Below are a list of the 400 Cid 1969 engines with HP heads and so on.

My question are as follows :

If you option for a -69 FB with a YS 400 cid automatic you would get a 330 HP engine with a 67 cam and std manifolds.

But then you want more power and think "Hey let's go for the HO option" but still want the automatic transmission and you will get a 400 cid YW RA III engine with the same camshaft and heads, sure you the manifolds and Ram air intake but only gain 5 HP...

The GTO with the YZ engine and RA III had 366 HP with an automatic trans and a 68 cam not available on the FB with auto trans, but Hey you you would get it with a manual transmission and a WQ engine but then "only" 335 HP..

So is this due to a HP limit on FB's ?? I have heard about secondary limiters on the carburetor and is that the only difference on the engines ?

And where the HP ratings only for the insurance companies ? has anyone ever taken a original engine to the bench to verify the HP ratings ?


HP CID Trans Code Comp Cam Heads Carb Year
265 400 A MM 8.6 254 45 4 69
345 400 M WH 10.75 41 722(RA IV) 4 69
335 400 M WQ 10.75 68 48(RAIII) 4 69
366 400 M WS 10.75 744 48(RAIII) 4 69
350 400 M WT 10.75 68 48 4 69
370 400 M WW 10.75 41 722(RAIV) 4 69
350 400 M WX 10.5 67 62 4 69
330 400 M WZ 10.75 67 16/62 4 69
350 400 A XH 10.5 66 62 4 69
265 400 A XM 8.6 254 45 4 69
345 400 A XN 10.75 41 722(RAIV) 4 69
370 400 A XP 10.75 41 722(RAIV) 4 69
340 400 A XZ 10.5 254 46 4 69
265 400 A YF 8.6 254 45 4 69
350 400 A YS 10.75 67 16/62 4 69
330 400 A YT 10.75 67 16/62 4 69
335 400 A YW 10.75 67 16/62(RAIII)4 69
366 400 A YZ 10.75 68 16(RAIII) 4 69

Engines were often underated. The horsepower is listed at a certain RPM, not necessarily the maximum horsepower. The firebird RAs were underrated.

The engines were the same. Some components between the Firebird 400 and GTO engines had different part numbers. If there was any difference at all, I'd give the nod to the Firebird 400 version, as it had a little better flowing exhaust manifolds over the GTO.

The 1967-1968 Firebird 400's had a different Quadrajet baseplate with linkage that only opened to around 3/4 full throttle. This was done for two reasons:

1) To even out the power between the Firebird 400 and GTO so the GTO would still be appealing to buyers. The GTO was Pontiac's flagship performance car.

2) To stay within the 10 lbs per 1 hp guideline that GM set. 3300 lb. Firebird verses 3500 lb. GTO, 330hp verses 350 hp.

The 67-69 Firebird 400's were faster than the 1967-1969 GTO's. But years later, people still look at the advertised hp ratings to compare, and many GTO guys believe their engines were 25-30hp stronger, but they weren't. The engines were the same.

Why the deception?

The story was that when the Pontiac engineers debuted the 1967 Firebird 400 for GM's top brass, management knew they used the GTO 350/360hp 400 engine, complete down to the chrome valve covers, and simply wrote 325 hp down on paper. That didn't cut it, and GM management would not approve the rating, so Pontiac had to cut down the hp output somehow. But rather than fiddling with compression, cam, or heads, they simply devised a throttle limiter. That made GM happy.

Pontiac engineers knew this would be easiest thing for a customer to correct. With just with a pair of pliers, and about a minute of time, you had full throttle again, and then the Firebird outperformed the GTO.

Tank you for a good answer StealthBird

What is the difference between the 67 and 68 camshaft and the 16 and 62 heads ?

And does anyone know the power gain on the RA exthaust mainfolds ?

No diff between the 62 and 16 heads on the earlier engines(I believe the 16's of later years were much different). Both are large valave(2.11/1.77) and are SAID to be 72CC(though often larger)...and both D ports.