Part seven of our continuing story on engine basics concentrates on strengthening the bottom end. Last month, we talked about the reciprocating bits like pistons, rings and connecting rods, but when power output is extremely high, even the block itself may need strengthening.
This chapter will be the last in our engine tech series to focus on the inner workings of the engine. After this, we will be discussing some of the peripherals that contribute to mega-power, such as turbos, superchargers and nitrous oxide, but, for now, let's finish off your understanding of the engine and how it works.
Here is an example of a stock pressed in oil galley plug. These should be drilled out and replaced with loctighted screw in plugs.
Stuff Going on Inside
A commonly known, but often forgotten fact is that the internal geometry of an engine can affect the engine's power delivery. Bore size, stroke and rod length all have a profound effect on an engine's power-delivery characteristics. An area of tuning just now being exploited by import engine builders is altering of the rod length to stroke ratio. The bigger the stroke-to-rod-length ratio (commonly referred to as the "rod ratio"), the more dwell time the piston has around TDC. This accomplishes several things. Since the piston is near TDC longer, the combustion event has a longer time to impinge upon the piston, allowing a better transfer of force to the piston, which slightly improves the engine's thermal efficiency. The longer dwell time also gives more time to fill the cylinders at bottom dead center on the intake stroke and more time to scavenge the cylinder during overlap. Since the piston is accelerated more gradually away from TDC, there is less mechanical stress on the crank, rods, pistons and cylinder walls. Reduced rod angularity at the point of highest cylinder pressure, also reduces mechanical stress, as the piston has less side load, and therefore rubs on the side of the bore less.
This Nissan SR20DE crank is full of features typical of import performance engines. It is made of strong forged steel, while domestics are typically cast iron. The crank also features generous roll-formed fillets on the journals, full counter-weighting, close tolerance balancing and shotpeening--all in stock condition. These features are normally found in the racing catalogs of the domestics. The SR20DE crank can take over 500 hp in stock form.
Higher rod ratios result in less velocity in the intake ports; there is a lower demand for the ports to flow as well, as there is more time available to fill and scavenge the cylinder. Conversely, this can also mean stagnant flow at low rpm, which is not good for low-end power production, either.
To increase the stroke-to-rod-length ratio, some tuners are running a longer connecting rod, moving the piston pin up higher into the piston to allow this. Some engine builders are even running deck plates to raise the engine deck so a longer rod can be utilized. Some import engines have rod-length ratios as low as 1.49:1. 1.7:1 or better is considered good. The most highly developed four-stroke engines in the world, Formula One and motorcycle engines, often have stroke-to-rod- length ratios of more than 2:1. Many tuners of production engines are attempting to emulate this.
The bore-to-stroke ratio of an engine can also affect the engine's power characteristics. Over-square engines, ones that have a bigger bore than stroke, have lower piston speeds and less internal stress at high rpm due to lower inertial loads. There is also more time to fill the cylinders because of the lower piston speed. Engines with longer strokes and smaller bores, called under-square, have more internal stress due to faster piston acceleration and higher piston speeds. This accelerates wear and can induce seal-killing ring flutter.
This Honda B18C has studs to help maintain good head gasket clamping. Some engine builders also prefer to stud the main bearing caps. Note the fine plateau honed cylinder wall finish and the high domes of this high-compression naturally aspirated engine.
Under-square engines have higher torque and low-end power producing intake port velocities to ensure more complete cylinder filling at low rpm. Many import engines, most notably Hondas, are under-square. High-performance motorcycles (with a few notable exceptions like the torquey Supertwin racing class bikes) and purpose-built racing engines like the ones found in Indy and F-1 are over-square to improve cylinder filling at high rpm and reduce piston speed.
By designing around them, engine designers can get around things like engines being under-square with short rods. Despite being under-square with a low rod ratio, most Honda engines can still rev to the moon because their port configuration has good airflow even at high port air velocities and the huge duration and lift of their high-speed VTEC cam lobes ensure good breathing at high rpm.
The AEBS water pump for the B18C eliminates the water pump as a parasitic power loss and ensures a good supply of coolant to the engine at all rpm with no fears of water pump cavitation.
