4/71 supercharged Holden 186 - Mill of the Month

This pump-fed 186 might look old-school, but it packs some killer tricks to make far more power than grandpa’s HR ever had!

Holden Red Six Mill 2 B Jpg
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WHILE we feature plenty of bent-eight motors, the sight and sound of a blown inline six is dear to the hearts of many at Street Machine, and looking at this masterpiece of a Holden red motor from Damian Baker and Mick Green at BG Engines in Sydney, it is easy to understand why. This pump-fed 186 might look old-school, but it packs some killer tricks to make far more power than grandpa’s HR ever had!

First published in the February 2021 issue of Street Machine. Photos: Cheryl Poulson & Jacqui Dean

To start with, there’s no cross-breeding of different six-pot generations, as Damian explains: “The block, head and crank are all HK-series red motor. And we go that way because they have a steel crank, but we have added an SRP 9:1 forged piston and a Scat H-beam forged rod. We’ve also half resin-filled the block for stability, and installed six thick-wall sleeves to avoid core shift.”

Holden red six mill
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Other bottom-end tricks include ARP fasteners for the main studs and a main stud girdle, as this screamin’ six is going to see fairly robust use once it goes into the HK Kingswood it’s destined for.

“This is a street/strip engine, so the customer wanted as much power as possible from 1960s technology, but he wanted it to live,” says Damian. “We also fitted an external, belt-driven oil pump from Savy because the factory pump simply doesn’t have the volume. We made the billet brackets in-house, and modified our own pan to suit and give the oil system some volume. When you’re putting boost – and therefore cylinder pressure – into these engines, the stock oil pumps don’t work, as they have tiny main shafts.”

Holden red six mill
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While you’d think they’d be slamming a fancy later-model head on the top, the stock 186 red casting has been retained, with single-piece stainless valves, Crow chrome-moly pushrods, ARP head studs, plus bronzed guides and hardened seats to suit E85 fuel. Along with the Yella Terra roller rockers, it’s also been fitted with a solid flat-tappet Crow cam spinning 252/260@0.50in, with roughly 0.575in lift on a 114 LSA.

“We have plenty of knowledge to suit what we want from these engines, so this is one of our own custom grinds out of the Crow masters,” says Damian.

Holden red six mill
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Sat underneath the Holley Hardcore E85 four-barrel carburettor is a GM 4/71 pump that has been set up by blown Holden six guru Jeff Ramsay. The blower drive and intake are all Mr Ramsay’s work. “We figured he’s the Godfather of supercharged drag Holden sixes in Sydney, so he should set it up,” Damian explains.

Finishing off the combo, the ignition system is by Aussie company ICE, using one of its boost retard systems and a 7amp box.

Holden red six mill
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“It made a touch over 500hp on the engine dyno, and it pulls the rpm so quickly,” laughs Damian. “It sounds amazing and it’s a crazy little thing. Aspirated 202s sound awesome, but this thing is hard to describe – it’s on another level!”

HEAVY LIFTING

“One of the trick pieces in this motor is the lifters,” says Damian. “It runs a cool-face lifter by Crow, which has a 12thou hole drilled into the face so it lubricates the cam lobe under load. This promotes much better longevity for the cam, so while people think it’s all old-school, there is some cool tech inside it.”

BG Engines
North Richmond, NSW

 

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