Words and Photos By Richard Holdener
When it comes to the number of cylinders in an engine, we say the more the merrier. If four is good, then six must be better, and eight borders on great. While more cylinders usually equates to more power, this line of reasoning limits the fun we can have on the dyno, by excluding a great many performance candidates. Looking back through our years of testing, the vast majority has been on some sort of V8. Whether it’s a Ford, Chevy, or Dodge, we seem to be drawn to those engines, but what about the other guys? Believe it or not, GM, Ford, and Dodge produced a great many engine combinations with fewer than eight cylinders. This means not every enthusiast roaming the streets will be sporting a V8. It is for the forgotten crowd we decided to run some testing on something with fewer than eight cylinders. If eight cylinders is the definition of a race motor, then think of our 4.3L V6 as at least three-quarters race.
The statement actually holds a certain element of truth, as displacement wise, the 262-inch, 4.3L V6 was exactly 75 percent of a standard 350-inch small-block V8. The architecture of the V6 was very similar to a small-block, with identical bore, stroke, and even rod length (though they are not interchangeable). The similarity to the small-block also extended to the cylinder heads and cam timing, and the V6 was treated to the same upgrades that were applied to the small-block, including the one-piece rear main seal and application of the (high-flow) Vortec-style cylinder heads. Introduced in 1985, the 4.3L replaced the previous 3.8L (229-inch) V6 and was offered in power outputs ranging from a low of 130 hp up to variants producing a solid 200 hp.
While 200 hp might not seem like a lot compared to the current crop of 400-plus-hp V8s, there was a time, not long ago, that the small-blocks of the world struggled to produce 200 hp with eight cylinders.
When you combine the power potential with the reduced weight (compared to a V8) and fitment into a tight chassis, the 4.3L V6 had a lot going for it.
As with any good thing, there is always the other side of the coin. Sure, the little V6 was a relative lightweight, will squeeze into tight engine bays, and can produce decent power, but what if you are looking for more than just decent power. Obviously, BIG power requires increased displacement, which means more cylinders, but there is an alternative to replacing the V6 with a larger V8. We call it boost!
The great equalizer for any motor is always forced induction. There is nothing better for making a little motor think like a big motor than some positive pressure. Boost works magic on the power curve of any motor, and can be applied every bit as successfully to a V6. An example works well here to illustrate the power potential, as boost works like a multiplier of the original power output. Since you motor operates under atmospheric pressure already, adding additional pressure will improve the power even further. If you add one bar (measured at 14.5 psi) of pressure (boost) to your engine, you can double the original power output. If you add just half a bar, you can increase it by 50 percent, and this multiplier works at any given pressure ratio.
If we apply our formula to a real world example, we see that running 7.25 psi of boost (.5 bar) on a 200-hp V6 can increase the power output by 50 percent. This would increase the output of our 200-hp V6 by 100 hp (half of 200 hp). Adding 7.25 psi to our 200-hp V6 could push the power output to 300 hp. If we increased the boost up to 10 psi (.689 bar), we could increase the power output by 68.9 percent (138 hp), bringing the total to 338 hp. Were we to run 14.5 psi (1 bar), we could double the power output of our 200-hp V6 to a full 400 hp.
You will note in each example, we used the word could, as the multiplier in not a certainty. There are a number of variables that must be considered, and obstacles overcome, for the power/boost formula to produce optimum results. To illustrate the potential of the power/boost formula, we decided to apply boost to a mild 4.3L V6. Our goal was not to build some fire-breathing dragon, but rather a boosted V6 that offered V8-like performance.
The majority of the basic components on the 1990 4.3L remained stock. The entire motor was rebuilt, which included new rings, bearings, and Fel Pro gaskets, but performance parts were limited to a cam, valve springs, and the induction system. Due to age and mileage, it was necessary to replace the factory damper with an SFI unit from Speedmaster. The 9.1:1 compression was ideally suited for boost, but additional power was supplied with the installation of a COMP Cams Magnum cam profile. The new COMP cam offered a .500/.515 lift split, a 215/220-degree duration split, and 114-degree lsa. Mild by most standards, the COMMP cam was still a healthy step up from the stock stick. The stock (non Vortech) heads were fed by an aluminum Edelbrock Performer intake. The intake was treated to some minor porting and fit with a Holley 650 XP carb for the break-in cycles and normally aspirated power runs. Once we applied boost, we swapped over to a dedicated blow-through carburetor from Carb Solutions Unlimited (CSU).
Run with an MSD distributor and breathing through the turbo headers feeding a single three-inch exhaust, the normally aspirated 4.3L V6 produced 218 hp at 5,100 rpm and 261 lb-ft of torque at 3,200 rpm.
With our baseline numbers established, it was time for some boost. Boost came courtesy of a set of custom turbo manifolds designed by JFab. The tubular manifolds were designed for a sand-rail application and merged together using a custom Y pipe to feed a T4 turbo flange. The Y pipe was also configured to accept a waste gate to control the boost pressure offered by a 72mm turbo from CX Racing. Capable of supporting more than 500 hp, the turbo was more than sufficient for the needs of the V6. The Holley 650 XP carburetor was swapped out in favor of a dedicated blow-through unit from Carb Solutions Unlimited. The CSU carb featured boost-referenced power valves and was combined with a blow-through carb bonnet. No intercooler was used on this blow-through application, but the carburetor itself dropped the inlet air temps by more than 100 degrees.
After dialing in the air/fuel and timing mixture on 10 octane race fuel, the turbo V6 eventually pumped out 414 hp and 415 lb-ft of torque at a peak boost reading of 13.6 psi. There was more power to be had with more boost, but the turbo V6 was now pumping out V8-like power. Maybe not full-race power, but at least three-quarters race.
Sources: ARP, Arp-bolts.com; COMP Cams, compcams.com; Edelbrock, edelbrock.com; Holley/Hooker/NOS, holley.com; JFab, 909.525.8220; MSD, Msdignition.com; Speedmaster, Speedmaster79.com