BritishV8 Forum

This 1974.5 MGB GT underwent a multi-year, bare-metal rotisserie restoration completed in the summer of 2025. It has been heavily modified as a Sebring-style V8 restomod, covering approximately 2,500 miles since completion. The car is finished in Aston Martin California Sage Green Metallic over a bespoke Prestige Auto Trim grey and black leather and Alcantara interior.

Power is supplied by a 4.6-liter Rover aluminum V8 built, machined, and blueprinted by HorsePower Research (HPR) with engine components supplied by D&D Fabrications. The powerplant features a Crower Level III performance camshaft, Holley Sniper electronic fuel injection, a Holley HyperSpark ignition system, and premium RV8 black powder-coated headers that exit through the fender wings into a dual custom exhaust. Power is sent to the rear wheels via a BorgWarner T-5 five-speed manual transmission equipped with a McLeod Racing hydraulic throwout bearing and a complete D&D Fabrications conversion kit. This feeds into a Fast Cars Ford 9-inch rear axle with a limited-slip differential and a 3.25:1 highway-friendly gear ratio.

Additional modifications include a Fast Cars Inc. front crossmember with adjustable coilovers, a custom-engineered 3-link rear suspension setup, four-wheel disc brakes, and 17-inch black Cosmis Racing wheels. The cabin features a custom black Alcantara-wrapped dashboard with integrated Speedhut electronic telemetry gauges, a Vintage Air climate control system, spray-in LizardSkin insulation with additional floor-level heat shielding matting, a modern Advance Auto Wire electrical harness, and a hidden integrated Bluetooth sound system preserving the factory clean dash look.
This meticulously sorted MGB GT restomod is now offered with a complete, organized binder tracking every receipt, a comprehensive restoration photobook, recent Blackstone Laboratories engine oil analysis reports, and a clean Texas title. I have videos I'm happy to provide as well.

I posted the car on Bring a Trailer and the car was received very well with 8000 views and nearly 800 watchers but unfortunately, the bidding stalled. I think the car is better suited for this group who will appreciate everything that's been done to bring this car to life. She's turnkey and ready for the next owner to drive and enjoy!


Technical Specifications Breakdown:
Body & Chassis
Restoration: Stripped to bare metal via media blasting on a rotisserie.
Metalwork: Full rust remediation completed using genuine British Motor Heritage steel panels.
Body Modifications: Sebring-style widebody flared arches.
Paint: Sherwin-Williams Ultra 7000 Aston Martin California Sage Green Metallic.
Insulation: Spray-in LizardSkin thermal and sound-dampening insulation with additional floor-level heat shielding matting.

Powertrain, Fueling & Cooling
Engine: 4.6L Rover Aluminum V8 machined and built by HorsePower Research (HPR); equipped with a Crower Level III performance camshaft. Built utilizing conversion components exclusively sourced from D&D Fabrications.
Exhaust: RV8 black powder-coated headers exiting through the inner fender wings; custom dual-exhaust system.
Fueling: Holley Sniper EFI system with a matching Holley in-tank fuel pump and a custom high-capacity fuel tank (Moss Motors 16-Gallon tank). Steel-braided fuel lines bring the fuel from the Holley fuel pump to the Holley Sniper.
Ignition: Holley HyperSpark distributor, coil, and CD control box.
Cooling: High-flow aluminum radiator equipped with an automatic electric cooling fan setup (D&D Fabrications supplied).
Transmission: BorgWarner T-5 five-speed manual with a McLeod Racing hydraulic throwout bearing (D&D Fabrications supplied).

Suspension, Drivetrain & Brakes
Rear Axle: Fast Cars Inc. Ford 9-inch housing with a Limited-Slip Differential (LSD) and a 3.25:1 gear ratio.
Front Suspension: Fast Cars Inc. independent front crossmember, tubular control arms, and adjustable coilovers.
Rear Suspension: Custom-engineered 3-link rear suspension setup with adjustable coilovers.
Brakes: Power-assisted four-wheel disc brake conversion (Wilwood).
Wheels & Tires: 17-inch black Cosmis Racing wheels.
Interior & Electrical
Wiring: Reconstructed from scratch using a modern Advance Auto Wire electrical harness. To ensure maximum reliability and safety with the modern upgrades, the car was completely re-wired from scratch using a premium Advance Auto Wire electrical harness. It features a modern fuse block with individual blade fuses, completely replacing the failure-prone factory Lucas system. Every modern system—from the Holley EFI and HyperSpark ignition to the Vintage Air A/C—runs on its own dedicated, properly fused circuit.
Upholstery: Custom grey and black leather/Alcantara kit sourced from Prestige Auto Trim (UK).
Dash & Gauges: Custom black Alcantara-wrapped dashboard with integrated Speedhut electronic telemetry gauges.
Climate Control: Vintage Air conditioning and heating system.
Audio: Hidden integrated Bluetooth sound system preserving the factory clean dash look.

