Project Nissan Sentra SE-R Jim Wolf Technology Cam Shafts

The traditional introductions for Project SE-R follow two standard formats. These stories inevitably start either with a long list of excuses as to why it has been so long since the last installment, or a fascinating recount of the recent abuses we have heaped upon the car in the course of testing. The latter is naturally followed by a final tally of the car's six-digit total mileage, and a few pro-Nissan remarks about how durable the engine is. Let's try both.

Way back in the June 2000 issue, we showed part one of what was to be a two-part cam test. In part one, we tested five different bolt-in cams (cams that didn't require additional parts, like custom valve springs). At the time, we promised a follow-up test of more aggressive cam and spring packages.

Little did we know it would take so long to pull this off. The problems started when we took the car to Jim Wolf Technology to install the first set of big boy cams. JWT's C2 grind requires JWT's valve spring package, since the ramp speeds and lift profile are so aggressive, they would cause valve float with the stock springs.

The problem, it turns out, is that while replacing a set of cams is a relatively simple two-hour job, replacing the cams and valve springs is about 10 times more tedious and complex. It only took one valve spring installation to decide to narrow the field to two cams offered by JWT. Two cams that share the same valve springs, most importantly.

Lazy? Perhaps, but we should also point out that the repeated cam changing was actually starting to wear out parts of the head. Several cam bearing cap bolts had to be replaced because of stretching, one snapped in half at a most inappropriate time, and yet another stripped its threaded hole in the head. We were clearly pressing our luck.

So with only two cams to test, what's our excuse for the delay? The battle for consistent, representative dyno runs stretched on for months as we chased after some mysterious inconsistencies in the car's performance. First, our baseline run was higher than it should have been, then the cams didn't make the power they should. Tests with a wideband O2 sensor showed the car running dangerously lean at times, and normally at others. In the process of chasing our car's demons, we made over 150 dyno pulls, none of which gave us results we felt we could trust.

On the bright side, our search did lead to a compression test and a leakdown test, both of which showed the cylinders to be in absolutely perfect shape. This is good news for the future of our project car, but only if we could find the problem. At the moment, we still don't know what's wrong with the car, but we do know how the cams perform.

Before each of its cams was tested in our car, JWT had the same cam installed and tested in the 1991 SE-R belonging to Rob Cadle. Until this most recent round of testing, every one of Cadle's dyno pulls was an exact match for ours. After months of searching for the problem with our car, we finally realized the only way the solution would materialize was if we no longer needed it to. Playing Murphy's Law in our favor, we decided to test Cadle's SE-R on our own dyno and present the results from his car instead. With the pressing need for a solution out of the way, we fully expect the car to miraculously cure itself.

The CamsJim Wolf Technology, like most companies offering cams, has a seemingly infinite variety of cam profiles available. The S-series cams (of which we tested the S3 and S4 last time) are street cams designed for use with stock valve springs. The C-series we tested this time have higher lift and more aggressive opening and closing ramps that require a special matched set of valve springs and titanium retainers in order to prevent valve float.

On the surface, valve float is a relatively simple phenomenon. A high-lift cam at high rpm can, if the spring isn't strong enough, make the valve open so fast the spring can't keep it pushed back against the cam lobe. This, naturally, makes cam timing erratic, causing power to drop dramatically and, in extreme cases, can even cause pistons and valves to start colliding. Even if there is no internal contact, valve float heats the valve springs so much it can actually anneal them, permanently lowering their spring rate and making them more likely to float in the future.

The valve float phenomenon is actually far more complex than it seems, however, as the compressing and releasing of the spring causes the spring itself to vibrate, and certain profiles combined with certain springs can cause the spring to resonate, causing valve float where you wouldn't normally expect it.

Worse yet, the spring can vibrate in several different modes at the same time, making predicting these resonances exceptionally complicated. So complicated, in fact, that JWT had to hire outside consultants to help perfect its cam profiles and to design a spring that would allow it to run the aggressive opening and closing ramps it wanted without causing valve float or any nasty resonances.

In addition to a stronger spring, valve float can be prevented by lightening the valvetrain. Less valvetrain mass makes the spring's job easier, which raises the terminal rpm at which the valves will float. This is why the valve spring package comes with a set of titanium retainers to replace the stock steel parts, saving 7.6 grams per valve. With the more aggressive C3 cams, the valvetrain should be stable to about 8200 rpm, though the rev limiter in the stock Nissan ECU, even when modified, cannot be raised above 7950 rpm. We had JWT leave our rev limiter at 7800 rpm, leaving the 400 rpm cushion for premature downshifts or similar critical driving errors.

JWT's C1 cams, which we did not test, actually have a shorter duration and less overlap than the most aggressive street cams, but because of the valve springs, they are able to use a much higher lift. These cams supposedly offer a smoother idle than an S4 cam, but more power. We skipped straight to the C2 and C3 grinds. The C2 grind can, in most cases, be used on OBDII cars without throwing any trouble codes for rough idle. The C3 cam cannot, unless a JWT ECU is used.

Aggressive cams like these inevitably offer a compromise between rough idle, reduced low-rpm power and high-rpm gains. To express this, we measured the average horsepower gain (or loss) over a low-rpm portion of the powerband from 2100 to 4400 rpm, and over a high-rpm band from 4400 to 7100 rpm. Shifted at 7100, engine rpm will never drop below 4400 rpm, so this is the operating band you will be in during any kind of aggressive driving. This measurement means little by itself, but it is an excellent way to compare the relative benefits and drawbacks of the different cams we have tested. In case your back issue library is a little too short, we've re-printed all the average power gains for the cams we tested last time, as well as the results of this test. These numbers make it abundantly clear the more aggressive cams both offer far more power at high rpm, and require you to sacrifice a lot more at low rpm.

As before, we tested both the C2 and C3 cams with the stock ECU and again with an ECU re-tuned by JWT. The dyno showed significant power gains with the ECU upgrade, but the benefits of the ECU are even greater than wide-open-throttle power gains. Idle quality and low-rpm driveability are dramatically improved with the ECU upgrade.

The power gains from the C2 and C3 cams are nothing short of amazing, as long as your car is willing to make the power. Ours will some day, Murphy willing.

*Low-rpm average gain is from 2100 to 4400 rpm, High-rpm average gain is from 4400 to 7100 rpm.