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| techtalk:ref:svcproc26 [2019/08/06 15:21] – [Indirect Method] hippysmack | techtalk:ref:svcproc26 [2024/01/22 21:42] (current) – hippysmack | ||
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| ====== Squish Band ====== | ====== Squish Band ====== | ||
| - | The squish (AKA " | + | The squish (AKA " |
| + | |||
| + | {{: | ||
| Even though the fire has already been lit, these areas still contain unburned air/fuel mix as the piston arrives. \\ | Even though the fire has already been lit, these areas still contain unburned air/fuel mix as the piston arrives. \\ | ||
| The piston sandwiches the air/fuel up next to the head, causing it to " | The piston sandwiches the air/fuel up next to the head, causing it to " | ||
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| ====== Measuring the Squish Band ====== | ====== Measuring the Squish Band ====== | ||
| ===== Indirect Method ===== | ===== Indirect Method ===== | ||
| - | |||
| You can use a piston height gauge to measure how far above or below the cylinder deck the piston is sitting at TDC. \\ | You can use a piston height gauge to measure how far above or below the cylinder deck the piston is sitting at TDC. \\ | ||
| Then add that measurement to the gasket thickness. \\ | Then add that measurement to the gasket thickness. \\ | ||
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| {{: | {{: | ||
| - | ===== Direct Method ===== | ||
| + | ===== Direct Method ===== | ||
| You'll be placing some soft material, such as .065" solder, onto the squish band area of the piston. \\ | You'll be placing some soft material, such as .065" solder, onto the squish band area of the piston. \\ | ||
| (clay has been used for this also but it's not as accurate as using solder which won't change thickness) \\ | (clay has been used for this also but it's not as accurate as using solder which won't change thickness) \\ | ||
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| But this method works great with flat or angled head surfaces. The tools required are no more than if you are installing the heads. \\ | But this method works great with flat or angled head surfaces. The tools required are no more than if you are installing the heads. \\ | ||
| - | Place the solder in multiple places around the piston top. \\ | + | * Place the solder in multiple places around the piston top. \\ Grease works best to hold the solder but if using tape, keep it below the squish band. \\ |
| - | Grease works best to hold the solder but if using tape, keep it below the squish band. \\ | + | |
| - | + | * Then measure | |
| - | | Solder held with grease. ((photo by aswracing of the XLFORUM ))| | + | * Write the measurements down to conclude and average the squish band dimension. |
| - | |{{: | + | |
| - | + | ||
| - | Install the head gaskets and heads then follow the torque procedure to full torque spec. \\ | + | |
| - | Next, remove the heads following the removal sequence in the FSM to keep from warping the heads. \\ | + | |
| - | | Remove the heads to reveal how far the solder was compressed. ((photos by JohnK of the XLFORUM | + | | Solder held with grease. ((photo by aswracing of the XLFORUM https:// |
| - | |{{: | + | |{{: |
| - | | Measure the compressed side of the solder pieces. ((photo by JohnK of the XLFORUM | + | | Measure the compressed side of the solder pieces. ((photo by JohnK of the XLFORUM |
| - | |{{: | + | |{{: |
| - | | Write the measurements down to conclude and average squish band dim. ((photos by JohnK of the XLFORUM http:// | ||
| - | |{{: | ||
| ====== Gaining a Squish Band Due to a Conversion ====== | ====== Gaining a Squish Band Due to a Conversion ====== | ||
| **Converting an 883**: \\ | **Converting an 883**: \\ | ||
| - | An 883 head has a hemi chamber with no squish band but it's chamber is only 3" in diameter to match the 3" bore size of the 883. ((aswracing of the XLFORUM | + | An 883 head has a hemi chamber with no squish band but it's chamber is only 3" in diameter to match the 3" bore size of the 883. ((aswracing of the XLFORUM |
| What's fundamentally wrong with the hemi design is that it gives very poor chamber turbulence. \\ | What's fundamentally wrong with the hemi design is that it gives very poor chamber turbulence. \\ | ||
| Poor chamber turbulence means poor air/fuel mixing, resulting in pockets of fuel. \\ | Poor chamber turbulence means poor air/fuel mixing, resulting in pockets of fuel. \\ | ||
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| This is because you're now putting a 3-1/2" (1200) or 3-9/ | This is because you're now putting a 3-1/2" (1200) or 3-9/ | ||
| - | | 883 head on 883 cylinder (no squish). ((drawing by aswracing of the XLFORUM | + | | 883 head on 883 cylinder (no squish). ((drawing by aswracing of the XLFORUM |
| |{{: | |{{: | ||
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| **Converting a 1200**: \\ | **Converting a 1200**: \\ | ||
| - | |||
| ====== Machined Squish Band ====== | ====== Machined Squish Band ====== | ||
| + | Deciding ahead of time on the performance upgrades you want is important. \\ | ||
| + | When you prepare heads, the chamber wants to get bigger. \\ | ||
| + | This happens for a variety of reasons. \\ | ||
