Crank, Rods, Bearings, Machining, Balancing, Coatings, Manifolds, etc.
The SR20 is blessed with a near bulletproof bottom end. The crank and rods are forged steel unlike the typical cast iron that most American motors run. The rod bolts are a beefy 9mm. The crank features rolled fillets, an uncommon strengthening operation used usually only for racing or heavy duty parts. The rod bolt registers are spot faced, leaving a generous amount of metal around the bolt holes, a traditional weak area in connecting rods.
Both the crank and rods are subjected to a severe shotpeening from the factory. Shotpeening microforges the surface of the part making it stronger and harder while leaving the interior soft and ductile. This step can improve the fatigue strength of a part by over 100% and is usually reserved for high end racing parts. The main caps are tied together with a stiff aluminum girdle which improves bottom end rigidity significantly. This feature is usually found in all out race motors. These design elements produce an engine that is nearly bulletproof. I have seen motors with over 100,000 miles on them with the factory honing marks still visible in the cylinder bores! The number of list members in the 100,000 Mile Club is a testament to the durability of the SR20.
The only catastrophic engine failures that I know of (Tom Paule and Zak Nilsson) were the result of low oil levels with spun bearings. Chuck Nibbana’s super trick engine also mysteriously disassembled itself but that might have been because of improper clearancing. I have screwed up 3 SR20’s myself but that was the result of not watching the temperature gauge while racing IMSA and SCCA. Gross overheating was an understatement. Clark Steppler of JWT has never seen a catastrophic failure that could be traced to the engines fault, either.
The same bottom end of our US model SR20DE also is used for the turbo SR20DET so we have a lot of headspace before we start to challenge the strength of the bottom end. The stock parts can be used until the hp climbs well into the 200’s. So bring on the NOS, turbo boost and compression! We have run Ryan Besterwich's turbo car (formerly Searl's) as high as 20 psi of boost which pushed the car into the low 12's with a completely stock bottom end with no harm. His car has over 80k miles on it and is still going strong. I estimate that his car is putting out over 400 hp with the stock bottom end! If detonation can be controlled the stock bottom end is pretty strong!
If you are building a hot street SR20, I recommend leaving the rods alone. By doing the traditional beam polishing you will be removing the factory tough shotpeened surface. If you reshotpeen the rods after polishing they will have to be resized and straitened as proper shotpeening distorts the parts. It is not likely that a local shotpeener can do as good of a job as the factory either. The same goes for the crank. It won’t hurt to do these traditional race prep steps but it is probably not worth the effort on the SR20.
If you do prep and re-shotpeen your rods make sure that the piston wall oil squirter hole does not get blocked or peened over. This hole sprays oil on the thrust side of the cylinder helping with lubrication and keeping the engine quiet.
In fact, I might say that no matter what you do to build a naturally aspirated motor, if you keep an 8000 rpm or less redline, you don’t need special rods.
I do not have any personal experience with the well-publicized-by-Turbo-magazine, Metalax treatment process but have heard good things about them. I do have plenty of good personnel experience with shotpeening solving many parts breakage problems. Recently I have had very good luck with cryogenic treatment preventing breakage of drivetrain parts with high powered SE-Rs and I am currently building a VG30DE motor using cryogenic treating extensively.
For extreme use in killer turbo motors running near 20 psi of boost or for those of you running 100+hp NOS units, racing rods may be in order. JWT can get Crower rods. I believe these rods are machined from 4140 billet. I am using Cunninham rods in another engine. These rods are a little lighter than Crower and seem just as high quality. Carrillo makes excellent rods also but they would be a custom application and take 6-12 weeks for delivery. These racing rods do not have the oil squirter hole in them which could result in slightly shorter life of rings and pistons.
The rods and pistons should be balance to within 1ž2 gram and the crank dynamically balanced. I have found that Nissans are generally within 1 gram from the factory! A typical American car is usually off by as much as 5-12 grams! I like to polish the journal surface of the crank. You can have a local machine shop do it using the lightest grit of polishing paper belt. You don’t want to remove so much material that the crank dimensions change, just reduce the RMS of the surface by knocking off the peaks of the machining marks.
The factory Nissan bearings are strong and durable. I recommend running bearing clearances in the middle of factory spec on a typical street motor. Clearances on an all out racing motor can be set on the looser side of factory. When buying bearings, Clark Steppler of JWT has told me (and I have also observed) that if an engine has any kind of mileage on it, the next tighter bearing size can be used other than the number that is stamped on each journal of the block and crank. Remember to mike and bore gauge all the journals to confirm proper dimensions before assembling. If you don’t have access to these , at least use plastigauge to make sure that you are in the ball park.
