Ls1 Engine Build - My First Stroker Part 4

Our project Trans Am's homebuilt 383 LS1 roars to life - will we have ourselves one helluva hot street/strip ride?

CONCLUSIONWith 383 super-reliable inches now under the hood of our Trans Am, the future is bright for this project car. Mods like a lower-ratio axle assembly, significant chassis bolt-ons, stickier rubber, and the like are all in the planning stages. But for the moment, it truly is one helluva stock-suspended, stroked F-bod, as the extra cubes have definitely forever transformed this Firebird for the better. Without a doubt, it drives and sounds like a totally new car.

That said, was the engine swap really all worth it? When we first began, we came out and stated that we wanted to "halve the cash" by building a stroked LS1 ourselves. Sadly, this statement simply didn't pan out. But as stated earlier, we were able to build in reliability and power potential we couldn't well have shelled out for otherwise; heck, this sucker isn't going to come apart unless the block itself gives up, and we will be throwing some nitrous at it presently to prove the point. Had we selected some real bargain-basement parts for the build, perhaps we could have met our goal as initially stated--but for a daily street driver that we plan on having see a bunch of recreational drag and road racing, that simply wouldn't have made any sense.

But we're forgetting to factor in the other half of the equation here: the satisfaction of a job well done. Like so many things in life, it's priceless. How many LS1 owners do you know can actually attest to building their car's motor themselves? Not many. Hopefully, that number will grow as the vehicles these engines came in become more affordable and owners are less afraid to tear into their hard-earned rides with their own two hands. I think we've shown--without a doubt--that to undertake and complete a full-on motor build such as this is within reach for a mechanically skilled, patient do-it-yourselfer. Having done it myself, I can tell you that the pride I now take in this car has gone up several notches, and nobody can put a price tag on that.

So I suppose the moral of the story should be this: if you're looking to bump up the cubes on your Corvette, F-car, or other Gen III-equipped GM, shop around. Based on your intended use, carefully weigh whether buying your own parts and bolting together your own motor will be worth your time and effort, as there are admittedly some decent deals on assembled and installed engines out there. But I can tell you this: I learned a heck of a lot of information about the LS1 during this build, and despite a few setbacks and delays along the way, enjoyed virtually the entire process. Had I let someone else turn the wrenches on my stroker, there's no way I could possibly have gotten as much out of it--and feel as much satisfaction as I do now rolling in my irreplaceable, 383ci WS-6 Trans Am.

4

With calibration complete, the wideband is just about ready to start providing AFR readings to the EFILive Scan Tool software installed on our laptop. As you can see, not much has been added to the standard setup one would use while scanning or tuning with EFILive--just an extra orange plug sticking into the FlashScan interface cable.

EFILive's Scan Tool software comes ready to read an Innovate LC-1, and getting at the signal coming into the FlashScan V1 Interface Cable is as simple as selecting the "AFR_LC11" PID. With this parameter selected, we can incorporate the LC-1's readout into our EFILive dashboard. EFILive has excellent tutorials showing how to do this, and it's very straightforward.

With the LC-1 signal now a part of our dashboard, the AFR reading seen by Innovate's wideband (shown here as the 4th parameter down, in light blue) can be viewed and logged simultaneously with any engine parameter--including rpm, MAP, knock retard, and so on--giving us very telling information about engine operation and helping immensely in diagnosing and changing PCM tuning. Pretty sweet!

Though the Trans Am started and idled flawlessly the majority of the time, one slight hiccup we noticed was that when the A/C was switched on, the idle speed would drop slightly, causing a little more shake to the engine and tranny than we'd like. Fixing this was a simple matter of opening up the EFILive tuning tool and adjusting the "Desired Idle Speeds" table, which were increased by 75 rpm for the "In-Gear A/C On" column (the "In PN" columns only affect an A4 vehicle, hence the zeros here). No more annoying shake, though some is always present in a cammed motor of course.

