408W Stroker Windsor Build - Big-Inch Boss
Using Ford’s Boss 351 Block to produce big, dependable power
From the November, 2011 issue of 5.0 Mustang & Super Fords
By Jeff Huneycutt
Photography by Jeff Huneycutt
When Ford introduced the new Boss 302 and 351 blocks, they were meant to consolidate a wide-ranging lineup of race-oriented blocks with one do-it-all solution. But you better believe that right away we started planning how to use these new babies in high-horsepower street applications. Especially since stock 351 Windsors are getting harder to find in the wild and can be a bit expensive if you have to send them to the machine shop to bring them back to spec.
The idea behind this build is to put together a 500hp Windsor that will be right at home in just about any Mustang. But 500 hp these days is too easy, so we decided to up the ante just a bit. First, it has to be naturally aspirated-no problem. Second, since most of us are still pinching pennies with the continuing poor state of the economy, it has to be easy on the wallet. So we stayed away from the exotic stuff and stuck to off-the-shelf parts that offer great value, but we didn't use any recycled stock parts because we want this engine to be super durable. Which brings us to the third requirement: It has to be dependable. So if anything, this engine is overbuilt. You should be able to take it to the track and wail on it all day long with no worries. Or say you want to add a little nitrous later on- no problem. As they say, let her snort and have fun.
With those requirements, using a Boss 351 block as a foundation became a no-brainer. At just under two grand, the block provides about the best bang for the buck anywhere and hardly costs any more than a stock Windsor block that has been fully machined and blueprinted. But the Boss block still has some advantages over that, namely it's cast using diesel-grade iron, which exhibits a much greater tensile strength than the stock casting. Plus, there's extra meat in all the critical stress areas. And then there's the standard four-bolt, nodular-iron main caps.
When you put it all together, you get a block that shrugs off 500-plus-horsepower blasts and asks for more.
On The Dyno
Although we just opened up...
Although we just opened up the bores 0.030 over to 4.030 inches, Ford says you can safely bore the cylinders out to 4.125.
One quirk of the Boss versus...
One quirk of the Boss versus a standard block is the cam bores are all equal diameter and do not step down in size. This requires you use a special set of cam bearings—Durabond 351HP in our case.
While pre-fitting, we discovered...
While pre-fitting, we discovered this spot where the No. 5 rod hit the side of the block near the oil pump mount. You can see the results of a little time with the grinder, which gave us the clearance needed.
Another difference with the...
Another difference with the Boss block is it uses aluminum screw-in freeze plugs. They seal with rubber O-rings, so only 25 lb-ft of torque is necessary. Also, use a little motor oil on the threads to keep them from seizing in the iron-block.
Four-bolt main caps help keep...
Four-bolt main caps help keep everything in place when the power numbers creep past 400. Also, the mains come in the larger 2.748-inch Cleveland size to be better able to handle big power.
To maintain rigidity even...
To maintain rigidity even at 4.125 inches, the cylinder bores are Siamesed. Steam holes have been added to aid cooling between the bores. You can just see them here.
The crank is from Eagle with...
The crank is from Eagle with Cleveland-size mains and Chevy 2.100 rod journals. Combined with the 4.030 cylinder bores, the long 4.00 stroke gives us a total displacement of 408 ci.
Engine builder Ken Troutman...
Engine builder Ken Troutman torques the inner main cap bolts to 100 lb-ft and the outers to 35—both after the threads have been lubricated with motor oil.
The forged H-beam rods are...
The forged H-beam rods are also from Eagle, and the long 6.200-inch length helps bring the rod/stroke ratio back into line when used with the 4.00-inch-stroke crankshaft.
The pistons are from Mahle....
The pistons are from Mahle. In addition to the coatings Mahle puts on its pistons, this design ditches the slipper skirt for a race-oriented strutted design. The advantage here is the pin towers can be moved inward so the pins can be shorter—making the overall package lighter.
With the extra-long stroke,...
With the extra-long stroke, the pistons use a 28cc dish to bring the compression ratio back into pump-gas range. Combined with 62cc combustion chambers, we expect to be in the pump-gas-friendly, 10:1 compression range.
A set of GFX rings are used...
A set of GFX rings are used to seal combustion. The 1.5mm, 1.5mm, 3.0mm ring pack uses a napier-style second ring for good oil control with less ring pressure. Gaps for the top two rings are in the 0.022 to 0.025 range.
Ken also spec’d out the hydraulic-roller...
Ken also spec’d out the hydraulic-roller camshaft. Comp Cams handled the grind, which has an advertised duration of 280/290 and a total valve lift of 0.571 on the intake and 0.576 on the exhausts.
The heads are Edelbrock Victor...
The heads are Edelbrock Victor Jrs. They came assembled, but KT Engines tore both down to check inspect the valves and springs individually.
After installing the pistons...
After installing the pistons and rods and torquing the rod bolts, the Melling high-volume oil pump is bolted down and the pickup checked to make sure there is approximately 3⁄8-inch of clearance between the pickup and the bottom of the pan.
The Boss block has special...
The Boss block has special provisions to check oil pressure at the rear of the block. Ken fabricated this pickup that threads into the block and simplifies hooking up a pressure gauge. He prefers measuring pressure at the rear of the block because you can see the pressure as it comes out of the engine instead of before it enters. This way you know you have good pressure all the way through. Also, it helps clean up the engine compartment since there’s one less line that has to run from the firewall to the front of the engine.
The Edelbrock chambers are...
The Edelbrock chambers are already good, but KT Engines did a bit of light porting work, which you can see here, to blend the bowl into the seats. Later, KT will be installing 2.05-inch intake valves and 1.60 exhausts.
The intake ports have also...
The intake ports have also been matched to the intake manifold runners but haven’t been worked all the way up. This handwork is relatively minor, but Ken estimates it’s worth 20-30 hp.
Ken drops the heads into place...
Ken drops the heads into place over the ARP head studs.
We were able to keep the valvetrain...
We were able to keep the valvetrain hardware that came on the heads. The springs measured out at 150 pounds at the 1.900-inch installed height and 400 pounds open.
Comp Cams lifters with integrated...
Comp Cams lifters with integrated tie-bars drop into place in the lifter bores.
Instead of a traditional stud-mounted...
Instead of a traditional stud-mounted rocker system, KT Engines prefers a more stable shaft-mounted rocker system whenever possible. This system is from Jesel, and the first step is to bolt the rocker stands into place. Valvetrain geometry is adjusted by using shims underneath the stands.
Then the aluminum rockers...
Then the aluminum rockers can be bolted to the stands.
Once all the rockers are in...
Once all the rockers are in place, the lash is adjusted. Since this engine uses hydraulic lifters, the rocker adjusters are tightened until all the slack is removed, and then given another half turn before getting locked down.
The engine is topped off with...
The engine is topped off with a single-plane Edelbrock Victor Jr. intake and a Holley four-barrel that has been tuned by AED.
An MSD distributor channels...
An MSD distributor channels the spark.
This engine has been internally...
This engine has been internally balanced, so an SFI-approved Professional Products damper is used with no balance weights.
The finished product exceeded...
The finished product exceeded our expectations. On the dyno it pushed out an even 510 hp and 520.3 lb-ft of torque. 5.0