Building a screaming flatplane LS...and a 35 Hot Rod Truck to put it in.
Hello FFR community! I'm new to the forums and don't post a lot of my creative automotive exploits online, but I learned so much from reading others' build threads that I feel like I should offer something in return.
Short story for my 35 project is that I'm building this truck for my wife to replace her Ford Fiesta daily driver, which became mechanically totalled in early 2024 when the wet oil pump belt failed and the engine digested its bearings. In this thread I'll share my truck build, but my content will have more focus on engine buildup than most that I've read on the forums. If that's what you're into, read on and feel free to comment!
Longer story:
Roughly 2 years prior to the Fiesta self-destruction event, my wife showed me a picture of a FFR Hot Rod Truck, which I'd never seen before. I was hooked right away, and so was she. Great style, super lightweight and undeniable performance potential, plus you completely build it yourself. The original intent was to build it for her since I have multiple projects to play with, so I didn't want to get too crazy with the specs. I thought about a lightly modded 4.8L LS with a couple bolt-ons for forward motivation paired with a slick 6-speed trans and we're golden. You don't need a ton of power in something that weighs 2300lbs, right? After a few weeks of tossing around some ideas, I think she could sense that I wasn't enthused with the idea of handicapping this incredible vehicle with a mostly bland powertrain, and she suggested I build the truck for myself however I wanted. Freed from the shackles of wife-acceptance, I went to work on a clean sheet engine build that would be worthy of this truck and provide an unforgettable driving experience.
After working on Ford FE big blocks for the last few years, I was really ready for something different. The small displacement LS idea seemed like a good fit for this chassis, plus they're lightweight, responsive, and a great platform to customize. The 4.8L was too mild, and a 6.2L LS3 felt out of character, but combining both was interesting. With the 4.8L crank in an LS3 block, the short-stroke/big bore combination allows for big valves proportional to displacement and lots of RPM potential (with the right cam/heads). While technically sound, this had been done before and seemed a bit too predictable. To take things to the next level, I drew on inspiration from the awesome LS7 and LT6 powerplants from Corvette Z06's, past and present. I figured a short-stroke flatplane crank, an aluminum block with enough bore size to support large valves, combined with lots of titanium bits to reduce reciprocating mass was a good recipe for success. After sketching it out on paper and running some dyno sims, I stopped by my trusted local engine builder to explain the whole concept. Their natural response was the typical "you can make that much power for a lot less money", which is true, but they also didn't find any major flaws in the plan and could tell that I wasn't going to be persuaded into a rational alternative. So with that, in January '24 I started making calls to piston/cam/cylinder head/crankshaft companies and over the course of many good conversations worked to lock in the dimensions of key components. The build started later in the year, and I'll explain it in the upcoming posts here.
So, how did the truck go from being intended for my wife, and then me, and then back to her again? Well, we took a trip to the FFR showroom in Wareham, MA during a summer trip last year, and after seeing the two floor model trucks in person, and being thoroughly impressed, she made the executive decision to claim the truck project again. By this point, I had custom pistons and solid roller cam in hand, an 8-pack of titanium rods, a donor L77 engine, and the custom 4340 billet flatplane crankshaft was halfway through production, so there was no going back! So maybe this is a win-win in the end? Time will tell!
I picked up the truck at the FFR HQ in Dec 24' and hauled it back to California on my Ford F750 flatbed. Knowing the engine was going to take about a year to build, I kicked it off in early 2024. So in the next couple posts I'll share some highlights from the engine building days, and catch up to present day building of the truck chassis. Then we'll proceed in more or less real time as it continues to progress.
Thanks for reading and sharing your thoughts about the build. I'm glad to be a part of this community of like-minded gearheads!
Hey Pat, great minds think alike, or we're both crazy. You have good questions and I've spent a lot of time considering the options, here are my thoughts:
-oiling will be by conventional wet sump. I seriously considered going all-out with a dry sump system to help reduce windage at high rpm. Absolutely this can work and would be more essential on a road track-focused build. This is one area where I erred on the side of street worthiness, figuring that a good windage tray combined with double-knife edge counterweights on the crank would be a good compromise. Also, the crank throws are pretty short, with only a 3 5/32" stroke.
-I spoke with the guys at ATI about the balancer/damper. I wanted to get something that would be tuned for the unique secondary imbalance harmonics associated with the flatplane crank. Unsurprisingly, they don't make something that specifically addresses this concern; in fact, all of the LS dampers have the same basic construction. That being said they are certainly a robust, well designed component. I haven't ordered anything yet, but likely will go with the ATI damper with 10% underdrive serpentine belt drive. If you have other recommendations, would love to hear them.
