How to Choose Your Cam.. Duration, Overlap and more.

Choosing performance cams can often seem like a difficult task for many, considering the many variables that can apply to any one camshaft profile or application. I’ve seen too many cars with the wrong cam profile struggle on the dyno or even worse make their owners struggle with just driving.

Before choosing a cam however, don’t forget to remember what you are choosing the cam for; drag racing? road racing? any daily driver usage?


Let’s begin by tackling each term and what it means.

What is valve lift?

How far the cam opens the valves, when increasing lift you increase the length the valve opens, which will produce positive gains in airflow. Be careful when selecting your cam, as too much lift may cause valve float as you will see many manufacturers list recommendations for upgraded springs, retainers or guides.

What is duration?

The amount of time that a valve is open, regardless of intake or exhaust and measured in degrees of crankshaft rotation for that period. What does this mean to you? It tells you what the cam’s potential is within a specific rpm range. Shorter duration cams provide low end torque, while longer duration cams allow for more top end flow.

For all the SOHC ninjas ­čÖé

What is overlap?

The amount of time that both exhaust and intake valves are open in any one cylinder at the same time. Usually this is close to Top Dead Center as the piston stroke begins down the bore and the exhaust valves must stay open until the piston pushed the gases out.


What is timing?

Enthusiasts most commonly mistake this term “timing” to ignition timing when it comes to valvetrain events. Trust me, this happens way too often to make any sense.

What is camshaft timing? It’s what you can adjust when you have an adjustible cam gear, that will allow you to alter the timing events.

When you advance the camshaft timing, you are making the intake valve open sooner which will give you more low end torque. As always, when advancing or retarding the camshaft timing you must be conscious of the safety window in piston-valve clearance as to avoid a “catastrophic” event.

Retarding the camshaft timing will delay the intake closing and keeps the intake valve open for longer. This is one of the oldest tricks in the book for turbo Eclipses, Talons and Lasers in the mid-90s by selecting just one exhaust cam and retarding it to -5.

EPSON DSC picture

By retarding the one exhaust cam you could sacrifice idle quality for some terrific top end by holding the intake valve open to move the overlap higher in the powerband.

This is a shot of my old 1999 Mitsubishi Eclipse Spyder, before AWD conversion, retarded negative -5 on the exhaust cam and putting down 395 to the wheels @ 22 psi on 91 octane, extremely reliable.

Of course in today’s age of variable valve timing in everything, many of these older tricks are not needed to generate huge amounts of power without sacrificing idle and start response. In the mid 90s however, you weren’t doing that unless you had a turbo VTEC motor, which had it’s own set of problems in that era.

Increasing the duration is increasing the amount of time the valve is open, therefore helping the engine effectively fill the cylinders and produce power. Many camshaft profiles maximize flow by opening the exhaust cam extremely early in the cycle, increasing exhaust output and increasing the exhaust valve fully open when the exhaust stroke begins. During the power stroke, the burning fuel has used about 80 percent of its available force on the piston by the time the crank has turned 90 degrees.

The bottom half of the power stroke actually provides very little in terms of engine power, and it can be better used to help exhaust the combustion chamber so that there is more efficient cylinder filling on the intake stroke.

Meanwhile a more aggressive profile with higher lift velocities will shorten the duration which will help power, but narrow the powerband.

What is LSA?

Lobe separation angle is the number of degrees between the centerlines of the intake and exhaust lobes on any one cam. The lower the LSA, the more overlap you create while increasing the separation decreases overlap.

Remember to avoid the most common mistake, and that’s going with the most aggressive cam available only because “It sounds so badass” An overly aggressive long duration cam may sound cool at idle, but will give you a very top heavy and small window of power in the rpm range.

Add to that equation the idle, emissions and starting issues, and you can quickly see how a mistake in cam selection can ruin your enjoyment with your car. Which isn’t the point… right?

In the end, choosing a cam that’s right for you is a big part of your performance equation. If you have any more questions, feel free to shoot me an email or post below! As always, if in doubt ask your nearby tuner in your area!

Happy shopping!


Piggyback Heaven – How to tune your Super AFC Neo

Hello everyone, Sorry but this complete writeup has been moved to

91 octane, 21 psi, full exhaust and cat

91 octane, 21 psi, full exhaust and cat

Click here for the complete writeup and additional chapters that have been added, from closed loop control to wot tuning.

Case Studies – Installing TEIN Stech Springs in a Evolution X

A good friend of mine recently picked up a slightly used Evolution X from a dealer, after trading in his S2000. He’s been around DSM’s for the better part of his professional career, having worked at Road Race Engineering and the now defunct BOZZ.

So to say the least, he knows his way around the 4G63, and while it’s not the same motor we’ve grown to work on, love and hate, it’s still a Mitsubishi.

