It’s 6/6, so let’s talk Pontiac’s 6.6-liter 400 V-8

The calendar on the wall shows it’s 6/6—close enough to Pontiac’s iconic “6.6 Liter” badging on its Trans Am shaker hood scoops to have us thinking about everything Pontiac 400. To celebrate the workhorse Pontiac V-8 (sorry Olds 403, today’s not your day) we’ll highlight some of our favorite applications of the staple muscle car engine.

Throughout the ‘60s, Pontiac’s 389-cubic-inch V-8 did most of the heavy lifting in the brand’s performance models with the 421 and its larger crankshaft main bearings handling the Super Duty work both in NASCAR and on the dragstrip. In 1967, Pontiac took the basic recipe of the 389 and added a bit to its bore, creating the 400. With a 4.12-inch bore and a 3.75-inch stroke, Pontiac’s 400 had similar bore and stroke to Chevy’s big-block 396 (even when the Chevy actually displaced 402 cubic inches).

As the large-main-journal Pontiac engines found in Pontiac’s full-size cars evolved from 421 to 428 and, finally, 455 cubic inches, Pontiac still went with the well-rounded 400 as its go-to muscle car mill. That made the 400 the top engine in Firebird and GTO for many years as it received a wide range of high-performance cylinder heads and camshafts through various iterations of the Ram Air package.

The most powerful version of Pontiac’s 400 to ever reach production was the Ram Air IV. With its improved cylinder heads and their round exhaust ports, they’re easy to spot. In 1969, it produced 370 horsepower in GTO trim and 345 horsepower in the smaller Firebird, making it the most powerful Pontiac pony car for decades. Muscle car aficionados will argue that, like many claimed horsepower figures in the heart of the muscle car era, it was underrated. Unfortunately, the wild Ram Air V never made it to production, but the planned street-going version of that experimental motor was also set to come in at 400 cubic inches.

Not only did the Pontiac 400 serve proudly when gasoline was leaded and octane was high, but it was one of the last stalwarts of performance in the waning years of muscle when the Malaise era was taking its toll on horsepower. Because of its place in Pontiac’s most brutal and outlandish muscle cars as well as fighting the good fight into the era of smog-choked, low-compression lameness, the Pontiac 400 remains one of our favorite V-8 engines.

So tell us in the Hagerty forums below—which Pontiac 400 spec is your pick?

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    The 1967 Firebird 400 had a weak valvetrain. Engine would float lifters easily. A design flaw with waterpump would allow dissimilar metal corrosion quickly without antifreeze. In a few months, corrosion would cause a high temp steam leak to be blown on the crank and bearings at operating temps. Crank would warp and lose oil pressure.

    That happened to me on a 350 in a 70 LeMans. The valvetrain floated at 5200, and the water pump leaked into the crankcase and spun a bearing.

    Sounds like lack of Maintenance, Oil Changes and Changing Coolant every Couple Years, my guess, You ran Straight Water and Never Changed the Oil.

    In defense of Pontiac 400’s. I’ve run a “weak crank” 76 and later 400 reman from Gopher Motors in Minnesota since 1988. I pulled their cam and replace it with a new GM sourced 9779016 cam. I bolted on 1968 #16 heads, and matching 1968 non EGR intake. That motor is still in my 1978 Grand Am. It rocks more now that ever!!!! The Edelbrock RPM intake really woke it up. The Regular Edelbrock Performer was not as good as the ’68 factory unit. The RPM unit is worth every penny!!@
    Ask me about the drive from Albuquerque NM to Green Bay wi. in 1998. 4,000 rpm for 8 hours a day for 3 days. Just sayin’ maybe you had bad luck, my luck with these motors has been better than good.

    The intake valley was built too flexible for heavy valve springs and they didn’t have any solid cams. A close contender the 390 FE was a much sturdier block, but you had to DIY big power. I also think Pontiac really built beautiful cars, and the A body was an excellent combination. You could put 427 FE parts on a 390, or 396 at .030 over, but the A body was a better all around car.

    I dropped a code YS with an 068 cam into my ’71 LeMans back in the early ’80s. I put tube headers and a Holley 650 on as a matter of course. Holy crap! More horsepower than God. Massive low end torque – more than the stock rear axle could handle. If I punched it at a stop, I just sat there smoking a rear tire. Once it hooked up though, away we go! Still, the engine served me well over the years. I drove that poor car back and forth up to college in the St. Lawrence Valley, over the Adirondack Mountains from Jersey over and over, loaded like a bus with college students and their luggage, bottoming out on frost heaves. The only trouble it ever gave me was when it fouled the spark plugs at -20F lugging over the High Peaks when the transmission kickdown cable broke. Eventually the intake valves clogged up because I was using Arco Graphite oil and low temperature thermostats and one of the exhaust valves cracked because of a chronic exhaust leak. Live and learn. I still have it, all pulled apart, waiting to be rebuilt and put into my ’71 LeMans Sport with an anemic 350. The previous LeMans went to the junk yard long ago with a cracked frame due to the massive torque from the 400 and bottoming out too many times while loaded with fat bottomed college girls.

    I have had a Gopher Motors from “Minnesota” reman 400 shortblock with the “weak” 76 and later blockto which I added the #068 cam, #16 heads and a q-jet atop a 1968 HO 400 non EGR intake since 1988. It’s in my 1978 Grand Am I’ve owned since 1980. Plenty of torque and power over the years. Way fun with tickets to prove it 🙂 My buddies thought I was nuts, sayin’ “you gotta put a small block Chevy in it, Pontiacs blow up!!!” My question is WHEN? Example; In 1998 on our way home to Marquette, Michigan from Flagstaff, Az, the wife drove it from Albuquerque, New Mexico to Green Bay, Wisconsin at 70 to 80mph with the tach zinging 4000 rpm at 80. Three 8 hour days to make that drive. Can you say “Endurance test” ?
    Still in the car, 2023, it recently got a new timing cover, timing chain and an Edelbrock Performer RPM intake. I should have done the intake long ago, the Performer is not so good, I tried one, the RPM added power high and low. Anyway, I have had GREAT luck with mine. AAAA++++++

    ’78 pontiac formula 4sp, WS6 A/c delete I blew the engine at 11,600 miles ug. Warranty replaced short block. Farking great car!

    1979 Trans-Am 455 1970 Motor and 12’s or 16’s 13’s 670’s rock bad boy toys Houston Texas

    400 heads on 455 bad ass with Pro flow Edelbrcok full length windage tray m54ds oil pump

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