-Flywheel: in keeping with the theme of lightweight responsiveness, a stock weight flywheel is ruled out. That leaves either the aluminum version as the most aggressive option, or the lightweight steel version as a compromise. If it was only me driving the truck, I would've went aluminum. But to help make it just a bit easier to get moving and slightly more friendly, I got a RAM 1550LW steel billet lightweight flywheel. It's 22lbs versus 13-14 for the Al units.
Here's a quick look into shop at the start of the build in early Jan. Had to reorganize the shop and build some shelving to arrange the pile of boxes from FFR. Body is stored outside for now, plan to get it to the body shop in late Feb to get them started on it.
Engine arrives in March '24. This is the L77 engine code, a 6.0L higher performance spec with an aluminum block. It was pulled from a 2012 Caprice PPV that was taken out of service by a front end collision. Despite the damage to the car, the only issue we found with the motor was a cracked oil pan.
As for the balancer, ATI seems like a good choice. One strong thought comes to mind though, are you going to key the crank? If not are you considering pinning the balancer using a kit from one of the supercharger mfr’s? I’ve had one come lose due to insufficient torquing of a factory bolt on a non supercharged application…they can and do spin on the crank. A flat plane application will see the damper undergoing significant acceleration/deceleration…one of these approaches might be helpful if not already part of your plan.
Cheers,
Pat
Once again with an 88 mm Turbo, Big Block Chevy powered, ‘35 Hot Rod Pickup
As for the balancer, ATI seems like a good choice. One strong thought comes to mind though, are you going to key the crank? If not are you considering pinning the balancer using a kit from one of the supercharger mfr’s? I’ve had one come lose due to insufficient torquing of a factory bolt on a non supercharged application…they can and do spin on the crank. A flat plane application will see the damper undergoing significant acceleration/deceleration…one of these approaches might be helpful if not already part of your plan.
Cheers,
Pat
Thanks for the thoughts, Pat. The custom crank is keyed on the nose so hopefully that will prevent the damper from walking it's way off!
The way I designed components of this motor was starting with the connecting rods, then worked outward from there. I wanted to use titanium rods to get quick response and reduce stress at high rpm, and custom Ti rods are available, but very pricey. So I turned to the used market and after some searching found a really nice set of take-offs from an LS7. Didn't really know if they were any good until the machine shop checked them dimensionally, and luckily all 8 are within spec. With no other signs of distress, I called it good. The only issue (for this build) with the LS7 rod is that they're pretty short...it's got a full 4.0" stroke compared to the typical 3.62" throw of the common LS engines, so the rods are only 6.067" long. On top of that, they have an oddball 0.9252" pin size. Custom pistons are a given for a build like this, and for this assembly to work out it was necessary to increase the piston compression height to compensate for the short rod and stroke. The result of that is a piston with a longer skirt than the typical LS slug, but the upside is that the pin bore is moved clear of the oil scraper ring, adding some stability.
Crankshaft stroke selection is a matter of displacement goal, block clearance, max rpm goal (piston speed), and in the case of a flatplane motor, secondary imbalance magnitude. Flatplanes are known to get buzzy when the stroke exceeds 3.5" in a V-8 configuration. For an all-out race application this could no doubt be exceeded, however remember the goal here is livable street manners and a reasonable maintenance schedule. After spending time with my design spreadsheets and running dyno sims, I went with 3 5/32" stroke or 3.156", yielding 320 in3. Having a small displacement has it's advantages from a component standpoint. All of the airflow constraints that typically would limit rpm in a larger engine suddenly are less of an issue, and an aggressive, but sane, configuration can push 8k rpm and beyond, and the engine has less of a tendency to want to destroy itself. At least, that is the thought process. So after some discussions with my piston, cam, head, and crank suppliers to reality-check the plan, I worked with Crower to lock in the print dimensions and put down a big deposit for a custom billet crankshaft in March '24. Right on schedule, six months later it was delivered and the workmanship is impressive. I unfortunately didn't get a lot of glamour photos of the crank because I was in a hurry to get the short block built before the holiday season. But I'll drop some in below.
Lifters, heads, pushrods, and rocker assemblies are all bolted on. Smiths Bros made a set of custom pushrods that worked out perfectly, 3/8" OD with 0.085" wall thickness in their 4130 chrome-moly tubing. With the Crower solid lifters and the extra height of the MAST head, the pushrods are over 8 3/4" long; pretty big increase over the OEM rods.
