What is a good rod to stroke ratio

what is a good rod to stroke ratio

Stroke to Rod Length Ratios and Building a Long Rod Stroker EJ205

15 rows · Apr 09,  · Stock Rod Ratio Info for Various Popular Engines; Block Rod length Stroke Rod ratio;. Oct 18,  · A rod to stroke ratio of or higher is a good general starting point for a performance engine. Although many respectable production engines don’t meet this. For example, the Honda B18C is and the K20A2 is The Chevy LS7 is and the BMW S54 is

Performance engine builders are always looking at changes they can make that will give their engine an edge over the competition. Rod ratio is one of those factors that may make a difference. Changing the length of the rods with respect to the stroke of the crankshaft offers some advantages in certain situations, and may allow the same number of cubic inches to deliver a little more power or a little longer ring life take your pick.

But experts disagree as to whether or not changing rod ratios really makes that much difference. Advertisement Click Here to Read More Advertisement Rod ratio is the mathematical relationship between the overall length of the connecting rods and the stroke of the crankshaft.

Divide rod length by the crank stroke and you get the rod ratio. The rod ratio in this engine would be 5. If you build the same engine with longer 6-inch rods, the rod ratio becomes 1. And if you are building a stroker with 6-inch rods, the rod ratio becomes 1. What do these numbers mean? They express a geometric relationship between the rods, crankshaft and pistons. The lower the rod ratio, the greater the side forces exerted by the pistons against the cylinder walls. This increases wear on the piston skirts and cylinder walls, and creates a higher level of vibration inside the engine.

The increase in friction can also elevate coolant and oil temperatures. On the other hand, what is a good rod to stroke ratio rod ratios do have some advantages. Shorter rods mean the overall height of the block can be shorter, which means the overall weight what is a good rod to stroke ratio the block can be lighter. The engine will how to download youtube videos for free without software pull more vacuum at low RPM, which means better throttle response and low end torque good for street performance and everyday driving.

Spark timing can be advanced a few degrees for some additional low speed torque, and the engine is less prone to detonation, which can be a plus in turbocharged, supercharged or nitrous applications. Advertisement What about longer rod ratios? Using longer connecting rods with the same stroke reduces the side loading on the pistons, which reduces friction. It also increases the piston dwell time at Top Dead Center.

Typically, an engine with a higher rod ratio will produce a little more power from mid-range to peak RPM. How to wordpress child theme rods require the wrist pin to be located higher in the piston, or the engine has to have a taller deck height to accommodate longer rods.

Longer rods also mean shorter and lighter pistons can be used, so the additional weight of the rods is more or less offset by the reduced weight of the pistons. One of the disadvantages of longer rods and a higher rod ratio is that low RPM intake vacuum what is a good rod to stroke ratio reduced somewhat. Reduced air velocity into the engine hurts low speed throttle response and torque, which is not good for everyday driving or street performance, but works well on a high-revving race engine.

Production engines may have rod ratios that range from 1. Four cylinders tend to have lower rod ratios 1. As for V8s, they typically range from 1. Often, the rod ratio is dictated by the design and deck height of the block, and the pistons, rods and crank that are available to fit the block.

Advertisement Best Rod Ratio? Even so, some engines that have lower rod ratios will out-perform engines of the same displacement that have higher rod ratios. How can this be? Because of differences in the design and porting of the cylinder heads, different valve sizes and valve angles, different camshaft lift and duration, different intake systems and different tuning.

For example, a BMW M3 has a rod ratio of 1. But the M3 engine also makes 2. Our take on the issue is that rod ratio is just a number that may or may not make much difference depending on the situation. In some cases, it can make a slight difference and in others it seems to make no significant difference whatsoever.

Peak horsepower and torque depend on too many other variables. The maximum achievable rod ratio is always going to be limited by the physical dimensions of the block deck height, tall or shortthe longest rods that are available to fit the engine off-the-shelf mass produced rods or custom madeand the shortest pistons that will work with the rod, block and stroke combination.

The combined weight of the rod and piston has more effect on momentum and throttle response than the rod ratio. Also, moving the wrist pin higher up in the piston and using a shorter piston may create some piston wobble and instability issues if you go too far.

Because of this, excessive rod ratio may actually be detrimental to engine performance. A closely related topic to rod ratio is that of bore and stroke. If the bore and stroke dimensions in an engine are the same say a 4. The Ford GT has a 5.

It has a 3. By comparison, a C7 Corvette with a 6. Both are excellent engines with lots of performance potential, but the Ford revs higher because of its overhead cam heads, and makes more horsepower vs As a general rule, large bore, short stroke engines are high revving, high power engines good for road racing and circle track applications. Small bore, large stroke engines, on the other hand, are better for low RPM torque, street performance, towing and pulling, but have limited RPM potential.

