The original "My First Stroker" series, the last installment of which was printed back in the January 2007 issue, was a success with GMHTP readers looking for in-depth coverage and analysis of a homegrown LS1 engine buildup. (It even got your author some great exposure and helped land me a sweet LS book deal, but that's another tale.) A stock LS1 block was honed 0.005-over and stuffed with a forged Lunati rotating assembly featuring a 4-inch stroke crank. A Lunati Voodoo cam spec'ing out at 232/238 duration at 0.050 and 0.599/0.601 lift was utilized to actuate the valves in 215cc ETP heads via a set of Jesel shaft rockers. Capping it off was a FAST 90mm intake manifold drilled to accept a 300-hp-capable ZEX direct port system. We left the story series off with the caveats that we'd update readers as improved drag strip times became available for our newly 383-powered Trans Am WS-6, and after we gave this engine the shot of nitrous it was built to handle.
But factors like a stock 10-bolt rear made serious efforts at such tasks ill-advised at best. So began the saga of upgrades to the rest of the vehicle to better complement its now-potent underhood powerplant. We beefed up the suspension with a best-of-all-worlds BMR setup ("Suspension Intervention," November 2007), then added a bulletproof-and-beautiful Moser M9 rear in the April 2008 issue ("Bulletproof Backends"), the latter including a fully adjustable, crossmember-mounted torque arm system. With all of that taken care off, only a few items were left to address. Recipe for success: (1) Reactivate the ZEX direct port nitrous that's been dormant since the stock LS1 was removed; (2) while we're tinkering around in the engine bay, reconnect the car's PCV system, the lack of which currently has us on the wrong side of emissions laws (and is causing a gradual-but-unrelenting buildup of oil residue along the passenger side of an otherwise-spotless engine compartment); (3) get a dyno tune for optimized N/A and nitrous power; (4) bolt some sticky tires onto the ends of the 31-spline alloy axles; finally, (5) Hit the strip and let `er rip.
As with any thorough project, the devil's in the details, so read on to see how we went about all of this in a careful and well-thought-out way.
First and foremost, let's talk about getting our stroker T/A ready for its ZEX nitrous system to come back to life. In part 4 of our series, we expressed concerns about lack of adequate fueling while on the spray. That uneasiness was quickly put to rest when renowned east coast tuner Matt Sorian, proprietor of TTP (a business that has recently relocated to a new, badass facility in Little Falls, NJ) assured us that our existing Racetronix system would be up to the task without the need for any sort of pump voltage booster or similar method of increasing flow potential. He was also adamant that he'd be able to give us a nitrous tune compatible with 93 octane fuel. No undercar wiring to do, and no having to scrounge up high-dollar, high-octane unleaded on race day? We were sold.
As far as nitrous tuning goes, we had originally mentioned looking at two options: one would be installing a product that would retard ignition timing automatically when the nitrous is engaged; the other would consist of running a "de-tuned," nitrous-friendly calibration at all times. Since no satisfactory auto-retard product has yet come to market for stock-PCM LS engines, and because running one tune at all times would result in non-optimal performance while naturally aspirated, we decided to split the difference. TTP would provide two separate tunes--one for N/A and one for spray--and we'd use a laptop and tuning suite to load the correct one into the PCM as needed. The only problem would be actually remembering to swap the nitrous tune in before heading out for a bottle-fed pass. But we could swing that... right?
The final piece of the laughing gas puzzle (other than a set of nitrous-friendly spark plugs) was our desire to avoid any possibility of a lean condition occurring while on the racetrack--despite the sturdy bottom end of our LS1, the stakes are high at these power levels. We were fully confident in Sorian's tuning ability, and the components of the nitrous system were pretty much up to snuff. (The ZEX kit had included a full-throttle switch, and we had also added an MSD rpm window switch. This way, the system could not be inadvertently activated at part throttle, it also couldn't turn on below a specified RPM, and would also shut off before hitting the rev limiter.) But there was one more potentially hazardous contingency that we could foresee, and that was the nitrous bottle getting overly warm on a hot day, sending bottle pressures substantially in excess of those used during tuning (and thereby sending air/fuel ratios into the realm of way-too-lean).