When boring or honing a block, it is better to use a torque plate. A torque plate simulates the stress of a cylinder head being bolted on your block. With a block that was machined with a torque plate, the bores will remain straight when the head is bolted on. Usually the block will distort and the cylinders will become out of round accelerating wear and reducing the effectiveness of the ring seal when the head is bolted on. Granted this is a small difference but is important if you want to build a good motor. For this reason the main caps should also be bolted on and torqued when the block is being machined.
Boring and honing should be done on a Sunnan CK10 machine. This is a high precision machining center that makes the honing of a good round bore almost idiot proof. Since today’s low tension rings require a smooth surface to seat properly, plateau honing after the dimensional honing reduces the RMS of the surface for lower friction, better sealing, less oil consumption and longer life. JWT has pioneered the use of plateau honing on the SR20 and has the process figured out for a smooth bore surface that will still allow the rings to seat. When properly machined with a torque plate and plateau honed, it is possible to have an engine that leaks down at 2% or less! [Editor's note: Nissan specifies that up to 10% is acceptable; most SR20DEs leak down at close to 5% (source: senior mechanic at Falore Nissan)]
JWT is the only company in North America to my knowledge that has a torque plate for an SR20 engine. JWT is most likely the best company to machine your SR20 block. JWT can also machine your block for SR20DET piston coolers. Piston coolers are oil jets that squirt oil onto the underside of your piston dome to help lubricate the piston pin and to help keep the piston cool. As aluminum starts to lose strength above 350 degrees, piston coolers can help quiet a bit. The SR20DET uses piston coolers as does the 11:1 cr SR16VVL N-1 spec motor. This Japan market hyper motor makes 200 hp from only 1600cc!
Since Nissan feels that this 11.6:1 motor needs piston coolers it is probably a good idea to put them in yours. The piston coolers have a spring loaded valve so they only open at higher rpms to maintain good oil pressure at idle and in bumper to bumper traffic. In my motor there was a noticeable drop in water temp once the coolers were installed. To my knowledge JWT is the only company that has the fixturing to machine a block for these piston coolers. Talk to Clark Steppler at JWT for machining.
When building a killer motor it is a good idea to replace the main cap bolts with the ones found in the SR20DET. These are about 20% stronger. Nissan Motorsports stocks these.
I am a believer in special coatings. Coatings are great for adding to reliability or to help control factors such as heat so special tolerances can be used. At the advice of Nissan Motorsports I used Swain tech coatings. Unlike the other to-be-named coating houses that use off the shelf coatings, Swain develops their own in-house coatings that are much more sophisticated. Where most other companies have a one layer coating, a Swain coating might have 3-4 different functional layers. I use Swain tech gold thermal barrier coating on my pistons. This is a severe duty 3 layer thermal barrier that reduces heat transfer by about 25%. This helps protect them from detonation and Nitrous abuse. By keeping the heat out of the pistons, I can run an amazingly tight piston to wall clearance of 0.0004 inches. That is 4 ten thousandths of an inch! My engine does not burn oil at all even with water-thin 5w30 Mobil 1 oil.
I also use Swain poly moly dry film lubricant piston skirt coating. This coating uses molybdenum disulfide and tungsten disulfide for a dimensionally stable heat conducting matrix. This is better than the teflon that most other companies use because teflon distorts and creeps under load. Teflon is also a heat insulator. Since the pistons cool themselves by conducting heat through the skirts, it is not to good to insulate them. Poly Moly can help tame the clatter of forged pistons. Poly Moly also tightens your piston to wall clearance by 0.0014 or so inches so you may have to compensate in your bore machining for this added clearance.
The guys at Nissan Motorsports tell me that poly moly significantly cuts piston and cylinder wall wear. Next time I go through the motor I will probably coat the valves and combustion chamber to protect them also. One of my friends had a 20 degree drop in water temperature, 300 rpm faster turbo spool, and 300 degree higher EGT's with a fully Swain coated motor. On my hopefully 700 hp Twin Turbo Z motor, I will be using Swain coatings on just about everything from the bearings to the undersides of the pistons. I believe that these coatings are like a cheap insurance policy.
Swain also makes slippery flow improving coatings, heat dissipation coatings, wear resisting coatings and stealth coatings that are not detectable!
List member Kurt Sussman is planning to build, test and manufacture a short runner intake manifold. When running computer simulations with Dynomation’s software, gains of up to 15 hp above 5000 rpm with losses of only 2-3 hp below 3000 were noted. This seems to indicate that Nissan sacrificed lots of top end power to gain a little below when designing the manifold. I noted that Nismo’s race manifold as well as GReddy and JUN’s race manifolds have short runners. The 196hp SR20VVL also has a short runner manifold. As these manifolds are designed for the RWD S13 and S14 chassis, Kurt took it upon himself to design one for the FWD cars. Yeah Kurt! We will be posting the results of this manifold as Kurt get around to it. However, he just had a baby girl which should postpone his manifold development for quite a while. If anyone else wants to do it, let me know