Rb26 Head Porting lb57

This is my engine from my car. It's a rebuild, not a new build. Some parts are ugly and show wear, like the crank pins not being perfectly polished, or scuffing in the oil pump housing. That's because the motor spun over 10K rpm and made over 1K hp. It's 11 years old. I don't do bling very well. I don't mind it if that's your thing, but anyone here can ask the people like Stony who know me personally, the term "drive it like you stole it", is very appropriate. Yes, those are the stock crank cap bolts. Guys were making over 1,000hp with them long before ARP started making studs, including this engine, with no problems. Maybe with individual caps, but not with a girdle that shares the load and keeps caps from walking around. Are studs a good investment? You bet!, Do I need them? Nope. I don't have a "clean room". I don't build enough engines to warrant the $50,000 it would cost me here in Japan. Occasionally some dust shows up in some pictures. Trust me that it get's cleaned out before anything is assembled... I'm obsessive with the air blower . I use lint-free paper towels on everything and then blow the hell out of it to get any lint off... There is no such thing as a "clean" engine. You just do the best you can. Seeing as how Arias doesn‟t seem to want to send me some piston rings, I‟ll stop on the bottom end for a while and get busy on the head. A few things have changed. When this engine started out, it was in excess of 1,000 HP. The original turbos were TD06SH-25G‟s, which I still have, and the head is rigged for max power drag. (for a turbo swap guide, check out this article: RB26 Turbo Swap Guide). Seeing as that‟s no longer the goal, I‟ve decided to do a little detuning. The new goal for this engine is around 600 HP with street performance/touge in mind. The original head is completely worthless for this kind of driving. 288-big lift Step Pro L cams, zero quench deck, big valves and ports, etc., aren‟t conducive to mid-range grunt. It would actually make less power across the curve than a properly prepped head for the intended application. Therefore, I‟ve decided to start over and use a new head that I‟ll prep for exactly this type of driving, and use a pair of new Tomei 260 cams.

I‟ll start with the clean up in a proprietary detergent I use for cleaning engines. This is the carbon-packed chamber and oil varnished head before the soak.

After a one-hour soak and some brushing with soft-bristle brushes, it comes out looking like this.

On to the important stuff. The RB26 has three major coolant outlets along the head on the intake side. A mild port clean-up will make the coolant flow a lot better and will trap air less. Here‟s the small front water port that you don‟t need to worry about. It only runs from a by behind the thermostat, and is closed off by the thermostat once the engine is at operating temperature.

Here‟s one of the three ports. You can see how much of it is blocked by bad casting… All three ports look like this.

After scribing it to the size of the gasket.

Looks a lot better after cutting. Next we’ll go into porting. Now with video! Ahh, porting. What fun… Fortunately Nissan left us room for improvement. For engines generating power upwards of eight or nine hundred HP, there‟s not a whole lot that needs to be done. However, the places that need attention will give the motor more power whether it‟s stock or in clapped-out drag trim. First item that needs attention is the big „ol hump in the exhaust port. If you‟re using an exhaust manifold other than stock, it needs to go. In this pic you can see the offending hump. The other thing you see is that the gasket is considerably larger than the port. Same goes for the stock gasket. If you really wanted to, you could gasket match the port as long as the exhaust manifold is the same size. Resist temptation to make the port runner the size of the gasket. RB26 ports don‟t need to be any larger than they are for all but the most extreme applications. You‟ll lose power in the low and mid rpm for sure, and can hurt top-end power as well.

Here‟s the port with the hump removed. When valve seats are installed, the throat is milled to remove any material overlap. While this is a good thing, it leaves the port “unfinished”. It leaves bad transitions and irregularities that create turbulence in the most critical part of the air stream. The goal it to make the transition through the turn and into the valve pocket as smooth as possible. In the following picture, you can see a small lip in the short-side radius. The short-side radius is where air is hanging on for dear life as it rounds the corner. Any disturbance here will cause the air to separate from the port floor and slam into the valve, rather than try to follow the port wall and exit around the valve. You can imagine how bad this is if you think about that air slamming into the valve and going all over the place, disturbing the rest of the air stream as it‟s trying to

enter the port. You can round this sharp lip, but under no circumstances should you remove material from the floor of the port. Lowering the floor makes the short-side radius even shorter. Big no-no.

Here you see the where the mill gets the outside radius of the port. Not as critical is the shortside, but needs to be smoothed, just the same.