Advertisement Formula 1 engines have an extremely short stroke, only 1. The bore size is limited to a maximum of 3.

This is a very oversquare design, but one that allows these engines to rev to an incredible 20, RPM and squeeze horsepower out of 2. One of the reasons they are able to rev so high is the extremely short stroke. The pistons are not moving up and down very far in their bores. At 20, RPM, the relative piston speed in a Formula 1 engine is 5, feet per minute. Formula 1 engines also use a pneumatic valve system that is far faster than any mechanical valvetrain.

A cubic inch Pro Stock drag motor may be running a bore size of 4. If they are running a smaller bore with a longer crank say 3. Advertisement High piston speeds not only increase friction and ring wear inside the engine, it also increases loads on the connecting rods dramatically.

Using longer rods with shorter, lighter pistons can help reduce the stress on the rods in these applications. Some say shorter rods work best with heads and intake systems that can flow big CFM numbers. The rod ratios that seem to work best in Pro Stock drag racing years ago was around 1. There is no magic formula for building a race-winning engine. Engines: Nissan Engines. Engines: Subaru EJ Engines. Engines: Engine Development. Engines: Engine Installations.

Magazine Current Issue Past Issues. Connect with us. Advertise Subscribe Contact Us. By Larry Carley. Rod ratio is the mathematical relationship between the overall length what does conficker worm do the connecting rods and the stroke of the crankshaft. Long Rods vs Short Rods On the other hand, lower rod ratios do have some advantages. What about longer rod ratios? Best Rod Ratio? Oversquare vs Undersquare A closely related how to plagiarize an essay without getting caught to rod ratio is that of bore and stroke.

Formula 1 engines have an extremely short stroke, only 1. High piston speeds not only increase friction and ring wear inside the engine, it also increases loads on the connecting rods dramatically. In this article: connecting rodsengine technology. Watch Engine Builder's latest discussions and explanations.

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Mar 27,  · Some engine builders say a “good” rod ratio is anything or higher. Production engines may have rod ratios that range from to over , with many falling in the to range. Four cylinders tend to have lower rod ratios ( to range) while many V6s have somewhat higher rod ratios of to Author: Larry Carley. 62 rows · Stroke Rod Ratio Notes; Ford Six: Ford Six: . There is a small range of ratios for most conventional piston engines: the rod is between.

Like resoling your favorite pair of shoes, we are going to refresh the engine of our project WRX. The EJ with its However, it seems a bit rough and not especially happy to rev. Conversely, the smaller EJ with its 92mm bore and shorter 75 mm stroke seems smoother and freer revving.

Both engines share a The EJ sports a stroke to rod length ratio of 1. So in the pretext of doing something different and unique, we decided to see what exactly we could do with the EJ This engine had a bore of 97mm and a stroke of 75mm for a displacement of 2.

This looks great on papers except the 97 mm bore which makes it not too practical to emulate as it would require the EJ block to be sleeved. We have reservations about sleeving engines due to the blocks structural integrity and issues that we have had in the past with sleeves staying put in race engines and even hot street engines. To keep our block intact we would have to resort to stroking.

Welcome Eagle Specialty Products to the project. They happened to have a slick EJ20 crank available with a very reasonable 83mm stroke. Although this is a whopping 8mm more stroke than stock, the stroke is still relatively short. Remember that an SR20 has an 86 mm stroke, so we will still have decently low piston speeds. Eagle Specialty Products also just came out with a longer We plan on having JE Pistons make us some This will give us a displacement of cc, which is slightly more than the EJ22G.

The stroke to rod length ratio falls to 1. This will be a very reasonable engine, as far as internal stress goes, with decent displacement for the numbers. The end result being a very well rounded engine. In the illustration above we have plotted piston position in the bore vs crank degrees.

With a very short imaginary rod vs an imaginary long rod. This is to exaggerate things so you can see it on the graph easier.

In the diagram, the piston with the longer connecting rod spends more time around top dead center 0-degree crank angle due to a slower acceleration rate towards and away from top dead center TDC. A longer dwell time around TDC makes better use of the combustion pressure and turning the pressure into torque.

This helps mechanical as well as thermal efficiency. This is because the combustion pressures are higher while the crank angle is lower.

The longer rod positions the piston to push down on the rod while it is straighter and the angle of the rod to the crank is more acute resulting in less side loading of the piston into the bore and offering more leverage of the rod to the crank for better energy transfer.

Less side loading results in less friction between the piston and bore, freeing up power and reducing wear. The reduced piston acceleration also improves piston ring life, as the lower acceleration equals less force on the rings. More critically, the slower acceleration around TDC on the exhaust and intake strokes improves volumetric efficiency at higher rpm.