The Crank
The crank is one of the strongest parts of your typical import engine. Most import engines have forged crankshafts, as opposed to the cast cranks found in most domestics. Like forged pistons, forged cranks have superior grain orientation and grain refinement from the forging process. On popular import engines, the crank is one of the parts that needs the least amount of work to ready it for even the most extreme use. Stock prepped Honda B and H series, Mitsubishi 4G63, Toyota 3SG and Nissan SR20DE and VG30DE cranks have supported upwards of 600 turbocharged hp, without failure, time and time again. So strong are some of these stock cranks that they have withstood use in SCCA GT class road racing as well as turbocharged IMSA GTO and GTP racing cars!
The beefy AEBS B18C cylinder sleeves shown here eliminate cylinder walking, cracking and any head gasket sealing issues caused by thin cylinder walls. A most impressive piece.
The crank of your typical engine only needs to have its pressed-in oil galley plugs drilled out and replaced with screw-in allen-type plugs that are loctited and staked into position to ensure they will not come loose. While the plugs are out, the oil galleys are thoroughly cleaned with a brush and clean solvent. It is amazing how much nasty gunk and debris get centrifuged into the plugged blind holes of the crank. The oil holes on the journals should be lightly chamfered with a die grinder (which is done stock usually!) and a good dynamic balancing job done. The journals can be given a light polish with micro-finishing paper and that's about it. Heroic measures are not necessary, even for wildly boosted engines! Many a 500-plus hp engine has been assembled with no crank prep work at all.
RD's stroker kit is one of the secret weapons behind many of the super-fast, all-motor class cars. RD can get upward of 2200cc's from the B18C. Shown here is a B18C 4340 stroker crank, Cunningham rod, high-compression domed piston with a tool steel lightweight pin and Speed Pro gapless piston rings.
The very anal retentive can take crank prep a step further by grinding off all forging parting lines and bullnosing (rounding) counterweights. This reduces stress risers by eliminating sharp edges where stress and cracks can concentrate. All-out drag racing naturally aspirated engines, where every ounce of power is critical, can benefit from knife-edging and lightening the crank. This is where the counterweights are given an aerodynamic profile with a sharp leading edge to reduce windage losses when the crank spins through the oil-filled mist created in the crankcase by bearing sling-off at high rpm. Lightening the crank reduces the power required to spin the engine to speed, freeing power to drive the wheels. Removing large amounts of material from the crank counterweights can create an under-balanced situation, where the counterweights do not cancel the weight of the rod and piston. This can create vibratory stress on the engine. Because of this, excess lightening should be avoided on road racing and street engines where long-term durability is important.
Here a D16 RD Stroker crank has had the counterweights knife-edged to lighten the crank and to reduce windage losses.
Other details that can be done and are nice, but not absolutely necessary (even for the most powerful engines), are shotpeening the crank journal fillets to improve fatigue strength and nitriding or cryotreating the crank. Shotpeening, like what we described for rods, creates a finely grained, compressed layer in the critical fillets area of the crank. This helps prevent the formation of cracks. After shotpeening, the crank should be checked for straightness and straightened, if necessary. As a side note, many import cranks (like Nissan), are pre-shotpeened from the factory. Look for the telltale pebbly surface texture on non-journal machined areas. Nitriding and cryotreating improve the abrasion resistance of the journal's surface. Nitrating surface hardens the journals and makes them more wear resistant. Nitrating also slightly improves the fatigue strength. Cryotreating also improves fatigue strength and relieves internal stress. These details are good, but many a 500-plus hp import engine has been built without them.
This crank has had its stock oil passage plugs drilled out and replaced with screw-in plugs. These plugs are more secure and allow removal for cleaning.
Unlike softer domestic cranks, the cranks from the beefy import engines rarely need to have the journals ground undersized and thicker bearings used to rebuild them. Just a light micropolish is all that is usually needed to make them good to go. For some engines, mainly the Honda B18B and C, the B16A and the Nissan SR20DE, stroker cranks are available. Crower and JUN are two of the main suppliers of these cranks. Stoker cranks have, well, longer strokes to gain power-producing displacement. Stroker cranks are usually made of high-quality 4340 (or other tough alloy) billet and are CNC-machined, from a solid chunk of the alloy steel, to final dimensions. Usually these strokers, or any billet crank for that matter, are nearly bulletproof--as well as super-expensive. Billet cranks normally don't need any prep work--just drop right in--but the anal retentive among us will still do the brush clean oil passages, check the balance (normally, it's perfect on a billet crank) micropolish the journals and deburr routine.