Before getting ahead of ourselves, we should note that ZEX utilizes patented Active Fuel Control technology in its nozzle design, and this feature (which is already incorporated into our direct port kit) can trim fuel delivery around 3 percent as bottle pressure varies. According to ZEX's Matt Patrick, "While this may not seem like much, it really helps to even out the overall nitrous tune so that as bottle pressure varies, you will see much more consistent air/fuel ratios. This feature will not necessarily take a bad tune-up and make it produce lots of horsepower, but it will take a correct tune-up and broaden out the bottle pressure `window' that you will make optimum power in. Also, if you have a poor tune-up, don't have the ignition timing set properly, have the wrong heat range of spark plugs, or anything that may put the engine close to a detonation condition, this feature could be the one thing that keeps the motor from damaging itself."
Still, there is no such thing as being too safe, and to make a dangerously lean condition a virtual impossibility, we decided to install ZEX's Nitrous Pressure Regulator, an easy-to-install add-on to any nitrous system. It ensures super-consistent nitrous pressures at the solenoid, and therefore prevents nitrous pressure entering the engine from exceeding a certain user-defined psi. Just to be clear, the regulator can't increase nitrous pressure; so while it would regulate 1,800 psi of bottle pressure down to, say, a safe 950, it can't compensate for the 550 psi bottle pressures you might see on a chilly day (that's what bottle warmers are for!). The regulator also prevents the typical loss in nitrous pressure experienced during a pass down the strip, making for steady nitrous flow throughout the run and therefore increasing top-end power.
To sum up, ZEX's Nitrous Pressure Regulator and Active Fuel Control really work in tandem. Says Patrick, "Think of the regulator as being able to keep major variances in nitrous flow to a minimum, while the nozzle has the ability to adjust fuel to widen the optimum tuning window. These two technologies together greatly increase the consistency and safety for any nitrous installation." Check out the accompanying photos for the install.
Back in part 3 of our series, this author disabled our LS1's PCV system. The reason was that in order to attain sufficient rocker-arm-to-valve-cover-clearance, I had (reluctantly) gutted the covers of all baffles. With them gone, I couldn't figure a way to keep the system intact without spewing unholy amounts of oil into my intake manifold. So, taking a page from drag racing experience, I capped off the system and installed a breather on the valve cover. Aside from being illegal and not exactly environmentally conscious, my solution was not very street-friendly; for one thing, I found myself regularly wiping slimy residue from my ignition coils and other items on the passenger side of the engine bay.
So what's the problem with doing this, oil-coated engine compartments notwithstanding? Some quick background information on what a PCV (Positive Crankcase Ventilation) system does is in order. One of the first emissions controls introduced in the U.S., the PCV system started showing up on production cars in the 1960s. Its function is to circulate fresh air (the source of which is typically located between the air filter and throttle body) through the crankcase of the engine. This clean air picks up nasty stuff like blow-by gases and their constituents (unburned fuel, water vapor, etc.) as it goes. Now contaminated, the air is then sucked by manifold vacuum through our friend the PCV valve, into the intake manifold, and finally into the cylinders to be burned during combustion. Now imagine not having such a system on a street-going car. Some of those blow-by gases wisp their way out of your valve-cover-mounted breather, but without intake manifold vacuum to suck new air through, lots of contaminated air festers inside the crankcase. Therefore, a lot of that unburned fuel and water vapor deposits itself into your engine oil. The result? Engine longevity and internal cleanliness suffers, no matter how often you change your oil.
