Jim, I am coming back to this as I have the car pretty much done now and running well. Fundamentally what I am struggling with is what to do with the motor. Currently the motor runs fine - no smoke on acceleration or engine braking, but just is not a monster. The motor appears to be out of a 1968 Catalina (400 with #14
heads) and according to Wallace Racing's site should have a ~8.6:1 CR. I don't have any pinging (that I can hear) using 91 octane and when I did a compression test on the motor the numbers were all low but consistent, so I suspect it is a low compression motor. From what I have read the Catalina had a small cam, although I haven't found details other than what apparent stock replacement cams advertise. Is there really a huge difference between 8.6:1 and 9:1 ?
Given that all D-port heads flow close to the same, why not just replace the HFT cam with a better suited cam for the tri power and displacement and see if I am happy with the power results? It sure seems better (financially), than buying a built motor and heads. Worst case scenario I blow the motor and have to buy the built motor anyway..... I am sure I am missing something....Thanks in advance
heads are press-in studs & small valves. 8.6 compression can be worked with. The draw back will be the press-in studs which will limit your lift. You probably don't want to go more than .440" lift to be safe. Factory lift is .406" and the H-O blueprint manual says that coil bind can occur at .446". Obviously larger lift cams can be used, but changes are in order and you want to use your stock heads "as is."
To take advantage of the 8.6 compression ratio, you want to build up Dynamic Compression
. This adds more cylinder pressure in loosely the same way a higher compression ratio does. The factory cam in your engine now is very mild - and 7.6 seconds for the 0-60MPH most likely reflects that. The valve overlap is at 47 degrees - not a very "hot" cam.
You can use the Wallace Dynamic Compression Calculator to get an idea of what it will take to raise the Dynamic Compression. However, this may require a custom ground cam. I did play around with a couple cams offered on line, but nothing really fit the bill with the limits of the stock heads.
I went with a Comp Cams XE cam on my previous 1972 400CI build with its stock 8.2 compression, maybe less with the aftermarket 8-eyebrow cast pistons I used. The heads were the 7K3 which had the big intakes and screw-in studs so I could use a high lift cam. The cam really made that engine perform - I was impressed. Ran on regular octane gas all day long.
The Comp Cams use a tighter 110 LSA vs the factory 113-116LSA. The tighter LSA can build more cylinder pressure. These cams have "explosive" power, but peak early as opposed to a factory grind that has a broader and more even power range for longer.
The XE series has steep ramps that throw the valve open faster, so be advised that heavier springs may be needed to keep the lifter on the cam lobe - depending on type of cam grind/series some companies offer.
That said, and in my opinion in keeping the stock heads and wanting to do just the cam/lifter swap, I would inquire about a custom ground cam that will build cylinder pressure (Dynamic Compression) to work with the 8.6 ratio you presently have.
So using the Dynamic Compression Calculator, and as an example
, you see how the Intake closing point affects Dynamic (cylinder) pressure.
67 degrees - 6.75 ratio (yours now)
64 degrees - 6.90 ratio
60 degrees - 7.10 ratio
So this is why I say you may need a custom ground cam to maximize your combination using the stock #14
heads. I think I might give it a try and then start saving for the "new" engine. You may even like the new installed cam in your present engine and just go with that.