He’s not completely sure what route he will take in this car, but he knows that the current
rock-climbing-Jeep stance is not what he wants to drive around in.

To remedy the solution, he picks up a set of TEIN Stech Springs for his Evolution X.

What you will need for this install :

  • TEIN part number SKE18-AUB00
  • 17mm socket and open end wrench
  • 14mm socket and open end wrench
  • 12mm socket
  • flat head screwdriver
  • needle nose pliers
  • Spring compressor ( optional )
  • * I am not liable for any damage, direct or indirect due to any modifications made on your car, related or unrelated to this writeup.
First, get the car into the air and secure the car safely using your jack stands. Next pop open your hood and locate the 3 14mm nuts that secure the shocks into your car.
Now crack those 14mm nuts loose, but do not remove them. Next take off your wheels and let’s get the shocks disconnected from your front spindles.
First undo the 12mm that holds your brake lines to the back of your shock assembly and pull away on the brake line.
Now undo the 2 main bolts holding your front shock assembly to the spindle and then use your needle nose to pull the bracket holding the brake lines to the mounting tab on the back of your shock.
After removing the nuts, use your jack to secure your spindle so that it wont fall.
Take care not to use the brake shield as a jack point, with the spindle and brakes secured, undo the nuts and pull the bolts out of your shock.
Now revisit the 14mm bolts in the engine bay and remove them, but make sure to hold your shock assembly so that it doesn’t fall.

Look ma! no shocks!

With the shock now removed, you must now mark the orientation of the top hat and mounting hardware. You will be best served to remember the layout of the top hat and the orientation of the shock itself. If you have a spring compressor, now is the time to tighten it down on the front spring coil as to prevent harm when it uncoils.

If you don’t own a spring compressor, u can place the bottom of the shock against your rim and tire and gun the top nut off. If you are not comfortable doing this and don’t own a spring compressor, maybe this job isn’t for you.

Remove the top hat and set to the side, you should now be able to remove the rest of the bushings and mounts to get to your stock springs.

Now, with the top strut mount removed, locate your bump stop as it will require modification.

Using a marker, mark where you wish to remove the excess material in your bumpstop so that the Evo’s new stance will not create any problems.

Now reassemble your front shocks with your TEIN Stech lowering springs, make sure that you are aligning the marks on your top mount, and make sure the spring is seated flush against the shock body as shown here.

With the front shocks buttoned back up, you can now reinstall the entire assembly into the car. If you are working on a lift, you can now move on to the rears. Open your trunk and locate the push pins that hold the rear panel in place in the trunk.

Carefully push in the pin and pull out the tabs to allow you to remove the back panel.

You may elect to remove the factory trays that cover the spare tire and wheelwells. We elected to do this step, as the car was still pretty new and we didn’t want to damage anything. To remove these panels, simply push in the tabs as you did with the rear trunk panel.

Now, remove the long bolt that secures your rear shocks to the lower control arm and spindle.

Push the rear shock in and away from the lower assembly, and then go back up top and remove the 2 14mm nuts holding the shock in place. As you did with the front shocks, make sure you have secured the shock to prevent it from falling.

You’re almost there! Now undo the top bolt to the rear shocks, for those who skipped ahead or with some sort of attention disorder, use a spring compressor if you are not comfortable unloading the tension in the coil.

Seat the spring into the rear shock housing, making sure to line up the spring as your oe coil sat.

Don’t forget to modify the bumpstop!

Now tighten up the rear shock assembly and re-install into the back of your Evolution.

Now you are ready to rock and roll! Happy boosting!

Case Studies – Converting the Ignitor setup on a 90 DSM Turbo to a 91.

A friend of mine recently picked up a 90 Eclipse Turbo for 400 dollars in non running condition. After a few minutes, we determine that the engine lacks spark and after a few tests, we find that the ignitor is completely dead.

As the 90 is the “black sheep” of the DSM family, I elect to rewire his 90 to a 91 ignitor setup to get him back on the road.

the dead unit is on the left, we are converting to the 1991 ignitor on the right

Parts you will need to perform this swap :

x1 1991 Eclipse / Talon / Laser Ignitor plus harness / wiring loom

x1 1991 Eclipse / Talon  / Laser instrument cluster.

Tools : Soldering Iron, Notepad, Solder, Flux.

A look at the new ignitor and flying loom

This conversion is fairly straightforward procedure, and can be installed by any average mechanic.

First, undo your positive terminal on your battery to prevent any accidental electrical problems.

Unplug the 1990 ignitor and coil assembly completely.

Rip out that old piece of crap

Next, strip the loom from your stock ignitor and coil plugs wide open.

Open 'er up

Now we take a look at the small markings on your stock J122 ignitor and compare them to the markings on the pinouts of the J722T Ignitor.

