Muscle Mustangs & Fast Fords
Installing A 331-Stroker Kit In A Small-Block - Stock-Block Stroke Swap Part 4
From The Engine Dyno To The Chassis Dyno, Our 331ci Small-Block Ford Is Put To The Test.
Over the past several months, we've been assembling and dyno testing a small-block 331ci engine. This month we conclude the buildup by installing the engine in the car and turning the chassis dyno rollers to see just what the powertrain loss is after backing it up with a C4 automatic transmission.
The engine in question began as a stock late-model 5.0L block, which subsequently had its cylinder bores enlarged 0.030-inch oversized. We then sourced the 331-cid rotating assembly from Competition Products. The assembly consists of a cast-steel crankshaft, Scat forged I-beam connecting rods, and forged-aluminum SRP pistons, and it comes with bearings and piston rings.
We chose the 331-stroker kit for the better rod ratio, and as we found out during installation, it didn't require any modifications to the block to clear the rod ends. Competition Products also provided a 157-tooth, small bolt circle, SFI-approved flexplate to connect the engine to the transmission; a Professional Products 28-ounce harmonic balancer; and a Melling standard-volume oil pump.
Knowing that the stroker small-block was going to move much more air than the stock 302, we called Trick Flow Specialties about an induction setup. To keep the fuel-injection (the engine is going in a late-model Fox coupe Mustang), Trick Flow provided us with its brand new "Fast As Cast" 190cc cylinder heads, which are a lower cost, cast version of the company's CNC-ported Twisted Wedge cylinder head. Trick Flow also supplied its Stage 2 hydraulic roller camshaft and a Trick Flow R intake manifold. We also sourced the needed pushrods, 1.6:1 roller rocker arms, timing chain, valve covers, gaskets, and TFX EFI billet fuel-rail kit from Trick Flow.
We buttoned up the bottom of the engine with a 7-quart oil pan from Milodon; the top of the engine was fitted with a BBK Power-Plus 70mm throttle body and EGR spacer from Brothers Performance Warehouse. We had a set of Ford Racing 30-lb/hr fuel injectors handy and used those in conjunction with a C&L mass air meter that we also had.
Summit Racing Equipment played an integral role in this buildup as well, supplying everything from ARP head bolts to gaskets to throttle cables. We often found ourselves in need of this or that, and Summit Racing had what we needed every time. And they got it to us usually the next day, thanks to the company's close Georgia location.
Hurricane Performance's Jason Combs assembled the engine, and we put it to the test on Horsepower By Hedrick's engine dyno. Once bolted to the Superflow dynamometer, Mark Hedrick proceeded with a programmed break-in routine, which seats the piston rings to the cylinder walls and ensures everything has been well lubricated. To get the fuel-injected engine to run on the dyno, we contacted Ford Racing Performance Parts and ordered a standalone EFI harness designed for 5.0L/5.8L engines. The harness just needed an A9L EEC-IV ECM, a 12-volt power source, and a ground to get the engine up and running. To make sure we maxed out the performance of the engine, we relied on Tony Gonyon of TunersInc to handle the necessary chip burning and datalogging.
On the dyno, the EFI combination produced a stout 396.7 hp at 5,800 rpm and 377.3 lb-ft of torque at 5,200 rpm. Readers who have followed this build may recall that we encountered a misfire after several pulls. After performing multiple checks and inspections, we opted to run the setup with a carburetor to see if it was a mechanical or electrical issue. The carbureted combination ran clean and posted 401.2 at 6,100 rpm, and peak torque checked in with 391.1 lb-ft at 4,700 rpm.
When we began this build, we had planned to compare the engine dyno numbers to the chassis dyno numbers to show exactly what the drivetrain frictional loss would be in this application. Engine dyno numbers are also helpful in choosing the right torque converter, as we recently found out. Unfortunately our limited window of time on the engine dyno had closed, so we reinstalled the fuel injection setup and pulled the engine to ready it for installation into its new home between the fenders of a Fox-body Mustang coupe.
To get the coupe cruising down the dragstrip, Hurricane Performance's Jason Combs procured a C4 automatic transmission, fortified with various high-performance components from Performance Automatic. After a quick rebuild, we had our transmission, but we needed a converter. For that, we turned to Transmission Specialties in Aston, Pennsylvania. With over 30 years of experience building high-performance transmissions and torque converters, Transmission Specialties knows a trick or two when it comes to transferring engine power to the ground. Our application was pretty simple, and the company pulled a 10-inch torque converter off the shelf. It features an approximate stall speed of 3,000-3,400 rpm, which should work well in both naturally aspirated, and if we like, supercharged forms.
Transmission Specialties' Ken Kelley had a few recommendations when shopping for a performance torque converter. "As with anything else in life, you get what you pay for," says Kelley. "Specify furnace-brazed fins, which improves the strength of internal blades of the pump and turbine, and ask if the torque converter has been rollerized with needle bearings. Roller bearings provide less internal drag which reduce friction inside the torque converter. You'll also want to ask if the cover is made out of a stock OEM four cylinder converter or if it is a billet front cover, which adds strength to keep the converter from ballooning under load."
Kelley also notes that even with all of these points met, the best thing you can do is match the stall speed to the peak torque curve of the engine. "The torque converter should reach its stall speed at the same time the engine hits its peak torque output. That information is consistent with an accurate dyno sheet."
With the transmission situation resolved, the last part of the equation was the exhaust system. We were running 1.75-inch headers on the engine dyno, and while they may be a bit on the large side for this engine, we're expecting more power out of the mill down the road, so we called up Latemodel Restoration Supply for a set of its Mac 1.75-inch long-tube headers. They're offered in chrome and ceramic coatings; we opted for the latter.
Kooks, Bassani, and Mac are the only companies that manufacture a full-length header that will fit an automatic. To control costs, we went with the Mac's as its mild steel construction keeps the price down.
One issue we ran into, the headers use a 3-inch collector and ball/socket flange. Mac offers a 3-inch ProChamber midpipe, as well as a 3-inch after-cat exhaust, but we wanted to use a 2.5-inch setup for better clearance. To make the headers and the exhaust mate up, Latemodel supplied us with one of its 2.5-inch H-pipes, and Summit Racing sent us a Flowmaster ball and socket flange kit, which allowed us to neck down the H-pipe. Working with companies like Latemodel Restoration and Summit Racing, which carry a vast assortment of parts and brands, allows you to easily remedy a situation with just a phone call and a credit card.
Well, our stock-block stroker 331 finally made it to the chassis dyno and we're pleased with the results. It produced 346 hp at 5,900 rpm and 343 lb-ft of torque at 4,700 rpm. This equates to a drivetrain loss of 13 percent-about 57 hp and 72 torque.
This 331 powerplant can be both an excellent bracket engine and a great street engine. That being said, we've got some ideas floating around upstairs, so you just may see it pop up again. We're thinking a set of Twisted Wedge pistons, a bigger cam, more compression, and a little tsst, tsst may be in order. Stay tuned.