| + | The valves are sunk in the heads to gain (valve to valve) and (valve to piston) clearance. \\ | ||
| + | As well as correct valvetrain geometry, and they' | ||
| + | As in the head picture above, all these things increase chamber volume and makes the compression ratio lower. \\ | ||
| + | |||
| + | At the same time, moving up the power scale really calls for more compression, | ||
| + | You can deck the heads to drop the chamber volume somewhat, but that has limitations and bad side effects. \\ | ||
| + | However, the coarse adjustment for the CR needs to be the piston and head decking should only be used for fine adjustments. \\ | ||
| + | |||
| + | Therefore, if you do your conversion with the standard dished conversion pistons, you put some constraints on future performance work. \\ | ||
| + | You're simply not going to be able to run as much cam or do as much head work so long as those standard conversion pistons are in your motor. \\ | ||
| + | |||
| + | Check with your engine builder / supplier for further assistance if you're looking for a complete performance package. \\ | ||
| - | | Piston and head with matched squish band. ((drawing by aswracing of the XLFORUM | + | | Piston and head with matched squish band. ((drawing by aswracing of the XLFORUM |
| |{{: | |{{: | ||
| + | ====== Reverse Dome ====== | ||
| A piston with a reverse dome has a dish in the middle of it. \\ | A piston with a reverse dome has a dish in the middle of it. \\ | ||
| That dish is needed because when doing a conversion, you've got a chamber that's sized for an 883 and a piston that's sized for a 1200 or 1250. \\ | That dish is needed because when doing a conversion, you've got a chamber that's sized for an 883 and a piston that's sized for a 1200 or 1250. \\ | ||
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| By dishing the middle of the piston deeply as shown below, the CR can be used on street bikes. \\ | By dishing the middle of the piston deeply as shown below, the CR can be used on street bikes. \\ | ||
| - | | Reverse dome piston. ((photo by aswracing of the XLFORUM | + | | Reverse dome piston. ((photo by aswracing of the XLFORUM |
| |{{: | |{{: | ||
| - | Deciding ahead of time on the performance upgrades you want is important. \\ | + | ====== Lightning Heads ====== |
| - | When you prepare | + | 1200S heads and the older (pre-rubber mount) SE heads, |
| - | This happens for a variety | + | These are what we call " |
| - | The valves | + | 62cc chamber with a 10° cast in squish shelf, 1.715/1.480 valve sizes, the old low floor, squared off bowl ports like all the hemi heads etc. \\ |
| - | As well as correct valvetrain geometry, and they' | + | All 1200S motors came with flat tops just like every other Evolution Sportster. \\ |
| - | As in the head picture above, all these things increase chamber volume and makes the compression ratio lower. \\ | + | |
| - | At the same time, moving up the power scale really calls for more compression, | + | The Lightning head was the first generation performance head from HD for the XL motor. \\ |
| - | You can deck the heads to drop the chamber | + | All they did was take the Hemi head and add a bunch of material |
| - | However, | + | And they dual plugged some of them (1200S and the later SE versions). Ports and valve sizes stayed |
| - | Therefore, if you do your conversion | + | Bringing the chamber volume down like that, with no change in the piston (i.e. they stayed with flat tops), bumps the compression up. \\ |
| - | You're simply not going to be able to run as much cam or do as much head work so long as those standard conversion pistons are in your motor. \\ | + | (from the stock 9:1 to about 10:1. That's the sole performance gain of a Lightning head) \\ |
| - | Check with your engine | + | The problem |
| + | |||
| + | ====== Thunderstorm Heads ====== | ||
| + | Two years after the Lightning head, HD came out with the Thunderstorm head. \\ | ||
| + | In the Thunderstorm, | ||
| + | They paired it with a domed piston to get the compression up to 10:1. \\ | ||
| + | They also improved the ports and went to larger valve sizes (1.810" | ||
| + | |||
| + | The angled squish bands direct the fuel being squeezed out of the squish bands more directly at the flame front. ((aswracing of the XLFORUM https:// | ||
| + | But the way it's done in the Thunderstorm, | ||
| + | Typically from the factory the clearance is .050" or more, and that makes the squish band largely ineffective anyway. \\ | ||
| + | |||
| + | Thunderstorm heads are obsolete now. \\ | ||
| + | They could be machined nice and even, but there' | ||
| + | So to machine it, typically .035" | ||
| + | |||
| + | Below is an example of before and after machining. This is much better with a nice even and consistent squish clearance. \\ | ||
| + | But cutting the deck this much has some side effects, like less valve to piston clearance. \\ | ||
| + | As well as potentially forcing the customer into short or adjustable pushrods. \\ | ||
| + | It also typically makes the chamber too small, forcing us to open it up in other areas. \\ | ||
| + | |||
| + | Also notice how there' | ||
| + | Anything higher than that and the dome goes past the squish band. \\ | ||
| + | |||
