Plenty of L28 engines have actually survived at this power level through years of abuse and hard use. When these motors do fail, it's usually because of one of two common mistakes - either you spend way too much money on expensive parts that don't actually help with reliability, or you try to save cash in the wrong places and skip the parts that actually matter. Upgrade your turbo and add a controller - you'll get some pretty wild numbers on the dyno. If you don't have the right fuel delivery system and proper tuning to back it up, the same setup is a ticking time bomb!
I'm going to break down where your money should go and where it'll just disappear with nothing to show for it. The target is 300HP you can count on - power that starts up every morning and gets you through track days without the need for endless repairs or extra care. Every part on this list is there for a reason, and they come from builds that have held up at this power level long after the excitement of the first few months wore off. This path lets you skip the trial-and-error tax that can cost most enthusiasts an entire second engine build.
Here's what parts you'll need to hit that 300HP goal!
Table of Contents
Which Stock Parts Need Your Attention
The block you start out with is the biggest part of this whole build. The L15B7 and L15B2 versions are capable of handling around 300hp without ever needing a teardown. These two engines do have some differences - mainly in which Honda model they originally came in and a handful of internal parts that got swapped between versions. None of these variations will actually change the power ceiling we're talking about here, though.
Honda built these engines with a closed-deck block design, and that's a big part of why they hold together well when you add boost. All that extra reinforcement around the cylinder walls is why these blocks take a lot of abuse when you start pushing power through them.
A full engine teardown with all new internals isn't necessary for most of the L15 builds. The stock parts can handle around 300hp pretty easily. What needs some attention are the two weak points that show up on this platform. Rod bolts and head studs are going to need upgraded parts before you push power into that range.
Your factory rod bolts weren't built to take care of the stress that forced induction creates at this power level. ARP rod bolts are the upgrade you want if you plan on keeping your connecting rods securely attached to the crankshaft (which is where they need to stay). Your head gasket is another concern - it needs a lot more clamping force if you want it to keep a solid seal. ARP head studs swap out the stock hardware and deliver the extra holding power that your engine is going to need.
This particular setup has actually been around for quite a while, and lots of enthusiasts have been running it successfully for years without running into any problems. Some of these engines have already pushed well past 50,000 miles at 300hp, and the only upgrades that they needed were better rod bolts and head studs. Everything else down in the bottom end can stay stock, and it'll all keep working just fine.
Whatever money you save when you skip the full rebuild can go toward better supporting mods instead. You're going to need that budget for the turbo kit, fuel system and tuning anyway, so it makes sense to put it there. This way keeps your build cost way lower, and you'll still have a reliable setup that won't leave you stranded.
How to Pick the Right Turbo
The factory K03 turbo does its job just fine when you're running stock power levels. But start making more power than that, and it turns into a bottleneck well before you'll ever hit 300 horsepower. Even with the right supporting mods already installed on the car, the power delivery up top is going to feel weak and flat because the turbo can't flow enough air to keep up with demand. Plenty of owners eventually replace it with a bigger unit to get around this problem.
The Garrett GT2860RS is a popular option for this build and for a few reasons. Boost starts to come on around 3,500 RPM, and from there it pulls strongly through the redline. Run it with those internal upgrades we covered earlier, and you can expect somewhere around 280 to 310 wheel horsepower. The main tradeoff with this turbo is the spool time - it takes a bit longer than the stock unit, which means it might feel a little sluggish at lower RPMs when you're just cruising around town.
The Precision 5431 is a step up from there and will get you to somewhere around 320 to 340 horsepower. It does need more RPM before it starts to build any real boost - you'll typically find that it doesn't hit full power until you're closer to 4,000 RPM. Driving this as your everyday car, that lag can start to get pretty annoying after a while. For track days or more spirited driving sessions, though, it's a strong turbo choice.
Hybrid K04 turbos sit somewhere in the middle of the turbo upgrade range. These units keep the factory K03 housing in place, but the internal parts get upgraded so they can handle more power. This way, you'll get nearly identical spool behavior to what you had before (which is a plus). But now you can support between 270 and 290 horsepower. The downside is the compressor housing itself - since it's still the smaller factory size, your maximum power ceiling is always going to be capped lower than if you went with a different turbo setup.
Whichever turbo you end up with is going to directly change how much work you'll need to do on your fuel system. A GT2860RS needs bigger injectors than a hybrid K04 would. The Precision 5431 goes even further than that - you'll need even bigger injectors and a stronger fuel pump to keep up with what it needs. In the next section, we'll break down what this actually means for your particular build and what budget you should be planning for.
The Right Fuel System for 300HP
The stock fuel pump in your car won't be able to handle this level of demand either. An in-tank fuel pump upgrade is the best way for you to take care of this because it solves the problem right at the source, and it's going to be far more reliable than if you just try to patch up the situation with an external pump. Engine damage from fuel starvation can happen really fast - even one split second where your motor runs too lean is enough to cause serious and expensive problems.
