stay allocated to that particular bore. So before I go through this process what I'm going to do is split my ring set down and allocate it to individual cylinders. And we can see that I've done that here. I've got them marked, I've labeled them FA because this is for an FA20. Cylinder one, cylinder two is the one that we're going to be working on, cylinder three and cylinder four.
So it's really important and once we've actually gone through this task that we make sure that the rings stay in the correct location inside the engine. Now we've got our ring here and this is a top ring for cylinder two. I've got our FA20 block here and I'm just going to locate this ring into the top of the number two bore. All I'm going to do here is just gently push the ring together and slip it down the bore and we'll push the ring down until it's located in the bore. There's a little bit more to it than this before we can actually take a measurement though.
The ring end gap that we're going to measure with our feeler blades is going to be very dependent on how square that ring is sitting inside the bore. So what we need to do before we make a measurement is make sure that our ring is squared in the bore so that it's sitting the same distance down from the top of the bore. We'll also want to locate it a little distance down from the bore to take out the effect of any wear or taper right at the top of the bore. Now there's a couple of ways of doing this. I've got here a piston ring locating tool.
Really really cheap so if you're doing a lot of engines it's certainly worth investing in one of these and all it has is a range of little steps that allow it to locate on the top of the cylinder bore, and push the ring down, around about 15 to 20 mils down the bore. It's universal so it doesn't matter what bore diameter you're dealing with, you can just squash it down to suit. So all I'm going to do is locate that on top of the ring in my bore, allow it to expand out, and I'm just going to gently push this down until it locates on the top of the bore. So that's going to ensure that my ring is square and it's located down a fixed amount from the top of the bore. I know that a lot of people won't have access to one of these tools even though they're really cheap and well worth purchasing.
So another technique that is really easy to use, particularly if you're dealing with a piston that has a flat top is to locate one of the rings that you're not working on, on the piston. So in this case for our FA20 I've located the second compression ring into its ring grove on the piston. It's a flat top piston so what I'm going to do now is I'm going to push this down the bore, just on top of the piston, and I'm just going to push it down until the ring makes contact with the top of the bore. And that's a really cheap and easy way of making sure your rings are correctly located. OK so we've got our ring located.
Let's just jump across to my phone cam, and we'll see if we can take much notice of what's going on in here. Again I can't get too close but what we can actually see is that ring end gap looks pretty parallel. And by eye it is actually a pretty good starting point. Alright I'll put this down and what we can do now is grab our feeler blades. And what you're going to find is that once you get a little bit more familiar with doing this, once you are regularly gapping piston rings, you'll be able to take a look and have a pretty good idea what sort of ring end gap you have to start with.
But other than that what we're going to do is just grab our feeler blades and start with a relatively small blade, so in this case I'm going to start with 10 thousandths of an inch and we can just push that through our ring end gap. Now I'll just try and show that process here again. So all we're going to do is just locate the feeler blade through the ring end gap. And at the moment with 10 thou, that's actually really really loose. So we know that we need a larger feeler blade and our ring end gap is already above 10 thou.
So we'll go through and I'm going to jump up to 12 thousandths of an inch. And as I put 12 thousandths of an inch through there, I can feel this just starting to get a tiny amount of tension so I'm pretty close. So we'll just go up one more step and we'll go to 13 thou. And now I've got a good amount of tension. Now talking about that tension, this is something that is going to be a little bit difficult to know if you're not familiar with using feeler blades.
When we're pushing a feeler blade through to measure a clearance, what we're actually looking for is just a light amount of tension and obviously if you're not familiar with using these blades, you're not going to know what that'll feel like. A really good way to get an idea of what that feels like is if you grab two A4 sheets of paper, and you then clamp those between two normal magazines, and you put your feeler blade between the two sheets of A4 paper and then pull the feeler blade out, the tension that you feel as you pull the feeler blade out through the A4 paper with the weight of the magazines, that's going to be pretty similar to what we're looking for. So we're looking for a light tension where we can just feel it. So once we know what our base starting point is, we can now actually begin gapping our piston rings. Obviously at this point we've already decided on what our piston ring end gap needs to be.
We're going to need a way of making those adjustments and I'm going to show you two different techniques. In front of me here I have an electric ring file and this is a Total Seal product and it is relatively pricey product. This is valued at around about USD$700 so particularly if you're only looking at building perhaps one engine it's going to be hard to justify that expense. On the other end of the scale we'll also look at the same process being applied using this manual ring file. These are available in the region of about USD$50-100 so certainly quite cost effective.
But there are some considerations we need to make if you are going to be using a manual ring file. In terms of the electric ring files though, this particular Total Seal product is a relatively high end product. Before this I was using a ProForm electric ring file which fits somewhere in between those two extremes. I believe they're around about USD$250. The consideration you need to make here is that if you are planning on building a reasonable number of engines the electric ring file can really quickly pay dividends.
