How to Build an LS/VTEC Frankenstein Motor
Why Build an LS/VTEC?
An LS/VTEC motor combines the bottom end of a non-VTEC b-series motor with a DOHC VTEC head. When using the bottom end from a b20 CRV motor, you get both the torque of a larger motor with the high-end power of a b18c. These motors are often called hybrid or Frankenstein motors. They get this name because they take parts from various motors, and their sum is greater than their parts.
A mild build can produce close to 200whp while some of the more extreme builds can produce close to 300whp. Combined with a light-weight car, such as a Honda CRX or Civic hatchback, you have a potent combination for a very fast time at the track.
The LS/VTEC will make more torque and have a wider power band than any other b-series motor. These motors sometimes get a bad rap because of people who haphazardly throw a VTEC head onto a non-VTEC block and call it a day. When properly built, this engine will be as reliable as any other b-series motor.
- B18 or b20 non-VTEC block
- DOHC VTEC head
- Golden Eagle LS/VTEC assembly kit
- ARP rod bolts
- ACL bearings
- APR head studs
- New oil pump
- GSR/ITR timing belt
- A Helms manual
- Any parts you plan to upgrade
Preparing the Head
Obviously, you must start with a VTEC head in order to build an LS/VTEC. Your choices are a b16, a TypeR, or a GSR. From the factory, the ITR head is the best. IT has stiffer springs, upgraded retainers, and better cams, along with a mild port on the intake side. As you are going want to upgrade these things even further yourself, the added price tag is not worth it.
When choosing between a b16 (pr3) and a GSR (p72), there are two major factors to consider. The b16 head is the same cast as the ITR, which means that the better flowing ITR manifold bolts on. The GSR uses a different intake manifold and has a smaller combustion chamber, which some prefer. But it can also lead to clearance issues. Some prefer the flow characteristics of the p72. Without a personal preference, the pr3 will keeps things simpler.
Once you have selected your head, you will want to send it to a reputable machine shop to have it prepared. Some quality machine shops include Port Flow, Headgames, and Alaniz. You can choose any shop you trust, but make sure they are familiar with performance Honda heads and not just domestics. While the head is there, you will want to replace the old worn springs, retainers, and seals. Titanium springs and retainers will help your motor sustain the high rpms and aggressive cams you will be exposing it to. This is the time you have your head ported for extra flow and possibly milled if necessary.
When you get your head back from the machine shop it is time to start preparing it for assembly. Remove the Allen plug from the back left of the head. Then tap into the head and attach the 1/8 NPT pipe fitting, included in your assembly kit, using Teflon tape. Use the two corner exhaust side head bolt holes to install the dowel pins found in your kit.
Preparing the Block
The stock pistons and rods are crap and should be immediately thrown away. If you are working with a tight budget, OEM CTR or ITR pistons are a good option. Shot peening your LS rods is one strategy you can use to strengthen them. After-market forged pistons and rods are a much better option as you only want to build this once. Paying a few hundred extra in prevention is worth thousands if a piston goes flying through your block. The stock OEM rings are perfect, and as long as you don't over-bore the motor there is no reason to use anything other than Honda OEM rings. Others prefer to use Hastings piston rings.
If you plan to use a turbo, low-compression pistons will help you make more power, however, I am writing this with the assumption you plan to stay naturally aspirated. For an all-motor compression, you will want high-compression pistons to get the most advantage from your cams. 11.5:1 is a minimum and up to 12:5:1 is perfectly safe on pump gas when properly tuned. Don't rely on what compression the piston manufactures claim the pistons will make. Instead, do the math. The actual compression can be very different in any build than the advertised compression.
The weak factory rod bolts are the most common cause of engine failures in an LS/VTEC. Replace these with ARP bolts to safely withstand the much higher rpm's your motor will be seeing. Also, have your rod ends resized to better fit your new rod bolts. It is recommended by ARP and is worth the extra money. As for as bearings, use either OEM or ACL. Many people have found ACL to work just as well as Honda bearings and they cost less.
