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horsepower calculator bore stroke compression

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Low Price Guarantee We're so confident in our low prices, we offer a Beat-a-Price Guarantee: We'll beat our competitors' advertised prices on any identical, in-stock product proof of advertised price required! Beat-a-Price Guarantee Details.For maximum power output and engine efficiency, you should use the maximum CR your engine can safely handle. Major determining factor is the fuel you intend to use.

Higher octane fuel is more resistant to detonation. I think in terms of an engine as having three compression ratios…. Static, Dynamic and Effective.

horsepower calculator bore stroke compression

Static CR is the mathematical ratio as measured on the assembly bench. Dynamic CR …. In theory, this is the point at which cylinder pressure changes from negative intake to positive compression. If you measure how much stroke is left before the piston reaches TDC, input this stroke figure into your normal CR formula.

Due to effective decrease in stroke the piston is already on its way up the bore when the intake valve shutsDynamic CR is always lower than Static CR. Take a street engine as an example… for best efficiency and good power output on regular fuel, you probably want to run Dynamic CR somewhere in the region of Effective CR is the term I use, others may call it something different.

Yes, Effective CR changes throughout the rpm range, generally maxing out at peak torque. Both formulae assume the intake charge stops entering the cylinder when the piston hits BDC on the intake stroke.

Ideally the intake charge will keep coming in up to the point the inlet valve closes. Using the same example engine as above, Effective CR now becomes… 8. To summarise…. The wilder the cam, you need more CR. Higher octane fuel can tolerate more CR. Intake and exhaust systems should also be taken into account because they have a major influence on VE, which in turn effects Dynamic CR etc etc.

Having said all that, minor increases in CR make very little difference to power output. The exact number to aim for will be a judgement call based on all that stuff I discussed above. What effect does compression ratio have on BHP?

Read more Tech Talks. Recent Posts.Compression Ratio is the ratio of an engine's cylinder volume vs. Static Compression Ratio numbers are the ones you hear thrown around the most " compression"and it takes into consideration the full sweep volume of the cylinder in regard to its range of crankshaft stroke.

Unlike Static Compression Ratio, Dynamic Compression Ratio takes into account camshaft timing by considering the intake valve closing point in relation to the piston position.

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To give an example, lets say you're considering only pump gas for your engine, and it has a static compression ratio of Therefore with the mild cam it will have a high dynamic compression ratio, probably 9. General rule of thumb for acceptable dynamic compression ratio to run safely on pump gas is maximum for engines with cast iron cylinder heads and 8. Intake valve closing point IVC is available on most cam spec cards which can be found on sites like summitracing.

Understanding & Measuring Compression Ratio : Static, Dynamic, Effective, Two & Four Stroke

Most camshaft manufacturers provide you with valve timing numbers '. However, Comp Cams will typically provide valve timing numbers '. If you only have an IVC.

You can calculate your. Summit Racing or Jegs.

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You can find out your intake centerline for your Comp Cams camshaft by searching its part or grind on the Comp Cams website and then finding your cam's specs page. Toggle Navigation. Have Questions? This calculator will calculate both Static and Dynamic compression ratio Compression Ratio is the ratio of an engine's cylinder volume vs.

Cylinder Bore:. Head Gasket Thickness:. Head Gasket Bore:. Deck Clearance:. Have Questions About this Calculator? Click Here to send us a message.This section is all about Jeeps.

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horsepower calculator bore stroke compression

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E Arcade. Home Page. Photo Album. Product Reviews. Tech Section. Jeep Central.Unlike mechanical compression ratio, corrected compression ratio takes into account the point at which the intake valve closes after the piston passes BDC on the intake stroke. The later the valve closes, the lower the corrected ratio.

Corrected compression should be matched to cam specs and fuel octane for optimized engine performance. Blueprinting is the term used for the careful selection, custom fitting, and meticulous assembly of engine, drivetrain, or chassis components to very precise high-performance specifications.