Most popular performance import engines also have strong bottom-ends. Note the deep block skirts, beefy main caps and huge, stiff main cap girdle on this Nissan SR20DE. With proper tuning, the stock bottom-end of these engines can take more than 400 hp--way more than the stock-rated 140 hp--without failure.
The Crower and JUN stroker kits include rods and pistons, as a long stroke necessitates a higher compression height. This means the pin location in the piston and or the connecting rod length must be changed, so the pistons don't poke above the block deck with the longer stroke. The bigger stroke also greatly increases the compression ratio, so changes to the piston's dish or dome are needed to maintain the same compression. These kits are expensive, but remember there is no replacement for displacement! Power gained from increased displacement is across the board, but more gain is usually found on the bottom-end of the rev range.
R&D Racing offers super stroker and big bore kits for the D, B and H series Honda engines, getting huge displacement increases in the order of half a liter or more from some of these engines. These kits are the secret super weapon of many of the leading all-motor class import drag racers. (Look for a full feature from us about these parts in the near future.)
The Block
Some import engines, like the SR20DE and the 4G63, have bulletproof blocks that need almost no work to ready them for mega power. Other blocks, like Honda's B and D series, are very well-designed and are strong, but need considerable prep to survive high power levels.
All of the popular import performance engines' blocks are strong enough to lead long and happy lives with bolt-on and even the most radical, but streetable, performance mods like 11:1 compression, under 100 hp nitrous shots and up to 15 psi of boost. Some are better than others; the 4G63, 3SGTE, VG30DE and SR20DE are most noted for their stout construction. These blocks are tougher than a brick...um, outhouse, with stout main cap girdles, thick cylinder walls and beefy reinforcing webbing around the main bearings. Little to no prep outside of boring, honing, cleaning and deburring needs to be applied.
Hondas are another story. Although the part of the block supporting the crank is nearly bulletproof, with either a full or partial girdle and beefy main bearing caps, the cylinder walls and deck are the Achilles heel of the mega-power Honda. The popular B series and D series engines have what is called an open-deck block construction. This means the cylinder is free-standing in the block's water jacket, with no support except at the bottom of the cylinder.
The Honda factory has two reasons for doing this. One, the Honda block is made with an advanced, high-pressure die casting process and the die for the water jacket must be able to be released as the freshly cast block clears the mold. It can only go upward, so the block's deck is open. The second reason is because coolant can freely circulate around the top of the bore, the rings can seal with less cylinder wall distortion. The top of the bore is the hottest area, and good, uniform cooling helps. Better ring seal means lower emissions. Even temperatures in this area and the combustion chamber also result in lower emissions.
The problem when these engines are taken to the limit--at high rpm when naturally aspirated or when boosted beyond 20 psi--is the unsupported cylinder walls crack from the side load. The narrow sealing surface of the open deck block can also blow head gaskets at high-boost levels. This is a shame, with the Honda's ultra-strong cranks and bottom-end.
All is not lost, though. To solve this problem, racers have been using several approaches. The cheapest and easiest involves installing a block guard. A block guard, available from Nu-Forms and STR, among others, is a CNC-machined piece of aluminum that is tapped into the top of the block deck, filling all the voids between the water jacket and the free-standing cylinders. The block guard is supposed to support the cylinders and keep them from moving around or cracking. The block guard has holes drilled in it so cooling water can flow through it to the head.
The block guard is highly regarded by some people and sworn at by others. I tend to be in the swearing category. For one, there are a lot of misconceptions of how to install a block guard, due to some misleading articles in the enthusiast press. One article showed a block guard being installed in a completely assembled, still-in-the-car engine merely by tapping it in place with a hammer. This sort of installation greatly distorts the upper part of the cylinder bore by up to several thousands of an inch, causing poor ring seal at best and seizing at worst. One very well known Quick Class competitor had his block and cylinders crack right at the point where the block guard was installed, probably because of the cylinder distortion and the huge stress riser the block guard created. There were also signs of seizure on both the piston and the cylinder wall in the area of the block guard.