Once you have all of the parts together you will need to have them assembled. At this point, you will also want to have a machine shop balance the rotating assembly. This is also a good time to have the crankshaft polished and knife-edged.
Preparing Your LS/VTEC for Assembly
Now that you have your head and block ready, it is time to actually put it all together and have an operational motor. Start by installing your ARP Head Bolts. Factory head bolts are going to too weak to handle the increased demands of an LS/TEC.
- First, cover the cylinders, and clean then clean out bolt holes using compressed air. Once the holes are clean, tighten down the studs all the way down and then back them off a 1/4 turn. Hand tightening, despite what the directions say, does not work. This technique gives you the tightness you need and keeps the bolts uniform.
- Install the oil pan and gasket. This is a good time to completely clean the oil pan from built-up gunk and debris. At this time you can also prime the pump by applying some oil to it. Once everything is dry, apply the gasket and tighten everything back up.
- If you need to buy a water pump it is better to use an ITR pump. If you already have an LS water pump you can use that but you will also need to use an LS timing belt. The ITR pump spins slower at high rpm's which will create less slosh when your motor is under heavy load. Spread some RTV compound in the gasket's groove and torque everything down according to your manual. Slip the gaskets onto both ends of your water pipe and connect one end to the water pump and the other to the thermostat housing.
- Next, you will need to install a fan oil pressure switches. A knock sensor is optional but your engine management should make this unnecessary.
- 96+ B18's and all B20 blocks do not come with breather boxes. To lower crankcase pressure, this is something you may want to add. If you have a 90-95 LS block you don't need to worry about this. Don't skip this part as it is something that will allow your motor to last longer.
- Next, install the alternator bracket and tensioner pulley. Leave the pulley loose because you will be tightening it down when installing the timing belt.
- The final thing left to do before moving onto the actually assembly of the motor is to attach the drivers-side engine mount bracket.
Assembling Your Motor
- Before assembling your motor you need to make sure it as top dead center. This means the #1 and #4 pistons are at the very top of their stroke. Attach the crank pulley and turn the crank counterclockwise until the crank gear and the arrow above it lines up. Do not turn clockwise as this may damage the motor. If you turn too far, just keep turning to you reach tdc again.
- Once you have it lined up, you can begin attaching the head to the block. Using the head gasket that matches the block you are using, place the gasket over the head bolts and onto the block. After installing the dowel pins on the exhaust side, you can place the head onto the block. It is extremely important that everything lines up and is straight at this point to prevent leaks in the future. Once everything is flat and lined up, tighten down the ARP nuts and washers following their instructions, not Honda's.
- Now connect the VTEC solenoid and both coolant sensors following your manual's instructions. You will also need to connect the coolant housing to the head with a bead of sealant.
- Now you are ready to move onto the camshaft and cam gear installation. Stick with a proven company when it comes to your camshafts. There are many cheap knock-offs that don't have the build quality you would expect from a maker such as Jun, Toda, or Skunk2. Which camshaft you use depends entirely on your goals and setup. Which one to use is entirely build-dependent and one of the most important pieces to making good power. Take time to research this thoroughly. As far as cam gears, the most important factor is that they are sturdy and will not slip.
- To install these parts, start by placing new cam seals on your camshaft behind the gears. Place the woodruff key in the slot and tighten down the bolts on the cam gears. With the gears installed, apply generous amounts of lube to the journals and place the camshafts in. Make sure the cam with the distributor slot goes on the intake side.
- With the camshafts installed, you can begin placing the caps. These are numbered and labeled from the factory with an I for intake or an E for exhaust, so it is pretty easy to figure out where they go. Then place the holders and tighten them following Honda's instructions. You will also want to make sure the cam seals stay beneath the first pair of caps.