In logging using EFILive's scan tool, we noted that the long term fuel trims were a little excessive. Some amount of trimming is normal while in closed-loop mode; the PCM is constantly monitoring the air-fuel mixture using the onboard narrowband O2s, and automatically adjusting fuel injector opening times in order to achieve near a stoichiometric 14.7:1 AFR. Though several tables work together to mathematically come up with the command to send to the fuel injectors, one of the main ones is the "Injector Flow Rate" table. An inspection here and running of some numbers revealed slight differences between the table values and our actual fuel injector specifications (which flow 630 cc/hr at 43.5 psi), so numbers in the table were fine-tuned accordingly.

Another table that has a substantial effect on the operation of the fuel injectors is the "Injector Pulse Width Voltage Adjust" table. Considered a more advanced table that won't often need to be messed with while doing basic tuning, a look at this can tell whether your fuel injectors are getting too big of a "boost" as alternator voltage increases, possibly resulting in commanding a too-rich condition--and resulting in large fuel trimming.

In terms of full-throttle operation, our Innovate wideband indicated AFR's richer than we'd like to see. While the Injector Flow Rate table has an influence here as well, the primary table that controls fueling of this type is known as the "PE Modifier Based on RPM" table. Crunching the numbers, we noted that this table was currently commanding a full-throttle AFR in the neighborhood of 12.1 to 1. We swapped the values out across the board to command a more horsepower-friendly 12.8 to 1 (= 14.7 x 0.87, which is the value we placed in the table cells).

The final "major" change made to our tune was with regard to ignition timing. EFILive's Scan Tool indicated up to a full 28 degrees of spark advance being utilized, but in a conservative decision to try and avoid any chance of detonation as we leaned out the AFR, we opted to retard timing slightly. Changes to the actual 3D color plot were imperceptible, as we basically took about a degree and a half out across most of the board--you can see the final curve here. (Note the extremely high spark advance values at very low rpm--the engine never actually runs at these rpm, so they have no effect except to reduce the visual appeal of the map).

So we've built and installed our own badass, big-stroke LS1. But how much green did we actually blow on this sucker, and how does this compare to other options out there for upping cubes in one's EFI GM ride?

For dyno testing we looked once again to Crazy Horse Racing's DynoJet 248H. Though this shop has a definite Mustang focus (as the name suggests), fellow citizens of NJ will be happy to know that these folks also now are in the business of building and installing stroked LS1 engines into hi-po GMs.

With our Thunder Racing tune loaded into the PCM, our 383-equipped WS-6 spun the dyno rollers hard enough to yield 436.8 hp and 427.0 lb-ft, SAE corrected. This graph is overlayed with our best N/A pull on our stock engine with bolt-ons--indicating that we've already added nearly 100 rwhp! Note the relatively rich AFR, which dips below 12:1 in some places.

After flashing the PCM with our adjustments to the fuel injector, spark advance, and PE tables, the Trans Am buckled down again and gave us a mild output increase, bringing totals to an SAE 438.8 hp and 429.2 lb-ft (which come out to 449.2 horses and 439.4 lb-ft if using a standard correction factor in lieu of SAE, if you're curious). Notice that now the AFR is a good bit leaner and hovers in the higher 12s, though we're still richer than we were with our 346-inch LS1.

As things stand, we pretty much met the minimums of what we expected in terms of horsepower, noting that more is on the table as further tuning is performed and synthetic fluid is used. This build has not been an all-out dyno and track effort, keep in mind; the point was always to stay streetable and build strong. Nearly 440 rwhp and 430 lb-ft is nothing to be ashamed of, and is almost exactly the same output as the already-legendary LS7 (try pricing one of these suckers out for an engine swap, by the way--it's up there!). But for now, our tune is very safe--just as it should be for a daily-driven street ride.

Sources

Lunati
662-892-1500
www.lunatipower.com
Innovate Motorsports
Irvine, CA
714-372-5910
http://www.innovatemotorsports.com
Crazy Horse Racing
South Amboy, NJ 08879
732-553-9050
Thunder Racing, Inc
Baton Rouge, LA 70817

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