Part 3: Included Documentation & Media Archive
Build Binder: A complete, organized binder tracking every receipt, component purchase, and professional service rendered from day one of the build.
Photobook: A comprehensive restoration photo book (Google Drive) documenting the bare-metal media blasting process, the installation of the British Motor Heritage metal, the LizardSkin insulation layers, and the meticulous chassis preparation.
Engine Health: Recent Blackstone Laboratories engine oil analysis reports validating engine health and proper break-in procedures.

Thanks guys, that looks like the fuse panel I have. I may have wired the starter (Mini High torque) wrong. The large red cable is on correctly but there is a 12 AWG red wire that may feed the ignition that I had going to ground which was stupid. Now I have to pull the starter to verify what  smaller wire I connected to it. I can't see from underneath but I think its a black wire which the builder noted that all  black wires  were grounds. I thought I labeled every wire when I took it apart, but this red wire wasn't labeled and it has a large connector that would fit the starter bolt.  I'll pull the starter tomorrow and see what wire I connected and if it is black, we know its incorrect. I'll connect the red wire and see if I get juice to the fuse panel.
Thanks!
I appreciate the help! 

Yeah, he mentioned a while back he used a Painless harness. I don't think all those red wires are in the color code though. Have to trace those individually.

That could be the one, see Fig 10-7.

Jim

I feel like I have now taken the MGB/BOPR swap to it's ultimate conclusion. Some finished specs like HP and torque will have to wait on dyno tuning, possibly next spring but as it currently stands the car is running with the following specs. As always, different builds may suit individual builders better:

Buick 300 block bored .030" oversized
TA Performance Rover heads, untouched ports
340/350 Buick crankshaft, 3.8" stroke
TA solid lifter Roller cam #TA264-74R .544/.274, .554/264, 112, 3
Carillo 6.2" rods
Wiseco custom forged pistons, 1mm rings, light weight floating pins 10.5 SCR, 8.3 DCR.
1.9/1.6" Ti valves, beehive springs
LS type adjustable roller stud rockers from TA
Eaton M112 blower
GM P-01 ECM ('411) with modded '02 Camaro tune
Projected redline: 7-7.5K, rev limiter currently active @ 5K during break-in
Boost levels observed this far: while driving 5-6psi, stationary at the rev limiter ~10. I have eliminated all the oil leaks finally. The pan and one of the big nuts on the oil pump needed attention but the front and rear seal are working flawlessly. I made a stiffener for the oil pan flange that finally did the trick. Oil leaks have been a big issue for me with these engines and it's nice to finally have it all sorted out. If there is enough interest I could start a thread on how to deal with those and hopefully others can contribute.

Oil pressure is good, using 5w20 dino oil for break-in but may not go high enough for the projected redline. It sits at about 30@1200rpm after complete warmup and limits at 45. Might need a stiffer spring or the TA adjustable cap. Warm idle has now smoothed out at 1200 and is not affected by PCV or the throttle plates so it should be controllable in software. Overall it's driveable but will need some fine tuning.

I think I can expect to see a minimum of 600 hp out of this engine. That might be conservative but we'll see. A typical stock 350 cid engine in the early 70's made upwards of 300, 10psi is 2/3 of sea level ambient pressure, so adding that to 300 gives 500 and I'm pretty sure the heads, cam and increased redline are good for more than another 60 which puts us at 600. Could be more, could be less but in any case it will be enough. It's entirely likely that I will have to resort to decreased ignition advance (already using that) and possibly liquid injection or even an E85 blend to avoid possible damage but those are feasible options.

The transmission is a Tremec 3350 in the GM case from Forte. Rear axle is Jaguar IRS, 3.08 Powerlok and ventilated Willwood rotors. Haltech now makes a standalone transmission controller for the Aisin AA80E so I have the option of swapping that back in at some point if I want to. Exhaust is custom full length fenderwell headers, 2-1/4" rebuildable cartridge glass packs and chambered resonators.