- Next up is the intake manifold and fuel assembly. As I mentioned previously, the benefit of using a pr3 head is you don't need to use a GSR intake manifold. Skunk2 makes an ITR style manifold that fits a p72 head, but that is a step worth skipping. Now you can use either an aftermarket intake manifold, an ITR manifold, or one from a B16. Besides being cheaper, a B16 manifold will make more power lower in the power band. The other options are designed for power higher in the powerband. For the gasket, I suggest the one from Hondata. Aside from producing a couple extra horsepower, they are reusable and will save you money in the long run. The stock fuel rail is good for upwards of 500hp, and aftermarket ones tend to be a headache. Stick with OEM. To prevent the need to run extremely high fuel pressures, I also suggest upgrading your fuel injectors to 310cc ones. Once again, consult your manual, and this part is pretty straightforward.
- To install the oil lines you are going to want to follow the instructions that came with your kit. If you use one other than Golden Eagle's the instructions may be different. Take care to use Teflon tape to ensure a good seal.
- Now, onto installing the timing belt. As mentioned previously, you need to use the same belt for the motor as the water pump you are using. Some people have reported that the ITR holds up best, so if you need to buy a water pump, that is the one you should buy. After making sure the motor is still at TDC, rotate the cam gears until they are also lined up. Slide it over the cam gears, then work down over the water belt and tensioner. Pull down on the tensioner until it is completely loosened and then tighten the bolt with the tension completely loose. Now you can slide the belt over the tensioner and finally the crank pulley. With the belt tight, tighten down the tensioner. Further instructions can be found in your manual.
- To install the LS timing belt cover, you will need to trim it over the oil pump before tightening it down. After this, place the woodruff key in the crank pulley and tighten the pulley down. Place the alternator but don't tighten the bolts yet. First, pull the belt over the alternator and crank pulleys and pry the alternator outwards, then tighten the alternator bolts.
- To install the distributor, start by aligning the inside marks. As long as your motor is still at TDC everything should go together smoothly and with perfect timing. If you used an LS distributor, you will need to cut off the bottom leg to avoid the VTEC solenoid. This may lead to a leak, so it is better to use a VTEC distributor.
- Now you can install the valve cover. Replace all the gaskets with new ones to prevent leaks, but first, make sure that all surfaces are clean. Now you put on the valve cover and tighten it down.
- The last step is to install the spark plugs and wires. This is simple maintenance, so if you are taking on this project, I assume you know how to do this. The main thing to note is that you have greatly increased the compression, so colder plugs are going to be needed. Start by moving down two steps and adjust accordingly. OEM spark plugs will perform just as well as after-market ones.
Breaking-In and Tuning
After going through so much time and money to build this Frankenstein motor, you are going want to make sure it lasts a long time. A proper break-in and engine tuning are required to make sure your motor lasts.
- Before tuning, you are going to need to use any VTEC-capable ECU. It does not matter which one because it is going to need to be chipped anyway. This will allow it to be tuned using your system of choice. Hondata is a popular and affordable engine management system.
- Obviously, you will need to add fluids before ever staring the motor. At this point, you can just use the cheapest 10W30 oil and filter you can find. Fill it with coolant too. Again, if you are doing this project you should know how to do this.
- With the fluids filled, you can start the motor. Disconnect the ECU and turn the motor over for about 30 seconds to increase oil pressure. You disconnected the ECU to keep ignition out of the compression chambers.
- Now, with everything primed, reconnect your ECU and start the motor again. Check for leaks and make sure the oil light quickly turns off. If there are any problems, troubleshoot and address them before continuing. Once everything checks out, continue running the motor until it reaches normal operating temperatures. First tune the motor for a 14.7:1 air/fuel ratio at idle. Then tune it at normal driving loads. Again, aim for a stoichiometric A/F ratio.
- Now your motor is safe to be driven to a shop for further tuning. Consult with your tuner about what break-in procedure they want you to follow. Some wait a few thousand miles before stressing the motor, while others want to tune at wide open throttle right away.
- Change the oil after 100, 500, and 1000 miles. It is not safe to use synthetic oil until the motor is broken-in. Use of a magnetic drain plug will help remove shavings from the build precess. Taking extra care while breaking-in your motor will pay off the in the future by prolonging the amount of time you will be able to enjoy your LS/VTEC Frankenstein monster.
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.