[caliking71]

Hello all, I am at a point in my restoration where it's time to start thinking about what is going under the hood of my 67 Tempest. While doing a little homework I found my 326 from the factory made the same horsepower as the 73 / 455 I was thinking of buying to replace it. The 455 is coming out of a 1973 Grandville. My question is if whether or not the 73 / 455 is worth purchasing and building up or should I have my 326 rebuilt with a few additions. Thanks in advance for any feedback.

[b-man]

Different HP rating systems were used, in '72 the ratings went from SAE Gross HP to SAE Net HP.

The standard 1971 455 was rated at 325 HP, essentially the same engine in 1972 was rated at 250 HP. Gross vs. Net, a 75 HP difference on paper only.

Gross was measured on a 'tweaked' perfect-world engine with no power-robbing accesories. Ignition timing and carb jetting were optimized, no fan, open exhaust, etc.

Net HP was measured on an engine in factory tune with the power-robbing accesories intact.

A 1967 2-barrel 250 HP 326 (Gross HP) certainly isn't equal in 'real' HP compared to the 1973 4-barrel 250 HP 455 (Net HP).

If you love 326 engines then hop it up.

If you want a really substantial HP and torque increase the 455 is the hands-down winner. A stock 455 will outrun the hopped-up 326 easily at the same cost.

[caliking71]

Thanks for the info B-Man, makes sense to me!

[b-man]

Factory HP ratings back then were sometimes accurate, sometimes not.

Advertising had a lot to do with the ratings, insurance regulations as well as GM corporate rules had influence as well.

A 1969 RAIV 400 engine is rated at 370 HP in a GTO and 345 in a Firebird. The reason for the different GTO vs Firebird ratings in the RAIV was the one-HP per 10-pounds of car weight GM corporate edict.

The GTO optioned out without a lot of accessories was about 3700 pounds and the Firebird was around 3450. Same engine, different ratings. The Firebird engine actually has a restriction built into the carb linkage so it wouldn't out-power the GTO, but this was easily bypassed.

I recently purchased a 1964 421 HO engine, the factory HP rating is 370 HP. The 1969 400 RAIV with vastly superior heads and a monster 230/240 @ .050 duration .517" lift cam (compared to the 212/225, .407" 421 HO cam) and was rated at the same 370 HP.

The '69 400 RAIV is easily a 425 HP engine, the '64 421 HO probably makes close to the factory 370 HP rating. Both are 10.75:1 compression engines rated using Gross HP.

It's a numbers game.

Today's new cars have much more accurate and correct HP ratings.

[BVR421]

Just one opinion: It appears you have a great start on a nice resto. Problem: your shop is too clean and orderly. shocking!
Personally I could be happy with the little 326 even in box stock condition with a weekend cruiser type car.
I can also tell you with great certainty that in spite of any factory ratings, a bone stock 5000lb Grand Ville with a 455 will run circles around that much lighter 326 Tempest. A 455 even with 8-1cr and a 066 cam is still an awesome torque monster. But then you already know that. You probably also already know that the lighter the car and the bigger the motor the more power is wasted in tire smoke. Great fun but discouraging if you are actually racing anyone. LOL
Id think that much of your decision about motor will depend on what you have planned for trans and rear end. The old ST300 and 10 bolt could live happily for many years with the 326 but may not last a week with the 455. With that in mind budget considerations come into play as drivetrain upgrades can mean 1000s more.

[caliking71]

I am weird when it comes to my garage, its the only room in the house which I feel is truly mine. That and the downstairs bathroom! Thanks for the input. I think I am gonna move forward with the 455.

[Steve Barcak]

Originally Posted by caliking71

I am weird when it comes to my garage, its the only room in the house which I feel is truly mine. That and the downstairs bathroom! Thanks for the input. I think I am gonna move forward with the 455.

If you can get a better deal on just the 455 short block, you would be wiser to buy it that way. The 73 455 top end is not all that desireable for what you will be doing and you would probably change the heads and intake anyway. If you have the option of just buying the short, be sure to get all the hardware for the entire engine when you tear it down.
Most would agree that the later 400 5c and x heads are a better choice on your 455 and do not cost much. You can also use a 72 intake which is lighter, less bulky and no egr. Just some ideas.


Steve

[caliking71]

Thanks Steve, not sure if you remember, but you sold me the frame in my signature. I drove out from California with my trailer. I couldnt believe all the Pontiacs you had out there! Thanks again.