The next big challenge for this install is going to be working out the header design, and fitting them into the chassis. So I reached out to Vince at Burns Stainless and had them run their header design program using parameters from my engine config. The result is a double stepped primary 4-1 design with a custom built merge collector that exits into 3" tailpipe. I've built headers for my F750, but this will be the first including stepped pipe diameters, and not once but twice: 1.75 - 1.875 - 2.0". How this will all fit in the truck's engine bay is a mystery at this point. Will have to get the motor in the chassis and fit up steering shaft, etc.. anything that shares space with the headers, to see what's left to work with.
Here's a look at the MAST LS3 Black Label 255 head. Heads were milled by MAST to reach 62cc combustion chambers. Titanium intake valves and upgraded valve spring package rated for 0.660" lift. Attachment 210763Attachment 210764
On to finishing the top end of the motor. Took about 2 weeks to receive the pushrods from Smith Bros, now ready to finish the valvetrain.
These are Crower's investment-cast stainless steel shaft rocker system. Each pair of intake/exhaust rockers rides on a shared shaft, which helps stabilize the rockers under high spring rate/rpm. Rocker ratio for this set is 1.7:1. I sprung for the DLC-coated roller upgrade to further reduce friction and wear at the valve tip. IMG_1797.jpgIMG_1798.jpg
Rolled the dice on an eBay 8.8" S197 rear axle from a 2014 Mustang. It was sold by a semi-local salvage yard which made it possible to pick it up in person, and argue with them about a refund if it was garbage. But to my surprise, it looked solid AND came with a warranty, so on the back of F750 it went.
Back at the shop, after closer inspection still couldn't find any major issues. Moved forward with removal of unneeded hardware...every ounce of weight matters, especially the unsprung kind! IMG_1766.jpgIMG_1773.jpg
After degreasing and pressure washing, it's on to the outdoor paint booth. Weather was just warm enough on this late-January day to properly cure the paint. 3 coats of primer and 2 top coats with black rustoleum and it's good to go. IMG_1777.jpg
The 2.73 gearing in the Mustang 8.8 was just not compatible with this build, but the 31-spline axles are probably OK for a little while at least. I ordered a 4.10 ring and pinion (USA-made Ford Performance), the matching installation kit with all pinion and carrier bearings/shims, and new torsen-style limited slip.
Ford Performance ring&pinion forged and machined in Sterling, MI IMG_1779.jpg
Axle shafts pulled, diff carrier removed, OEM pinion out. A can of degreaser later and it was ready for replacement of axle bearings and seals, then rebuild of differential. IMG_1821.jpg
Used a cheap hot plate to preheat the ring gear, then carrier bearings. Also helped with install of pinion inner bearing. No idea what temperature it reached but level 3 for 10 minutes did the trick! IMG_1822.jpg
After several iterations of trying different shims stacks on the crush sleeve eliminator kit, the pinion rotating torque of 21in-lb was achieved. Used the same pinion shim as the OEM setup as a starting point for mesh pattern later. IMG_1823.jpg
Carrier installed, was able to use the original carrier shims, but swapped DS/PS sides to hit 0.012" backlash. Amazingly, the contact pattern was good on the first try with the OEM pinion shim thickness. And also consistent on various points on the ring gear. Really like the Ford Performance gear set. IMG_1826.jpg
Finished rebuild with Perfect Launch cast aluminum diff cover. LSD calls for straight-weight 140 gear oil, so good thing this is a California truck or I'd have to preheat the differential before leaving the garage on a cold day! IMG_1827.jpg
With lots of positive momentum after an easier-than-expected rebuild of the 8.8 axle, we moved right into hanging it on the truck. No issues here except lots of grinding of steel sleeves to make things fit together properly. At least FFR gives you extra raw material to work with, so there's no concern of running out even if your handmade spacers have to be redone.
Front and rear suspension done, this is starting to look more and more like a finished product.
Time to get the engine and trans shoehorned into the chassis so I can get to work on the header fab. For now, the LS and T-56 were mated with no flywheel or clutch, since it's going to come apart for dyno breaking-in and tuning pretty soon. But this is also a great time to look at accessory mounting options for the alternator and A/C compressor. There's lots of space in front of the engine, but not much to the sides. Going to be looking at a lot of other build pages to get ideas on what works and doesn't. I am planning on running the hood and side covers, so having parts pushed far out to the sides isn't going to work.
LS is blocked and T-56 is lowered and slid into place. IMG_1832.jpg
Dropping in the LS. Lots of room for maneuvering at this stage but I wonder how things change when the firewall is installed. The T-56 was a bit longer than the frame mount could accept, requiring minor mods. IMG_1834.jpegIMG_1835.jpg
Got the transmission tail oriented toward the center of the driveshaft hoop and made the mount permanent. IMG_8515.jpeg
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Originally Posted by Pat Landymore