E85 deserves some attention at this stage because plenty of engine builders have moved over to it. The ethanol blend does a much better job at resisting knock than normal pump gas, and it also burns quite a bit cooler when you run it under boost. These two benefits make it a whole lot easier to hit that 300 hp mark without the stress about detonation. The catch, though - E85 is thirsty. You'll burn through about 30% more fuel by volume compared to what normal gasoline would need.
Your fuel system only has one job, and it's to give your tuner a strong, stable foundation to work with. As long as your injectors and fuel pump can supply the right amount of fuel that your engine needs at whatever load you're under, the entire tuning process gets much safer. You won't run into any dangerous lean conditions, and your tuner won't have to compensate for a fuel system that can't take care of the demand. Once your fuel delivery is dialed in, the tuning work can start, and everything from that point forward gets much easier to manage.
How to Tune Your Turbo Engine
The tuning system is what controls your entire build, and you have two options on the market. Hondata FlashPro runs around $695, and it gives you full control to reprogram your engine computer any way you want to set it up. KTuner does the same job for roughly $50 less, just with a different interface layout to work with. Either one of these systems will let you dial in and fine-tune the engine settings that matter most when you're running a turbo L-series motor.
A professional dyno tune is how you should get everything dialed in and running correctly. A skilled tuner will spend a few hours on the dyno and make adjustments to your air-fuel ratios and ignition timing as the engine is running under load. Your cam timing tables are going to need to be adjusted as well to work with your turbo setup. Street tuning will save you a few hundred dollars up front. You'll have to find a tuner that can monitor the knock sensors and exhaust temperatures as they happen, as your engine is under heavy stress.
Every single load point in your fuel map needs to get dialed in right if you want to protect your engine and make sure that it holds up for the long haul. Plenty of builds put their time into wide-open throttle pulls and skip over part-throttle tuning, and that's actually a big mistake. When those areas get ignored, lean areas start to show up during normal driving, and eventually those lean conditions can wreck your engine.
Plenty of tuners make the mistake of cranking way too much timing advance when they chase peak numbers on the dyno. The other big issue that I see is when tuners copy map files from another build without adjusting them for their own fuel quality or elevation. Either one of these shortcuts has destroyed plenty of engines that could have run strong for years if they'd been set up correctly from the start.
A proper tune will also help you keep your engine temperatures under control when you're pushing the car hard. A tune by itself won't solve your problems, though - you're still going to need hardware upgrades for your cooling system to take care of the extra heat. Let's talk about which parts you actually need in the next section.
What Your Build Will Actually Cost
All the supporting parts matter too, and that's each connector, fitting and adapter that actually holds the entire system together. Adding up the parts and labor, most 300HP builds cost between $4,000 and $7,000. The labor is what makes that price range swing so dramatically. Taking care of the installation work yourself will probably land you closer to $4,000. Bringing everything to a shop for professional installation means you'll almost surely hit $7,000 or pass that.
These smaller costs add up fast during a build like this. A gasket set to cover every seal point in your engine will run you a few hundred dollars on its own. Fresh fluids are another cost to factor in - you're going to need enough oil and coolant just to get the motor running again. Every build also needs a bunch of miscellaneous hardware like bolts, clips and different fasteners that somehow never make it onto the original parts list.
Some builders will map out their budget based on just the big parts, and this tends to cause some problems once the work gets started. You might pull the old motor out and discover that the mounts are shot. Or half of your exhaust studs could be stripped out and useless. Unexpected problems like this will drain your time and money very quickly if you never factored them into the budget from the start.
Cheap turbos can save you $500 or so up front. But they usually fail pretty fast - a lot of the time within just a few months of the installation. Once one fails on you, you're stuck with buying the replacement part all over again and covering the labor costs a second time. Budget-grade bearings and low-quality gaskets will create these exact same problems for you down the line.
Splitting up your purchases across a few months makes the whole project much easier to handle financially. You can pick up your block parts first and then come back for the turbo kit once your budget has had a chance to recover. A staged build like this will stop you from draining your entire bank account all at once.
Build Your Dream Car
Building an L-Series engine that makes 300 horsepower reliably means every component matters, and the order matters too. A lot of builders obsess over which turbo to choose because it sounds cool. But the fuel system, the tune and the cooling upgrades are what will help your engine last for years after the build is done. Cut corners or try to save a few hundred dollars in the wrong areas, and you'll wind up spending twice that amount later to fix problems that were avoidable. A gradual build with quality parts from the beginning gives you time to learn what your setup does and to make small adjustments along the way, and it means fewer disasters and a lot more time behind the wheel of the car you built.
An engine build is one part of what you need if you want a car that you'll actually be proud to drive around and to show off. Maybe you're after big dyno numbers, or maybe you just want to restore your 240Z, 260Z or 280Z back to its former glory. In either case, the quality of your parts is what makes or breaks the entire build. At Skillard, we make custom parts just for Datsun owners who care about upgrading the performance and the look of their cars. Aluminum door cards, bumpers, center consoles and spoilers - we carry the parts that can take your project from solid to exceptional.
Check us out at Skillard.com and browse through our full catalog to find just what you'll need to build the car you've been planning for all this time.