In hindsight, I should have thought a bit harder about how to keep an operational PCV system on this engine. Heck, had I spoken to some experts or even just perused the message boards, I would have known the valley cover-mounted LS6 PCV system would have been an easy fix for my baffle-less valve cover conundrum. But let's let bygones be bygones-time to correct past wrongdoings. Since I am not about to pull my FAST intake to get at the valley cover (I'm not sure that would even be physically possible at this point, as I routed the entire nitrous system and wiring harness with the engine out of the car), I would still need to use the LS1 PCV system in some form. This left me stuck with the valve covers as the only route to access crankcase air; but with no baffles, I couldn't keep prodigious quantities of oil from getting in the PCV system's lines. My solution is not to prevent this from happening, but rather to remove the excess oil from the contaminated air before it reaches the intake manifold by using a so-called catch can. A catch can is a great thing to have on any modded high-performance engine, as excess oil vapor entering into the combustion process is said to sometimes cause detonation and even harmful buildup inside the cylinder. In this case, there is a lot more oil vapor involved than usual, so it's even more critical.
We picked up a Gen2 PCV Catch Can from Norris Motorsports; check out the photos for the install. While this catch can is meant to be a plug-and-play design into a factory PCV system, I had to do a bit of homemade engineering thanks to the previously gutted nature of my particular system. Despite my best attempts, I could not reach where I had originally snipped and blocked off the contaminated air source at the "balance pipe" connecting the rears of the LS1's valve covers (I've since discovered, by the way, that this is part of a "dual draw" system designed to suck air from one or the other valve cover under extremely hard cornering; good thing I'm not headed to Road America anytime soon with this bad boy.) In order to create a new source, I bought a cheapo PCV valve at Pep Boys along with an equally cheap oil cap to go where my breather formerly was. I drilled a hole in the top of the cap and stuck the valve in with a grommet. Combined with the factory oil cap "riser," I figured this would lift the PCV valve far enough away from the fast-moving, pressure-fed rockers to suck in at least a little less pulverized oil mist. (As it turns out, my system seems to have worked flawlessly since installation, so I must have done something right!)
Tunin' & Trackin' It
TTP was only too happy to strap our project WS-6 to the rollers of its Dynojet and iron out some potent-but-safe tunes for our 383 in both N/A and nitrous-assisted form. Astute readers may recall that this engine never actually was tuned on a dyno, relying instead on the slightly altered mail-order tune we discussed in part 4. Check out the accompanying dyno graphs for the additional power Matt Sorian was able to eek out N/A as well as the tune he came up with for the spray.
After grabbing some sticky Hoosier tires (and mounting them on nothing finer than Scott Parker's discarded 3-spoke, 16-inch LT1 Formula rims), it was time to make some hits at Englishtown. Arriving to find cool November temps and a track scale showing 3,774-lb. of race weight, your author dropped the tire pressures, turned on the bottle warmer, and made a bunch of passes both with and without nitrous assist. Check out the accompanying table for the best three of each (and note the super-consistent nitrous MPH I was able to achieve-a testament to the effectiveness of the ZEX nitrous pressure regulator).
OK, so 60-ft. times in the 1.9s and 2.0s are not impressive at all, but the problem does not lie in the Hoosier Drag Radials-I found them to work great, biting hard or giving just the right amount of slip for my 3000-3500rpm clutch drops, given a sufficient burnout having been performed. Instead, I feel strongly that the issue lies with my having chosen a relatively-tall 3.70 axle ratio, combined with my personal unwillingness to sidestep the clutch at six grand (and possibly have a shiny new piece of flywheel replace the lower portion of my femur). The short sidewalls of the Hoosiers probably would not have been able to absorb the extra shock loading anyhow; this is no fault of theirs, but rather due to my selection of the combination of a 16-inch wheel and 26-inch tire.
It should be obvious that that this red rocket easily has the potential for 11s N/A and 10s on spray, given a few easy changes such as tire sizing, gearing, and perhaps a clutch scattershield. And for even more fun, there's lots more nitrous flow waiting to be tapped in the ZEX direct-port system (though at some point that would require fuel system upgrades and something more than 93 octane). The future may well bring these or other surprises, but for the moment, this project car is being retired from active duty. That's right, it's time for some garage-kept pampering and car show duty-they don't make Trans Ams anymore, and I'm keeping this one forever!