Boss 340 Project Engine - Sonic Zoom!

Horse Sense: Believe us when we tell you, nothing sounds sweeter than our project small-block Ford at full scream. Check out the video clip of Boss 340 at full spin. It's on our website right now, click here to see and hear for yourself, then drop us an email and tell us what you think.

This report on our project engine (Boss 340 Version 2.0) brings a close to the first stage of our effort to resurrect the Boss 302 Mustang theme. (Remember, a full-on drag-'Stang build is yet to come).

Boss 302 'Stangs ruled the roost on the streets and road courses back in the early '70s. The muscle-bound Ponies featured stout, high-winding small-block engines highlighted by high-lift, solid camshafts and big-port/big-valve, cast-iron cylinder heads that flowed like rivers. While all of the parts collectively make original Boss 302s worth a mint these days, the top-half pieces that we commonly refer to as heads/cam/intake on the original Boss 302s are the items that make the engines special.

With that in mind, we decided to build a new-era, Boss-style powerplant around the Boss 302 engine block from Ford Racing Performance Parts. With its 8.2-inch deck height, meaty 4.000-inch Siamese bores and screw-in core plugs, the new Boss block is quite similar to the original, but that's pretty much where the buck stops for similarities. We've definitely gone in a different, more-current direction when it comes to the rest of the engine's major components, especially its heads, camshafts, and intake manifolds.

With Version 1.0 of our Boss 340 completed and dyno-tested (see "Boss Power," Sept '08, p. 60) and its streetwise Edelbrock heads, Comp hydraulic-roller camshaft, and Wilson Manifolds intake all swapped for bigger, better-flowing, more race-oriented H/C/I hardware from Air Flow Dynamics, Comp, and Wilson (see "Top Loaded," p. 58, Nov '08), the stage is set for another round of performance evaluation on the SuperFlow engine dyno at Westech Performance Group in Mira Loma, California-and hopefully some eye-popping horsepower for our 340ci stroker.

The rest of this final engine story is best told through the following photos, captions, and dyno information. Once again, your tech editor and Westech dyno-specialists Ernie Mena and Eugene Walde spent a long, hot, challenging day (see Avoiding Near Disaster) in Westech's dyno cell to give Boss 340 absolute hell.

Although we escalated the Boss' redline far beyond that of any other project engine in our history, we also shot the engine with a few hits of nitrous oxide from Zex's new EFI Perimeter wet system. Not once did it flinch, become erratic, or completely fail during our test session.

Our canted-valve engine is a tremendous success. The new-school Boss is higher revving and far more powerful than its '70 namesake (in Version 1.0 and Version 2.0 trims), and with the availability of modern-day, Boss 302-specific parts such as intake manifolds and headers, it's no longer a fantasy engine for any 'Stangbanger out there who dares to be different and is up to the challenge of building one for their Pony.

Boss 340 Version 2.0 definitely is definitely a sexy beast. The engine, based on Ford Racing Performance Parts' Boss 302 engine block, features Air Flow Dynamics' SP4VS Extreme Complete Competition aluminum Cleveland-style heads; Wilson Manifolds' new Boss 302 intake manifold, fuel rails, a 1,136-cfm throttle body and 1.5-inch spacer; a Meziere electric, factory-style water pump; and Kook's 2-inch Boss 302 exhaust headers for Fox-body Mustangs. ACCEL's EFI Thruster engine management system and ignition electronics once again are controlling our bullet's air, fuel, and spark sequences.

Autolite's 3924 plugs take a 0.040-inch gap for our test engine's naturally aspirated performance. With nitrous, we're dropping one heat range to the company's 3923 plugs and closing their gaps to 0.023 inch.

Adding oil is another prerequisite for dyno testing an engine. We use 7 quarts of Royal Purple's XPR 20W-50 in Boss 340.

Cool heads definitely do prevail, especially when they're as radical as the AFD canted-valve goodies installed on our project bullet. Gary G at Probe Industries made up this sano distribution block...

...that allows water to flow out of the two heads and recirculate through the water tower on the dyno.

The discovery of a potentially critical oiling problem was made just before starting Boss 340 for testing and tuning. Oil pressure would not rise higher than 10 psi while the engine was spun (without ignition or fuel).

Westech's Steve Brule cited our big-block lifters as the probable source of the problem. While our intentions for using big-block, solid-roller tappets were good (to promote better oiling in the heads), the lifters apparently allow far too much oil to pump into the pushrods and reach the heads. This condition results in solid oil pressure for only a brief moment when the engine is running, and then a sudden drop in pressure when oil in the pan has been pumped out.

With the dyno portion of our project on a must-complete-today schedule, calls were made to obtain a set of Comp small-block Ford solid-roller lifters. Thanks to George of Speed-'O-Motive in West Covina, California, and Hailey Naylor of Comp Cams for their assistance with securing lifters. Props also go to Steve Brule, Ernie Mena, and Eugene Walde of Westech, who worked with your tech editor to get Boss 340 apart and reassembled with the correct lifters without compromising time for our proposed tests.

The rocker arms are fine. It's the large pool of engine oil in this cylinder head (the sight was similar on the other head) that is cause for alarm. Unfortunately, our decision to use big-block solid-roller lifters proved to be a wrong move. The big-block tappets' raised bands allow far too much oil to reach the pushrods and the top of the engine, which results in premature scavenging of the oil pan, and thus, alarmingly low oil pressure.

