Cylinder Head 206 - Valve Clearance (& LSA)

This video is the companion and continuation video for Cylinder Head 205. In Cylinder Head 205 we covered the tools and technique for setting valve timing versus the factory-recommended specifications. It didn't work, thus; this video. How do I know it didn't work? Watch this video.

The reason this is a companion video is because anyone changing their valve timing must also CHECK their valve clearance or risk bending valves. If I can install aftermarket cams, then I have made significant changes to my valve clearance. If I move cam gears on an engine that was previously running, then I have made significant changes to my valve clearance. If I have milled my head or block, I have made significant changes to my valve clearance. If I have installed larger valves, I have made significant changes to my valve clearance. Mitsubishi doesn't build a whole lot of wiggle room into their valvetrains. They keep the valves pretty tight to maximize performance and a 4g63 IS an interference engine. Note that if you follow the recommendations in this video and damage your valvetrain that I am not responsible. Here I demonstrate all of the techniques to ensure that damage never occurs because these tests are performed PRIOR to the engine ever starting, and prove that clearance is adequate for THE PARTS I SHOW HERE ON CAMERA. There can be components installed in other rotating assemblies that require additional clearance to be built into your valve clearance such as aluminum rods, or other alloys employed in the casting and forging of rotating assembly parts and valves. I strongly urge you to check with those manufacturers for their recommendations regarding thermal expansion, stretch, bounce rocker gap or float prior to making any adjustments, and use this video only as a documentation of my experience. In other words, it's my opinion. What works in your engine will likely be very different from mine, but the tests and the math shown here will work the same with your build.

To find your intake camshaft duration... Add your intake valve opening degrees (btdc) to your intake valve closing degrees (abdc) to 180°.

IO + IC + 180 = DURATION
DURATION ÷ 2 = LOBE CENTERLINE
LOBE CENTERLINE - IO = INSTALLED INTAKE CENTERLINE

To find your Exhaust camshaft duration... Add your exhaust valve opening degrees (bbdc) to your intake valve closing degrees (atdc) to 180°.

EO + EC + 180 = DURATION
DURATION ÷ 2 = LOBE CENTERLINE
LOBE CENTERLINE - EC = INSTALLED EXHAUST CENTERLINE

To get your Lobe Separation Angle, ADD your INSTALLED INTAKE CENTERLINE to your INSTALLED EXHAUST CENTERLINE and divide that result by 2.

Intake Centerline + Exhaust Centerline ÷ 2 = LSA

Tight Lobe Separation Angles
* MOVE TORQUE LOWER IN THE POWER BAND
* INCREASE MAXIMUM TORQUE OUTPUT
* INCREASE CYLINDER PRESSURE
* INCREASE CRANKING COMPRESSION
* INCREASE EFFECTIVE COMPRESSION
* INCREASE COMBUSTION CHAMBER SCAVENGING EFFECT
* SHORTEN YOUR POWER BAND
* REDUCE IDLE VACUUM!
* REDUCE IDLE STABILITY
* INCREASE LIKELIHOOD OF KNOCK!
* INCREASE OVERLAP
* DECREASE PISTON TO VALVE CLEARANCE!

Wide Lobe Separation Angles
* MOVE TORQUE HIGHER IN THE POWER BAND
* DECREASE MAXIMUM TORQUE OUTPUT
* LENGTHEN YOUR POWER BAND
* DECREASE CYLINDER PRESSURE
* DECREASE LIKELIHOOD OF KNOCK
* DECREASE CRANKING COMPRESSION
* DECREASE EFFECTIVE COMPRESSION
* INCREASE IDLE VACUUM
* IMPROVE IDLE STABILITY
* DECREASE OVERLAP
* DECREASE COMBUSTION CHAMBER SCAVENGING EFFECT
* INCREASE PISTON TO VALVE CLEARANCE

There's more that I want to say about Lobe Separation Angle (LSA). If you're tuning a DOHC engine with cam gears, you're very lucky to go through all this trouble. The pushrod and SOHC crowd can't change their lobe separation angles without replacing their camshaft, and on many engines that means removing the cylinder heads. On a 4g63 with adjustable gears, you loosen the lock bolts, turn, lock it back down and you've adjusted your LSA. This is a luxury which if you've never had to build a SOHC or a pushrod engine and install camshafts that you take for granted. DOHC tuning permits the ability to alter the opening and closing events of the valves independently of one another and perfect the valve timing during tuning without having to completely remove and replace the valvetrain. What this also means is that the pushrod crowd needs to know and understand a lot more about their camshaft profiles prior to making their purchase as we [the DOHC crowd] do. They have to be on their A-game when they drop the coin on a new cam or else things get expensive really quick. Lobe separation angle says more about how camshafts behave than duration and lift, but all 3 should be carefully scrutinized when you're making that determination.

Yes, I did actually animate my engine's valve timing exactly the way HKS said to set it up. Yes those are all actual photos of my parts. Yes that was the biggest Photoshop file I've ever created.