Like the rest of the performance community, we were very excited when Dart announced its new Special High Performance (SHP) line of engine components and assemblies last year. With such a great starting point at its disposal with its blocks, it was only natural that they use them as the basis for impressive short-block assemblies. Now throw in Dart's heads and intake manifolds and you have what amounts to a seriously stout engine.
Looking over the specs, the Dart SHP short-blocks were assembled using all the right stuff. Naturally, we couldn't wait to get our hands on one and strap it to the dyno. On the Chevy side, Dart offers both small- and big-block combinations. Looking for large power numbers, we opted for not only a big-block, but the biggest one offered in the SHP line up. Displacing 540 ci, the SHP 540 was a result of combining a 4.50-inch bore with a 4.25-inch stroke. The Dart Sportsman Big M block was more than up to the task of our intended abuse, but we specified upgrades to the reciprocating assembly to suit our needs. Since both nitrous (and blowers) were in the cards, we upgraded the cast crank to a 4340 forged unit. The SHP short-block already featured 4340 forged I-beam rods (with 7/16 cap screws), but we stepped up to the forged (flat-top) pistons as well.
In order to keep costs reasonable, the SHP short-blocks are available with cast cranks and hypereutectic pistons, which are more than strong enough for most normally aspirated combinations. Since our blower applications would likely exceed 1,000 hp, the forged components were deemed mandatory. With the Big M block stuffed to the gills with a forged reciprocating assembly, the Dart short-block was ready for action.
Mild 540 Combo
We planned on illustrating both the strength and possibilities offered by the Dart SHP short-block by building mild and wild normally aspirated combinations. We figured there would be enough power here for just about any '55-57 Chevy fan. But just to keep things interesting, we decided to throw in a little nitrous. First up was the mild combination. The term mild only compares to the wild combination, as the mild version exceeded 630 hp and 640 lb-ft of torque. Hardly mild by most standards, but the numbers get pretty big when you are starting with 540 ci. By keeping the short-block the same, we were able to replace the power producers, namely the heads, cam and intake manifold and dial up the power output. For the mild combination, we chose a set of as-cast, bolt-on aluminum heads, a streetable (but powerful) hydraulic roller cam and a single-plane intake manifold. Some may question the choice of a single-plane intake on our mild combo, but were this motor in a street car, you'd have no shortage of low-speed torque that might require a dual-plane design. Remember, we are talking about 540 ci!
One area of concern during the build up process was the use of flat-top pistons (with valve reliefs). This combined with the near 120cc combustion chambers on most performance BBC heads created a static compression ratio near 9.0:1. For a dedicated normally aspirated combination, we'd recommend a bit more squeeze, but our multi-purpose motor was to receive boost at a later date and as such, a compression compromise was necessary. The low compression ratio did mean that this power output was easily doable on pump gas and very likely on 87 octane if no premium is available.
Our mild combo started out with a set of as-cast, 320cc Power Port heads from Trick Flow Specialties. Designed as a direct bolt on, the 320 cc aluminum heads offered 137 cc exhaust ports, 122cc combustion chambers and a 2.25/1.88 stainless steel valve combo. The impressive heads offered peak flow numbers of 362 cfm on the intake and 301 on the exhaust (measured at 0.800 lift), meaning our mild combo would not be taking full advantage of their ability to support well over 700 hp. The assembled heads even featured hydraulic roller valve springs (up to 0.700 lift), guide plates and 7/16 rocker arms. The heads were installed using Fel Pro 1017 head gaskets and ARP head studs.
Working with the heads was a hydraulic roller cam and Weiand Team G single-plane intake manifold. For this mild combination, we chose an Xtreme Energy hydraulic roller cam and matching hydraulic roller lifters from Comp Cams. The XR288HR cam offered a 0.521/0.540 lift split, a 236/242 duration split (measured at 0.050) and a 110-degree lobe separation angle. Cam specs like this would be healthy on a small block or even a smaller displacement big-block, but 540 ci has a way of taming the cam considerably. The aggressive ramp rates offered by the Xtreme Energy line of cams was designed to maximize power production through the entire rev range.
This combo was completed with a Holley 950 Ultra HP carburetor, an MSD billet distributor and a set of 2.25-inch Hooker Super Comp headers. Additional components included an adjustable timing chain, Ultra Pro Magnum rockers and one-piece chrome-moly pushrods, all from Comp cams. Since we were running this on the engine dyno and not in a specific chassis, we chose a Pro Eliminator oil pan from Moroso.
The Moroso pan featured a number of impressive features including an internal windage tray. Moroso also included one of its trick billet oil pumps. The billet pump featured larger inlet and oil passages to increase oil flow, reduced weight compared to a cast-iron pump (by 1 pound) and increased the mounting boss cross section to help spread the load. The integral bottom-fed design eliminated the need for an external oil pickup tube, the bypass system returned oil to the pickup area to reduce aeration and oil temperature and best of all the billet pump used the stock mounting stud and oil pump shaft. Use of the Moroso pan on a production Chevy block would require drilling and tapping the block for the revised mounting holes (inline with main caps-see photo), but our Dart block was already drilled and tapped for use with this pan.
The finishing touch was a two-piece timing cover from Comp Cams that allowed cam adjustments and swaps without dropping the oil pan (important when swapping components to our wild configuration).
