Long-Rod 225 Slant-6 Street Build

This long-rod 225 slant-6 high-performance engine rebuild (now at 231-CID & 3.8L) uses the 198-CID slant-six engine connecting rods to facilitate the use of better sealing and lighter weight pistons & valvetrain components as well as mods to create a strong performance street-cruiser (not a red-light racer). Emphasis was on creating high air velocity through the entire intake tract, reducing parasitic power loss everywhere possible, and lightening the reciprocating mass where budget allows - with all these stealthy mods hidden behind an otherwise plain-wrapper engine.

Since this engine build was done during the height of the pandemic, parts were scarce, and as you'll see, I had to get creative. But that makes for a better story.

Here's how I did it…

Induction

• Spectre Performance's #98881; 14" (356 mm), 180-degree dual-inlet aluminum air cleaner assembly was fitted with the base from the Edelbrock #1221 cleaner assembly to clear the Edelbrock carb fittings and staying low to clear my hood. Not only great looking, but also stops pulling in the hot air directly above the headers.
• Edelbrock's carburetor #1901 Thunder AVS-2 @ 500CFM w/electric choke was modified with one-step smaller jets and rods to run better with the smaller displacement and is set to run mostly on the primaries. Throttle tip-in with this is nearly instantaneous and almost feels like I'm running EFI.
• Offenhauser's #5270 [vintage piece] four-barrel manifold, which has been modified for water-heating under the carb baseplate by routing the heater core inlet/outlet hoses through a custom milled baseplate. This manifold has the same runner volume as the OE piece but saves several pounds from the heavy original cast manifold and, with the manifold being heated, allows me to cruse throughout the year. Heat to the carb is critical to vaporize extra fluid gas in the intake tract before it gets into the head, and with the original heat source removed due to the headers, some form of provisioning needs to happen. The water heat trick is old school, and works.
• Remflex's #6008 carbon intake/exhaust gasket provides a leak-proof seal for the intake and exhaust against the cylinder head. Install this, and you'll never have a leak or hear ticking again.
• Exhaust/Intake attaching studs & nuts have been replaced with same-size parts from McMaster-Carr #94358A270 with an Allen-head recess to make installation and servicing super easy. The nuts were replaced with mil-spec flex-top locknuts #99638A300 that won't loosen over time.
• Lokar's carburetor throttle #XTC1000HT & transmission kickdown #KD2904HT60 cables with bracket #SRK4000 replace the floppy mechanical linkage. These not only look outstanding, but also make for an unbelievably smooth action with good feedback through the pedal.

Cylinder Head

• The bowls received the typical street pocket-porting, with the short-turn on the floor being radiused. General cleanup and smoothing was also done to improve airflow. All work was done with the goal of increasing air velocity but not volume - to make for a strong street engine that's in the power band most of the time. Other than that, the head was just cleaned where needed and kissed with a mill to get a gasket seal. Because of the long connecting rods, the head doesn't need milling to boost the compression.
• Elgin supplied a full set of Ford 289 intake valves #I-1670 @ 1.78" (45.2 mm) & exhaust valves #E-1669 @ 1.45" (36.8 mm). These are typical oversized diameter valves for a slant-6, and were modified with a back-cut to improve flow. These valves have a smaller diameter stem at 5/16" (7.9 mm) vs. the original 3/8" (9.5 mm) and have been fitted with positive oil seals and bronze guides.
• Street-performance valve/seat angles have been cut into the head to match the intake to the valve flow.
• K-motion's #K-800 valve springs, using only the outer spring, resulted in 110/280 pressure to nail the requirements of the camshaft.
• Comp-Cams' valve spring locks & retainers hold the valve gear together without much fuss.
• OE rockers & spacers were thoroughly cleaned and hand-fitted.
• Endurotec #AS0193 BigBore cylinder head gasket from Australia, seals it all up, and provided a bit of wiggle-room for the valve to piston clearance I needed that other head gaskets did not have.

