RROLDSX

Does anyone know what I can expect for compression ratio and horsepower range for a 1973 455 with 1969 C Heads (hopefully the large ones) stock quad/manifolds and a decently coordinated street performance cam?

I'm assuming some type of new thinner head gaskets (I hear Cometic).

I have the original 69 400 block and am currently deciding which one to go with. I like the cubes on the 455 and would prefer to keep the original block shrink wrapped but if I have to rebuild one or the other with new pistons for performance sake, I'll rebuild the 400.

oldsmobiledave

Pull the C heads off of your 400 & then wrap the 400 & put it under the bench for safe keeping. Pull the 455 out of the 442 & freshen it up adding the 1969 heads, your rebuilt carb and an appropriate cam (based on the calculated resultant compression ratio & your planned gear set).


Reinstall, tune it & Enjoy! I call shotgun!

RROLDSX

That's the plan so far, I'm really looking forward to some fresh fried tires though.

Then we'll stop into to Sharky's for another round of fish & chips (it'll be the 2nd round by then).

cutlassefi

What's your goal? An 8.25:1 455 won't automatically be a screamer.

RROLDSX

Is that in fact the CR I can expect? This is what I am trying to determine. If 8:25 to 1 is the CR, what kind of HP using the C heads and a decent street cam? I kinda of know I would like at least 300 to 350 HP. I'm curious as to what I can expect using what I have before I go broke ( I mean go for broke ).

cutlassefi

A 73 455 will have about 8.25:1 stock.
That combo with C heads and a mild cam will get you low 300's.

RROLDSX

Thanks! That will likely satisfy me for awhile anyway. Then after all else is taken care of then we'll see how fast I can go (broke?)

joe_padavano

Keep in mind that Olds varied the CR by changing the size of the dish in the pistons, so simply changing the heads does nothing for the CR.

RROLDSX

Thanks Joe, I can assume you don't gain a whole lot of compression by the thinner head gaskets either then.

oldsmobiledave

Randy


Play around with this calculator & you will easily see how compression changes with gasket thickness, Cylinder CCs & piston dish.


Dave


http://www.4racecars.com/calculators...alculator.html

MDchanic

You will lose about half a point of compression going from the factory ~0.017" steel shim gaskets, with a volume of about 3.85cc to the "standard" ~0.040" Fel-Pros with a volume of about 9.30cc.

- Eric

RROLDSX

Well the calculator was interesting. Too bad you couldn't change pistons as easily.

Thanks everyone.