This version of our 540 was installed on the dyno with a pan full of Lucas 10W-40 oil and a tank full of pump gas. It was treated to a pair of computer-controlled break-in procedures lasting a total of 25 minutes. After a quick oil change, we were off and running. Some minor jetting on the Holley 950 Ultra HP carb was necessary and after running through a quick timing sweep to see where the engine made the best power, we were rewarded with peak power numbers of 635 hp and 646 lb-ft of torque. Though labeled mild in this instance, know that 635 hp would easily push your average Tri-Five well into the 11s, and possibly the 10s.
As expected, the 540 Dart motor offered an exceptional torque curve, with torque production exceeding 600 lb-ft from 3,300 rpm to 5,500 rpm. Remember our previous comment about the single-plane intake hurting low-speed torque production? Do you think you will really be able to harness 600 lb-ft of torque at 3,000 rpm? That is the great thing about large displacement motors, the abundance (or excess) of torque. No need to rev one to the moon to get decent motivation; just step on the gas and let the cubes do the work. Best of all, this simple combination should offer literally thousands of miles of trouble-free motoring, not to mention create more than a few furious Ford owners.
Wild 540 Combo
After our success with the mild combination, it was time to step up to something a bit wilder. In this case, it meant swapping out the heads, cam and intake. The as-cast Trick Flow heads were replaced with a set of CNC-ported Dart Pro 1s, while the hydraulic roller cam was ditched in favor of a more aggressive solid-roller design. On the intake side, we ran the new combo both with the single-plane Weiand Team G as well as a dual-quad tunnel ram (a Weaind Hi-Ram). The Team G was used so we could mount the NOS Cheater Competition nitrous system, while the tunnel ram was installed because tunnel rams are inherently cool. We know, you have to cut a hole in the hood, synch the linkage and they are less than ideal in the rain, but tunnel rams make lots of power and are flat-out bad to the bone.
The remainder of the 540 remained unchanged, including the Dart SHP short-block, the oiling, ignition and exhaust systems. Even the static compression ratio remained relatively unchanged due to a difference of less than 1cc between the chambers on the Trick Flow Power Port and Dart Pro 1 heads.
The Dart Pro 1 heads featured full CNC porting that produced 345cc intake ports and 129cc exhaust ports. The precision-machined and ported heads offered a 2.30/1.88 valve combination, a Vasco-Jet spring package (max 0.790 lift) that offered 250-pound seat pressure to work with our solid roller cam and impressive flow numbers. According to Dart, the Pro 1 heads flowed 397 cfm on the intake and 280 cfm on the exhaust (using the Dart-supplied valves). This is enough airflow to support 800 hp, meaning more than enough for our low-compression 540. The Comp solid roller cam for our wild combination offered a 0.742/0.715 lift split, a 271/280-degree duration split and a 112-degree lobe separation angle.
Topping off the new Dart heads and solid roller cam was a Hi-Ram tunnel ram intake and a pair of 950 HP carburetors. Before you get all up in arms about us effectively doubling the amount of carburetion, know that the 950 HP is actually a 750 HP body with an 850 base plate. Sure, the combination would likely work well with a pair of smaller carbs, but the 950 HP combo metered perfectly on our roller-cammed 540, even down at 3,000 rpm. We took the liberty of setting up the linkage prior to the swap, so installation of the Weiand tunnel ram was no more difficult than a conventional intake swap. Since no break-in procedure was necessary with the roller cam, all we had to do was adjust the valves and start tuning. Thanks goes to Westech's Steve Brule for all his hard work on making the SHP test sessions go smoothly. As it turned out, very little tuning of the 950 HP carbs was required from their out-of-the-box condition. The wild 540 ran best with 38 degrees of timing and after the tuning sessions were over, the big-block pumped out 777 hp and 681 lb-ft of torque.
The new combination shifted the power higher in the rev range compared to the previous mild combo. Where the mild combo produced peak power at 5,700 rpm and peak torque at 4,600 rpm, the wild combo elevated the horsepower and torque peaks by 1,000 rpm, to 6,600 rpm and 5,600 rpm, respectively.
Remember, these numbers came with a static compression ratio of just 8.8:1, hardly what you'd consider optimum for performance use. Two more points of compression (to 10.8:1) would easily increase the power output by a solid 50 hp or more. Best of all, the power gains would occur throughout the rev range (basically a jump of 7-8 percent). As it was, the wild combo produced a broad torque curve, bettering 600 lb-ft of torque from 3,900 rpm to 6,700 rpm. Basically, step on the gas of this 540 and watch the tires go up in smoke.
Nitrous 540 Combo
Happy as we were with our two distinct mild and wild combinations, we ran one more test. By adding nitrous oxide to the mix we could further transform our wild combination into a serious street/strip terror. Anytime you add an extra 250 hp to the mix, things really start getting interesting.
To add the nitrous to the 540, we decided to remove the Weiand tunnel ram and replace it with the Weiand Team G. Unlike the intake used on the mild combination, this team G was designed to accept a larger 4500-sereis carburetor. Plenty capable of supporting the power output of the wilder combo, the single-plane Team G allowed us to install the awaiting NOS Cheater Competition system. Adjustable from 150 hp to 250 hp, the NOS Cheater system was perfect for our large-displacement, low-compression 540.
Replacing the tunnel ram with the Team G resulted in a change in peak power numbers from 777 hp and 681 lb-ft of torque to 770 hp and 663 lb-ft of torque. Adding a 250hp shot of nitrous (102 fuel and 93 nitrous jetting) resulted in a final power number of 1,022 hp and 839 lb-ft of torque (though it was necessary to run a smaller fuel jet to lean the mixture out).