Block

• The block itself was cleaned and line honed, with new cam & crank bearings installed. The block also received some spot-grinding to clean things up, with the deck just kissed with the mill for gasket sealing.
• Cylinder bores were piston-matched to 3.445" (87.5 mm), bringing the displacement to 231-CID (3.8L), from 225-CID (3.7L).
• Wiseco's #PTS536A45 4032 forged aluminum pistons were installed using the press-pin option for endurance, bringing the static compression to 9.6:1; running 91 pump-gas. These pistons check-off all the performance boxes being smaller in overall size, 2.0 ounces (75.6 g) lighter in weight each (piston only), having a shorter compression height, pre-cut valve pockets, and with anti-friction coating on the skirts.
• Wiseco fit these pistons with ring kit #8750XX, which includes modern-sized 1/16, 1/16, and 3/16 (1.6, 1.6, 4.8 mm) rings that are higher up the piston to provide for better sealing while also being significantly thinner to reduce parasitic drag.
• Chrysler connecting rods from 198-CID slant-6 were sourced used. These are longer than 225-CID rods at 6.699" (170.2 mm) for the 225, vs 7.005" (178 mm) for the 198 engines, and form the basis for the long-rod rebuild. I was extremely lucky to have found a complete set of rods with pistons attached that were all straight. Still, they were checked for size and straightness, cleaned, and had new bushings & bearings installed.
• ARP connecting rod bolts from a Pontiac SD-455 engine [yeah, they fit!] connect the rods to the crank.
• NOS oil pump #2808507 was found. This has the standard pressure & volume, and is just the ticket for this build.
• Crankshaft journal bearing #1 received a chamfer on the outside (chain facing) for proper timing chain oiling. It's amazing that replacement bearings lack this.
• Crankshaft oil holes were also chamfered, and all journals polished.
• Lifter bore tops received a wide chamfer to increase oil pooling at the top of the lifter, which provides for better oiling. Being a solid lifter engine, this is a non-pressurized oil system at the lifters, so every bit counts.
• Oregon Cam Grinding's #346 camshaft was spec'd and custom profiled to use Ferrea Racing's lightweight .904" lifters, which require a custom ramp angle.
• Cam Specs: duration @ .050 234/228, Lobe Separation 106, Valve Lift .476/.479
• Ferrea lightweight solid lifters #LF1004 at 66 grams each, vs. 99 grams OE, were used to lighten inertia parasitic loss. Overkill? Heck yea!
• CompCams pushrods #7864-12 were used. Nothing special, just stock replacements at 5/16" and 9.954" overall length (7.9 and 252.8 mm).
• True-roller timing chain set was custom-built by Elgin (an OE supplier to Chrysler in the day) using the chain & crank sprocket from 440/426 Hemi mated to their HP camshaft sprocket for the slant-6. I sourced these parts from their catalog, and they were cool enough to have an engineer spec the parts before shipping to make sure it all works. Sure, there are other options readily available, but I like having a set put together by an OE supplier that celebrated their 100th year in business. They were awesome to work with and super supportive of the build.
• Specta's Premium #SP1051MP fuel pump was installed delivering 4-6PSI @ 30-GPH, which has ample supply at just the right amount of pressure for this build.
• Felpro and Mahle gaskets were used throughout the build and based on availability.
• Driven GP-1 15W-40 Synthetic Blend High-Performance Oil with a Baldwin #BT216 filter (this one has the integral standpipe) provides the lube. The oil has a lot of ZDDP for use with flat tappet engines and runs super clean.

Ignition

• OE alternator was rebuilt to factory specs @ 50-AMP, and just cleaned up otherwise.
• HiRev-7500 electronic ignition module [from Rick Ehrenberg] provides the spark.
• NGK Iridium spark plugs #97382 are used. These run clean and draw fewer AMPs to fire than other plug types.
• NGK spark plug wires #6716122 gets the spark where it needs to go.
• My vintage electronic distributor, an OE MOPAR dealer upgrade part, but not original to the car, received a full rebuild and was custom-curved on a Sun machine.
• Pertronix's #40011 Flame-Thrower ignition coil was selected for its quick saturation, which helps deliver more torque at lower RPMs.
• A mini-starter [another part from Ehrenberg, there were many] which draws significantly less amperage and startup than the OE was also installed and also shaves several pounds.
• YearOne's ignition/engine/lighting wiring harness #HU226A was installed to ensure continuity and full-system reliability to everything connected. This actually made a significant difference to all things electrical and, in an odd way, I liked the process of installing it.

Cooling

• Unbelievably - I'm still running the stock radiator! Yep, even after a full summer, no overheating.
• SuperStat's 195F (91C) Thermostat #STA45359 keeps things in check, while a 16-LB (1.1 bar) closed radiator cap seals the radiator.
• A coolant expansion/recovery tank was also installed to play nice with the environment.

Transmission

• The original Torqueflite 904 three-speed has been rebuilt & up-fitted with HD internals, including steels & frictions. Fun fact, with a date code of Sept. 12, 1967 and sequence of 0651, this was the 651st 904 Torqueflight built for model year '68 according to its stamping.
• TransGo's #TF1 reprogramming kit was installed to tighten shifts and correct some funky Torqueflite stuff.
• Edge Racing Converters built a custom 2800 RPM stall high-efficiency torque converter with a 9.5" impeller & turbine, Torrington bearings, and 4130 chrome moly steel drive hub & spline insert. ARP 7/16" (11.1 mm) #240-7302 bolts hold it to the flexplate.
• 440source's flexplate #200-1040 (yes, for a 440 CID engine) transfers the motion to the driveshaft.
• MOPAR's full-synthetic AFT+4 fluid was poured in.

Performance estimates are 235-HP & 240-Ft/Lbs. of torque [conservatively].

This turned out to be a great cruiser, and weighing less than 3,000 lbs, the car is nimble and responsive with a lumpy big-cam sound from idle to as fast as I want to go (which isn't much). Pop the hood anywhere and conversations begin, it surprises a lot of people. Sure, I could have built a more powerful V8, but I've had a few of those and wanted to do something different. This certainly is different, and fits the bill.

Suspension & brake mods are next up…stay tuned as I share the details of installing an 8.25" rear with 3.21 gears and 15" wheels in 2024. And maybe a disc brake upgrade while I'm at it. Of course, like the engine, it'll all look factory-fresh(ish).