With the electric ring file it's much quicker to gap rings so particularly if you are doing this for a living, if you're actually going to be charging out your time then the electric ring file is really the way to go. What it also means is it's much easier to get consistent ring gaps from one piston to one cylinder to another. Very very easy to make small and accurate adjustments which is much harder to do with a manual ring file. Alright so we'll start with our electric ring file. And then we'll go and have a look at what we need to do with our manual ring file.
So we know that we're at about 13 thousandths of an inch now and we're going to assume at this point we want to take two thou off to achieve a ring end gap of 15 thou. So what we want to do is place the ring in our file. Now I'll just put this in here and then we'll grab our other camera so we can have a better look at some of the aspects of this ring file. So let's have a look. Now we've got our ring as we can see clamped here and this clamps the ring right at the point where it's actually going to end up contacting the grinding wheel.
What we want to do is install the ring so it is just protruding a small amount off the table. And we can also use the table as a bit of a guide to whether or not we're going to be grinding an even amount off our ring. So this is important to understand when it comes to fixing a ring end gap that isn't parallel. We may want to file more material off the inside edge or perhaps the outside edge depending on what our end gap is doing. Now one of the valuable aspects of this particular product is that it has this adjustable stop here.
And this adjustable stop allows us to set essentially the bore diameter and once we've got our rings set up in this file what it's going to mean is that we can really quickly and easily get consistency and parallel ring end gaps. So we're always going to be installing our piston rings as we move through our set evenly. This particular model also has a dial gauge here which we can use to help us make very accurate adjustments to our ring end gaps. So the process here once we've actually got our ring installed is we can move our table down. And I'll just try try and get in here.
We can move our table down and then we have a wheel on the left hand side of the table that we can just wind in until we're just barely making contact with the grinding wheel. This ring file is also supplied with a diamond tip for surfacing or dressing that wheel as well. So once we've zeroed that which I've just done now, what we can then do is zero our dial gauge. So what we want to do is just turn that so that our gauge is reading zero. So this essentially zeros our adjustment.
And what we should be able to do here is now start grinding that ring and we can simply move the little thumb wheel again or the little wheel at the end of the table and we can adjust exactly how much we are taking off. OK so after using a couple of these models now of electric ring file that include a dial gauge, I would still urge a little but of caution here. It's always easiest to start with small adjustments to your ring end gap and check frequently. Rather than making a large adjustment of perhaps three or four thousandths of an inch, fit the ring back into the cylinder and find that you've actually gone too far. In particular once we have our ring file operating what we'll find is that the dial gauge tends to move around a little bit.
So it is very hard to be 100% accurate. And often it's easier to actually use the dial gauge as a bit of a guide once we've shut down the ring file to see exactly where we're at. So the process there is to simply grind our rings until we end up with the correct ring gap. We're going to be constantly checking our progress, constantly checking to make sure that our end gaps are remaining parallel and we'll work through our entire set. Now another thing actually that I haven't quite mentioned here that I should .
FA20 engine block that I've got here for our demonstration. You can see that we've just got the bare block sitting here. Now this block was torque plate bored and honed. And the torque plate process is designed to ensure that our cylinder walls remain perfectly round and parallel under the operating conditions when the cylinder head is installed. Now if we've gone to the trouble of torque plate honing our cylinders then we also really would be best to check and set our piston ring end gaps with the torque plate also installed, because the torque plate can end up distorting the cylinders.
So that's an important consideration. I'm not using it here just because it makes it much easier for me to demonstrate. OK so we've talked now about how to use our electric ring file. I'll just take our ring out of our electric ring file and we'll swap over and we'll have a look at our manual ring file. Now with our manual ring file there is a little bit more to consider.
Now what I'll do is I'll just move this into camera view so we can look down on the top of it. So we've got a basic little ring file. These are pretty common. You'll see them on a lot of supplier's websites. And it's just got an abrasive wheel which in this case is turned by a bell crank.
So we're turning it by hand. We've also got a couple of little stops located on the bed here to locate the ring against while we are grinding. OK so there's a couple of considerations as I mentioned. The first thing is when we are filing our ring, what we want to do is make sure that we file from the outside edge of the ring back towards the inside. That's really really important.
A lot of rings will have an inlay in the face of the ring and if we grind from the inside edge to the outside of the ring that can very quickly rip that inlay out of the ring and damage our ring, rendering it essentially useless. So we always want to grind from the outside to the inside. Now another thing that I see some novice engine builders do is when they're using this sort of ring file, they'll tend to grab the ring, push it against the stops and then squeeze it together so that essentially we are filing both ends of the ring together, well both ends of the ring at the same time. Now the problem with that is that our ring end gaps are only ever going to be parallel when the ring end gap is the thickness of our grinding wheel and there's not too many circumstances I can think of where we'd want a ring end gap that's that wide. So the correct process is to only grind one edge of our ring one side of our ring end gap, and this actually goes for an electric ring file as well.