If a block guard is to be used, the best way to install it would be the way JG and other engine builders do it. They hand fit the block guard to the block for a close fit before any other machining operations are done to the block. The block guard is then TIG welded in place. Skip welding is used to minimize distortion to the rest of the block. After welding, the builder machines the deck of the block flat, then the final bore machining is done. In my opinion, this is the correct way for a block guard to be used. At the very minimum, the block's bores need to be machined after the block guard is installed. Again, in my opinion, a block guard should never be installed in an assembled engine that is sitting in a car with its head off; instead, it should only be installed when building a new engine and the bore honing can be done after the block guard is installed.
A better way to beef up a Honda's cylinders is to resleeve the block. This involves boring out the thin cylinder wall liner and press fitting in new bore sleeves made of a thicker, superior material, like chrome-molybdenum steel. The best sleeves, in my opinion, are those made by AEBS. These sleeves feature a thick deck plate built into the sleeve, which solves both the sleeve cracking and any head gasket sealing issues in one easy operation. The deck plates abut each other and brace against the outer flanges of the block so they cannot move. This gives a superior strength to the cylinder wall, lots of clamp area for the head gasket, as well as a load of support, preventing the sleeves from walking around.
STR also makes excellent thick-wall sleeves that brace against the block wall to prevent shifting under load. The top of the STR sleeve is more open than the AEBS sleeve, which allows even coolant circulation, but does not give as much gasket seating area. This may be better for strong, naturally aspirated engines, but boosted or nitrous-equipped engines would still probably be better off with the thick-decked AEBS sleeves.
Other than re-doing the cylinders, the rest of the Honda block is built like a tank and needs very little modification in order to reliably handle the most extreme power demands. The H series Honda engines have a closed deck and do not exhibit these problems.
Generally, the bulletproof bottom-end and block premise carries to the other popular import engines as well. There are a few prep tasks to be considered, but for the most part, the blocks can be run pretty much as-is.
When boring and honing a block,, a deck plate should be used, if possible. This is a thick metal plate that simulates the distortion that bolting on the cylinder head causes. This helps ensure the cylinder bores stay round and the ring seal remains good, even once the head is torqued. Although this is less critical on a beefy import engine than it is on a flexy domestic V8, and plates for import engines are hard to come by, it should still be done. The cylinder bore can distort as much as 0.0005-inch on some engines, which is an amount that does make some difference in friction and ring seal. Each piston should be measured and instructions given to the machinist so he can keep the piston-to-wall clearance equal on each individual piston and bore. Open deck blocks like the B and D series Hondas don't need a deck plate because the free-standing cylinders are not distorted by the bolts.
Proper cylinder wall finish is also important. It is critical to use the exact finish prescribed by the maker of the rings for both longevity and good power-producing ring seal. As I mentioned earlier, I believe the stock ring packages that come with most import engines are better than aftermarket. These rings are chrome faced for long life and are usually thin in profile and low in tension to help seal at high rpm. For these rings, a smooth cylinder wall finish is required in the 600-grit range. All honing should be done on a Sunnen CK-10 machine, because it is the best for accurate work, utilizing diamond grit stones, which control tolerances better. After honing, a few passes need to be made with a plateau hone, which uses cork-bonded grit stones, or a fine grit flex hone. Plateau honing removes the microscopic high peaks in the honed surface. This speeds up break-in and reduces wear during break-in.
Although import engines (unlike domestics), rarely need it, all blocks should be checked to see if align boring is needed. Align boring is used to correct the straightness of the main bores if they changed during the engine's life. Although this is a common operation when building a domestic engine, an import hardly ever needs this done; nevertheless, it should always be checked when building any engine.
The block should be fully deburred with cartridge rolls and deburring tools to get rid of sharp edges and casting flash. All freeze plugs should be staked in place and some engine builders go as far as to set screw them in place. All press-fit oil galley plugs should be replaced with screw-in plugs. The really anal-retentive types will polish the block's interior to remove embedded casting sand, eliminate anything that could possibly be a stress riser and aid oil return and reduce windage losses. Some guys don't do any of this and still go fast with lots of power; this is a testimony to the strength and sound engineering behind many import engines!
Before assembly, it is important to thoroughly clean the block. After machining, the block is heavily contaminated with honing shavings and debris embedded in sticky, cutting oil. Sludge builds up in the block's oil passages with use and really piles up in blind ends of the passages.
