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"There's no replacement for displacement" is it true?

Discussion in 'Engine Compartment' started by Sat-Chit-ananda, Aug 31, 2012.

  1. "There's no replacement for displacement" is a phrase heard over and over again. While the phrase has been proven to be totally inaccurate (nitrous oxide system, higher engine speeds and forced induction systems have proven to be ideal replacements for displacements), there is a reason why the belief surfaced.
    The reason is simple; increasing an engine's displacement will increase torque output and in most cases horsepower output also. It can be a great thing. So how do you add displacement to an engine? There are two ways: boring and stroking.
    By "boring" the engine, you can bore and hone the cylinders to a larger diameter and fit them with the proper pistons and rings. By "stroking" the engine, you can purchase or put together a stroker kit that consists of a longer-stroke crankshaft, shorter rods and custom pistons. For maximum displacement increases, boring can be combined with stroking. Bigger in the Bore
    Increasing an engine's bore is a very typical operation when rebuilds or ground-up buildups are performed. Depending on the construction of the block, a number of options are usually present. If one is building up a cast-iron shortblock, the cylinder is integral with the block and no liner is used. In these cases, the typical overbore will be .5mm or 1.0mm. If the intent is to maximize the life of the block and also allow a future rebuild for the block, the best strategy is to just go the minimum oversize to get round fresh cylinders again.
    Of course if maximum horsepower is the target, a 1.0mm or larger overbore may be advisable. Qualified machine shops can sonic-test the block to determine the maximum advisable overbore that can maintain the necessary minimum wall thickness. When the shortblock is aluminum, cylinder sleeves or liners are the actually cylinder for the piston. Depending on the engine family, there may be aftermarket sleeve kits that allow for significant bore increases. This is especially true for B-series Honda and SR20-series Nissan short block.

    Longer in the Stroke
    As for increasing the stroke, companies such as HKS, TOMEI, GReddy, AEBS, JUN, SCAT, Jackson Machine, SPOON Sports, A'PEX Integration, Eagle Specialties Products, Crower make stoker crankshafts and even some complete stroker kits. Where the stroke is increased, some other action needs to be taken to position the piston correctly in the bore.

    If no action was taken and a stroker crankshaft was used that increased the stroke by 4mm, the piston would be sticking out of the cylinder by 2mm (half the stroke increase). So how does the piston get relocated? If the same piston is going to be used, the distance must be removed from the connecting rod. Thus, custom connecting rods that are 2mm shorter would be needed in this example if a +4mm stroker crankshaft was being used. When a custom piston is being built for a stroker engine, there may be an opportunity to move the piston pin higher than it's original location (this is also known as reducing the piston's compression height). In the case of the HKS 2.8-liter stroker kit, HKS repositions the piston pin 2mm higher in the piston. This allows the use of stock-length connecting rods.

    So what are the drawbacks of stroking an engine? First, it can be expensive as the procedure will require replacement or the crankshaft along with replacement of the pistons and/or connecting rods. Second, increasing an engine's stroke decreases the engine's maximum rpm. The reduction in maximum rpm potential results because the additional stroke increases piston speed in the cylinder. Once piston speeds exceed 4000 ft/s, only the strongest pistons, rods and crank available should be used. As speeds approach 5000 ft/s, the outer limit may cause bottom end parts to come apart. Third, longer strokes increase the side loading of the piston against the piston walls.

    Why not look at bigger / better turbo's get the torque and horsepower required than going for just higher displacement.

    Bore and Stroke Basics - Adding Inches Where It Counts | DSPORT Magazine #23
  2. gurjinder

    gurjinder Staff Member Janitor

    High displacement engines will soon be confined to the following :

    1. History books.
    2. Commercial sector
    3. Exotic super/hypercars

    Also, Naturally aspirated engines in cars will be the next in line to extinction. The FIAT TwinAir 800cc is a sign of things to come.

    I've never been a fan of these ultra-gizmo laden modern engines. Toyota Diesels from the 80's remain my favourite! Powerful and simple. And they sounded 10x better than any modern diesel too. :p
  3. sungoa2010


    In fact the turbos should do the job. For some people it is like taking extension of existing house. They don't like it they like to get a big house even though both will have the same area. Driving a higher displacement car for Americans is like Potato and onion for Indians. Difficult to live without it.:)
  4. With forced induction small 1248 cc engine can deliver power and torque figures of naturally aspirated engines of higher displacement of the past but today all higher displacement engines are also having forced induction!!

    Example 3.0 ltr Toyota Fortuner,Don't know whether these big engined cars are going to extinct soon unless price of Diesel becomes Rs100,even then some status conscious people still like to commute in such cars.
    I read some where that reason for high selling Scorpio/Bolero in some parts of India not due to engine or power or technology but simply it's height.
    I seems sitting in higher in a vehicle satisfies the ego of the person as he feels above all others on the road!! this was one studies by IIMB.
    I am not finding that link now.
    1 person likes this.
  5. theblack

    theblack Esperto

    Yes i do agree.. there is a market for huge butch looking SUVs in the world the best example being the US.
    So probably the "Big engine" syndrome wont die down so soon but I'm guessing before the syndrome dies out , Fuel itself will ;-)
  6. bhai

    bhai Esperto

    Grande Punto 1.3 90 HP
    High displacement means high power & torque this is big misunderstanding.

    Many engines which can produce more power & torque as compared to other higher cc engines. MJD is the great example.

    Power & torque are based upon combustion efficiency,valve timing etc.

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