We're only making the adjustment to one side of the ring. And generally what I do is I support the ring with my forefinger and my thumb. I'll be looking down on the top to ensure that I've got my alignment with the grinding wheel correct. And this is how I'm going to be making my adjustments if our ring end gap isn't parallel. What we can do is we can just pull the ring slightly off the grinding wheel and this will allow us to view the angle that we have to the grinding wheel and make sure that we have that square.
Then what we're going to do is just simply turn the bell crank. I can't do that here while it's still in camera shot. So what I'll do is I'll just move off to the side. We're just going to rotate that bell crank, move the grinding wheel against the ring surface. We're going to do that for a few seconds, applying some light pressure.
And then of course we're going to take our ring out and we're going to check our progress in the bore. What we find is that if we make small adjustments, we start to build up a bit of an idea of how much adjustment we need to make, or how much grinding we need to make in order to correct any error in our ring end gap so we'll know how aggressively we'll need to grind the rings. We also need to be careful as well because depending on the material that the ring is made from, you're going to find that some rings will grind much quicker so for the same amount of effort you're going to be removing a lot of material. Whereas other rings are a lot harder and it will take a lot more effort to adjust the ring end gap. OK I'm going to move into some questions and answers really shortly so if you do have any questions that have cropped up, please ask those in the chat and Colin or Ben will transfer those through to me.
I wanted to just touch on the last step of our job here, our last task with our ring gapping job. Is that once we've completed our ring end gaps and we've got them exactly where we want, what we're likely to find is that we'll end up with slight burrs on the end of the piston ring that we've just ground from the grinding process. We need to remove those before we go and install the piston ring onto the piston and then into the bores. It's easy enough to do that, all we need to do is have a small needle file. We want a really fine needle file like this one that I've got here.
And all we're going to do is just dress the ends of our end gap, our ring. And we're just going to, just break down the edges that we've just ground so it doesn't need a lot of work. We're not trying to chamfer anything here. We really want to retain a nice sharp end gap. We shouldn't be filing on the actual face that runs against the cylinder wall either.
And we're just going to break down any burrs that we have on that ring end gap. And at that point our task's finished. We can clean down our rings, install them on our pistons and move on with our assembly process. Alright I'll stop here and we'll have a look and see what questions we've got. Our first question comes from Barry G who's asked are those Wiseco pistons? No they're not, they are JE forged pistons.
Although I actually think, if I remember correctly, JE and Wiseco essentially are one and the same company. I think that's my vague recollection. Looks like we haven't got any more questions at this stage. Maybe I was a little bit slow to ask for questions. So hopefully that's given you some insight into the task of filing piston rings.
It is a really important task and it needs to be treated with care and you need to take your time. It's really really difficult if you go too far with your piston ring end gaps to go back, you can't file material back onto the pistons. So it's always easier to start making small adjustments, following up your progress and that way you're going to be able to creep up on the correct size. So I've got another question from Barry who's asked are gapless rings really any good, do you have any experience with them. Yeah I've used gapless rings in my own drag engines, the 4G63 drag engines that I ran in my own shop car.
I've also used conventional rings. And what I find is that the gapless rings do tend to reduce the leak down. So particularly if you're doing a compression test or a leak down test on an engine that's fitted with gapless rings you're going to end up getting better results than a conventional piston ring. In use though the results I could measure in terms of horse power gains I really couldn't see the benefit in that respect. What we did find though was with the very high boost turbo charge engines that we were running, the reduction in blow by with the gapless ring did help.
When we're running 40 or 50 psi of boost pressure, this inevitably results in a lot of combustion pressure making its way into the sump. So the gapless rings tended to help reduce that and reduce the engine's ability to breathe. The other aspect which probably wasn't a consideration with my own engines due to their use as a drag application is from what other engine builders that I've talked to, a lot of the gapless rings tend to have a relatively short service life compared to a conventional ring. So there's some information for you. Hopefully that's of some use.
Raisin has asked have you ever seen a piston ring gap specified by a manufacturer where the ring prefiling has been at the upper threshold of the suggested gap? For example factory Nissan GT-R VR38 piston rings. Those are a Mahle piston ring that Raisin was talking about there. Yeah absolutely I have. It's actually not that uncommon and it's a frustrating situation. There was a particular brand of piston that I was dealing with at one point.
We did a few engines back to back and every time I went to check the piston ring end gaps, they were already excessive. So this obviously makes it a bit difficult, there's not a lot you can do in this situation short of finding another ring set to work with. I dealt with the manufacturer over that particular situation. They weren't really particularly interested in helping out or doing anything about it. So my hands were pretty well tied.