All oil passage plugs need to be removed and the passages need to be brushed out with rifle brushes or cleaning brushes, especially designed for engine oil galleys. Summit Racing sells block-cleaning kits for this purpose. A rust-inhibiting degreaser like Motul Moto Wash should be used on the brushes, in the passages and generously sprayed around to get off every bit of crap. The oil passage plugs must be re-installed with locktite after cleaning or horrendous internal oil leaks will instantly destroy the new engine! After scrubbing, the block should be flushed with lots of water and blown dry with compressed air, especially the oil passages. Care should be taken to avoid wetting the freshly machined bores at this point, as they will rust almost instantly with any contact with water.
Once the block is clean, the bores can be wiped with carb cleaner and clean, white cotton rags until the rag is absolutely white after wiping the bore. After the bore is completely clean, it should be sprayed with a rust inhibiting oil like Motul Protect to prevent any rust from forming.
A trick used on many domestic engines is studding. Studding is replacing the bolts that hold the head and main caps in place with high-strength threaded studs. A stud has the potential to be stronger than a bolt because it holds the parts in compression instead of tension. ARP and SPS make ultra, high-strength metric studs with various metric threads for import engines. However, the bolts used for the main caps and cylinder heads of our beloved imports are already pretty high quality and very strong. Failure is rare, even with mega boosted engines and many a 9- and 10-second engine has been held together with good, old stock bolts. Still, the most anal retentive may opt to stud the engine.
An important point to remember is many imports use what is called a stretch bolt for these parts. Stretch bolts have a section of the shank with a reduced diameter that stretches when tightened to the correct tension; this ensures the correct tension will be applied. The sure sign of stretch bolts is the torquing procedure will include an angular method of tightening the bolt. This is when the bolt is tightened to a low torque first with a torque wrench, the turned a given amount of degrees to the final tightness. Stretch bolts give superior performance, but must be carefully inspected and measured after each use for overall length and thread distortion to ensure they are not over-stretched or deformed.
The Oiling System
Most imports have good oiling systems. Most feature stout gears pumps driven directly off of the crank with no failure prone drive systems. Little modification is needed, even at extreme power outputs. Some anal retentives close the end gaps of the pumps to reduce internal pump blowby by lapping the housings. Others shim the oil pump relief spring to increase the oil pressure. Most do nothing.
If you are building a Honda hybrid, like an LS engine with a non-VTEC head or a B20 block with a VTEC head, you might consider swapping in the higher capacity oil pump from a VTEC engine. Also, if building an SR20 or VG30, you might want to consider using the higher capacity oil pumps from the turbocharged versions of these engines. Sometimes oil pump rotors can fail. Although it is rare for this to happen, this usually results in a complete and disastrous failure of the engine. JUN and Toda make high-strength oil pump rotors for some Hondas and Nissans to prevent this failure.
Since most oil systems are engineered so well, the main mods to the oiling system are simple, to do a thorough job cleaning the passages, adding screw in galley plugs to ensure nothing will make them blow off and loctiting them in. Chamfering the sharp edges of the galleys on the crank journals and anywhere the oil flows cannot hurt, either. Other than that, there is not much to do.
If you suffer from a blown engine, it is super-important to check the oil pump for internal scoring and jammed relief valves as well as other damage from debris. Clean all of the oil passages and any external oil coolers and lines. Failure to do this has caused many a newly rebuilt engine to blow again, right after the fresh rebuild.
Cooling System
Very little needs to be done to the cooling systems of an import engine, Fluidyne makes aluminum radiators for most of the popular Hondas and sometimes you can run a radiator from another model of car for more cooling capacity, running a Japan market only, turbo Pulsar GTI-R radiator is a common trick used for cooling a turbo SE-R. SR20 water pumps tend to cavitate above 6500 rpm, so running a higher pressure 300ZXTT cap helps, as do underdrive pulleys. AEBS has electric water pumps for drag racing Hondas to avoid parasitic power loss and to ensure that a good volume of coolant reaches the far corners of the engine under all speed conditions. JUN makes special, high volume water pump impellers for SR20 and a few other engines. The painfully careful will break the edges on water pump impellers, radius the cooling passages and remove accessible casting flash from the blocks water passages. That is about it. Many a fast car has no work done at all here.
