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 cam advice for 455 in full size '74 please?
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Tribal Scout

4 Posts

Posted - 20 Apr 2017 :  07:51:41 AM  Show Profile  Reply with Quote
G'day All,

I've read many of the post here about cams to the point my head is spinning a little (a lot).
I'm hoping to find some up to date info on a cam for my '74 Pontiac Grandville.

My '74 has the HO option (Y code), which I don't think actually means anything different to other 455's of the same year apart from dual exhausts? The engine has been rebuilt 7000miles ago with a mild (very mild) cam that the previous owner fitted for economy...
Static compression sits at just a smidge over 8:1, which is what they were standard? I think its 4x heads on it from memory, but whatever was factory as they werent changed (previous owner rebuilt the engine as he didn't use the right oil and wiped a couple of cam lobes).
I have some bits and pieces i've collected here that havent been fitted as yet, just sitting in the boxes. I have edelbrock performer manifolds, a holley 850cfm 4150 vac sec that i'm thinking is too big now but come as a package with a manifold, a quickfuel 750, a couple of pertronix flamethrower HEI distributors, along with aluminium water pumps and some cosmetic stuff. I'd like to think I might have a set of the RamAir manifolds by the time I get to putting a cam in it to flow thru the dual 2.5" exhausts and fit some of the bits as well.

As you know (or not) the Grandville convertibles are heavy cars. The 74 in question has 2.92 gears with TH400 with a shift kit and stock converter.
Its never going to be a race car of course, but I would like to not only waken it up a bit, but also have it sound like its got some mumbo (read noticeable idle) and pull hard thru to a mind numbing 4500 or so. I guess sound fast with reasonably decent manners is the order of the day. We live outside the city, so most of the cruising is 50-60mph, but we like going to show'n'shines and classic car cruises in town.

I've read so many posts, i'm plain confused as to what cam I should be looking towards to build some dynamic compression and also what is going to be more suited to a very heavy car with stock converter.

I've been offered a Magnum 270H cheap, which reads ok but seems to be yesterdays technology after reading (and reading) and just because its cheap, it won't work out to be a good deal if its just wrong for the car. I'm thinking maybe one of the Lunati Voodoo or Comp Cams XE family grinds, which are a popular recommendation around here, but usually for much lighter cars.
I did have recommended the .041 factory grind cam, but i'm thinking its not going to be stock converter friendly. I have been offered another cam for free along with the Magnm 270H, but the owner isn't sure what it is (engraved on the end is 5667/5676 CC Y3913-12 with an 'A' stamped in it) and nor am I. The guy has got a Butler built engine and thinks it may have been one of the cams he got and didnt use, but isn't sure hence why it is offered free. I'm aware that free is no good either if it means pulling it out if it doesn't suit.

If anyone has a few moments to provide some advice or can even advise on what the cam listed above actually is, that would be most appreciated. As you can imagine, early Pontiac experience is rather thin on the ground down here and if I can get a head start in the right direction from you guys who have probably forgotten more than i'm ever likely to learn (especially starting at my age) about these engines, that would be beaut!

Blued and Painted

3292 Posts

Posted - 20 Apr 2017 :  11:58:03 AM  Show Profile  Reply with Quote
We will need the secondary head number. http://butlerperformance.com/files/images/cylinder_heads/6xheadlocate.jpg ..
850 cfm is not to much for a 455.
Test show the factory intake will make more power than the base model eldebrock performer.
If it is a low compression engine, i would not go over 220 degrees intake duration for drive-ability and tune-ability. This cam will have some attitude and would be as large as i could recommend. https://www.crower.com/camshafts/pontiac-287-455-hot-street-beast-hydraulic-cam-278-h.html
Complementing components might be a 331 rear gear ratio, 2500 stall converter, modified log manifolds or ram air exhaust manifolds with mandrel bent exhaust pipes.

Bull Nose Formula, 461, TH400/ 3.08 8.5 / R44TS.
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Tribal Scout

4 Posts

Posted - 21 Apr 2017 :  07:38:53 AM  Show Profile  Reply with Quote
I think I got some info of help.
The heads are 4X, are both date coded K193 (Nov 19 1973?) and have screw-in studs (which I checked to be sure). Unfortunately, and im sorry i looked, they are stamped 1H which are btwn 112-114cc?

I'm fortunate that the previous owners brother who put it back together was a mechanic and wrote everything down. I'm sure the previous owner kept every single piece of paper related to the car also and gave the lot to me when I bought it.

The scribble sheet has a chamber CC of 109, which means it probably got milled around .020"? It also says the pistons are between .012" and .015" down the hole at TDC. The gaskets fitted are 8518PT Felpro, which list as .045" compressed thickness?
The only thing i cant be sure of is what volume is consumed by the crap pistons, which are 4 valve relief cast Badger #P591 +.030". I have assumed 6-8cc for valve reliefs, which is all I can find for similar (TRW/SpeedPro etc) but may be way off.

I've plugged the above figures from what I can find into Butlers compression ratio calculator just now.
With bore of 4.181" and stroke of 4.21" and using .015" piston to deck, .045" gasket and 109cc head volume, it gives me 8.43:1 with 5cc valve reliefs and 8.26:1 with 8cc valve reliefs, so if i've done that correctly and it's accurate, i'm somewhere inbetween?

I don't want to fit alloys to gain static compression. I would love to, but the exchange rate, tax and freight makes them very expensive downunder and I would probably rather spend less money on a Pro-Charger or some other under bonnet/hood supercharger and run mild boost than put a set of alloys on unless a head crapped itself. Iron heads aren't plentiful downunder, so buying another set to probably rebuild is in the same basket to be honest.

Whats in it now is an Aussie brand "Crow Cams" HFT #90631.
Duration is 200/208 @ .050" and advertised 260/266. Lift is .4017/.4154 with 1.5 rockers (.2678/.2769 at the lobe) on a 112LSA with 2degrees advance ground on the cam and installed straight up. Valve timing is -10deg BTDC inlet/+38deg BBDC exhaust @.050" or 20deg BTDC inlet/67deg BBDC exhaust advertised. It also says inlet lobe lift at TDC on overlap is .033".
It sounds pretty much stock to my old ears.
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Tribal Scout

4 Posts

Posted - 21 Apr 2017 :  07:42:44 AM  Show Profile  Reply with Quote
ps: i don't want to fit a high stall or change gears, but will fit RamAirs to run into the dual 2.5" system that has single offset mufflers (Lukey I think).
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