Combine a used 350ci small-block and a Weiand mini-blower and you have an affordably powerful combination.
We can hear the hue and cry already-"Man, not another small-block Chevy story!" We hear you, but when was the last time you attempted to build a complete blower motor from carburetor to oil pan for under $3,995? We even avoided digging too deeply in the used-parts bin. In fact, the only previously owned parts in this whole buildup are the short-block, a portion of the carburetor, and the distributor. Everything else was purchased new with an eye toward balancing the budget below $4,000. As you can see from our price chart we just barely came in under the budget, but the numbers add up.
That's the financial side of the story, but the much more interesting information is based solely on the dyno side of things. The idea was to build as much power as we could without just throwing dollars at it. The star of the show is clearly the Weiand blower, but with a twist. No, the impellers are still straight, but Weiand has created a new Vortec cylinder head-compatible intake manifold. That opens up several horsepower-friendly doors, so we decided to see how much power we could make on our peanut butter-and-jelly budget.
You can skip to the power curve, but the numbers crunch down to a stout 455 lb-ft of torque at a reasonable 3,900 rpm, while horsepower clicks in at 445 ponies at 6,000 rpm. This creates an outstanding 2,100-rpm broadsword powerband that would make this a superb street small-block in front of a tight- converter automatic. Think how this combo would roast the hides at will and still offer great street manners. All that's left to do now is fill you in on the details.
Vortec Head Tricks
The whole reason for doing this story revolves around the Vortec heads. These are iron heads with 1.94/1.50-inch valves that offer better intake-port flow characteristics than the older, iron Bow Tie heads. But the real beauty of these castings is that they are very affordable. The stock assembled iron Vortec (PN 12558060) sells through Scoggin-Dickey Performance Center for just under $500 for the pair. You can barely rebuild a stock set of iron heads for that price. Unfortunately, the Vortecs present a couple of restrictions on their use.
First of all, the Vortec family of cylinder heads uses a specific intake bolt pattern requiring a matching intake manifold. That's why we got excited when Weiand offered a mini-blower manifold for the Vortec. The next point that actually played in our favor was the Vortec's 64cc combustion chamber. Normally, with four-valve relief, flat-top pistons and composition head gaskets, a standard-bore 350 would have 9.7:1 compression, which is a bit high for a pump-gas blower motor. But because the stock cast pistons in this engine employ both a dish and a horrible chamfer around the piston's outside diameter, the static compression ratio is more like 8.6:1, which is far more blower-friendly.
Since we wanted to run a mild camshaft that would generate almost a half inch of lift, we knew we would have to modify the Vortec heads. The stock Vortec's Achilles heel is that the valvespring/retainer/seal combination is limited to a maximum of about 0.460 inch of valve lift. One solution is to change valvesprings, but that involves expensive machining operations. This is where Scoggin-Dickey enters in the game again with a set of affordably priced heads that are already modified for additional valve lift and come with slightly stiffer valvesprings to accommodate a bigger cam. If you have experience modifying cylinder heads you might be able to do the work yourself for less coin, but assuming you don't have the specialized cylinder-head tools, the Scoggin-Dickey heads are an excellent bargain at $680 for the pair, and all you have to do is bolt them on.
Cam SpecsDescriptionDutation (Adv.)Dyno Numbers
The following dyno curves show the progression of our boneyard motor from a normally aspirated baseline (Test 1) through bolting on the out-of-the-box Weiand 142 supercharger (Test 2). The test also included using a set of 151/48-inch headers through a pair of Flowmaster 211/42-inch mufflers.
Note that the boost level on this engine is very conservative, only reaching 5 psi at the very peak rpm point. This is with the stock pulley supplied with the kit. A smaller blower pulley would spin the blower faster, making more boost and perhaps more low- and mid-range power. But this also would heat up the air and probably cost some top-end power. More importantly, extra boost would be a very bad idea with our stock cast pistons.
The Scoggin-Dickey modified heads widen the spring pads for larger-diameter valvesprings (which weren't used on these heads) and also cut down both the valveguide diameter and the guide height for more spring clearance.<BR><BR>
Note how the blower torque gains tend to be greater below and above the normally aspirated engine's peak torque of 4,200 rpm. Since peak torque is where peak volumetric efficiency (VE) occurs, the blower helps make the most power in the rpm ranges where the engine needs the most help-on either side of peak VE.
Track Times
We plugged this power curve into the Quarter Pro drag racing simulator from Racing Systems Analysis (quarterjr.com) to simulate a 3,500-pound street car with a TH-350 trans, a 2,600-rpm converter with 3.31:1 rear gears, and sticky M/T DOT tires to help it hook. Shifting at 6,500 rpm, the simulator spit out a 11.97/113.5-mph pass. Subtract a couple of tenths on general principles and you're still looking at a 3.31-geared street car that can run low 12s on pump gas with an engine that costs less than $4,000. And this baby will do it all day long 'cause that blower never needs a bottle refill. It doesn't get much better than that. END
Carb Swap
We began with a used Holley 650 double-pumper for $60 that we found on eBay. We then swapped in one of Holley's new HP main bodies for a mere $125. (The details on this are outlined in "Holley HP Main Body Swap" in the Feb. '06 issue.) The key point is that a mechanical-secondary 650 uses the same throttle-blade size as a 750 carb. So we converted a small carb into a bigger one for less than $200 including new gaskets. A new, Holley non-HP 750 double-pumper is $400.