Good head gaskets are hard to find
The ubiquitous, often-ignored head gasket is an important link in the building of an all-out engine. Interestingly enough, the stock head gaskets of most of the popular import engines are perfectly adequate for pretty severe use. Stock head gaskets are usually made of steel shim stock covered with graphite filled composite. Some stock Honda gaskets are even made of tough PFTE coated stainless-steel shim stock. These combinations of gasket materials seal well and are reasonably strong, even to large amounts of boost, unless the engine has detonated. In that case, the high pressure of pounding detonation can often cause the stock gasket, or any gasket for that matter, to blow.
Some tuners O-ring the block or cylinder head to help the stock gasket resist blow-out. O-ringing is the addition of a machined groove around the circumference of the cylinder bore in either the block or the head where a wire made of either copper or soft annealed stainless steel is inserted by tapping it into place. The fit between the wire and the groove is a tight, interference fit. This wire digs into the head gasket and helps pin it in place to resist blow-out. O-ringing should be done before the final honing of the bores, as the groove machining process and the inserting of the wire can cause the bore to close slightly.
HKS and GReddy offer head gaskets made of tough, Teflon-coated steel shim stock. These gaskets are very strong and blow-out resistant. For extreme turbo and NOS use or for extra large sleeved bores, where a custom head gasket is needed, soft annealed copper is the material of choice. There are quite a few companies that can laser-cut custom head gaskets from copper. The difficulty with copper is it is hard to get a good seal with the water jackets. The copper gasket must be re-annealed after cutting to ensure it is soft and thoroughly coated with Hylomar or a similar semi non-hardening sealant. Even then, copper often weeps coolant slightly, limiting its recomended use to very built drag racing engines. GReddy and HKS also sell thick, 2mm (or sometimes thicker) headgaskets for the purpose of lowering the engines compression ratio for a turbo kit without spending money on special pistons. Although this is a cheap way to lower compression, it is not the best way to do so. A thicker head gasket is more likely to blow out, because there is more surface area around the bore for detonation pressure to impinge upon.
A thick head gasket also makes the cylinder head's quench areas ineffective, increasing the propensity to detonate more than the suggested reduction of compression the head gaskets would seemingly indicate. An engine that has the compression ratio reduced to 8.5:1 via a thick headgasket may have a detonation threshold of a 9:1 compression engine due to the loss of quench.
Conclusion and Delusions
Because of their precise tolerances, beefy construction and high-tech engineering, many import fans have an illogical smugness when comparing the prowess of their rides with the big displacement domestic camp. This infuriates the typical domestic owner. Although most of the domestics in stock condition cannot compete in the hp-per-liter game or the have ability to withstand unheard-of boost levels in stock form, like it or not, the vehicles are still capable of being faster when modified to an equivalent level. Although it is fun to put the smackdown on an unsuspecting domestic owner at the track, small-bore imports are not faster than the fastest of the domestics.
There is no replacement for displacement when it all comes down to it. It is all relative. A silly Civic Si owner who confidently revs on an LS-1 powered Camaro or a Cobra Mustang at a light, cocky in the fact his engine makes more power per liter and his JD Powers quality score is higher, is going to get swatted like a pesky little fly, VTEC or no VTEC. Strap a well-tuned turbo kit on the little B16A, though, and the big boys may get a glimpse at the Civic's Si trunk emblem. That kind of fun is what import performance is all about to some.
Even the fastest Outlaw Cars in the Import NIRA or IDRC series would not even qualify for an NHRA Pro-Stock or IHRA Pro Mod weekend finals. This may change in the near future, as import racing is still young, but right now, that is what the facts are. As bad as the baddest of the Outlaws are, they are still no match for the equivalent class of domestics. If the big-bore V8 guys were allowed to turbocharge their huge engines by the rules, the tiny imports would not stand a chance--multivalves, variable cam timing, overhead cams or not.
However, the import fan can still revel in the fact that for the most part, their engines are much more solidly built in stock form and can be modified to produce way more hp per liter than the big bruiser V8s. In our smaller lighter cars, we can still get the satisfaction that we can surprise many a domestic at the track. This much is true. This is fun. Until next time...