All components of a blueprinted engine are checked for proper dimensions, concentricity, perpendicularity, and fit. When deemed necessary, proprietary modifications to components are made. Finally, the engine is mocked up and checked as a rotating assembly. Pistons are available in different dome shapes to fit a variety of combustion-chamber designs and compression ratios. Be sure to match the piston dome to your combustion-chamber design and intended compression ratio.

In last month's installment, we explained several critical engine dimensions, along with key terminology that will help you avoid making costly mistakes when buying or building your engine.

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Mechanical compression ratio also known as static ratio is a mathematically calculated number derived from the relationship of combustion-chamber volume and cylinder volume. Mechanical compression ratio is determined by adding net combustion-chamber volume, which includes head-gasket volume, to cylinder volume.

The sum is then divided by net combustion-chamber volume. A mechanical compression ratio of means that the intake charge is compressed down to one-ninth of its original size. Within certain limits, the higher the ratio, the greater the combustion heat and cylinder pressure, resulting in increased efficiency, power, and fuel economy.

Compression ratios for Harley-Davidson overhead-valve V-Twin engines typically range between and Keep in mind that increasing displacement without increasing the combustion area will increase the mechanical compression ratio.

Corrected compression ratio is similar to mechanical compression, with the exception that the corrected ratio takes into account the point at which the intake valve closes when determining cylinder volume. Knowing the corrected compression ratio is important for building a "happy" engine, especially if it will be run on pump gas.

The corrected compression ratio will always be less than the mechanical ratio because the corrected ratio is calculated using a smaller cylinder volume since the piston is past bottom dead center and moving upward when the intake valve closes.

horsepower calculator bore stroke compression

This results in a smaller cylinder volume being used for the calculation, thus a smaller ratio. The corrected compression ratio is important for optimizing the mechanical compression ratio to cam specifications and gasoline octane.

By now it should be clear that selecting the wrong combination of parts or inaccurate machining can cause major problems when building an engine.

A slight error or accumulation of errors can easily cause piston deck height to be too high, so the piston hits the cylinder head, or too low, resulting in excessive squish clearance and lower-than-anticipated compression.

This calculator will calculate both Static and Dynamic compression ratio

When buying new or used parts or even a complete engine, never take for granted the dimensions of any of the specifications previously discussed, which brings us to another misunderstood term: blueprinting. An engine can be assembled to either stock specifications or high-performance specifications, which is also referred to as blueprinted specs. Stock specifications have a very wide tolerance range due to production-line manufacturing variances. And, as you can imagine, these specifications are not optimized for best performance.

On the other hand, in regard to performance specifications, blueprinting is the term used for the careful selection, custom-fitting, and meticulous assembly of engine, drivetrain, or chassis components to very precise high-performance specifications. The specifications are generally collected from engine or parts manufacturers, previous experience, and intended application, and possibly are limited by a sanctioning racing organization.

And, when deemed necessary, proprietary modifications to components are made. Finally, the engine is mocked up. The combustion chamber is usually cc'd to verify the mechanical compression ratio, and adjustments to components are made as necessary.

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Finally, the engine is disassembled and meticulously cleaned for final assembly. Blueprinting also includes checking everything. For example, never install a new part directly out of the box.At first glance, the concept of engine compression is simple enough:It's the ratio of the volume of the combustion chamber and bore when thepiston is at bottom dead center BDC versus when it is at top deadcenter TDC.

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Easy as pie. That's fine in concept, but in stock carracing, where the competitors are so equal, a car that is giving away afew tenths of a point of compression can be at a significantdisadvantage.

A droplet of race fuel has a specific amount of energycapacity that is released when burned, so it only makes sense that themore fuel you can squeeze into a given area and burn efficiently, themore power you can produce.

Increasing the compression effectively doesthe same thing because you are packing the same amount of air and fuelinto a tighter bundle, so when the spark ignites the burn, it packs thatmuch more punch. Of course, that's the reason many racing series limitcompression--because they know that's one of the surest ways to limitpower. That's fine, as long as everybody is following the same rules,but are you sure you are taking advantage of all the compression you areallowed?