Here‟s what the bowl looks like when it‟s been smoothed out. It‟s hard to get a picture of the short-side radius. Just use your finger and you‟ll feel when the lip is gone and it‟s nice and smooth. This bowl could be considered finished, but I‟ll hit it with a 120-180 grit cartridge roll later on. You do not polish ports. Polished ports leave nothing for a boundary layer to hold on to, and will hurt power. The stock ports are smooth enough from the factory that you‟ll gain nothing by sanding the entire port with a cartridge roll, other than a pretty port that no one will ever see.

Another thing is to try as hard as you can to remove as little material as possible in the bowl. You do not want the port to be larger than the seat ring. The port should be expanding out as it gets to the valve seat. This makes air want to exit around the valve. If the port is larger than the seat and has to compress again to get through it, it focuses the air more towards the valve.

Other than cleaning up, this port is done. In the following three pictures, you can see the mill cut into the intake valve bowl. The third picture shows just how bad this transition really is, with a large lip.

Here is the port after cutting. And the port after it‟s been smoothed with a 120-180 cartridge roll. Can you guess how important it is to stay off of the valve seat with the carbide cutter and sand paper? Coming up against it is OK as long as you stay away from the 45 degree seat cut where the valve seats.

The reason for three and five angle valve jobs is to make the air flow smoother as it makes the turn around the seat ring, and into the cylinder. It is possible to grind the valve seat with the carbide up to the 45 degree cut and obtain another 2mm or so of port opening. While this may sound good because it makes the port opening larger, you lose the third angle in the valve seat and outflow becomes very turbulent, making the port actually flow less. Don‟t do it.

Here‟s the four ports cut, but not yet smoothed. Once again, do not open the intake port larger than stock. Even with a 1mm larger valve, the only thing that should be opened is the bowl as it transitions outward toward the valve seat. If you open the port in the turn to the valve very much, the air will lose velocity and become sluggish right where it needs to be going fastest. Simple steady-state flow bench #‟s don‟t mean anything here; the air flow is anything but steady state and relies on velocity to fill the cylinders. Big ports will kill sub-10,000 rpm flow. I made this short video for cutting the intake bowl to show how quick and easy it is. The key is going slow and easy. Once you remove material, you can‟t put it back easily.

It‟s been a while, and the engine is now almost complete. I‟ll finish up the head in this post. While most of this stuff (steps) is available in the FSM, it‟s good to see the stuff in action with real photos and video. Please keep in mind that I skip lots of steps in this thread. To list and show every little thing would consume huge amounts of time to write up. I‟ll try to get the important stuff in. Not going to show the valve clean up. It‟s really messy. I‟ve found that the best way to clean the valves if you don‟t have access to specialized cleaning detergents, etc., is with a drill press, some 240+ grit cloth, and WD40. Chucking the valves up in the press won‟t hurt them at all, just do it lightly. Be careful to keep the paper off of the seat area, and don‟t go any higher on the stem than the carbon. The valves are very hard, and you won‟t be removing material with simple sandpaper any time soon… Hard carbon is almost impossible to remove from the valves by any other process than mechanically, like this. Once the valves are clean and all the carbon is removed, the first thing to do is to check the guide play. The FSM gives the distance for the valves to be off the seat. The back and forth movement is checked with a dial gauge. Bucket-type lifted valves fare much better than rocker-type lifted

valves. Rockers put a side load on the valve as it sweeps across the tip, opening and closing. Buckets take up the lateral load from the cam sweep.

Checking the valve guide clearance. Here I‟m lapping the valves. This involves a special grinding compound that essentially mates the valve to the seat. There are different grits, but 99% of the time, only the finest grit will be needed. Over time small pits develop in the seat and valve area, which can cause valve leakage. Most of the time lapping will remove the pits and restore a perfect seal. I set a stopwatch and do each valve for 1‟ 30”, taking the next 30” to change to the next valve. Total time for each valve is 2 minutes. This ensures I lap each valve the same amount of time. After 12 valves straight (just for the intake), your arms and wrists have had it. If the first round doesn‟t remove all the pits, I do it one more time. If this still doesn‟t work, I cut the seats and valves. Too much grinding can cup the area. The other thing lapping does is allow you to see if the valve and seat are ing 360*. If the valve was a little bent, or the seat was damaged and sunk in one place, there would be no mark. You can also see the size of the ring, but that‟s for another day…

Here you can see the gray ring on the intake and exhaust seat where the valve was making during grinding.

