Here’s the latest reader question – on my favorite topic! – along with my reply:
Evan asks: Just got turned on to your site today, loved the article on the 76 Trans Am. As the owner of a mint, original, 76 black and gold 400/4 speed car, it captures why I love the car so much! My question is, do I leave mine stock, or do some tweaks to the engine to get some more power out of it. The exhaust has been done, but heads, intake etc are all stock. I also have a 73 Formula ram air 455/4 speed as well, which I am restoring, so I will be checking your site regularly as well as passing it on to my other gear head friends. Keep up the great work AND the outstanding political content!
My reply: Whether to mod – or not to mod. That is the question! It is also very subjective and personal. I personally would not perform any mod that permanently alters the car in a way that changes its historic character – for example, replacing the Pontiac V8 with a modern crate LS1. That sort of thing makes my teeth hurt.
But tweaks to the original/correct engine? Sure!
I’ve owned several of these cars over the years – including my current ’76. They respond really well to basic mods which undo the gimping the factory had to do to get them past emissions back in the mid ’70s. The worst gimp being the factory exhaust, which as you know comprises a set of awful (restrictive) manifolds that feed into a Y pipe that is corked by probably the most restrictive single catalytic converter ever made. From there, a single pipe into a dual outlet muffler located behind the axle.
I installed a set of the cast iron header-style Ram Air factory high performance exhaust manifolds that Pontiac installed at the factory on earlier (1970-’73) high-performance V8s, including the RA III 400, 455 HO and SD 455. These are outstanding pieces, better than headers in some ways (clearance, they don’t leak and are pretty quiet). You can get them from Pypes or Ames Performance, among others. The repros are actually better castings than the originals and they make them for D port Pontiacs such as ours.
From there, you’ll want a proper dual exhaust (Pypes sells mandrel bent components, beautiful stuff; I use these on my cars) probably 2 1/4 for a stock/mild-performance 400/455. Then you can decide whether to go with the twin under-the-floorpans mufflers and dual outlets or the dual crossflow muffler (not stock, a high-performance one) behind the axle. The behind the axle one eliminate the ground clearance issues the under-the-pans mufflers sometimes have unless they are snugged up really close to the floorpans!
If you have to have cats, get a pair of high-flow units and install in line. Keep the factory pellet cat, though – it’s a historical item and someday you may want to return the car to factory.
Contact Cliff Ruggles about a jet kit/metering rods/high-flow needle and seat. He will send you a kit designed to optimize your particular set-up. He speaks Pontiac!
Believe it or not, the stock Pontiac intake manifold is pretty good. The ’76s do have a restrictor cast into the secondary wells, but these have not been shown to appreciably impede flow or negatively affect performance in mild street applications. Remember: The Pontiac V8 is not really a high RPM V8.
However, you could save some weight by replacing the factory cast iron intake with an Edelbrock Performer aluminum intake (as pictured here). It is very similar to the factory Pontiac intake but much lighter and without the secondary restrictors and it does not alter the height of the engine appreciably, so the air cleaner/shaker scoop line up correctly. I painted mine the factory blue metallic and unless you look really closely, it looks stock!
I would make your shaker functional. This is very easy to do to a ’76 scoop, which still has the bolted-on rear door. This is very easy to remove without damaging the scoop, so you can always return it to stock, if you wanted to. The ’77 up scoops have to be cut to make them functional – and once you cut them, they’re cut forever. Here’s an article I did on making the scoop functional and where to get the parts.
You’ll want to experiment with ignition timing; get a spring/weight kit (Summit or JEGS) for the HEI and try the various combos; play with the initial advance.
In my experience, replacing the factory exhaust as above and car/ignition tuning to complement it really wakes up these cars. The dual exhaust alone is probably worth about 30 hp and that’s a difference you can feel.
If you want more – without obviously altering the car or affecting its historicity – a cam swap is the next step. As you know, the stock cam is not really a performance cam. Both the 400 and 455 in ’76 were basically the same engine as used in Bonnevilles and Safari station wagons.
And if you do the cam swap, I’d consider swapping heads, too. The ’76 400/455 have extremely low compression, which can be sneakily rectified by using a set of earlier heads, which bolt right up and no one will know unless they check the casting numbers.
An excellent choice is the 6X head Pontiac used on the W72, “T/A 6.6” 400 in ’77-’79. These give you appx. 8.2:1 CR vs the 7-something that our cars had originally. It accounts for much of the performance uptick the ’77’79 “T/A” 400s got.
I have the higher-CR heads on my 455, along with a computer-optimized reproduction of the ’70 Ram Air III 400 cam. I’ve never dyno’d it, but it feels plenty strong! It’s also very streetable; decent idle and does not overheat.
You might also want to consider changing your axle ratio to something more aggressive. IIRC, your combo had a 3.08 (maybe 3.23) ring and pinion. Changing to a 3.42 or 3.73 will also noticeably improve the car’s quickness off the line and no one will be able to see any difference as far as how the car looks.
Keep me posted on the doings – and send some pics of your car!
Got a question about cars – or anything else? Click on the “ask Eric” link and send ’em in!
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