The bands on small-block, solid-roller lifters are lower than those of their big-block counterparts, and thus retain and release oil (that is fed to the top of the engine) on a sequential basis as opposed to the all-at-once flooding of oil that we had.

The lifter problem forced us to remove the complete top section of our Boss engine. Because of the size of our AFD heads, it's impossible to remove or install lifters with the heads in place. As a precaution (and since using nitrous is part of the game plan), a fresh set of Fel-Pro 1134 multi-layered steel head gaskets is laid in place before the heads are reinstalled and tightened with 95 lb-ft of torque.

As we mentioned earlier in this report, finding Boss 340's performance potential with nitrous oxide is a part of our study. Due to our engine's unique fuel-injection system with its four-hole, carb-style throttle body, we decided to give a new EFI wet system from Zex a try.

The EFI Perimeter Plate nitrous system (PN 82221) is designed specifically for engines similar to ours, which use carb-style, four-barrel intake manifolds and throttle bodies. The system, highlighted by a billet aluminum plate that injects nitrous around the perimeter of an intake's plenum instead of through old-school spray bars, is all-inclusive (save for the nitrous, of course) and completely adjustable from 100 to 300 hp.

Although operating a nitrous system can be done manually, we also tested the nitrous controller function of the ACCEL EFI Thruster engine-management system. Connecting the two (Zex and Thruster) is a simple plug-and-play process that involves the nitrous unit and a harness for the controller.

As with all of EFI Thruster's functions, we found the nitrous controller easy to use and great for setting up custom-dialed (specific amounts of timing retard, nitrous delay, safe activations and shutoffs, and more) nitrous blasts that will allow us to focus on driving once the system is set.

After warming the full nitrous bottle and adding race fuel to the dyno's tank, we hit Boss 340 with 250 hp from the Zex kit (#88 N2O jet, #38 fuel jet), and it wasn't the least bit disappointing.

Wondering about the engine's performance with the Zex EFI Perimeter Plate nitrous system? Keep reading!

We were excited about using the new Zex EFI Perimeter nitrous system on our project engine. The billet aluminum plate in this system features cryogenic technology, which creates something of a cooling effect on the intake manifold. Nitrous is injected from 12 points around the plenum, so juice is sprayed in a complete 360-degree ring to ensure optimal fuel and nitrous distribution in the cylinders.

The Zex nitrous system links into the controller through a single harness that is in turn connected to Thruster's main wiring harness.

The nitrous controller function of ACCEL's EFI Thruster is intuitive and impressive. In short time, Ernie had our nitrous shot set to engage at 5,300 rpm (the point where the engine makes peak torque) at 90-percent throttle, and run up to 8,000 rpm.

Also using the controller, 8.25 degrees of timing was programmed to retard with the nitrous hit. Timing-retard amounts should be calculated off the base timing, retarding two degrees for every 50hp nitrous shot (100 shot=4 degrees, 150 shot=6 degrees, 200 shot=8 degrees, and so on).

The dyno test ultimately proved that our AFD-headed, Comp solid-roller-cammed, Wilson single-plenum intake'd small-block is built to rev high. The engine zings smoothly to 8,000 rpm on muscle, reaches the same plateau even quicker when nitrous is applied, and lays down impressive power at the crank either way.

Due to time constraints, we didn't get too deep into tuning Boss 340 in this session (idle and such). Instead, Westech's Ernie Mena and Eugene Walde conducted sweeps within specific rpm ranges, which allowed Ernie to make the appropriate changes in ACCEL's EFI Thruster's fuel and timing tables to stabilize the WOT air/fuel ratio at 12.8 with 37 degrees of timing.

As you see in the chart, our project engine likes nitrous oxide. With a 250 shot from the Zex EFI Perimeter Plate nitrous system, Boss 340 gained tremendously at the flywheel. We cited the engine's solid-roller camshaft as a contributor to its ability to reach 8,000 rpm with literally no effort, but the cam's 112-degree lobe separation and 0.274-inch exhaust duration at 0.050 are big reasons why our engine is so nitrous compliant.

With 598.56 horses ready to play and over 200 or more available with Zex's nitrous kit, we can't wait to get the engine in our Boss '90 LX and see what the combination will do on the chassis dyno and, of course, on the dragstrip!

Click here for the Mustang Boss 340 engine dyno chart

An optimal air/fuel ratio is the most-important element of dyno-tuning a naturally aspirated or power-adder-assisted engine. With ACCEL's EFI Thruster, the primary changes for Boss 340 are made in the base fuel and timing tables. "We didn't do much with fuel on the low end for this test," says Ernie. "We basically looked at fuel injected at 5,500 rpm and above, as that's where the camshaft in this high-revving engine really starts working."

This is ACCEL's 1,350-cfm throttle body. If we were dealing with carburetors, this piece would be similar to a 1250 Dominator. We believe there may be significant all-motor power gains. There definitely will be improved power-adder performance from Boss 340 when we give this baby a try. Time fell short for installing it during this dyno session, but you can bet we'll use this piece once the project car is complete and mounted on a chassis dyno for rear-wheel-horsepower testing.