I did another short video to show you a couple of the lapping techniques. Next the valve spring seats go in. Don‟t forget them. Valve springs will grind into aluminum. Once all the seats are in, you can install the seals. A six-point, 10mm socket for the intake, and 11mm socket for the exhaust work well to install the seals. The size is just perfect for holding the seal without damaging the rubber, but small enough to push down on the steel collar. Dip them in oil, and push them onto the guide. You‟ll feel them “pop” into place. This shouldn‟t need to be

said, but clean the sockets before you use them for this. For that matter, clean any tool you use for assembling an engine. It‟s not a good practice to install head bolts with the same socket you just used to change the brakes without cleaning it first.

Here‟s the spring seats and guide seals installed. Next you can slide all the valves in. Use a drop or two of oil and spin them in to lube the guide. The seals will now hold them in place so they won‟t slide out.

Next I put all the springs and retainers in. Many valve springs have a top and bottom. Look at the coils. If it has tighter coils towards one end, that‟s the bottom that goes towards the spring seat. I have a spring tool that allows me to install all the gear at once. Most will have to do one at a time.

I took the next two shots to show you the normal way of compressing the spring, and then installing the locks. The other tool I have lets me place all the locks on top of the retainer and just collapse it. The locks install automatically.

This shot shows the locks on. Dip them in oil so they‟ll stick better. The frustration you‟ll have here will help you understand why I have the other $350 compressor that installs the keepers automatically…

Here‟s the finished product. Here‟s where the shims go. Make sure the side that was against the valve is still against the valve. Sometimes it‟ll be slightly dented (only by micrometer), and will change the gap. It‟s just good practice to place things the way they were, even if they don‟t need to be.

However, the first thing you‟re going to do is measure all the shims. Even with “pon” cams, chances are you‟ll be changing a few, and it‟s better to know what the beginning thickness is. Some cams you‟ll be changing all 24. This shim is 2.99mm

Here‟s the new Tomei 260 compared to a stock cam. Big difference. Place the cam in a “neutral” position where it‟s close to where it would be at #1 TDC. “Neutral” means not just lifting one set of valves to max lift, but putting even pressure on at least two sets of valves. Then tighten the caps evenly, and DO NOT BEND THE CAM. It needs to drop into the front thrust area evenly and straight down.

Once all the caps are down, torque them appropriately. I lay all the thickness gauges I‟m going to use out, so I‟m not constantly looking for the one I need in the pack.

Checking the clearance. It‟s tricky with the RB26. Too much clearance, add shim in the amount it‟s out. Not enough, take shim away in the amount it‟s tight. Simple. Bad thing is you need to take the cams back out to change them. Before checking anything, turn the cam at least twice to make sure everything is seated. The head needs to be propped up front and rear because the valves will protrude past the deck.

On the final cap installation, you need to add some sealant to the front of this cap. Very sparingly. There is a small age in there from the rear of the seal to the inside of the head. If you block it, oil pushing out of the front journal to behind the seal won‟t have anywhere to go and will blow out the seal. Not fun to take it all back apart and clean it up. Wipe off the excess or it will cause the cover gasket to leak.

All done. Like I said, I skipped some steps. Installing the lifters, make sure they spin freely once installed. They turn while in action, and if they‟re tight, it‟ll burn up a lifter and cam lobe. The baffle plates only go on one way. Installed any other way, the covers won‟t go on. They're on in the pics, but need to be off for timing the cams, which I'll cover later. Dirt is the enemy. Compressed air is your ally. Be as clean as you can and try to use lint-free rags for touching the motor. Cheap paper towels work well. Shop rags do not. I know my blue bench top looks dirty in these pictures, but I assure you it's sterile (literally) before I start. All the discoloration is from years of burn marks from welding. At over US$40,000 for 500 square feet (just for the property, not the structure) I don't have a clean room yet.

On valve lapping: Someone asked me, why not just cut the valves and seats? The main answer is because there's nothing wrong with the valves and seats that are in this motor. If it requires more than about 2 minutes of lapping with a fine compound, I'll usually cut them. Cutting is not so simple in a high performance application. You also need to cut the other two angles in the seat to adjust the placement and size on the valve. Then you need to completely reshim everything. The above "pon" cam installation required changing three shims vs. 24.

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