| + | | Stock Thunderstorm Heads ((photo by aswracing of the XLFORUM https:// | ||
| + | |{{: | ||
| + | |||
| + | ====== Buell XB/04XL Heads ====== | ||
| + | As delivered, they have flat squish bands with a 62cc chamber. ((aswracing of the XLFORUM https:// | ||
| + | This lets you toss them on over flat tops and have a squish band with lots of area and 10:1 compression. Not a bad way to do it. \\ | ||
| + | If you want to angle it, it's not a problem, you've got lots of material to work with. \\ | ||
| + | You can make the squish band as big or small as you want. \\ | ||
| + | You can make it match the piston | ||
| + | You can do all this without excessive deck milling and all the problems that come with it. \\ | ||
| + | |||
| + | The stock valves are the same sizes as the Thunderstorms, | ||
| + | The springs and guides can support up to .550" lift safely, though, versus .500" | ||
| + | The ports are actually | ||
| + | The Thunderstorms were a major step forward from the Lightning/ | ||
| + | |||
| + | | Stock Buell XB Heads ((photo by aswracing of the XLFORUM https:// | ||
| + | |{{: | ||
| + | |||
| + | ====== Compression Ratio ====== | ||
| + | Since the beginning of the Sportster line, Harley Davidson has changed head gaskets as way of changing or adjusting compression ratio. \\ | ||
| + | Some were lowered for gas mileage / EPA or raised for performance. \\ | ||
| + | The first thing usually thought of is to change the piston and/or head type to change the compression ratio. \\ | ||
| + | Then you can fine tune with gasket thickness. \\ | ||
| + | However; \\ | ||
| + | < | ||
| + | In other words it's entirely possible your motor is already 10:1 or higher and likewise it's possible it's already 9.4:1 or lower. \\ | ||
| + | There' | ||
| + | And the 9.7:1 etc. they advertise is just a nominal number, it's somewhere around there. \\ | ||
| + | | ||
| + | |||
| + | My advice would be to not worry about the exact CR so much (few people do). \\ | ||
| + | But if you want a worthy reason to go into it and make it better, look at optimizing your squish clearance instead. \\ | ||
| + | That will increase chamber turbulence (and thus efficiency) and bump up your compression a bit and actually reduce detonation in the process. \\ | ||
| + | Thin gaskets are an excellent way to do that. \\ | ||
| + | With N4's, stock pistons and dropping the top the typical .030" or so to get a real good squish clearance, you most likely will not cause yourself a clearance issue. \\ | ||
| + | Personally I'd check it anyway. \\ | ||
| + | |||
| + | If you want to understand the relationship between gasket thickness and compression ratio, it's not that hard to do. \\ | ||
| + | Let's say for example that your motor is 10:1 and each cylinder is 600cc (round numbers just to keep it simple). \\ | ||
| + | That means that at BDC, there' | ||
| + | * 667 minus 67 = 600cc of displacement | ||
| + | * 667 divided by 67 = 10:1 compression ratio | ||
| + | |||
| + | Now let's say you've got a .050" head gasket in there, and it's I.D. is 3.550" | ||
| + | You can calculate it's contribution to the volume using the formula for cylindrical displacement, | ||
| + | * 3.14 x 1.775 x 1.775 x .050" = .495ci, multiply by 2.54 cubed to get 8.11cc | ||
| + | |||
| + | So let's say you go to a .025" head gasket. That 8.11cc will be cut in half to 4.06cc, right? \\ | ||
| + | So what does that do to the CR? \\ | ||
| + | * 667cc at BDC minus 4cc = 663cc | ||
| + | * 67cc at TDC minus 4cc = 63cc | ||
| + | * 663cc divided by 63cc = 10.52:1 | ||
| + | |||
| + | So in this example, taking .025" of thickness out of the head gasket bumped the cr about half a point. \\</ | ||
| + | |||
| + | You can also [[http:// | ||
| + | |||
| + | ====== Effects of Deck Height ====== | ||
| + | In general, deck height has nothing to do with the squish band. \\ | ||
| + | In the example below with a 3-9/ | ||
| + | Since you have a 3" diameter chamber over a 3-9/ | ||
| + | Notice how the piston is a flat top for a little over 1/4" around it's perimeter. That's not an accident. \\ | ||
| + | |||
| + | If you look at the drawing below, \\ | ||
| + | You can see that cutting more off the deck isn't going to change the clearance between the top of the piston and the head deck. \\ | ||
| + | To change that clearance, you've got to use a thinner head gasket, or mill the top of the cylinder so the piston sits higher in it. \\ | ||
| + | (or use a thinner base gasket which accomplishes the same thing) \\ | ||
| + | |||
| + | {{: | ||
| + | |||
| + | \\ | ||
| + | However, there are situations where decking the head does change the squish clearance. \\ | ||
| + | Look at a Thunderstorm or Lightning head with their angled shelf and massive overhang for example. \\ | ||
| + | In the pic below, you see it's got a cast-in squish shelf. That shelf is angled, and the heads were paired with a piston that had a matching angle. \\ | ||
| + | But see that big overhang around the perimeter of the chamber? \\ | ||
| + | If you deck this head, you reduce or remove that overhang. That most definitely changes the squish clearance. \\ | ||
| + | So there are situations where decking does change the squish clearance and situations where it doesn' | ||
| + | {{: | ||
| + | |||
| \\ | \\ | ||
