455 cam theory

[Bonnewagon]

I am looking for input on cam selection for a Pontiac 455 which currently has no cam at all. I expect other 455's would be similar considering that they all share a long stroke which places the torque peak at a lower rpm than most V-8's. It is a well known fact that 455's are bottom end torque monsters and were used in huge land yachts back when gas as cheap. This would be an otherwise bone stock motor with no modifications that would raise the rpm potential. I am leaning towards a high lift, short duration cam that in a smaller motor would be considered an "economiser". I figure the high lift would feed the cylinders better at lower prm's while the short duration would keep the power at a street usable level well under 5000 rpm. The Pontiac in particular has heads that flow their max at about .450" lift with the stock springs and valves so I would not go past that. I also figured the duration should be kept at around 250 to 270 degrees (advertised) or 200 to 218 degrees ( at .050") which would result in a motor that would make power from off-idle to around 4500 rpm. There are several off the shelf cams with these specs and I am not looking for a specific grind, but rather some input on cam selection that has worked for others in regard to theory. What rpms is your usable power peaking at and what sort of idle do you have? Has anyone tried high rpm cams and how did they perform? Is the factory cam the best for a stock motor? Am I on track with the high lift- short duration idea or is that wrong, and why?

 

[G-Body_Vet]

I was just thinking about that myself and came across this thread. May or may not give you some ideas.
http://www.78ta.com/smf/index.php?topic=19488.0
*edit*....well maybe not exactly what you're getting at, but 455 cam selection

 

[Bonnewagon]

Ah yes, Mr P-body used to be on another site years ago. Good man. But see how as soon as you get over 268* you are needing better springs and converter. Converter not an issue as I am strictly manual trans. I ran a 278* cam in a 400 and needed a vacuum canister for the brakes and 10 to 1 overall 1rst gear ratio to rev but it was a beast. I ran a 262* cam in the same 400 and it was as smooth as a stocker. The duration means everything to idle quality and power band.

 

[G-Body_Vet]

I've been thinking about what I want to do with the 455 I'm getting soon. I don't have a whole lot of experience with Pontiacs but I read everything I come across.

I'm trying to keep costs down and torque up! Not looking to build anything radical but definitely better than what the factory gave us. Plans include an OD trans and better gears too. I have leads on a few 3.73 rear ends if that's not too much. I understand most of the 455's power is made down low. All I want a decent cruiser with some balls when it needs it.

 

[Bonnewagon]

We have the same goals, but may arrive there differently. I want all the low end grunt I can get yet cruise economically (relatively at least). My usual plan is to use a manual trans with a super low 1rst gear and then have granny gears out back for a poor man's overdrive. The factory did the same up until OD trannys came out. Right now I have a Saginaw 4 speed w/3:50 1rst and a 2:78 rear end. I cruise at 2000 rpm for 55mph and never get over 2500 to keep up with the everyday lawbreakers. For the 455 I have a ST-10 w/3:42 1rst gear. I'm thinking the Crane 262 cam would work well as it has 262/272 adv dur and .427"/.454" lift. Pontiacs like a bit more exhaust opening. Notice it has the high lift/short duration I was talking about.

 

[G-Body_Vet]

I don't mind rowing gears either, but....the stop and go traffic drove me insane last time I had a manual trans. Then again who am I to complain when you live in NY? I'm sure Chicago traffic can't compare.

My next question is heads and compression. The engine is a '76. Do I stand to gain much by raising the compression with different heads or just leaving the stock ones in place? The Edelbrock heads are a little out of the budget at a grand a piece right now.

 

[anakputa]

I ran a stock 455 SD spec cam in my 76 455 I yanked out of a Trans Am and stuffed in 72 California Edition Lemans..I sold that car like an EEDIOT!!!

 

[G-Body_Vet]

.I sold that car like an EEDIOT!!!

Let's not get started on cars we regret selling.

 

[Bonnewagon]

The 455 SD used 308/320 adv dur and .470"/470" lift but, and this is a big but, came with forged connecting rods and round port heads for that level of power. As far as the stock 455 low compression heads, I like burning cheap gas and never pinging, so for me low compression is the way to go but I travel far with my cars, no weekend "toys". An increase in compression would allow a more aggressive cam but octane would need to go up. Yeah, the traffic sucks, but like I said I go for 10 to 1 overall ratio so I can tolerate stop and go traffic. I flip on the AC, the idle jumps to 1000 rpm and I just work the clutch in and out to creep along. By the way I lived in Rogers Park as a kid and when I used to go back and visit I marveled at the lack of traffic and the general cleanliness of Chicago. NYC is a bumper to bumper toilet in comparison.

 

[shotgun]

Pontiac "068".