The Mouse has hatched! Our budget-conscious 383 is ready for its in-car test. In Part Four of this five-part series on building your first engine (Dec. '07), we lashed the 383 to the dyno at JMS Racing Engines and registered a peak output of 442 hp at 5,800 rpm and 436 lb-ft at 4,900. That's with a set of Patriot Super Street 215 heads, a solid flat-tappet Isky cam with 0.544/0.547 lift and 284/294 advertised duration, an Edelbrock Victor Jr. single-plane intake, and a 750-cfm Edelbrock Performer 1407 carb. For a wallet-friendly investment of just over $4,200, we got an aluminum-head, 9.8:1, billet rod-equipped Mouse that runs great on 91-octane and should continue to do so for a long, long time, thanks to its modest 6,500-rpm rev ceiling.
But as they say, you don't race dynos. What's this thing do when we stick it in a car? To find out, we grabbed Mike Morgan's 3,200-pound '69 Nova and started spinning wrenches. You might remember our original intention, to test this mill in a '66 Chevy II, but those plans fell through at the last minute. All the same, the cars are similar test beds (frontal area, curb weight), so the impact on the results is negligible, though we did make an interesting oil pan discovery. (More on that in a minute.)
Here's the punch line: On the Superior Automotive Dynojet chassis dyno, the 383 delivered 353 hp at 6,100 rpm and 331 lb-ft at 5,250 to the tires. Newbies might wonder where all the power went. After all, a drop of 89 hp and 104 lb-ft doesn't go unnoticed. But you must remember that it requires horsepower to turn the transmission, spin the driveshaft, twist the ring gear, and rotate the tires. Parasitic losses build up quickly; by most accounts, you can expect a 20-25 percent drop in measured output at the rear tire versus the crankshaft. And there's also the question of mufflers. Sure, Morgan's Nova runs a pair of massive 3.5-inch Borlas and a Dr. Gas X-pipe, but there's still a bit of backpressure entering the picture compared to the straight-out header exits used on the engine dyno.
In-car performance on the chassis dyno and at the dragstrip
It's all in the combination.
But the most telling indicator is what happens at the dragstrip. At the eighth-mile Irwindale track, Mike made a bunch of passes, all within a whisker of the 7.363-second, 93.9-mph best. To get an approximate quarter-mile prediction, we multiply the e.t. by the NHRA's 1.57 correction factor, and it's like the Nova cranked an 11.55 in the quarter. So don't get bummed out by deceptively soft chassis dyno figures; the e.t. doesn't lie--and neither does that 93-plus eighth-mile trap speed.
Because Morgan's Nova has been a street/strip test mule for numerous small-block powerplants for more than two decades, he's got it pretty well sorted out, as proven by its 1.614-second 60-foot times. But if you're a first-time installer, you'll want to make certain the cooling and fuel systems are up to snuff and that, in general, your car is capable of handling the power infusion. After all, there's no sense sticking a 442-horse mill in a car that isn't properly set up.
We always say, for the best results, build the car from the back to the front. That means a limited-slip differential with axles and related parts tough enough to handle the job (the Nova runs a Moser 12-bolt with a spool), appropriate gears that offer the best balance of dragstrip capability and street cruising to suit your needs (Morgan's a bruiser and tools the street with 4.30 cogs), appropriate suspension and springs (he runs Calvert split monoleafs and CalTracs bars), and tires.
Ah yes, tires. We've seen altogether too many guys go out and cram massive power under the hood only to totally drop the ball in the traction department. In fact, we love it when these guys are in the other lane! When it comes to rubber, we like to set a car up with what we call a traction surplus. That means serious rubber in the form of soft-compound, D.O.T. treaded skins; all-out slicks (strip only, please); or a set of the modern drag radials everybody used to scoff at but now see as the miracle workers they are. Naturally, make sure there's plenty of sidewall clearance so there aren't any top-end surprises. You'd be amazed at how much tire growth there is at even 90 mph. If you need more clearance, make it happen before hitting the strip.
This traction-surplus philosophy seeks to ensure that you don't have to worry about how the car is going to launch. Your trust in its traction capacity should be strong enough that you can simply concentrate on cutting a good light then mashing your foot into the floor on the green. If you add big power but don't meet it more than halfway down, you don't have a traction surplus. You'll know right away if your car has the magic. Any tire spin, yaw, or smoke is your sign to step things up. As the wheels-up action shot proves, Morgan's Nova has traction in spades. Alternating between MT 28x10.5-15s and BFG P275/60R15 drag radials, he used a bottle jack to gently bulge the Nova's quarter-panels outward to gain needed sidewall clearance then smoothed the wheel-lip seams to eliminate sharp edges. Now it's all good.
Moving forward in our rear-to-front strategy, make sure the driveshaft and U-joints are beefy enough for the job. Nobody has to remind you about the need for a driveshaft safety loop. Nobody, that is, except for the NHRA tech inspector (if he sees slicks on the back axle). If you're running a manual transmission, make sure the clutch and pressure plate are fresh and contained by an approved scattershield with a block-saver plate. We've seen plenty of perfectly good blocks go to the scrap heap after chunks are knocked loose by flying clutch parts. Motor mounts are also a classic trouble spot on clutch cars. Worn-out mounts let the left side of the motor lift a bunch and can even bind mechanical throttle and clutch linkages with spooky results. Get fresh mounts, maybe even step up to a solid mount on the driver side of the block if you won't mind a little vibration at cruise speeds.
Automatic transmission users must make sure the clutches are healthy enough to handle added power without slipping. Maybe now's the time to freshen things up with a basic rebuild kit. Another detail to consider is a properly matched torque converter. Vehicle weight, cam timing, axle ratio, and engine displacement are all key specs you must provide to your converter supplier so you get the right unit for your combination. When it comes to choosing a stall speed, street guys should be thinking about speeds ranging from 1,800 to 2,800, occasional strip trippers should consider 2,500-3,500, and weekend warriors will want to start at 3,500 and work up from there.
Generally speaking, increased stall speed allows engine rpm to rise into the fat part of the torque curve so there's more grunt available to move the car on the launch. But remember to always err on the side of caution. Too much stall speed can put the engine past its ideal rpm spot and actually dull the launch while generating wasteful slippage and heat on the boulevard. And naturally, be sure to plumb in a transmission fluid cooler any time stall speed is increased over the stock level.
Flying directly in the face of our somewhat conservative ground rules, Morgan's Nova runs an 8-inch Munsinger Stock Eliminator converter in front of its manual valvebody Turbo 400. Coupled to the 600hp 414 stroker small-block previously powering the car, it stalled at 6,200 rpm against the transbrake. But with the comparatively modest 442 hp and 436 lb-ft generated by this 383, foot braking delivered a 4,000 stall speed and surprisingly pleasant street manners. Sure, the mill winds up a bit before the car starts rolling in traffic, but it isn't as obnoxious as we feared it might be. All told, we're pleased with how the 383 runs and drives. CHP
GET THE HOOKUP
JMS Racing Engines
El Monte, CA
626.579.4567 · jmsracing.com
Linn Creek, MO
888.737.2970 · percyshp.com
714.503.1880 · superiorautomotive.com