It is important though to understand that within reason the ring end gap has a relatively minor effect on power. So a lot of people think that if their ring end gap's two thou larger than they wanted it to be then the engine's never going to perform and that's simply not true. We're talking very very small percentages in power that we can gain by getting our ring end gaps minimal. One of the bigger things that we will tend to see though is when our ring end gaps start to become excessive, the engine will breathe more so that's really a consideration in terms of the crank case ventilation from the engine block as well as the rocker covers and your requirements for a breather tank or whatever you're going to be running for the engine. So just if your ring end gaps are a little bit larger than the recommendations then it doesn't necessarily mean that your engine is never going to perform.
Obviously there's a limit to that. If we end up with massive excessive ring end gaps then of course yes that's going to affect our performance as well. Barry G has asked does the choice of fuel have an influence on what ring gap is used? E.g. would you suggest running tighter clearances when running alcohol based fuel since they run cooler cylinder temps? Yeah it's a really good question Barry. I'm glad you asked that because yes that is my firm belief.
And this is one of the reasons I kind of alluded to with our drag engine program. I was running predominantly on alcohol for my own engine and that runs a lot colder than a gasoline based fuel. So despite the fact we were running at very very high specific power levels and we were also running very very high boost pressures, we were seeing much lower exhaust gas temperatures than what we would see on a gasoline based fuel. And for this reason I ended up actually reducing the ring gaps over what our piston ring manufacturer recommended and I never ended up having any problems with doing so. Definitely noticed a reduction in the engine's breathing as well as a result of that.
Whether I could say I made any more power because of it, probably not to be honest, nothing I could measure. Raisin's asked any experience using the Total Conform piston rings where the rings are designed to conform to the piston bore? Do these rings follow similar gapping procedures? Look it's not a ring that I have had any personal experience with so hard for me to really talk too much about that. The ring end gaps though I can't really see any reason why those aren't going to follow a conventional sort of technique. What we need to understand, well what we're seeing actually, I should say, is the more modern ring packs that we're seeing on our engines, on our pistons are going smaller and smaller or thinner and thinner. And what this does tend to do is allow them to better conform to any irregularities in the bore walls.
This improves the power, the sealing, also the thinner rings reduce the frictional losses as well so there's an advantage there. One consideration with very thin rings is that you're actually likely to see for the same amount of heat potentially a slightly larger expansion. So that may affect their requirements for ring end gap. However of course you're still going to get a recommendation from the ring manufacturer as well. Barry G has asked would you recommend gas ported pistons on a daily? OK so for those of you who aren't aware what gas porting is, it's a technique where ports are drilled through the piston to allow combustion pressure to get directly to the back of the ring.
So there's a couple of ways of doing it. One of the techniques is the ports are drilled vertically down through the crown of the piston. And this just intersects the back of the top ring groove. That's called vertical gas porting. The other way is where the ports are drilled through horizontally through the top of the ring groove.
So the idea behind these gas ports, either vertical or horizontal is that they allow the combustion pressure to get indirectly behind the piston ring. And it's actually the combustion pressure during the power stroke that forces the ring out to seal against the cylinder wall. It's not the radial tension of the ring that's the key here to success. We're really relying on that combustion pressure. So if we can allow that combustion pressure to get directly behind the ring, it can improve the ring seal.
Now this is something I again ran in my drag engines, but we do need to give some consideration to how those ports are going to be affected in a daily driver. In particular if you're running on a gasoline based fuel this tends to result in carbon deposits on the piston crown. And in particular these could end up clogging up your vertical gas ports relatively quickly. And this isn't necessarily going to result in a failure but it would certainly render them relatively useless. Horizontal gas ports may fare slightly better.
I was using them for a drag application on an alcohol based fuel that runs very very clean so it wasn't a consideration. But in a more direct answer to your question, I don't run these on a daily driver application. I've only ever used them for specific race applications. Raisin's asked with larger end gaps, could a vacuum pump be used to improve crank case evacuation or breathability as he's put it there. Yeah absolutely that's a possibility.
Of course the best idea would be to minimize the amount of blow by and pressurizing the crank case or breathing in the first place. That's going to give us the least amount of work to do. But certainly that was one of the drivers as well. In our drag car to go to a dry sump system where we were running three stages of scavenge, which essentially, very similar to a vacuum pump, it's actually pumping air and the oil back out of the sump. And we were monitoring the crank case pressure both before and after we did that.
And on very high boost pressures we noticed a significant reduction in the pressure inside the crank case when we went to a dry sump system. So simply able to scavenge a lot of that waste, the blow by gases out of the engine. Alright looks like that's brought us to the end of the questions so hopefully you've enjoyed today's webinar and hopefully you've learned a little bit more about how to gap a piston ring. As usual if you do have any questions following this webinar please ask them in the forum and I'll be happy to answer them there. Thanks for joining us, I'll look forward to seeing you all next week.