This is because you have more time to fill and empty the cylinders on the intake and exhaust strokes. Other things we have noticed with longer rod engines is that the torque and power peaks become closer in rpm. The engines are less sensitive to timing, so you can often get away with a few degrees less advance with no loss of power. The engines also rev more freely, seemingly with less effort and vibration. We have found in experimenting with Nissan, Honda and Chevy engines that even small changes in stroke to rod length ratios can make very feel-able differences in how the engines react and how long they last under racing conditions.

A rod to stroke ratio of 1. For example, the Honda B18C is 1. The Chevy LS7 is 1. High revving cc sportbike engines tend to be around 1.

Bespoke racing engines can have even higher rod ratios. For instance, the Toyota F1 engine had a ratio of 2. The F1 engines of that period spun to 18, rpm. With those extremely high performance naturally aspirated engines the longer rod to stroke ratio was very important to making power, because the piston spends so little time around TDC due to the extremely high revs. Anything that can be done to improve dwell time near TDC, improve mechanical energy transfer, and reduce friction will greatly benefit performance.

Not everything with long rod engines is all advantages. We have found a slight trend in a long rod engines having a slightly greater propensity to detonate. Another thing is that when the torque peak and power peak become closer together, peak torque is made at a higher rpm. This can make the engines bottom end response soggy. We think that because the piston moves away from TDC slower, the intake and exhaust port velocity is reduced at lower rpm actually hurting VE at lower engines speeds.

This is partly mitigated because the engine wants to rev freely. Lastly, because exhaust port velocity is reduced at high RPM there is a slight tendency to spool the turbo slower. So, controversial opinion ahead — I honestly think that rod ratio is lately really overstated as something to shoot for. If you look at that BMW S14 graph, going from the I think the big thing driving the characteristics of the Subaru engine are not enough port and not enough cam.

The EJ25 could easily have had the valve centerlines moved to take advantage of 7. Try building a long rod engine and driving it, you can really tell the difference.

The engine even sounds a lot different. Have less peaky power delivery, but generally can give more revs than the turbo has powerband. Big bore, sleeved, has always been the ticket here. I also have seen the EFR line expanding now too. Why not build a block with the EJ as a basis, and go the other way around of doing it?

Same bore 99mm stroke of the Ej 75mm. Same rod stroke length as before althou thats still can be altered by moving the wrist pin further up , but a displacement of cc. Still as rev happy, but also more torque albeit higher in the rev range. As for detonating: Did you look into the cam timing? As the main problem lies there: More overlap is less detonation, because of a lower dynamic compression.

It all comes down to revs basicly. The more you run, the higher the chances detonation occurs. Calculating dynamic compression is everything to prevent that, which can be done fairly easily. To mitigate responsiveness: Just measure exhaust flow. What you mentioned above is true, but can be compensated for by high intake timing and less exhaust timing, with a further improvement in pickup speed by leaving the exhaust as small as possible while improving the intake side.

The one thing that really becomes an issue though: Is looking for the right turbo: As the redline is increased this becomes especially critical for low end response, as you actually making the performance envelope bigger.

A turbo that is happy to spool low down will be less efficient up top and vise versa. As for Dan Rosia: No they are designed als a long block. Thats the only way to get that type of RPM. The Toyota engine was capable of How I know? I Was there as one of the engineers. So yes, they are built as short as possible, but are still a relatively long block. Its only because the stroke is so short that they appear to be short blocks, but in comparison they are not.

Kevski — Speedhunters deleted my rebuttal, but luckily we frequent the same websites. Do you remember? There are many schools of thought on addressing knockback, each with their own pros and cons. While it may sound obvious, making sure that your wheel bearings are fresh and tight is the first major step toward addressing knockback. Following the wheel bearing itself, upgrading hubs and other suspension components to achieve less deflection during cornering will also serve to minimize knockback.

At times, heavy-duty or race-specification components may be available for bolt-on installation. A little bit of research here can go a long way. I want to build a destroked long rod EJ too but we wanted to try messing around with the EJ as it gets overlooked a lot. There is no such thing as dynamic compression ratio. Compression ratio is a mechanical relationship that never changes, even when the engine is running.

The best way to eliminate detonation is to fix the root cause which is fuel octane, combustion chamber design and compression ratio, then taylor the ignition timing and AFR around that. Older American domestic pushrod engines, for example, will often prefer the other way around. Reversion should be the first thing to tackle on any car: NA or FI. Flow alsways needs to be in one direction and restricted in the other.

Thats what grooves are for. And do that as much as you can troughout the whole exhaust. Same for the intake, except the other way around.



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