If you don't know how to precisely calculate your enginecompression, there is no way you can know. Before you can calculate compression, you have to know your engine'sdisplacement. The easy answer is just to list the displacement listedfor your block in the catalog, but we need more precision than that.

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Displacement is defined simply as the area swept by the top of thepiston as it moves up or down the cylinder bore one time. It does notinclude any area above TDC, meaning the combustion chamber. Let's take astock Chevy as an example.

It has a four-inch bore and 3. The total displacement is eight times If youare racing a four-cylinder engine, you would multiply by four instead ofeight. That strange number Calculating the displacement is the easy part. All you need to know for that is bore and stroke. To understand the compression ratio, you also need to take into account all of the area that remains in the combustion chamber when the piston is at TDC.

Easy enough--that's just the combustion chamber volume, right? Unfortunately, that's only part of the equation. There are more things inside the combustion chamber that can affect compression ratio than Richard Petty has cowboy hats. Chamber design, seat depth, valve pockets, piston dish, ring depth, gasket thickness, the list goes on. Variables that affect piston volume are domes, dishes which includevalve pocketsand the side clearance which also includes the openarea inside the top ring groove that isn't occupied by the ring.

If youare purchasing off-the-shelf pistons, the manufacturer can tell youthese volumes. For instance, a 5cc dome on the top of a piston willincrease compression ratio versus a flat-top piston. Likewise, largevalve pockets will decrease compression.

We'll get into the calculationslater. Less critical--but still important--when it comes to understandingcompression is the piston's side clearance. Side clearance is the areabetween the side of the piston and the cylinder bore. It extends fromthe top edge of the piston down to the top ring.

A little-known factabout most racing pistons is that the diameter of the piston above thetop ring land is smaller than the rest of the piston.With the combustion chamber being the root of all horsepower, it only makes sense that you start spec'ing an engine build there.

One of the key variables in engine building is compression ratio, or the ratio between the swept volume at bottom dead center BDC and the clearance volume at top dead center TDC. How do you calculate a static compression ratio, and what's the ideal number for your build?

To find out, we found ourselves at CPR Racing Engines with a bevy of instruments for gathering your clues to show you just how to measure your own engine. We also spoke to Kenny Duttweiler, master engine builder, to poke his brain a little given his experience in class-restricted engine builds, like Bonneville's displacement-based classing.

If it's a street-driven car, you'll want to be conservative with it—we're not going to go over But if it's a full-blown, drag-race engine with a very controlled [quality of] fuel, you'll run it between And boosted methanol engines, something under And that's all short-duration runs; our Bonneville stuff is normally 9 to 9.

While fuel is the ultimate limitation, ensuring that the compression ratio you aim for can be supported by your fuel's octane, Duttweiler emphasized the trade-off between compression and timing: "Compression versus timing is your big trade. For example, when we were testing the Magnuson blower [on an LS] a few years ago.

You start at So drop the compression torun 20 or 21 degrees of timing—which is quite a bit more—and the engine actually made more power at the same boost. The reason for this, Duttweiler explained, is in the time it takes for the flame to propagate during the crankshaft's rotation.

He's looking for peak cylinder pressure at 15 degrees after top dead center ATDCwhere the most power is made. Looking at the combustion chamber's efficiency, you can begin to look at compression as a function of the timing advance. On the older, junk cylinder heads, you may have 45 degrees of total timing approximately a degree time frame. If you look at the work being done, if you have to fire the engine 10 degrees earlier on the compression stroke, the engine is now going to have to produce more work because you've started the burn earlier to achieve the same peak ATDC," he said.

As you go larger, you start to revert more to a flat piston, which has the best of the flame travels of all of them.

The small engines, like a inch motor, and put a big dome on it, that's not really good for flame travel. On a decent-sized engine, inch and up, you start getting close to flat pistons to get Say a you've got a to inch engine with a cc chamber and you want to run 15 tothat's going to be easier because the chamber volume relative to the cylinder volume will be quite small, and consequently, you get a better piston design out of it.


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