Now we cut and solder the wires in corresponding order :




After cutting and resoldering the wires, we have VB, TACH wires left over.

Now, take the white wire from the coil plug on the ECU side, and solder it to the tach wire on the J722T Ignitor Plug. Then, we slice VB ( the black / white wire ) of the J722T Ignitor plug to the Black / White wire on the coil plug ( ECU Side )

Shown is the 1990 Tacho Interface, which isn’t needed now since we have eliminated and rewired it.┬áSince the new ignitor now sends the tachometer signal to the new cluster, we no longer need the white wire, simply tape it up.

With the old ignitor and the tacho interface removed, the 90 fires right up and drives fine. However the tachometer doesn’t work as he needs a 91 instrument cluster to make it all work as it should.

Note : If you cannot source a 91 instrument cluster, you can simply swap the ECU pins 6 and 14 to complete the job.

A Blast from the Past – One of the original Pro Street DSM’s

When Jesse spoke to me about purchasing my Talon, one sentence made me pause and think about exactly what this car was. The conversation went something kinda like this :

Jesse : “What’s up with your Talon, I want to buy it.”

Me : “Oh yeah? lets work it out”

Jesse : “I want the car you built a decade ago”

Me : “………you’re an asshole”

After the purchase, it struck me how old the Talon really was. Here is a complete mod list.

  • Fully Built Stage III Pro Street Shortblock
  • Eagle H beam Rods
  • ACL Bearings
  • Extreme Motorsports Stage 2 head
  • Ferrera 1m oversize valves
  • Ferrera dual springs and titanium retainers
  • Web Cams 562/565 intake and exhaust cams
  • Wiseco 8.8:1 compression pistons
  • Mitsubishi Ralliart 4 layer MLS HG
  • ARP head studs
  • ORIGINAL 1g Pro Street Street Intercooler kit
  • ORIGINAL Pro Street Race Intake Manifold
  • Pro Street 8 point ┬áRace Cage
  • 62-1 stage III T3/T4 turbo
  • 720cc injectors
  • Aeromotive AE1000 Fuel pump
  • Fidanza flywheel
  • ACT 2600 clutch
  • Aeromotive Drag FPR
  • JLB Fuel rail
  • Haltech E6X Standalone engine management
  • 3 inch downpipe
  • Apexi N1 exhaust system
  • 12 gallon JAZ fuel cell

I’m sure I’m missing quite a few other mods, but at this stage I think you get the hint.

With a bevy of old school original Pro Street parts, it’s safe to say that waves of nostalgia and memories wash over me as we begin to clean the car up.

On to the eye candy :

Before :

Surface rust abound

After a few hours of the wire wheel and 2 cans of appliance paint in flat gray, we had a much cleaner interior.

Ahhh.. so much nicer

We also took the liberty of addressing the rear sump and mount for the fuel cell.

A shot before of the tank and the AE1000 before taking everything out and flushing, cleaning and polishing.

This pump is a tad...... um.... noisy.

After the interior was addressed, we moved on to the engine bay and turbo. A shot of the beast before :

yes, I didn't take care of it... sue me

After taking the turbo, manifold, valve cover and downpipe off, Jesse cleans up and polishes the intake manifold and valve cover along with the original Pro Street 1g Street Intercooler kit.  

A shot of the original Pro Street Intercooler kit for the 1g DSM, circa 2001.

And of course, the after shot of Jesse’s polishing and detail work.

so fresh and so clean clean

Next up for the Talon, cleaning up the Haltech wiring, wrapping the headers and taking it to the dyno and chasing 500 whp.

What’s a StockSpyder

It’s been almost 10 years to the date when I said bye to the car that was once my pride and joy, that gave me a shop, a business, a lifestyle but also broke my heart more than a few times.

So when a friend recently asked me “What’s a StockSpyder”, it brought back memories of my 1999 Spyder, and the many adventures I’ve had in it.

Back in the days.....

400hp, 91 octane, 21 psi, full exhaust and cat. STOCK BOTTOM END

The name is part of the old school DSM chat rooms in California where Ty@Road Race Engineering had the name StockGST for his 1g FWD Eclipse. I always had a place to crash when I drove to LA, not sure where Ty is now, but I hope his family and (three?) kids are doing well.

It seems like a lifetime ago and we were tuning cars with crude piggybacks but it was a great time to be an enthusiast back then.

Back when kids didn’t buy chinese parts to modify their cars, and the names Greddy, Apexi, HKS actually still meant something. Back when EBAY wasn’t the first place you look when shopping for a turbo, and shops were actually shops instead of absolute jokes.

Seems like a lifetime ago, but thanks to Ty and Road Race I had the experience of a lifetime building my “StockSpyder”





I will always choose to remember the good times, and good friends in relation to the car and not dwell on the many bad times and backstabbers that went along for the ride.