The car drives well. I'll be adding a hydroboost to the brakes to reduce pedal effort this winter. At present there are instrumentation issues I'll be chasing before really giving it a workout or driving very far. Looks like a power feed issue is most likely at this point, affecting my ammeter, wideband and rear stereo amp. So typical British car stuff right? Except there's not much British in those systems anymore. In any case it will be so nice not to have to worry about the car marking it's spot.

Now you might wonder why I feel I've reached the ultimate conclusion of the BOPR swap, and the answer is that the Buick 300 stands at the pinnacle of that series of engine's development, provided the right conditions are met. One is displacement. No other engine in the family is capable of more displacement except a marginal increase via overbore in the Buick 350 and that engine is not a very suitable swap candidate in the MGB. With the 340/350 crank and a .030" overbore it is a 5.7L engine, .7L larger than the largest displacement Rover ever built. It can use the TA-Rover heads, the best heads ever made for that engine family and competitive in every way with the best GM or Ford aftermarket heads. It weighs about 50lbs more than the late Rover but for this weight you get an iron block which is much stronger and has been proven in engines of over 1000hp output. All this and it fits in the car just the same as the BOP/Rover, has a MUCH cheaper bellhousing and mini starter, and can be installed under a stock hood. In the RB cars it is a bolt-in swap. Ergo, ultimate BOPR swap.

I mentioned evolved. That's because this car has seen a wide variety of BOPR engines, all GM incidentally not that it matters much. First engine back in '88 was a Hi-Po Buick 215 with the hottest cam you could buy and a 650 Holley carb, the current headers and a set of glass packs. That combo was a little tricky just off idle but it would absolutely scream all the way up to 7 grand, but I ran it very hard and it had a limited lifespan as a result, eventually cracking a piston skirt and wiping out a rod bearing. Next came a couple of Olds 215's including the turbocharged Jetfire running a 2" SU with 6 pounds of boost and an Eaton M90 supercharged Olds with a heatpipe intercooler that exceeded 16psi of boost. After those came an M112 boosted long rod 340, an almost completely stock low mileage iron head 300, and finally the current engine. The 340 and iron head are still in good shape but I wanted to build this particular engine specifically for the car. I think it is likely to be the last one, but if it's not the 340 stands ready to serve, with a few improvements. Note, the 340 is NOT a good choice for an MGB conversion but once done it works well.

My car is a bit radical and that's old hat but for an MGB I've come to the conclusion that for a new BOPR conversion you can't do better than the Buick 300. It's hands down a better, stronger and more reliable engine than the other options and easier to drive. Even as an iron head it makes a great swap and it's inexpensive. As for availability for an MGB conversion, with about 525K MGBs made in total and perhaps 400K 300's produced the chances of finding a Buick 300 engine are about as good as finding an MGB and certainly much better than finding an MGB that needs an engine. With it's 9:1 CR the iron head 300 2bbl is a great candidate and does very well indeed on regular gas, having no trouble at all keeping up with the pack.

Jim

Scott, this may be helpful:

https://painlessperformance.com/wp-content/uploads/2024/07/90501-Manual.pdf

It appears you have a non-standard fuse box. Do you have any documentation for the wiring at all? It's not the AAW power block but could be one of the other aftermarket ones or even a junkyard pull. You might have to unbolt it so you can see the back to tell how power is distributed. It looks perfectly usable, just pay careful attention to what power feed goes where and write it down. The fuses are at least labeled so maybe the feeds are too. You should have unswitched, ACC, and run or switched power.

Jim

Today I checked each of the 5 wires going into the front of the fuse block. Only the yellowish wire showed continuity at the battery and it is the ground. The other 3 red and 1 blue wires show no continuity to any wires attached to the battery and show no voltage with the battery switched on. My question is: would the 12 volt power wire  possibly be connected to the back of the fuse panel? Are these wires plugged into the front taking voltage out of the panel? I made the assumption they brought voltage in and now that seems ridiculous as there would only need to be one wire bringing voltage in. Ignorance is a terrible thing!

Ok, I'll try that.

If you have a voltmeter you might want to put that on the acc circuit too. It's the w/g wire off the switch.

Jim